Regular readers of the AMPTIAC Quarterly will have noticed that

we’ve published several ‘special issues’ over the past few years. The

common aim of these publications has been to highlight topics of

special interest to targeted technological communities. Examples

include our issues on nanotechnology (May 2002) and blast mitigation (Protecting People at Risk, February 2003). Both issues were 

well received by our readers but for different reasons: Nanotechnology represents an exciting and

unexplored frontier with intense 

scientific interest; while protecting people and structures from

explosions has gained national attention, especially since 9/11. 

This current issue addresses perhaps an even more important topic:

the development of new technologies to enable our ground troops

to become more effective in the war against terror as well as other

emerging global threats.

All one has to do is follow the news reports to appreciate the

major technological hurdles now facing the Army. Gone are the 

days when we faced large standing armies, consisting of heavily

armored units employing traditional tactics much like our own.

Today, we face adversaries that seemingly have no qualms at sacrificing their lives or those of innocent bystanders in an attempt to

inflict damage on our troops. Through a mix of conventional and

unconventional weapons (such as improvised explosive devices 

or IEDs) these fanatics have forced us to adopt new tactics while

relying upon our existing weaponry and equipment.

To be totally effective against our new and other possible future

enemies, the Army must transform from a force relying on heavy

armor to one employing a broad spectrum of lightweight, yet survivable systems and equipment that will enhance their ability to

fight. In this context, the word ‘transform’ means to change doctrine, tactics, and assets to respond rapidly to the environments of

the new battlefield. The challenge for our community is to develop

the advanced materials that will provide the Army improved effectiveness across the full spectrum of operational environments. To

make things even more complex, researchers must address additional 21st Century requirements beyond mere system performance.

They must give greater consideration for ‘green’ solutions that

reduce the generation or introduction of toxic materials into the

environment during production, training, deployment, or other

military operations.

Much recent work has been undertaken to improve the survivability of vehicles and their occupants subjected to fire from ballistic weapons as well as blast and fragmentation from mines, Rocket-Propelled Grenades (RPGs), and IEDs. Discussed in this

publication are several of the emerging materials that will enable

improved yet lighter armor for future systems. Included are ceramic, metal, and composite material research programs that show

tremendous promise. Past

armor research has yielded the

effective but heavy systems we

employ today. Becoming more

effective against insurgents requires lighter armored vehicles

employing innovative materials including transparent armor for

windshields and visors. Armor research has been and continues to

be a significant activity at the Army Research Laboratory.

Other subjects of significant interest are those related to ordnance

materials, including propellants, projectiles, and even the systems

used to shoot them. One area of concern lately has been to find

replacements for lead bullets and depleted uranium (DU) kinetic

energy penetrators. Environmental concerns are the primary reasons

for finding alternative materials for these applications, and several of

the articles here discuss the programs addressing the problem.

One approach to reduce the weight and complexity of systems is

to develop multifunctional materials that perform two or more primary functions. Army researchers have many programs underway

that are leading to technologies that exploit this concept and several of them are mentioned here. A multitude of other technology

development efforts are also being examined to develop the new

generation of lighter, higher performance materials needed to

improve warfighting effectiveness. 

The twenty separate articles contained in this issue of the 

AMPTIAC Quarterly will provide you with a glimpse at some of the

technologies that will enable the Army to transform into a more

mobile, survivable, and lethal force while simultaneously becoming

a better steward of the environment. There are numerous technical

challenges yet to be overcome, but as the reader will notice the Army

Research Laboratory’s Weapons and Materials Research Directorate

(ARL/WMRD) is actively pursing those technologies necessary for

the Army to transform the face of the new battlefield.

David H. Rose 

AMPTIAC Director

Editorial:

Adapting to a Changing Battlefield

The AMPTIAC Quarterly is published by the Advanced Materials and Processes Technology Information Analysis

Center (AMPTIAC). AMPTIAC is a DOD-sponsored Information Analysis Center, administratively managed by

the Defense Technical Information Center (DTIC). Policy oversight is provided by the Office of the Secretary of

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Inquiries about AMPTIAC capabilities, products, and services may be addressed to 

David H. Rose

Director, AMPTIAC

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Section I: New Approaches for a Changing Army

The US Army is undergoing a transformation that will enable it to better protect the Nation throughout the 21st Century. Advanced 

materials will be pivotal in achieving the Army’s Future Force characteristics of responsiveness, deployability, agility, versatility, lethality, 

survivability, and sustainability.

Materials, Disruption and Revolution: New Materials Will Benefit Tomorrow’s Soldier... 5

This article describes some of the toughest problems facing the materials community as we strive to enable the Army’s vision of

rapidly deployable, lethal, and survivable fighting systems.

Meeting New Challenges: Advanced Materials Aid the Army’s Transformation ... 8

Revolutionary developments in advanced materials will drive the Army’s Transformation, but there are a number of challenges in

their development and implementation that first must be overcome.

Section II: Survivability Materials – Protecting the Future Force

Significant advances in survivability technology are required to achieve armor performance exceeding that in current combat vehicles.

Advanced materials and their multifunctional integration are critical to the successful design of new lightweight armors to protect the Future

Force.

A New Generation of Metallic Armors Leads the Way ... 15

Metallic armor has proved its worth throughout history and remains an integral part of the Army’s protection strategy for the Future

Force. More recent advancements include hybrid metallic technologies designed to meet future armor requirements.

Ceramics Research Leads to Improved Armor Performance ... 21

Ceramic armor technology offers the best potential for meeting future protection requirements, particularly for the US Army’s

Future Combat Systems. Ceramic properties important for armor applications are understood, but their exact correlation with

armor performance remains elusive, partly due to numerous defeat mechanisms invoked by a wide variety of threats.

Transparent Materials Safeguard the Army’s Vision ... 28

The Army Research Laboratory (ARL) has invested consistently to bring the best technical advancements in polymers, glasses,

ceramics and adhesives to transparent system designs. These materials have application not only in ballistic glass but also in infrared

(IR) windows, radomes, sensor protection, and personnel protection.

Advanced Materials and Analysis Enable Robust Composite Armor ... 37 

Advanced materials and their multifunctional integration are critical to the successful design of new light armors. One such light

armor solution being developed is an advanced composite armor that combines ceramics, metals, and polymeric composites to provide unmatched mass efficient protection.

Manufacturing a More Affordable Army through Low Cost Composite Processing ... 44

Composite materials lead the way for the revolutionary development of advanced materials in the Army’s Transformation. But more

affordable and versatile composite material systems must be realized through advances in manufacturing technology.

Section III: Ordnance Materials

Which came first, armor or anti-armor? This section discusses research and development efforts to enhance the field of ordnance materials;

including those used in gun barrels, projectiles, energetic materials, and electromagnetic guns.

Army Targets Age Old Problems with New Gun Barrel Materials ... 49

Higher performance cannons continue to be a goal amongst the Army’s armament community. Many of the materials and processes currently under investigation will serve as the foundation for advanced cannonry in the 21st century.

Issue Focus: 

Army Transformation
Bridging the Gap between the Art and Science of Materials 

for Small Caliber Ammunition ... 57

Replacing the lead core in small caliber ammunition with a “green” material has resulted in erratic projectile performance. Careful

study, simulation, and experiments have revealed the nature of the problem, corrected through an understanding of basic mechanics of materials and an appropriate manufacturing process.

MaterialEASE - Amorphous Materials: A Tutorial on Noncrystalline Solids ... 65

This issue of MaterialEASE will explain at a basic level what amorphous materials are, how they differ from crystalline materials,

some of their important properties and attributes, and give examples of how they are used in Army systems.

New Materials for Large Caliber Projectiles Take Aim at Future Threats ... 71

Research and development of materials fabricated through newer processing methods will produce the next generation of large caliber projectiles and produce non-lethal weapon technologies.

Advanced Materials Bring Electromagnetic Gun Technology 

One Step Closer to the Battlefield ... 79

The Army Research Laboratory and the Armament Research and Development Center are developing new technologies in an effort

to scale-up prototype technology railguns into fielded systems.

The Army Pursues the Next Generation of Propellants and Explosives ... 85

Novel energetic materials hold the promise of providing mission enabling lethality as well as increased insensitivity to accidental

and cross detonations.

Section IV: Multifunctional and Special Function Materials

The efficiency of military systems will experience marked improvements through the use of multifunctional and special function materials.

This section covers efforts to explore and implement high performance materials for multifunctional components.

Multifunctional Composites Integrate Power, Communications, and Structure ... 91

This article discusses a number of promising areas for using materials to design multifunctional systems including those which provide both power or communications and structural members.

Chemical Agent Resistant Coatings Reach Higher Levels of Performance ... 96

ARL is a leader in chemical agent resistant coating (CARC) technologies; developing formulations to meet performance requirements and environmental regulations while providing camouflage.

The Army’s Latest Developments in Polymer Nanotechnology ... 101

This article presents an introduction to controlling and manipulating polymer functionality at the nanoscale. Moreover, it discusses resultant applications that are of particular interest to the Army.

Nanotechnology Research Uncovers New Multifunctional Materials 

for Future Army Systems ... 107

Nanostructured materials offer great potential for vast improvements for all types of military systems. The Army is actively researching new materials and processing methods to enhance transparent armor systems, structural and functional carbon nanotube-based

materials, and metal/polymer composites for optical applications and actuation devices.

Cutting Edge Infrared Detector Materials Enhance Army’s Night Vision 

and Targeting Capabilities ... 111

The Army is the largest consumer of infrared detectors in the DOD, with most every component and system being slated for

upgrade to some level of infrared capability. There is a whole family of technologies that have been developed to meet these needs,

including pyroelectric thin film detectors, quantum well infrared detectors, and mercury-cadmium based detectors.

Clearing the Air: Army Composites Research Reduces Harmful Emissions ... 118

The military and commercial sectors haves large needs for high performance thermoset resins and coatings with lower volatile 

organic content (VOC) emissions. The Army Research Laboratory has developed materials and processes which realize significant

reductions in VOC as well as nitrous oxide (NOx) emissions, while producing resins and coatings that have comparable or in some

cases, superior properties to commercial resins.

Running Hot: High Temperature Materials Research is Leading 

to Improved Turbine Engine Efficiency ... 126

The research and development of ceramic matrix composites and ceramic-based coatings for use in turbine engines components has

the potential to achieve increased levels of efficiency and push the performance of Army vehicles to new heights.

About the Cover and Acknowledgements

The cover represents how new materials – from the nanoscale up to the macroscopic, are being harnessed to deliver the systems 

necessary to make the Future Force a reality. We would like to thank Ms. Amy Kehring of ARL for creating it. We would also like to 

thank the following personnel for their support and guidance in the preparation of this issue: Dr. Bruce Fink, Chief of Ordnance Materials;

and Dr. James McCauley, ARL Fellow; both of the Army Research Laboratory at Aberdeen Proving Ground. Lastly, AMPTIAC would like

to extend our sincere appreciation to all our authors and contributors who helped to make this issue the best yet!
The AMPTIAC Quarterly, Volume 8, Number 4 5

Throughout the history of warfare, materials technologies have

had a significant impact on land-combat force capabilities.

Today, materials scientists and engineers from government

laboratories, industry, and academia are working diligently to

achieve a common goal of transitioning advances in materials

research to improved warfighting capabilities for the Soldier.

Research is being performed at the Army’s corporate materials laboratory within the Army Research Laboratory (ARL); at

several Army Research, Development,

and Engineering Centers (RDECs);

and other laboratories, such as the

Army Corps of Engineers and the US

Military Academy. This special issue

of the AMPTIAC Quarterly highlights

a number of the critical materials

technologies currently being explored

and developed within these laboratories. This article aspires to

describe to non-materials scientists and engineers, some of the

toughest problems facing the materials and processing community as we strive to enable the Army’s vision of rapidly

deployable, lethal, and survivable fighting systems.

Materials, as a technical discipline, is by nature horizontal

in its scope – meaning that it horizontally feeds and serves as

the basis for vertically-integrated technologies such as munitions, cannons, and ground vehicles. As research programs are

defined to impact a number of technologies, both basic and

applied research programs in materials are inherently capable

of feeding multiple vertically-integrated technologies. Hence,

there can also be multiple methods to realize the benefits of

materials research; whether embodied in engineered materials, new processing capabilities that reduce the cost of commodity, or in new analytical and computational models that

enable the design of engineered systems through advanced

materials. Even though specialty materials may have been

developed for a singular purpose, they are quite often

serendipitously relevant and thus may be suitable for myriad

alternate applications; many of which were not considered or

even dreamed of during the original research effort.

As an example, consider the evolution in our understanding

of the mechanics and processing of thick-section advanced carbon-fiber composite materials; developed for and used in the

design and fielding of the Army’s M829A2 kinetic energy projectile sabot (described in more detail later in this issue) in the

late 1980s and early 1990s. Analytical and computational models were developed, validated, maintained, and improved over

the next decade, and were subsequently used to develop the

Army’s lightweight composite armors

for the Future Combat Systems. Similarly, electromagnetic induction-based

heating of carbon fibers (developed for

the repair of thermoplastic-based thinsection composites on rotorcraft) was

adapted to process the sabots for the

M829A3 projectile, resulting in substantial cost-reductions. These are just two examples of how

materials technology, unlike many other fields, can be timeless.

That is, materials-related technologies do not become obsolete.

Instead, they often find practical (performance plus cost benefits) application in systems far different than those for which

they were originally developed.

A fundamental attribute of materials technologies is their

inherently disruptive nature. Acclaimed author and Harvard

economist Clayton Christiansen defines disruptive innovation

as products or systems that create entirely new markets. The Army

materials community has long embraced this concept. Disruptive technologies can also be thought of, in part, as a new

understanding of existing materials and techniques; which in

turn may be used to synthesize and process them into new 

and useful forms, thus creating new opportunities to be exploited for previously unanticipated yet critical applications (i.e.,

new markets). Luckily for Army materials experts, the Soldier

“marketplace” is quite broad and its future is wide open.

Consider the following. If a specific solution path were 

pre-defined to attack a certain problem, it is less likely that

engineers would be able to take advantage of any disruptive

technologies, since they would need to rely on commodity

Bruce K. Fink 

Weapons and Materials Research Directorate

US Army Research Laboratory

Aberdeen Proving Ground, MD

A fundamental attribute 

of materials technologies 

is their inherently 

disruptive nature.

New Approaches for a Changing Army Section I
6 The AMPTIAC Quarterly, Volume 8, Number 4

In 1996, the Army created the Materials Centers of Excellence (MCOE) program at to work with

leading materials research universities and corporations. In contrast to “knowledge driven” basic

research, the approach of these Centers is to conduct high risk, large potential payoff, strategically

focused basic research and exploit the development of new materials and related materials technologies for future Army applications; they are basically science-driven, problem-directed Centers. 

Strategically focused, linked, and agile collaborations involving equipment, people, and publications are established creating seamless and synergistic teams between personnel from Army laboratories and their University partners including equipment, people, and publications. Using cooperative

agreements instead of traditional contracts or grants, each institution collaborates with Army scientists and engineers to create programs that are redefined annually, where projects can be modified,

terminated, enhanced and new ones started at any point in time. Additional funding, if available, is

easily added to enhance or start new work. The close connections to ongoing work in the Army also

allow for the rapid transition of breakthroughs. Centers are nationally competed every 3-5 years and

the current centers are described below.

COMPOSITES: 

The Army Center of Excellence in Composite Materials Research (CMR) began in 1996 at the

world-renowned Center for Composite Materials at the University of Delaware (UD-CCM). The

program has produced over 100 journal publications and 14 patents with more than half of these

being a joint effort between University and Army researchers. UD-CCM has hosted dozens of Army

researchers including several full-time Army research staff members in residence at the Center’s

Newark, Delaware facility. Notably, research from this program has resulted in receiving two of 

the last three biennial Army Siple Memorial Medals, which is the highest award for science and 

engineering in the Army. 

In 2000, the Army instituted a sister program at UD-CCM called the Composite Materials Technology (CMT) Program. CMT is an applied research program designed to accelerate the transition

of basic research efforts developed under CMR to the Soldier. The program is funded by multiple

Army laboratories including the Army Research Laboratory (ARL), the Tank-Automotive Research,

Development and Engineering Center (TARDEC), the Armament Research, Development and

Engineering Center (ARDEC), and the Aviation Missile Research, Development and Engineering

The Army 

Materials Centers 

of Excellence: 

A New Model for 

Government-University

Collaborations

materials that could be engineered into the desired solution.

Therefore, if one were to say: “There is a ceramic-based armor

for ground vehicles, and I need a ceramic with certain properties and performance characteristics to be able to mitigate this

defined threat,” we would be asking for an evolutionary

approach and an incremental solution. This approach is often

warranted, but requires a vast knowledge of materials and

extraordinary expertise in the

art and science of armor 

design and optimization.

However, because revolutionary advances in warfighting

capability only come about

through broadly enabling

advances in science or technology (and materials advances are historically the most 

profound agents of change in technology), we need to ask the

question differently: “There is a need to protect soldiers from

these defined threats.” This is the same requirement stated 

in a very different way – but now it has the opportunity to

capitalize on novel engineered solutions that take advantage of

a spectrum of materials and technologies, whether they are

commodity, engineered, or synthesized.

Interlaced throughout this special issue are examples of the

insertion of new materials, development of engineered materials, and the creation of new classes of materials for Army applications. Predictably, yet not without ingenuity and difficulty,

engineered composites are applied to pull back the center of

gravity of steel cannons, commodity ceramics are applied to

composite armors, and synthesized organic nanomaterials are

specifically designed to improve

the energy absorbing capabilities of composite structures. On

the other hand and quite unpredictably, ferromagnetic nanoparticles designed for rapid curing

of adhesives are poised to revolutionize treatment of cancerous

tumors; advances in ceramic processing and statistical failure

analysis techniques are enabling hotter propellants and longerlasting gun tubes; and alumina-based metal matrix composites

(originally designed for high-tension power lines) may turn out

Materials-related technologies do

not become obsolete ...they often

find practical application in systems

far different than those for which

they were originally developed.
Dr. Bruce K. Fink received his BS in Civil Engineering in 1985 and his MS in Applied Mechanics in 1987, both at

the University of Nebraska-Lincoln; and his PhD in Materials Science and Engineering in 1991 from the University

of Delaware. Dr. Fink has 20 years of service with the Army, including 10 years as a Combat Engineer Officer. He

is currently serving as Chief of Ordnance Materials at the Army Research Laboratory.

The AMPTIAC Quarterly, Volume 8, Number 4 7

Center (AMRDEC). The combination of these programs has resulted in several major technologies, including the design and testing of a lightweight composite-overwrapped gun barrels, the field-testing of composite wheeled vehicle components, and the

development of building-block structural design protocols for lightweight armors. 

METALS AND CERAMICS: 

In 2001, MCOE programs were established at Johns Hopkins and Rutgers Universities. The program at the Johns Hopkins 

“Center for Advanced Metallic and Ceramic Systems” focuses on the dynamic behavior of non-crystalline and nano-structured

metallic systems, while a Rutgers – Johns Hopkins team focuses on the high fidelity design and processing of high performance

structural ceramics. The underpinning technical philosophy consists of integrating processing and characterization with the visualization, identification, modeling, and simulation of dynamic failure and damage mechanisms within metallic and ceramic systems. The primary technical focus in the Johns Hopkins program is on shear band formation in nano-structured metals and bulk

amorphous metals during largely compressive loadings. In the Rutgers – Johns Hopkins ceramic program, the technical focus is

on the quantification of the effects of processing defects, identification of high strain rate damage and failure mechanisms, and

the control of grain size and macrostructures to mitigate high strain rate failure. 

POLYMERS: 

The Army Center of Excellence in Polymeric Materials was established in 2001. Serving as the core institution, the University 

of Massachusetts at Amherst has partnered with a number of other institutions, including the University of Tennessee and

Amherst College, focusing on the development of new concepts in polymer materials technology. Currently, this program has two

overarching thrusts. The first is to develop functional polymeric materials through the combination of novel polymer chemistry

and self-directed assembly processes. At the foundation of this research has been the development of nanostructured templates

materials with ordered nanoscopic patterns using block copolymer technology, the continued optimization of which has resulted

in materials with unique optical, electrical, and magnetic properties. On-going research in this thrust area includes the chemical

modification of carbon annotates nanotubes and quantum dots to allow for controlled incorporation of these materials into polymers, and the development of new polymeric materials for applications such as fuel cells, flexible displays, and photovoltaic cells.

The second thrust of this Center is to develop technologies capable of enhancing the performance of polymeric materials used in

Army applications. Examples of on-going research efforts in this thrust area include the development of sprayable coatings systems with antimicrobial activity, (i.e., that are self-decontaminating with regard to biological agents); the use of organosilicate

nanoparticles for enhancing the mechanical performance of polymers used in transparent armor applications; and the control of

surface topology for tailoring interfacial interactions between dissimilar materials.

to be the critical enabling technology for high-stiffness, highconductivity electromagnetic gun tubes.

Each step in our quest to understand materials, and to apply

that knowledge judiciously toward improved warfighting capability for the Soldier, can take us down many alternative paths

– both ultimately fruitful trails and frustrating dead ends. As

the Army materials community, our daily responsibility is to

move forward without trepidation or doubt, but with eager

resolve and continuous focus on the Soldier. Just as together we

will often fail, we will also often succeed. Failure is, in fact, an

integral part of ultimate success. As surely as our soldiers in uniform risk life and limb, we must heed their example by taking

intellectual risks. Only by accepting that risk of failure will we

truly revolutionize warfighting capabilities through the application of advanced materials. The Soldier depends on that.

REFERENCE

Clayton Christiansen, The Innovator’s Dilemma, HarperCollins

Publishers Inc, New York NY, 2003
8 The AMPTIAC Quarterly, Volume 8, Number 4

James W. McCauley

Weapons and Materials Research Directorate

US Army Research Laboratory

Aberdeen Proving Ground, MD

INTRODUCTION

As threats to the United States become more asymmetric, the

US Army is transforming itself by adapting its operational

strategies to better protect the Nation. In The Way Ahead – Our

Army at War – Relevant and Ready,[1] General Peter J.

Schoomaker, Chief of Staff of the United States Army lays out a

vision of a more relevant and ready Army. This vision is grounded in the Army’s longstanding core competency, i.e., training

and equipping soldiers and growing leaders, and providing 

“relevant and ready land power capability.” The Way Ahead

clearly articulates that the Army must transform for operations

different from those it has been traditionally structured to face.

In order to defeat new threats such as the largely transnational

terrorist organizations with worldwide infrastructure, resources

and sponsors, a “capabilities-based modular, flexible and rapidly

employable Joint-Army team” capable of controlling the battlefield and dominating the enemy is required.[1] This article

highlights the role of advanced materials in the Army’s transformation, and the challenges inherent in developing and implementating of new materials in combat systems.

Cross-cutting characteristics of Army transformation

include responsiveness, deployability, agility, versatility, lethality, survivability, and sustainability. These characteristics fully

support the “Future Joint Force Attributes”[2] to achieve 

“Full Spectrum Dominance.” On-going capability gap analyses are being carried out for the Current and Future Force by

TRADOC, the Army’s Training and Doctrine Command.

In many, if not most of the cross-cutting characteristics 

and identified gaps, new and improved materials used in innovative designs offer significantly enhanced, and in some 

applications, revolutionary

capabilities. Advanced materials are the enabling underpinning for the evolutionary

improvement of the Current

Force, as well as for the revolutionary invention of weapon

systems for the Future Force.

However, as suggested in

Alternative Approaches to Army Transformation,[3] the tradeoffs on mobility, survivability, and lethality that result from

“reducing the weight of single platforms presents the greatest

challenge to transformation.” Advanced materials and structures, incorporating multi-functionality, can significantly

improve Army capabilities by providing lighter weight,

stronger and more durable materiel but not without additional challenges.[3]

CHALLENGES IN DEVELOPING AND IMPLEMENTING 

ADVANCED MATERIALS

Throughout human existence, people have used natural (e.g.

stone arrow heads) and synthetic (e.g. steel Samurai swords)

materials as means of preserving their security. In these two

examples, the importance of the materials used in the weapons

was obvious and visible. As weapon platforms have become

more complex, it has become increasingly more difficult to

appreciate the importance of materials to the performance and

capabilities of the system. All engineering systems require certain material properties for performance. As a result of this

complexity, materials decisions become further removed from

total system decisions, as illustrated in Figure 1. Thus, it is

extremely difficult for materials scientists and engineers to convince the decision makers at the component and full system

levels of the advantages of advanced materials technology without extensive data bases and prototype experiences.

Future Joint Force Attributes

➢ Fully Integrated

➢ Expeditionary

➢ Networked

➢ Decentralized

➢ Adaptable

➢ Decision Superior

➢ Lethal

Figure 1. Scale Progression of the Composition of a System[4].

Material

Element

Component

Subsystem

Plant/Platform
The AMPTIAC Quarterly, Volume 8, Number 4 9

The utilization of advanced materials in the early design

stages (Figure 2) of the acquisition cycle has always been problematic. To minimize risk, design engineers typically utilize

commercial, off-the-shelf materials rather than advanced materials with limited property data. From a materials perspective,

this results in fielded systems being obsolete almost from the

day they roll off the production line. Figure 3 illustrates this ongoing problem for materials. As seen in the figure, it often takes

20-30 years to mature a material to the point of widespread

commercialization or use in engineering systems.

THE ARMY’S PROCESS FOR MATERIALS DEVELOPMENT

It is useful for people who are not routinely exposed to advanced

materials to have working definitions of various aspects of the

field: in particular, the relationship between materials science,

materials engineering and materials technology.

• Materials Science – the creation of new materials and the

understanding of the relation of material characteristics

(unique signature = chemistry, microstructure, defects) to

properties.

Property = f (c, M, PD)

Any material is a population of identifiable constituents (c)

in a certain physical array (M) with certain, almost unavoidable defects (PD).

• Materials Engineering – the processing/manufacturing of

materials with controlled properties and geometries for 

certain performance. Materials Figures of Merit (FOM) are

critical links here as they define a quantitative relationship

between combinations of properties to desired performance.

Performance = f (property 1, property 2, property x, ...) 

• Materials Technology – the successful or highly likely

application of materials science and materials engineering

knowledge to the improvement, development and enabling/invention of useful products and systems.

Materials scientists and engineers often work in collaboration with other engineers (mechanical, electrical, aeronautical, civil etc.) in refining or developing engineering systems.

This involves a range of activities from selection of the best

available material to optimizing existing materials or creating

new ones with the desired properties. The process of generating advanced materials technology incorporates the synthesis,

processing, characterization, properties, performance and predictive modeling of materials; as well as manufacturing,

including miniaturization technologies; and nondestructive

testing technologies to reduce the time, risk, and cost of

acquiring materials. In addition to these activities, materials

scientists and engineers work on processing and manufacturing technology to reduce costs and improve the reproducible

quality of existing materials. This usually involves material

characterization (determination of the unique signature) by

Figure 2. Materials Selection Process in the Various Stages 

of Design[5].

Market Need

Design Tools

Function 

Modeling

Viability 

Studies

Approximate

Analysis

Geometric 

Modeling

Simulation

Optimization

Methods

Cost Modeling

Component

Modeling

Finite Element

Analysis

Material 

Selection

All Materials

(low precision

data)

Subset of 

Materials 

(higher data 

precision)

One Material

(best available

data precision)

Concept

Embodiment

Detail

Product

Figure 3. Materials Technology Evolution[6].

-5 or more

Discovery of

• Concept

• Material

• Method

Years

New Technology

or Rediscovery

Emerging

Technology

Maturing

Technology

Successful

Application

Failure Due To:

• No Performance Improvement

• No Cost Improvement

• Lack of Reproducibility/Reliability

• Lack of Design Data Base

Incorporation in

System

Prototype

10 20

• Scale-up

• Data Bases: Materials/Properties

• Design

• Nomenclature Uniformity

• NDT Characterization

• Standardization

0

Demonstration of Feasibility

(Possible Application)

1) Synthesis

2) Processing

3) Characterization

4) Property Evaluation
non-destructive or destructive means and materials

testing/evaluation of the desired electrical, mechanical or

durability requirements, including property design allowables

used by design engineers. (See for example, MIL-Handbook17, a composites materials handbook for organic matrix,

metal matrix and ceramic matrix composites.) Of course,

there are always the underlying competing goals of performance, cost, production capacity and strategic availability, as

modified by environmental and safety issues, which may have

to be traded off to achieve the desired performance within

budgetary constraints. All of these issues should be taken into

account during the research, development, design and acquisition cycle.

New materials technology emerges from a systematic

research and development strategy. Basic (6.1) and applied

research (6.2) agendas typically can be determined in two ways:

• Strategic (technical) opportunities – knowledge driven

• Strategic objectives – application pulled

Armor Materials by Design is an example of a basic research

Strategic Research Objective (SRO) that the Army uses to help

guide the basic research agenda; it is an application pull, strategically focused process. This Armor Materials by Design SRO

is not how to design components (systems) with existing materials, but rather how to select and design materials for very

demanding passive armor applications. Conventional materials

research and development typically follows a more sequential

process as illustrated in Figure 4. Figure 4. Conventional Materials Research and Development

Flowchart[7].

10 The AMPTIAC Quarterly, Volume 8, Number 4

Scientists, engineers, and technologists form a very small segment of our national workforce – only

about five percent. The National Science Foundation (NSF) reports in “Science and Engineering

Indicators 2004” that while Americans express strong support for science and technology (S&T),

they are not very well informed about these subjects.[1] For instance, in the US and Europe, most

adults pick up information about S&T primarily from watching television; the print media are a

distant second. In addition, most Americans (two-thirds in the 2001 NSF survey) do not clearly

understand the scientific process. Knowing how ideas are investigated and analyzed – a sure sign of

scientific literacy – is important.

A recent Building Engineering and Science Talent (BEST) publication entitled “The Quiet

Crisis: Falling Short in Producing American Scientific and Technical Talent” reports that a

quarter of the current science and engineering workforce, whose research and innovation 

generated the economic boom in the 1990s, is more than 50 years old and will retire by the

end of this decade.[2]Because it is essential to keep a minimum number of scientists & engineers in the workforce and to have a reasonably educated and interested population with

regard to scientific issues, the US Army has been engaged in a number of programs designed

to encourage young students to consider science as a possibility for their future.

Most Army S&T labs have outreach programs at the local level. These programs range from

judging at science fairs to participating in career day at schools to going out to classrooms to

work with kids in hands-on science activities. Two of the local programs at Aberdeen Proving

Ground (APG) are the Kids & Chemistry Program and the Science-in-the-Library program.

These programs involve materials scientists and engineers from the Army Research Laboratory

and Edgewood Chemical Biological Center. In the Kids & Chemistry Program, Army volunteers go into local schools and perform hands-on science experiments (e.g. Jiggle Jelly, What’s

In a Color? and The Cool Blue Light). In Science/Chemistry-in-the-Library Program, Army volunteers go into libraries and schools in Baltimore City, Howard, Cecil and Harford County, Maryland,

and New Castle County Delaware and work with kids doing hands-on experiments ranging from

“Monster Snot!” (the Science of Slime – Polymers) to “It’s Gross and We Ate It!” (Food Chemistry)

Passing the Torch:

Materials Engineers

Turn Young 

Americans 

on to Science

Generalized Needs

1. Present or Potential Use

2. Present Material Limitations

3. Required Properties: 

Actual or Predicted

4. Estimated Cost Effectiveness

Material Conceptualization

1. Single Crystal

2. Particulate Dispersion

3. Polycrystalline – Single Phase

4. Amorphous Material

Crystallography

1. Synthesis

2. Crystal Structure

3. Crystal Chemistry

4. Compositional Variations

Single Crystal 

Characterization

1. Mechanical

2. Electromagnetic

3. Physical/Chemical

4. Optical

5. Defects

Constituent Component 

Selection and Fabrication

1. Phase Equilibria

2. Compatibility: 

Physical and Chemical

3. Powder Preparation

Characterization

1. Optical

2. X-Ray

3. Trace Analysis

4. Grain Size, etc.

E/M-Optical

1. Conductivity

2. Mag. Suscep.

3. Dielectric K

4. Loss Tangent

5. Temperature 

Dependence

6. VIS - IR - UV 

Transmission

Thermal

1. Conductivity

2. Expansion

3. Specific Heat

4. Shock 

Strength

Mechanical

1. Strength

2. Stiffness

3. Hardness

4. Impact Strength

5. Fracture Energy

6. Friction

7. Compressive 

Strength

Microstructural

1. Texture

2. Void - Cracks

3. Grain Sizes

4. Defects

5. Fracture Surfaces

Compositional

1. Inclusions

2. Grain Boundary

3. Phases

4. Homogeneity

Processing

1. Standard

2. New

Existing

Material

Characterization

Optimization Loop

Engineering Properties

Scaleup

Actual or 

Simulated 

Utilization

Tests

Flow Chart for Materials Research and Development
The AMPTIAC Quarterly, Volume 8, Number 4 11

DEMANDS AND REQUIREMENTS OF MATERIALS 

FOR THE CURRENT AND FUTURE FORCE

The revolutionary demands of the Future Force will require

tailor-made materials (materials by design), multifunctional

materials, biomimetic and biologically-inspired materials,

nanostructured materials, hybrid materials, coatings and ultra

light structures. When compared to existing materials, these

new materials should show major performance improvements

at the same or significantly reduced weight, and must also

meet safety and environmental requirements. Research to

describe and characterize the fundamental physics and

mechanics of damage and failure, especially in dynamic 

environments unique to the Army will also be critical. In

addition, requirements for cost reduction and reliability

to “Chemistry of Crime” (Forensic Science), along with a variety of other experiments. The kids always get a hand-out that

includes take-home experiments. None of the chemicals involved require ventilation (therefore making them safe to work with

at libraries and schools). Both programs have National Chemistry Week activities and work with approximately a thousand

kids annually.

In the Fall of 2002, the US Army initiated a nationwide “electronic science fair” called eCybermission. eCybermission is 

an on-line competition for students in 6th through 9th grades. Students form teams of 3-4 students and have a team 

advisor. The team members pick a real-life problem that applies to one of the four science, math, and technology challenge

areas: Sports and Recreation, Arts and Entertainment, Environment, or Health and Safety. Then the challenge is for the 

students to develop a solution to the problem using science, math, and technology while having a positive impact on the

community. All projects are submitted and judged on-line. There are regional and national awards given out. For the 2003-

2004 competition, there were over 1,600 projects submitted for evaluation, involving almost 6,000 students nationwide!

A new initiative that has started within the last two years at a few Army S&T labs is regional outreach directly at schools

through the Materials World Modules (MWM) Program. MWM is an inquiry-based science and technology program developed at Northwestern University with funding from the National Science Foundation. The MWM program was designed to

serve as a resource for teachers to help them to excite their students about materials science and the world we live in. Rollout

of the program by the Army was begun in 2003 by a team at Picatinny Arsenal. The Army Research Lab joined the effort in

2004, and currently several dozen schools are involved. The Army program offers schools one free MWM kit per year (kits

include supplies for various experiments, as well as teacher and student manuals), along with support from the Army S&T

staff. Schools may choose to have a researcher come to their school and work with students as they perform exploratory experiments and/or the design phase of the module, or they may prefer to have a researcher support the schools in the role as guest

lecturers on specific topics. The MWM kits focus on topics in materials science, and include biodegradable materials, biosensors, composites, ceramics, concrete, food packaging, polymers, smart sensors, and sports materials. The modules emphasize

active, hands-on learning and provide students of all ability levels with opportunities to apply what they learn in the classroom

to real-world problems. 

The challenge of engaging adults in science is a daunting task. The key is to engage students before they decide that science,

math and technology are either too hard for them to master or not relevant to their lives. The sciences typically involve a 

significant amount of non-trivial in-class and laboratory work. If the interest of students can be piqued at a young age, they

will be more excited about learning necessary basics of science and math and more motivated about moving on to advanced

levels of learning and discovery. In order for this to happen, it is essential that young students be exposed to real-world applications of materials science (versus just facts in textbooks). It is important for them to realize that science is all around them,

and essential for them to have role models and mentors in their lives that will open up the world of science and technology to

them. The Army is striving to help schools fulfill these needs and thereby foster the development of the S&T’s of tomorrow.

FOR MORE INFORMATION PLEASE SEE:

Kids & Chemistry Program – http://www.ecbc.army.mil/about/kids&chemistry/index.htm

Science-in-the-Library program – http://mdchem.org/citl/citl_main

eCybermission – http://eCybermission.com

Materials World Modules – http://www.materialsworldmodules.org

ACKNOWLEDGMENT

The MWM Program was made possible through the leadership of the late Dr. John H. Hopps, Jr., Deputy Undersecretary of

Defense for Laboratories and Basic Sciences.

REFERENCES

[1] Science and Engineering Indicators 2004, National Science Board, National Science Foundation, 2004

[2] S.A. Jackson, The Quiet Crisis: Falling Short in Producing American Scientific and Technical Talent, Building Engineering

and Science Talent
12 The AMPTIAC Quarterly, Volume 8, Number 4

enhancements will continue to push the limits of manufacturing science and technology.

In order to expedite the incorporation of new materials

technology into the Army’s Current or Future Force, the existing paradigm of a culturally comfortable sequential R&D

process must be modified. The adapted process would accelerate the progression of critical research needs by concurrent

experimental validation coupled with modeling and simulation and rapid bracketing of 6.1 and 6.2 R&D for strategically focused efforts. For example, in the Armor Materials by

Design SRO three underpinning science and engineering goals

have been established:

• Full Length Scale Modeling/Simulation

• Ballistic Energy Absorption Mechanisms

• Hybrid Multifunctional Integration

Figure 5 schematically illustrates the concurrent approach

envisioned for the Armor Materials by Design SRO.

One of the key elements in the Armor Materials by Design

SRO is determining the various performance requirements

(capabilities) and then the related technical metrics as shown in

Table 1. These metrics can then guide the research program and

allow for evaluation of progress toward the goals.

FUTURE OF ADVANCED MATERIALS DEVELOPMENT 

FOR THE ARMY

Most systems are critically dependent on materials technology and there is no reason to believe that the properties of

materials will not continue to advance either in a predictive,

linear way (evolutionary – Figure 6), as illustrated below for

the thermal conductivity improvement of certain ceramics.[8]

Likewise, properties can experience exponential growth, as

for the case of high temperature superconductors[9] (revolutionary – Figure 7), as they have over the past 30 years. Other

examples of phenomena that have experienced revolutionary advances include transistor densities (Moore’s Law),

specific strength and stiffness of composites, flux magnetization product of permanent magnets, optical transparency of

glass fibers, critical temperature of superconductors, sonar 

Table 1. Performance Requirements for Future Force Systems 

and Functions.

FUTURE FORCE

SYSTEMS/FUNCTIONS PERFORMANCE REQUIREMENTS

INDIVIDUAL Ultra-lightweight and Conformable

PROTECTION Multiple Threat Protection

Target: 3.5 lbs/ft2

Signature Management and Control

ARMORED FUTURE Lightweight/Mobile

LAND SYSTEMS Threat Designable/Repairability

Target: Med. Threat at 30% of Present Tech.

Multifunctional: Ballistic/Structural/Stealth

TRANSPARENT ARMOR Designable for Personnel and Vehicles

(EM WINDOWS) Multifunctional: Microwaves, IR, Visible

ADVANCED AIRCRAFT Lightweight/Mobile

Repairability/Multifunctional

Signature Management and Control

SRO Vision

Full Length Scale Modeling and Simulation

• Individual Protection

• Armored Future

Combat Systems

• Transparent Armor

• Advanced Aircraft

• Hardened Shelters

Constraints

• Performance • Manufacturing

• Environmental • Cost

• Logistics

Examples

• Penetration Algorithm

• Low Observable

• Signature Management

• Chem/Bio Protection

SLAD

Models

AMSAA

Logistics

Design Materials for Armor - SRO

Computational Materials 

Science and Engineering

Micro-Macro Structure Property

Processing 

Micro-Macro 

Structure

Force on Force

Modeling

Modeling

Critical for 

Armor Material 

Design Tool

Design 

Path

MANUFACTURING 

& COST

SCIENTIFIC 

VISUALIZATION

VIRTUAL

PROVING

GROUND

Grain/

Fiber-Matrix

Micro-Macro

Structure Control

Component

Property

Requirements

Objective

Force

Unit Systems

Cell

Figure 5. SRO Vision.
The AMPTIAC Quarterly, Volume 8, Number 4 13

sensitivity, and size of manufactured detail (chips).

The development of armor materials has shown a similar 

revolutionary trend (Figure 8). Armor materials have progressed

from heavy (high areal density) metallic systems to advanced,

lightweight (low areal density) composite and hybrid materials

that can provide structural support to a weapon system as well

as threat protection. The figure shows that the development of

armor materials has led to a decrease in areal density which corresponds to an increase in mobility for weapon systems.

Examples of revolutionary engineering systems using

advanced designs and materials include the Hindenburg 

Zeppelin, the Rutan Voyager aircraft, and a more recent

example is the bicycle used by Lance Armstrong in the Tour

de France. All of these depended on visionary people who

employed leap-ahead design and advanced materials. Over

the next 30 years there exists a very high probability for

unprecedented developments in materials, computers, miniaturization and sensor technology, as well as the blurring of the

clear distinction between synthetic and biological materials.

Energy will be supplied from miniature fuel cells, batteries or

micro machinery/engines. For the first time in our history,

materials can be designed and synthesized atom by atom for

specific applications. Computer modeling and simulation

technology will be advanced to the point of being able to

design armor and systems and to simulate their performance

on the battlefield.

The revolutionary advancement of materials has already had

an impact on the performance of weapons systems, and it will

continue directly to enable higher mobility systems for the

Future Force. Figure 9 shows the progression of weapons systems over the past 25 years toward the higher mobility systems

of the near future.

Figure 8. Revolutionary Composite Armor Improvements. Figure 9. Revolutionary Impact of Advanced Materials on the

Mobility of Weapons Systems.

Figure 6. Trends in the Enhancement of Thermal Conductivity 

of Ceramics[8].

Figure 7. Progress of Critical Temperature of the Best 

Superconducting Materials as a Function of Time[9].

1911 1953 1973 1988

Year

Critical Temperature (K)

4.2 K

SiC AIN

Si3N4

Development 

of Orientation 

Technology Firing under 

Reducing Atmosphere

Firing at High Temperature

(>2200 K)

Development of Raw Powder

Oxygen Trapping by Formation

of Grain-boundary Phase 

Development of Densification Technology

Search for Sintering Aid

Development of Raw Powder

300

250

200

150

100

50

0

17 K

23 K

39 K

125 K

1980 1985 1990 1995 2000

Year

Thermal Conductivity (W m-1 K-1)

■

●

●

●

●

▲

▲

▲

▲

■

Search for

Sintering Aid

Search for

Sintering Aid

●

●

●

●

●

● RHA Steel (2.74”)

Aluminum (2.72”)

Titanium (3.01”)

Increasing Mobility Areal

Density

Aluminum-Ceramic (3.40”)

CAV-ATD Composite-Ceramic (1.77”)

Recent Integral Armor Advancement

Past Present Future

Strategic Research Objective

“Armor Materials by Design”

★

★

★

★

★ M2/M3 BFV Turret = 15.5 Wt. % Reduction

M113

Increasing Mobility

Composite BFV Hull Demonstrator

CAV-ATD Composite

Future Force/FCS

1980 85 88 1997 >2010

Innovative Processing is

Key to Affordability
14 The AMPTIAC Quarterly, Volume 8, Number 4

Dr. James W. McCauley is the Senior Research Engineer (ST) in Ceramics and an ARL Fellow in the Army Research

Laboratory. He holds a BS in geology from St. Joseph’s College (Indiana); and a MS in mineralogy and PhD in

solid state science, both from Pennsylvania State University. He is a former professor and past Dean at the New

York State College of Ceramics at Alfred University. Prior to joining Alfred, he was employed at the Army Materials Technology Laboratory for 22 years. He is the author or co-author of about 75 open literature publications 

and reports, the editor/co-editor of five books, and holds four patents. He has served on the Army Science Board

and the external review committee for the Materials Science and Technology Division of Los Alamos National 

Laboratory. He is a Fellow, Distinguished Life Member and Past President of the American Ceramic Society.

Dr. Sandra Kay Young is the Deputy Chief of the Materials Applications Branch in ARL-WMRD. Dr. Young has a

diverse research portfolio, including work in the areas of organic-inorganic nanocomposite materials, polymer modification, polymer analysis, polymer synthesis, telechelic polymers, organically modified silicates (ORMOSILs),

silsesquioxane materials, Nafion®, ionomers, ion exchange in polymers, structure-property relationships, and membrane materials. She has authored over 40 published papers and technical reports. She is an active member of the

American Chemical Society (slated to be local chair in 2006). She holds a BS in Chemistry from DePaul University and a PhD in Polymer Science and Engineering from the University of Southern Mississippi in Hattiesburg.

Dr. Rose Pesce-Rodriguez is a research chemist in the Ballistic and Weapons Concepts Division of the US Army

Research Laboratory. She serves as the leader of the Advanced Energetic Materials Team and is also the Directorate Representative for ARL’s post doctoral research programs. She earned BAs in Chemistry and Russian from

Queens College, City University of New York (CUNY); and her PhD in Polymer Chemistry from the CUNY Graduate School. She is very active in educational outreach programs including eCYBERMISSION, “Chemistry in the

Library,” and “Materials World Modules” programs.

ADVANCED MATERIALS GOALS FOR THE FUTURE FORCE

Advanced materials will play a crucial role in the Army’s Transformation to meet current and future threats faced by the

United States. Several key factors will contribute to the development of these materials and their implementation in the

Army’s forces. The bottom line for the Future Force is to

reduce weight while maintaining or enhancing performance.

In order to accomplish this goal, the following materials science and engineering research and development priorities need

to be addressed:

• Performance based strategic focus with the appropriate technical metrics based on property Figures of Merit for the 

specific applications

• Development and exploitation of advanced, hybrid and 

multifunctional materials

• Novel designs/structures that exploit materials properties

• Integration of computational modeling for materials design,

processing and performance prediction and appropriate testing for validation

The following articles present a variety of functionally oriented materials programs being carried out in the Army Research

Laboratory. We believe the technologies developed under these

programs will have profound impact on the development and

capabilities of the Army’s Future Force while simultaneously

allowing the improvement of Current Force capabilities.

REFERENCES

[1] P.J. Schoomaker, The Way Ahead – our Army at War – Relevant and Ready, Army Strategic Communications, Pentagon,

Washington, DC

[2] P.J. Schoomaker and R.L. Brownlee, 2003 United States

Army Transformation Roadmap, US Army, 1 November 2003,

http://www.army.mil/2003TransformationRoadmap/

[3] J.N. Mait and R.L. Kugler, Alternative Approaches to Army

Transformation, Defense Horizons, No. 41, July 2004

[4] K.C. Becker, C.S. Byington, N.A. Forbes, and G.W. Nickerson, Predicting and Preventing Machine Failures, The Industrial Physicist, Vol. 4, No. 4, American Institute of Physics, pp.

20-23, December 1998

[5] M.F. Ashby, Materials Selection in Mechanical Design, 2nd

Ed., Butterworth Heinemann, Oxford, 1999

[6] J.W. McCauley, The Role of Characterization in Emerging

High Performance Ceramic Materials, ACerS Bull., Vol. 63, No.

2, pp. 263-265, 1984

[7] J.W. McCauley, Structural and Chemical Characterization of

Processed Crystalline Ceramic Materials, Characterization of

Materials in Research, Ceramics and Polymers, J.J. Burke and V.

Weiss, eds., Syracuse University Press, Syracuse, NY, pp. 175-

209, 1975

[8] K. Watari and S.L. Shinde, High Thermal Conductivity

Materials, MRS Bulletin, Vol. 26, pp. 440-441, 2001

[9] Materials Science and Engineering for the 1990s, National

Academy Press, Washington D.C., 1989

Advanced Materials Aid the Army’s Transformation

Turning Young Americans on to Science
The AMPTIAC Quarterly, Volume 8, Number 4 15

INTRODUCTION

Metallic armor is the most mature class of armor materials and

is still widely used for ballistic protection today. Although the

materials for metallic armor are highly developed, new and

innovative metallic armor systems are being used to improve

the ballistic protection (while reducing the weight) of various

weapons systems. Historically, most

metallic armor evolved from designing materials to meet structural or

other requirements rather than from

designing specifically for ballistic

protection. This design paradigm is

changing; partly to meet the requirements for the Army’s Transformation

to a lighter, more survivable force.

Metallic armor systems are now

being designed to optimize mass,

space, and cost efficiency. This article briefly reviews the history, testing, and types of modern passive

metallic armor materials, and also highlights the emerging

hybrid metallic technologies designed to meet future armor

requirements. Current design approaches for modern metallic

armor materials systems are also discussed.

HISTORY AND MATERIALS

The use of metals for armor dates back to the discovery of

bronze in 3000-2000 B.C. The advantage of metallic armor

over softer materials, such as leather and wood, was obvious.

However, the trade-off between mobility and protection for

survivability was recorded as early as the battle between David

and Goliath where agility, accuracy, and mobility defeated

heavy armor. This very delicate balance is still a challenge in

implementing armor for system survivability today. This section covers some of the traditional and current monolithic

metallic armor materials, and also discusses metallic composite

and hybrid armor systems.

MONOLITHIC METALLIC ARMOR

Development of Steel Armor

Steel armor comprises the bulk of

past, present, and likely, future armor

materials. This is because it possesses

a number of desirable attributes that

should not be overlooked. Steel is

inherently inexpensive due to the low

raw material and fabrication costs, as

well as the enormous commercial

steel production capacity. It provides

good ballistic protection from a wide

spectrum of threats with excellent

multi-hit capability. It can be easily cut, machined, formed, and

welded, is easily field repairable, and has good degradation

resistance against the ambient environment.[1]

In the latter part of World War II and in the decade following, there was an intense period of investigation into the physical metallurgy and mechanical properties of high strength

steels at the Army’s Watertown Arsenal Laboratories. It was

found that steel at maximum hardness, but with enough toughness to resist cracking in all situations, provided the best ballistic performance.[2,3] The optimum combination of strength

and toughness was obtained with a medium-low carbon, low

Jonathan S. Montgomery

Ernest S. Chin

Weapons and Materials Research Directorate

US Army Research Laboratory

Aberdeen Proving Ground, MD

Figure 1. RHA and CHA Has Been Used in Tanks

for Decades, such as in the M60 Patton Tank.

Survivability Materials – Protecting the Future Force Section II
alloy steel with a Stage III* tempered martensite microstructure. At present, the two major types of steel armors are Rolled

Homogeneous Armor (RHA, MIL-DTL-12560) and Cast

Homogeneous Armor (CHA, MIL-DTL-11356). The specifications for these steels have changed substantially since their

inception between the World Wars (Figure 1).[4] As commercial steels’ production capability improved, both in terms of

quality and output, the armor steel specifications were modified to reflect these changes. Inclusions, sulfur, phosphorus and

tramp element levels have been drastically reduced, while

strength and, particularly, toughness have increased. The

Charpy V-Notch test for toughness was popularized by Watertown Arsenal specifically for the quality control of armor steel.

Resistance to adiabatic shear has been increased with improved

steel cleanliness and microstructural refinement.[5]

High hardness steel armor (HHA, MIL-DTL-46100) was

developed during the Vietnam War era for use against ball

ammunition. The composition is similar to RHA, but it has a

maximum of 0.32 wt. % carbon and it is tempered to Stage I.*

This steel is extremely mass efficient against ball ammunition,

particularly at highly oblique angles of impact. It was initially

developed as appliqué (i.e., nonstructural) armor, but welding

techniques have been refined to the point that vehicles can be

manufactured using this alloy as the structural material without cracking in service. The Light Armored Vehicle (LAV) is

made of this steel above the beltline, while RHA is used below

the beltline.

Development of Aluminum Armor

Aluminum alloy 5083-H131 (MIL-DTL-46027) is a nonheat-treatable, strain-hardened aluminum-magnesium alloy. It

is very resistant to cracking and stress-corrosion cracking. It is

readily weldable and corrosion resistant. It has excellent resistance to fragmentation threats. The M113 Armored Personnel

Carrier, M109 Paladin Self Propelled Howitzer (Figure 2), and

the lower half of the Bradley Fighting Vehicle (Figure 3) are

made from 5083.

Aluminum alloy 7039-T64 (MIL-DTL-46063) is an aluminum-magnesium-zinc alloy that is heat-treatable to a hardness higher than that of 5083. It exhibits better performance

against ball and armor piercing (AP) threats than 5083 with

some loss in performance against fragmentation threats. It is

susceptible to stress corrosion cracking, particularly in the

short-transverse longitudinal (S-L) direction, and thus it is not

recommended for future vehicles. The upper half of the Bradley

Fighting Vehicle is made from 7039 (Figure 3).

Aluminum alloy 2519-T87 (MIL-DTL-46192) is an aluminum-copper-manganese alloy that is heat treatable to hardnesses between those exhibited by 5083 and 7039. It exhibits

better performance against fragmentation threats than 5083,

and has almost the same performance against ball and AP

threats as 7039. It has good resistance to stress corrosion cracking, but poor resistance to general corrosion. There is a dramatic loss of ballistic properties near welds (metal in the heataffected zone is much weaker), so joints are designed to

minimize this effect. The first production armored vehicle utilizing 2519 aluminum will be the Marine Corps Expeditionary

Fighting Vehicle (formerly known as the Advanced Amphibious Assault Vehicle, or AAAV, Figure 4).

Future development in aluminum armor focuses on attaining

higher strength without sacrificing dynamic ductility, while maintaining all the corrosion and weldability characteristics of 5083.

The 5059 alloy, much like 5083 but at a

higher strength level, is currently being

evaluated as an aluminum armor candidate.

Development of Titanium Armor

The high cost of weight-efficient titanium

relative to steel has previously limited its

application to aircraft armor where weight is

a premium. However, recent investment in

low cost titanium has enabled its application

16 The AMPTIAC Quarterly, Volume 8, Number 4

Figure 3. The Bradley Fighting Vehicle Makes Use of Both 

7039-T64 (Upper Half) and 5083-H131 (Lower Half).

Figure 2. Aluminum 5083-H131

Armor is Now Common in

Army Land Systems.

M109 Paladin Self Propelled Howitzer

M113 Armored Personnel Carrier
The AMPTIAC Quarterly, Volume 8, Number 4 17

in advanced lightweight armored ground vehicles. The armor

composition of 6 wt. % aluminum, 4 wt. % vanadium (Ti-6Al4V) was developed by Watertown Arsenal for armor applications (MIL-DTL-46077). This material is used in the annealed

condition, rather than the much harder solution-treated and

aged (STA) condition, as employed by other metallic armors.

The best performance is normally obtained when this alloy is as

soft as possible.

METALLIC HYBRID LAMINATES

Metallic Laminates

Dual hardness armor steel (DHA, MIL-DTL-46099) was

developed to achieve improved performance over HHA. Armor

piercing threats are typically defeated by fracturing them using

a hard face plate, and then catching the debris with a softer

back plate. DHA steel has a 59-63 Rockwell C hardness (HRC)

steel for the face plate, normally S-7 tool steel, roll-bonded to a

50-53 HRC low alloy steel back plate. The steel compositions

are carefully chosen to match the martensite start temperatures

to avoid plate warping during quenching. This is the best performing steel armor against small arms ammunition, both ball

and AP, but it is also the most expensive. It is difficult to form

and weld, and large plates often have areas that are not completely bonded.

Very hard steel in the vicinity of 55 HRC backed by 2519

aluminum armor has been shown to have favorable mass, space

and cost efficiencies against certain AP threats. Conversely,

5083 aluminum armor backed by HHA has been used for protection from ball and fragmentation threats. Having the aluminum alloy on the front face changes the penetration mode of

the HHA backing from plugging to ductile tearing, thereby

improving its mass efficiency.

Metal-Composite Hybrids

Monolithic metallic armor is now routinely backed by a polymer matrix composite in armor systems. The composite serves

as a spall shield that minimizes the trauma to the interior of the

vehicle if the metallic armor is penetrated. Typically, the fibers

that are used to reinforce the polymer matrix are ballistic nylon,

Doron, S-2 glass, or KevlarTM aramid. (See our article on composite armor for more information on these and other composite materials.) Nearly all modern systems employ spall liners.

The costly ceramic-faced armor used in pilot and copilot

seats aboard the UH-60 Blackhawk helicopter were replaced

with AISI 4350 steel at 60 HRC. Both the ceramic and the steel

are backed with KevlarTM to contain spalled fragments of the

armor that may result from a ballistic hit. While the steel armor

is heavier than the ceramic, no weight penalty was incurred

because some existing nose counterweight material was eliminated. The replacement of steel for ceramic saved the Army

millions of dollars over the production run.

Figure 4. The Marine Corps Expeditionary Fighting Vehicle

(EFV) Will Be the First to Utilize 2519-T87 Armor.

Figure 5. Dragon Skin® Flexible Body Armor Vest Completely Repels Eleven Rounds of 7.62mm Ammunition. a) Vest View – Strike Points

Highlighted by Red Circles, b) View of Individual Scales.

a) Vest View b) Scale View

Reprinted by Permission

of Pinnacle Armor, Inc.
PROCESSING/

MANUFACTURING

STRUCTURE/

COMPOSITION

PROPERTIES/

BEHAVIOR

PERFORMANCE/

FUNCTIONS

Non-Skid Surface

Laminate Kevlar

Laser Cut to Size

Surface Treatment

Roller Level

Quench

Hot Roll

Cast

PLATE

high quality steel

stage I tempered martensite

Stops Threat

Weight

Space

Rapid Install 

& Remove

Airworthy

Modular

Hardness

18 The AMPTIAC Quarterly, Volume 8, Number 4

High hardness steel or titanium armor that has been tightly

wrapped with a thin layer of KevlarTM has been shown to have

improved ballistic performance. This effect has been exploited

in the Dragon Skin® flexible body armor manufactured by Pinnacle Armor, Inc. (Figure 5). Individual “scales” of titanium

composite are assembled into flexible, breathable body armor

which successfully repels rifle fire through Level III ballistic

protection, and into Level IV§.

Metal-Ceramic Hybrids

Typical metal-ceramic armor consists of a hard ceramic face

supported by a metallic backing. As a concept proven with

DHA, a hard strike face is very effective in breaking up the

threat. Ceramics can have a higher hardness than the hardest

steels, and thus they are an efficient material to break-up, shatter, erode, dwell or condition the projectile before it hits the

back plate. The metal back plate catches the fragments of both

the ceramic and the projectile.

Recent research at ARL has led to the development of

metal-encapsulated ceramic armor. In this concept, the armor

ceramic is strongly confined to enhance dwell†. Metal-ceramic

bonding with increased shear strength and reduced impedance

mismatch at the interface have shown to have a significant

affect on promoting dwell, and delaying ceramic failure for

improved ballistic performance. Currently, there are efforts to

design titanium and aluminum alloys with enhanced bonding

to the encapsulated ceramic and also improved performance as

a structural backing material. In addition, stiffening the metallic backing can further enhance the ceramic’s performance by

resisting bending during a ballistic event. Therefore, continuous ceramic fiber and particulate-reinforced metal matrix composites are being exploited as a stiffening layer between the

armor ceramic and metal backing.

Metal-Ceramic-Composite Hybrids

There are several metal-ceramic-composite hybrid armors in

development, while others have already been fielded. These 

systems utilize hard ceramic as the strike face to break up the

threat and a metal to provide structure and catch fragments

from the ceramic and the projectile. A polymer matrix composFigure 6. System Flowblock Diagram for Helicopter Armor.

Non-Skid Surface

Wear-Indicating Surface

Apply Coatings

PROCESSING/

MANUFACTURING

STRUCTURE/

COMPOSITION

PROPERTIES/

BEHAVIOR

PERFORMANCE/

FUNCTIONS

Laminate Kevlar

Laser Cut to Size

Surface Treatment

Temper

Roller Level

Quench

Hot Roll

Cast

COATING

multilayer paint

rubberized, sanded topcoat

TEXTILE

Kevlar

adhesively bonded

PLATE

high quality steel

stage I tempered martensite

alloy

matrix

strengthening dispersion

grain refining dispersion

microsegregation

macrosegregation

inclusions

Stops Threat

Weight

Space

Rapid Install 

& Remove

Airworthy

Modular

Energy-Absorbing

Mass-Efficient

Space-Efficient 

Multi-Hit Capability

Plate Sets

Durability

Hardness

VALUE

COST

Table 1. Armor Design Rules of Thumb.

Monolithic Systems Multi-Material (Hybrid) Systems

Harder is better, “adequate” hardness to break up the projectile Harder may not be better, but a hard face usually is

Tougher is better, “adequate” toughness to resist cracking Tougher may not be better, but a tough backing usually is

Thicker is better Thicker may not be better

Heavier is better Heavier may not be better

One thick plate is better than two thin laminated plates Two thin laminated plates may be better than one thick plate

More obliquity(angle of impact) is better More obliquity may not be better
MH-47 Chinook

The AMPTIAC Quarterly, Volume 8, Number 4 19

ite is also used to catch any spall off the back of the metal. The

Stryker-Interim Armored Vehicle and the EFV utilize this type

of metal-ceramic-composite armor system to provide superior

ballistic protection.

CURRENT DESIGN APPROACHES FOR 

METALLIC ARMOR MATERIALS SYSTEMS

The historical approach to metallic armor development has

been based on the trial-and-error, “heat and beat, shoot and

see” philosophy. In the past, armor designers relied on empirical data and engineering judgment aided by analytical models

to design candidate systems. The candidate armor materials

were then tested, and the design was refined or discarded.

Today, however, metallic armors are designed with knowledgebased alloy development (both in chemistry and thermomechanical processing), coupled with a phenomenological understanding of the penetrator-target interaction.

Present metallic armor research is directed at the metallic

component in a hybrid materials design. Within a hybrid system, the properties that are desired are often not the same as

those desired in a monolithic system (Table 1).

Present Research

The Ballistic Protection System (BPS) was developed by the

Protective Materials Company with assistance from ARL in

response to a request for helicopter armor from the Technology

Applications Program Office (TAPO) of Special Operations

Command (SOCOM) in 2000. The system design approach

can be represented by the flowblock diagram of Figure 6.[6]

The helicopters of interest were the UH-60 Blackhawk and the

MH-47 Chinook, and the areas of protection were both the

crew and cargo areas. (Figure 7)

The designed armor uses a high quality, high hardness steel,

and is wrapped by a thin layer of Kevlar. A multilayer paint is

applied to give the top surface non-skid and wear-sensing

properties, as well as environmental resistance. The overall

thickness of the system is less than 3/8 inch, giving excellent

space efficiency, and allowing easier installation. Because the

steel can be laser cut to high precision without further

machining, significant cost savings are achieved.

The armor system consists of a set of plates for an individual aircraft (Figure 8), which enables the system to be tailored

to specific missions in a modular fashion. It can be rapidly

installed and removed. Since the predominant material is

steel, it has excellent multi-hit capability, durability, and 

cost efficiency. For all these reasons, it has received an airworthiness readiness (AWR) certificate. This armor system 

has also recently been deployed on the US Marine Corps 

CH-53E Super Stallion.

“Cybersteel 2020: Naval Materials by Design,” [6] is an

ongoing research program by Northwestern University’s Materials Technology Laboratory under funding by the Office of

Naval Research to develop improved blast-resistant alloys. With

computational thermodynamic and strength design methods,

this particular project investigates models for new secondary

hardening martensitic steels that may reach previously unattainable levels of extreme dynamic fracture toughness and

ultrahigh strength. Secondary hardening steels rely on alloying

elements, such as Cr, W, Mo, and V, to precipitate fine dispersions of alloy carbides during tempering heat treatments. The

Figure 7. Emerging Armor Systems are Being Employed to Improve Survivability of Helicopter Cargoes and Crews.

Figure 8. BPS Installation in an MH-47 Chinook Helicopter.

UH-60 Blackhawk
20 The AMPTIAC Quarterly, Volume 8, Number 4

nucleation of this stable phase replaces coarser cementite

(Fe3C) particles, resulting in a microstructure that imparts

improved strength and fracture resistance. By optimizing other

compositional and processing components that meet requirements for weldability and cost, these new concepts for achieving enhanced blast-resistance will also provide the basis for the

next generation of naval hull steels.

CONCLUSION

Advanced metallic armor materials continue to exhibit properties that cannot be matched by other materials. Among them

are cost, fabricability, durability, multi-hit capability, and a

broad threat spectrum resistance. Metallic armor is evolving

into the role of a structural armor backing that motivates the

development of metal-matrix composites, micro-intermetallic

laminates, and hybrid periodic core materials. On the horizon

is the reality of multi-functional metallic armor by design.

NOTES

* Stage refers to the fracture mechanism of the steel. Stage I

tempered alloys are composed primarily of austenitic structures, which are very strong, hard, and extremely crack-resistant, but are brittle. Stage II tempered materials feature some

combination of austenitic (hard) and martensitic (soft) morphologies, thus representing a compromise of strength and

toughness. Most structural steels are Stage II. In Stage III tempers, martensitic effects dominate over residual austenite fractions. These materials are much more ductile than their more

austenitic counterparts, and thus are far better at absorbing and

mitigating kinetic energy from shock and blast – these are

desirable qualities in armor materials.

§ Ballistic Level of Protection pertains to the total kinetic energy of a single representative round of ammunition that an

armor system can mitigate. Established by the National Institute of Justice (NIJ) standard, Level III is defined as full protection against high-powered rifle rounds at representative muzzle

velocities (e.g. 7.62mm full metal jacket at 2750 ft/s or less).

Similarly, Level IV is defined as protection against armor-piercing rounds (e.g. 0.30 cal APM2 at 2850 ft/s).

† Dwell occurs when a projectile erodes and flattens on the

armor surface with no significant penetration into the armor.

GENERAL REFERENCES

S.J. Manganello and K.H. Abbott, Metallurgical Factors 

Affecting the Ballistic Behavior of Steel Targets, J. Materials, 

Vol. 7, No. 2, 1972, pp. 231-239

Engineering Design Handbook – Armor and Its Applications (U),

Army Materiel Command Pamphlet AMCP-706-170, Alexandria VA, November 1973

C.W. Amos, Lightweight Armor Design Handbook – Monolithic

Armor (U), MTL Technical Report MTL TR 90-40, Watertown MA, August 1990

A. Doig, Military Metallurgy. IOM Communications Ltd,

London UK, 1998

REFERENCES

[1] F. Mascianica, Ballistic Technology of Lightweight Armor (U),

MTL Technical Report AMMRC-TR 81-20, Watertown MA,

May 1981

[2] J.H. Hollomon and L.D. Jaffe, The Metallurgical Design of

Steels for Optimum Mechanical Properties, Experimental Report

WAL 320/28, Watertown Arsenal Laboratories (now MTL), 22

October 1945

[3] J.H. Hollomon, L.D. Jaffe, D.E. McCarthy and M.R. Norton, The Effects of Microstructure on the Mechanical Properties of

Steel, Trans. AIME, Vol. 38, 1947, pp. 807-844

[4] M.G.H. Wells, J.S. Montgomery and E.B. Kula, High

Strength Steels: Army Research and Applications, Proceedings of

the Gilbert R. Speich Symposium, Montreal, Quebec Canada,

October 1992

[5] J.H. Beatty and M. Azrin, Correlation of Ballistic Performance to Shear Instability in High Strength Steel, Proceedings of

the Army Science Conference, Orlando FL, June 1992

[6] G.B. Olson, et al., Naval Materials by Design, Cybersteel

2020: Blast-Resistant Naval Hull Steel, Undergraduate Materials

Design Project, Northwestern University Department of Materials Science, June 2003

Dr. Jonathan S. Montgomery has been at the Army Research Laboratory and its predecessor organizations as a

Materials Research Engineer since 1985. He works on stronger, more durable, lighter weight metals for armor, guns,

projectiles, missiles, helicopters, combat vehicles, and other Army systems. He received his BE in Engineering Science from the State University of New York at Stony Brook in 1980, an MS in Metallurgy from MIT in 1984, and

a PhD in Materials Science from Northwestern in 1990.

Dr. Ernest S. Chin is the Armor Materials Team Leader at the Army Research Laboratory (ARL), Aberdeen Proving

Ground, MD. He received his BS and MS from Brown University and his PhD in Materials Science and Engineering from Worcester Polytechnic Institute. Since joining ARL in 1982, Dr. Chin’s research activities have focused on

understanding the relationship between processing and ballistic performance in armor ceramics, lightweight metals,

and composites.
The AMPTIAC Quarterly, Volume 8, Number 4 21

INTRODUCTION

Ceramics have been used in armor systems for the last half-century, mainly for personnel and light vehicle protection against

small arms and machine gun threats. The widespread use of

two-layer, ceramic-based body armor by US Soldiers in

Afghanistan and Iraq is helping to save lives (Figure 1). Other

currently fielded ceramic armor technologies include helicopter

seats (Figure 2) and the US Army’s armored mobile gun system

as shown in Figure 3. Future applications include the US

Marine Corps Expeditionary Fighting Vehicle (formerly known

as the Advanced Amphibious Assault Vehicle, or AAAV) and

the US Army’s Future Combat System.

Ceramics are attractive as armor materials because they are

more weight-efficient than traditional monolithic armors, such

as “rolled homogeneous armor” (RHA), against a variety of

threats. Properties that make ceramics efficient include low

density, high hardness, high compressive strength, and high

elastic modulus. However, the low tensile strength typical of

ceramics severely limits their performance, and thus standalone ceramic armors can be inferior to traditional steel armors.

To exploit an armor ceramic’s high compressive strength, it

must be properly integrated into a ceramic armor system. It is

important to make the following distinction between ceramic

armors and armor ceramics: “Armor ceramics refer to the actual ceramic materials themselves. Ceramic armor refers to an

armor system designed to defeat specific ballistic threats and

which contains ceramic components.” [1]

Ceramic properties important for armor applications are

understood, but their exact correlation with armor performance remains elusive, partly due to numerous defeat mechanisms invoked by a wide variety of threats. A particular ceramic that is optimal in one application may perform poorly in

another. Other reasons are the complexity of the impact

process: spatial and temporal stress state variation, damage generation and propagation, and stress wave interactions. This 

article presents an overview of the fundamental defeat mechanisms of ceramic armors (the application) and provides interpretations of the impact and shock response of ceramics so that

the role of advanced armor ceramic materials within armor 

systems can be better understood. Ceramic armor designers

know that performance is strongly system- as well as threatdependent. Therefore, it is essential to discuss these aspects to

bridge ceramic armor and armor ceramic development.* 

FUNDAMENTALS OF CERAMIC ARMOR 

The purpose of armor is to enhance personnel and vehicle 

survivability by defeating projectiles and fragments, that is, to

prevent target perforation and structural failure, which can

occur with or without penetration. For example, a cannon ball

may cause massive deformation and structural failure without

Michael J. Normandia

Jerry C. LaSalvia

William A. Gooch Jr.

James W. McCauley

Weapons and Materials Research Directorate

US Army Research Laboratory

Aberdeen Proving Ground, MD

A.M. Rajendran

US Army Research Office

Research Triangle Park, NC

Figure 1. Examples of Ceramic Body Armor Plates and Inserts[i].

Figure 2. Helicopter Seats[i]: European Tiger Helicopter Seat, 

Cercom Inc. (Left); AH64 Apache Helicopter Seat Using 

Hot-Pressed Boron Carbide, Simula Inc. (Middle); and 

MH-60 Blackhawk Seat, Ceradyne Inc. (Right).

a)

b)

c) d)

a) Boron Carbide Small Arms Protective Inserts (SAPI) Interceptor Plates, Cercom Inc.; 

b) Ceradyne Body Armor and Inserts; c) Interceptor Body Armor, Simula Inc.; 

d) M-Cubed Reaction-Bonded Silicon Carbide SAPI Interceptor Plates, Simula Inc.
22 The AMPTIAC Quarterly, Volume 8, Number 4

penetration, or shock waves may result in spall or behind

armor debris due to tensile wave reflections. Consequently, the

armor must absorb the ballistic impulse without failure (by

structural deformation and attenuation of elastic waves), while

dissipating the projectile’s kinetic energy (KE). The primary

role of the armor ceramic is to convert the projectile’s KE into

elastic stored energy or plastic work on the projectile. For brittle projectiles, the elastic stored energy can result in projectile

fragmentation. As a result of either plastic work or fragmentation, the “failed” projectile remnants may also disperse, which

distributes the projectile’s KE over a greater target area. The

high elastic wave speeds in armor ceramics also increases the

amount of material involved in the defeat process. Finally,

ceramics absorb the ballistic impulse by spreading the load

onto the backing armor components, and in effect increasing

the amount of backing material involved with the impact. The

deformation of the backing material absorbs the momentum

of the projectile and target debris, in essence, catching them.

The armor response to ballistic impact consists of: impact,

pre-penetration, material failure, penetration, and momentum

absorption. Impact is studied using shock physics to understand dynamic material properties and stress states within both

the penetrator and the target. Pre-penetration refers to penetrator shatter, fracture or erosion prior to penetration. These

impact loadings typically result in damage accumulation and

target material failure, such as ductile material plasticity or brittle material fracture, studied using fracture mechanics, and

materials science, such as indentation testing. 

The penetration process may be categorized by the penetrator response. The penetrator may just make a hole in the target,

slowing down until stopped or until target perforation occurs.

During this process, the penetrator may remain rigid, or it may

deform plastically (if it is fashioned from a ductile material like

lead, steel, or copper), or it may shatter and penetrate as a concentrated debris cloud, or it may erode. Finally, the impactor

momentum is absorbed by target deformation or elastic wave

dissipation. The backing material catches the remaining projectile and fractured ceramic, termed the capture phase. Composites and fabrics are often used for this role, and are discussed in

other articles.

Basic components of a two-component ceramic armor are a

hard face (ceramic) bonded to either a soft backing (composite

or fabric) or a hard backing (metal). Fielded ceramic armors,

(Figures 1-3), have more elaborate designs, due to the need to

satisfy a multitude of performance and environmental requirements. These include multiple impacts and impacts at edges

and joints, which significantly affect the ceramic armor designs.

In some designs, for example, ceramic tile edges are raised to

equalize protection across the ceramic tile. However, simple

two-component systems are adequate to understand how

ceramic armors work.

Threat Classes

Threats are delineated by type, kinetic energy (KE) or chemical

energy (CE) and by penetrator caliber, length to diameter

aspect ratio (L/D) and impact velocity. Fragments from fragmenting munitions (grenades) and from improvised explosive

devices (IED’s) are threat classes not discussed in this article.

Small-Caliber KE Projectiles

Small-caliber projectiles typically include bullets and fragments

with sizes up to 7.62 mm (0.30 cal.) and velocities below 1

km/s (3281 ft/s). L/D ratios vary from 1 to about 5. They may

be composed of steel, lead, tungsten carbide, or tungsten alloy.

For armor piercing projectiles, core nose shapes may be blunt

or sharp. Projectile energies are typically on the order of several kilojoules (kJ).

The interaction between a 7.62 mm APM2 steel core and a

boron carbide based target is shown in Figure 4 using a

sequence of 1 MeV flash X-ray radiographs taken at various

times during the ballistic event. After the initial impact phase

at 6 μs, the nose of the core has eroded without penetration

into the ceramic. During this initial time period or pre-penetration phase the high ceramic hardness overmatches the impact

load, causing the penetrator to dwell on its surface. However,

ceramic damage is accumulating, and by 16 to 25 μs, the core

has entered the penetration phase, having begun to penetrate

while shortening (eroding) the penetrator. Even though the

ceramic has failed, it continues to offer sufficient resistance to

continue to erode the

projectile and even

contribute to its fracture. The reason why

dwell ends in this particular case is simply

because the backing

material fails and cannot properly support

the ceramic. The loss

of support allows the

back of the ceramic to

experience large tensile stress, which combines with the compressive stress to induce damage and cause a

loss of load-bearing capacity. Thus, the back of the ceramic can

no longer support the top of the ceramic, and dwell ends. The

opening of a Hertzian cone§ crack and bulging of the back of

the ceramic is also evident.

At 35 μs, the bulging is much more severe and fracture of the

core is evident. At 56 μs, the core has completely penetrated the

ceramic and continued into the backing material. The residual

core was fractured into at least two pieces that were stopped

within the backing material (capture phase). If it completely

penetrated through the backing material, this would be termed

break-out or perforation. The impact velocity at which this

Figure 3. Stryker Combat Vehicle Mounts a Licensed Version 

of the MEXASTM System† and is Based on the Light Armored

Vehicle 3rd Generation (LAV III) Chassis and Hull. General

Dynamics Land Systems – Canada[ii].

0 μs 6 μs 16 μs

35 μ 56 μs 25 s μs

Ceramic

Backing

Figure 4. X-Radiographs Showing Time

History of a 7.62 mm APM2 Bullet Core

Impacting Boron Carbide Illustrating

Dwell, Penetration by Erosion, Bullet

Fragmentation and Capture.
The AMPTIAC Quarterly, Volume 8, Number 4 23

break-out just occurs (velocity at which 50% of projectiles are

stopped and 50% completely perforate the armor) is referred to

as the ballistic limit velocity of the armor.

In summary, the role of the ceramic is to erode the projectile

nose and spread the resulting ballistic load onto the backing

material (e.g. the bulge diameter is larger than the bullet diameter). In this case (but not always) the projectile fractures. For

small-caliber KE threats, the important ceramic properties are

low density and high hardness. A lower density enables the use

of a thicker ceramic for a given weight, which would be more

effective in spreading the load.

Medium- and Large-Caliber KE Projectiles

Medium and large-caliber threats, 20-140 mm, intended to

defeat heavy armor applications, typically have an intermediate

velocity, 1.3 - >1.6 km/s, and are composed of a high density

metal (~ 18 g/cm3) that is resistant to shattering. These high

L/D ratio penetrators (currently fielded threats exceed 30:1)

impact with megajoules (106 J) of KE‡ The primary mechanism

to defeat these threats is erosion. In order to erode the projectiles, high ceramic compressive strengths are required to generate several GPa of pressure on the penetrator tip for an extended period of time (tens to hundreds of microseconds) causing

the penetrator to yield and flow laterally. The damaged, failed

and comminuted (pulverized into small particles) ceramic

properties dominate the erosive behavior and the damaged

ceramic must be confined, either inertially or geometrically, to

maintain adequate pressure on the penetrator to continue this

process, while consuming the KE penetrator. In these systems,

the confining backing and lateral materials are chosen to provide stiff supporting structural elements.

The penetration and erosion process are often approximated

by analytical models based on hydrodynamic principles (such

as Bernoulli’s laws) modified to account for target and penetrator strengths (~3 times the dynamic ceramic yield strength).

These lumped strength parameters make direct correlations of

ballistic performance with basic armor ceramic properties challenging. [2]

Shaped-Charge Jets

For high velocity impacts of shaped-charge jets, the ceramic

strength is overwhelmed by the high impact pressures as the

process is more purely hydrodynamic. These jets (typically copper) are formed using high-explosives upon impact and produce a long metallic stream or a plasma jet with a variable

diameter and velocity along its length, which stretches during

the penetration process. Hence the rod, or jet, stretches during

the penetration process. The tip velocity is between 6 and 10 or

more km/s, and the tail velocity is typically ~2 km/s producing

impact pressures on the order of 100 GPa. The ceramic’s low

density makes it efficient on a mass basis (but not on a space

basis) relative to armor steels. The ability of the ceramic to bulk

(increase volume) upon failure within a confined armor

impinges debris on the jet helping to misalign a jet that is

inherently weak in the lateral direction. 

The effectiveness of ceramic armor against shaped-charged

jets is important, as these threats become more common in the

battlefield, which is evident with the Rocket Propelled

Grenades (RPGs) being used in Iraq. Defeat of shaped-charge

jets is a much more complicated process than for KE threats,

and thus will not be addressed in this article.

Recent Ideas: Interface Defeat**

Ceramic armor enhancements continue as penetrator threats

evolve. Increased ceramic efficiency is possible by delaying 

penetration and/or by increasing the comminuted ceramics’

erosion efficiency; for example by using modest lateral confinement to constrain broken ceramic pieces. A most historic and

significant observation was made in 1987 during ballistic

experiments where a tungsten-alloy, long-rod penetrator

impacting a highly confined ceramic target at 1.6 km/s, was

completely consumed, without penetration (Figure 5) [3]. It

was also observed that with less confinement, partial penetrator

dwell occurred on the surface prior to penetration. This work

led to a better understanding of the importance of delaying,

mitigating, and confining the damaged ceramic. The practicality of these laboratory targets as armors is limited. However,

much of what was learned is now being explored and incorporated into practical ceramic armor designs which promise substantial improvements in weight efficiencies.

This experiment was significant as it demonstrated that brittle

ceramics are impenetrable by most common threats if the ceramic is prevented from failing (although it may be highly damaged). Systematic laboratory experiments determined a critical

velocity (impact load) that armor ceramics (of a given thickness)

can withstand before penetration occurs [4]. This critical velocity was approximately 1.5 km/s for tungsten-alloy penetrators

(and greater than 2 km/s for lower density penetrators), providing total interface defeat of very long rods. Another demonstration of ceramic impenetrability is shown in Figure 6 for a

25.4 mm thick aluminum oxide tile with a steel backing [5].

CERAMIC DAMAGE

Ceramic armor performance is system- and threat-dependent as

these affect the type and distribution of damage within the

ceramic. This damage results from activation of pre-existing

defects caused by hydrostatic, shear, and tensile stresses. During

a ballistic event, these stresses interact with pre-existing defects

Figure 5. Schematic Illustration of Highly Confined Ceramic 

Target (Left). X-Ray Radiograph of a Long-Rod Penetrator

Dwelling on a Ceramic (Right) [3].

Felt

Copper

Granite

Ceramic

Shrink

Fit

Front Steel Confinement

Back Steel Support

Weld

Shock-Wave

Attenuator

Mild Steel

17-4 PH

Steel
24 The AMPTIAC Quarterly, Volume 8, Number 4

Figure 6. Dwell of a

Hard-Steel Core APM2

Bullet on a Steel-Backed

Alumina Tile.

Figure 7. Tensile and Compressive Damage in a Post-Impact

Silicon Carbide Ceramic Recovered from an Interface Defeat

Experiment.

Photos Courtesy of Southwest

Research Institute (SwRI), 

San Antonio, TX [5]

Photo Courtesy of Dr. J. Shih

generating tensile and compressive damage regions within the

armor ceramic. The silicon carbide shown in Figure 7 was recovered from an interface defeat experiment where impact occurred

at the top-middle surface. Both damaged and undamaged

regions can be seen. Tensile damage consists of relatively large

macrocracks that may actually split the ceramic tile into several

large pieces, while compressive damage consists of a high density of microcracks. A ceramic’s resistance to penetration is the

result of the integrated mechanical response of these damaged

and undamaged regions coupled with the mechanical response

of the entire system. This is why a ceramic’s performance is system- and threat-dependent, and also why understanding the

mechanisms responsible for damage is so important.

Pre-Existing Microstructural Defects

Ceramics are inherently brittle when subjected to tensile stresses because of their atomic bonding, and also because they lack

an adequate number of independent dislocation slip systems or

adequate dislocation mobility to support bulk plasticity, in contrast to most metals. Lack of metal-like ductility makes the

mechanical response of ceramics very sensitive to intrinsic and

extrinsic material defects. These defects range in size from subnanometers to hundreds of micrometers. They are detrimental

because they act as stress risers, which can result in crack formation and cause failure when the ceramic is subjected to an

applied stress. Microstructural defects such as pores, inclusions,

large grains, and microcracks are the most detrimental because

of their relatively large size (micrometers).

Armor ceramics are available as pressureless sintered (lower

cost) or hot-pressed (higher cost). Table 1 lists a sampling of

ceramic producers used for current armor applications. The origin of microstructural defects is intimately connected to the

methods by which ceramic bodies are fabricated and finished.

Armor ceramics are normally produced via powder processing

routes, that is, micron-sized ceramic powders are pressed into

“green bodies” that are less than 60% dense (i.e., porous) and

then are densified (sintering process) at high temperatures

(2000°C) with or without an applied pressure (0-200 MPa) to

achieve a 98-100% theoretical density. Sintering additives are

typically used to decrease the densification temperature, and as

a result cost. 

An exception to the sintering process is reaction-bonding

where the porous powder body is infiltrated by a liquid, such as

aluminum or silicon, in a vacuum or reactive atmosphere. This

liquid may react with powder additives or atmospheric gases to

minimize the residual solidified liquid. For these processes, the

nature, size, and frequency of microstructural defects is very

dependent on the quality (e.g., size distribution, level of impurities), preparation (e.g., mixing and milling), and processing

(e.g., densification) of the powders. Incomplete sintering or

trapping of volatile impurities or contaminants results in residual porosity (faceted or irregularly-shaped pores), as shown in

Figure 8, for a commercially-available pressureless sintered silicon carbide.

Inclusions (metallic, carbon, and possibly brittle second

phases), can be present in the densified ceramic because they

often exist in the starting powders as impurities, introduced

inadvertently during powder preparation, or created as a result

of high temperature reactions (Figure 9). Large grains can result

from a broad particle size distribution in the starting powder,

incomplete powder milling operation (used to reduce the size

of the largest particles), or abnormal grain growth (poor distribution of sintering additive).

Microcracks can form from pores and inclusions because of

differences in elastic and thermal expansion properties between

them and the parent phase. They can also form within the grains

and along grain boundaries of the parent phase because of the

crystallographic orientation dependence of the elastic and thermal expansion properties. During the cool-down period from

exposure to high temperatures, each individual grain or phase

wants to contract, but this contraction is resisted by neighboring grains or material. This results in residual stresses due to the

Table 1. Current Ceramic Armor Producers.

Ceramic Type Ceramics Producer

Sintered 99.5% Alumina CoorsTek

Alumina Morgan Matroc (UK)

Alumina ETEC

Sintered SiC Ceradyne

Pure Carbon SiC

Reaction-Bonded SiC M-Cubed (Simula)

SiC MC2 (Australia)

B4C

Hot Pressed B4C Cercom

TiB2

WC

SiC

B4C Ceradyne

TiB2

SiC

B4C Saint-Gobain

SiC
The AMPTIAC Quarterly, Volume 8, Number 4 25

build-up of tensile stresses at some grain boundaries, but more

importantly, at junctions of multiple intersecting grains. The

magnitude of this residual stress increases with increasing grain

or inclusion size. Thus, for sufficiently large grain or inclusion

size, spontaneous microcracking occurs, which relieves the residual stresses. Lastly, microcracks can also be introduced into surface regions of ceramics during final machining and surface finishing operations (e.g., cutting or surface grinding). These

operations essentially involve the oblique impact of hard particles, such as diamond, on the ceramic. This impact creates a

region of localized surface damage, which may include relatively long microcracks that penetrate into the ceramic. If subsequent surface finishing operations are poor in terms of quality,

they will fail to eliminate these microcracks.

Tensile and Compressive Failure

For penetration to occur, ceramic material must be displaced,

either pushed aside or through the back of the target (i.e., plugging), by the projectile. Both tensile and compressive damage,

initiated from pre-existing defects, if sufficient in severity, may

allow displacement of the fractured ceramic to occur.

In a ballistic event, tensile cracking normally leads to both a

loss of mechanical confinement of compressively damaged

regions and concentration of the impact load on the target

material directly underneath the projectile. This further leads to

an increased likelihood of compressive damage (pulverization)

of the ceramic or plugging of the target. Understanding of this

pulverization (failure) process in brittle solids like ceramics is

not as complete as that for tensile failure. Part of the reason is

that there are a number of micromechanisms for compressive

damage and these can be Mode I (also called tensile crack initiation or opening cracks), Mode II (shear), or mixed-mode in

nature depending on the magnitude of the shear and hydrostatic stresses. Another reason is that unlike tensile failure, where a

single flaw can cause failure, compressive failure occurs as a

result of complex interactions between billions of microflaws,

dislocations, and crystallographic twins under multiaxial, high

pressure, high strain rate loading conditions. Note that in the

compressive damage region, the ability to resist shear deformation is based upon the interlocking of and frictional resistance

between micron-sized fragments. From the very fact that penetration did not occur in regions as shown in Figure 7, it is safe

to say that the amount and distribution of compressive damage

was below the critical value.

Some factors that govern compressive damage can be found

in the geological literature [6] and also within the compressive

damage region itself (as shown in Figure 7). Consider the

micromechanism illustrated in Figure 10, which shows a preexisting microcrack of length 2c subjected to compressive

stresses σ1 and σ2. The stresses are such that shear or sliding

failure (Mode II) of the pre-existing microcrack occurs. Frictional resistance (but m=μ is the coefficient of sliding friction)

must be overcome for the cracks to grow. As a result of sliding

failure, dislocations and wing-cracks†† (at an angle θ) can be

initiated at the tips of the pre-existing microcrack. For the sake

of simplicity, we designate a ductile response if dislocation

emission dominates and brittle response if wing-crack formation dominates. The formation of the wing-cracks is actually a

crack opening or Mode I event even though the process is shear

driven. Therefore, intuitively, for an increasing σ2 confining

stress, wing-crack formation would be suppressed and a ductile

response encouraged. Consequently, any process that decreases

the σ2 confining stress (e.g. tensile cracking) encourages a brittle ceramic response. The critical applied stress σ1 (i.e. caused

by ballistic impact) needed to initiate and grow the wing-cracks

is dependent upon a number of factors including pre-existing

flaw size (frequently assumed as proportional to grain size),

coefficient of sliding friction, wing-crack length, fracture

Figure 8. Pores (Dark Spots) in a Commercially-Available

Pressureless Sintered Silicon Carbide [5].

Figure 9. Graphite Inclusions (Arrows) in Hot-Pressed Boron

Carbide (Left) and Vanadium Carbide Inclusion in Hot-Pressed

Tungsten Carbide (Right) Ceramics [5].

Figure 10. Possible Micromechanism for Compressive Damage

in Ceramics [6].

σ1, σ2 - Compressive Stresses

⊥ - Dislocations

θ - Angle between Wing 

- Crack and Dislocations

Pre-Existing Flaw

(length=2c)

σ2

σ1

θ

⊥ ⊥ ⊥ ⊥

⊥ ⊥ ⊥ ⊥
26 The AMPTIAC Quarterly, Volume 8, Number 4

toughness (short-crack), and confining hydrostatic stress.

A convenient way to illustrate this dependence is by the “ductility map” shown in Figure 11. This map displays the regions

where dominantly brittle and ductile responses would be expected depending upon short-crack fracture toughness (KSC

IC), preexisting flaw size (2c), and relative confining stress (σ2/σ1). The

coefficient of sliding friction is 0.4 for this map. Decreasing

coefficients of sliding friction expand the brittle region. Consideration of this map shows that increasing short-crack fracture

toughness, sliding friction coefficient, and confinement stress

while decreasing pre-existing defect size suppresses compressive

damage. This has implications for ceramic improvement.

MODELING CERAMIC IMPACTS

As illustrated in Figure 10, the micromechanisms associated

with compressive strength degradation of ceramics from impact

began from damage accumulation under time-dependent,

high-amplitude loads which are extremely complex. Understanding and modeling of the fracture process in ceramics

began with a detailed study on quasi-static fractures induced by

indentation loading. The indentation modeling effort mostly

focused on the contact-load induced micro/macro cracking

that occurs due to contact loading [7]. Since then, numerous

studies have clearly established the presence of dislocations and

twinning in the brittle ceramics due to high pressures and high

strain rate loading conditions [8-9].

Resistance to projectile penetration is greatly influenced by

the boundary conditions and intrinsic dynamic properties of

the ceramic. The initially intact ceramic uses its full, pressuredependent, compressive strength to prevent projectile penetration until a damage threshold condition is reached. While the

stress state at the penetrator tip remains in compression (shear),

the ceramic accumulates damage through shear (Mode II) until

a threshold condition is reached. However, the inertially confined cracked-up ceramic continued to resist projectile penetration, suggesting that damage threshold doesn’t degrade ceramic performance. However, the compressive failure due to axial

splitting and faulting can occur through creation of wingcracks at pre-existing defects as illustrated in Figure 10. Eventually, tensile stresses generated by complex wave interactions

with lateral boundaries degrade ceramic properties further and

enable projectile penetration. 

In thin ceramic tiles, a complex pattern of ring, radial, cone,

and lateral cracks are formed prior to projectile penetration. In

thick, confined tiles, as shown in Figure 7, the ceramic material directly beneath the nose of the eroding projectile can form

a region of finely comminuted, pulverized ceramic, referred to

as the “Mescal Zone,” but that even though severely damaged

the ceramic continues to resist projectile penetration [10].

Prior to 1988, very few material models that could describe

the inelastic behavior of brittle ceramics under shock and high

strain rate loading conditions were implemented in hydrocodes

(shock-wave propagation based finite element/difference

numerical codes). Several ceramic damage models have now

been successfully implemented in design hydrocodes during the

late 1990’s, and model parameters for several armor ceramics

have been determined. These models predicted the unconfined

thin tile response to APM2 projectile impacts as well as the

confined thick tile response to a KE projectile extremely well.

THE FUTURE OF CERAMIC ARMOR TECHNOLOGY

The applications of ceramics for armor are growing rapidly as

the need for lighter and more agile combat vehicles increases.

Ceramic armor technology offers the best potential for meeting

future protection requirements, particularly for the US Army’s

Future Combat System. Armor ceramic performance strongly

depends upon the threat conditions and the ceramic armor

design or configuration. 

Improvements in armor ceramic performance requires, as a

first-step, elimination, or reduction of, the size of pre-existing

microstructural defects. It is also possible to reduce the armor

ceramics’ sensitivity to these types of defects. Understanding

the micromechanisms responsible for tensile cracking and compressive damage helps to identify directions for both material

and computational modeling improvements. While these areas

have been the focus of numerous research efforts for many

years, it is only now that with a renewed emphasis on understanding damage and its implications, as well as better experimental and computational tools, that the science to advance

ceramic armor and armor ceramic development exists.

NOTES & REFERENCES

[i] Images reprinted with permission of Cercom Inc., Ceradyne

Inc., and Simula Inc. 

[ii] Images reprinted with permission of General Dynamics

Land Systems – Canada.

* Interested readers are encouraged to contact the authors for

recommended review articles, textbooks and journal publications, in which numerous additional technical publications are

referenced.

† Manufactured by IBD Corporation (Germany).

§ A conical-shaped crack that forms in a brittle material (typically ceramic) when struck by a projectile on its surface.

‡ 1 Megajoule (106 J) of kinetic energy (KE) is roughly equivalent to a 16-lb bowling ball traveling at 147 miles per hour.

** Upon impact, the projectile material (typically metal) is

forced to flow radially outwards on the surface of the ceramic

without penetrating it significantly.

†† Wing-cracks are cracks that extend out of the plane of the

original crack in the direction of maximum principal stress.

Figure 11. Ductility Map [6].

σ2/σ1

0 0.1 0.2 0.3 0.4 0.5

KSC

______ IC

τy√π•c

2.1

2

1.9

0.3

0.2

0.1

0

Ductile

μ = 0.4

Brittle
Dr. A.M. “Raj” Rajendran is a Senior Research Scientist in the Mechanical Sciences Division of the Army Research

Office, (ARO), in Research Triangle Park, NC. He also serves on several high-level tri-service (USA/USAF/USN)

and cross-agency (DOD/DOE/NASA) panels. In the past, he has served as the Chairman of DOD/DOE coordinating group for computational and material modeling group. Furthermore, Dr. Rajendran is the Computational 

Technical Area (CTA) Leader for Structural Mechanics at the High Performance Computing Modernization Office

(HPCMO) in the Office Of The Director, Defense Research and Engineering (DDR&E). Dr. Rajendran holds a PhD

in Aeronautics and Astronautics (Applied Mechanics) from the University of Washington.

The AMPTIAC Quarterly, Volume 8, Number 4 27

The catalysis for the extension of wing-cracks is shear failure of

the initial crack.

[1] D.J. Viechnicki, M.J. Slavin, and M.I. Kilman, Development

and Current Status of Armor Ceramics, Cer. Bull., 70 [6], 1991

[2] J. Sternberg, Material Properties Determining the Resistance

of Ceramics to High Velocity Penetration, J. Appl. Phys., 65 [9],

pp. 3417-3424, 1989

[3] G. Hauver, P. Netherwood, R. Benck and L. Kecskes, Ballistic Performance of Ceramics, US Army Symposium on

Mechanics, Plymouth MA, 17-19 August 1993

[4] P. Lundberg, R. Renstrom, and B. Lundberg, Impact of

Metallic Projectiles on Ceramic Targets: Transition Between Interface Defeat and Penetration, Int. J. Impact Eng, 19, pp. 1-13,

1997

[5] C.E. Anderson and J.D. Walker, Ceramic Dwell and Defeat

of the 0.30-CAL AP Projectile, Proceedings of the 15th US

Army Solid Mechanics Symposium, Eds., K. Iyer and S.C.

Chou, pp. 17-28, 1999

[6] H. Horii and S. Nemat-Nasser, Brittle Failure in Compression: Splitting, Faulting, and Ductile-Brittle Transition, Philosophical Transactions, Royal Society, A319, pp. 337-374, 1986

[7] B. Hockey, Plastic Deformation of Aluminum Oxide by

Indentation and Abrasion, Journal of the American Ceramic

Society, 54 [5], pp. 223-31, 1971

[8] D.A. Shockey, A.H. Marchand, S.R. Skaggs, G.E. Cort,

M.W. Burkett, and R. Parker, Failure Phenomenology of Confined Ceramics Targets and Impacting Rods, Int. J. Impact

Engng., 9, pp. 263-275, 1990

[9] D.R. Curran, L. Seaman, T. Cooper, and D.A. Shockey,

Micromechanical Model for Comminution and Granular Flow of

Brittle Material under High Strain Rate Application to Penetration of Ceramic Targets, Int. J. Imp Eng., 13, pp. 53-83, 1993

[10] J.F. Mescal and C.A. Tracy, Improved Modeling of Fracture

in Ceramic Armors, 1986 Army Science Conference Proceedings, West Point NY, 1986

Dr. James W. McCauley is the Senior Research Engineer (ST) in Ceramics and an ARL Fellow in the Army Research

Laboratory. He holds a BS in geology from St. Joseph’s College (Indiana); and a MS in mineralogy and PhD in

solid state science, both from Pennsylvania State University. He is a former professor and past Dean at the New

York State College of Ceramics at Alfred University. Prior to joining Alfred, he was employed at the Army Materials Technology Laboratory for 22 years. He is the author or co-author of about 75 open literature publications 

and reports, the editor/co-editor of five books, and holds four patents. He has served on the Army Science Board

and the external review committee for the Materials Science and Technology Division of Los Alamos National 

Laboratory. He is a Fellow, Distinguished Life Member and Past President of the American Ceramic Society.

Mr. William A. Gooch Jr. is a Materials Engineer and the Team Leader of the Small Arms, Heavy Machine Gun,

and Fragment Defeat Team, residing in the Armor Mechanics Branch, Terminal Effects Division, of the Weapons and

Materials Research Directorate, US Army Research Laboratory, Aberdeen Proving Ground. His 35 years of professional experience includes the initiation and direction of a wide range of research programs. His current projects

include the development of expedient light armors for wheeled tactical vehicles as well as passive armors for the

Future Combat System. Mr. Gooch has authored over 100 papers and reports, and holds a number of patents. He

received his BSE and MSE in Structures, Materials, and Fluids from the University of South Florida.

Dr. Jerry C. LaSalvia is a materials engineer in the Survivability Materials Branch of the Materials Division, Weapons

and Materials Research Directorate US Army Research Laboratory (ARL), Aberdeen Proving Ground, MD. Since

joining ARL in 1996, Dr. LaSalvia’s research has focused on the physics and mechanics of penetration, and ceramics processing. Areas of expertise include dynamic and ballistic response of materials (including energetic), solid

and fluid mechanics, heat transfer, microstructural and mechanical characterization, and processing of ceramics and

ceramic composites. Dr. LaSalvia holds a BS in Mechanical Engineering from the University of California, Berkeley,

and a Doctorate in Materials Science from the University of California, San Diego. 

Dr. Michael J. Normandia is a Research Physicist in the Armor Mechanics Branch within the Terminal Effects 

Division of the Weapons Materials Research Directorate at the US Army Research Laboratory. Since 2001, Dr. 

Normandia has led a multi-divisional basic and applied research effort on the onset, evolution, and propagation of

damage in brittle materials. His areas of expertise include continuum, solid and fluid mechanics, combustion and

energetic materials, survivability, lethality and vulnerability analysis, and armor design. Dr. Normandia received 

his doctorate in Theoretical & Applied Mechanics from Cornell University and a BS in Mathematics from Cooper

Union. Dr. Normandia has over 80 publications throughout his career. 
28 The AMPTIAC Quarterly, Volume 8, Number 4

INTRODUCTION

While many of the hazards faced by our soldiers in the field are

apparent, a more thorough assessment of a typical soldier’s

“theater of risk” reveals some suprising findings. A significant

portion of a soldier’s duties involve protection of facilities and

personnel in confined environments. These

tasks are akin to providing guard duty at

military posts and check-points in strategic

locations. The soldiers posted at these positions become the front lines of defense

against impending attack; however, they

are often also the target of terrorist-based

actions because of their relatively exposed

position. One manner of reducing the risk

to the soldier is to provide enhanced protection in equipment that allows the soldier

to perform the assigned duties efficiently,

while offering some ballistic safety. Current

system ballistic safety is limited by the mass

efficiency of existing materials designs. One

of the key protection capabilities for successful improvements in mission safety is

transparent ballistic glass that enables 

soldiers to observe the potentially hostile

environment through a protective shield.

Therefore, transparent armoring technologies are a significant component of military effectiveness.

Transparent materials are a subsection of materials that are

transparent to certain wavelengths of energy. Window glass,

for example, is transparent in the visible frequencies, while a

radome material, such as fused silica, is transparent to radar

frequencies. The Army Research Laboratory (ARL) has invested consistently to bring the best technical advancements 

in polymers, glasses, ceramics and adhesives to transparent

system designs. These materials have application not only in

ballistic glass but also in infrared (IR) domes, radomes, sensor

protection, and personnel protection. This

paper will provide an overview of the technology and applications, give specific

examples of materials of interest, and relate

the challenges that have been overcome

during the past decade while also discussing

those that remain.

Ballistic glass is a material or system of

materials designed to be optically transparent, yet protect against ballistic impacts,

and resist fragmentation. This class of materials is used in such diverse applications as

protective visors for non-combat usage,

including riot control (Figure 1) or explosive ordinance disposal (EOD) (Figure 2)

actions, to protect sensors from debris, and

to protect vehicle occupants from terrorist

actions or other hostile conflicts. Each of

these systems is designed to defeat specific

threats; however, there are general requirements common to most. The primary

requirement for a transparent armor system is to provide a

multi-hit defeat capability while retaining visibility in the surrounding areas. Land and air platforms of the future have several parameters that must be optimized, such as weight, volume, and cost. Often, these ballistic protection materials must

James M. Sands

Parimal J. Patel

Peter G. Dehmer

Alex J. Hsieh

Weapons and Materials Research Directorate

Army Research Laboratory

Aberdeen Proving Ground, MD

Mary C. Boyce

Department of Mechanical Engineering

Massachusetts Institute of Technology

Cambridge, MA

Back in the fall of 2000, AMPTIAC printed an article on transparent armor in our quarterly journal (known then as the AMPTIAC

Newsletter). It was written by four gentlemen from ARL – Parimal Patel, Gary Gilde, Peter Dehmer, and James McCauley. Note that

two of these men, Dr. Patel and Mr. Dehmer, have returned to help prepare this update (please also note that Dr. McCauley has written

the leadoff article in this issue). From the time of its publication to the present day, it has been, by an overwhelming margin, the single

most popular article in our history (as measured by reprint requests and downloads off our website). There was some initial hesitation to

write this piece, as we tend to shy away from revisiting old ground unless some significant advance in the state of the art has taken place

since initial publication. However, we pressed ahead for two very important reasons: First, we could not dedicate a section of the Quarterly to Survivability Materials without covering Transparent Armor. Second, we were (and are) confident that our readers, both new and

old, will find this a fascinating treatment of the subject. Readers familiar with our earlier article will find some familiar portions in this

piece, but will also be gratified to learn of the great advances made in the past four years. It will quickly become apparent to all that the

“torch” that is transparent armor has been successfully passed from one team to the next. Enjoy! - Editor

Figure 1. Face Shield and Body Shield.
The AMPTIAC Quarterly, Volume 8, Number 4 29

be compatible with night vision equipment to allow the soldiers to be effective in all environments. One potential solution to increase the ballistic performance of a window material is to increase the thickness. However, this solution is

impractical in most applications, as it will increase the weight

and impose space limitations or impact other systems in the

fielded environment. In addition, thick sections of transparent

materials often experience greater optical distortion than thinner sections, which reduces the transparency.

The development of modern armor systems is driven by the

doctrine of fire and maneuver. The

demand is for lightweight solutions

that enable soldiers and vehicles to

be highly mobile, destroy their targets, and return home safely. The

armor must provide protection from

a wide variety of bullets and fragments, and must not hinder the soldier’s ability to do their job. The

modern battlefield has evolved to

the point that there are no defined

battle fronts, and therefore everyone

is at risk and must be protected.

Each of these issues must be considered when designing any armor system. As opposed to conventional

armor, transparent armor has an

additional requirement in that the material must be transparent

to visible light, which dramatically limits the material choices

for an armor system.

Among the transparent materials available, new material systems being explored to meet the requirements for ballistic

applications include crystalline ceramics, new polymer materials, new interlayer technologies, and new laminate designs. The

fundamentals of transparent ballistic materials are discussed

here, along with insights for future designs and potential

approaches to advanced technologies.

APPLICATIONS AND REQUIREMENTS

Common military applications for transparent armor include

ground vehicle protection, air vehicle protection, personnel

protection, and protection of equipment such as sensors. Commercial applications requiring transparent armor include items

such as riot gear, face shields, security glass, armored cars, and

armored vehicles.

Visors

With the onset of many new peacekeeping roles within the military, it is necessary to provide a greater degree of protection to

the individual soldier. Facial protection via the use of transparent armor is one area of interest within the Army, marked by a

recent program within the Army Research Laboratory to

improve the current visor design.[1] Two types of visors were

marked for improvement, the riot visor, and an explosive ordnance disposal (EOD) visor.

Riot visors are typically made from injection-molded polycarbonate that has an areal density of 1.55 lb/ft2 (0.25” thick).

The riot visor is a piece of equipment that is designed to defeat

threats from large, low-velocity projectiles, such as rocks and

bottles, and small, high velocity fragments. Recent research and

development has focused on replacing the baseline polycarbonate designs with improved polymer materials. Among the candidate materials for riot visor improvements are advanced

polyurethane polymers. Polyurethanes possess a wide range of

properties that can be exploited to improve performance or

reduce weight. However, due to the limited size of the window

element in the riot visor configuration, the decision was made

to keep the existing platform design weight and improve the

ballistic performance. A target performance enhancement of 30%

improved fragment protection was

selected. In addition, the improved

ballistics element means that riot

visors achieve new standards for 9

mm handgun protection.

A second application for lightweight armors is in the EOD visor.

Because the EOD visor covers a significant facial area, the contribution

of the transparent laminate to the

overall system mass is significant.

Therefore, ballistic programs to

improve performance in EOD

designs sought to reduce the weight

of the overall application. For an

equivalent protection baseline, a 30% reduction in total mass

was desired as a success metric. 

Unlike the monolithic riot visors discussed previously, the

EOD visors are composed of laminated plastics. ARL attempted to reduce the weight of EOD visors by varying both laminate construction and material selection. Laminate designs

investigated included plastic/plastic, glass/plastic, and glassceramic/plastic.[1] Ballistic testing of these material systems

particularly encompassing polyurethane showed a marked

reduction in areal density from the current laminated design.

Among the laminates tested, those possessing hardened designs,

e.g., those with VycorTM fused silica and TransArmTM, provided the best ballistic performance.

Electromagnetic Windows

Many ceramic materials of interest for transparent armor solutions are also used for electromagnetic (EM) windows. These

applications include radomes, IR domes, sensor protection, and

multi-spectral windows. Optical properties of the materials

used for these applications are very important, as the transmission window and related cut-offs (UV, IR) control the electromagnetic regime over which the window is operational. Not

only must these materials possess abrasion resistance and

strength properties common of most armor applications, but

because of the unique high-temperature flight environment of

aircraft and missiles, they must also possess excellent thermal

stability. 

Artillery Projectiles

EM window materials are also currently being investigated by

the Army for use in artillery projectiles. While the optical transFigure 2. EOD Helmet.
30 The AMPTIAC Quarterly, Volume 8, Number 4

parency is not important for this application, material properties

such as low dielectric constant and low loss tangent are imperative.[2] Future artillery projectiles will be subjected to much

higher muzzle velocities (Mach 3), where aerodynamic heating

becomes a concern. New window materials must be capable of

withstanding 15,000 g’s of inertial setback loads with 15,000

rad/s2 of angular acceleration. Additionally, as communication

requirements change, the transmission and reception frequencies are changing to accommodate the more rapid exchange of

data. Available plastic window materials are incapable of surviving in these environments. The new operational demands

require new polymeric and complex laminate constructions 

for the radome and EM window designs. Prototypes for new

systems utilize a glass-ceramic material known as Macor® for the

nose tip*, which was chosen for electrical properties, high temperature capability, and ease of machining. However, replacement ceramics with a reduced dielectric constant and higher

operating temperature capabilities are still sought.

Ground Vehicles

Ground vehicles represent one of the largest application needs

for transparent armor, including high mobility multi-wheeled

vehicles (HMMWVs), tankers, trucks, and resupply vehicles

(Figure 3). There are several general requirements for the

application of transparent armor to windshields and side windows on these vehicles.[3] The first is that the armor must be

able to withstand multiple hits since most threat weapons are

typically automatic or semiautomatic. The windows must also

be full-size so that the vehicle can be operated without reducing the driver’s field of view. One of the requirements for

future transparent armor systems intended for vehicle use[3] is

a reduction in weight. The added transparent armor weight

can be significant, often requiring enhancement of the suspension and drive train to maintain the vehicle performance capability and payload capacity. Thinner armor systems are also

required, as thinner windows can increase the cabin volume of

the vehicle. Future systems must also be compatible with night

vision goggle equipment and offer laser protection.

Due to their size and shape, the majority of armor windows

are constructed of glass and plastic, but reductions in weight

and improvements in ballistic protection are needed. Based on

the number of vehicles in service, the window dimensions, and

the associated costs, improved glasses, glass ceramics and polymers appear to be the new materials of choice. Compositional

variations, chemical strengthening, and controlled crystallization are capable of improving the ballistic properties of glass.

Glasses can also be produced in large sizes with curved geometries, and can be produced to provide incremental ballistic

performance at incremental cost. The use of a transparent

ceramic as a front-ply has been shown to improve the ballistic

performance further while reducing the system weight. 

An excellent example of the current need for transparent

materials is represented by the recent fielding of add-on armor

kits for the military line of HMMWVs. In an effort to

improve the protection of soldiers in theater operations, the

Army designed an add-on armor capability that was developed

and fielded in a very short suspense. More than 4000 of these

armor survivability kits (ASKs) have been produced in less

than one year. However, the kits add significant weight to the

transport platforms, and therefore, impact mission loads for

the vehicles. The transparent armor in these kits is a significant

burden, contributing as much as 30% to the overall weight but

only covering 15% of the total area. Developing lighter weight

solutions with improved protection will allow transition of

these armor upgrade kits to vehicles without dramatically

impacting mission capability.

Air Vehicles

Air vehicles include helicopters, anti-tank aircraft, fixed wing

aircraft, and other aircraft that are used in combat and support

roles. Transparent armor applications in these vehicles include

windshields, blast shields, lookdown windows, and sensor protection. Requirements for aircraft systems are similar to those

for ground vehicles, and systems are designed for use against

7.62 mm, 12.7 mm projectiles, and 23 mm High Explosive

Incendiary (HEI) threats. 

The Army Aviation Applied Technology Directorate has an

Advanced Lightweight Transparent Armor Program (JTCC/AS)

to develop advanced transparent armor with an areal density 

no greater than 5.5 lb/ft2†. The goal of this program is to defeat

a 7.62 mm PS Ball M 1953 threat. This constitutes a 35%

reduction in weight over currently fielded systems. Optical

requirements include a minimum 90% light transmission with

a maximum haze of 4%. A second goal of the program is to

defeat the blast and fragments from a 23 mm HEI projectile

detonated 14 inches from the barrier, without exceeding a 

6 lb/ft2 areal density limit.[4] Many of these transparent armor

systems utilized for military applications would also have use 

in commercial systems, such as law enforcement protection

visors, riot gear, and windows in cars, trucks, and buses, as well

as structural hardening in buildings. The cost/performance

trade-off is not as critical in the commercial arena since VIP protection systems can use more exotic and expensive materials to

protect against significant threats. 

DESIGNING A TRANSPARENT ARMOR SYSTEM

Polymeric Materials

Amorphous glassy polymers are used in a wide variety of 

applications in which transparency is critical; these include

lenses, goggles, and face shields for soldier, law enforcement,

and medical personnel; ballistic shields for explosive ordnance

disposal personnel; windows and windshields for vehicles; and

Figure 3. Army Ground Vehicles.
The AMPTIAC Quarterly, Volume 8, Number 4 31

canopies for aircraft and helicopters. The vital consideration

for materials selection is the behavior of the material in

response to mechanical deformation, chemical exposure,

ultraviolet irradiation, heat, humid environments, and other

potential in-service hazards.

Two distinct groups of glassy polymers are classified in relation to their physical and thermo-mechanical properties as

thermoplastics and thermosets. Thermoplastics are linear or

branched polymers that become soft and deformable upon

heating, while thermosets, on the other hand, are rigid and possess an interconnected three-dimensional network that limits

flow under elevated temperatures. Both types of polymers have

a subset of materials that are visibly transparent.

Transparent polymers can be fabricated with sufficiently

high strength and stiffness and developed as lightweight, lowcost alternatives to traditional glass components. Unlike glass,

the physical properties of amorphous polymers vary significantly with temperature and rate of deformation. In general,

material characteristics of a polymer change from being a rigid

glass to an entangled rubbery-like structure once heated above

a critical temperature known as the glass transition temperature. This critical temperature is indicative of an upper limit

for the service temperature applicable to these amorphous

polymeric materials.

Thermoplastics

As a thermoplastic material, poly (methyl methacrylate)

(PMMA) has better impact resistance than most types of glass

and is commonly used as a substitute for glass housings or

enclosures, where hardness, optical clarity, and ultraviolet (UV)

stability requirements are essential. The use of PMMA for military applications dates back to World War II. PMMA was the

material of choice (really the only material available) for lightweight domes and canopies on aircraft of that era. 

PMMA is manufactured in sheet form via casting or extrusion, and the product sheets can then be thermally formed into

complex shapes. Casting is used to produce the thicker sheets

usually used in transparent armor applications. As casting technology has improved, PMMA has found wide use as bullet

resistant glazing for protecting against handgun threats. Monolithic PMMA is nevertheless brittle, and polycarbonate (PC)

has been used as a substitute in applications where impact performance is most critical. PC has outstanding impact toughness

(almost 300-times stronger than single-strength glass), and it

has a higher glass transition temperature and better flame and

fire resistance than PMMA. However, one of the drawbacks of

PC is its susceptibility to degradation upon exposure to organic solvents, UV-irradiation, scratches, and abrasion. To be used

in outdoor applications, PC requires UV-stabilizers and surface

modification with hard coatings to ensure long-term durability. Despite these limitations however, polycarbonate (PC) has

been the material of choice for both military and commercial

eye protection since its introduction nearly 40 years ago. 

For thermoplastics including PC and PMMA, extrusion

molding and injection molding are the predominant processes

for making an end product. The choice of proper molecular

weight of polymers is critical in these processes to ensure

desired rheological characteristics at elevated temperatures.

Alternatively, some commercially available PMMA are fabricated by casting the material between two glass plates to achieve a

cast sheet with excellent optical clarity at a desired thickness.

An advantage of this casting process is the ability to produce a

PMMA sheet with a significantly higher molecular weight and

enhanced mechanical properties, which are not attainable in

thermo-molding processes due to the practical limits and

degradation of polymers. 

Polycarbonate is the most common plastic used for transparent armor applications. It is an inexpensive thermoplastic material that is easily formed or molded, and offers excellent ballistic

protection against small fragments. PC has been used by the US

Army for aircrew visors and sun, wind, and dust (SWD) goggles

since the early 1970’s and spectacles since the mid 1980’s. This

equipment provides protection from small (1 gram or less), slow

moving (650 ft/sec) fragments, but does not provide full-face

coverage. It is currently used in applications such as goggles,

spectacles, visors, face shields, laser protection goggles, and is

also used as a backing material for enhanced protection from

more advanced threats. It has been found to be more effective in

the thinner dimensions required for individual protection than

in the thicker sections required for vehicle protection.

Several investigations have been undertaken to develop new

thermoplastic polymers for improved ballistic protection. The

efforts uncovered several candidate materials, including transparent nylons. However, many of these promising materials are

not available in commercial quantities which limits their use for

future designs. 

Thermosets

In the ophthalmic industry, CR-39® allyl diglycol carbonate

monomer is sometimes used for casting plastic lenses for prescription eyewear that require high quality optical properties.

During World War II, CR-39® resin was used to produce transparent tubes that were embedded in fuel lines to function as a

visible gage that indicated fuel flow to each engine. These new

plastic tubes replaced glass tubes, which often shattered during

combat, spraying gasoline throughout the cockpit. Plastics made

from CR-39® exhibit excellent chemical resistance and thermal

properties, yet are thermosets in nature and do not possess high

impact strength. A new series of thermoset polyurethane-based

polymers are currently commercially available, which offer

excellent chemical resistance and impact strength and can be

formulated to meet the desired physical and mechanical 

properties. Lenses or other forms of plastics fabricated from 

castings of either CR-39® or polyurethane-based thermoset

polymers are commercially available.

Polyurethanes (PU) have a unique morphology, possessing a

combination of hard and soft domains. The properties of a PU

can be tailored to specific applications by adjusting the size and

ordering of these domains, yielding materials that range from

being rigid and brittle, like a glass, to flexible and ductile, like

an elastomer. It is becoming increasingly common to use a

number of specially formulated urethanes in transparent armor

designs. Thermoset PU’s can be processed via casting or liquid

injection molding. They are clear with a very light tint and

demonstrate very good impact resistance, even when fabricated

in thick sections. 
32 The AMPTIAC Quarterly, Volume 8, Number 4

The result of ballistic testing an all-polyurethane visor

showed that it performed better than both polycarbonate and

PMMA, on an equal weight basis. Because of its physical properties, this PU shows promise as a replacement for PC for

monolithic eye protection and as the backing plies in all-plastic

and glass/plastic laminated armor systems. Thermoset

polyurethanes have also demonstrated promise in mechanical

and ballistic screening and are an example of a research area

with a broad horizon for future applications. The specific character of urethanes can be specifically tailored by selecting the

concentration of backbone monomers, resulting in a very

diverse set of material parameters. A wide range of transparent

urethanes have demonstrated improved fracture performance

compared to polycarbonate but with improved durability and

improved scratch resistance. Some basic properties of these

polymeric materials are shown in Table 1.

Material Characteristics and Design of Transparent 

Polymeric Materials

As pointed out, monolithic PC has outstanding impact toughness particularly at low temperatures, while PMMA has better

hardness and environmental durability. The ductility of PC is

reported to be associated with the molecular motion of main

chain molecules at low temperatures[5]. The molecular motion

is presumably present even upon exposure to high-rate impact,

and can therefore provide efficient dissipation of impact energy. This molecular mechanism is not prevalent in PMMA; and

in fact, monolithic PMMA has significantly lower impact energy absorption capability than PC, particularly in the thickness

range of interest for eye/face protection applications. As a consequence, the potential of monolithic PMMA has not been 

historically realized in the ophthalmic industry due to the concern of spall upon impact, and thus PC is the predominant

choice of material for eye protection. 

Recent experimental results revealed that monolithic PMMA

exhibits a greater increase in energy absorption when the plate

thickness is increased compared to PC.[6] Furthermore, PMMA

and PC plates with an equivalent thickness of about 12 mm

have displayed similar impact performance against 0.22-caliber

fragment-simulating projectiles, albeit absorbing the energy by

different deformation and failure mechanisms. The challenge is

to choose an adequate transparent armor from the numerous

commercially available products that are claimed to be capable

of withstanding a level of ballistic impact according to the

National Institute of Justice (NIJ) specifications and standards. 

In general, the material characteristics of most concern to

system engineers include the overall weight (or areal density),

optical clarity, and cost. However, from a material scientist’s

perspective, a better understanding of molecular mechanisms

on high-rate mechanical deformation is important to facilitate

the synthesis and design of next generation transparent polymeric materials with desired strength and toughness.[7] 

Recently, Dr. Boyce’s team at the Massachusetts Institute of

Technology’s Institute for Soldier Nanotechnologies has

demonstrated a new approach to design novel hierarchical

assembly materials with significantly improved ballistic impact

resistance against a fragment simulating projectile[8,9]. The

new macro-composite material assembly, shown in Figure 4,

encompasses a distribution of discrete lightweight components,

such as platelets, discs, tablets, etc., dispersed in a continuous

matrix of another lightweight material possessing contrasting

and complementary mechanical behavior (e.g., hardness, stiffness, ductility, and strain-hardening). In

this macro-scale demonstration, the

dimensions (thickness, t2 and diameter,

d) of the discrete components are small

(but still macro-scale) in comparison to

the overall sample thickness (t1). In addition, the geometrical parameters such as

the size and distribution of discrete discs

can be tailored. 

Preliminary findings, obtained for a

simplified materials assembly design

Table 1. Typical Polymer Properties for Materials Found in Military Ballistic Systems.

Lexan Simula Plexi Glass G

Polycarbonate Polyurethane PMMA

Density, g/cm3 1.2 1.104 1.19

Areal Density at 1” thick lb/ft2 6.2 5.7 6.2

Tensile Strength MPa 66 62 72

Tensile Modulus MPa 2208 689 3102

Shear Strength MPa 45 – 62

Shear Modulus MPa 1000 – 1151

Compressive Strength MPa 83 72 124

Compressive Modulus MPa 1660 1241 3030

Flexural Strength MPa 104 89 104

Flexural Modulus MPa 2586 2020 3280

Max Operating Temperature °C 121 149 95

Glass Transition Temperature °C 145 -75 100

Uniform, Graded or

Random Distribution

d t

2

t

1

Figure 4. Hierarchical Material Assembly for Macro-Scale Demonstration.
The AMPTIAC Quarterly, Volume 8, Number 4 33

consisting of PMMA discs distributed in a PC sample, demonstrate that the overlapping of discs increases the interaction

zone between the projectile and the target by forming a network of interacting energy absorbing components. Experiments and computational simulations indicate that this magnification in the interaction zone results in a greater energy

absorption and increased penetration resistance. This new

design also demonstrates an enhanced multi-hit defeat capability. Figure 5 shows the impact zone of a recovered hierarchical

assembly sample. The brittle failure of PMMA discs facilitates

the impact energy dissipation, yet it is confined locally and the

cracks are arrested at the matrix-platelet interface, thus inhibiting catastrophic failure. 

The above configuration is an example of how engineering

composite designs can improve energy absorption by inducing

desired failure criteria into the polymer matrix. Future efforts

seek to extend this knowledge of polymer failure during ballistic defeat into

designing nanostructured

polymer matrix materials.

The proposed outcome

from such research is to

increase the multi hit performance of polymer matrix

transparent armor solutions

by reducing the probability

of catastrophic failure for

each impact.

Regardless, the performance parameters of both

thermoplastic and thermosetting polymer materials are being advanced, and

can be exploited to improve ballistic protection limits in military and commercial applications. There is significant work to

be performed, however, to transform ideas into fieldable and 

reliable designs.

Glasses and Glass-Ceramics

Greater requirements for optical properties and ballistic performance have generated the need for new armor materials. The

major challenges for these materials are cost, available sizes, and

the ability to produce curved products at reasonable delivery

costs. Chemical or thermal treatments can increase the strength

of glasses, as can the controlled crystallization of certain glass

systems to produce transparent glass-ceramics. AREVA, Ltd.§

currently produces a recrystallized lithium silicate-based glassceramic known as TransArmTM, for use in transparent armor

systems. It has all the workability of an amophorous glass, but it

demonstrates properties similar to a ceramic after it has been

crystallized. VycorTM is a 96% fused silica glass, which is waterclear, high-strength, and shows promise as an armor material,

especially because of its low specific gravity. 

There are several inherent advantages of glasses and glassceramics. First, compared to more traditional ceramics, the cost

of glass-ceramics is lower. Glass-ceramics can be processed to

produce curved shapes that are often achieved only by costly

machining for traditional ceramics. Finally, the fabrication

methods of glass-ceramics allow large material shapes to be

achieved, since much of the processing is akin to glass manufacturing. All of these advantages lead to an improved readiness

level for inclusion in window designs. 

Transparent Crystalline Ceramics

Transparent crystalline ceramics are used to defeat advanced

threats. Three major transparent candidates currently exist: 

aluminum oxynitride (Al23O27N5) (ALONTM‡), magnesium 

aluminate spinel (MgAl2O4) commonly referred to as just

spinel, and single crystal aluminum oxide (sapphire).

ALONTM, one of the leading candidates for transparent armor,

is patented by the US Army and its production and development was advanced by the Raytheon Corporation. Figure 6

provides a comparison between representative sections of

ALONTM and some glassbased ballistic standards

(BAL 31 and BAL 38).

Thicknesses of comparable

ballistic performance are

highlighted.

The incorporation of

nitrogen into aluminum

oxide stabilizes the matrix,

and results in a cubic crystal structure that is isotropic and can be produced as a

transparent polycrystalline

material. Polycrystalline

materials can be produced

in complex geometries

using conventional ceramic

forming techniques such as

pressing and slip casting. Table 2 lists some properties of

ALONTM compared with other ceramics and glass-ceramics.

Although becoming commercially viable, ALONTM still is

available only in limited sizes and at relatively high costs, owing

in large part to the post manufacturing polishing costs, particularly for armor based needs where optics are important. 

The Surmet Corporation has acquired Raytheon’s ALONTM

business and is currently building a market for the technology

in the areas of point of sale scanner windows and as alternatives to quartz and sapphire in the semiconductor market. The

BAL 38 Plus -3.62” thick 41.45 lb/ft2

BAL 38 -3.07” thick 34.68 lb/ft2

BAL 31 -2.48” thick 27.8 lb/ft2

ALON Laminate

1.33” thick 16.7 lb/ft2

ALON Laminate

0.921” thick 10.5 lb/ft2

Comparable

Performance Image furnished courtesy of Surmet Corporation

Figure 5. Cracks Arrested at the Interface of PC Matrix and

PMMA Disc (~1” Dia.).

Figure 6. Comparison of ALONTM to Standard Armor Systems**.
34 The AMPTIAC Quarterly, Volume 8, Number 4

high hardness of ALONTM provides a scratch resistance that

exceeds even the most durable coatings for glass scanner windows, such as those used in supermarkets, thus leading to

enhanced life cycles. Leveraging ALONTM into new applications is a mechanism to increase ALONTM production and

capabilities, which will facilitate the fielding of armor designs

for military applications.

Surmet has successfully produced a 15′′ x 18′′ curved

ALONTM window and is currently attempting to scale-up the

technology and reduce the cost. Through government small

business innovative research (SBIR) and other investment

funding, the US Army and US Air Force are pushing the envelope of development into next generation applications, including domes for advanced missile targeting systems and armor

for commercial and military vehicles. 

Ceramic magnesium aluminate spinel (spinel) is transparent

in its polycrystalline form and

possesses a cubic crystal structure. Transparent spinel has

been produced by sinter/hot

isostatic pressing (HIP), hot

pressing, and hot-press/HIP

operations. The use of a HIP

can improve optical and physical properties of spinel by

increasing density and reducing voids resulting from powder consolidation and binder

volume. Some typical properties of spinel are listed in

Table 2. 

Spinel offers some processing advantages compared to

ALONTM, especially since

spinel powder is available

from commercial powder

manufacturers in bulk quantities, while ALONTM powders are

proprietary. Spinel is also capable of being processed at much

lower temperatures than ALONTM and has been shown to possess superior optical properties within the IR region.[10] The

improved optical characteristics make spinel attractive in sensor

applications where effective communication is impacted by the

protective dome’s absorption characteristics. Opening the

transparent frequency range implies that spinel-based sensor

protection may offer enhanced performance capability. The

spinel products business is being pursued by two key manufacturers in the United States, Technology Assessment and Transfer (TA&T) and the Surmet Corporation. Despite significant

investments in the technology, spinel products are still available

only in research applications at this time. 

Polishing the finished ceramic products is an essential process

to achieve optical clarity and low haze. Whether for scanner or

armor applications, windows require a high degree of mechanical polishing with diamond pastes to achieve an optical finish.

The number of processing stages and length of processing time

drives up final production costs and limits the supply rates for

many of the advanced polished ceramic designs. Additionally, as

curvature is introduced into the formulation of new armor platforms, more complex and automated polishing equipment

becomes essential to keeping distortions low, allowing parallel

surface machining in curved structures. New approaches intended to reduce finishing costs are underway and may lead to

improved capability for fielding large-dimensional transparent

ceramics. Clearly opportunities to produce optically

transparent ceramics with

minimal polishing would

reduce overall product costs

significantly. 

Sapphire is a transparent

ceramic possessing a rhombohedral crystal structure.

From a production and

application perspective,

sapphire remains the most

mature transparent ceramic

and is available from several manufacturers, but the

cost is high due to the 

necessary high processing

temperatures and machining and polishing steps.

Sapphire has a very high

strength, but clarity and transparency are still highly dependent on the surface finish. Limitations to larger area sapphires

are often business related, in that larger induction furnaces and

costly tooling dies are necessary to increase beyond current

fabrication limits. However, as an industry, sapphire manufacturers have endured significant competition from coating

hardened glass and new ceramic alternatives, such as ALONTM

and spinel, and still managed to offer advanced capabilities

and expand business markets. 

The high level of maturity in sapphire can be attributed to

two business areas, EM windows and electronic/semiconducFigure 7. Three Product Stages of a Saphikon® EFGTM Sapphire 

Window; Including As-Grown, Rough Cut and Optically Polished.

Table 2. Selected Mechanical Properties of Transparent Glasses and Ceramics.

ALONTM Fused Silica Sapphire Spinel Zinc Sulfide 

Density g/cm3 3.69 2.21 3.97 3.59 4.08 

Area Density (at 1” thickness) lb/ft2 19.23 11.44 20.68 18.61 21.20 

Young’s Elastic Modulus GPa 334 70 344 260 10.7

Mean Flexure Strength MPa 380 48 742 184 103

Fracture Toughness MPa√m 2.4 - - 1.7 -

Knoop Hardness (HK2) GPa 17.7 4.5 19.6 14.9 2.45

Image Furnished Courtesy of Rob Nash Studios, LLC
The AMPTIAC Quarterly, Volume 8, Number 4 35

tor industries. One producer, Saint Gobain Group, produces

transparent sapphire using an edge-defined growth technique

(Saphikon® EFGTM Sapphire) that offers unique potential.

Sapphire grown by this technique produces an optically inferior material to single crystal sapphire, but is much less expensive and retains much of the hardness, transmission, and

scratch resistant characteristics. With optical polishing, large

area windows can be fabricated to meet commercial demands.

Saint Gobain is currently capable of producing 0.43′′ thick 

(as grown), by 12′′ x 18.5′′ sheets (Figure 7), as well as thick,

singly-curved sheets. They have commercialized the capability

to meet requirements for flight on the F-35 Joint Strike Fighter and F-22 Raptor next generation fighter aircraft. Saint Gobain, however, has not expanded production to make sapphire

plates larger than 12′′ x 18′′. ARL has investigated edge

defined growth sapphires for ballistic window applications 

and determined that sapphire is a competitor to ALONTM and

spinel if product demand can drive production. In a free market, sapphire producers are limited in production volume

because of the growth methods and product demand, and business needs and commercial value drive production decisions.

There are some challenges that must be overcome for these

materials to be viable for window applications. The major

challenge is in manufacturing large plates (curved and

uncurved) that can be made reproducibly with high yields.

Another challenge is in finishing the final part. This encompasses the grinding steps to get the correct geometry and more

importantly, the final polishing. As the size of the plates get

larger, the equipment available to polish these windows is

scarce and is currently, a limiting step in the production of

windows. Novel techniques need to be developed to grind and

polish windows in a timely, cost efficient manner. Still, the

future of these technologies offers great promise in dramatically improving soldier protection and in reducing system weight

for future fighting platforms.

CONCLUSIONS

Protection of all vehicles in the combat theater has become a

realized need over the past couple of years. The realization that

future business of the United States military will involve regular combat actions in hostile environments, where single vehicles and supply convoys are as great a target as organized troop

formations, brings with it the realization that all military personnel are at great risk. Coupled with the need to reduce the

logistic burden in theater environments, the military leadership

continues to strive for weapons and transportation systems that

possess reduced weight and operational costs, and increased

maneuverability and transportability.

The approach discussed here involves reducing the weight of

transparent armor systems by incorporating the most advanced

technical capabilities available from a wide range of materials

types, specifically polymers and ceramics. Transparent ceramics

were shown to offer significant ballistic protection at reduced

weights over conventional glass/plastic systems. Although significant advances in production capability for advanced ceramics has been realized over the past five years, several major issues

remain, such as availability, the shapes and sizes available, and

cost. Although they are now capable of meeting size demands

for flat plate ceramics, with transparent areas greater than 12

inches by 18 inches, low demand and high production costs

have prevented businesses from investing in putting larger

dimensions into production. Furthermore, producing transparent ceramics that possess compound curvatures remains predominately a research and development program for all of the

ceramics industry.

Costs also remain high for ceramic armors due to the high

purity powder requirements, the high processing temperatures,

long processing times, complex processing steps, and high

machining and polishing costs. Several programs continue to

reduce these costs. However, expectations to reach current

glass/plastic systems costs are unrealistic.

Polymeric material advancements, such as the improvement

of the optical properties of polyurethane, have led to a renewed

interest in these materials to reduce the overall weight of armor

systems. It has been shown that polyurethanes offer superior

ballistic performance at a reduced weight, as compared to current polycarbonate backing materials.

Numerous polyurethane materials are currently being

explored as direct replacements for polycarbonate. In addition,

there are significant research and development activities on

design, synthesis and processing of advanced, high performance

hierarchical assembly or nano-engineered polymeric matrix

materials among government laboratories, industry, and academia. With successful insertion of these new materials into

transparent armor systems, a significant weight reduction could

be realized, along with an increase in ballistic performance and

ability to defeat future threats. Still, the road ahead has danger

lurking in the unseen byways and beyond the next ridge.

Therefore, transparent materials for armor applications must

continue to improve and increase the protection at the individual, vehicle, convoy, and battalion levels.

NOTES & REFERENCES

* Corning Inc., One Riverfront Plaza, Corning, NY 14831

† Areal density, in units of weight/area, is the typical method 

of normalizing ballistic performance of materials of varied 

construction. In general, this can be converted to a traditional

density by summation of component densities; however, this is

not usually reported. For a monocoque design, areal density

divided by thickness is the density

§ AREVA T&D UK Ltd., Registered Office. St. Leonards

Avenue, Stafford ST17 4 LX

‡ Raytheon Electronic Systems, Lexington Laboratory, 131

Spring Street, Lexington MA 02421. Registered trademark No.

2554362. March 2002

** Property of Surmet Corporation. Used with permission.

http://www.surmet.com/alonArmor.html

[1] P. Dehmer and M. Klusewitz, Proceedings of 8th DOD

Electromagnetic Windows Symposium at the USAF Academy,

24-27 April 2000

[2] M.J. Hollis and F.J. Brandon, Design and Analysis of a FuzeConfigurable Range Correction Device for an Artillery Projectile,

ARL-TR-2074, Army Research Laboratory, Aberdeen Proving

Ground, MD, December 1999
36 The AMPTIAC Quarterly, Volume 8, Number 4

[3] R. Gonzalez, and G.J. Wolfe, Ballistic Transparencies for

Ground Vehicles, Proceedings of DARPA/ARL/ARO Transparent Armor Materials Workshop, Annapolis MD, November

16-17, 1998

[4] R.A. Huyett and F.S. Lyons, Advanced Lightweight Transparent Armor (ALTA), USAAMCOM TR 02-D-18

[5] D.J. Williams, Polymer Science and Engineering, PrenticeHall, pp. 333-334 (1971)

[6] A.J. Hsieh, D. DeSchepper, P. Moy, P.G. Dehmer, and J.W.

Song, The effects of PMMA on Ballistic Impact Performance of

Hybrid Hard/Ductile All-Plastic- and Glass-Plastic-Based Composites, ARL Technical Report, ARL-TR-3155, February 2004

[7] A.D. Mulliken and M.C. Boyce, Understanding the High

Rate Behavior of Glassy Polymers, Proceedings, 24th Army Science Conference, Orlando FL, 2004

[8] M.C. Boyce, A.J. Hsieh, A.D. Mulliken, and S. Sarva,

Transparent Lightweight Composite Armor for Protection against

Projectile Impact, MIT Technology Disclosure Case #11256,

July 7, 2004

[9] S. Sarva, A.D. Mulliken, M.C. Boyce, and A.J. Hsieh,

Mechanics of Transparent Polymeric Material Assemblies under

Projectile Impact: Simulations and Experiments, Proceedings,

24th Army Science Conference, Orlando FL, 2004

[10] D.C. Harris, Infrared Window and Dome Materials,

SPIE, Washington, pp. 32, 1992

Professor Mary C. Boyce is the Kendall Family Professor of Mechanical Engineering at the Massachusetts Institute

of Technology. Her research areas focus primarily on the mechanics of elastomers, polymers, and polymeric-based

micro- and nano-composite materials, with emphasis on identifying connections among microstructure, deformation

mechanisms, and mechanical properties. She has published over 100 technical papers in the field of mechanics

and materials. Professor Boyce has received numerous awards and honors recognizing her research and teaching

efforts; among them are the NSF Presidential Young Investigator Award, Fellow of the American Academy of

Mechanics, Fellow of the ASME, and Fellow of the American Academy of Arts and Sciences.

Dr. Alex J. Hsieh is a Materials Research Engineer in the Survivability Materials Branch at the US Army Research

Laboratory, Aberdeen Proving Ground, MD. He is experienced in the design, development, characterization and

ballistic testing of high performance polymeric materials for transparent visors and ballistic shields applications. His

research interests include studies of molecular mechanisms on high-rate mechanical deformation and evaluation of

nanocomposite hardcoatings. Currently, he serves as a visiting research scientist at the MIT’s Institute for Soldier

Nanotechnologies.

Mr. Peter G. Dehmer is currently conducting work in the development, processing and testing of transparent armor

for the both the individual soldier and vehicles. He has over 25 years of work experience in this area. He holds a

BS in Plastics Engineering from Lowell Technological Institute (now the University of Massachusetts at Lowell). 

Dr. Parimal J. Patel has fourteen years of experience in processing of ceramics including high modulus oxynitride

glasses and fibers, Si-N-O dome materials, and aluminum oxynitride (AlON). He is currently investigating the 

processing of AlON as well as testing and evaluation of ceramics and glasses for transparent armor applications.

He received his BS in Ceramic Engineering from Rutgers University in 1990, with a focus on processing of oxide

and non-oxide glass optical waveguides. He received his PhD in 2000 from Johns Hopkins University. His dissertation topic was “Processing and Properties of Aluminum Oxynitride Ceramics.” 

Dr. James M. Sands is currently the Leader of the Transparent Materials Technology Team in the Survivability 

Materials Branch of the Weapons and Materials Research Directorate at Aberdeen Proving Grounds, MD. 

Dr. Sands began his research career at the US Army Research Laboratory in 1998, working as a contractor, 

until joining as a civil servant in 2000. He earned his doctorate in Materials Science and Engineering from the 

Pennsylvania State University; and a BA degree in Chemistry and Mathematics from Augustana College (SD). 

Dr. Sands has more than 20 combined refereed publications, conference proceedings, and Army technical reports

to his credit.

Photo

Not

Available
INTRODUCTION

The US Army is undergoing a paradigm shift toward highly

mobile, rapidly deployable, readily sustained units of action having unprecedented lethality and survivability. While current

ground fighting vehicles have evolved to their 70+ ton status, in

part to defend against the ever-increasing lethality of ballistic

threats, their sheer mass and support requirements do not make

them easily transportable or readily sustainable. Therefore, as

the US Army transforms, future combat systems (FCS) will

employ lightweight, highly mobile, transportable, and lethal

armored vehicles that maintain the highest level of survivability. 

To achieve armor performance exceeding that of the current

combat vehicles for new vehicular systems weighing less than

20 tons, significant advances in survivability technology are

required. Advanced materials and their multifunctional integration are critical to the successful design of new light armors.

One such light armor solution being developed is an advanced

composite armor that combines ceramics, metals, and polymeric composites to provide unmatched mass efficient protection.

Such rapid advancements are only possible with similar developments in individual materials and modeling technology. As

ceramics and metals are the focus of other articles in this issue,

this paper will first highlight the evolution of ‘the plastic tank’

and then detail the recent advancements in organic materials

technology and advanced simulation capability for application

of composites in vehicle armor.

THE ‘PLASTIC TANK’ - A HISTORY 

OF COMPOSITE STRUCTURAL ARMOR

Composite armor systems are not new. During the pioneering

light armor experiments against small arms threats conducted in

the late 1960’s, Wilkins and co-workers [1-3] determined that

hard ceramics coupled with a thin ductile backing form effective, mass efficient armor systems. These researchers recognized

that ceramics possess characteristics such as low density, high

hardness, and high compressive strength; all of which were wellsuited for light armor systems. When coupled with composite

materials having superior strength-to-weight and stiffness-toweight properties, ceramic/composite armor provides mass efficient ballistic protection against a number of threats. Integrating

these materials as a mass efficient armor system on armored

vehicles has been reported in the open literature since the 1980’s

[4], and the US Army’s efforts in the development and application of composite armor during this time are detailed below.

Through several key R&D programs during the 1980’s and

1990’s, the Army established a confidence-building baseline for

the application of polymer matrix composites (PMCs) to lighten heavy forces while also improving survivability for light

forces. The first application of thick-section PMCs to armored

vehicles was in a demonstration program in the late 1980’s

under which a polyester/glass composite hull was developed to

replace the aluminum hull on the Bradley Infantry Fighting

Vehicle (BIFV). The resulting vehicle, with a thick-section

composite hull and appliqué ceramic armor tiles, became

known as the Composite Infantry Fighting Vehicle (CIFV) and

demonstrated the ability of PMCs to perform well structurally

in an armored vehicle [5]. This vehicle was followed by the

Composite Armored Vehicle (CAV) program; established to

assess the application of PMCs in the ground-up design of an

armored vehicle [6]. To meet the stringent weight and ballistic

performance requirements of the CAV, which is shown in Figure 1, the concept of a multifunctional PMC-based armor was

developed. The resulting composite integral armor (CIA) performed exceptionally well and was subsequently adapted for

Bryan A. Cheeseman

Robert Jensen

Christopher Hoppel

Weapons and Materials Research Directorate

US Army Research Laboratory

Aberdeen Proving Ground, MD

The AMPTIAC Quarterly, Volume 8, Number 4 37
38 The AMPTIAC Quarterly, Volume 8, Number 4

incorporation into designs for the Army’s Crusader Self-Propelled Howitzer (SPH) and its Resupply Vehicle (RSV) [7].

An example of the armor designed for the CAV is shown in

Figure 2. Each layer serves a specific purpose, yet combinations

of layers provide role-sharing multifunctionality. A thin, protective PMC facesheet on the outside of the vehicle serves to

protect the ceramic ballistic tiles from incidental damage, while

the ceramic tiles are utilized to break up and/or erode the projectile upon impact. The subsequent rubber (EPDM) layer is

utilized to improve multi-hit ballistic performance. The thicksection composite plate serves as the structural support for the

vehicle, a structural backing for the ballistic tiles and also catches the remnants of the projectile and fractured ceramic, while

absorbing the residual kinetic energy. Finally, a fire-protective

“spall” layer of phenolic is incorporated on the inner surface 

of the vehicle. Other layers can be incorporated to provide

additional functionality, such as electromagnetic ground

planes, signature control, etc.

While composite integral armor developed under the CAV

and Crusader programs engendered confidence in the ability 

of PMCs to simultaneously meet ballistic and structural 

properties in combat vehicles, the mass efficiency (ballistic performance per unit areal density) falls significantly short of the

current requirements. Advancements in materials technology

and numerical simulation capabilities were identified as enabling technologies to aid in future developments of advanced

composite armor, and some of these recent efforts are detailed

in the following sections.

FIBER COATINGS: SIZING MATTERS

Composites used for structural armor are different from those

used in appliqué or body armor applications. Typically, bodyarmor grade composites are resin starved, consisting of approximately 80 weight percent fiber, and are engineered to readily

delaminate, which enables the high strength, high modulus

fibers to elongate and absorb the impact energy. These nonstructural armor textiles are highly mass efficient, and there are

a number of composite vehicle armor appliqués that incorporate them. However, they serve only to increase ballistic protection, not support load. Composites being considered for FCS

vehicle applications are being

designed to be multifunctional,

and as in the CAV detailed

above, the FCS composite armor

will be an integral part of the

vehicle, carrying typical vehicle

kinematic loads. These composites under development are comparable to traditional structural

composites having approximately

50 volume percent fiber.

While efficient for carrying

load, composites used for structural armor are not as mass efficient ballistically as their armor

grade counterparts. However, if

these composites were to possess

strong fiber-matrix interfacial

adhesion at structural loading rates, and weak interfacial

strength at ballistic loading rates, they would behave structurally under vehicle loads, yet absorb energy like an armor

grade composite under ballistic impact. The result would be an

optimized multi-functional armor composite. Recent research

has indicated that this may be possible through innovative

manipulation of the chemical and physical interactions

between the matrix and fibers.

Woven and non-woven fabrics constructed using continuous glass-fiber reinforcements are commonly used in PMCs.

During industrial glass-fiber manufacturing a multicomponent thin coating, known as a sizing, is applied to the fibers for

protection against damage during processing and to control

their performance in composite articles. Conventional glassfiber sizings incorporate organofunctional molecules, known

as silane coupling agents, to enhance the adhesion between the

glass-fiber reinforcement and the polymeric matrix and to

increase the durability of the composite. The complex chemical and physical interactions due to the silane coupling agent

result in the formation of a nanometer sized interphase region

between the glass-fiber surface and the polymeric matrix. 

The interphase region that surrounds glass-fibers in a composite is essential to its performance, yet is poorly understood.

For example, existing traditional fiber sizings are not optimized

to tailor simultaneously a composite’s static and dynamic

response. Yet, it has been recognized that these sizings affect

structural durability, impact resistance, and damage tolerance. 

Published research indicates that the impact response of a

PMC can be tailored for high-energy absorption by designing

Figure 1. Composite Armored Vehicle (CAV).

Figure 2. Example of the Composite Integral Armor Developed

under the CAV Program.

Phenolic Inner Liner

Structural Composite

EPDM

Ceramic (Alumina)

Armor Tiles

PMC Outer Face-sheet

Secondary

Adhesive

Bonds
The AMPTIAC Quarterly, Volume 8, Number 4 39

weak fiber-matrix interfacial interactions. Conversely, structural performance (strength) is achieved by strong fiber-matrix

interfacial interactions. Hence, the aforementioned trade-offs

exist. Although the achievement of simultaneous high strength

and energy absorption levels is desirable, the technology has

not been available. New approaches are now available to overcome these traditional materials shortcomings.

The glass-fiber sizing research being performed at ARL has

systematically examined the nature of the glass-fiber/thermosetting polymer interphase region to develop the fundamental understanding necessary to propose and validate an entirely

new class of sizing materials. Specifically, mixed organofunctional silane coupling agents are being employed to vary the

chemical reactivity toward the polymeric matrix phase to produce bond strengths that are dependent on the viscoelastic

properties of the matrix and fiber-coating. This results in an

inherent “viscoelastic switch” at the fiber-matrix interphase that

yields strong fiber-matrix interactions (high structural strength)

at low strain rates and weak fiber-matrix interactions (ballistic

performance) at high strain rates. This triggered response is

coupled with the application of inorganic-organic sol-gel

processes to develop silane-based, glass-fiber sizings that

increase the surface roughness of commercially produced glass

fibers. The result is an increased coefficient of friction between

the fiber and matrix during the fiber pullout stages of composite failure, further resulting in enhanced energy absorption in

the composite during ballistic events. These results were first

documented mechanically on micro-scale model composite

specimens. Subsequently, the experimental inorganic-organic

hybrid fiber sizings were scaled-up and applied using commercial manufacturing equipment to demonstrate their behavior in

macroscale composite materials.

Figure 3 shows the successful nano-texturing of the fiber

surfaces produced on a commercial scale using atomic force

microscopy (AFM). Glass reinforced composite materials were

manufactured using these specialized fabrics, and the structural and impact energy responses were measured. Figure 4 captures the impact energy absorption and structural performance

of composites produced using state-of-the-art commercial sizings and the ARL inorganic-organic hybrid sizings. These

results show the traditional trade-offs found when using commercially available fibers that have been coated with either a

structural or ballistic sizing. In comparison, these trade-offs do

not exist for the ARL inorganic-organic hybrid sizing, and the

impact and structural performance of this optimized sizing are

both excellent. A 40% increase in the energy absorption of

composites fabricated with no loss in structural properties will

enable the use of PMCs in ballistic applications where they

have not been used previously, perhaps with reduced cost.

ADVANCES IN MODELING: ROBUST COMPOSITE 

MATERIAL MODEL FOR IMPACT AND BLAST

Less than ten years ago, a review paper on the state-of-the-art

in numerical modeling of high-velocity impact stated that

there was no definitive computational model for ceramics and

that high velocity impact calculations of fiber-reinforced composites were a research task [8]. These limitations in numerical

techniques and robust material models resulted in much of the

design of composite armor systems being guided by experimental efforts. However, since then the advances in numerical

techniques and development of robust material models have

allowed modelers to simulate accurately what is observed

experimentally, and this has allowed greater insight into how

the components of the composite armor work together during

the impact event. These recent developments have allowed

experiments and simulations to be utilized together to improve

the performance of composite armor for FCS.

MODELING COMPOSITE ARMOR

Accuracy in modeling of ceramics has been aided by the use of

LaGrangian particle techniques, either smooth particle hydrodynamics (SPH) or general particle algorithms (GPA), which,

when coupled with a validated material model, have given very

good correlation with experimental observations of impact into

Figure 3. Surface AFM Images of 

Standard Commercial Fiber (Left) in 

Comparison to ARL Nano-Roughened

Commercially Produced Fiber (Right).

Figure 4. Mechanical Performance of Composites with Various

Sizings. The ARL Sizing Shows Exceptional Performance in both

Energy Absorption (Shown in Green) and Compressive Strength

(Shown in Orange).

“Structural” ARL Hybrid “Ballistic”

Fiber Sizing Fiber Sizing Fiber Sizing

120

100

80

60

40

20

0

160

140

120

100

80

60

40

20

0

Energy Absorption Max Load (J)

Compressive Strength (MPa)
40 The AMPTIAC Quarterly, Volume 8, Number 4

ceramics. One such material model, the Johnson-Holmquist

ceramic model, has been able to accurately simulate the full

gamut of ceramic response: everything from the phenomenon

of interface defeat, where a projectile is stopped on the surface

of the ceramic, to the dwell-penetration transition and direct penetration

[9]. Thus, as the issue of ceramic modeling may have evolved toward a

(somewhat accepted) phenomenological material model (though an accepted micromechanical model is still

being sought), composite material

modeling for dynamic events has also

seen significant advances. Detailed

below are some of the extensive efforts

to develop, characterize and validate a

robust material model, specifically for

the analysis of a composite undergoing

highly transient and damage-inducing

(blast or ballistic impact) loading.

The modeling of ballistic impacts

into composite materials has evolved

from two different analysis methodologies. One set of models has been

developed from the analysis of high velocity impacts into

metallic materials, where the response of the material is governed by wave propagation. The second set has been developed

from the quasi-static damage mechanics analysis of composite

materials. In the former case, the behavior of a material is modeled by analyzing the hydrostatic and deviatoric components of

stress. However, due to its inherent orthotropy, decoupling of

the stress tensor of a composite material proves to be problematic: there are terms related to the deviatoric stress that affect

the hydrostatic components and vice versa. Nonetheless, with

suitable assumptions and corrections, Anderson and co-workers [10, 11] overcame this issue, and

several models have evolved using this

formulation. These models have

proven unique in that they allow a

polynomial equation of state to be utilized, which has proven important in

the analysis of armor grade composites

and for hypervelocity impact simulations (Figure 5) [12].

The present model, developed by

the Materials Sciences Corporation

(MSC) and the US Army Research

Laboratory, has been generalized from

the quasi-static damage mechanics

analysis of composite materials [13,

14]. Further improvements of this

model have recently been made at

ARL and the University of Delaware

[15] under the Army’s Materials Center of Excellence. Composite materials

mitigate impact energy through a number of different material

damage mechanisms. This is unlike many metallic components, where localized impact energy is typically mitigated by

localized plastic deformation. Shown in Figure 6 are a number

of these mechanisms, such as fiber shear fracture, fiber tensile

rupture, matrix cracking, delamination and fiber crushing, that

are observed experimentally and must all be taken into account.

Figure 5. Modeling Ballistic Impacts into 

Composite Armor Has Evolved Significantly 

in Recent Years.

Table 1. Input Parameters Required for the Composite Material Model.

Material Properties Required in the MSC Composite Material Model

Mass density

Young’s modulus – longitudinal direction

Young’s modulus – transverse direction

Young’s modulus – through 

thickness direction

Poisson’s ratio ba direction

Poisson’s ratio ca direction

Poisson’s ratio cb direction

Shear modulus ab direction

Shear modulus bc direction

Shear modulus ca direction

Material axes option

BETA Layer in-plane rotational 

angle in degrees

Longitudinal tensile strength

Longitudinal compressive strength

Transverse tensile strength

Transverse compressive strength

Through thickness tensile strength

Crush strength

Fiber mode shear strength

Shear strength, ab plane

Shear strength, bc plane

Shear strength, ca plane

Scale factor for residual compressive

strength

AMODEL Material models:

EQ. 1: Unidirectional layer model

EQ. 2: Fabric layer model

Coulomb friction angle for matrix and

delamination failure

Element eroding axial strain

Scale factor for delamination criterion

Limit damage parameter for elastic 

modulus reduction

Limit compressive relative volume for 

element eroding

Limit expansive relative volume for 

element eroding

Coefficient for strain rate dependent

strength properties

Coefficient for strain rate softening property

for fiber damage A direction

Coefficient for strain rate softening property

for fiber damage B direction

Coefficient for strain rate softening property

for fiber crush + punch shear damage

Coefficient for strain rate softening property

for matrix and delamination damage

Coefficient for strain rate dependent 

axial moduli

Coefficient for strain rate dependent 

shear moduli

Coefficient for strain rate dependent 

transverse moduli
The AMPTIAC Quarterly, Volume 8, Number 4 41

Generally, in composite damage mechanics models, material

damage and failure are accounted for only by a resultant

decrease in the material stiffness in the corresponding material

directions. The current model utilizes this concept, but also

accounts for the inter-relations of the different failure modes

through quadratic failure criteria and a novel damage tensor

that relates the specific failure modes to the extensional and

shear moduli that are compromised. The formulation is based

on the continuum damage model for composite failure developed by Matzenmiller et al. [16] and has been extended to

incorporate strain rate sensitivity of both stiffness and strength

and post failed material softening.

While the details of this elegant and complex material model

are beyond the scope of the current article (for further details,

refer to [13]), it is not surprising that there are a number of

material constants that must be determined in order to

generate accurate simulations. Table 1 shows a list of the

constants required by the composite damage model,

which has been incorporated into the commercial

dynamic finite element analysis software LS-DYNA,

where it is known as MAT 161/162. Obviously, in order

to perform accurate simulations of a composite material

using the current model, a substantial material characterization program is required. As part of the Composite

Material Technology (CMT) program, the Center for

Composite Materials (CCM) at the University of

Delaware has been working with ARL and MSC to fully

characterize materials of interest and validate these values

by performing simulations of the experiments using LSDYNA and the current material model.

Figure 7 depicts the effort of determining the material behavior associated with the punch shear of S2-

glass/epoxy composites. Punch shear experiments were conducted for a number of punch-die diameters at a variety of rates

from quasistatic, to drop tower, to split Hopkinson pressure

bar. Simulations were then performed, and the quantitative values were compared with those obtained from the experiments.

Materials that have been characterized include S2-glass/SC15

epoxy, S2-glass/SC79 epoxy and IM7 carbon/SC79 epoxy.

COMPOSITE ARMOR SIMULATION

To illustrate the insights that can be gained from simulations of

composite armor, consider the following problem shown in

Figure 8. The simulation, conducted using the nonlinear analysis software Autodyn, consists of a half-symmetric model of a

ceramic tile with a thin composite cover plate on top and supported by a thin PMC, all of which is backed by a glass-fiber

Figure 6. Damage Mechanisms Observed During the Impact and 

Penetration of a Composite.

Figure 7. Experimental Set-ups for Quasistatic and Drop Tower Punch Shear Experiments, Simulation of the Punch Shear Experiment

and a Comparison of the Load vs. Displacement Curves from the Experiment and the Finite Element Analysis.

In-plane Shear Failure

Delamination

Fiber/Matrix Shear

Failure (Punch Shear)

Fiber/Matrix

Tension Failure

Crush

1-inch

Support

Span

Punch Shear Fixture on

INSTRON 1332

Simulation of Punch Shear Test:

1-inch Span

Quasistatic Punch Shear Experiments Low Velocity Impact Punch Shear Experiments

Load vs. Displacement for 1-inch Span Plate

4-inch

Support

Span

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Displacement, cm

70

60

50

40

30

20

10

0

EXP

FEA

Load, kN
42 The AMPTIAC Quarterly, Volume 8, Number 4

PMC. In the impact region, all of the materials are modeled

using smooth particle hydrodynamics (SPH). The tile itself is

surrounded and confined by steel brackets modeled using

LaGrangian elements.

As a measure of how the composite armor reacts upon

impact, the deceleration of a target point on the rear surface of

the fragment-simulating projectile (FSP) is tracked during the

impact event. The deceleration of the FSP for this baseline case

is given in Figure 9. From this figure, it can be seen that the

deceleration curve of the FSP has three distinct portions: an

initial steep deceleration up to approximately 35 μs, a transition region from roughly 35-45 μs, and a final, more moderate

deceleration curve from 45-90 μs. 

By observing the plots of the material damage through time,

an understanding of the mechanisms behind these regions

becomes discernible. The initial rapid deceleration is caused by

the hard ceramic deforming the FSP. During this time, the

ceramic itself fails, its failure starting on the surface opposite

the impact surface due to the tensile reflections from the initial

compressive stress wave. In Figure 9, green regions indicate

undamaged material, and colored regions indicate material that

is either plastically deformed or damaged. The cyan color of the

projectile indicates that it is plastically deforming. For the composite, the cyan and orange coloring indicates transverse shear

damage, the purple indicates in-plane tensile failure and for all

materials, red indicates bulk failure. The cracking of the ceramic leads to the formation of a conoid (a cone of ceramic material under the impactor) which loads the backing plates. 

Extensive transverse shear damage mechanisms appear in all

of the composites by 20 μs. The initial deceleration of the projectile transitions to a more moderate deceleration of the projectile at approximately 30 μs, and it is at this time that the

damaged composites have displaced enough locally to allow the

failed ceramic in the conoid to start moving, both in the direction of the projectile and laterally, out of the way of the projectile. The effectiveness of the ceramic diminishes greatly from 30

μs to 45 μs. After 45 μs, the damaged glass/epoxy composite

catches both the ceramic rubble and the plastically deformed

projectile.

SUMMARY

The application of polymer-matrix composite materials to

armor systems has principally been driven by the need to

increase performance (survivability) in very lightweight fighting vehicles. The stringent weight requirements for these types

of applications have provided the motivation for the development of multi-functional armor systems. Ceramic-composite

armor systems have been developed to provide ballistic protection from a range of battlefield threats and also serve as the

vehicle structure. 

Substantial progress has been made in the development of

materials technology for lightweight fighting vehicles, including advances in fiber sizings that have been formulated to provide strain-rate sensitive response (strong fiber-matrix interfacial adhesion at structural loading rates, and weak interfacial

strength at ballistic loading rates). Additionally, the development, characterization and validation of improved material

constitutive models have allowed ballistic experiments to be

studied using numerical simulations, which have provided new

insight into how the materials behave and interact during

impact. Further advances in materials technology and their

incorporation into lightweight armor will focus on the

increased integration of multifunctionality, such as the incorporation of power storage, communication, sensing, and health

monitoring, which are described elsewhere in this issue of the

AMPTIAC Quarterly. Numerical simulations will allow engineers to examine the influence of multifunctional materials on

improving the performance of ceramic composite armor that

will be utilized in future combat systems.

REFERENCES

[1] M.L. Wilkins, Second Progress Report of the Light Armor Program, Lawrence Livermore National Laboratory, Livermore,

CA, Technical Report No. UCRL 50284, 1967

[2] M.L. Wilkins, Third Progress Report of the Light Armor Program, Lawrence Livermore National Laboratory, Livermore,

CA, Technical Report No. UCRL 50349, 1968

[3] M.L. Wilkins, C.F. Cline, and C.A. Honodel, Fourth

Progress Report of the Light Armor Program, Lawrence Livermore

Figure 8. Model Used for the Numerical Simulation of a

Composite Armor System.

Figure 9. Projectile Velocity as a Function of Time for the

Baseline Configuration.

Steel Projectile (SPH) Composite Tile

Support Layer

Composite

Cover Steel 

Surrounds

Glass Composite Backing

0 0.02 0.04 0.06 0.08 0.1

Time (ms)

FSP Velocity (m/s)

1000

800

600

400

200

0

SPH

LaGrange

Elements

Ceramic

I

II III

FSP Velocity vs. Time for Ceramic Backed 

by Carbon Fiber Composite Configuration
The AMPTIAC Quarterly, Volume 8, Number 4 43

National Laboratory, Livermore, CA, Technical Report No.

50694, 1969

[4] R.M. Ogorkiewicz, Armored Vehicles of Composite Materials,

International Defence Review, July 1989

[5] G. Thomas, A. Larson, and J. Garces, Composite Hull 

Program Final Technical Report, Army Research Laboratory

Contractor Report No. ARL-CR-179, December 1994

[6] T. Pike, M. McArthur, and D. Schade, Vacuum-Assisted

Resin Transfer Molding of a Layered Structural Laminate for

Application on Ground Combat Vehicles, Proceedings of the 28th

International SAMPE Technical Conference, Seattle, WA, pp.

374-380, November 4-7, 1996

[7] B.K. Fink, Performance Metrics for Composite Integral Armor,

Journal of Thermoplastic Composite Materials, Vol. 13, No. 5,

pp. 417-431, September 2000

[8] J.A. Zukas, Numerical Modeling of High Velocity Impact in

Non-Metallic Materials, Vol. 48, High Strain Rate Effects on

Polymer, Metal and Ceramic Matrix Composites and Other

Advanced Materials, ASME, New York NY, 1995

[9] T.J. Holmquist and G.R. Johnson, Response of Silicon 

Carbide to High Velocity Impact, Journal of Applied Physics,

91(9), pp. 5858-5866, 2002

[10] P.E. O’Donoghue, C.E. Anderson, Jr., G.J. Friesenhahn,

and C.H. Parr, A Constitutive Formulation for Anisotropic

Materials Suitable for Wave Propagation Computer Programs,

J.Comp. Materials, pp. 26(13), pp. 1860-1884, 1992

[11] C.E. Anderson, Jr., P.A. Cox, G.R. Johnson, and P.J.

Maudlin, A Constitutive Formulation for Anisotropic Materials

Suitable for Wave-Propagation Computer Programs 2, Computational Mechanics, 15(3), pp. 201-223, 1994.

[12] W. Riedel, W. Harwick, D.M. White, and R.A. Clegg,

ADAMMO Advanced Material Damage Models for Numerical

Simulation Codes, EMI Report No. 175/03, Freiburg Germany,

October 31 2003

[13] C.F. Yen, Ballistic Impact Modeling of Composite Materials,

Proceedings of the 7th International LS-DYNA Users Conference, Dearborn MI, May 19-21, 2002

[14] C.F. Yen, and A.A. Caiazzo, Design Methodology and 

Validation for Multifunctional Composite Armor, MSC 

Technical Progress Report, US Army Research Laboratory,

Contract No. DAAD17-01-C-0111, July 2002

[15] C.F. Yen, B.A. Cheeseman, C.P.R. Hoppel, B.A. Gama,

and J.W. Gillespie, Modeling of the Compressive Failure of Plain

Weave Composites, ASC/ASTM-D30 Joint 19th Annual Technical Conference, Atlanta Georgia, October 17-20, 2004

[16] A. Matzenmiller, J. Lubliner, and R.I. Taylor, A Constitutive Model for Anisotropic Damage in Fiber-Composites,

Mechanics of Materials, 20, pp. 125-152, 1995

Dr. Christopher Hoppel leads the Kinetic Energy Defeat Team in the US Army Research Laboratory. He oversees

the development of structural armor for the Army’s Future Combat Systems. He serves on the executive committee

of the American Society of Composites and Leads the joint DOD/DOE TCG XII program (Advanced Composite

Materials for Munitions). Dr. Hoppel earned his BS, ME, and PhD in Engineering Science and Mechanics from

Pennsylvania State University.

Dr. Robert Jensen is a Research Chemist in the Engineering Materials Team of the Multifunctional Materials Branch,

at the US Army Research Laboratory, Aberdeen Proving Ground, MD. Dr. Jensen’s research involves the development of novel sol-gel based fiber sizings for energy absorption in composite materials as well as the investigation

of surface and adhesion phenomena. Dr. Jensen holds a BS in Chemistry from Francis Marion University; and a PhD

in Physical Chemistry from Virginia Tech, specializing in structure-property relationships in polymeric materials.

Dr. Bryan A. Cheeseman is a mechanical engineer in the Survivability Materials Branch of the US Army Research

Laboratory’s Weapons & Materials Research Directorate. He leads numerical simulation efforts investigating 

ballistic impact into fabrics, composites, and lightweight composite armor. In addition, he also conducts coupled

Eulerian-LaGrangian blast-structure interaction simulations. Dr. Cheeseman earned his BS, MS, and PhD in

Mechanical Engineering from the University of Delaware.
44 The AMPTIAC Quarterly, Volume 8, Number 4

INTRODUCTION

The United States Army is currently undergoing one of the

largest and most significant transformations in its history. The

ultimate goal is to ensure the overwhelming superiority and

effectiveness of both its defensive and offensive systems in the

face of constantly evolving threats and technological advances.

To do so, the Army will have to become lighter and more

lethal; and will have to gather and synthesize information in

new ways to optimize its performance. A key component of

this transformation is the transition from “legacy” systems to

next-generation systems that are lighter, rapidly deployable,

and highly networked. A second and equally important element is the exploitation of new materials and technologies to

deliver the weight reduction, mobility, survivability, and

lethality performance required by the Army Transformation.

There will be a period of transition wherein both current

and future Army systems will constitute the overall arsenal of

Army weaponry and equipment. This provides a unique

opportunity to compare historical system production levels

with anticipated production levels of entirely new systems. In

addition, it emphasizes both the scale and scope of systems the

Army requires to execute its mission. Figure 1 highlights the

challenges associated with manufacturing an array of Army

systems, and specifically, the broad and unique applications of

polymer-based composites across systems of varying complexity and production levels.

ENABLING MATERIAL AND PROCESS TECHNOLOGIES

The Army’s goal is not simply to “keep pace” with technology

but rather anticipate the trajectory and evolution of strategic

technologies, and thereby develop new and effective means to

defeat emerging threats and preserve a superior tactical advantage. Exploiting materials technology is central to this basic

goal, and polymer-based, fiber-reinforced composite materials

have and will continue to play a critical role in this area.

Advances in composite systems are basically two-fold: the first

is the development of fundamentally new fibers, resins, and

other “constituent” materials. The second is the integration of

available materials into new composite and multifunctional

material solutions that give significantly improved sets of properties (for example, mass-efficient structural armor). Advances

in constituent materials, such as low viscosity, high performance epoxy resin systems, have enabled a shift from capitalintensive equipment such as large pressurized autoclaves to

lower cost vacuum driven processes based on liquid injection

molding technology.

Process Models, Sensors, and Control

The Army has made substantial and sustained investments in

high performance computing (HPC), having established several centers to develop and apply computing excellence. These

computing resources have been leveraged by both government

and university researchers through the Army’s Major Shared

Resource Centers (MSRC) to develop increasingly complex

models of various materials and processes of interest to the

Army. However, a trend is underway to develop more computationally efficient codes that can operate on platforms that are

likely to be found on manufacturing shop floors – such as personal computers. Process simulation, together with sensor and

control technologies, constitutes a research area known as

“intelligent processing.” Traditional processing relies largely on

historical information gathered by trial and error; by contrast,

Shawn M. Walsh

Michael Maher

Weapons and Materials Research Directorate

US Army Research Laboratory

Aberdeen Proving Ground, MD

Suresh Advani

Center for Composite Materials

University of Delaware
The AMPTIAC Quarterly, Volume 8, Number 4 45

intelligent processing uses both predictive and diagnostic tools

to optimize the composite manufacturing process. Unforeseen

disturbances during processing can be actively compensated for

and minimized. In addition, the introduction of automation

reduces labor, improves repeatability, and increases yield. Figure

2a demonstrates the various tools that must be developed and

integrated to obtain this goal.

Simulation tools such as LIMS (Liquid Injection Molding

Simulation) and SLIC (Simulation-based Liquid Injection

Control) developed at the University of Delaware were used to

demonstrate and experimentally validate the intelligent processing approach [1, 2]. Figure 2b shows how

one can model resin flow in the hood

of a HMMWV using modeling and

simulation tools. Placement of sensors in the mold will allow one to

detect flow disturbances and re-direct

flow through pre-selected auxiliary

gates to ensure successful manufacturing despite unforeseen variations.

The strategic control environment

could be developed off-line using the

simulations to create all the different

possible scenarios. The control strategy can then be implemented on the

manufacturing floor using a computer to interface with the sensors in the

mold and the auxiliary gates. This

concept has been integrated in a

Resin Transfer Molding (RTM)

workstation. The workstation can

accept the data created by the simulation environment for detecting the

disturbance and for triggering the control action for that 

particular scenario.

In order to meet the requirements of the Army Transformation, selected materials must be able to solve a host of system

issues while remaining weight efficient and cost effective. The

tailorability of composites allows designers to maximize performance at a minimal weight. In addition, the ability of composites to perform multiple functions as a material system

offers the flexibility to maximize the efficiency of designs. 

In the past, the Army has segregated ballistic and structural

requirements; composite systems now combine these two

requirements in certain applications. Current efforts are

focused on combining power, sensor suites, communication,

and health monitoring with structural composite elements. The

only way to accomplish these tasks is to take a holistic approach

to developing systems for the Army. The total requirements for

the system have to be considered while the designer is selecting

materials. In addition, the tooling schemes and manufacturing

processes should be considered to ensure that the most costeffective material solution is chosen. 

As these multi-functional composite materials are being

designed into future platforms, new test methods are being

developed to ensure that the systems will perform as required.

While developing manufacturing technologies, the Army considers repair concepts to reduce the life-cycle costs and logistics

footprint of future platforms. Innovative approaches towards

composite manufacturing are essential to prepare for these and

other requirements.

Novel Fabrication Technologies

Process innovations have led to the development of more flexible manufacturing technologies for both prototype and production operations. For example, the Army has co-sponsored

the development of a new, highly flexible process that provides

Figure 1. The Diverse Array of Current and Future Army Systems.

Figure 2. The Application of Intelligent Processing Tools to a

HMMWV Hood Structure [1].

Rotorcraft

Missiles

Sabots

Personnel Protection Systems

Unmanned Aerial Vehicles

Ground

Vehicles

• Increase production repeatability

• Reduce trial & error in process design

• Improve quality

• Reduce cost

Specification of 

Material Parameters

Filling

Simulations Design 

Methodologies

Versatile Resin

Injection Systems

Sensor

Technology

Active Process

Control

a)

b)
46 The AMPTIAC Quarterly, Volume 8, Number 4

a rapid, low cost means of fabricating components with various geometric, material, and design complexities. The process,

invented at Florida State University and known as Resin Infusion between Double Flexible Tooling (RIDFT), uses vacuumbased infusion to wet-out a fibrous preform and then draw it

down to fully conform to the desired tool shape (Figure 3a). A

particularly novel feature is the ability to use inexpensive, rapidly prototyped tooling; this permits one to move seamlessly

from concept to design to near-net fabricated component [3].

The process enables the cost-effective ability to fabricate customized components or replacements parts, and is capable of

low to intermediate production runs. RIDFT is a particularly

conformal process that allows for “deep draw” of fibrous preforms. For example, the process was used to fabricate curved

components for Army unmanned aerial vehicles (UAVs), as

well as prototype Army helmet shells for human factors testing. More recently, the RIDFT process was demonstrated as an

effective method for producing a leg brace for an individual

impaired by a leg injury while serving in Iraq.

Anthony P. Muller, HMC (Chief Hospital Corpsman),

NMCB (Naval Mobile Construction Battalion) 14 based in

Jacksonville, Florida was injured in a mortar attack in Iraq in

May 2004. He is undergoing therapy and rehabilitation and as

part of the process he is required to wear a supporting leg brace.

This presented an opportunity to demonstrate RIDFT’s rapid,

flexible, and low cost means of developing a lightweight brace

for an individual. Compared to the conventional brace, the finished RIDFT brace was 22% lighter, covered 40% less of the

sailor’s skin, and had an integrated carbon fiber/epoxy structural spring to assist with impaired ankle/foot functioning. More

importantly, the brace was both customized to the sailor’s leg to

ensure optimal performance (Figure 3b) and delivered to him

within hours of the initial design requirements assessment. This

is a technology that could not only benefit Army, Navy, and

other members of the military community, but a host of individuals who could use customized, lightweight braces.

Integrated Composite Manufacturing Approaches

There are three emerging areas that could significantly shape

the future of manufacturing Army systems. The first is the

development of multifunctional material solutions to address

weight and volume constraints of future Army system designs.

The essential challenge is to provide the same functionality at

reduced weight. This functionality could, for example, simultaneously require armor, structural support, EMI shielding, lightening strike protection, and communication hardware.

Advances in materials, design, and integration techniques offer

the potential to produce a truly “multifunctional” composite

system. Figure 4 displays a notional section of structural armor

wherein an electromagnetic radiating element serves as an

antenna. This system has four distinct types of materials: a

polymer resin, a fibrous glass reinforcement, a metallic film,

and an array of ceramic tiles. The processing challenges are

obvious: each material potentially introduces an additional processing step (and hence, labor, time, and expense). There is relatively little processing science associated with manufacturing

of this kind, and the Army has initiated several programs to

explore these issues.

Figure 3. a) The RIDFT Process and b) a Custom Fabricated 

Leg Brace.

Figure 4. A Notional Multifunctional Structural Armor and Antenna Concept.

Conventional Brace

Fiber Preform Resin is Infused

Mold

Surfaces

Preform is Drawn Over

Mold Shape by Vacuum

Step 1: Load Fiber & Seal Frame

Step 3: Vacuum Form Part Step 4: Demold Part

Step 2: Infuse Fiber

RIDFT Brace in Use

b)

a)

RIDFT Brace

Co-processing of Preform, Ceramic Tiles,

and Antenna Element

Fabrication of “Smart” Perform with Conductive Back-plane Elements Integration into Notional Vehicle Structure
The AMPTIAC Quarterly, Volume 8, Number 4 47

The second area influencing composite manufacturing is

that of structural health monitoring (SHM). SHM is an

enabling technology for condition-based maintenance and it

has the potential to reduce significantly the overall “cost of

ownership” of fielded systems. The Army has leveraged both

academic and industrial sectors to begin identifying the type of

process technologies that will be appropriate for embedding

and connecting the type of promising SHM sensor hardware

that is currently being developed. Fiber optics, for example,

have proven successful as temperature, pressure, and strain

measurement devices. Fiber optics are also attractive in that

they closely resemble the fibers used in many continuously

reinforced composites, though their diameter and flexibility

may vary greatly from the reinforcing fiber. 

Mentis Sciences Inc. has been developing a highly novel

fiber feed system which they have integrated with their missile

radome fabrication technology (Figure 5). Essentially, this

technique uses braiding to both form the structural radome

component and simultaneously co-locate with a high degree 

of accuracy a series of fiber optic sensors. The use of such

structural health monitoring sensors in missile structures has

the potential to assess damage of a missile component during

transport, use, and storage.

A third area is that of intelligent component integration. 

Previous studies and programs have indicated that 10-20%

weight reductions and 30-50% fabrication cost reductions are

possible if new technologies could be developed to minimize or

eliminate the number of fasteners and mechanical attachment

systems currently used with composite materials. Drilling bolt

holes into a composite not only reduces the load bearing capacity of the structure, it also greatly increases overall manufacturing costs due to machining, cleansing, fastener installation, 

and assembly steps. The remedy to this problem is two-fold: 

(1) better designs that minimize or eliminate the need for traditional mechanical fasteners; (2) new process and fastening

technologies that are compatible with composite materials. 

For example, the Army is developing the “soldier as system”

concept and as such will require not only more mass-efficient

ballistic protection materials but also an array of hardware to be

both permanently and temporarily attached to the helmet shell

(Figure 6a). This has stimulated the exploration of thermoplastic-based composites. Traditional helmets have been made with

Figure 5. A Braiding Process for Embedding Structural Health Monitoring Sensors.

Figure 6. Thermoplastic Bonding Technology Applied to Prototype Helmet System.

Braiding of Radome Structure

Graphite Fiber

Fiber Optic Cable Embedded Fiber Sensors

Fabricated 

Radome

Ultrasonic Energy

Attachment

Thermoplastic/Keviar

Bond Line

a) Bonded Helmet Shells b) Ultrasonic Bonding Process
48 The AMPTIAC Quarterly, Volume 8, Number 4

a thermoset phenolic resin. In addition to improved ballistic

performance, thermoplastic materials (unlike thermosets) can

be remelted and reformed several times. Ultrasonic, infrared,

and induction processes can be used to bond one type of polymer system to another. This opens up significant possibilities

not only for the design of attachment systems (Figure 6b) but

also for low cost manufacturing techniques that can reduce or

eliminate the need for drilling, clamping or other purely

mechanical fastening techniques.

SUMMARY

The Army, with a few notable exceptions such as personnel

protection, sabots, and rotorcraft, currently makes relatively

low use of polymer composites. Collaborations between government, academia, and industry have been vital in reducing

the risk and expanding the role of composites in both current

and notional systems. As the Army transforms its heavy forces

will become lighter and more lethal. 

The future of Army process and manufacturing technology

will be guided primarily by the new and evolving requirements

that will be developed to provide the United States with superior land combat systems and technologies. Both current and

emerging materials will be examined for their strategic benefits,

and the appropriate manufacturing technologies will be developed to implement them into Army systems. It is increasingly

likely that combinations of materials will become the standard,

rather than the exception: lethality, survivability, and multifunctionality all demand “more for less.” Future developments

will provide innovative solutions to co-processing dissimilar

materials so as to minimize overall cycle times, touch labor, and

manufacturing costs. Manufacturing in the future is likely to be

as much about processing information, such as model, sensor,

and control data, as it is about processing the material itself.

ACKNOWLEDGEMENTS

The authors gratefully acknowledge the following for their contributions: Kirk Tackitt, James Campbell, Roderic Don, Eric

Adler, Steven Weiss, Eric Wetzel, Ozlem Kilic, Clinton Isaac,

Walter Roy, James Keithley, and Robert Lempicki, all of the

Army Research Laboratory; James Thagard and Ben Wang,

Florida A&M University; John Dignam, Brad Mate, and

Thomas Raskow, Mentis Sciences Inc.; Dave Krasnekcy and

Matthew Correa, Natick Soldier Center; David Rogers,

Artisent Inc.; and Vasilios Brachos and Gary Robblee,

Diaphorm Inc.

REFERENCES

[1] P. Simacek, and S.G. Advani, Desirable Features in Mold

Filling Simulations for Liquid Molding Processes, Polymer Composites, Vol. 25, pp. 355-367, 2004

[2] J.M. Lawrence and S.G. Advani, Use of Sensors and Actuators to Address Flow Disturbances During Resin Transfer Molding

Process, Polymer Composites, Vol. 24, pp. 237-248, 2003

[3] J.R. Thagard, O.I. Okoli, Z. Liang, H.P. Wang, and C.

Zhang, Resin Infusion Between Double Flexible Tooling: Prototype

Development, Composites Part A, 2003

Dr. Suresh G. Advani is a Professor of Mechanical Engineering Department and Associate Director of the Center 

for Composite Materials, at the University of Delaware. He holds a PhD in Mechanical Engineering from the 

University of Illinois at Urbana-Champaign. His research interests are in rheology, fluid mechanics, and heat 

transfer; as they are applied to manufacturing processes. He has co-authored over 200 journal articles and 

conference presentations; and has co-authored or co-edited over twenty books.

Mr. Michael Maher is Chief of the Materials Applications Branch of the Army Research Laboratory’s Weapons

and Materials Research Directorate. He received his BS from Loyola. He has over 22 years experience in the

development, prototyping, and program management of systems utilizing advance materials and manufacturing

technologies.

Dr. Shawn Walsh leads the Survivable Systems Integration Team of the Army Research Laboratory’s Weapons

and Materials Research Directorate. He received his Doctorate from the University of Massachusetts at Lowell. 

His research interests include low cost manufacturing, novel application of polymer composites, multifunctional

materials, and structural health monitoring. He has published over 60 papers, and received several patents for

process and materials technology. 
The AMPTIAC Quarterly, Volume 8, Number 4 49

INTRODUCTION

For centuries, gun barrel designers have focused their efforts on

the development and use of steels that possess higher strength

and toughness. Good mechanical properties are required to

withstand the high interior ballistic (explosive) loads to which

these pressure vessels are subjected. In addition to high internal

pressure, the cannon bore (internal surface of the cannon cylinder) is exposed to very high temperatures, as the propellant

ignites and begins the evolution of hot gases to provide the

propulsive force for the projectile. With the advent of ever

more robust propellants, bore surface erosion has become

increasingly problematic. This has forced barrel designers to

implement various means that include coatings and alternate

material liners to combat the phenomena. The desire for longer

lasting tubes has been a major motivator for research of new

and more robust materials for cannon design. Likewise, gun

barrel manufacturers have committed significant effort to

developing processes that result in high quality cannons capable of withstanding these erosive environments.

The Army’s desire to reduce the weight of its fighting force

to improve mobility on the battlefield (thus making it easier to

deploy assets to wherever they are needed around the globe) has

further challenged gun designers and manufacturers. This article provides some insight into the various materials and processing approaches being investigated to provide extended life

and/or reduced weight of gun barrels.

HISTORICAL PERSPECTIVE

One of the first major advances made to iron cannons was the

development of a technique in the 1850’s by Captain Thomas

Jefferson Rodman to cast a cannon over a water cooled core in

a heated flask. In addition to a number of processing advances,

the technique resulted in a significant improvement in tensile

fracture strength of the metal as it left the bore in a state of

residual compression [1]. The slow cooling of the iron resulted in a material having a tensile strength of approximately

30,000 psi. Through a series of tests, Rodman was able to

demonstrate clearly the superiority of his gun steel and casting

methods; however, he did not fully understand the importance

that the pre-stress condition played in the improved performance of the cannon.

By 1880, Army engineers at the US Ordnance Department

had a full understanding of the presence of the compressive

residual stress within the bore of guns cast by the Rodman technique (Figure 1). A full description of this method of casting

and finishing an iron cannon, as well as the testing procedure

used to verify the residual stresses, is documented [2].

In the 20th century, variations in the chemistries of Chromium-Molybdenum-Vanadium (Cr-Mo-V) steels have been

introduced that allowed for moderate increases in strength,

toughness and fatigue properties. Most of these improvements

come from superior processing and techniques that produce

higher-quality steels (less contaminants and defects). The last

major advancement in armament steels occurred in the 1970’s

with the introduction of ASTM A723 steel, which has yield

strength more than five times that of the steel produced by

Rodman more than a century earlier. It replaced the 4335-V

modified steel that had been in use since before World War II.

The A723 steel is processed through either vacuum arc re-melt

(VAR) or electro-slag re-melt (ESR). Both processes significantly reduce the amount of sulfur and phosphorus and, combined

with an increase in the nickel content, make A723 steel an

excellent candidate for “modern” armament applications. More

recently, the armament community has pushed for materials

with even higher strength and toughness due to more aggressive

environments and higher cannon firing pressures.

Larry Burton

Robert Carter

Victor Champagne

Ryan Emerson

Weapons and Materials Research Directorate

US Army Research Laboratory

Aberdeen Proving Ground, MD

Michael Audino

Edward Troiano

Benet Laboratories

Watervliet Arsenal, NY

Ordnance Materials Section III
SYSTEM IMPLICATIONS

As research of advanced gun barrels moves to materials other

than steel, it is important to point out the implications associated with barrels having a hybrid material construction, and

quite possibly, reduced mass. The introduction of multiple

materials into the construction of cannons is likely to result in

mismatches of thermal expansion, and consequently, stresses

that must be accounted for in the design. In addition, these

materials often have different thermal conductivities that can

result in insulative behavior through the thickness of the barrel

wall. Finally, many of the lightweight reinforcing materials that

have been considered have melting points well below that of

steel resulting in the need for more careful monitoring of cannon thermal stresses and the impact of relatively high rates of

fire on barrel temperature.

It is also important to understand the significance that gun

barrel mass plays in the overall system design. Weapon recoil

force, Fr, can be expressed as

Where I is the impulse imparted by the cannon to the system, mr is the mass of the recoiling parts, and Lr is the length

of the recoil stroke. From this equation, it is clear that reducing

the mass of the recoiling parts adversely increases the total force

and imposes additional system burdens on the recoil mechanism. Because of this deleterious effect of reducing barrel mass

on the management of the recoil force, weight reduction of

cannons has not been heavily pursued. However, several techniques to manage the recoil more effectively have resulted in

renewed interest and emphasis on lightweight barrels utilizing

advanced materials.

The fire-out-of battery concept invokes the release of the

recoiling parts from the latch position prior to firing, and

allows for the forward motion of these components. This forward momentum must then be countered and overcome upon

firing and results in a net reduction in the total recoil force.

Such an approach can be used to reduce the total force that

must be mitigated by the recoil system and has been demonstrated in both 105mm direct fire [3] and 155mm howitzer test

beds [4].

A more recent advanced gun system is the Rarefaction Wave

Gun (RAVEN), shown in Figure 2. This concept utilizes a sliding breech block that is timed to open such that the venting of

combustion gases takes place without degrading the performance of the propellant [5]. The early venting significantly

reduces the total recoil force imparted and minimizes the accumulation of heat in the barrel, thus enabling the consideration

of advanced lightweight materials.

STRESSES IN GUN TUBES

Autofrettage is a process unique to large caliber gun fabrication, where beneficial residual stresses are developed at the

bore surface. Autofrettage induces compressive residual stresses that can result in thinner walled gun tubes. As such, these

stresses provide added fatigue resistance and lower overall barrel weight. The compressive residual stresses are largest at the

bore surface and act to resist crack initiation as well as subsequent crack propagation. Historically, these residual stresses

were approximated utilizing approaches such as that presented

by Hill [6]. Hill’s approach accounted only for closed-ended

pressure vessels, and does not consider the Bauschinger effect

[7]. Recent work published by Parker has taken the classical

approach further to include the Bauschinger effect for a typical open-ended steel pressure vessel. Parker and Underwood

[8] further improved this work to include the Bauschinger

effect on several different candidate pressure vessel steels.

Referring to Figure 3, when a gun tube undergoes autofrettage the stress within the gun tube follows path O-A-B during

the initial loading and path B-C-D-E during the removal of

this loading. Hence, a family of uniaxial cycles, O-A-B-C-D-E,

each a function of initial plastic strain and radial location,

defines the equivalent stress for the gun steel during the autofrettage process. This, along with appropriate equilibrium,

compatibility and boundary conditions, is sufficient to calculate numerically the residual stress locked into the tube by

1 I 2

Fr = – ––––– 2 mr Lr

















,

50 The AMPTIAC Quarterly, Volume 8, Number 4

Figure 1. The Rodman Cannon (ca. 1860 to 1900) was a Staple

of Coastal Defense (Model 1861 15-inch Columbiad in the 1860’s

[Left]; and Today [Right] at Fort Mason’s Point, San Jose, CA.)

Figure 3. Uniaxial Stress – Strain Behavior during Initial Cycle.

B

C

D

E

A

◆

◆

◆

◆

◆

◆

0

Strain (%)

Stress/Yield Strength

Figure 2. Rarefaction Wave Gun or RAVEN[1].
The AMPTIAC Quarterly, Volume 8, Number 4 51

autofrettage. Results of such calculations are well documented

for the current range of gun steels [7] and conform extremely

well to the ASME Pressure Vessel and Piping code [9].

Accurate numerical analyses of stress, strain and the

Bauschinger effect in gun tubes require high quality uniaxial

stress-strain data and an accurate numerical fit to such data

[10]. These data provide the equivalent stress input to yield criteria such as Von Mises and Tresca [7] for the solution of complex 2D and 3D problems. It has been shown numerically that

the loss of compressive residual hoop stress at the bore of an

autofrettaged pressure vessel can be accurately predicted when

accounting for the loss of stresses due to the Bauschinger effect

and open-ended pressure vessel conditions.

Composite Overwraps for Improved Gun Barrel Performance

Another method for developing pre-stress in the cannon is to

use an external sheath. With external sheathing, it is possible to

induce the beneficial pre-compression in gun bores through

elastic material deformations rather than the plastic deformations imposed via autofrettage. For brittle bore materials (such

as ceramics that lack any plastic deformation capability), a

sheathing layer is the only avenue for achieving pre-stress in the

bore. External sheaths may be metallic cylinders that are

shrink-fit or press-fit over the bore liner, but another attractive

technique is to overwrap the bore with a polymer-matrix,

fibrous-composite sheath. Sheathing with composites offers the

advantages of relatively simplified manufacturing and lighter

weight. In the fiber direction, glass/polymer composites are

nominally as strong as steel, but are one-third as dense. Carbon/polymer composites are nominally three to four times

stronger in the fiber direction than steel, but one-fifth as dense.

Composite-overwrapped gun barrels are typically fabricated

using the filament winding process. The most efficient technique for fabricating an overwrapped gun barrel is to simply filament wind directly onto the outer diameter of the bore liner.

Additionally, the fibers must be deposited in layers at prescribed angles in order to achieve the strength and stiffness

requirements for a given design. For maximum pre-compression and ballistic strength (resistance to firing loads), the layers

comprising the overwrap require a fiber architecture with fibers

oriented predominantly in the hoop-direction. To achieve a

stiff barrel (i.e., a barrel that resists “whip” deformations), it is

necessary to orient fibers in the axial direction. Typically, overwraps are designed with a balanced fiber architecture that varies

along the length of the barrel. A gun barrel design tool has been

developed by the University of Delaware to facilitate designing

composite overwrap cannons. The tool has been used by Benet

Laboratories, part of the US Army Armaments Research,

Development, and Engineering Center (ARDEC), to design

the 105 and 120mm cannons (Figure 4) that have been fabricated and tested.

To achieve the pre-compression, significant levels of tension

must be developed and maintained in the fiber overwrap during the filament winding process. The US Army Research Laboratory (ARL) has undertaken efforts to increase the level of

tension (of the fibers) that can be developed via overwrapping

in order to achieve significant increases in pre-compression of

the barrel liners. Compared to the levels of tension available

using conventional equipment and techniques, the ARL technique has been shown to realize a four-fold increase. Extensive

experimental testing has been performed to validate modeling

of the high-tension overwrap process, and it is currently being

applied to ceramic tubes to enable structural integrity under

ballistic firing conditions.

IMPROVING BARREL LIFE

The US Armed Forces currently use chrome plating in their

large caliber, direct-fire weapon systems to protect the barrel’s

bore surface against the harsh effects of hot propellant gases and

from the mechanical wear of projectiles during firing. The electroplating process is used to deposit chromium onto these large

caliber gun barrels. The process involves applying a chromium

coating by passing an electric current through an electrolyte in

contact with the gun barrel. The essential components of the

electroplating process include the barrel (electrode to be plated), an anode to complete the circuit, an electrolyte containing

the chromium metal ions to be deposited, and a direct current

power source. The barrel and the anode are immersed in the

chromium-rich electrolyte with the anode connected to the

positive leg of the power supply and the barrel connected to the

negative leg. As the current is increased from zero, a point is

reached where chromium metal plating begins to occur on the

barrel. The advantage of chromium electroplating is that it will

deposit a relatively thick layer of chromium directly on the gun

barrel’s interior surface providing a surface with high wear

resistance, a low coefficient of friction, and excellent hardness

and corrosion resistance.

Unfortunately, recent advances in armament munition technology have deemed chromium electroplating as insufficient in

protecting the bores of large caliber gun barrels. Increasing

muzzle velocity and range requirements have forced the development of advanced propellant formulations that wear and

erode current chromium plated barrels resulting in severe

reductions in barrel life. The M1A1 Abrams tank main armament, 120mm M256 cannon, has lost significant barrel life

throughout the evolution of the current family of 120mm carFigure 4. 105-mm Composite Overwrap Cannon.
tridges (Figure 5). Recent candidate propellant formulations

have condemned 120mm barrels after as few as 50 rounds were

fired in them. Improvements in propellant formulation have

been made so that the current barrel life is approximately 260

rounds but this still falls short of the earlier 400 to 500 round

life. In addition, the chromic acid used in the electrodeposition

process is a hazardous substance because it contains hexavalent

chrome, a known carcinogen. Watervliet Arsenal, the producer

of the 120mm tank gun, realizes significant annual environmental compliance costs associated with the chromium electroplating of 120mm barrels.

Chromium electroplating can no longer support these

advanced propellant formulations for a number of reasons.

Most notable is the fact that as-deposited electroplated chromium experiences a significant amount of cracking during the

plating process. These cracks are a result of volumetric changes

in the chromium layer when electroplating process contaminants outgas. This volumetric change results in a severe tensile

load that is only relieved by the formation of micro-cracks. Further cracking occurs during the gun firing cycle when significant hoop strains are realized. These cracks offer a path for the

hot propellant gasses to reach the steel substrate. These gases

cause the steel, with its lower melting point, to convert to carbides and oxides further compromising the “foundation” to

which the chromium layer is attached. As a result, the “compromised layer” spalls off revealing more unprotected steel and further propagating the erosion mechanism.

Advanced materials and application technologies are one way

to provide adequate bore protection. A number of requirements must be met if an alternative material coating is selected.

It must have a melting point higher than that of chromium

(1875 °C). Such a requirement defines eleven refractory metals

for consideration. In addition, it is desirable to have a coating

material with an elastic modulus nearly equivalent to the steel

substrate to prevent the on-set of cracking. Imposition of this

constraint leaves three refractory metals for consideration – tantalum, rhenium, and niobium. For reasons of cost and reactivity, tantalum has been the primary coating material of choice

amongst these three.

New Coating Processes

In addition to the investigation of new materials, significant

effort has been devoted to developing a new coating process to

overcome the inherent problem of cracking associated with the

electro-plating process. The autofrettage process is followed by

a thermal soak operation that aids in “normalizing” the stress

variations (minimize thermal mismatch stresses) imposed during autofrettage. Exceeding the post-autofrettage thermal soak

temperature (357 °C) will compromise barrel strength by

reducing the beneficial residual stresses previously developed.

Therefore, any coating deposition process must have a processing temperature less than the post-autofrettage thermal soak

temperature. This eliminates consideration of many deposition

techniques. Most spray, chemical vapor deposition (CVD), and

laser-based technologies process at a far higher temperature.

Benet Laboratories has developed an ion-based physical

vapor-deposition (PVD) process known as cylindrical magnetron sputtering (CMS) that is considered acceptable since it

stays below the critical process temperature. CMS is a vacuum

coating process in which positive gas ions are formed and accelerated to high speeds to strike a negatively charged target metal

source (see Figure 6). The momentum of the gas ions is transferred to the metal atoms of the target in the form of energy,

causing them to be ejected or “sputtered” from the surface. The

substrate to be coated (the gun barrel) is placed in the direct

path of the ejected neutral atoms and a film is formed as they

strike the surface. This process produces high quality coatings

with good adhesion and uniformity. It is limited by high cost,

coating thickness, and line-of-sight restrictions for coating

complex shapes. Sputtering is a non-aqueous, non-polluting

coating process that is essentially benign, as only minor

amounts of residue are produced from the vacuum systems

associated with the equipment.

Explosive Bonding

Another technique for application of desirable refractory metal

coatings is explosive bonding, commonly referred to as

“cladding.” It has been in use for over 40 years and has proven

capable of joining any combination of dissimilar metals that

are otherwise difficult to bond or metallurgically incompatible. The process involves the use of energy from a controlled

explosive detonation to force a coating material or clad up

52 The AMPTIAC Quarterly, Volume 8, Number 4

+

+

+

+ +

+ + +

Figure 6. Schematic of a Physical Vapor-Deposition Coating

Process.

Negatively Charged

Target Material

Ejected Surface Atom

Substrate

Positive Ions

Figure 5. The M1A1 Abrams Tank’s Main Armament:

The 120mm M256 Cannon.
The AMPTIAC Quarterly, Volume 8, Number 4 53

against the parent material at high pressures, causing a large

amount of plastic strain and resulting in the formation of a

metallurgical bond. Carpenter and Wittman [10] provide an

excellent review of explosive bonding and identify four boundary condition requirements to produce an adequate bond,

specifically the critical angles for jet formation, the critical

impact pressure, the critical flow transition velocity, and a

maximum impact velocity [11].

Explosive bonding has advantages over conventional chrome

plating and physical and chemical vapor deposition techniques.

The time duration for forming an explosive bond is seconds as

opposed to the typical rates of

0.001 inch thickness per hour

associated with the other techniques. Hydrogen embrittlement, a degradation process that

can occur during the electrolytic

chrome plating process, has

caused numerous failures of gun

tubes over the years and is not a

concern with explosive bonding.

Unlike physical and chemical

vapor deposition processes, surface preparation is not a significant consideration for explosive

bonding, where plasma is formed

on the surface of the clad, and the

parent material. The plasma is

forced ahead of the collision

front resulting in a scrubbing

action on both surfaces, leaving behind virgin material free of

undesirable oxides and debris that is conducive to providing an

optimal bond.

Over the past 25 years, tremendous advances have been

made in characterizing and defining the important process

parameters. TPL, Inc. has demonstrated the ability to explosively clad both a Ta-2.5W alloy and pure Ta to thicknesses of

0.027 inch and 0.063 inch, respectively, in a 120mm tube. In

addition, they have employed the process to clad the inside

diameter of both a rifled as well as a honed out, smooth-bore

M242 Bushmaster 25mm gun barrel (Figure 7) with pure tantalum [12]. As a result of testing on a rifled barrel and the subsequent analysis, it has been determined that pure tantalum is

too soft to withstand the forces exerted on the lands and

grooves of rifled guns. Tantalum alloys with 5-10% tungsten

are being examined as viable alternatives, as well as Stellite, a

cobalt-based alloy.

Supersonic Particle Deposition

A third process under consideration for application of refractory

metal coatings is Supersonic Particle Deposition (SPD) also

referred to as “Cold Spray”

because it is performed well

below the melting temperature

of the deposited materials. In the

process, a metal powder (that

can contain significant amounts

of ceramic particles) is accelerated at supersonic velocities and

propelled against a suitable substrate. The powder diameter is 1

to 45mm with velocities ranging

from 300 to 1,200 m/sec. ARL

has successfully deposited pure

tantalum with desirable microstructural characteristics (see Figure 8) and is expecting to test and evaluate such coatings via

vented combustion chamber tests at Benet Laboratories to simulate the 120mm tank gun environment. SPD generates no

thermal stresses since there is no melting and re-solidification,

and yet is still capable of forming a bond similar to explosive

Figure 7. The Bushmaster 25mm Gun

is the Primary Weapon of the 

M-2 Bradley Fighting Vehicle.

M242 Bushmaster 25mm Gun

Bradley Fighting Vehicle

Figure 8. Optical Micrograph of Ta-Deposited on 7075 

Aluminum Using SPD.
bonding due to the intimate mixing of the clad and substrate

material in what ARL has defined as “Super Plastic Agglomerate Mixing” or SPAM [13].

Ceramic Liner Research

Another approach to improving barrel life that has been

attempted repeatedly over the past 30 years is to insert alternate materials for the bore surface, typically refractory materials, or ceramics. These materials exhibit superior melting

temperatures and high temperature behavior (mechanical

property retention, erosion/corrosion resistance, and hardness) when compared to gun steels. This leads to reduced rates

of erosion and mechanical wear and makes them an obvious

choice for gun barrel liners. Unfortunately, the limitations of

these materials, and what has kept them from use in this

application, are low tensile strength, brittle fracture, low

toughness, a high degree of variability in the measured

strength, and high cost.

Currently, ARL has renewed investigations into ceramiclined gun tubes. Over the past three decades different refractory material lined gun designs have been attempted. In the

1970’s, groups from each of the services developed gun

designs using refractory liners to improve gun tube life [14-

17]. Each of the programs identified the need to compressively pre-stress the liner material to minimize tensile stresses and

overcome the material’s low tensile strength. Different problems arose, ranging from poor thermal management to the

inability to control precisely the liner pre-stress that led to

failures in the programs [18, 19]. In the late 1980’s and into

the early 1990’s, new programs were initiated that were more

focused on finding the best liner materials and designing the

system around the liner material selection [20-23]. As a result

of this approach, it was demonstrated that silicon carbide,

SiAlON, and silicon nitride all exhibited excellent erosion

resistance and were capable of surviving the stresses and temperatures experienced during firing [20]. When subjected to

erosion tests in a ballistic simulator, the erosion rate of the

different ceramic materials was reported to be on the order of

1% of that of the steel samples investigated.

In each attempt, the programs met with varying degrees of

success. Some systems successfully fired in excess of 1000

rounds without failure, while others failed due to unexpected

excursions in temperature or by what was then an unexplained material behavior. Fortunately, over the past decade,

ceramic materials, material failure modeling, and sheathing

material technologies have advanced. Improvements in the

ceramics industry have led to increased material quality,

improved strength, and decreased cost. 

Understanding the need for designing around a material

with a high degree of variability in strength has led to the

development of probabilistic modeling approaches that use

statistical analyses to calculate the probability of failure for

the ceramic liner when subjected to a specific load scenario.

These models are used to analyze experimental results and

will serve as tools for developing the optimal design for a

ceramic-lined barrel.

Figure 9 illustrates two prediction curves that account for

high and low values due to different combinations of flaw

populations and shows data for the burst pressures from eight

different experimental samples of a silicon nitride material

(SN47) falling within the predicted strength range. Figure 10

depicts a plot of the optimal design surface for a 5.56mm barrel calculated using the probabilistic models. The yellow area

indicates probable ceramic failure, green indicates failure in

the composite sheath, and blue signifies a high probability of

success and thus defines the design space. The x-axis is the

wind tension applied to the composite sheathing material to

pre-stress the ceramic and the y-axis is the ratio of the ceramic wall thickness to the total barrel wall thickness. Barrels fabricated with these designs are currently undergoing ballistic

54 The AMPTIAC Quarterly, Volume 8, Number 4

Figure 9. Experimental Results from an Internal Pressure Test of

Ceramic Tubes with High and Low Failure Prediction Curves. Figure 10. Optimal Design Surface for a 5.56mm Barrel.

100%

75%

50%

25%

0%

100

75

50

25

0 10 20 30 40 50

Internal Pressure (ksi) 0 50 100 150 200 250

Wind Tension (lbs)

Percent

Ceramic

Pf

SN47

Experimental

Probability of Failure (Pf

)
The AMPTIAC Quarterly, Volume 8, Number 4 55

testing. The combination of improved materials and probabilistic modeling, coupled with sheathing techniques that ideally generate a triaxial compressive state, has positioned

ceramic barrel technology as a viable alternative to coatings.

CONCLUSION

The combination of advanced materials and new innovative

processes are being employed to develop cannons that have

improved erosion and wear life, reduced weight, and improved

structural and thermal capabilities that allow for the use of

more energetic propellant charges. Higher performance cannons, across all calibers, continue to be a goal amongst the

Army’s armament community with the materials and processes

currently under investigation serving as the foundation for

advanced cannonry of the 21st century.

GENERAL REFERENCE

L.D. McCaskill, AMC Honors Top 10 Greatest Inventions, RDECOM Magazine, November 2003, http:// www.rdecom.

army.mil/rdemagazine/200311/images/raven.jpg

REFERENCES

[1] T.J. Rodman, Reports of Experiments on the Strength

and Other Properties of Metals for Cannon, with a Description of the Machines for Testing Metals, and of the Classification of the Cannon in Service, US Ordnance Department,

1861

[2] S. Chrispin, T.G. Baylor, and C. Comly, Description of the

Process of Manufacturing Cast-Iron Cannon Upon the Rodman

Plan, Reports of the Ordnance Board, Ordnance Department;

Appendix 9, Field, Siege, and Sea-Coast Cannon, pp. 93-104,

1880

[3] E.L. Kathe, and R. Gast, A Fire Out-of-Battery Tank Gun:

Theory and Simulation, ARCCB-TR-02007, Benet Laboratories, US Army Armament Research, Development, and Engineering Center, Picatinny Arsenal, NJ, September 2003

[4] J.K. Boyd, J.M. Wall, and T. Murchison, Precision Investigation of the 155-mm Future Direct Support Weapon System: Test

Bed 1, ARL-TR-2509, US Army Research Laboratory,

Aberdeen Proving Ground, MD, August 2001

[5] E.L. Kathe, Rarefaction Wave Gun Propulsion, Rensselaer

Polytechnic Institute, Troy NY, May 2002

[6] R. Hill, The Mathematical Theory of Plasticity, Oxford

University Press, Oxford UK, 1967

[7] A.P. Parker, Autofrettage of Open-End Tubes – Pressures,

Stresses, Strains and Code Comparisons, ASME, J. Pressure Vessel Technology, Vol. 123, No. 3, pp. 271-281, August 2001

[8] A.P. Parker, and J.H. Underwood, Influence of the

Bauschinger Effect on Residual Stress and Fatigue Lifetimes in 

Autofrettaged Thick Walled Cylinders, Fatigue and Fracture

Mechanics, Vol. 29, ASTM STP 1321, T.L. Panontin and 

S.D. Sheppard, Eds., 1998

[9] ASME Pressure Vessel and Piping Design Code, Design Using

Autofrettage, Division 3, Section 8, Article KD-5, pp. 71-73,

1997

[10] E. Troiano, A.P. Parker, J.H. Underwood, and C. Mossey,

Experimental Data, Numerical Fit and Fatigue Life Calculations

Relating to the Bauschinger Effect in High Strength Armament

Steels, ASME, J. Pressure Vessel Technology, Vol. 125, No. 3,

pp. 330-334, August 2003

[11] S.H. Carpenter, and R.H. Wittman, Explosive Welding,

Annual Review of Material Science, p. 5, 1975

[12] R.F. Lowey, Gun Tube Liner Erosion and Wear Protection,”

TPL-FR-ER 31 under contract DAAD19-99-C-0002, TPL,

Inc, Albuquerque NM, 28 May 2002

[13] V. Champagne, D. Helfritch, P. Leyman, S. Grendahl, and

B. Klotz, Formation of ‘Super Plastic Agglomerate Mixing’

(SPAM) Between Copper and 6061-T6511 Aluminum Deposited by the Supersonic Deposition Process (SPD), ASM Surface

Engineering Congress, 15-18 September 2003

[14] R.A. Harlow, and R.C. Kimball, Composite Barrel Materials Research and Development, Air Force Armament Laboratory

Technical Report AFATL-TR-72-3, Eglin Air Force Base, FL,

January 1972

[15] R.A. Harlow, B.N. Briggs, and R.C. Kimball, Development

of Full Length, Insulated Composite Barrels for Aircraft Machine

Guns, Air Force Armament Laboratory Technical Report

AFATL-TR-73-10, Eglin Air Force Base, FL, January 1973

[16] S.G. Fischman and C.B. Palmer, The Design and Fabrication of a Ceramic-Lined Gun Barrel Insert, Naval Surface

Weapons Center/Dahlgren Laboratory Technical Report TR3342, Dahlgren VA, July 1975

[17] G. D’Andrea, R.L. Cullinan, and P.J. Croteau, Refractory

Lined Composite Pressure Vessels, Technical Report ARLCB-TR78023, US Army Armament Research and Development Command, Benet Weapons Laboratory, Watervliet NY, December

1978

[18] R.A. Giles, E. Bunning, and D. Claxton, Feasibility of

Ceramic Lined Gun Tube, US Army Armament Research and

Development Command Report ARLCD-CR-80058, prepared by Maremont Corporation, Saco ME, February 1981

[19] P.M. Stephan, and A.R. Rosenfield, Survey of Ceramics in

Gun Barrels, Report AMMRC SP-82-1, Materials Technology

Laboratory, Watertown MA, 1982

[20] R.N. Katz, Ceramic Gun Barrel Liners: Retrospect and

Prospect, Proceedings of the Sagamore Workshop on Gun Barrel Wear and Erosion, sponsored by the Army Research Laboratory, Wilmington DE, July 1996

[21] Saco Defense, Inc., Advanced Materials Gun System

(AMGS) Program, Phase I, Final Report - Contract DAAA21-

88-C-0037, US Army AMCCOM, Picatinny Arsenal, NJ,

August 1989

[22] Saco Defense, Inc., Advanced Materials Gun System

(AMGS) Program, Phase II, Final Report - Contract DAAA21-

88-C-0037, US Army AMCCOM, Picatinny Arsenal, NJ,

August 1992

[23] Saco Defense, Inc., Advanced Materials Gun System

(AMGS) Program, Phase III, Final Report - Contract DAAA21-

88-C-0037, US Army AMCCOM, Picatinny Arsenal, NJ, 

February 1995
56 The AMPTIAC Quarterly, Volume 8, Number 4

Dr. Ryan Emerson is a materials engineer at the Army Research Laboratory’s Weapons and Materials Research

Directorate. He holds both a BS (1996) and a PhD (2002) in Engineering Science and Mechanics from Pennsylvania State University. Dr. Emerson came to the Army Research Laboratory in 2002 to conduct post-doctoral

research and joined the staff a year later. He is currently working on the ceramic gun barrel and the electromagnetic gun programs, specializing in polymer matrix composite materials.

Mr. Edward Troiano is presently a laboratory experimentalist with the Fatigue and Fracture Mechanics Team at

Benet Laboratories. He holds Mechanical Engineering degrees from the University of Buffalo (BS, 1984) and Rensselaer Polytechnic Institute (MS, 1992). Mr. Troiano has been involved in testing and modeling of protective coating and hydrogen embrittlement for over ten years. He is an active member in the American Society for Testing of

Material (ASTM) in both the Fracture Mechanics committee (elastic/plastic fracture mechanics) and Environmental

Fracture Committee. Mr. Troiano has over 61 government and open literature publications, and has presented much

of his work at national and international symposiums. 

Mr. Victor Champagne is the Team Leader of the Materials Analysis Group at the Army Research Laboratory’s

Weapons and Materials Research Directorate. He holds a BS in Mechanical Engineering (1984) from Central

New England College and an MBA (1986) from Anna Maria College. Mr. Champagne has served at ARL for

nearly 20 years. His current areas of research are Supersonic Particle Deposition (SPD), ElectroSpark Deposition

(ESD), and Metal Spray.

Dr. Robert Carter is a materials engineer with the Ordnance Materials Branch in the Army Research Laboratory’s

Weapons and Materials Research Directorate. He received his PhD in Materials Science and Engineering from Virginia Tech in 2001. Dr. Carter joined the Army Research Laboratory in 2002 after spending a year as a post-doctoral research associate in the ceramic gun barrel program. He is currently leading development of probabilistic

modeling approaches for the design of ceramic-lined gun barrels and developing novel multifunctional material

structures.

Mr. Michael Audino is presently the branch chief for the Protective Coatings Branch at Benet Laboratories (2000-

present). Mr. Audino leads a group of scientists and engineers in the area of advanced bore coatings for large caliber gun barrels with emphasis on PVD-based processes. Mr. Audino earned a BS in Mechanical Engineering from

Clarkson College and a MBA from the College of St. Rose. Mr. Audino has authored 22 government and open

literature publications, and has presented much of his work at national symposiums and conferences. Mr. Audino is

also the holder of one patent with a second currently pending in the US Patent Office.

Mr. Larry Burton is the Deputy Chief of the Ordnance Materials Branch at the Army Research Laboratory’s

Weapons and Materials Research Directorate. In addition, he has management oversight for the Lightweight Ordnance Work Area and Ceramic Gun Barrel Science and Technology Objective Program. He has degrees in

Mechanical Engineering from Virginia Tech (BS, 1984) and The Johns Hopkins University (MS, 1992). He has

served more than 20 years at the Army and Ballistic Research Laboratories with expertise in lightweight mortar and

howitzer systems, kinetic energy tank ammunition, advanced cannon technologies, and materials for indirect fire

munitions.
The AMPTIAC Quarterly, Volume 8, Number 4 57

INTRODUCTION

Small caliber projectiles, such as the M855 ball round, are some

of the simplest munitions in the Army inventory. The M855

projectile depicted in Figure 1 is comprised of three components: a lead slug, a steel core penetrator and a copper jacket;

and is similar to the ammunition that has been used for the last

century. This ammunition is

used in service and training

for the M16A2/A3/A4, the

M4, and the M249 weapons.

Use of small caliber munitions during training and

conflict leaves behind a significant amount of material

from the projectiles in the

environment. The US Army

has a program to investigate

alternative “green” materials, such as tungsten/nylon, to replace

the lead slug in the projectile and effectively reduce the environmental impact of these munitions. The tungsten and nylon

are particulate composites which are consolidated using cold

compaction. The basic premise of this program was to develop

a non-polluting “green” material that will match the performance of lead. This match would result in maintaining the mass

properties, stability, and flight dynamics of the M855 projectile. These changes would be transparent to the soldier, and

would therefore avoid potential costs and complications that

result from introducing a new type of ammunition into the

Army’s inventory.

This program progressed for several years from small-scale

testing to initial production. During the soldier qualification, it

was noted that a significant percentage of the rounds were creating “key-holes” as they penetrated the target. Figure 2 shows

that well-behaved projectiles penetrate the target with a circular hole on the order of the projectile diameter, but the shot

labeled as 23050 had a very high yaw angle* as it passed

through the target, thus creating an elongated hole. The implication from the target is that

the projectile was gyroscopically or dynamically unstable

as a result of the low spin rate

as it exited the weapon.

The high yaw, demonstrated in Figure 3, causes the

projectile to fly erratically

and results in the round

either missing the intended

target or not having enough

velocity to penetrate the target. Figure 3 illustrates the importance of controlling yaw. A projectile in proper flight has a uniform flow-field around it, thus ensuring accurate movement.

Conversely, a projectile in the yaw condition will experience

turbulent conditions and increased frontal area which decreases both the speed and accuracy.

In response to the soldier qualification issues, additional

investigations were conducted. While Figure 2 showed only

one unstable round, some of the follow-on testing produced a

larger number. In contrast, other testing only periodically produced high yaw rounds. It was demonstrated that the projectile high yaw rate can go from 0% to 50% depending on the

type of ammunition and weapon used. While M855 ammunition produced from lead will occasionally show similar erratic

Joseph South 

James Newill

Weapons and Materials Research Directorate

US Army Research Laboratory

Aberdeen Proving Ground, MD

Dipak Kamdar

Alliant Techsystems Inc. (ATK)

Plymouth, MN

John Middleton

US Armament Research, Development, and Engineering Center (ARDEC)

Picatinny Arsenal, NJ 

Frank Hanzl

Gregory DeRosa

Program Manager – Maneuvering Ammunition Systems (PM-MAS)

Picatinny Arsenal, NJ

Figure 1. M855 Projectile[1].

Projectile Jacket

Slug Core
58 The AMPTIAC Quarterly, Volume 8, Number 4

behavior, the percentage of these

occurrences is very low, implying that the slug material change

was responsible for the faulty

behavior.

The data from these experiments implied that by changing

the slug material the basic functioning of the system was modified. The testing in various

weapons and using different lots

of ammunition showed that even

though the failure was intermittent, the functioning of the

“green” material in the system

was fundamentally different

than lead. It should also be noted

that the weapons variability and

manufacturing likely also played

a major role. This article identifies how the green slug material

contributed to the failure, along with the approaches used to

diagnose the issue to understand this “simple” ammunition 

system. In doing so, some of the critical materials issues associated with small arms ammunition are highlighted.

Approach

A team led by the Project Manager for Maneuver Ammunition

Systems (PM-MAS) and comprised of the Joint Munitions

Command (JMC), the Armament Research, Development,

and Engineering Center (ARDEC), the Army Research Laboratory (ARL), and Alliant Techsystems (ATK) was convened to

study and resolve the problems with the green M855 projectile. A Keppner-Trago (KT) process control decision-making

analysis was used to diagnose the multi-variable problems. The

KT analysis identified and eventually proved that a low spin

rate was the cause for the rounds exhibiting a high degree of

yaw. The flight instability resulted from gaps between the jacket and slug and was exacerbated by the high yield strength of

the slug material, as compared to lead, which reduced the ability of the projectile to adapt to variability in both manufacturing and the weapons.

Figure 2. Target Showing Normal M855 Impacts and

a Key-Hole Impact[2].

Figure 3. Shadowgraph of a High Yaw Projectile (Left) and Stable Projectile

in Flight (Right)[2].

Figure 4. A Definition for Jump[3].

Figure 5. Average Jump from 60 Round Groups for Several

Types of M855 Projectiles Fired from a Single M16A2 Barrel[3].

2.0

1.5

1.0

0.5

0.0

-0.5

-1.0

-1.5

-2.0

-2.5

-3.0

-5.0 -2.5

Tungsten/Nylon Slug

Lead Slug

Horizontal (mrad)

Vertical (mrad)

Y

X

Muzzle Boreline

Range

Trajectory

Projectile

Impact

Gravity

Drop

Aim Point

Boresight Point

Boresight Line of Fire

Target

θv

θh

θv = Vertical Jump Angle

θh = Horizontal Jump Angle
The AMPTIAC Quarterly, Volume 8, Number 4 59

As a result of the KT findings, ATK led the investigation into

potential manufacturing problems, and ARL led the investigation into launch mechanics and material characterization. The

results of these investigations are covered in the remainder of

this paper.

Projectile Launch Mechanics

A simple ballistic experiment that characterizes the nature of projectile launch is to measure the projectile jump. Jump can be

measured by sighting a gun, aligning the muzzle with the aim

point on the target, firing a projectile and measuring the distance

from the hole in the target to the original aim point, Figure 4.

While jump is an indirect measure, it provides insight into the

in-bore mechanics (gun/projectile interaction) of the system.

For a given type of cartridge coupled with a particular barrel

fired under similar conditions, the jump is relatively constant.

While the round will not impact the same spot each time, this

spread, or dispersion, is a measure of precision, whereas the

average jump for a group of projectiles fired from the same barrel can be compared to infer changes in in-bore mechanics. Figure 5 shows the results of two types of M855 projectiles, tungsten/nylon, and lead, shot from the same barrel. Each point on

the graph shows the average jump obtained from sixty rounds.

It can be seen from the figure that the lead rounds jump in a

downward direction, while the tungsten/nylon rounds jumped

in an upward direction. The difference in jump is on the order

of 4 mrad.§ This is a significant deviation in the behavior that

is an order of magnitude larger than the system precision. The

dispersion of the M855 projectiles is typically less than 0.3

mrad. While this type of testing does not show how the launch

mechanics differ in the system, it does show that the mechanics changed with the slug material change.

IN-BORE PROJECTILE MECHANICS:

To obtain a better understanding of the change in mechanics, a

more detailed insight into the initial portion of launch is necessary. The first step was to perform rigid body calculations to

show the interaction of each projectile component during

launch initiation. The mass, force, and acceleration that each

projectile component would experience due to a 51 ksi peak

pressure are shown in Table 1. The parts of the projectile are

referenced in Figure 1.

While the force imparted to the jacket of the projectile is

lower (33.9% of the total force) than the force transmitted to

the slug/core, the mass of the jacket is only 30% of the total

mass. This translates into the jacket “wanting” to accelerate

faster than the slug/core; but the jacket is physically constrained in the boat tail region (tapered section at the rear) of

the projectile. The net effect is that the jacket creates a seal

against the slug which helps prevent pressure from leaking

inside the projectile.

Implicit and explicit finite element simulations were used to

study the initial portion of the projectile launch in more detail.

Figure 6 shows the transverse displacement at peak acceleration. Several key features can be seen on this figure. The first is

that the jacket in the rear portion of the projectile is clamping

down on the back of the slug, and there is a slight gap in the

front of the projectile between the jacket and the penetrator.

The gap shows that the jacket is trying to ride forward on the

back of the slug and that the penetrator is being carried by the

Table 1. Breakdown of the M855 Components and Their Forces[4].

Mass (g) % Mass of Projectile Force (N) % Force Acceleration (m/s2) Acceleration (g’s)

Bullet 4.033 – 9073.56 – 2,249,828 229,340

Slug/Core 2.823 70.0 5996.12 66.1 2,123,765 216,490

Jacket 1.210 30.0 3077.43 33.9 2,544,061 259,333

Figure 6. Transverse Displacement of the Projectile at Peak 

Acceleration[5].

Figure 7. Effect of Gaps between the Slug and Jacket[4].

Transverse Disp 10-4 inch)

-5 0 5

0.004 inch gap

No Gaps

Projectile with Gaps

Transverse 

Displacement 

(inch)

0.0005

-0.0005
60 The AMPTIAC Quarterly, Volume 8, Number 4

slug. The behavior confirms that the rear jacket/slug interface

acts as a pressure seal. This is consistent with the relative accelerations shown in Table 1 as the jacket acceleration is greater

than the slug/core acceleration thus creating the seal. Secondly,

the figure shows that the cylindrical section of the projectile

provides the projectile/bore

gas seal known as obturation†.

Both the front section and

rear section of the cylindrical

portion of the slug are

expanding in the radial direction forcing the jacket into

the bore of the gun barrel. In

addition to obturation, this

expansion provides the pressure necessary to cause the

jacket to flow around the

rifling as the projectile engages the lands‡ in the gun. It

was hypothesized that low

spin rate was due to projectile

swaging (reduction in projectile diameter instead of the

jacket material flowing

around the lands)[5].

From the theory, two causes were determined to explain

the differences between the

ammunition made from

tungsten/nylon and that

made from lead. The first

cause was that gaps between

the slug and jacket, resulting

from the manufacturing process, altered the amount of

pressure, thus forcing the

jacket into the lands of the

rifled barrel. The second cause

was that the mechanical properties of the slug also affect

the expansion pressure.

The mechanism showing

how gaps between the slug

and jacket affect the projectile in-bore mechanics can be seen

in Figure 7. The figure has a picture[6] of the cross-section of

the projectile showing a gap between the jacket and the slug.

From the results presented in the figure, it is easy to see large

differences in the displacement state when the gaps are introduced between the slug and the jacket. The location where the

jacket experienced the greatest expansion, at both ends of the

cylindrical section of the projectile, is significantly reduced.

This decreased expansion shows that the pressure available to

force the jacket to engage the rifling was sharply reduced.

Manufacturing and Gaps

To demonstrate how these gaps could have been produced

inside a projectile and how they can affect launch mechanics,

a number of experiments were devised by ATK.[7] A series of

projectiles used in these experiments were produced by a

manufacturing process which applied varying amounts of

load to consolidate the slug inside the jacket. This approach

deviated from the current bullet assembly machine (BAM)

process at Lake City Army Ammunition Plant (LCAAP) in

Missouri, which utilizes displacement control during the

consolidation process. The

projectiles were produced at

different displacement settings while generating realtime force data during consolidation. The results of this

analysis showed that there is

a critical consolidation condition (Figure 8). This condition is directly related to the

amount of load exerted on

the projectile. Projectiles

consolidated below this critical consolidation condition

had slugs that were loose and

fell out of the jacket. Loose

slugs, or slugs with incomplete consolidation, could

result in gaps. Loads above

this critical value would produce bullets with an acceptable degree of consolidation.

Ballistic tests were performed to determine the

effect of the unconsolidated

slugs on performance. Bullets

were produced using consolidation loads that varied above

and below the critical load.

The projectiles were fired, and

their performance was characterized by whether or not they

resulted in a high yaw condition. Bullets that were manufactured with loads at or

above the critical load did not

result in failure, while bullets produced below the critical load

demonstrated failure rates between 82 and 100%, as shown in

Figure 9. These test firings confirmed that projectiles produced

with gaps inside the jacket consistently exhibited high yaw during flight.

Mechanical Requirements for a Slug Material

A confounding issue to the gap is related to the mechanical

properties of the slug materials. Lead slugs have been used in

the current M855 manufacturing process for over two

decades and have shown tolerance to the displacement controlled consolidation process. Introducing a new material

with different mechanical properties affects the projectile’s

tolerance to both the consolidation process and the related

problem of in-bore mechanics.

Figure 8. Results of the Manufacturing Consolidation Study for

Projectiles Made with Tungsten/Nylon Slugs[8].

Figure 9. Effect of Slug Consolidation Force on Bullet 

Performance[8].

Station 4 Slug Consolidation

Slug falls out of jacket

0.15 0.20 0.25 0.30 0.35 0.40

Gap between Top Platen and Nut at Station 4, inch

Slug Consolidation Force, lb

Minimum

Average

Maximum

2000.0

1800.0

1600.0

1400.0

1200.0

1000.0

800.0

600.0

400.0

200.0

0.0

0 200 400 600 800 1000 1200

Minimum Slug Consolidation Force, lbs

Correlation of Slug Consolidation Force with Ballistic Performance

Cliff

Un-Acceptable Bullet Acceptable Bullet

High Yaw Failure Rate (%)

120

100

80

60

40

20

0
The AMPTIAC Quarterly, Volume 8, Number 4 61

Shown in Figure 10 is an approximate propellant pressuretime history for the initial portion of the launch cycle. Plotted

on the graph are the points where the propellant pressure

matches the yield strength for lead and also for tungsten/nylon.

What is inferred from the graph is that as the yield strength of

the material increases, the amount of time within the launch

cycle necessary to reach the yield point also increases. The yield

strength marks the beginning of where the material becomes

incompressible. An incompressible material does not change

volume when it is loaded. This is a driving attribute since it represents the maximum value of gas propellant pressure that can

cause transverse displacement (same as radial displacement for

cylindrical geometries) of the slug material, which was illustrated in Figure 7.

In order to determine the effectiveness of alternative materials for bullet components, the mechanical response of the materials must be determined. One of the critical attributes underpinning both understanding of material behavior and modeling

is the selection of material properties. Due to the size

of the slug materials, which has a diameter of 0.18

inches, testing techniques need to be modified and

developed in order to obtain good material properties.

Figure 11 illustrates how small the slugs are by comparing them to other small items.

A characterization study was conducted to determine the compressive stress – strain response of both

the slug material and the sheathed slugs from manufactured bullets. Samples were strain-gauged with

parallel and perpendicular gage orientations. Two

axial gages were used at 180° positions to correct for

any slight bending of the samples. Polymer-based

samples required a plasma treatment in order to

obtain adequate adhesion of the gage to the sample.

To minimize damage, special grips were fabricated to

hold the polymer-based samples during mounting of

the strain gages. Results of the compressive testing are

shown in Table 2 and plotted in Figure 12. The difference in the material response between the lead and the

tungsten/nylon specimen is quite evident, particularly the

yield point of the materials. The inset figures show the difference in the failure mechanisms between the two material systems. The lead specimen exhibits a ductile failure while the

tungsten/nylon exhibits a brittle failure. Figure 12 shows the

importance of materials to the performance of bullets. Both

materials have approximately the same density and yield but

their compressive behavior and ultimate failure are completely different.

Another way of looking at this argument is to examine the

behavior of a section of the slug/jacket material. A test was

Figure 10. M855 Base Pressure Compared to the Yield Strength of the Slug

Materials[9].

Figure 11. Size of Core Testing Samples[10].

Table 2. Averaged Compressive Mechanical Properties 

of Slug Materials[9].

Modulus (Msi) Compressive Yield (Ksi)

Tungsten/Nylon 1.2 – 1.4 9.7 – 10.2

Lead 1.5 – 2.0 ~2.5

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2 0.22 0.24 0.26 0.28 0.3

Time (ms)

Base Pressure (Mpa)

200

180

160

140

120

100

80

60

40

20

0

Projectile Base Pressure

0.095 ms

0.1625 ms

Yield Strength of W/nylon

Yield Strength of Lead

Figure 12. Stress-Strain Behavior of Lead vs. Tungsten/Nylon. 

The Inset Shows the Difference in the Failure Behavior between 

the Two Materials[12].

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14

Strain

Compressive Stress (MPa)

120

100

80

60

40

20

0

Pb

W/Nylon

W/Nylon Data Lead Data
62 The AMPTIAC Quarterly, Volume 8, Number 4

developed to look at the unconstrained loading behavior of

small sections of the projectile[11]. This is a non-conventional test method that was developed in order to evaluate the

potential performance of the slug material on the inside of a

bullet. Prior to testing, the boat tail and the tip of the bullet

forward of the cannelure** were removed. The bullets were

then ground to a final height of 0.375 inches. Strain gages

were mounted in the axial and hoop directions. Only the slug

material was loaded in compression, and the jacket was left as

a free surface. Typical results from the sheathed compression

tests are shown in Figure 13. The effect of yield strength on the

performance of the slug material was quite evident, with tungsten/nylon exhibiting much higher loads during the test. For

small strains, approaching those seen in a weapon system, the

lead exhibited ten times more hoop strain than the

tungsten/nylon slug samples. This difference is directly attributable to the yield strength of the material and the point the

material achieves incompressibility. This testing arrangement

can also further evaluate the effects of a gap between the slug

and the jacket as the system would respond with a rapid

increase in load without an increase in strain.

CONCLUSIONS

The M855 three-piece projectile represents a very basic design.

A simple modification, a material replacement, was perceived as

a benign change but resulted in erratic occurrences of high yaw

rounds when fired. Through careful study, simulation, and

experiments it was shown that the change in performance resulted from the manufacturing process and the basic mechanics of

the materials. Once these issues are addressed and the problems

corrected, the new “green” ammunition will become a suitable

replacement for lead-based ammunition. The example illustrated in this article demonstrated that a thorough understanding of

the interaction of the components within a system is required

prior to implementing material substitutions.

NOTES & REFERENCES

* Yaw angle is the angle between the longitudinal axis and the

direction of travel.

§ A milliradian (mrad) is 1/1000th of a radian.

† Obturation is the sealing of the gun barrel to prevent the propellant gases from escaping.

‡ Lands are the ridges inside a rifled gun barrel.

** The cannelure is the ring around the body of the projectile

where the case is crimped.

[1] M855 Technical Drawing Package, Armament Research,

Development and Engineering Center Picatinny Arsenal, NJ

[2] J.F. Newill and B. Guidos, Aerodynamic Range Experiments

for M855 Green Ammunition, presented to PM Maneuvering

Ammunition Systems, 12 November 2003, Lake City Army

Ammunition Plant, MO

[3] J.F. Newill, P. Weinacht, R. Pearson, P. Hill, W. Oberle, Trajectory Match, Jump, and Error Budgets for M855 presented to

PM Maneuvering Ammunition Systems, 14 September 2004,

Lake City Army Ammunition Plant, MO.

[4] J.F. Newill and J. South, M855 In-bore Projectile Mechanics

presented to PM Maneuvering Ammunition Systems, 29 January 2004, Aberdeen Proving Ground, MD.

[5] Personal communication, Lee Magness (ARL)

[6] Tim McFarland and Todd Botcher ATK

[7] Dipak Kamdar, D. Mansfield, and J. Westbrook

[8] F. Hanzl, G. DeRosa, M. Newman, J. Middleton, R. Contaldi, D. Kamdar, K. Enlow, M855 Material Replacement presented to PM Maneuvering Ammunition Systems, 26 May

2004, Lake City Army Ammunition Plant, MO

[9] J.F. Newill, Comments on Material Testing presented to PM

Maneuvering Ammunition Systems, 9 March 2004, Lake City

Army Ammunition Plant, MO

[10] T. Weerasooriya and P. Moy, Green Bullets Core Material

Properties presented to PM Maneuvering Ammunition Systems, 9 March 2004, Lake City Army Ammunition Plant, MO

[11] M. Staker and P. Moy of ARL

[12] J. South and J.F. Newill, Finite Element Modeling of Experimental Testing presented to PM Maneuvering Ammunition

Systems, 9 March 2004, Lake City Army Ammunition Plant,

MO

Figure 13. Results of the Sheathed Compression Testing. The Inset

Picture Shows the Testing Arrangement[12].

0 5000 10000 15000 20000 25000

Hoop Strain (Microstrain)

Load (lbs)

100

0

900

800

700

600

500

400

300

200

100

0

■ W/Nylon ◆ Pb
The AMPTIAC Quarterly, Volume 8, Number 4 63

Mr. Frank Hanzl is currently assigned as the Small Caliber Engineering Team Lead for the Project Manager -

Maneuver Ammunition Systems. He earned his BS in Mechanical Engineering from Manhattan College, and his

MS in Management from Florida Institute of Technology. In addition, he is Level III certified in test and evaluation;

systems planning, research, development and engineering; manufacturing, production and quality assurance.

Mr. Gregory DeRosa is the Project Officer in the Small and Medium Caliber Product Office for the Project 

Manager – Maneuver Ammunition Systems. He earned his BS in mechanical engineering from New York Institute

of Technology and his MS in Management from Florida Institute of Technology. In addition, he is Level III-certified

in test and evaluation; systems planning, research, development and engineering; manufacturing, production and

quality assurance.

Mr. John Middleton is the Team Lead for the Small Caliber Ammunition Production Team in the Mounted/Dismounted Infantry Munitions Division of RDECOM-ARDEC. He has been involved in small caliber ammunition since

1985. Mr. Middleton earned his BS in Mechanical Engineering from Clarkson University in 1981, and his MS in

Mechanical Engineering from Stevens Institute of Technology in 1991. In addition, he is Level III certified in Systems

Planning, Research, Development and Engineering and is a member of the Acquisition Corps.

Dr. Dipak Kamdar is a Senior Engineering Fellow at ATK Ordnance Systems. His area of expertise is in large caliber

ammunition design. His recent work has contributed to a highly successful M829A3 kinetic energy tank round. His

patented composite architecture and sabot design has resulted in the lowest parasitic mass ratio among all the tank

rounds. Besides projectile design, his work on the spring disc (that holds the cartridge case to the case base) has

resulted in large caliber ammunition that, for the first time in army history, has fulfilled army cartridge chamber and

extraction requirements. He has also been involved in modeling and optimizing the manufacturing process. His work

on a 5.56 mm ‘Green Ammo’ manufacturing process has contributed to a successful non-lead small caliber round.

Dr. James F. Newill currently serves as the small caliber coordinator for the Weapons and Materials Directorate at

the Army Research Laboratory and where he’s also the Deputy Chief of the Aerodynamics Branch. He has worked

at ARL since 1995 on munitions research for a variety of systems; including tank munitions, electromagnetic rail 

guns, and medium and small-caliber munitions. He has authored over 50 publications on dynamics simulation of

projectile gun interaction, accuracy of army systems, and other munitions related issues. He received his PhD in

Mechanical Engineering from the University of Delaware in 1996.

Dr. Joseph South is a materials engineer with the Ordnance Materials Branch in the Weapons and Materials

Research Directorate of the US Army Research Laboratory. He received his PhD in Materials Engineering Science

from Virginia Tech in 2002. He officially joined ARL after working there as a post-doctoral research associate 

for one year. His research has focused on the computation mechanics evaluation of small caliber ammunition. 

He currently manages the lightweight cartridge case technology work unit, centered on lightening small caliber 

cartridge cases.

Photo

Not

Available

Photo

Not

Available

Photo

Not

Available
64 The AMPTIAC Quarterly, Volume 8, Number 4

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This product was prepared in collaboration with Drexel University and

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Applications of Structural Materials 

to Protection from Explosions

This state-of-the-art review provides an examination of existing technologies for protecting structures from explosions. The report does not

discuss materials and properties on an absolute scale; rather, it addresses

the functionality of structural materials in the protection against blast.

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mitigation. For example, the section on military structures describes concrete in arches, and concrete in roof beams for hardened shelters. The discussion on concrete is not limited to materials only; rather, it addresses

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And you thought we only printed this magazine!

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The AMPTIAC Quarterly, Volume 8, Number 4 65

INTRODUCTION

Amorphous materials are an integral part of many of the current

weapons platforms for the US Army, and have considerable potential for

contribution to the Army’s Future Force applications. The Army is

engaged in efforts to further develop these materials and utilize the

many benefits they offer. In general, amorphous solids consist of thermoset plastics, transparent polymers, elastomers, oxide glasses, and

metallic glasses. This issue of MaterialEASE will explain at a basic level

what amorphous materials are, how they relate to crystalline materials,

some of their important properties and attributes, and give examples of

how they are used in Army systems.

What is an Amorphous Material?

Amorphous – from the Greek for “without form” – refers not to materials that have no shape, but rather to materials with no particular

structure. The atoms or molecules of amorphous materials are

arranged in essentially the same manner as they are in a liquid. An

amorphous material is still solid – the molecules are closely packed

and chemically bonded, and the material exhibits an elastic response 

to shear stresses – but the spatial arrangement of the atoms is nearly

random. In contrast, the building blocks of crystalline solids are

arranged in orderly, 3-dimensional, periodic arrays. Figure 1 illustrates

the difference between a crystalline material

and an amorphous solid. A crystalline material

is analogous to a formation of troops on parade,

while an amorphous material is more like a

crowd or mob. Just as formations and crowds

are both groupings of people, amorphous and

crystalline materials are both groupings of

atoms. In both cases, the manner in which the

components are arranged influences how the

assemblage behaves.

Also known as noncrystalline solids, glasses, or disordered solids, amorphous materials

are characterized by their structure rather

than their composition. This is because, under

the right conditions, any material can be prepared as an amorphous solid. All amorphous

materials have crystalline counterparts. An

important aspect of this is that of the two structures, the crystalline

form will generally be more stable. This is because the crystalline

solid is at chemical equilibrium, whereas the amorphous form is not.

Preparing an amorphous solid requires rapid cooling to avoid crystallization. The cooling rate that constitutes rapid cooling varies

with the type of material.

The structures of materials affect their properties, and the properties of amorphous materials are no exception. Metallic glasses exhibit

mechanical properties outside the range observed in other materials,

combining high strength with a high elastic limit, as shown in Figure

2. This leads to elastic recoil not seen in other materials. A dramatic

demonstration of this is how long a steel ball bearing will bounce

when dropped onto a plate of metallic glass [1]. A more familiar property inherent in amorphous solids is optical transparency, as exemplified by such materials as plate glass, acrylic (polymethylmethacrylate), and Lexan® (polycarbonate). However, atomic arrangement is

not the sole determinant of properties. For example, metallic glasses

are optically opaque.

Amorphous vs. Crystalline Structure

The telltale sign of an amorphous solid is its diffraction pattern.

Whether x-rays, neutrons, or electrons, radiation which is short enough

Material EASE

AMORPHOUS MATERIALS:

A Tutorial on Noncrystalline Solids

Robert Woodman

Weapons and Materials Research Directorate

US Army Research Laboratory

Aberdeen Proving Ground, MD

28AMPTIAC

Figure 1. Schematic Illustration of the Structures of Crystals and Glasses.

Crystal Glass
in wavelength to pass between atoms will interact with the atomic

structure in the same way that visible light interacts with a diffraction

grating. Regions of constructive and destructive interference develop,

and a pattern emerges. The location and intensity of peaks in the diffraction pattern is determined by the location and arrangement of

atoms. For a crystalline solid, a diffraction pattern is analogous to a

fingerprint, and can be used to identify the material.

The diffraction pattern is a direct consequence of the ordered

nature of the structure of crystalline solids. Amorphous solids have no

such order, and as a consequence, their diffraction pattern is diffuse as

displayed in Figure 3. Consequently, the pattern can only be used to

determine that a material is amorphous, but not to determine its chemical composition. For comparison, the diffraction pattern from a liquid

is similar.

The Glass Transition

While amorphous materials are solid, they are often described as highviscosity or supercooled liquids. Amorphous materials are also characterized by the absence of a pronounced discontinuity in their properties

when the liquid solidifies and becomes a glass. This is in contrast to

crystalline materials, which experience a distinct transition from liquid

to solid as the temperature decreases to below the melt temperature

(Tm), as shown in Figure 4. The physical process by which a liquid

solidifies to form an amorphous solid involves more gradual changes

than the crystalline solid, and is known as the glass transition. During

the glass transition, there is a detectable change in the slope of properties, such as density, with temperature. The glass-transition temperature, Tg, occurs over a range of temperatures, and is often defined as

the mid-point of this range.

Unlike well-defined transformation temperatures in crystalline

solids, such as freezing points or boiling points, Tg is not uniquely

defined, but varies with cooling rate. Typically, the slower the cooling

rate, the lower the temperature at which the glass transition occurs

(Figure 5).

AMORPHOUS MATERIALS – 

EXAMPLES AND PREPARATION TECHNIQUES

Theoretically, any material can be formed into an amorphous solid as

long as the cooling rate is sufficient to prevent crystallization. However,

some materials more readily form amorphous solids compared to others. Furthermore, there are often limitations on the size of the amorphous solid that can be formed by current techniques.

66 The AMPTIAC Quarterly, Volume 8, Number 4

Material EASE

Figure 2. Strength vs. Elastic Limit for Several Classes of 

Materials – Metallic Glasses Offer a Unique Combination of

High Strength and High Elastic Limit [2].

Figure 3. Characteristic Diffraction Patterns from Crystalline

Material (Top) and Amorphous Material (Bottom). [3]

Figure 4. Liquid-Crystalline Solid Transition (Left) and LiquidGlass Transition (Right).

Glassy Alloys

Strength (MPa) Intensity

01 2 3

Elastic Limit (%)

0 0.04 0.08 0.12 0.16 0.20 0.24 0.28

sinθ ____ → λ

2500

2000

1500

1000

500

0

Titanium

Alloys

Polymers

Steels

Woods

Silica

Liquid

Specific Volume

Crystal

Tm

Temperature

Crystal Transition

Liquid

Specific Volume

Glass

Tg

Temperature

Amorphous Transition
The AMPTIAC Quarterly, Volume 8, Number 4 67

Amorphous Ceramics

Ceramic glasses are the oldest known and, not surprisingly, the easiest

to prepare [4]. Alkali silicates, in particular, form glasses so readily that

preparation of glass objects from alkali silicate melts came to be known

as the glass industry. Ceramic glass production is a mature industry; a

thorough discussion of the processes is beyond the scope of this article.

The reader is referred to various reviews and textbooks, such as ASM

handbooks [5].

Amorphous Polymers

Due to the size and configuration of the large, chain-like molecules of

which they are made, most commercial polymers are amorphous materials. However, nearly all polymers have some degree of crystallinity.

While the molecules of polymers are much larger than those in ceramics or metals, the essential features of amorphous structure

and the glass transition are the same. Preparing an amorphous polymer is largely a matter of cooling a molten polymer blend through its glass transition. As with most oxide

glasses, special equipment and techniques for cooling are not

typically required.

Metallic Glasses

Metallic glasses are a greater challenge to make than oxide or

polymeric glasses, and are the most recent development. In

fact, for years it was argued that metallic glasses would be

impossible to make for a couple of reasons. First, the crystal

structures of metals are simple, and have a strong tendency to

form (crystallize) near the solidification point. Secondly, molten metal

near the solidification point has a low viscosity, facilitating rapid

atomic rearrangement. Over the course of the middle decades of the

20th century, as more metallic glasses were prepared, it became evident that all solids have the potential to be prepared as glasses.

As mentioned earlier, the challenge to preparing metallic glass is to

cool it at a sufficiently rapid rate. This rate for many metals can be as

high as 106 °C/s. Unfortunately for the prospects of engineering with

metallic glasses, the maximum rate at which an object can be cooled is

limited by the thermal conductivity and heat capacity of the material.

This, in turn, limits the maximum thickness of the material that can

be prepared with an amorphous structure. The higher the critical cooling rate of the materials, the smaller the maximum thickness. So, while

there are techniques for achieving rapid cooling – such as melt spinning and splat quenching – the amorphous product is often quite thin.

Some metallic glasses can be prepared only in sheets or ribbons a few

microns thick.

During the 1990’s, several alloys were developed that had critical

cooling rates in the range of 1-100 °C/s, with corresponding critical

dimensions in the range of 1-100 mm [6]. Most of these alloys have

chemical compositions with at least five components, and achieve their

glass-forming properties from what has come to be called the “confusion principle.” If the atoms in the melt must rearrange themselves

into three or more coexisting crystal structures on cooling, then the

probability of cooling them rapidly enough that the rearrangement

becomes impossible is increased. The atoms can be said to be “confused” about where to go and, like the last person to sit down in a game

of musical chairs, unable to find a place in the ordered structure. Arbitrarily taking 1 mm to be sufficiently thick to be considered “bulk”, the

new class of alloys came to be called bulk metallic glasses (BMGs). It is

important to note that many of the BMG-forming alloys still require

cooling rates considerably higher than those required to make oxide or

polymeric glasses. Even the best bulk metallic glasses cannot be made

with a critical dimension greater than 100 mm. Despite the vast

improvement in metallic glasses that BMGs represent, the materials

remain largely developmental.

A DVANCED M A TERIALS AND P ROCESSES T ECHNOLOGY AMPTIAC

Figure 6. Anatomy of an M829 Tank Round.

Figure 5. Schematic Representation of the Glass Transition.

Note that the Glass-Transition Temperature (Tg) Shifts to a

Lower Temperature with Slower Cooling (T’g).

Specific Volume

Temperature

Slow Cool

Fast Cool

T’g Tg

Primer

Propellant

Combustible

Case

Case

Adapter

Composite

Sabot

Subcaliber

Projectile
68 The AMPTIAC Quarterly, Volume 8, Number 4

APPLICATIONS

Amorphous materials have contributed substantially to the success of

military technologies, and there is potential for further contributions.

Substitution of an amorphous thermoplastic polymer matrix for a 

thermosetting polymer in a composite drastically reduced the cost of

the sabots used in the M829A3 tank round. Tempered glass backed by

amorphous polycarbonate has long served as transparent armor. 

Careful engineering of the degree of crystallinity of polyurethane makes

possible lighter, more effective transparent armor. Metallic glass may 

be the key to achieving the lethality of a depleted-uranium kineticenergy penetrator using a nonradioactive material.

Transparent Armor

Amorphous polymers are transparent and tough, making them effective

against ballistic threats such as fragments and pistol rounds. The most

commonly used transparent armor polymers are polymethylmethacrylate and polycarbonate. Polyurethanes belong to a class of polymers

known as block copolymers. Blocks of hard and soft urethanes can be

mixed to engineer optimum transparency, hardness, and toughness.

Urethanes offer the opportunity for weight savings compared to polycarbonate, but have not been widely adopted because of their high

cost.[7] When combined with a high-hardness strike-face plate like

tempered glass, polycarbonate is effective against heavier ballistic

threats, such as assault-rifle rounds.

Sabot Materials

A sabot is a composite structure used to hold a projectile (penetrator) in

place (as part of a round) while in the barrel of a gun (Figure 6).

Sabots also help to accelerate the projectile upon combustion of the

propellant when the gun is fired. The sabot then falls away, leaving the

projectile to fly in a ballistic trajectory (Figure 7).

Sabots are used in the US Army’s M1 tank, where they support the 

use of dart-like depleted uranium

penetrators. In this application,

sabots are fabricated from composite materials. Composite

materials are made by reinforcing either thermoplastic or thermoset polymers with fibers.

Because thermoplastics soften

at higher temperatures, they are

readily prepared for mechanical

forming operations in a manufacturing setting. In contrast, thermosetting polymers such as epoxies form cross-linking bonds that create a

rigid 3-D network when heated. The M829A2 kinetic-energy cartridge

featured a sabot formed from graphite-reinforced epoxy. Use of the

epoxy in a manufacturing setting required the use of freezers for epoxy

storage and careful control of the time that the epoxy spends in processing. Substitution of an amorphous thermoplastic-based composite

reduced the manufacturing costs, and is now implemented in the

M829A3. The reduced costs were a result of increased shelf-life since the

properties of thermoplastics don’t degrade over time like they do with

thermosetting polymers. Furthermore, less processing infrastructure

(e.g. freezers, autoclave) is required to produce thermoplastic-based

composites, which also led to a reduced manufacturing cost.

Kinetic-Energy Penetrators

Depleted uranium penetrators derive their superior penetration performance from an unusual erosion-and-wear mechanism that leads to

self-sharpening during penetration. Due to their structure, bulk metallic glasses exhibit a similar mechanism during fracture. In order to

match the penetration performance of uranium, a replacement material will have to be comparable to uranium in density (18.95 g/cm3).

Penetrator development is directly affected by the criticalcooling-rate issue mentioned earlier. One of the best BMGs,

Zr41.2Ti13.8Cu12.5Ni10.0Be22.5, has a critical cooling rate of ~1 K/s,

and can be readily made into objects with critical dimensions as

large as 12.6 mm.[8] Unfortunately, the beryllium content of the

alloy makes it too hazardous to replace uranium. While alloys of

similar composition have been developed, none has exhibited a critical dimension greater than 10 mm. Most importantly, a BMG 

composite penetrator which can be made to quarter scale or medium

caliber cannot necessarily be scaled up to a full-scale, tank maingun round in a straightforward way. Alternate alloys or fabrication

techniques must be developed for the potential of BMGs to be realized

in kinetic-energy penetration applications.

SUMMARY

Amorphous materials – whether metals, ceramics, or polymers – are

characterized by a liquid-like structure. This structure is readily evident

from a comparison of the diffraction pattern of an amorphous material to that of a liquid. However, amorphous materials are solid. They

enter the solid state when a cooling liquid undergoes a change in its

physical properties known as the glass transition.

Any material can be prepared as an amorphous solid if it is cooled

quickly enough. For metals, the speeds of cooling limit the size of

metallic glasses, even for the newly developed bulk metallic glasses.

Many ceramics and many polymer blends are more easily prepared as

glasses; some are ubiquitous and familiar.

The structure of amorphous materials leads to distinctive properMaterial EASE

Figure 7. A Sabot Falling Away

from a Projectile 

After Firing.
The AMPTIAC Quarterly, Volume 8, Number 4 69

ties, such as transparency, plasticity, and elastic recoil. Their properties

make amorphous materials useful to the Army’s mission, particularly

as transparent armor and in munitions manufacture. The Army 

continues to pursue the development of amorphous materials with

desirable properties.

GENERAL REFERENCES

C. Kittel, Introduction to Solid State Physics, 6th ed., John Wiley &

Sons, New York, 1986, p. 495

R. Zallen, The Physics of Amorphous Solids, John Wiley & Sons, New

York, 1983

X. H. Lin, and W. L. Johnson, Formation of Ti-Zr-Cu-Ni Bulk Metallic

Glasses, J. Appl. Phys. 78 (11), 1995, p. 6514

REFERENCES

[1] Liquidmetal® vs. Titanium – Pure Energy TransferTM Demo,

Liquidmetal Technologies, http://www.liquidmetal.com/news/dsp.multi

media.asp

[2] M. Telford, The Case for Bulk Metallic Glass, Materials Today, 

March 2004, pp. 36-43

[3] W.D. Kingery, H.K. Bowen, and D.R. Uhlmann, Introduction to

Ceramics, 2nd. ed., John Wiley & Sons, New York, 1976, p. 96

[4] A. Macfarlane and G. Martin, A World of Glass, Science, 305, 

September 2, 2004, p. 1407

[5] W.R. Prindle, P.S. Danielson, and J.W. Malmendier, Glass Processing,

ASM International Engineered Materials Handbook Vol. 4, Ceramics and

Glasses, ASM International, Materials Park OH, 1991, p. 377

[6] W.L. Johnson, Bulk Glass-Forming Metallic Alloys: Science and

Technology, MRS Bulletin, 24 (10):42-56, 1999

[7] P.J. Patel, G.A. Gilde, P.G. Dehmer, and J.W. McCauley, Transparent Armor, The AMPTIAC Newsletter, IIT Research Institute/

AMPTIAC, Rome NY, Fall 2000, p. 1

[8] W.L. Johnson and A. Peker, Applied Physics Letters, Vol. 63, No.

17, pp. 2342-2344, 1993

A DVANCED M A TERIALS AND P ROCESSES T ECHNOLOGY AMPTIAC

Dr. Robert Woodman is an American Society for Engineering Education Postdoctoral Fellow with the Army Research

Laboratory. He received a PhD in Ceramic Science & Engineering from Rutgers, the State University of New Jersey,

in 1996. He earned his BS and MS degrees in Materials Engineering from Virginia Tech. He has been studying

bulk metallic glasses for the last 3 years.

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70 The AMPTIAC Quarterly, Volume 8, Number 4

2005 MRS Spring Meeting

03/28/05 – 04/01/05

San Francisco, CA

Contact: Materials Research Society

506 Keystone Dr

Warrendale, PA 15086-7573

Phone: 724.779.3003

Fax: 724.779.8313

Email: info@mrs.org

Web Link: www.mrs.org

WESTEC APEX

04/04/05 - 04/07/05

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Contact: Society of Manufacturing 

Engineers

One SME Dr, PO Box 930

Dearborn, MI 48121-0930

Phone: 800.733.3976

Fax: 313.425.3407

Email: service@sme.org

Web Link: www.sme.org

107th Annual Meeting & Exposition 

of The American Ceramic Society

4/10/05 – 4/13/05

Contact: American Ceramic Society

PO Box 6136

Westerville, OH 43086-6136

Phone: 614.794.5890

Fax: 614.899.6109

Email: customersrvc@acers.org

Web Link: www.acers.org 

3rd Missile Defense Conference 

& Exhibit

04/11/05 - 04/15/05

Washington, DC

Contact: Customer Service

American Institute of Aeronautics 

& Astronautics

1801 Alexander Bell Dr

Reston, VA 20191

Phone: 703.264.7500

Fax: 703.264.7657

Web Link: www.aiaa.org

46th AIAA/ASME/ASCE/AHS/ASC 

Structure, Structural Dynamics,

& Materials Conference

04/18/05 - 04/21/05

Houston, TX

Contact: Customer Service

American Institute of Aeronautics 

& Astronautics

1801 Alexander Bell Dr

Reston, VA 20191-4344 

Phone: 703.264.7500

Fax: 703.264.7657

Web Link: www.aiaa.org

2005 Meeting the MSS Specialty Group

on Infrared Countermeasures

04/25/05 - 04/28/05

Eglin AFB, FL

Contact: Veridian Systems Division, Inc

PO Box 134008

Ann Arbor, MI 48113-4008 

Phone: 734.994.1200 x2821

Fax: 734.994.5550

Email: mss@gd-ais.com

Web Link: www.iriacenter.org

2005 Sagamore Conference 

on Transparent Materials

05/09/05 - 05/11/05

St. Michaels, MD

Contact: Dr. James Sands

US Army/ARL

Phone: 410.306.0878

Fax: 410.306.0806

Email: jsands@arl.army.mil

EASTEC APEX

05/24/05 - 05/26/05

West Springfield, MA

Contact: Society of Manufacturing Engineers

One SME Dr, PO Box 930

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Phone: 800.733.3976

Fax: 313.425.3407

Web Link: www.sme.org

International Conference on 

Solid-Solid Phase Transformations 

in Inorganic Materials 2005

05/29/05 - 06/03/05

Phoenix, AZ

Contact: TMS Customer Service

184 Thorn Hill Rd

Warrendale, PA 15086-7514

Phone: 724.776.9000

Fax: 724.776.3770

Web Link: www.tms.org

16th Aeromat Conference & Exposition

06/06/05 - 06/09/05

Orlando, FL

Contact: ASM International

9639 Kinsman Rd

Materials Park, OH 44073 

Phone: 800.336.5152 ext 6

Fax: 440.338.4634

Email: CustomerService@asminternational.org

Web Link: www.asminternational.org/aeromat

International Committee on 

Aeronautical Fatigue

06/06/05 - 06/10/05

Contact: Klaus Schubert; ICAF 2005

Bonn D-53175 Germany 

Phone: (+49) 228-30805-18

Fax: (+49) 228-30805-24

Email: klaus.schubert@dglr.de; 

Web Link: www.www.icaf2005.org

2005 Army Materials Summit 

6/19/05 – 6/22/05 

Gettysburg, PA 

Contact: Dr. Bruce Fink 

Phone: 410.306.0755 

Email: bfink@arl.army.mil 

2005 National Space & Missile 

Materials Symposium

06/27/05 - 07/01/05

Summerlin, NV

Contact: M. Kubal; Anteon Corporation

5100 Springfield St, Ste 509

Dayton, OH 45431 

Phone: 937.254.7950 ext 1168

Fax: 937.253.2296

Email: mkubal@anteon.com

Web Link: www.usasymposium.com

2005 Advanced Gun Barrel Materials

and Manufacturing Symposium

07/12/05 - 07/14/05

St. Michael, MD

Contact: Dr. William de Rosset, USMA

United States Military Academy

West Point, NY 10996

Email: aw2604@usma.edu

Web Link: www.dean/usma.edu/departments/

math/ARL-BENETGUNSYMPOSIUM/

Materials Science & Technology 2005

9/25/05 – 9/28/05

Pittsburgh, PA

Contact: TMS Meeting Services

184 Thorn Hill Rd

Warrendale, PA 15086 

Phone: 724.776.9000 ext 243

Fax: 724.776.3770

Email: mtgserv@tms.org

Web Link: http://doc.tms.org

International Symposium 

on Superalloys 718, 625, 706 

and Derivatives

10/02/05 – 10/05/05

Pittsburgh, PA

Contact: TMS Meetings Services

184 Thorn Hill Rd

Warrendale, PA 15086

Phone: 724.776.9000 

Fax: 724.776.3770

Email: mtgserv@tms.org

Web Link: http://doc.tms.org

FABTECH International Forming 

& Fabricating - Stamping - 

Tube & Pipe - Welding

11/13/05 - 11/16/05

Chicago, IL

Contact: Society of Manufacturing Engineers

One SME Dr, PO Box 930

Dearborn, MI 48121-0930

Phone: 800.733.3976

Fax: 313.425.3407

Web Link: www.sme.org

Mark Your Calendar Army-specific events are highlighted in green
The AMPTIAC Quarterly, Volume 8, Number 4 71

INTRODUCTION

All materials used in large caliber projectiles share a common

feature; their design and use requires knowledge of their deformation behavior up to and beyond failure at high strain and

heating rates. Crucial to the development of these materials is

the ability to describe the life of the material from its synthesis

and process development to a complete description of the terminal ballistic performance, platform structural response, and

ultimate structural failure under dynamic loading. Materials for

this application include those used in kinetic energy penetrators, sabots, fins, cartridges (Figure 1), and liner materials for

shaped charge and explosively

formed projectile warheads.

One will find that a complete

spectrum of materials is used

for these components, including metals, ceramics, polymers and composites. 

Materials under current

development for large caliber

projectiles come from unique

sub-classes of conventional

disciplines. These include

nanocrystalline metals, bulk amorphous metallic glasses, 

polymer matrix composites, and metal matrix composites.

Also, beyond just materials selection is the consequent need 

to develop the processing of these materials so as to maximize

the desired mechanical and physical properties, and thus optimize munition lethality. These materials technologies have

been vital to past battlefield successes and will be essential to

future victories.

KINETIC ENERGY PENETRATORS

The standard high performance material used for kinetic energy penetrators (KEPs) is a depleted uranium (DU) alloy. Its

performance is attributed to its high strength and density (18.6

g/cm3) and a localized flow softening behavior, more commonly referred to as adiabatic shear. This allows the DU penetrator,

upon impact, to maintain a ‘conical-nose’ shape favorable for

enhanced penetration. A longstanding goal of current research

has been to replicate this deformation and flow behavior in

non-DU materials. More recent processing technologies with

nanocrystalline tungsten (W) and bulk metallic glasses (BMGs)

have shown promise in reaching the desired performance levels

of DU alloy penetrators.

Defeating armor requires that the maximum kinetic energy

be delivered to a given area of armor, for the longest time duration, and at a velocity as high as possible. Geometrically, execution is via a long thin (high

length-to-diameter, L/D

ratio) high-density, highstrength rod striking the

smallest armor area. The

early use of uranium alloy

penetrators was based on

this understanding but not

on the knowledge that

additional performance is

achieved by controlling the

deformation and fracture

modes of the penetrating rod. A high L/D ratio extends the

time of penetrator-target interaction, but high strength alloys

also extend the time of interaction by allowing more deformation and fracture of the target relative to the erosion loss of a

higher strength penetrating rod. If the deformation and failure

mode of the long rod is adiabatic shear (as opposed to stable

deformation), a smaller diameter of penetrator/armor interaction occurs with a “sharpening” effect of the penetrator tip,

allowing spent rod and target material to flow backward easier

and escape the on-coming active rod, see Figure 2. Less kinetic

energy per unit of rod length is consumed and the effectiveness

of the munition is increased [2]. Use of uranium alloys as long

rod KEPs is now governed by the following parameters: velocity, L/D ratio, and material properties of density, strength, hardRobert J. Dowding

Kyu C. Cho

William H. Drysdale

Laszlo J. Kecskes

Michael A. Minnicino

Michael R. Staker

Weapons and Materials Research Directorate

US Army Research Laboratory

Aberdeen Proving Ground, MD

Primer Cartridge

Kinetic

Energy

Penetrator

Sabot

Base

Fins Propellant

Figure 1. Typical Components of a Large Caliber Projectile.
72 The AMPTIAC Quarterly, Volume 8, Number 4

ness, and propensity for adiabatic shear [3-7], which includes

flow stress increase with strain (work hardening) [4,6], strain

rate [4,6,7], temperature sensitivity of flow stress [4,5], volumetric specific heat[4], and flow localization parameter [4,5,6].

Uranium Alloys for Long Rod Kinetic Energy Munitions

Uranium alloys, depleted of the highly fissionable U235 isotope are referred to as depleted uranium and if used as KEPs are

called staballoy. Their radioactivity is 40% below natural uranium, which is already low enough to be handled and used safely with a few basic precautions. This includes minimizing the

ingestion of air-borne particles, a safety precaution necessary

for all heavy metals regardless of whether or not they are

radioactive. Depleted uranium’s low radioactivity does aid in

locating finely divided metal particles easily with a Geiger

counter during clean-up operations in ranges and post-battle

fields. Cleaning-up other heavy toxic metals, after use, with or

without target interaction, is virtually impossible.

Uranium must be alloyed and strengthened with other elements such as titanium, molybdenum, vanadium or niobium

with a small alloying content near 1 or 2 wt% so that the density remains high. Uranium alloys have three allotropic phases

referred to as α, β, and γ. Alpha uranium is a base-centered

orthorhombic crystalline phase, existing below 668°C [8]. Beta

uranium is a tetragonal crystal phase existing between 668 to

776°C. The gamma phase is a body-centered cubic crystal

structure existing from 776°C up to uranium’s melting point 

of 1135°C. The room temperature phase, α, and the highest

temperature phase, γ, are the two most important. The intermediate temperature phase, β, is too brittle to be useful as a

penetrator. Solubility of alloying elements is higher in the γ

phase, and taken advantage of during heat treatments producing a supersaturated room temperature α′ phase, strengthened

either by pure solid solution or subsequent aging. Aging reactions often precipitate intermetallics of the form U2M, where

M is a solute element, such as titanium, molybdenum or niobium. These intermetallic precipitates are usually inherently

brittle, but are effective in strengthening provided their morphology is small, spherical, and non-planar. Over-aging leads to

a tradeoff of ductility for strength when U2Ti, for example,

grows preferentially along lenticular-shaped martensite (α′)

boundaries. Small U2Ti, precipitates are observed preventing

dislocation motion, Figure 3, resulting in increased strength

[9]. However, deformation is predominately by twinning at

high strain rates.

Texture development during deformation processing also

plays a major role in strengthening uranium alloys [10]. The

Army Research Laboratory and its predecessor, Watertown

Arsenal, played a major role in developing and understanding

uranium alloys[11], including the current production alloy,

Uranium - 3/4 wt% Titanium (U-3/4 Ti), although Sandia[12]

and Los Alamos National Laboratories also played major roles.

New alloy development builds on the control of all the materials parameters influencing propensity for adiabatic shear of the

projectile in addition to velocity, L/D ratio, and density. Ultra

high strength and ductility must be maintained as well as low

work hardening [3,4] and high flow stress-temperature sensitivity [4] and high flow localization parameter [4, 5] that allow

early onset of adiabatic shear [13]. Present work on uranium

alloys continues to refine our understanding of the crystalline

phases and is leading to some revisions of phase diagrams [12,

13] and enhanced properties [13, 14].

Nanocrystalline Tungsten Penetrators

Tungsten has been researched quite extensively for the

replacement of DU penetrators. It has a high density (19.30

g/cm3) but has lacked the ability for adiabatic shear. Powder

consolidation methods including microwave sintering and

plasma pressure compaction (P2C) followed by mechanical

Figure 3. Transmission Electron Micrograph of U2Ti in an ARL-Made U-3/4 Ti Alloy.

Stable Deformation Adiabatic Shear

Figure 2. Penetrator Rod Deformation, after Magness [1].

a) U2Ti precipitates with Dislocations Slightly Visible Due 

to Diffraction Conditions.

b) Dislocations (More Visible) Interacting with U2Ti, 

After Tilting the Foil.
working, and an alternate approach using severe plastic 

deformation, are being investigated to produce ultrafine grain

and nanocrystalline tungsten which have potential for a high

performance KEP.

Particulate consolidation is a solid-state densification technique used to bond individual

particulates or aggregates of 

particulates using thermal and

sometimes mechanical energy to

convert them into a solid load

bearing structure. Particulates

consist of small particles with

wide ranges of shapes. In most

cases, pure bulk tungsten is produced by a particulate consolidation technique followed by one 

or more post consolidation

mechanical working methods

such as swaging, forging, and

rolling. 

In tungsten, or any other material, the conventional grain sizes

are typically micrometers in size

while for nanocrystalline materials

the grain size is usually defined as

1-100 nm. Ultra fine grain sizes

fall in the range of approximately

100 to 500 nm. A material’s properties are dependent upon grain

size with an abrupt change occurring in the nanoscale region

referred to as the critical grain size.

It is widely considered that the

critical grain size is a material

characteristic. On the other hand,

it is also well understood that

materials with the same crystal

structure have similar plastic

deformation characteristics. Tungsten is a high density refractory

metal with a body centered cubic

(BCC) atomic unit cell structure.

Micrometer grain size BCC metals, such as conventional tungsten

and conventional iron, have

extremely stable compressive

dynamic plastic deformation

behaviors (e.g., resistance to compressive plastic deformation is

proportional to the cumulative

compressive plastic strains at high strain rates). This behavior,

known as stable plasticity, is not a desirable property for KEP

materials. Unlike conventional iron, however, ultra fine grain

iron and nanocrystalline iron have shown unstable dynamic

compressive plastic deformation behavior accompanied by

dynamic shear band formation at or below average grain sizes

of 250 nm. Based on the results with iron, it has been widely

postulated that ultra fine grained tungsten may show similar

shear localization type plastic deformation characteristics at

high dynamic compressive strain and strain rate regimes. Shear

band formability in ultra fine or nanosize-grained tungsten

would produce a high performance KEP.

Tungsten densification is mainly promoted by grain boundary diffusion that naturally encourages grain growth. In order to

consolidate ultra fine grained

tungsten and nanocrystalline

tungsten, therefore, the densification processes should provide

extremely rapid heating rates in

order to minimize the grain

growth. High applied pressure is

also desirable as it provides additional driving force for densification. In general, shorter processing time and lower temperature is

beneficial for retaining fine grain

structure. Currently, two particulate consolidation techniques for

nano and ultra fine grained tungsten are being examined. They are

microwave sintering and plasma

pressure compaction (P2C). Both

techniques utilize rapid volumetric heating which does not promote thermal diffusion and therefore should, in theory, prevent

grain growth.

Tungsten particulates are not

subjected to pressure during

microwave sintering while in contrast, during P2C, tungsten particulates are placed in a graphite die

and pressure is applied through a

set of graphite punches. Consolidation results from these processes

can be seen in the secondary electron images (SEI) of nanoparticulate tungsten in Figures 4. Secondary phases can artificially pin

the tungsten grain boundaries

during the densification stage of

processing. The grain boundary

pinning agents may allow an 

elevation of the consolidation

temperature to achieve full densification without sacrificing grain

growth. An SEI of microwave sintered tungsten doped with a small amount of hafnium dioxide

(HfO2) is shown in Figure 5 and illustrates the pinning effects.

Severe Plastic Deformation

There are two approaches for making a bulk nanostructured

material. The first is to build it from the bottom up using

nanoparticles and consolidating them to a fully dense structure.

Controlling grain growth, however, is a difficult task because of

The AMPTIAC Quarterly, Volume 8, Number 4 73

Figure 4. SEI of Consolidated Tungsten.

Figure 5. SEI of Microwave Sintered Tungsten Doped

with a Small Amount of HfO2.

a) Microwave Sintering Technique

b) Plasma Pressure Compaction

2 μm

20 μm

2 μm
74 The AMPTIAC Quarterly, Volume 8, Number 4

the heat involved. Often, particles that are initially less than

100 nanometers can grow to several microns in diameter. An

alternate approach is to deform plastically the material to break

down a coarse grain structure into a very fine nanocrystalline

structure. The amount of cold work required is large and the

total strain necessary can be 500% or more. The process of cold

work and recrystallization is well known, and is commonly

used in metalworking.

Equal channel angular pressing (ECAP) offers a cold working method that is unique, see Figure 6. It can impart very large

amounts of cold work without changing the original cross sectional shape or area. In an ECAP die, two channels intersect at

a predetermined angle, θ, where the work piece is processed in

pure shear. This angle is usually 90° for ductile metals such as

copper and aluminum. The angle is set at higher values for

more difficult to work metals like tungsten.

Recent ECAP of pure tungsten has shown that refinement of

coarse grains to the nanoscale is possible. Commercially pure

tungsten has a grain size of approximately 70 mm. After ECAP

processing where the work piece was processed 16 times, the

grain size was reduced to approximately 100 nm, Figure 7. A

reduction in the ductile to brittle transition temperature of

80°C has been observed in nanostructured tungsten in comparison to conventional tungsten. It is reasonable to expect this

structure will deliver properties previously unobtainable by

other means.

Bulk-Metallic Glass-Matrix Composites 

Conventional tungsten heavy alloy (WHA) penetrators are

two-phase composites of nearly unalloyed tungsten particles

embedded in a nickel alloy matrix. Because the tungsten phase

itself is very resistant to adiabatic shear localization, efforts have

primarily focused on replacing the nickel alloy matrix with one

having a greater susceptibility to adiabatic shear failure. The

Army has led a concerted effort wherein bulk metallic glass

(BMG) alloys with unique shear deformation and failure mechanisms are being examined as candidate matrix materials for use

in novel tungsten based composites. Unlike conventional materials, BMGs are amorphous, that is they do not have a longrange ordered crystalline structure. At ordinary temperatures,

BMGs are in a deeply under cooled state. That is, below their

glass transition temperatures (Tg), BMGs have an extremely

high viscosity causing randomly dispersed atoms to be immobile. Above their Tg, there is a rapid decrease in viscosity. However, as atoms become mobile above a certain temperature,

crystalline phases form and BMGs devitrify. 

Typically, the formation of BMGs necessitates fairly high

cooling rates to retain their disordered, amorphous structure.

The best zirconium based BMGs have critical cooling rates of

about 10 to 100 degrees/second and densities of about 7 g/cm3.

The disordered atomic arrangement also leads to mechanical

properties that are quite different from those of ordinary crystalline materials. It is this distinct property of BMGs that is of

greatest interest. Specifically, when subjected to a compressive

mechanical load, they deform uncontrollably by shear localization, in a manner very similar to the way depleted uranium

alloys deform and fracture.

Fundamental research has lead to a significant technical

achievement in solving two simultaneous problems: (1) identify a BMG with higher than 7 g/cm3 density and, (2) achieve

control over the deformation mechanism. This was accomplished by concurrently attacking the problem with three

approaches. First, a new high-density BMG was synthesized

that nearly doubled the density of the previously available zirconium-based BMGs. This alloy, based on hafnium, was developed using first principles, modeling, and a semi-empirical

experimental method [15]. Second, and just as significantly,

using a liquid-infiltration technique, a composite was created

that incorporated fine particulate tungsten powder which further raised the density and allowed for control of the shear

banding. Lastly, intensive mechanical and ballistic characterization provided the proper path for the material and composite

synthesis activities [16].

Figure 7. Pure Tungsten That Has Been Subjected to Severe Plastic Deformation.

Pressure

As-Received Tungsten 

Grain Size 70 μm

6 Passes ECAP

Grain Size ~1 μm

16 Passes ECAP

Grain Size ~100 nm

θ

Figure 6. Equal Channel Angular

Pressing (ECAP) Die Schematic. Two

Intersecting Channels of Equal Shape

and Size Guide the Work Piece as it

is Deformed. Multiple Passes Allow

for Accumulation of Strain.
The AMPTIAC Quarterly, Volume 8, Number 4 75

The ultimate discovery of the alloy, the processing methods,

and a verification of the preferred ballistic deformation behavior achieved two things. First, it raised the density to an acceptable level for kinetic energy penetrators (about 17 g/cm3) and

second, it allowed for control of the shear localizations that are

so important to the performance of the KEP. This new, hafnium-based BMG-tungsten composite provides new options in

materials selection for KEPs. It performs substantially better

than existing conventional WHAs and on a par with DU alloys.

Current and future efforts focus on developing a reliable

process to produce large-scale composite structures beyond the

dimensions of sub-scale projectile devices [17]. To address this

issue, a powder metallurgy-based approach was invented that, in

part, depends on a hot isostatic pressing (HIP) technique,

equipped with a sensor system to monitor and optimize the consolidation process. Instrumentation allows real-time control of

the HIP process, with adjustments to alter exposure time of the

composite powder blend to pressure and temperature, in order

to achieve full densification and bring about the proper evolution of the desired amorphous structure. Prudent control of the

HIP and post-HIP processing are used to bypass detrimental

conditions that otherwise would devitrify the composite.

COMPOSITES FOR LARGE CALIBER SABOTS

Advanced lightweight composites are being utilized or considered for large caliber munitions in both the direct and indirect

fire modes. Increased armor penetration, lethal radius, effective

range, and accuracy of the projectile are the major factors promoting the use of these engineered materials.

In the direct fire role, the primary anti-armor ammunition

for current main battle tanks is the sabot-launched KEP. The

sabot is the portion of the round which cradles the long rod

penetrator. Its primary functions are to (1) support the dense,

low structural efficiency penetrator during the high axial acceleration of launch, (2) to seal the gun barrel to hot, high pressure gas, (3) to protect the long, high length-to-diameter ratio

rod from transverse balloting loads, and (4) to launch the flight

penetrator or payload so that it may fly accurately to the target.

Since the sabot is discarded at muzzle exit and does not fly to

the target, any kinetic energy resident in the sabot was lost after

firing. Thus the minimization of the sabot mass leads directly

to increased kinetic energy in the penetrator. An axisymmetric

view of a sabot-launched kinetic energy projectile is shown in

Figure 8, which also indicates the stress state and primary loading of the different portions of the sabot. The obturator prevents explosive gases from escaping around the projectile, maximizing the load transferred to the projectile. The rear bourrelet

handles the loads transferred to the projectile upon discharging

the weapon. The forward bourrelet provides the loading surface

for separation of the sabot from the penetrator rod after emerging from the gun barrel.

Since one of the functions of a sabot is merely to occupy volume (sealing the gun tube) a low density material is needed.

Another of the design requirements calls for a high axial modulus to provide support for the rod. This combination of design

criteria suggests a graphite fiber/ polymer matrix composite

(PMC) material as providing the optimum combination of

properties. The identification of zones of the sabot needing high

shear strength then suggests a plus/minus off-axis laminate.

Analysis and design of projectiles that employ a PMC sabot

is complicated by the lack of an accepted laminate failure criteria that considers thick sections and three dimensional (3D)

loading. To meet this challenge, an assessment methodology

was developed using LAMPAT modeling software. Besides providing a quick determination of relevant 3D elastic properties

for use in finite element (FE) codes from unidirectional ply values, LAMPAT calculated the stress or strain in individual plies

from the global 3D FE results, allowing a more rational failure

assessment.

Using these analysis techniques, two generations of composite sabot KEPs have been fielded. The first, the M829A2,

reduced the sabot mass from the comparable aluminum sabot

M829A1 by 35%. The second generation, using a more optimum lay-up in the laminate, resulted in an additional 30%

equivalent sabot mass reduction for the M829A3 projectile.

These are the only composite sabots successfully fielded.

An additional savings that occurred in the evolution of the

M829A2 to the A3 was in the area of cost. The A2 version used

an epoxy matrix sabot. Epoxy resins used for sabot applications,

and many others, require storage freezers and special monitoring of the material on the factory floor. The A3 version

switched to a thermoplastic matrix sabot, which made possible

Figure 8. Axisymmetric View of a Kinetic Energy Penetrator System. Major Regions of the Sabot and Their Loading Requirements 

Are Indicated.

Fins

Penetrator Rod

Radial (90°)

Direction

Axial (0°) Direction

Sabot Aft Ramp

(Axial Tension) Obturator

Tip/Windshield

Sabot Rear Bourrelet

(Shear Loading)

Sabot Forward Bourrelet

(Shear Loading)

Sabot Grooves

(Shear Loading)

Sabot Saddle

(Axial Compression) Sabot Forward Ramp

(Axial Compression)
76 The AMPTIAC Quarterly, Volume 8, Number 4

the use of an induction laminator as well as the elimination of

special storage needs. The laminator was the result of the joint

Army Research Laboratory/University of Delaware Center for

Composite Materials (CCM) program. By using inductive currents in the graphite fibers to heat the prepreg plies and then

immediately compacting them with consolidation rollers, an

eight ply laminate of the basic lay-up building block of the

sabot was rapidly fabricated at less cost.

METAL MATRIX COMPOSITES 

FOR HIGH PAYLOAD MUNITIONS

A slightly different set of requirements are needed for the

Beyond-Line-of-Sight and Non-Line-of-Sight projectiles, more

similar to traditional artillery rounds. Here, light weight is still

desired, but the crucial need is for increased cargo volume.

Since the diameter of the round is strictly curtailed by the cannon caliber and the length is limited by cartridge compatibility, any means of increasing interior volume for the explosives,

propulsion, or guidance components adds directly to the effectiveness of the munition. While PMCs can deliver very competitive projectile sidewall weights, the more than double wall

thickness cuts unacceptably into payload volume. Steel sidewalls represent an acceptable material solution for the shell

from consideration of payload volume; however they are excessively heavy compared to metal matrix composite (MMC)

materials. One such material is the system of alumina ceramic

fibers in an aluminum metal matrix. The tensile strength of this

material is similar to high strength steel; the compressive

strength of uniaxial plies is phenomenal, approaching 800,000

psi, all at a density similar to aluminum.

Besides their extraordinary specific strength advantages, laminated MMCs are superior to isotropic materials in their ability to modify the material to best handle the stress distribution

for the application. For

example, one possible configuration for an extended

range cargo round has the

sidewall for a rocket motor

buried deeply within the

propellant bed. When the

propellant burns, the external pressure acts to collapse

the sidewall as well as accelerate the projectile. The resulting stress state can have hoop

stresses which are several times larger than the axial stress. Conversely, for a more conventional artillery shell where the projectile is seated in the gun and the propellant separately loaded,

the resulting stress state is almost entirely axial. By changing the

ratio of hoop to axial plies in the composite lay-up used for the

projectile sidewall, the differences in strength requirements are

easily satisfied.

Projectiles designed for the standard configuration projectile

were fabricated and tested in a 105 mm smoothbore gun, see

Figure 9. The MMC sidewall had the same thickness but less

than half the weight of a steel design. All tests have been successful for the new material. The MMC tubes used for the sidewalls

in the successful firing tests were fabricated by infiltration of

molten aluminum into a mold containing the ceramic fiber layup. A joint program to develop other potentially cheaper fabrication techniques is being pursued by ARL and CCM. This

effort begins with an MMC tape, thin ribbons of ceramic fibers

already encased in an aluminum matrix, and develops an analogy between this material and thermoplastic tape for use with

robotic tape laying processes. The CCM has developed extensive

software to simulate the fabrication of large parts by thermoplastic tape laying methods, including models of various means of

applying heat to the interface, heat lost to conduction into the

part and to the consolidation rollers, effects of consolidation

pressure, etc. Depending on time at temperature and pressure,

the degree of consolidation of the tape can be predicted.

In extending the simulation to MMC tapes, several key differences appear besides the obvious similarities. The melting or

softening temperature of aluminum is much higher than thermoplastic polymers. Additionally, the rate of heat conduction

away from the joining interface is much higher in aluminum

(polymers act almost as insulators). Both of these differences

indicate the need for more robust heat deposition for MMC

tape placement. Inductive heating is currently being studied for

this very application. A patent application has been submitted

for the robotic induction head/compaction roller developed

from the MMC simulation.

ENABLING MATERIALS FOR FRANGIBLE PROJECTILES

United States military forces are increasingly finding themselves

in situations where the use of non-lethal weapons is desired.

Shaping the battlefield with non-lethal payloads delivered by

these weapons is considered to be an essential option in future

conflict scenarios. To be a truly non-lethal weapon, both the

delivery vehicle (aeroshell) and the payload must be non-lethal.

Non-lethal weapons are designed to disable a vehicle or personnel without excessive physical damage or fatality. ARL has

determined that fragmenting the aeroshell mass in a

manner that produces high

aerodynamic drag staves is

an attractive solution for

achieving a non-lethal large

caliber weapon.

ARL has demonstrated

that an adhesively bonded

bimetallic nano-layered

composite, with a designable level of electrical or thermal initiation, can completely and quickly separate two adhesively coupled surfaces. Unlike other de-bonding approaches, this

method allows for remote and virtually instantaneous, on-command separation of structurally bonded materials [18]. This

rapid de-bond technology enables the development of a frangible non-lethal artillery aeroshell.

Typically, these reactive nanocomposites are made by sputter

deposition of alternating bilayers 10-100 nanometers thick of

metallic and/or intermetallic materials. An illustration of the

nanocomposite is shown in Figure 10. The bilayer constituents

and thicknesses can be chosen on the basis of their reaction

temperatures and their propagation rates (typically 1-10 m/s).

The propagation rate is typically inversely proportional to the

bilayer thickness [19]. 

Figure 9. Photograph of an MMC Projectile just after Exiting 

the Muzzle.
The AMPTIAC Quarterly, Volume 8, Number 4 77

Nanocomposite stability appears linked to the sharpness 

of bilayer interfaces on the nanometer scale. Typical bilayer

systems are aluminum/nickel or aluminum/titanium with the

total bilayer thickness in the 0.1-0.2 mm range. ARL has

investigated atomic diffusion at the bilayer interface and its

effect on propagation velocity and initiation sensitivity. 

Figure 11 is an energy spectrum of 2 MeV helium ions elastically backscattered via Rutherford Backscattering Spectrometry (RBS) from a four period bilayer stack of Ni/Al nanocomposite. The periodic variation in yield is directly due to the

two element composition of the nanocomposite and can 

be converted into their relative thicknesses and interfacial 

diffusion, which governs exothermic rates and initiation 

sensitivities.

SUMMARY

Research and development of materials fabricated through

newer processing methods will produce the next generation of

large caliber projectiles and produce non-lethal weapon technologies. These processing techniques, in some cases, open the

door for alternate materials due to the enhanced performance

that may be achieved, especially for nanostructured materials.

The Army Research Laboratory is leading the way to develop

materials and technologies for large caliber projectiles that will

result in a more effective force for future operations.

REFERENCES

[1] L.S. Magness Jr., Properties and Performance of KE Penetrator Materials, Proceedings of the 1st International Conference

on Tungsten and Tungsten Alloys, 1992, pp. 15-22

[2] L.S. Magness and T.G. Farrand, Deformation Behavior and

Its Relationship to Penetrator Performance of High Density Kinetic Energy Penetrator Materials, Proc. of 1990 Army Science

Conf., Durham NC, Vol. 1 and 2, (1991) 149 and 465

[3] M.R. Staker, Effect of Strength of Martensitic Steel Armor on

Penetration of Long Rods, ARL-TR-139, Army Res. Lab. Tech.

Report, May (1993)

[4] M.R. Staker, Relation Between Adiabatic Shear Instability

Strain and Material Properties, Acta Met., 29 (1981) 683 and

32 (1984) 987

[5] M.R. Staker, On Adiabatic Shear Band Determinations by

Surface Observations, Scripta Met. 14 (1980) 677 and The

Influence of Dynamic strain Aging on the temperature Dependence

of Flow Stress and the Impact of This on Adiabatic Shear Analysis,

Scripta Met. 18 (1984) 735

[6] S.L. Semiatin, M.R. Staker, and J.J. Jonas, Plastic Instability and Flow Localization in Shear at High Rates, Acta Met. 32

(1984) 1347

[7] M.R. Staker, High Strain Rate Testing, Chapter in Mechanical

Testing, Vol. 8, Metals Hdbk, (9th edition), ASM (1985) 187

[8] C.T. Olofson, G.E. Meyer, and A.L. Hoffmanner, Processing and Applications of Depleted Uranium Alloy Products, Battelle’s Columbus Laboratories, MCIC-76-28, September 1976

[9] M.R. Staker, Micro-constituents of U-3/4 % Ti Alloy Using

Trans. Electron Microscopy, Unpublished Research at Army

Res. Lab. (1986)

[10] C.S. Choi and M.R. Staker, Neutron Diffraction Texture

Study of Deformed Uranium Plates, J. Mat. Sci. 31 (1996) 3397

[11] J.J. Burke, D.A. Colling, A.E. Gorum and J. Greenspan,

Physical Metallurgy of U Alloys, Proc. 3 Army Matls. Tech.

Conf., February 1974, Publ. in cooperation with Metals

Ceramics Info. Center Columbus OH, by Brook Hill Publishing Co., Chestnut Hill MA (1976)

[12] K.H. Eckelmeyer, U and U Alloys in Properties and Selection, Vol. 2, Metals Hdbk (10th Ed), ASM (1990) 670, and

Metallography of U and U Alloys in Metallography and

Microstructure, Vol. 9 (1985) 476

[13] M.R. Staker, U-V Phase Diagram, J. Alloys Comp. 266

(1998) 167, and J.F. Smith, U-V, J. Phase Equilibria. 19, No.

6 (1998) 603

[14] M.R. Staker, Stakalloy, and Hypereutectoid and Hypoeutectic Binary U-V Alloys, US Patents 6,726,876 and 5,963,777,

(27 April 2004 and 5 October 1999)

[15] L.J. Kecskes, B.T. Edwards, and R.H. Woodman, HafniumBased Bulk Metallic Glasses for Kinetic Energy Penetrators, Proc.

24th Army Science Conference, Orlando FL, December 2004

[16] L.J. Kecskes and L.S. Magness, Behavior and Performance

of Amorphous Metal Alloys and Tungsten Wire-Reinforced

Amorphous Alloy Matrix Composites, Proc. 20th International

Symposium on Ballistics, Orlando FL, September 2002

Figure 10. Nanocomposite Illustration Showing Composition,

Bilayer Thickness, and Bilayer Diffusion Region.

Figure 11. RBS Spectrum of ARL 4-Period Array of Sputtered

Ni [85 nm]/Al [45 nm] Nano-Composite Stack.

Region of Atomic

Bilayer Diffusion

Bilayer

Thickness

Nano-layered Bimetallic

Element A

Element B

80

60

40

20

0

100 200 300 400 500 600 700 800

Channel

Energy (MeZ)

0.5 1.0 1.5

Normalized Yield
Dr. Michael R. Staker is a registered professional engineer, a registered patent agent and patent law practitioner.

He works at ARL in the Ordnance Materials Branch conducting basic research on various topics of interest to 

the Army including advanced armor, kinetic energy munitions, high strain rate behavior of materials, uranium 

metallurgy, metal hydrides, thermodynamics, phase diagrams, calorimetry of phase changes and low energy

nuclear reactions. He has published over 50 papers and reports; and holds several patents related to failure 

analysis, armor and kinetic energy penetrator materials and their behavior at high strain rates. Dr. Staker earned 

his PhD from the Massachusetts Institute of Technology.

Mr. Kyu C. Cho is a Materials Engineer at the Army Research Laboratory in Aberdeen Proving Ground, MD. He

holds a BS in Mechanical Engineering, and a MS in Materials Science and Engineering, both from Worcester 

Polytechnic Institute (WPI). He joined the Army in 1994. His current work includes development of refractory metals

for ordnance applications with a particular emphasis on synthesizing bulk nanocystalline refractory metals by 

particle consolidation. He has coauthored more than 35 publications.

78 The AMPTIAC Quarterly, Volume 8, Number 4

[17] T. Zahrah, L.J. Kecskes, and R. Rowland, Unpublished

Research, September 2004

[18] M. Minnicino, J. Sands, J. Hirvonen, and D. Demaree,

Reactive Nano-layered Bimetallics for Non-Destructive Debonding of Munition Components, Proc. 24th Army Science Conference, Orlando FL, December 2004

[19] A.B. Mann, A.J. Gavens, M.E. Reiss, D. Van Heerden, 

G. Bao, and T.P. Weihs, Modeling and characterizing the 

propagation velocity of exothermic reactions in multilayer foils, 

J. Appl. Phys. 82 (3), August 1997

Mr. Michael Minnicino currently works on a number of programs; including nano-layered bimetallics for debonding, frangible munitions, and other munition structural analyses related to interior ballistics at WMRD. From 2002-

2004 he was employed as a Geo-Centers, Inc. contractor and was subsequently hired as a mechanical engineer

at the ARL Weapons and Materials Research Directorate, Aberdeen Proving Ground, MD. He earned a BS (2000)

and a MS (2002) in Mechanical Engineering, both from Pennsylvania State University.

Dr. William Drysdale has been employed by the Army Research Laboratory and, prior to that, the Army’s Ballistic

Research Laboratory for a total of 30 years. His specialty has been structural integrity and integration of projectiles

during launch and flight. He has a PhD in Aeronautical and Astronautical Engineering from the University of Illinois.

Since 1985, Dr. Laszlo Kecskes has been a Research Physical Scientist with the US Army Research Laboratory,

Aberdeen Proving Ground, MD. His primary responsibility relates to the development, evaluation, and use of 

novel amorphous alloy materials in advanced kinetic energy penetrator concepts. Dr. Kecskes is the lead for a multidisciplinary team of scientists and engineers from government, industry, and university, utilizing fundamental 

physics, chemistry, and materials science principles that recently demonstrated a new ballistically superior tungsten

(W)-based composite, based on the use of amorphous alloys.

Mr. Robert Dowding has been employed by the Army Research Laboratory and the Army Mechanics and 

Materials Research Center for 18 years. He is the team leader for the Ordnance Materials team. He holds a MS

in Materials Science and Engineering from Worcester Polytechnic Institute.

Photo

Not

Available
The AMPTIAC Quarterly, Volume 8, Number 4 79

INTRODUCTION

Electromagnetic (EM) launch has the potential to revolutionize

a wide range of defense applications including tank gun,

artillery, and aircraft launch. The EM launch concept has been

demonstrated as the Army and other services have recently fabricated and tested several prototype gun systems. Advanced

materials and manufacturing

techniques played a major role

in this achievement [1]. The

engineering development necessary for a fieldable system is considerably more difficult than the

laboratory systems. The design

of the current laboratory system

is not fully optimized from a

mechanical and materials performance aspect. Application of

advanced materials with innovative design concept in various

critical components of the system is in progress under the current program at the US Army Research Laboratory (ARL) and

Armament Research and Development Center (ARDEC).

ELECTROMAGNETIC LAUNCH TECHNOLOGY

The schematic in Figure 1 illustrates the essential components

of an electromagnetic gun system, including a pulsed power

supply, a rail gun, and a projectile package. A current level of

one million amps is generated from the pulsed power supply,

a capacitor bank, or a rotating machine, providing propulsion

energy for the gun system. The current flows from the gun

breech through one rail, across the armature (part of the projectile package), and then returns through the other rail. As a

result, an intensive magnetic field is generated perpendicular

to the plane of rail/armature. Accordingly, the current flowing

through the armature and rails

interacts with the magnetic field

and results in an electromagnetic (Lorenz) force. The forces

generated during operation act

to accelerate the projectile forward and push the rails apart. In

theory, the projectile can be

accelerated to any velocity, but it

is limited by the physical constraints of material strength and

structural design.

Rotating machinery has been

identified as the most feasible

solution to provide pulsed current at several million amps. The

machine converts kinetic energy

into electrical current over a short duration equivalent to interior ballistic cycles of traditional guns. Within weight and volume design constraints, the machine has to store energy as well

as deliver enormous power. Figure 2 shows the progress of

pulsed-power devices resulting from recent engineering design

and materials advancements. One is an extremely large

homopolar generator and inductor built in 1985, which stores

60MJ of energy. The other is a subscale compulsator that stores

20MJ energy and was developed by Scientific Applications

Jerome T. Tzeng

Edward A. Schmidt

Weapons and Materials Research Directorate

US Army Research Laboratory

Aberdeen Proving Ground, MD

Figure 1. A schematic of an Electromagnetic Gun. Current

Flowing in the Rails Creates a Magnetic Field That Interacts

with the Current in the Armature to Generate a Lorenz (JxB)

Force. The Force Acts to Accelerate the Projectile Forward.

Driving Current

Armature (Projectile)

Armature 

Current (J)

Power Supply

Magnetic Field

(B)

Rails

Force (JxB)
80 The AMPTIAC Quarterly, Volume 8, Number 4

International Corporation and the University of Texas under

the Army Research Laboratory’s electric gun program in 1998.

The compulsator achieved most of the performance as predicted, although this required many iterated modifications of

design and engineering development. In terms of mechanical

performance, the machine was spun up to 12,000 rpm and 1.0

J/g energy density, defined as energy delivered divided by total

mass of the system. For an objective system, however, it will

need a much higher energy density and storage capability. This

will require a higher spin rate, packing ratio, and material performance due to high stress and strain developed in the

machine. 

There have been many EM rail launchers built in the past two

decades. Most of them were built as laboratory launchers and

designed mainly from an electrical performance aspect. Figure 3

shows the test fire of a 90-mm rail gun developed by Maxwell

Corporation, sponsored by the Defense Nuclear Agency in

1989. Like most EM guns built in the past, the rails were supported by a massive laminate steel containment with a very large

breech (not shown in Figure 3). The muzzle blast caused by electrical short as the projectile passed through the muzzle needs to

be further reduced for a tactical application. A few tactical

weapon-like guns were developed in the last fifteen years. Composite containment and lightweight insulator materials were

used to enhance gun designs. However, they either lacked performance or were short in service life. Currently, a tactical EM

launcher is being developed at ARL. Advanced polymer composites, lightweight reinforced metals, and various cladding and

coating materials are considered for the gun tube, breech, and

muzzle shunt construction. In addition, manufacturing techniques and assembly procedures are being investigated.

Figure 4 shows an EM kinetic energy projectile. A major difference between an EM launch package and a conventional

projectile is the armature that allows current to pass through

the projectile package by connecting two rails electrically. The

interface between the projectile and rails has been the focus of

recent research. The rapid change of material properties due to

the high intensity of current, heat, and stress does not occur in

conventional material applications and is a challenging materials research issue.

PULSED POWER MATERIALS

As an energy storage device, the rotating machine must be operated at high speed to achieve the required energy density. Centripetal forces from high-speed rotation cause significant stresses and deformations in the rotor. During discharge, the stored

energy is extracted to generate electric current for launching

projectiles from a rail gun. Magnetic forces are also not trivial,

Figure 2. Homopolar Generator (1985) and Subscale Compulsator (1998) Developed under Army Contracts at the Center for

Electromechanics, the University of Texas in Austin.

Figure 3. 90-mm Rail Gun Test.

Figure 4. An EM Projectile for Rail Gun Launch.
The AMPTIAC Quarterly, Volume 8, Number 4 81

as millions of joules of energy are extracted from the rotating

body within a few milliseconds. Additional stresses are generated from the deceleration. It is a considerable challenge for

advanced materials and machine design, especially since a long

service life span is required for the rotor, stator, and converter.

The rotor in Figure 5(a) is composed of three parts from the

aspect of mechanics as shown in Figure 5(b). From the inner to

the outer radius of the cylinder, there is a strong metal or composite substrate, a relatively compliant field coil (FC), and composite banding that provides the essential structural integrity.

The FC is generally made of a soft electrical conductor insulated and embedded in a fiberglass epoxy composite. Structurally,

it is mostly a parasitic mass supported by the composite cylinder and the substrate. The composite cylinder is primarily reinforced in the circumferential direction to provide strength and

stiffness to the rotor that is subjected to centripetal and EM

forces. In order to achieve the required performance, the rotor

has to operate at high stress and strain in comparison to a utility generator. The mechanics of the composite rotor have been

investigated and reported previously [2].

In order to overcome the strength requirement of the FC, the

rotor is designed with significant built-in prestress through a

“press-fit” procedure during fabrication. Accordingly, the composite band is in a state of tension prior to rotation, while the

FC is under a state of compression. The pre-compressive stress

in the FC can compensate part of the tensile stress while the

rotor is at speed. This is a key process of the design to enhance

the mechanical performance and fully utilize the tensile

strength of composite materials. However, centrifugal force

from high-speed rotation can be large enough to generalize tensile stress, deformation, and radial growth in the FC even

though it is pre-stressed in compression. 

High-strength and high-temperature materials with innovative design methodologies are currently being developed to

enhance machine performance. For example, high strength 

carbon fibers, such as T1000 and IM9, and high strength conductor materials are considered for construction of the composite shell and the FC conductors, respectively. Table 1 illustrates

recent developments to achieve high strength composite shells.

A composite cylinder with various fiber volume fractions was

fabricated and hydro-burst tested. High circumferential

strengths can be obtained by packing more fiber (high fiber

content) in the composite cylinder. Additional tests were also

performed to evaluate shear and transverse properties of composite cylinders, since composite materials are anisotropic in

nature. A high fiber volume fraction generally degrades these

properties. The goal of future development is to achieve the

maximum hoop strength with balanced shear and transverse

properties.

Table 2 illustrates the properties of potential conductor

materials for EM gun applications. The 6061 aluminum alloy,

with moderate electrical conductivity and mechanical properties, is considered as the baseline material for the field conductor. It is a very complex materials problem to determine a suitable conductor material. Electrical conductivity, mechanical

properties, densities, materials availability, and manufacturing

Figure 5. a) Rotating Machine. b) Schematic of Rotor Cross Section.

a) b)

Field Coil Composite Banding

Metal Shell

r

Table 1. Hydroburst Test Results Showing the Relation of Strength and Translation Efficiency to the Fiber Content of Composites [2].

Banding Material Fiber Content Burst Strength Theoretic Max Translation 

(% vol) (ksi) Strengtha (ksi) Efficiencyb (%)

Standard T1000/epoxy 60 475 540 85.6

Medium Fiber Vol. IM9/cyanate ester 67 518 620 83.5

High Fiber Vol. T1000/cynate ester 76 585 703 83.2

aTheoretic strength = 925 ksi (high fiber volume for each banding); 925 ksi is a general number (T1000) used for comparison.

bTranslation efficiency = burst strength/theoretic strength.
82 The AMPTIAC Quarterly, Volume 8, Number 4

feasibility are parameters to be evaluated for the potential conductors in terms of the final machine performance.

The 7075 series aluminum has high strength and is commercially available but it is slightly low in conductivity (33%

IACS*). Recently, a relatively new aluminum alloy 7055 was

considered for the application because of its high strength (90

ksi) and high conductivity (38% IACS). Efforts continue to

enhance the conductivity of these high-strength aluminum

alloys while maintaining excellent mechanical properties.

Non-conventional materials such as fiber- and particulatereinforced metals (composite conductor) are also being evaluated. The aluminum oxide (Al2O3) fiber-reinforced aluminum

can be fabricated by protrusion, press-molding, and pressinfiltration. The properties of a composite conductor can be

tailored by varying the fiber and matrix contents to meet the

mechanical and electrical requirements simultaneously. For

example, for an Al2O3-reinforced conductor, the aluminum

oxide fiber content can be varied from 45% down to 30%.

The electrical conductivity then increases from 34% to 43%

IACS while the mechanical strength decreases from 180 to

120 ksi. The composite conductor gives the engineer flexibility to design a machine. However, manufacturing processes for

large scale and complex components still need to be developed

for the composite conductors.

Rate of fire is a critical performance metric for any tactical

gun system. The pulsed power supply will need an active cooling mechanism and efficient thermal management. However,

the thermal capability of materials drives the operating temperature of the machine. The most thermally-sensitive component

in the rotating machine is the electrical insulation, which is a

polymer-based materials. Research has been conducted on high

temperature polymers and their composites to replace the baseline material of glass/epoxy. Particularly, the study emphasized

thermal degradation, creep, and durability of the potential

insulation materials. The objective is to push the operating

temperature up and ease the design difficulty of the machine

cooling system. Similar efforts were conducted for the armature

and supporting structure of the stator.

The alternating current output from the rotating machine is

converted into direct current by a converter. Switch materials

development is another area that has great potential to impact

the machine size, weight, and performance. It is a considerable

challenge to convert several million amps of current, even for a

short pulse using solid state switches. Silicon (Si) is the baseline

and the state-of-the-art switch material produced at a reasonable cost. Resources have been invested in building a compact

and efficient converter with silicon switches.

Silicon carbide (SiC), a wide bandgap semiconductor, has

been frequently mentioned as a candidate switch material for

the EM gun application. Compared to the current Si switches,

SiC switches can be operated at a relatively higher temperature.

Accordingly, there is a significant weight savings (vs. Si) with

improved performance at a higher operating temperature and

breakdown voltage although it is currently limited by the wafer

size and materials cost. A research effort to leverage other DOD

programs was conducted in two areas related to SiC switch

development including durable high-power ohmic contact

materials design and surface-smoothing techniques to reduce

the cost of a SiC wafer. A nickel/tungsten-silicon/titanium/

platinum composite contact for n-SiC (doped SiC having free

electrons which carry electric current) was investigated with the

annealing temperatures up to 1000°C. Results showed the

composite contact maintains the desirable electrical properties

and possesses excellent interfacial, compositional, and surface

properties required for high-power and temperature applications. A surface-smoothing process for SiC wafers was investigated by using a gas cluster ion beam. The technique may be

applied to smooth low-cost SiC epitaxial layers cleaved from

costly SiC wafers. A successful development of this process can

allow production of SiC wafers at a significantly lower cost.

LAUNCHER AND PROJECTILE MATERIALS

Three EM rail gun designs built in the past are illustrated in

Figures 6. They are a laminated steel barrel [3], a 90 mm 9 MJ

range gun [4], and the Cannon-caliber electromagnetic

launcher [5], respectively. Many similarly laminated barrels

have been designed and used in the laboratories because they

are electrically efficient and easily assembled and disassembled

(for replacing rails, insulator, etc.). The laminated steel construction provides good circumferential stiffness and confinement for the rails and insulator. However, it lacks strength

in the longitudinal direction and is too heavy for a tactical

application. The 90-mm, 9-MJ gun in Figure 6(b) is another

version of a laminated steel core structure utilizing a composTable 2. Mechanical and Electrical Properties of Potential Conductor Materials.

Material Yield Ultimate Modulus Density Conductivity Resistance

Strength (ksi) Strength (ksi) (msi) (g/cm3) (IACS)* (%) (10-9 Ohm-m)

6061 T6 40 45 10.0 2.70 43 40

7075 Al 73 — 10.2 2.85 33 —

Gigas 30 Al 102 110 10.3 2.85 (25) —

Gigas 24 Al 75 — 12.8 2.95 (25) —

Al/Al2O3 (45%) — 180 24.0 3.4 34 66

Al/Al2O3 (30%) — 120 20.0 3.2 43 —

Cu/Ultra SiC (30%) — (300) (20.0) (8.0) (70) —

Cu/Al2O3 (1.1 wt%) particle 80 — — 8.9 78 —

Pure aluminum — — — — 65 26

Parentheses indicate theoretical values
The AMPTIAC Quarterly, Volume 8, Number 4 83

ite overwrap for axial stiffness and strength. The Cannon-caliber gun uses a steel flatjack as a prestress mechanism to keep

the components in intimate contact during launch. Concerns

for this type of design are the possible loss of preload over time

and the feasibility for a tactical weapon system. 

Based on the lessons learned from the previous design, the

Army has recognized a need to develop an integrated structure

that provides electrical insulation, support, and stability of the

rails within a weight limit [6]. The electromagnetic force in rail

guns is not axisymmetric, such as those in conventional guns

that use propellants. Instead, the forces concentrate only on the

rails and part of the containment/support structure. The electromagnetic forces and possible plasma pressure typically vary in

time and space along the length of the rail gun during launch.

During a hypervelocity launch, the dynamic response of the gun

is highly transient in nature. Accordingly, rail guns cannot possibly be constructed from a single material and a simple geometry due to the severe electrical and mechanical requirements. It

is therefore a significant challenge to design the individual components and the interfaces between components in a rail gun,

particularly to optimize the material selection to achieve balanced electrical and mechanical performance.

The previous rail guns all had a relatively short service life

compared to conventional cannons. Test results show that most

Figure 7. a) Schematic of a Rail Gun Cross Section, b) Copper Rail Gouging, c) Ring Test of Insulation Material,

and d) Tension Winding Experiment [7].

Figure 6. a) Laminated Steel Rail Gun [3], b) 9MJ Range Gun [4], c) Cannon-caliber Rail Gun [5].

a)

Longitudinal

Stiffener

Mulitiple

Rails

Integral

Rail Fins

Reinforced Thin Film

Backing Insulator

Laminated Containment

Structures Preload Wedges/

Bore Insulator

Pultruded Epoxy

S-glass Insulator

Gligcop 

AL-60 Rail

Teflon Shrink

Tubing

Axially-laminated

Stainless Steel Composite Droop

Management 

Overwrap

b) c)

a) b) 

c) d)

Composite

Overwrap

Flatjack

Mica Insulator Augmenting

Turn Rail

Main Rail

Ceramic

Sidewall

Cooling 

Passages

Insulator

Containment

Insulator

Rail Rail

Rail Surface Gouges
84 The AMPTIAC Quarterly, Volume 8, Number 4

failures occur in the rails and insulators, such as gouging and

melting of the rail surface, cracks developing in the ceramic

insulator, delamination in the glass insulator, and transitionassociated failures. These failures are influenced by material

performance (i.e., strength, melting temperature, hardness,

etc.), as well as structural support from the containment. 

A schematic of the rail gun cross section is shown in Figure

7(a). Three major components including rails, insulators, and

containment have to be integrated. Figure 7(b) shows gouging

of a copper rail due to thermal, electrical, and mechanical

loads resulting from armature/rail interaction. Extensive tests

have been performed on the rail materials such as copper, 

aluminum, alloys, and metal composites. There is no single

conductor material so far that can satisfy all requirements in

various rail sections. One approach is to build the rails with

different materials for various sections. Figure 7(c) show a

ring-test setup for evaluation of insulator material. Various

non-conductive polymers and composites have been evaluated. High-strength composites have been identified as possible

candidates for the containment. Figure 7(d) illustrates the 

tension winding of the composite overwrap. The test setup

measures the radial pressure that can be utilized for the application of the preloading mechanism.

The projectile armature, which current passes through, interacts with the rail surfaces. Heat and stress resulting from electrical resistance, friction, and concentrated magnetic fields

cause the material degradation at the surface of the armature.

Aluminum alloys are commonly used for the solid armature of

a projectile because of high electrical conductivity and strength.

Various metals and alloys are being evaluated in addition to the

configuration of the armature and current distribution in the

projectile. A continuous study is needed to explore new alloys

or multi-material integrated conductors.

An EM projectile can be designed as a base push (artillery

type) or a mid-ride as in a conventional kinetic-energy projectile. Accordingly there are supporting materials, such as sabots,

to provide structural support and reliable accuracy to hit the

target just like conventional projectiles. These supporting

materials have property requirements similar to those for conventional projectiles.

SUMMARY

Electromagnetic launch railguns require the development of

advanced materials and material processes in order to scale-up

prototype technology demonstrators into fielded systems. Significant challenges must be tackled to design components able

to meet the combination of material properties required. The

Army Research Laboratory and the Armament Research and

Development Center are developing new technologies in an

effort to solve these challenges.

NOTES & REFERENCES

* IACS stands for International Annealed Copper Standard. It

is a measure of conductivity used to compare electrical conductors to standard copper-wire and expressed as a percentage.

Standard copper wire is 100% IACS which equals a conductivity of 58 megasiemens per meter (MS/m).

[1] J.T. Tzeng, A Summary of materials and mechanics research

for electromagnetic gun pulsed power applications, ARL-TR2948, April 2003

[2] J.T. Tzeng, Mechanics of Composite Rotating Machines for

Pulsed Power Applications, IEEE Transactions on Mechanics,

Vol. 37, No. 1, January 2001, pp. 328-332

[3] J.M. Juston and D.P. Bauer, A High Performance Railgun

Launcher Design, IEEE Transactions on Magnetics, Vol. 33,

No. 1, 1997

[4] J.D. Herbst, Installation and Commissioning of the 9 MJ

Range Gun System 90 mm High L′ Laminated Railgun, IEEE

Transactions on Magnetics, Vol. 33, No. 1, 1997

[5] A.E. Zielinksi and M.D. Werst, Cannon-Caliber Electromagnetic Launcher, IEEE Transactions on Magnetics, Vol. 33,

No. 1, 1997 

[6] J.T. Tzeng, R. Emerson and R. Kaste, Material Development

of a Fieldable EM Gun, Proceedings of Classified Ballistics Symposium, Monterey CA, August 2004

[7] R. Emerson, D. Spagnuolo, and J.T. Tzeng, Optimized 

Filament Winding of Composites for Overwrap Applications, 

Proceeding of SAMPE 2004 Symposium and Exhibition, Long

Beach CA, May 2004

Dr. Jerome T. Tzeng joined US Ballistic Research Laboratory/Army Research Laboratory in 1991. He works in the

area of composite material for ballistic applications, such as advanced projectiles and gun systems. His current

research has concentrated on the electromagnetic rail gun including pulsed power machine and rail gun since

1995. Prior to the civil service, he worked with DuPont and Bechtel Corporation. Dr. Tzeng is also actively involved

in the basic research, as a journal editor and an adjunct professor at Drexel University. He has authored about 100

technical publications. Dr. Tzeng received his PhD in engineering mechanics from Virginia Tech and Master in civil

engineering from Rice University.

Dr. Edward A. Schmidt received his PhD from the Polytechnic Institute of Brooklyn in 1969. Since that time he 

has worked for the Army, either on active duty or as a civilian. His areas of technical interest are unsteady flow,

aeroballistics, tank ammunition, and recently electric guns. Currently, he is the Manager of the ARL Electromagnetic Gun Program.
The AMPTIAC Quarterly, Volume 8, Number 4 85

INTRODUCTION

The changing nature of international conflicts requires the

development of new war-fighting capabilities within the

Department of Defense. It is recognized by the US technology

community that advanced energetic materials with substantially enhanced performance, reduced sensitivity, and controlled

(or manageable) energy release will be critical enablers for precision weapons. In the past ten years revolutionary breakthroughs in munitions technology were made through aggressive development of advanced energetics by the worldwide

community.

Much of the synthesis effort over the past 50 years has been

directed toward compounds that contain only carbon, hydrogen, nitrogen, and oxygen (CHNO explosives). For most of the

past 40 years the benchmark against which high energy CHNO

ingredients have been compared was cyclotetramethylenetetranitramine (HMX). 

In 1987, a new compound, hexanitrohexaazaisowurtzitane (CL-20)

was synthesized for the

first time by the Navy. It

is more energetic than

HMX and does not have

most of the instabilities

of other high energy

compounds that have

precluded their use. The

traditional procedure for

formulating new materials such as CL-20 has

been largely guided by

intuition, experience, and

testing, relying heavily on

trial and error. The everincreasing need for rapid

deployment of emerging

weapons systems dictate a

streamlining of the development process of advanced highenergy insensitive materials tailored for optimal performance in

advanced weapons. 

Developments in computational chemistry and physics

based modeling using High-Performance Computing (HPC),

chemical synthesis and formulation, and materials science are

providing the key factors that will provide breakthroughs in the

performance of energetic materials. The DOD HPC network

and advanced modeling science and technologies afford a critical means to rapidly close the technology gap and expedite the

design and prediction of new revolutionary advanced energetic

materials (Figure 1). 

ADVANCED GUN PROPELLANT MATERIALS

The Army initiated a significant effort in the design, formulation, and fabrication of future insensitive high-energy materials

for Future Force weapons

and is extensively leveraging science and technology from the national

energetics community. 

A key objective is to

develop advanced gun

propellants having high

energy release, increased

burning rates, improved

mechanical and environmental properties using

nanomaterials and other

novel high energy ingredients, while ensuring

compliance with insensitive munitions requirements. The reduction in

carbon content is also

favorable as it reduces

degradation and wear of

steel gun barrels. Recent

Pamela J. Kaste

Betsy M. Rice

Weapons and Materials Research Directorate

US Army Research Laboratory

Aberdeen Proving Ground, MD

Figure 1. High-Performance Computing Modeling and Simulation 

of Energetic Materials and Advanced Propulsion.
86 The AMPTIAC Quarterly, Volume 8, Number 4

work in synthesis and characterization of new novel energetic

materials has centered on the following energetic materials:

• Nano-particulates (metals, crystalline solid organics)

• Metal hydrides

• CHNO and CHNOF compounds

• All-nitrogen species

• High-nitrogen species

• Boron containing compounds (e.g., carboranes)

• Energetic liquids with potential as monopropellants

Gun propellants in layered disk geometries are of interest for

applications in which an outer, slower burning layer is sandwiched

with a center, faster

burning layer to produce what commonly

is referred to as “fastcore” propellant using

chemical progressivity.

The advantage of the

fast-core concept is

that at times early in

the ballistic cycle

before the projectile

has moved significantly, a lower volume of

gas is generated by the

slower burning layer,

so that pressures do

not exceed the maximum pressure sustainable by the gun system. However, once

the projectile begins to

move and the volume

available for expansion

of the propellant gases

increases, the inner, faster-burning core provides a greater level 

of gas to maintain work against the projectile for improved performance over that achievable with a uniformly-burning material. In practice, with energetic materials currently available, realization of this concept requires charge designs for which aspect

ratios (length/diameter) are an order of magnitude less than in

conventional charges and the individual layers are nominally 2-3

mm thick. This makes the mechanical properties requirements

much more stringent than for colayered propellants.

High Nitrogen Compounds

High nitrogen compounds, including azo-tetrazolates,

dinitramide salts, tetrazine derivatives, amino-azo-furazans,

guanidine salts and diazido-nitrazapentane, have been investigated as burning rate modifiers for energetic formulations. Formulations using high nitrogen compounds have increased the

burning rate differential to 3:1 between inner and outer colayered formulations required for performance improvements by

chemical progressivity. Additionally, these formulations result

in lower gas temperatures during expansion into high flow areas

and increased ratio of nitrogen to carbon monoxide in the combustion products, compared to conventional propellants. Thus,

wear and erosivity is reduced, increasing gun barrel lifetimes by

reducing the dissociation of carbon monoxide and subsequent

adsorption/absorption of carbon into the steel barrel [1].

New Energetic Binder Components

Energetic thermoplastic elastomers (ETPEs) are being considered for a wide range of applications, including binders 

for large caliber gun propellants. In addition to the fact that

they can be processed without the use of solvents that pose

health problems, they also offer potential performance

improvements in weapon systems. The oxetane chemistry has

been the basis for the polymer backbone, to which energetic

pendant groups have

been attached, including nitro, nitrate ester,

nitramine, and in particular, the azide

group. The ETPEs

enable compositions

with different energetic crystals to be

readily processed into

a stable layered geometry with good adhesion and without

problems associated

with plasticized propellants, such as diffusion between layers of

different compositions, and oxidizer

migration to and crystallization on the outer

surface. The azidoETPE polymers are of

particular interest because of potential for high burning rates afforded by the azide

group, and also the higher nitrogen content has been shown to

help reduce the adverse effects of gun erosion.

Plasma Ignition Technologies 

Electrothermal-chemical (ETC) and electrothermal ignition

(ETI) gun technology is an advanced gun propulsion concept

that utilizes both chemical and electrical energy for initiation

of high-energy, high-loading density propellants to provide

increased performance, lethality, and range. ETC gun propulsion technology utilizes electrical energy to form a hightemperature, high-energy plasma that augments the control

and release of chemical energy stored in advanced highperformance propellants, in order to achieve significant performance enhancements over existing conventional guns.

ETC technology offers many advantages over conventional

gun propulsion including:

• An ability to tailor the pressure (thrust) of the propulsion

gases of the chemical reaction through the electrically generated superheated plasma and propellant gases, resulting in

increased projectile range or reduced acceleration-loading on

the projectiles.

Figure 2. Advanced Gun Propellant Formulations with Energetic

Nanomaterial Ingredients.

Nano-Energetic Propellant Formulations

Nano-Al Rods C-Tubes Nano-Boron Nano-Al
The AMPTIAC Quarterly, Volume 8, Number 4 87

• An extremely reproducible ignition, providing precise and

predictable muzzle velocities and gun tube dynamics, culminating in increased ordnance on target and less ordnance

required to achieve a given hit probability, and gun recoil

mitigation.

Nanoenergetic Materials

Energetic nanomaterials offer the potential of extremely high

heat release rates, extraordinary combustion efficiency, tailored

burning rate, and reduced sensitivity. However, exploiting these

possibilities requires an understanding of: (a) properties of 

the individual nanoscale material, (b) the interaction of the

nanomaterial with the matrix; (c) the interface behavior of 

the nanomaterial and the matrix; (d) energy release and dynamics of combustion and initiation processes on such short length

scales (e) high-rate synthesis and practical scale-up of nanomaterials. Nanoscale energetic materials are currently being

exploited to improve

the combustion efficiency of advanced gun

propellants, Figure 2.

Nanometals

The primary nanometals being considered 

for energetic material

applications are aluminum and boron. 

Aluminum has long

been an important burn

rate accelerator for 

rocket propellants, especially in the nanoparticle form. The hope is

that burning rate promotion obtained at

modest pressures in

rocket propellants will

be realized for the high

pressure regime of gun

propellants. An oxide

coating naturally forms

on aluminum which detracts the energy available to the system.

Ultra-high resolution microscopy techniques have enabled the

imaging of an oxide surface 2.5 nm thick, mainly amorphous,

but with crystalline layers which appear to exfoliate[2,3].

Prompt gamma neutron activation analysis has revealed

greater levels of hydrogen and water present in nanoaluminum than for flake aluminum, which could enable

porosity. Additional elements, which may also modify the initiation and energy release of aluminum, have been detected in

nano-aluminum by X-ray Photoelectron Spectroscopy. In fact,

since manufacture of nano-aluminum relies on recrystallization and quenching of aluminum from the high temperature

plasma condition, doping of the bulk aluminum and/or oxide

surface offers a tool for tailoring the atomic scale structure of

nanometals.

Boron hydride compounds demonstrated great potential as

burning rate accelerators, but spontaneous ignition of these

materials rendered them too hazardous for practical application. Recently, ARL produced the ability to synthesize boronbased nanoparticles [4]. Future efforts will address coating particles of boron with other energetic materials which offers

promise for taking advantage of the high heat of combustion

and potential for burning rate promotion of nanoboron.

Extended Carbon Structures

Extended carbon structures, such as carbon nanotubes (CNTs)

are being investigated for application to controlled performance

(through burning rate modification and the increased energy of

strained structures), and improved insensitivity (by encapsulation to control particle size and to buffer the effects of accidentally applied stimuli). The structure of CNTs gives them unique

properties, including high thermal and electrical conductivity,

and a very high aspect ratio, since their diameters are nanoscale while their lengths

can be micro-scale.

Their high conductivities and aspect ratio

make them attractive

candidates for serving 

as a type of “mini-fuze”

distributed throughout

energetic materials,

yielding the potential for

burning rate and combustion tailoring with

very little parasitic mass. 

Through the use of

carbon nanotubes it

may also be feasible to

enhance the specificity

of a propellant formulation to initiation due to

the high electron density and conductance

localized on the nanotube walls. Moreover,

because of their unique

structure, they may be

used for confining energetic molecules in a nano-matrix with a

positive effect on sensitivity properties.

Nano-Crystalline Energetic Materials 

Anti-solvent recrystallization techniques, in both the liquid and

supercritical phases, as well as rapid expansion of supercritical

solutions, are being used for preparing nanocrystals of energetic

oxidizers. Ultimately the goal is to prepare ultrafine particles

with tunable particle size and morphology as well as a uniform

size distribution. Crystals with fewer voids and uniform morphology are expected to yield decreased sensitivity results

through the reduction of sites for possible hot spot formation

that can lead to energetic material initiation. Nanocrystals of

energetic compounds including, but not limited to

cyclotrimetylenetrinitramine (RDX) and CL20 have been prepared and characterized [5]. Although optimization of process-

(DEGDN – Diethylene Glycol Dinitrate, NG – Nitroglycerin)

Figure 3. The First Molecular Model of JA2 Advanced Gun Propellant.

DEGDN

NC3

NC2

JA2 Propellant Simulation

NG
88 The AMPTIAC Quarterly, Volume 8, Number 4

ing variables of the various techniques is ongoing, preliminary

characterization of the products generally show fewer irregularities and lower void content.

Smart Design of Energetic Materials Using 

Theoretical Chemistry

An accurate and reliable predictive capability can provide the

information and insight needed for the intelligent design of

energetic materials. The refinement and implementation of key

computational chemistry methods are being used in a modelbased design process for new energetic materials to achieve a

process for atomistic model-based screening of notional materials. Included are methods that involve quantum mechanical

predictions of properties of isolated and condensed phase

explosives that are related to their performance and vulnerability. Other methods involve the utilization of intermolecular

interaction potential energy functions that can be used in

molecular simulation to explore the response of a material to

initiation events. The methods and software are being developed within the Army Research Laboratory mission program

and in conjunction with the DOD HPC Modernization Common High Performance Computing Scalable Software Initiative to provide an automatic and seamless set of procedures for

the simulation and screening of potential energetic materials.

In addition, molecular models are being developed to predict

chemical and physical properties of propellant formulations

such as JA2 used in 120 mm tank ammunition, Figure 3.

Quantum Mechanical Predictions of Properties of Notional

Materials Associated with Performance or Sensitivity

Computational tools have been developed that are based on

quantum mechanical calculations that describe relationships

between the quantum mechanical properties of an isolated

molecule and its behavior on the macroscale [6-8]. The predictive methods all use quantum mechanical predictions of the

electrostatic potential that surrounds an isolated molecule. The

first two computational tools that were developed have reasonably predicted Heats of Formation [6] and Detonation [7] for

a large variety of CHNO explosives. The most recent application of quantum mechanical predictions of isolated molecules

has shown that the electrostatic potentials for surfaces of equal

electron densities surrounding CHNO explosive molecules are

useful guides in assessing the degree of sensitivity of a CHNO

explosive [8].

Crystal Structure/Density Prediction Using Molecular Packing

The property of solid-state density, required to assess accurately the ideal performance of gun propellants in current interior

ballistics calculations, is not obtained from computer calculations but rather from known experimental values. The reliance

on external sources for something as important as density is, of

course, an unacceptable situation for a practical and widely

applicable modeling system. A procedure for the prediction of

possible crystal structures for an unknown compound has

been developed [9], which accounts for factors such as the

structure and conformation of a molecule, probable crystal

packing arrangements and packing efficiency. The so-called

“model-MOLPAK-WMIN” procedure consists of three steps:

(1) construction of a reasonable three-dimensional model for

the compound of interest (the search probe) followed by ab

initio quantum mechanical geometry optimization; (2) determination of a number of possible crystal structures for the

search probe (MOLPAK program); (3) refinement of the unit

cell parameters (WMIN program[10]), search probe orientaFigure 4. Theoretical Chemistry Predictions of Novel Energetic Molecular Properties.

Modeling Predictions of Notional Energetic Molecules

Tetradecanitrobicubans

Heat of Formation (solid): 113.1 kcal/mol

Heat of Detonation: 1.41 (kcal/g)

h60%: 9 cm

Density of low-energy structure: 1.77 g/cc

Heat of Formation (solid): 242 kcal/mol

Heat of Detonation: 1.81 (kcal/g)

h60%: 68 cm

Density of low-energy structure: 1.81 g/cc
The AMPTIAC Quarterly, Volume 8, Number 4 89

tion and position by lattice energy minimization for the best

of the crystal structures derived in Step 2, using a model function to describe interatomic interactions. The model being

employed has been shown to reproduce the crystallographic

parameters of over 80 crystalline systems, whose molecules

contain functional groups common to explosives [11]. The

suite of molecular simulation tools are now being employed to

a priori predict properties on notional (new) candidate energetic materials, Figure 4.

SUMMARY

Novel energetic materials hold the promise of providing the following payoffs: (1) mission-enabling lethality at range by

enhanced lethality and effectiveness and (2) crew survivability

under ambush for the full range of Future Force weapons. The

increased energy and efficiency of new energetic materials concepts will enable increased lethality through additional propulsion energy or impulse on the target. Alternatively, the same

amount of energy as delivered by existing systems could be

delivered to the target using less energetic material or a multipurpose energetic material, thus minimizing logistics burdens. 

Decreased sensitivity of energetic materials will significantly reduce platform vulnerability. By managing the energy

release of specific systems, it will be possible to maximize ballistic efficiency in advanced gun systems while also increasing

the performance of compact rockets/missiles. In addition, it

may be possible to minimize collateral damage with the use of

powerful precision strike weapons against hard targets or targets surrounded by noncombatants, and also maximize effectiveness against soft yet distributed targets by spreading

impulse and heat over time and distance. Finally, it seems reasonable that these new energetic materials may enable novel

and efficient methods for eliminating incoming threat munitions, or they could be utilized as multi-purpose energetics

(e.g. to provide thrust and/or detonate on target).

REFERENCES

[1] C. Leveritt, C. Walsh, P. Conroy, R. Yetter, Advanced, Low

Erosivity, High-Nitrogen Gun Propellants; ARL-TR-xxx; US

Army Research Laboratory: Aberdeen Proving Ground, MD,

(in press)

[2] A.L, Ramaswamy, M.A. O’Keefe, S.F. Trevino and P.J.

Kaste, Morphology and Degradation of Nanoaluminum, Proceedings of the 32nd JANNAF PDCS Meeting, Seattle WA,

26-30 July 2004

[3] A.L. Ramaswamy, P. Kaste, S.F. Trevino, Micro-vision of 

the Physio-Chemical Phenomena Occurring in Nanoparticles of

Aluminum, Journal of Energetic Materials, Vol. 22, No. 1, pp.

1-24, January-March 2004

[4] B. Homan, Plasma Generation of Nanoboron for Nanoenergetic Applications, Proceedings of the 32nd JANNAF PDCS

Meeting, Seattle WA, 26-30 July, 2004

[5] J.B. Morris, P.J. Kaste, S.M. Piraino, and B.E. Homan,

Supercritical Fluid Processing of Nano-RDX, Proceedings of the

32nd JANNAF PDCS Meeting, Seattle WA, 26-30 July, 2004

[6] B.M. Rice, S.V. Pai, and J. Hare, Predicting Heats of 

Formation of Energetic Materials Using Quantum Mechanical

Calculations, Combustion and Flame, 118, 445 (1999).

[7] B.M. Rice and J. Hare, Predicting Heats of Detonation

Using Quantum Mechanical Calculations, Thermochemica Acta,

384 (2002)

[8] B.M. Rice and J. Hare, A Quantum Mechanical Investigation of the Relation between Impact Sensitivity and the Charge

Distribution in Energetic Molecules, Journal of Physical Chemistry A, 106, 1770 (2002)

[9] J.R. Holden, Z. Du, and H.L. Ammon, Prediction of 

Possible Crystal Structures for C-Containing, H-Containing, NContaining, O-Containing and F-Containing Organic Compounds, Journal of Computational Chemistry, 14, 422 (1993)

[10] W.R. Busing, WMIN, A Computer Program to Model Molecules and Crystals in Terms of Potential Energy Functions, Report

ORNL-5747, Oak Ridge National Laboratory, Oak Ridge,TN,

1981

[11] D.C. Sorescu, B.M. Rice, and D.L. Thompson, Intermolecular Potential for the Hexahydro-1,3,5-trinitro-1,3,5-s-triazine

Crystal (RDX): A Crystal Packing, Monte Carlo, and Molecular

Dynamics Study, Journal of Physical Chemistry A, 103, 989

(1999)

Dr. Pamela Kaste is a research chemist in the Ballistic and Weapons Concepts Division of the US Army Research

Laboratory. Her main area of research has been Energetic Materials, but her analytical work has spanned many

topics pertinent to soldier and weapon systems. She earned her BS in biochemistry from Pennsylvania State University, and her PhD in Analytical Chemistry from Ohio University.

Dr. Betsy Rice is an ARL Fellow in the Propulsion Science Branch, Weapons and Materials Research Directorate of

the Army Research Laboratory. She performs and oversees research to determine microscopic details of the physical and chemical processes of materials of interest to the Army. These include energetic materials, chemical agents,

and materials related to armor/armaments. Dr. Rice also develops computational screening tools based on theoretical chemistry methods that will predict properties associated with performance and sensitivity for notional energetic materials. Dr. Rice began her tenure with the Army in 1989 as a National Research Council Postdoctoral Fellow. She received her BS in Chemistry from Cameron University (OK) and her PhD in Chemistry from Oklahoma

State University.

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Not

Available
NAMIS Focus Areas:

Conferences And Workshops

This area contains modules on conferences and workshops sponsored by 

organizations such as the DOD, DOE, and NASA. Topic areas include high 

temperature polymers, aircraft structures, high temperature composites, and 

electromagnetic window materials.

Material Property Databases

This area contains specialized databases. The Infrared Materials Database is 

currently available.

Virtual Libraries

This area features a variety of informational libraries containing electronic 

technical reports addressing research results and lessons learned. Information is

currently offered on thermal protection systems, cryogenic tanks, advanced 

turbine engine development, and the National Aerospace Plane (NASP) initiative. 

http://namis.alionscience.com
The AMPTIAC Quarterly, Volume 8, Number 4 91

INTRODUCTION

The increasing complexity and mission requirements of US

Army materiel systems, over a range of platforms, require a corresponding increase in the efficiency with which these systems

utilize their mass and volume. For example, individual soldiers

are required to wear an array of armor, sensors, communication

equipment, and power sources. Limits on the total load that an

individual soldier can carry, directly limits the mass of these

subsystems. This constraint incurs measurable penalties on 

system efficacy, such as the ballistic resistance of the armor or

the range and operating time of the communication system. 

Ground vehicles currently under development are required

to maintain survivability and lethality while reducing total 

system weight. Achieving this goal requires efficient implementation of all of the vehicle’s subsystems, including armor, power

systems, sensing, and communication. Smart munitions are

designed to sense targets, adjust trajectory, and communicate

with remote control interfaces. These additional subcomponents must be incorporated into the munition in a way that

does not significantly degrade payload mass or volume.

Conventional design approaches address system performance

issues by maximizing individual subcomponent efficiencies

through the use of advanced materials or new performance

technologies. A different approach is to create materials which

have the capability to perform more than one function simultaneously. This article discusses a number of promising multifunctional material concepts including structural batteries, fuel

cells, and capacitors, as well as data and power wiring, and

antennas.

DESIGNING FOR MULTIFUNCTIONALITY

While various definitions and interpretations of “multifunctionality” have been proposed [1-3], here we define a multifunctional material as one which individual material elements

are simultaneously participating in distinct, beneficial physical

processes. As a simple example, consider high tension power

lines. These cables are required to both support their weight

across a large span while simultaneously transporting electrons. Conventional designs utilize aluminum conductors

wrapped around a steel core. The relatively high resistivity 

of the steel core limits its ability to conduct electricity, so it

primarily serves as structural support. Newer designs utilize

metal matrix composite cores, which offer higher specific conductivity and specific strength than steel cores [4]. Because 

this novel core material is providing significant structural and

electrical functions, the overall system efficiency is improved

and cabling weight is reduced considerably.

For US Army applications, subsystem functionalities include

structural support, ballistic protection, energy storage, power

generation, power and data transmission, and communication.

To utilize multifunctional design to reduce system mass, the

heaviest subsystems must be addressed first. Over a range of

platforms, such as the soldier and vehicle applications cited

above, the most burdensome components consistently include

structure, armor, and energy-power components. Multifunctional materials that combine structure and armor functions, in

fact, have already demonstrated significant weight savings (refer

to the article “Protecting the Future Force: Advanced Materials

and Analysis Enable Robust Composite Armor” that appears in

this issue). We believe that similar system-level performance

enhancements are possible by combining structure and armor

functionalities with power and energy functions.

Consider a future ground vehicle with a hybrid power system. The vehicle structure consists of 2000 kg of polymer composite material. The hybrid power system, with a combined

output of 750 kW (1000 hp), includes 750 kg of batteries. We

define a structural mass efficiency, σs, to represent some structural property (e.g. stiffness or strength) relative to the conventional polymer composite material, for which σs = 1. Similarly,

the conventional battery material is described by an energy

mass efficiency factor, or energy density, of σe = 1. In the nominal design, the battery is non-structural (σs

batt = 0) and the

structure has no energy density (σe

struct = 0). If instead the battery material is allowed to contribute structurally to the overall

Eric D. Wetzel

Weapons and Materials Research Directorate

US Army Research Laboratory

Aberdeen Proving Ground, MD

Multifunctional and Special Function Materials Section IV
system, the total system mass is governed by the relation

system mass = 2000 kg + ( 1 - σs

batt)·(750 kg / σebatt) (1) 

where we assume that σs

struct = 1 and σestruct = 0. Figure 1 shows

the resulting system mass for various structural and energy efficiencies. In the nominal design (σs

batt = 0, σebatt = 1), total system mass is 2750 kg. If the battery has full structural and energy performance (σs

batt = σebatt = 1), total system mass is reduced

to 2000 kg, since 750 kg of structure can be removed and

replaced by the 750 kg of structural battery. The performance

gains for this design are unrealistic, since they require the synthesis of a “perfect” structural battery. However, reasonable performance gains are possible for more compromised systems.

For example, 250 kg of system mass can be eliminated for

structural batteries with σe

batt = 0.8 and σsbatt = 0.47, or σebatt =

0.5 and σs

batt = 0.67. Note that, in these examples, the performance efficiencies of the structural battery fall significantly below

those of the monofunctional materials. However, beneficial system-level mass savings are possible because the structural battery material elements are performing multiple functions

simultaneously.

MULTIFUNCTIONAL ENERGY AND POWER STRUCTURES

Three potential multifunctional energy and power structures

are currently under consideration: structural batteries, structural fuel cells, and structural capacitors.

Structural Batteries

As outlined in the Introduction, structural batteries could find

application in ground vehicles or soldier systems. For example,

in a ground vehicle, panels of structural batteries could be integrally fastened behind structural armor plates, providing

enhanced stiffness and penetration resistance for the structural

armor. For soldier applications, it may be possible to replace the

conventional polymer composite used for helmet construction

with a composite battery with both ballistic protection and

power storage capabilities. 

Batteries store energy and produce power through an electrochemical reaction. The electrochemical half-reactions take

place at the electrodes, which are bridged by an electrolyte that

conducts ions but not electrons. The reagent materials contained in the electrodes determine the maximum voltage of

the cell. The speed at which ions travel through the electrolyte impacts the current of the cell. Polymer lithium ion

(PLI) battery chemistries, utilizing lithium ion chemistry and

polymer gel electrolytes, are one of the highest energy density

batteries commercially available today.

Efforts are underway to produce structural PLI batteries

based on the design shown in Figure 2a. The battery consists

of a metal mesh cathode doped with a lithium donor salt, a

carbon fiber fabric anode, a glass fabric separator layer, and a

structural polymer electrolyte. The metal and carbon fiber

electrodes both carry load and conduct electrons. The glass

fabric separator layer provides structural support and acts to

ensure electrical isolation of the anode and cathode layers. The

structural electrolyte both conducts ions and provides load

transfer between the reinforcement phases.

The main barrier to structural battery development is formulation of a structural electrolyte polymer. Typical routes for

improving polymer structural properties, such as increasing

crosslink density, lead directly to decreases in ion conductivity.

However, through careful design, acceptable compromises in

properties may be achievable. We have chosen to focus our

study on resins that include oligo(oxyethylene) units owing to

the known ion conductive properties of poly(ethylene oxide),

PEO, and the ease with which lithium salts may be dissolved

into PEO oligomers. To balance mechanical and electrochemical properties, partially crosslinked polymer electrolyte matrices

that combine monofunctional and difunctional resin mono92 The AMPTIAC Quarterly, Volume 8, Number 4

Figure 1. System Masses for Designs Utilizing Structural Batteries

with Various Structural Efficiencies (σs) and Energy Densities (σe).

Figure 2. a) Schematic of a Structural Battery Composite, and 

b) Photograph of Structural Electrolyte Polymer and a 

Structural Battery Composite.

a)

b)

Polymer 

Electrolyte

Metal Mesh 

Current Collector

(cathode)

Glass Fabric

Discharge Charge

Carbon Fabric (Anode)

Li+ Source

Li+

Energy Density: σe

batt

0 0.2 0.4 0.6 0.8 1

Structural Mass Efficiency, σs

batt

System Weight = 2500 kg

System Mass (kg)

σe

batt = 0.5

σe

batt = 0.8

σe

batt = 1.0

3500

3000

2500

2000
The AMPTIAC Quarterly, Volume 8, Number 4 93

mers have been synthesized, as well as interpenetrating networks of difunctional resins and linear PEO. To further

improve mechanical properties of the electrolyte, we are investigating the addition of sub-micron fillers such as colloidal silica and alumina whiskers. Some studies indicate that such reinforcing fillers may also enhance ion conductivity. Figure 2b

shows a demonstration (non-functional) battery composite fabricated from one of these structural electrolyte polymers.

Processing and packaging of such structural batteries also pose

challenges. Many polymer electrolytes are extremely sensitive to

moisture. This restriction requires careful handling of fiber preforms and resins during processing, and development of integral

barrier layers to protect the electrolyte during its lifetime.

Structural Fuel Cells

Similar to the structural battery concept, a structural fuel cell

could find use in a ground vehicle power system while simultaneously providing additional rigidity to armor and vehicle

structures. Another concept would be to utilize a structural fuel

cell within the wing of a powered unmanned aerial vehicle

(UAV) [1].

Proton exchange membrane (PEM) fuel cells generate 

electricity through the controlled reaction of hydrogen and

oxygen. The hydrogen source, such as hydrogen gas or an

aqueous dilution of methanol, is separated from the oxygen

source, typically air, by a membrane electrode assembly

(MEA). The MEA consists of a thin PEM combined with conductive and catalytic electrode surface layers. The PEM allows

for the selective transport of hydrogen ions to the oxygen

source, which generates an electrical potential across the electroded surfaces. Commercial fuel cells typically consist of a

series-connected stack of individual fuel cells. Each fuel cell

contains an MEA assembly sandwiched between permeable

layers, such as machined carbon plates, which allow for the circulation of fuel and air sources.

Figure 3 shows a structural fuel cell prototype. The 

sandwich-structure composite consists of thin carbon fiber

composite skins with a fuel cell core. The core consists of a

conventional MEA between layers of open-cell aluminum

foam. The foam core provides the shear and compression

properties necessary to achieve high sandwich stiffness, while

simultaneously allowing for the circulation of air and hydrogen sources to the MEA. A critical shortcoming of this design

is the low shear strength of the MEA, which greatly limits the

overall bending stiffness of the structure. To overcome this

limitation, novel structural MEAs and core architectures are

under development. The foam pore size, density, and layer

thickness must also be optimized to reconcile mechanical

properties with air and methanol flow permeability.

Structural Capacitors

Army systems such as electromagnetic armor or electromagnetic rail guns require banks of capacitors to provide

power conditioning or rapid electrical discharge. Structural

capacitors could enable a reduction in system mass by storing

electrostatic potential while carrying vehicle static loads.

Capacitors consist of dielectric layers, such as polymers and

ceramics, with integral electroded surfaces. A simple structural

capacitor can be constructed by metalizing a glass fabricreinforced polymer composite, as shown in Figure 4. In this

Figure 4. a) Schematic and b) Photograph of a Structural

Capacitor Composite.

Figure 3. a) Schematic, b) Top View, and c) Cross-Sectional 

View of a Structural Fuel Cell. d) Structural Fuel Cell Undergoing

Bending Test.

a)

b)

c)

d)

a)

b)

Film Adhesive

Composite Skins

Metal Foam

Polycarbonate

Dielectric

Sputtered Al

Electrode

Glass Fabric

MEA
example, the electrodes consist of 30 nm thick sputtered aluminum surface coatings, while polycarbonate is used for the

composite matrix. The energy density of such a structure is

fixed by the dielectric constant and dielectric strength of the

polymer composite. The capacitance of the structure is governed by the number and thickness of the dielectric layers.

The principal hurdle in composite capacitor development is

maintaining high dielectric strength in the polymer composite.

Composite fabrication must ensure low void, moisture, and

inclusion content to prevent premature dielectric breakdown of

the dielectric layer. Some flaw tolerance is enabled by the use of

thin “self-healing” aluminized electrodes. Arcing from dielectric

breakdown causes the aluminized coating to sublimate in the

vicinity of the short, insulating the breakdown region from the

rest of the electrode area. 

A second challenge is achieving sufficiently high levels of

capacitance. In commercial capacitors, high capacitance is

achieved by using thin (~1-100 μm) dielectric layers, significantly thinner than typical polymer composite ply thicknesses.

This restriction does not limit overall composite electrostatic

energy density, but will influence discharge times and circuit

conditioning characteristics.

MULTIFUNCTIONAL COMMUNICATION 

AND BUS STRUCTURES

Integrating communication components, data busses, and

information busses into structural materials are unlikely to

result in significant weight savings, due to the relatively low

weight penalty associated with these systems in typical US

Army platforms such as ground vehicles. However, integration

of these structures can provide secondary benefits, such as

increased durability, simplified manufacturing, redundancy

(for improved reliability and damage tolerance), and increased

coverage.

Data Wiring

Data wiring consists of low power analog and digital signals

transmitted within a system, such as a ground vehicle or

rotorcraft. Optical fibers provide the highest information

density, but are more susceptible to damage and harder to

connect than metal wiring. To overcome these limitations,

optical fibers can be directly integrated into the composite

structure. For example, optical fibers can be directly woven

into conventional glass fabrics, and processed like conventional composites [5]. 

Embedded optical fibers are more durable than traditionally

clad and hung optical fibers. Furthermore, due to their small

size and mass, these optical fibers can be pervasively integrated

into the vehicle’s primary structure. This strategy provides a

high level of communication redundancy, and eliminates the

need for structural cut-outs or channels for passage of cabling.

Direct physical connection to these embedded optical fibers is

difficult, and introduces potential flaw initiation sites. We are

instead pursuing embedded line-of-sight optical transceivers,

so that non-invasive, non-contact links can be established

between the integrated data network and the external sensing

and control elements. One such device is shown in Figure 5.

A dual photovoltaic element is directly coupled to a light

emitting diode (LED). Light incident on the photovoltaic,

such an external LED or laser source, powers the LED which

then couples into an embedded optical fiber. This particular

prototype device is around 1 cm in size, but the package can

be significantly reduced by using smaller integrated elements.

Power Wiring

Power wiring often presents a more serious system-level mass

penalty, as compared with data wiring, due to the large areal

cross-sections required to transport power at high current and

voltage levels. It may be possible to directly embed metal elements, such as aluminum ribbons, directly into composite

structures. For some weight-critical structures, such as satellites or rotorcraft, these conductors could be engineered to act

as structural elements. This approach is truly multifunctional,

as the electrical conductors also carry loads, while the structural polymer composite provides electrical insulation between

metal elements. 

As with data wiring, special techniques need to be developed

to enable efficient and safe connectorization* to the embedded

metal conductors. Processing will also require special engineering, as the differences in thermal expansion between a polymer

composite and embedded metal element could introduce significant internal residual stresses during processing.

Antennas

For ground vehicles, antennas typically account for only a

small fraction of total system mass. However, integrating

antennas into structural materials could provide secondary

performance benefits. For example, embedding antennas provides more rugged packaging than traditional exposed antennas. If antenna elements can be integrated transparently into

the manufacturing and design process, these elements could be

ubiquitously positioned over the entire surface of the vehicle.

This approach provides full coverage and line-of-sight capabilities, as well as a high level of system redundancy.

94 The AMPTIAC Quarterly, Volume 8, Number 4

Figure 5. a) Schematic of Integrated Optical Communication 

Bus Concept. b) Photograph of Prototype Self-Powered Dual

Photovoltaic Optical Transceiver.

b)

a)

Photodetector

Photodetector / Photovoltaic

LED

LED

Structure

Embedded Optical Fiber
The AMPTIAC Quarterly, Volume 8, Number 4 95

A potential structural antenna design appears in another 

article published in this issue: “Manufacturing a More Affordable Army Through Low Cost Composite Processing.” Designing such integrated antennas introduces many complexities, as

the high frequency dielectric properties of the structural and

ballistic materials must be compatible with the antenna design.

These radiating elements also must be reconciled with shielding and signature layers in the structure. Connection of the

antenna to the system wiring also must be performed without

degrading the structural or ballistic properties of the surrounding materials.

CONCLUSIONS

Multifunctional structural materials offer the potential for 

significant savings in system-level mass and volume, or performance benefits such as improved durability or redundancy.

This design approach is in its infancy, and faces significant

design and material synthesis challenges. Disparate material

properties, such as structural and electromagnetic properties,

need to be engineered and optimized simultaneously. These

technical challenges require the close coordination of interdisciplinary teams.

Beyond multifunctional material design, manufacturing 

and repair also present difficult barriers to implementation.

Fabrication approaches must allow for incorporation of many

different material types and form factors, without introducing

prohibitive cost or complexity. Repair of such structures could

be difficult or impossible, since many critical functional elements are likely to be permanently embedded within structural materials. For some applications, these concerns could be

addressed through modular design. For example, structural

batteries or fuel cells could be mechanically fastened or

reversibly bonded to other structural elements. Other sustainability strategies are also possible, such as redundant elements

or self-healing systems. In some cases, single-use designs (such

as munitions or disposable UAVs) are acceptable.

ACKNOWLEDGEMENTS

This review summarizes ongoing Army Research Laboratory

efforts led by Jim Snyder, Rob Carter, Joe South, Kirk Tackitt,

and Keith Goossen (University of Delaware), in collaboration

with Shawn Walsh, Rod Don, Jim Hirvonen, Derek Demaree,

Jim Campbell, Jim Catalano, Eric Adler, Steve Weiss, and

Ozlem Kilic.

NOTES & REFERENCES

* Connectorization is a technical term specifically pertaining to

connecting data and power components. Within the field, the

term is customary and preferred to connected.

[1] L. Christodoulou and J.D. Venables. Multifunctional 

material systems: The first generation. JOM. Vol. 55 No.12.

December 2003, pp. 39-45

[2] J.P. Thomas and M.A. Qidwai. Mechanical design and performance of composite multifunctional materials. Acta Materialia.

Vol. 52. 2004, pp. 2155–2164

[3] Materials Research to Meet 21st Century Defense Needs.

National Materials Advisory Board, National Research Council. The National Academies Press: Washington DC. 2003,

pp. 27-54

[4] Power grid of the future. ORNL Review. Vol. 35 No. 2.

2002, pp. 24-27

[5] J. Gubbala, R. Caruso, D. Fecko, S. Yarlagadda, E.D. 

Wetzel, K.W. Goossen. An automated process for embedding

optical fibers in woven composites. Proceedings of 36th International SAMPE Technical Conference. San Diego CA. November 15-18, 2004 (to appear)

Dr. Eric Wetzel received his PhD in Mechanical and Industrial Engineering from the University of Illinois at UrbanaChampaign. At the Army Research Laboratory, he leads research efforts in multifunctional composite materials, novel

bonding methods, and body armor utilizing shear thickening fluids. In 2002, Dr. Wetzel received the Paul A. Siple

Award, the US Army’s highest recognition for excellence in scientific research.
96 The AMPTIAC Quarterly, Volume 8, Number 4

INTRODUCTION

The US Army employs a wide variety of equipment for tactical

applications. Notable items are tanks, trucks, missiles, aircraft,

artillery, and shelters. Less obvious equipment includes water

purification units, generators, and high mobility forklifts. This

tactical equipment is usually painted during the original manufacture and repainted as necessary at facilities ranging from

large-scale Army depots and small “touch up” operations to

unit level organizations. The same coatings systems, defined by

their military specifications, are used at all facilities under many

different environmental conditions. 

The coating systems used to paint Army equipment are highly engineered materials that are formulated to meet multiple

performance requirements. The selection of coating ingredients, formulation conditions, application methods, and curing

conditions can influence the final properties of the coating, see

Figure 1. Generally, Army coatings are formulated using polymer binders, a variety of solvents, pigments for tinting, extender pigments for control of gloss, and functional additives. In

this paper, we discuss recent research findings and product

developments that have led to the next generation coating systems for Army applications. 

CHEMICAL AGENT RESISTANT COATINGS

Chemical Agent Resistant Coating (CARC) systems represent

an important category of products that are researched, developed, and implemented by the Army. Finishes under this

umbrella resist penetration by chemical warfare agents and can

be readily decontaminated. This threat, identified in the early

1970’s, led to the development of the Army’s first generation

CARC (MIL-C-46168) in 1974[2]. In 1983, the Department

of Army required implementation of CARC systems for combat, combat support, tactical wheeled vehicles, aircraft, and

essential ground support equipment (i.e. tactical equipment)

beginning in Fiscal Year 1985. The Army Research Laboratory

leads the research and development of CARC systems and also

is the approving authority of CARC products for DOD.

The chemistry of the initial CARC finishes in the early

John A. Escarsega

Kes Chesonis

Dawn M. Crawford

Jeffrey L. Duncan

Pauline Smith

Weapons and Materials Research Directorate

US Army Research Laboratory

Aberdeen Proving Ground, MD

Figure 1. CARC Ingredients [1].

Resin

Pigment(s)

Extenders

Additives

Solvents

Important Factors

Chemistry, degree of cure, 

uniformity, cured resin structure,

impurities, UV absorption

UV absorption, surface chemistry,

particle size, crystal form, etc.

UV absorption, surface chemistry,

size, type, distribution

UV inhibitors, antioxidants, 

surfactants, adhesion promoters

Film carrier, flow properties, 

initial intercoat adhesion,

compatibility, and cure times

Tailored Coating

• Pigment-resin interactions

• Primer-topcoat interactions

• Application

• Defects and morphology

• Synergy exists! Non-linear

relationships between 

components exist!
The AMPTIAC Quarterly, Volume 8, Number 4 97

1970s and 1980s were alkyd enamels that were modified

depending on their application. Primers utilized heavy metal

pigments, in particular lead and hexavalent chromium and

inert iron oxides to arrest and prevent corrosion. CARC topcoats employed a variety of organic and inorganic pigments to mimic woodland or desert

surroundings; and silica and talc were used to

lower the gloss of the coatings. The first generation polyurethane based CARC topcoat

(MIL-C-46168), proved to be a tremendous

improvement over the enamel finish it

replaced (MIL-E-52798). However, while the

high pigment content and low resin volume

met the Army’s low gloss requirement, it did

so at the expense of long term durability, mar

resistance and flexibility. 

The Army’s current topcoats are based on

aliphatic polyurethanes that meet requirements of MIL-C-46168, MIL-C-53039 or

MIL-DTL-64159 military specifications [2, 3,

4]. These coatings provide excellent performance characteristics, such as exterior durability

and excellent chemical resistance. They also

withstand decontamination procedures and

provide camouflage properties in the visible and near infrared

regions of the spectrum.

When assessing the inherent balance of properties found in

the CARC coating system, the Army’s coatings research program began embracing three principles to guide and assist in

formulation, scale-up, and final implementation of new coating products to the field. The three primary principles are

Durability, Environmental Compliance, and Survivability, Figure 2. The approach has produced products that ensure the

best durability, meet or exceed current or proposed environmental and user safety laws, and meet survivability requirements for camouflage coatings. Survivability requirements

drive two military unique technical challenges: camouflage

that blends with a given background, while also providing

resistance to live chemical warfare agents.

Figure 2. Guiding Principles for CARC System [1].

Figure 3. Elimination of HAPS in CARC Primers is a High Priority.

The Army also utilizes coatings on munitions. Recent research has resulted in a universal ammunition

coating (UAC) with improved performance [1]. Prior to the development of this coating system, ammunition coatings were subject to premature and severe film failures, offered poor corrosion resistance,

were incompatible or reactive with energetic materials, and failed to meet National Emission Standards

for Hazardous Air Pollutants (NESHAPs). To improve coating performance, a new class of corrosioninhibiting pigments was incorporated into an alkyd polymer system consisting of durable fast-drying

chain stopped alkyd (drying oil modified polyester). 

In addition to meeting the requirements for substrate adhesion and long-term storage stability with

energetic materials, the UAC provides vastly improved corrosion resistance, eliminates the primer coats

on certain munitions applications, and is “a drop in replacement” for existing materials. After extensive

laboratory evaluations, the UAC was qualified on artillery and mortar projectiles at the Scranton Army

Ammunition Plant (AAP) and the Crane Army Ammunition Activity (AAA) munitions manufacturing

and maintenance sites. The benefit of this new coating to the Army is superior single-coat performance,

enhanced durability, environmental compliance and elimination of production rejects and reworks. The

UAC is being employed in the production of 120-mm and 155-mm projectiles at AAP and AAA.

Implementation of the UAC will allow these facilities to meet local environmental regulations during

the renovation of artillery projectiles. 

[1] P. Smith and K. Chesonis, Recent Advance in Ammunition Coatings. ACS Preprint Aug 2004 

Soldiers Loading a

Mortar Round.

AMMUNITION

COATINGS

Enivonmental Survivability

Durability
98 The AMPTIAC Quarterly, Volume 8, Number 4

A variety of environmental regulations and worker safety

issues has motivated our research to develop environmentally

compliant CARC coatings. For example, Federal and local regulations resulting from the Clean Air Act and its amendments

restrict the amount of volatile organic compounds (VOCs)

emitted during the application of protective coatings, and

Occupational Safety and Health Administration (OSHA) regulations on worker safety restrict exposure to many of the

materials used in their manufacture. To address these regulations, the coating has been reformulated to be lead and hexavalent chromate free, low in VOC content, and in many

instances free of hazardous air pollutants (HAPs), Figure 3.

This is significant since recent National Emission Standards

for Hazardous Air Pollutants (NESHAPS) from the Environmental Protection Agency (EPA) are working to restrict and

specifically regulate these materials.

From a historical perspective, the two main avenues to VOC

reduction in coatings are formulations with lower molecular

weight polymers and the use of waterborne, water-dispersible,

or water-reducible polymers. Reducing a polymer’s molecular

weight usually reduces its viscosity, and introduces the need for

solvents to control the system viscosity during application.

This is the traditional high solids solution to VOC problems.

The high solids versions of the CARC topcoats did not meet

VOC regulations in certain localities, and a new technology

was needed to develop a CARC to solve current and anticipated VOC problems. Alternatively, systems in which water can be used for

this viscosity control can greatly alleviate the need for solvents altogether.

Until recently, water-compatible coatings did not match the performance of

solvent based analogs, but recent

developments in polymer technology

have enabled the development of high

performance polyurethane systems

with excellent performance and chemical agent resistance.

The recent development by our

group of a water-reducible, two-component polyurethane CARC topcoat

has been a significant achievement.

This product employs water-dispersible hydroxy-functional polyesters

and water-dispersible polyisocyanates. Traditionally, the presence of water must be eliminated in non-aqueous two-component polyurethane formulations due to the unfavorable reaction with isocyanate. The reaction forms an unstable carbamic

acid, which quickly decomposes to generate carbon dioxide

and an amine (Reaction 1). The amine then reacts with further

isocyanate to yield the substituted urea (Reaction 2).

RNCO + H2O → [RNHCOOH] → CO2 ↑ + RNH2 (1)

RNH2 + RNCO → RNHCONHR (2)

This reaction may inhibit or adversely affect the stoichiometry and development of crosslinking that is crucial to the

integrity and performance typical of two-component

polyurethanes [5, 6]. Developments in waterborne polyurethane technology have enabled high performance coatings

to be formulated using water-dispersible polyisocyanates and

hydroxyl-functional polyurethane dispersions [7]. While

there is a competing reaction occurring with water, the 

kinetics, raw materials selection, and proper indexing of 

isocyanate (NCO) to hydroxyl (OH) groups can ensure that

sufficient crosslink density is established. Dynamic Mechanical Analysis, Fourier-transform infrared spectroscopy and 

desorption-gas chromatography/mass spectroscopy has shown

the role of indexing on final physical properties of these

polyurethane materials [8].

The research on water-dispersible urethanes has resulted in a

new CARC coating system [9] that will

replace the first generation MIL-C46168 CARC with the waterdispersible technology and one component solvent based technology. The

VOC of the regulated solvent is less

than 180 g/L (a 60% reduction) and

contains zero HAPs. At the same time

through careful selection of pigmentation, the survivability and durability of

this environmentally compliant coating

is outstanding.

Chemical agent resistance is provided by the aliphatic polyurethane binder

and the camouflage properties are provided by the appropriate selection of

tinting pigments for visual color and

near-infrared reflectance, plus extender

Figure 4. Army Vehicles Painted with the MIL-DTL-64159 CARC [1].

Figure 5. ARL Continues to Develop FieldReady Coatings with Improved Properties.
The AMPTIAC Quarterly, Volume 8, Number 4 99

pigments for gloss control. Camouflage requirements complicate development of Army coatings because of the need for

low gloss that leads to proportionally higher pigment to binder

ratios. Higher binder content in the formulation enhances

chemical agent resistance while high pigment content reduces

gloss. ARL has replaced the solvent borne polyester and polyisocyanate binder components of the current CARC with 

the water-dispersible system. At the same time, an improved

pigment package has been developed to reduce the problems

(such as marring and reduced flexibility) resulting from high

pigment content required for low gloss. The resulting coating

formulation survives decontamination and provides chemical

agent resistance. The use of novel pigmentation has improved

the low temperature flexibility, mar resistance, and weathering

durability of this coating.

The selection of binders and pigments also affects the degradation of CARC coatings [10]. Research has demonstrated

that replacing diatomaceous silica and talc with polymeric

based extender pigments enhances the durability of CARC 

systems. Alternate pigment materials such as a blend of urea

resin containing negligible quantity of free methlylol groups

have been explored. The primary particles with an average

grain diameter of 0.1-0.5 μm form agglomerates of approximately 4-5 μm. This results in a high pore volume and a steep

grain distribution, two important factors that form the precondition for excellent matting effect. As a result of the almost

ideal spherical form of the particles, the coating rheology

remains unaffected, opposed to the more needle shaped silica

particles. The other active flattening agents used are ones that

have a polyurethane composition with a medium particle size

of 18 μm. Most are spherical vesiculated type materials that

have enhanced matting properties and are extremely chemical

resistant as well. The combination of these materials provides

a very dynamic and active flattening package. Currently, MILDTL-64159, water-dispersible CARC using polymeric beads

is readily used by many weapon platforms in the DOD, as

shown in Figure 4, the Canadian Armed Forces, and for

preservation efforts in non-military applications.

CURRENT RESEARCH DIRECTIONS

Working throughout the DOD with Program Managers, the

acquisition community, end users, paint vendors, and raw

material suppliers, ARL continues to develop field ready coatings with improved properties (Figure 5). One current focus 

is developing formulations with minimal solar loading. 

These coatings are expected to exhibit slower degradation by

minimizing ultraviolet (UV) absorption. Also, reduced solar

loading will reduce equipment temperatures and lessen the

need for cooling of interior compartments. Low solar loading

coatings will provide tremendous enhancements to the field.

Additionally, we continue to work on the prevention and

early detection of corrosion to maintain readiness and minimize equipment life cycle costs. Our corrosion research and

expertise in the area of pretreatments, primers, and material

substrates have enabled advances to lessen the need for heavy

metals such as hexavalent chromium while enhancing 

durability and performance. Most recent, ARL in collaboration with paint suppliers has evaluated and identified viable

alternatives to DOD-P-15328, a wash primer high in VOC

content and containing hexavalent chromium [11].

SUMMARY

ARL is a leader in CARC materials technologies, developing

coating formulations to meet both performance requirements

and environmental regulations. In addition, today’s CARCs

function as camouflage and have increased environmental

degradation resistance. These newer CARC systems meet the

Army’s current design strategies of providing durability, survivability, and environmental compliance.

ACKNOWLEDGEMENTS

The Coatings and Corrosion Team of ARL would like to

thank and acknowledge our colleagues within the TankAutomotive and Armaments Command (TACOM), the 

Aviation and Missile Command (AMCOM), the General Services Administration (GSA), and the various Armament

Research, Development and Engineering Centers (ARDECs).

The team would also like to acknowledge the paint vendors,

raw material suppliers, and end users who collectively have

enabled and assisted our effort to provide durable and robust

products to the field.

REFERENCES

[1] J.A. Escarsega, Multifunctional Protective Coatings For

Weapon Systems: Chemical Agent Resistant Coatings (CARC)

Technical Exchange, TACOM Briefing, September 5, 2002,

(http://www.arl.army.mil/wmrd/coatings/Current/TECHNICALEX090502.ppt)

[2] US Department of Defense. Coatings Aliphatic Polyurethane,

Chemical Agent Resistant. MIL-C-46168, Amendment 3, May

1993

[3] US Department of Defense. Coatings Aliphatic Polyurethane,

Single Component, Chemical Agent Resistant. MIL-C-53039, 28,

November 1988

[4] US Department of Defense. Coatings Water Dispersible

Aliphatic Polyurethane, Chemical Agent Resistant. MIL-DTL64159, 30, January 2002

[5] G. Woods, The ICI Polyurethane Book. New York: John

Wiley, 1990 

[6] G. Oertel, Polyurethane Handbook. New York: Hanser, 1985

[7] P.B. Jacobs and P.C. Yu, Coatings Technology. Vol. 65, p. 45,

1993 

[8] J.A. Escarsega, D.M. Crawford, P.J. Kaste, Analysis and 

Performance Evaluations of Chemical Agent Resistant Coating 

Systems, ARL-TR-2545, July 2001 

[9] J.A. Escarsega and K. Chesonis, United States Patent,

5,569,410, Water Dispersible Low-Reflectance Chemical Resistance Coating Composition, November 25, 1997 

[10] W. Kosik, et al. Mechanism of Military Coatings Degradation, SERDP Pollution Prevention Project 1133, FY99-02 

[11] P. Smith, K. Chesonis, C. Miller, J.A. Escarsega, Replacement Alternatives to the Chromate Wash Primer DOD-P15328D, ARL-TR-3220, June 2004 
Dr. Dawn M. Crawford has served as a Research Materials Engineer in the Army for 20 years. Presently Dr. Crawford serves as the project leader of the Permselective Membranes program at ARL-APG in the Multifunctional Materials Branch, where she has been instrumental in developing a novel selectively permeable polymeric membrane for

protective clothing applications. Dr. Crawford is a co-inventor on three patents, has been awarded two Army R & D

Achievement awards and has authored numerous journal articles. In addition to her work in membranes, Dr. Crawford

has also made contributions to Army programs in the areas of elastomer and coatings research. Dr. Crawford holds

a BS in Materials Engineering from Virginia Tech and a PhD in Chemistry from Virginia Commonwealth University.

100 The AMPTIAC Quarterly, Volume 8, Number 4

Mr. John A. Escarsega is a research chemist and leader for the Coatings and Corrosion Team in the Materials Application Branch for the US Army Research Laboratory. He received his BS in chemistry from the University of Mary

Washington. He is the Commodity Manager for chemical agent resistant coatings (CARC) for the Department of

Defense for military tactical vehicles, aircraft, and support equipment. He has been active in coatings research for the

Army since 1981, and is the primary patent holder for the novel water dispersible coating, which is currently being

implemented on Army and Marine Corp assets. He is the author of over fifty publications. He is an active member of

the American Chemical Society as well as a member of the Federation for Coatings Technology. 

Mr. Kestutis Chesonis is in the Weapons and Materials Research Division at Aberdeen Proving Ground. He received

his BS in Chemistry from Johns Hopkins University and began his career in industrial coatings. He was involved in the

formulation, manufacture, and application of various mil-spec coatings. In 1986, he started working for the Army at

Fort Belvoir in the Organic Chemical Coatings Group. He has specialized in developing camouflage and ammunition coatings. Among the awards he has earned are The Commander’s Award for Technological Achievement, the

ARL Associated Achievement Award for Technology Transfer, the Cross Functional Teaming Award, and the Army R&D

Achievement Award for outstanding scientific and technical achievement.

Mr. Jeffrey L. Duncan is a materials engineer in the Coatings and Corrosion Team of the Materials Application Branch.

He holds a MS from Carnegie-Mellon University and has performed R & D in protective coatings for the US Army for

over 30 years. He is a principal investigator for the research, development and implementation of protective coatings

with environmental compliance and performance improvements within the chemical agent resistant coating system

used by the US Army on all tactical equipment, including topcoats and corrosion resistant epoxy primer systems. Over

that time, he has managed and/or participated in a number of Army, Tri-Service, and NATO task groups to develop,

test, and standardize CARC-related technologies. Mr. Duncan retired in the fall of this year.

Ms. Pauline M. Smith is a Research Chemist and a member of the Coatings Technology Research Team at ARL. Her

activities are primarily to formulate and design novel coatings for all types of Army equipment, with particular emphasis on tactical vehicles and ammunition. Her research has focused in four primary areas: Chemical Agent Resistant

Coatings (CARC); Corrosion Resistant Ammunition Coatings, Camouflage Coatings, and Pollution Prevention/VOCCompliant Coatings; all of which are being developed for the direct support of current Army assets and the ArmyAfter-Next. Ms. Smith is the author of numerous publications.

answers materials engineering questions

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The AMPTIAC Quarterly, Volume 8, Number 4 101

INTRODUCTION/BACKGROUND

Nanomaterials technology offers tremendous potential for

reducing weight and increasing performance of the materials

used in Army applications. While nanotechnology, and specifically nanomaterials research, are still nascent in their development, there are trends emerging and applications becoming

realized.

The nanomaterials technology discussed here and in the following article “Small Features Enable Big Results: Nanotechnology Research Uncovers New Multifunctional Materials for

Future Army Systems” is focused on synthesizing and processing materials that exhibit unique and often tailored properties

at the nanometer scale (1-100 nm). Characterizing, controlling

and utilizing these nanoscale properties in practical ways are

some of the challenges that scientists and engineers face in

developing nanotechnology to solve relevant problems for the

Army. It is a challenge for scientists, for example, to modify

materials at the nanoscale with great uniformity without using

complex, time-consuming methods such as nanolithography.

Ongoing nanomaterials research within the Army includes

the synthesis and assembly of new nanomaterial building

blocks, as well as the development of nanoscale characterization

and metrology tools that can probe the structure and response

of nanoengineered materials. Potential Army uses for nanomaterials can broadly be classified into structural and functional

applications. Inorganic and organic nanomaterials are being

explored in lightweight structural applications, and potentially

for personnel and vehicle ballistic protection concepts. The

ability to control the microstructure and response of materials

at the nanoscale can lead to new mechanisms for load bearing

and energy dissipation. As seen in the article on composite

armor in this issue of the AMPTIAC Quarterly one such effort

involving the application of nanotextured fiber coatings for

composites applications is described. Likewise, transparent

polymer nanocomposites are being explored for use in transparent armor and scratch-resistant transparent coatings.

Functional nanomaterials can improve performance of

existing applications or enable new uses or capabilities. These

two articles describe several research activities involved in

developing nanofunctional materials and understanding and

utilizing their unique properties. They further explain how

these properties may be exploited to address the needs for new

Army materials.

NANOFUNCTIONAL POLYMER MATERIALS

The fundamental units of organic materials are ideally suited

for the development of nanofunctional materials. Synthetic

chemists have developed numerous tools to create new

nanoscale materials from the “bottom-up.” Recently these tools

have been applied to create materials with unique and desired

characteristics and properties at the nanoscale. Nanofunctional

organic materials are of particular interest to the Army, with

specific examples described later in this article.

Introduction to Dendritic Polymers

In the field of polymer chemistry, the dendritic polymer 

architecture has been established as the fourth major class of

macromolecular topology. These materials have earned this

distinction based on a unique set of properties that are

observed in this class of polymers. [2, 3, 4]. Dendritic polymers can be described by the level of control of their structure.

Dendritic polymers are comprised of building blocks with

characteristic branching units. The synthesis and assembly of

these building blocks determines the type of dendritic polymer

Some nanotechnology applications have been briefly mentioned elsewhere in this Special Issue, but this article and the next, “Small 

Features Enable Big Results: Nanotechnology Research Uncovers New Multifunctional Materials for Future Army Systems”, focus solely

on the development of nanotechnology to support the Army’s Transformation. These articles provide updates and describe additional 

activities that are ongoing in the Army nanomaterials research that was first presented in the AMPTIAC Quarterly Special Issue on

Nanotechnology in 2002. [1] This article presents an introduction to the control and manipulation of the functionality of polymers 

at the nanoscale and the resulting applications for this technology. The next article describes various efforts involved in developing 

multifunctional nanomaterials and nanocomposites. We open with an introduction to nanotechnology and provide some background

information suitable for both articles that address the impact of these ongoing efforts to the Army Transformation. - Editor

Matthew Bratcher

Steven H. McKnight

Weapons and Materials Research Directorate

US Army Research Laboratory

Aberdeen Proving Ground, MD
102 The AMPTIAC Quarterly, Volume 8, Number 4

that is produced. Hyperbranched polymers (HBPs) have the

least controlled structure and consist of random branch points

and are usually synthesized in “one-pot” reactions. Figure 1

schematically shows a random hyperbranched polymer structure as a tree-like structure, as shown in Figure 1. Hyperbranched polymers are often of interest in chemistry and

materials engineering because they are easily synthesized and

can possess a number of functional groups depending on the

length and composition of the building blocks. The terminal

groups in a hyperbranched polymer (located at the chain ends)

are very important because to a large extent they determine the

characteristics including reactivity and properties of the hyperbranched polymer as a whole. 

Dendrimers and dendrons also possess a highly branched

structure, but dendrimer structures are very precisely controlled

resulting from the careful synthetic routes that are used to produce these materials. These polymers are precise core-shell

materials that have been intensely studied in recent years [2, 3,

4]. An elementary schematic representation of a dendrimer

illustrating its highly branched symmetrical structure around a

core is shown in Figure 2. Polyamidoamine (PAMAM) dendrimers developed by Tomalia have received a great degree of

attention and derive their precise structure and chemistry from

a highly controlled polymerization scheme [2, 3]. Unlike their

hyperbranched relatives, dendrimers can be synthesized to be

monodispersed, even at very large molecular weights. This 

feature makes dendrimers very attractive nanoscale building

blocks for materials scientists, chemists, and biologists.

While dendritic polymers have many properties that are

similar to the traditional linear, cross-linked, and branched

polymers, they possess certain properties that are significantly

different from these other conventional polymers. A significant advantage of these types of polymers is the large number

of terminal units (end points of polymer chains) available for

chemical modification and the controllable degree of branching within the polymer. Traditional linear polymers possess

very few branch points in the polymer backbone, and their

physical properties are derived largely from entanglements

between adjacent-polymer chains. Dendritic and hyperbranched materials, however, possess chains that have branches upon branches (analogous to a tree limb), and results in a

number of chain ends that scales with the degree of polymerization. Because of their branched nature, they form negligible chain entanglements. These features make dendritic polymers attractive candidates for a number of applications

ranging from structural composites to biosensors.

Dendritic polymers have precise and tunable nanoscale 

features that, when manipulated or controlled, can be used to

tailor their properties and performance. Properties and characteristics such as molecular weight, geometric dimension,

shape, and chemical functionality can be controlled using suitable initiators (compounds used to begin polymerization reactions), reagents, and reaction chemistry at the nanoscale.

Unlike other macromolecules, the architecture (structural

design) of dendritic polymers includes a distinct core, interior,

and exterior [2]. Control of the chemistry, size, and geometry

of these architectural features creates a very diverse set of nanomaterial building blocks. These features have led to great interest for dendritic polymers in widespread Army applications

related to chemical and biological agent defense, multifunctional protective coatings and finishes, adhesion promoters,

additives for polymer compounds, energetic materials, electronics, and optoelectronics.

Dendritic Polymers for Polymer Matrix 

Composites Applications

Dendritic polymers have been examined for several composites

applications. Due to the large number of terminal units, the

chemistry of dendritic polymers can be tuned to become a very

effective coupling agent (a chemical agent that facilitates the

adhesion of two components) for fiber-matrix combinations

that have been considered incompatible or troublesome to

composites engineers. For example, composite materials fabricated using liquid molding methods and vinyl-ester resins are

attractive in a number of military applications. However, the

use of higher performance carbon fibers in these vinyl-ester

composites has been hindered by less than optimal bonding

between vinyl-ester resin and carbon fibers. The use of dendritic polymers as adhesion promoters can improve the bond

between the carbon fibers and the vinyl-ester matrix. 

Dendritic polymers can be incorporated into vinyl-ester carbon fiber composites as fiber sizings (coatings on individual

fibers) applied from aqueous solutions to the fibers directly, or

alternatively, via a self-assembly method. Self-assembly is a

nanoscale process where molecules are inserted into a system

and assemble themselves naturally at a desired location. Thus,

when the terminal units of dendritic polymers are configured

with the proper functional groups at the nanoscale they can be

added to the vinyl-ester resin and will naturally migrate to the

fiber-matrix interphase* via self-assembly.

Figure 1. Illustration of a Hyperbranched Polymer. Figure 2. Symmetrical Structure of a Dendrimer [2, 3, 4].

Terminal

Groups

Core

Branch Points
The AMPTIAC Quarterly, Volume 8, Number 4 103

Figure 3 shows a scanning electron micrograph of a composite failure surface from a modified vinyl-ester carbon fiber

composite. In this case, the carbon fiber was coated with a

modified polyamidoamine (PAMAM) dendritic polymer, 

containing several different types of functional groups specifically tailored for this application. The failure of the composite

occurred in the vinyl-ester resin; well-removed from the interface, indicating that the fiber-matrix interface maintained

optimal adhesion. The resulting short-beam shear strength of

this composite was improved by 40% through the use of the

dendritic polymer based sizing.

Another application of dendritic polymers for polymer

matrix composites is in creating low-viscosity toughened

resins. Cost-reduction efforts in composites manufacturing

have led to an increased use of liquid molding techniques for

composite materials, and also created a need for low-viscosity

toughened resins. Traditional tougheners, including rubbers

and thermoplastic polymers, increase resin viscosity to levels

that prohibit their use in many of these low cost liquid 

molding manufacturing methods. Since dendritic polymers

have less of an impact on the viscosity of the resin than the 

traditional tougheners, their judicial use as tougheners in 

thermosetting resins results in relatively low-viscosity resins

that perform comparably to higher-viscosity rubber-modified

systems. During cure, micron-sized phases comprised of dendritic polymer-rich material separate from the bulk resin

resulting in a toughening mechanism similar to rubber-modified systems. This microstructure is shown in Figure 4 where a

polyester-based dendritic polymer has been added to a low viscosity epoxy resin resulting in a significant increase in polymer

toughness without significantly increasing resin viscosity.

Dendritic Polymers for Surface Modification

The functional groups on a dendritic polymer can be modified

in such a fashion as to create a macromolecule that exhibits

self-assembly. For example, these dendritic polymers can be

intentionally designed such that when added to an uncured

polymer resin system, they migrate to the surface and orient

themselves preferentially. An example of where this is useful is

in the surface modification of polymer matrix composites to

create a specific set of properties on the exposed surface of the

material system without sacrificing the composite’s bulk properties. This natural migration and orientation of dendritic

polymers can be achieved by making some of the functional

groups of the dendritic polymer branches incompatible (insoluble) with the resin matrix. Likewise, other functional groups

on the same dendritic polymer would be made compatible

(soluble) with the resin matrix. 

An example of a self-segregating dendritic polymer is

schematically shown in Figure 5. Proper control of the functional groups creates a dendritic material that remains soluble

in the uncured resin, while creating a thermodynamic driving

force for the incompatible functional groups to migrate the

dendritic polymer to the surface of the resin. After curing, there

exists a high concentration of dendritic polymers at the surface. 

Dendritic materials with very strong surface migration tendencies have been developed by modifying the terminal units

with low surface energy, perfluorinated functional groups†. The

aliphatic functional groups‡, which are compatible with the

bulk matrix, permit the homogeneous mixing of the additive

and bulk material, and the entire assembly serves to transport

the delivered group§ to the surface in significantly higher concentration than in the bulk material.

A practical example utilizing nanofunctional dendritic polymers for surface modification is the creation of a self-assembling

catalytic layer on the surface of polymers, which could be used

to make thin film catalysts, that could potentially be painted

onto other surfaces. For instance, a polyethyleneimine dendritic

polymer with perfluorinated functional groups and aliphatic

chains containing a catalytic metal center can be mixed within a

polyurethane resin. The catalytic dendrimer migrates to the surface of the polyurethane, and upon curing forms a polymer with

a catalytic surface layer. At a cast polyurethane surface, the surface properties are dominated by the dendritic polymer additive

and the composition of its functional groups. The modified

dendritic polymers, complexed with a catalytic metal center,

serves as a nanodelivery system, bringing the catalyst to the

polymer surface. The polymer-metal complex has been observed

Figure 3. Electron Micrograph of Carbon Fiber Vinyl-Ester

Composite That Has Used Dendritic Polymers to Modify the

Fiber-Matrix Interphase. The Presence of Resin on the Fiber

Surfaces Indicates Excellent Fiber-Matrix Adhesion.

Figure 4. Micrograph of Dendritic PolymerToughened Epoxy Resin.

1 micron
104 The AMPTIAC Quarterly, Volume 8, Number 4

at the surface of a polyurethane film in a quantity approximately ten times greater than its loading in the bulk. These results

suggest that small amounts of additive could be used to provide

truly functional materials, with active sites embedded or reacted

into the polymer. Such an approach has the potential to be more

robust than secondary coating treatments such as spray-on

applications.

Dendrimer Enhanced Immunoassays

Rapid and reliable detection of biothreat agents is of paramount importance to a variety of defined operational requirements in the biodefense, counterproliferation, and domestic

preparedness programs. Current point detection capabilities

require expensive equipment and extensively trained personnel

to perform their tasks. While many research teams focus their

efforts on a “top-down” approach by shrinking existing bulky

detectors using a “lab-on-a-chip” strategy, other teams are effectively using a “bottom-up” strategy whereby nanoscale manipulations improve device performance. Dendrimers are ideal

nanoscale building blocks for nanomanipulation. [5]

Nanoengineered dendrimer-antibody conjugates can be

appropriately designed to possess both antibody (protein that

binds with high specificity with an antigen, which is a substance that can initiate an immune response) and dendrimer

properties because they are about the same size (i.e. 5-10 nm in

diameter). [6] The antibody maintains its primary antigen

recognition capability, while the dendrimer strongly adsorbs on

a substrate through dendrimer terminal unit surface interactions. The adsorbed conjugate will tend to self-orient the antibody binding domains, known as Fabs (areas on the antibody

protein that bind to the antigen), for greater availability in the

immunoassay (a technique or system used to detect and possibly identify biological substances, such as biothreat agents,

through a binding event with antibodies).

Receptor antibody materials (bot-Fab) are currently used

on gold substrates for the detection of biowarfare agents.

Because of weak interaction with the gold particles used for

the substrate, the gold particles within these bot-Fab/gold

complexes tend to aggregate and form clusters. This can

obstruct some of the antibody receptor sites from the surrounding environment, reducing their efficiency in detecting

biowarfare agents. Research on combining antibody receptor

materials into the structure of a dendrimer molecule has

shown promise in reducing this problem. The functional

groups terminating the branches of dendrimer molecules can

be selected so as to enhance surface interaction with the gold

nanoparticles (20-70 nm in size). Furthermore, the structure

of the dendrimer/bot-Fab complex can be designed such that

Figure 5. Pictorial Representation of Self-Segregating Macromolecule in a Bulk Sample.

Figure 6. The Effect of Dendrimers on the Aggregation Behavior

of Colloidal Gold Conjugates.

High Surface

Concentration

➢ Monomer Unit

➢ Prefluorinated Group

➢ Aliphatic Group

➢ Delivered Group

Low Bulk

Loading
The AMPTIAC Quarterly, Volume 8, Number 4 105

the dendrimer strongly adheres to the gold surface while

simultaneously forcing orientation of the bot-Fab materials

outward so as to maximize their interaction with the environment. Testing of these dendrimer/bot-Fab complexes showed

a marked reduction in the aggregation of the gold particles,

improving their interaction with and detection of biowarfare

agents. This is shown in the electron micrographs in Figure 6.

A new immunoassay formulation was created using this 

technology. Testing of the device showed that at least a 20 fold

sensitivity enhancement was achieved with the dendrimeranti bot Fab conjugates vs. the anti bot Fab alone. Similarly,

production costs might be reduced by as much as 10-fold. 

Other Self-Assembled Nanostructured 

Polymer Materials

This research focuses on the creation of nanostructured polymer and organic-inorganic hybrid materials in order to achieve

unusual mechanical, transport, or electro-optical properties.

One of the most promising routes to these materials is through

the exploitation of the self-assembling characteristics of carefully chosen block copolymer** templates.

In utilizing these templates it may be important to have

control of the orientation (parallel or perpendicular to a substrate) and long range order of the block copolymer morphologies. Innovative techniques, such as the application of

electric field or the modification of substrate surface energies,

to control orientation and long range order in block copolymer thin films are being explored. These efforts are being performed both internally and through collaborative research

with the Army’s Polymer Center of Excellence at the University of Massachusetts.

Permselective Membranes for Protective Clothing

The Army has a need for materials that exhibit selective permeability and favor water transport (for breathability) while

inhibiting transport of larger organic molecules such as chemical agents. One approach to achieving this behavior is through

the use of self-assembled block-copolymers. Through appropriate processing and suitable chemical modification, a tri-block

copolymer with tailored chemistry and structure has been

developed to create a material with nanoscale water transport

channels embedded in a barrier matrix of polyisobutylene. [7]

The parent tri-block copolymer is based on a poly(styreneisobutylene-styrene) that is chemically modified by sulfonation

of the styrene domains (blocks). Using this sulfonation process

on the styrene domains of a lamellar structure, hydrophyllic

nanoscale channels embedded in the polymer material are

formed that preferentially favor water transport, while acting as

a barrier to other permeants. Because of this attribute, these

polymers are being studied for use in protective clothing, serving as a barrier to hazardous materials, while still allowing

moisture to escape. These polymers, therefore, have the potential to be used in protective suits that may breathe better than

current designs.

Water vapor transport data of the modified membranes and

other commercial materials are shown in Figure 7. Initial studies with live chemical agents indicate that the sulfonated elastomer exhibits excellent barrier potential. Further live agent

evaluations are in progress on optimized formulations. Textile

design and engineering efforts using the novel membranes as a

component in protective clothing are currently underway.

SUMMARY

Nanomaterials technology holds tremendous promise for creating the next generation of materials for Army applications.

Ongoing research has been developing the building blocks and

tools necessary to create and control materials at the nanoscale.

Applications that utilize the unique properties of nanomaterials are emerging and increasing in complexity. As these technologies continue to mature, the basic building blocks and

tools that are being presently researched will continue to find

widespread application.

ACKNOWLEDGEMENTS

This article represents the work of the authors and has

reviewed the work of several researchers who have made 

formal and informal contributions to the efforts that have

been described. Dr. Gary Hagnauer, (recently retired as ARL

Senior Scientist for Polymer Materials) was instrumental in

establishing the nanomaterials initiatives that have developed

into significant research efforts. The dendritic polymer initiatives were developed under his leadership. Dr. Hagnauer and

Dr. Donald Tomalia (Central Michigan University) are

acknowledged for their numerous contributions to the Army’s

Figure 7. Water Vapor Permeation of ARL Membranes Compared to Commercial Materials.

ARL-1

Nafion

ARL-2

Commercial B

Commercial C

Commercial D

30 40 50 60 70

Mean Relative Humidity, %

Permeation, g/m2 day

2500

2000

1500

1000

500

0
106 The AMPTIAC Quarterly, Volume 8, Number 4

collaborative dendritic polymer research programs that have

led to the successful utilization of dendritic polymers for a

number of applications. 

The dendrimer enhanced bioassay work that was described

here resulted from the extensive efforts of a research team led

by former ARL scientist Dr. Ray Yin, who has since founded

and led the nanotechnology firm ANP Technologies, Inc. The

research on dendritic fiber coatings was conducted by ARL in

collaboration with Professor Giuseppe Palmese from Drexel

University. ARL scientists Dawn Crawford, Jim Sloan, and

Gene Napadensky are acknowledged for their contributions on

permselective membranes based on modified block-copolymer

materials.

NOTES & REFERENCES

* Interphase is the boundary region between two phases, in this

case a fiber and a matrix, containing elements of each phase.

† Perfluorinated groups are organic groups that have had all the

hydrogen atoms replaced by fluorine.

‡ Aliphatic groups are typically defined as non-aromatic 

organic groups. These groups are composed of chains, such as

alkanes, alkenes, alkynes or other groups that do not have the

stability of aromatic compounds.

§ Delivered groups are the groups that are oriented in such a

way that they can provide a specific functionality to the area of

the bulk material where they are transported to.

** Block copolymers are polymers assembled from segments of

different polymers whose ends have been terminated with select

functional groups. These functional groups are designed to

react favorably, upon polymerization, only with those groups of

another select polymer segment. Carrying out polymerization

in this fashion allows one to control the structure and hence the

properties of a polymer chain. Through careful control of the

chemistry during polymerization these polymer segments selfassemble into a large polymer with a well-defined structure.

Using this technique, polymers having repeating units of three

segments of polymer material within the backbone (tri-block

copolymers) have been designed.

[1] AMPTIAC Quarterly, Vol. 6, No. 1, Spring 2002

[2] D.A. Tomalia, A.M. Naylor, and W.A. Goddard, Starburst

Dendrimers: Control of Size, Shape, and Surface Chemistry,

Topology and Flexibility in the Conversion of Atoms to Macroscopic Materials, Anew. Chem. Int. Ed. Engl., Vol. 29, pp. 138-175,

1990

[3] D.A. Tomalia, Birth of a New Macromolecular Architecture:

Dendrimers as Quantized Building Blocks for Nanoscale Synthetic Organic Chemistry, Aldrichimica Acta, Vol. 37, No. 2 (2004)

[4] D.A. Tomalia Frechet, J.M. J., Journal of Polymer Science

Part A: Polymer Chemistry

[5] J.D. Reuter, A. Myc, M.M. Hayes, Z. Gan, R. Roy, D. Qin,

R. Yin, R.T. Piehler, R. Esfand, D.A. Tomalia, J.R. Baker Jr.,

Bioconjugate Chemistry, Vol. 10, p. 271, 1999

[6] R. Yin, M.S. Bratcher, A.L. Jenkins, R.P. Hydutsky, 

R. Cheng, H.D. Durst, P.A. Emanuel, and G.L. Hagnauer, 

Presented at the National Meeting of the American Chemical

Society, Polymeric Materials: Science & Engineering Division,

San Diego CA, Spring 2001

[7] N.C.B. Tan, D.M. Crawford, J.M. Sloan, and E. Napadensky, Self-assembled Sulfonated Block Copolymer Semipermeable

Membranes and Uses Therefore,” US Patent 6,579,948

Dr. Matthew S. Bratcher is currently a research chemist at the Weapons and Materials Research Directorate of the

US Army Research Laboratory at Aberdeen Proving Ground, MD. He studied chemistry as an undergraduate at the

University of San Diego and earned his PhD in Organic Chemistry from Boston College. His technical areas of interest include polymer science, carbon nanotubes, metal-polymer composites, and polymer actuators.

Dr. Steven McKnight has worked at the Army Research Laboratory (ARL) since 1996, and he presently serves as

Chief of the Multifunctional Materials Branch at Aberdeen Proving Ground, MD. He is responsible for managing

the ARL Enabling Materials Work Area, which includes many of ARL’s nanomaterials research and technology activities. He is also Co-chair for the US Army RDECOM Nanotechnology Working Group. Dr. McKnight holds a PhD

in Materials Science and Engineering from the University of Delaware; a BS in Materials Engineering from Virginia

Tech. Dr. McKnight has published extensively in the areas of composite materials and adhesion science. His professional recognition includes the Army R&D Achievement Award and the Paul Siple Memorial Medal.
The AMPTIAC Quarterly, Volume 8, Number 4 107

INTRODUCTION

The US Army Research Laboratory is pursuing research efforts

that apply advances in materials engineered and designed at the

nanoscale to enable enhancements of military capabilities. These

projects include transparent armor materials and coatings, carbon nanotube composites, and metal/polymer composites.

Nanostructured transparent armor materials and coatings

have the ability to provide increased protection beyond currently used polymeric systems. They may be applicable to both personnel armor in the form of visors and for windshield/canopies.

Carbon nanotubes offer potential use in several areas due to

their excellent mechanical, electrical, and thermal properties.

Current research revolves around dispersing the nanotubes into

a polymer matrix, creating materials applicable for future military systems. Metal/polymer composites are also being evaluated for multiple applications. These include optical displays,

data storage, and actuation devices. This research along with

additional ARL projects concerning nanotechnology (see

“Small Features Enable Big Results: The Army’s Latest Developments in Polymer Nanotechnology” in this edition of the

AMPTIAC Quarterly) will provide the foundation for performance enhancements to Army systems and capabilities.

TRANSPARENT NANOCOMPOSITES

Nanostructured materials have the ability to transcend material limitations previously met in the development of high performance transparent armor. Polycarbonate and acrylic polymeric materials have been the standard for decades providing

protection against small arms projectiles. The need for

increased performance brought about the use of ceramic materials, usually laminated between layers of polycarbonate or

acrylic materials. This layered approach improved ballistic performance, but at a substantial cost. Nanocomposite transparent

armors have the potential to increase ballistic performance at a

cost amenable to wide scale usage. 

The use of high-performance polymer nanofibers and/or

elastomeric nanofibers as reinforcements has received much

recent attention. The advantages of using nanofibers for reinforcement in transparent nanocomposites are twofold. First,

the small diameter of the fibers (about 100 nm) is well below

the diffraction limit of visible light (wavelength = 400-700

nm), therefore nanofibers dispersed in a transparent medium

should not scatter light in the visible spectrum. Second,

nanofiber textiles have fiber surface areas that are orders of

magnitude greater than conventional fabrics due to the small

fiber diameter. The greater surface area will provide more interaction between the resin and reinforcing fiber, improving

mechanical properties and potentially increasing the amount 

of energy dissipated during an impact event due to sliding friction associated with fiber pullout. Finally, as has been demonstrated in the case of inter-penetrating network (IPN) resins,

the incorporation of a continuous elastomeric phase into a rigid

thermoset can enhance the fracture toughness of the matrix. 

Nanofibers are easily produced using electrospinning methods and a variety of polymers have been spun into fiber mats

including structural materials such as nylon and more compliant materials including polyurethane elastomers. Recent results

achieved through collaborative research with the Army’s Composite Materials Center of Excellence at the University of

Matthew Bratcher

Carl Krauthauser

Weapons and Materials Research Directorate

US Army Research Laboratory

Aberdeen Proving Ground, MD

Gregory A. Gaddy

Beta Analytics International, Inc.

Upper Marlboro, MD

(formerly from the Sensors and 

Electronic Devices Directorate, ARL)

Joseph Deitzel

Center for Composite Materials

University of Delaware

Figure 1. Electrospun TPU Fibers Used for Transparent

Nanocomposites.
108 The AMPTIAC Quarterly, Volume 8, Number 4

Delaware Center for Composite Materials have shown that

transparent composites can be made by using nanofiber mats

that are impregnated with various thermoplastic and thermoset

polymers. Figure 1 shows thermoplastic urethane (TPU) 

electrospun fibers while Figure 2

shows TPU/polymethylmethacrylate (PMMA) composites that possess high transparency and optical

clarity (95 and 85% respectively)

when compared to neat resin

properties. In this case, a 

catalyst was added, followed by

curing to produce a thermoset

PMMA resin (PMMA is typically

a thermoplastic polymer). Thermoplastic resins, including

PMMA, have also been used to

produce transparent nanocomposites. Mechanical properties of

these materials show that incorporation of polyurethane nanofibers

into PMMA resin increases the

elongation at break by as much as

700% in comparison to pure PMMA. Ongoing research is

assessing the impact performance of these systems and developing design rules for these new materials.

Transparent nanocomposite hard coatings represent a successful example of hybrid hard/ductile nanomaterials that may

have use for soldier systems, including the next generation

Joint Services Military Eye Protection Systems (MEPS) and

headgear displays/visors for the Future Force Warrior. Figure 3

shows the optical clarity of silica (SiO2)/PMMA nanocomposites for various silica content, prepared by sol-gel synthesis.

Incorporation of silica increases the modulus and hardness of

polymer matrix composites. The hardness of silica/PMMA

nanocomposites were tested to reveal an increase from 0.21

GPa for 0 vol% silica content up to 0.34 GPa for a 30 vol%

silica content composite.

POLYMER-MODIFIED CARBON NANOTUBES

While carbon nanotubes have received an enormous amount

of publicity, several hurdles need to be overcome to fully

exploit their properties. Carbon nanotubes (CNTs) have

unique properties that provide the potential to advance material systems in several areas. CNTs have a high Young’s 

Modulus, high electrical conductivity, high thermal conductivity, and excellent chemical resilience. One specific hurdle to

overcome is to effectively disperse CNTs into a polymer

matrix, producing a composite with enhanced properties.

In order to facilitate favorable energetic interactions (which

can lead to good dispersion of CNTs in a polymer matrix),

the Army has investigated new

methods to modify the multiwall CNT surface by attaching

polymer chains at the surfaces of

functionalized CNTs. Working

with researchers at the University

of Tennessee, the ability to grow

polybutadiene (PBD), polyisoprene (PIP), polystyrene (PS),

PMMA, and polyethyleneoxide

(PEO) on CNT surfaces and

directly control the solubility and 

dispersion of CNT materials has

been developed. Using these

methods, CNT modification can

produce materials with different

solubilities tailored for specific

applications. Figure 4 shows 

various modified multi-wall nanotubes (MWNTs) dispersed in solvents. The polymer modification has a tremendous effect on the quality and stability of

the dispersion.

SILVER PARTICLE/POLYMER FILMS

Many visual display devices make use of liquid crystalline

polymers. These polymers change optical properties upon

exposure to an electrical current. Therefore, light radiated

through these displays is altered by the optical absorption and

diffraction properties of the liquid crystal polymers. These

changes in light transmission allow us to see images such as

text or pictures. Currently the Army is looking at the use of 

silver nanoparticles for use in possible visual displays and/or

optical data storage applications.

The in-situ formation of metal clusters in polymers is an

attractive synthetic route for producing these materials [1-3].

The introduction of peroxide into a polyvinyl alcohol system

facilitates the oxidation of the photoreduced metal particles, silver particles in this case. In short, the polymer films are doped

with silver ions in a low concentration of peroxide. The films

are subsequently dried and irradiated with photons of sufficient

intensity and wavelength. The photoinduced formation of silver particles shows a strong dependence upon the induced

wavelength and intensity. 

(a) Pure PMMA (b) 4% TPU Nanofibers/PMMA

Figure 2. Transparency of Pure PMMA Versus TPU/PMMA Composites.

(c) 15% TPU Nanofibers/PMMA

Figure 3. Transparent Nanocomposite Materials That

Have Demonstrated Increased Hardness Suitable for

Scratch Resistant Coatings.
The AMPTIAC Quarterly, Volume 8, Number 4 109

After the formation of particles is achieved, the samples are

protected from all sources of light, and a dark oxidation reaction is observed. Ideally, materials for these applications should

possess both quick and good reversibility (the ability to lose

their optical signal completely). Although the tested films do

not exhibit good reversibility as shown in Figure 5, this research

demonstrates the possibility of using metal particles in polymer

films for Army display and information storage applications.

This system is robust and was demonstrated in ambient atmosphere without the need for additional packaging. Efforts are

underway to improve the kinetics and thereby optimize

reversibility and speed.

PALLADIUM/POLYMER NANOCOMPOSITE ACTUATORS

Formation of palladium interlayers in polymer films for use 

as actuators is another area of research for organic/

metal nanocomposites. Typically, thin metal layers on polymer

films must be created using physical vapor deposition (PVD)

under high vacuum.

In PVD, the metal 

is resistance heated

under a high vacuum

which effectively reduces its melting and

boiling point. The

polymer film is placed

in front of the flux of

molten metal particles,

and the polymer film

is soon coated with a

thin metallic film.

ARL is currently

optimizing a nonvacuum process to

produce polymer films with surface and embedded continuous

metal layers. This process uses ultraviolet light to initiate 

photosensitive components within the polymer chain. The

depth of the photoinduced chemistry is both wavelength and

intensity-dependent. The metal-doped polymer films are heat

treated at temperatures less than 325°C, and films with four

distinct regions are produced, see Figure 6. The films are comprised of: 1) a resistive metal surface layer, 2) metal particle

layer where the particle size is less than 10 nm, 3) a semicontinuous inter layer, and 4) a bulk region of metal particles

where the particle size is greater than 10 nm. The films show

an ability to actuate (bend) when exposed to white light 

and elevated temperatures. The radius of curvature in the

bend is linearly dependent on the intensity of the light source

and temperature. 

GLASS/METALLIC NANOCOMPOSITES

Much like the two previous nanocomposite systems, the photoreduction of silver and gold ions to form metallic nanoparticles within porous glass can create interesting composite

materials. These systems are simple to produce and data indicates that the extent of metal particle formation is dependent

on the wavelength and intensity of the impinging photons

during the photoreduction process. This process can be used

to control the color and reflectance of the glass. Some resulting irradiated samples are depicted in Figure 7. 

Figure 4. Various Polymer-MWNT Composite (1%wt MWNTs) 

Solutions in Dichloromethane Photographed after 3 Days. 

Sample 1) PBD, 2) PIP, and 3) PS, All with Initial Composite 

Solution Concentration, [composite]0 = 0.2 mg/mL, 

[MWNTs] = 0.02 mg/mL, 4) PMMA, [composite]0 = 0.2 mg/mL,

[MWNTs] = 0.014 mg/mL.

Figure 5. Absorptance at 280 nm (Absorption Band for 

Silver Clusters) as a Function of Time during Irradiation and

Decay Cycles.

Figure 6. Transmission Electron Microscope

Image of Metal Interlayer Polymer Film.

Irradiation Process

Decay Process

200 nm

0 200 400 600 800 1000 1200 1400 1600 1800 2000

Time (min)

Absorptance (280 nm)

0.10

0.09

0.08

0.07

0.06

0.05

0.04

0.03

0.02

0.01

0.00

Figure 7. Representative Depiction of Color Variance and 

Transparencies of Porous Glass Containing a) Gold Particles, 

b) Silver Particles, and c) No Particles.

a)

b)

c)
Dr. Joseph M. Deitzel is an Associate Research Scientist with the Center for Composite Materials, at the University

of Delaware. Dr. Deitzel has 12 years experience working in the field of polymer science. He received his BS in

Physics from the University of Akron and his PhD in Polymer Science from the University of Akron. Dr. Deitzel was a

Research Fellow in the Polymers Research branch at the US Army Research Laboratory, where he contributed to

research projects dealing with materials issues related to soldier protective clothing. His research interests include:

polymer nanofibers, high performance polymer fibers, polymer surfaces and interfaces and phase behavior of 

complex polymer systems. Dr. Deitzel has authored numerous publications and presently holds one patent.

ARL is currently developing metal particle-based systems

that would allow for a palette of colors that could then be

selectively activated by careful selection of impinging wavelength and intensity of light. Efforts are underway to render

the system reversible, where the photoreduced particles would

undergo an oxidation reaction. During the oxidation of the

photoinduced particles, the color of the systems will become

less intense as the optical properties of metal nanoparticles are

size dependent.

SUMMARY

Research into nanostructured materials and nanocomposites

are of utmost importance for the improvement of Army systems. The Army is actively researching new materials and processing methods for the advancement of current systems. This

research will provide insight to the development of enhanced

systems in the fields of transparent armor, structural and

functional carbon nanotube based materials, and metal/polymer composites for optical applications and actuation devices.

Nanostructured materials bestow the potential for vast

improvements across the board for military systems. The

Army will continue its research into nanostructured materials

that will provide benefit to future systems.

ACKNOWLEDGEMENTS

This article represents the work of the authors as well as many

additional researchers who have made formal and informal contributions to these efforts. Alex Hsieh has worked with Professor

Wei from Drexel University to develop the sol-gel transparent

nanocomposite materials. Some of the research described was the

result of collaborative research performed under two Materials

Centers of Excellence programs for Polymers and Composite

Materials. Professor Jimmy Mays from the University of Tennessee has worked with ARL researchers to produce the modified

carbon nanotubes with controlled dispersion. Prof G. Mills and

his group at Auburn University have contributed to the development of hybrid materials using photoreduction methods.

REFERENCES

[1] G.A. Gaddy, E.P. Locke, M.E. Miller, R. Broughton, T.E.

Albrecht-Schmitt, and G. Mills, J. Phys Chem. B., Vol. 108, pp.

17378-17383, 2004

[2] G.A. Gaddy, A.S. Korchev, J.L. McLain, B.L. Slaten, E.S.

Steigerwalt, and G. Mills, J. Phys Chem. B., Vol. 108, pp.

14850-14857, 2004

[3] G.A. Gaddy, J.L. McLain, A.S. Korchev, B.L. Slaten, and

G. Mills, J. Phys Chem. B., Vol. 108, pp. 14858-14865, 2004

110 The AMPTIAC Quarterly, Volume 8, Number 4

Dr. Matthew S. Bratcher is currently a research chemist at the Weapons and Materials Research Directorate of the

US Army Research Laboratory at Aberdeen Proving Ground, MD. He studied chemistry as an undergraduate at 

the University of San Diego and earned his PhD in Organic Chemistry from Boston College. His technical areas 

of interest include polymer science, carbon nanotubes, metal-polymer composites, and polymer actuators.

Dr. Carl Krauthauser was an Associate Research Scientist at the Center for Composite Materials at the University

of Delaware for 3 years (2001-2004), and is now a Research Physicist with the Armor Mechanics Branch of 

the US Army Research Laboratory. Dr. Krauthauser has 12 years experience working in the field of Atomic and 

Molecular Physics, with current interest in long chain high performance rigid-rod polymers. He received a BS in

Physics and a BS in Mathematics from Villanova University in 1987, and his PhD in Atomic and Molecular Physics

from the University of Delaware in 1994. His research interests include: polymer nanofibers, high performance 

polymer fibers, polymer surfaces and interfaces and phase behavior of complex polymer systems.

Dr. Gregory A. Gaddy is currently a senior technology protection engineer with Beta Analytics, Inc. in their

Research, Technology, and Program Protection Center. Dr. Gaddy is an emerging authority in metal particle 

formation and assembly in polymeric systems. His primary interests are developing and studying methods for the

photoreduction of metal ions in polymeric materials. Dr. Gaddy received his BS in chemistry from Valdosta State

University in 1996, and his PhD in Physical Chemistry from Auburn University in 2001.
The AMPTIAC Quarterly, Volume 8, Number 4 111

INTRODUCTION

Advanced electronic materials supply the cutting edge that the

Army is relying on to deliver the next generation of sensing

devices and provide the foundation that will allow a new era of

sensors for applications only previously imagined. Electronics

now dominate nearly every aspect of the military with applications in the mess hall to the battlefield. The Army is currently

developing these new applications, and researching dozens

more that have yet to be realized. With so many demands, the

field of electronic materials is vast. This paper will focus on one

specific sensing application, infrared (IR) detectors, and the

work that Army researchers and developers have done to transition this technology to soldiers in the field. Infrared detector

materials, while only one example, represent a bell weather

technology for electronic materials as a whole. As such, one

needs to understand their importance to the Army, before

examining recent advances in the field. 

It should be noted that there is not one solution to the

Army’s needs for infrared technology. There are applications

that require an extremely high sensitivity and refresh rate 

(the time between distinguishable signals), and there are applications with less stringent requirements that must be less

expensive. There is a whole family of technologies that have

been developed to meet these needs, and the three areas, pyroelectric thin film detectors, quantum well infrared detectors,

and mercury-cadmium-telluride based detectors, discussed

here are representative but by no means all encompassing of

infrared detector technologies and materials being researched

in the Army today.

THE ARMY HAS A LONG HISTORY OF INFRARED 

DETECTOR USE

Infrared detectors have been an increasingly important part of

the Army’s arsenal since the early 1960’s, when a cooled forward-looking infrared (FLIR) detector was the first night

vision system developed. The Army adapted this system in

1972 into a common module FLIR system. In 1978,

uncooled thermal imaging was demonstrated to the Army,

and 1985 welcomed the first battery operated night vision

system. Shortly thereafter, in 1988, the first commercial IR

cameras became available. The focal plane size, and the resolution, was increased to 256x256 pixels in 1990, and

512x512 in 1992. Presently, IR imaging systems, cameras,

and detectors can be found commercially in everything from

medical devices, fire control, surveillance, and even driver

vision enhancement in some automobiles [1]. Military use

includes night vision, rifle sights, surveillance, missile guidance, tracking, and interceptor applications[2]. Uncooled

detectors, which typically require long exposure times and

large lenses are unsuitable for the latter applications, while the

cooled systems, which are somewhat bulky and expensive, are

unsuitable for some of the former applications.

The Army is the largest consumer of infrared detectors in

the DOD with most every component and system being slated for upgrade to an infrared capable environment. There are

more than 500,000 vehicles Army wide, and they are each

scheduled for an upgrade to a Drivers Vision Enhancement

system to incorporate nighttime imaging[3]. Man-portable

thermal weapons sights and vehicle mounted heavy weapons’

William. D. Nothwang

Melanie. W. Cole

Weapons and Materials Research Directorate

US Army Research Laboratory

Aberdeen Proving Grounds, MD

Arnold Goldberg

Sensors and Electron Devices Directorate

US Army Research Laboratory

Adelphi, MD
112 The AMPTIAC Quarterly, Volume 8, Number 4

currently account for 800,000 and 180,000 units respectively[3]. This brings the current Army investment in IR imaging

to just over $6.5 billion.

TYPES OF INFRARED DETECTORS

The situational awareness provided by infrared detectors allows

for advanced lethality and survivability across the full spectrum

of military operations. Infrared sensors are used to detect energy emitted from targets, and their surroundings for a wide range

of defense applications. The spectrum for IR detection and the

associated thermal imaging equipment has been in the Short

Wavelength InfraRed (SWIR) at 1-3 μm, the Medium Wavelength InfraRed (MWIR) at 3-5 μm, the Long Wavelength

InfraRed (LWIR) at 8-12 μm and the Very Long Wavelength

InfraRed (VLWIR) at >12 μm wavebands, corresponding to

regions of atmospheric transparency (i.e. low absorption) and

also to thermal blackbody maxima at around room temperature[2]. A combined image using multiple wavelengths within

the IR spectrum increases the ability to discern between a variety of potential threats as seen in the fused image of Figure 1.

Enhanced weapon system performance may be achieved in several complimentary ways including the use of integrated sensors

and munitions which are lightweight, have low power consumption, are producible at high rates, and reliable.

In general, the IR detectors can be classified as either photon

detectors or thermal detectors. In the first category, photons

interact directly with the charge carriers in a semiconductor or

metal to generate a photocurrent. Two families within photon

detectors are those made using quantum confinement in the

compound semiconductors GaAs and AlGaAs called Quantum

Well Infrared Photodetectors (QWIPs), and those fabricated

using an alloy of the semimetal Mercury Telluride and the

semiconductor Cadmium Telluride (HgCdTe) generally called

“MerCad” or MCT. Thermal detector materials, on the other

hand, are characterized by the modification in properties due to

the change of temperature, arising from absorption of the IR

radiation. Photodiodes such as the InSb family deployed on the

F-23 JSF, while not being directly addressed here, are important DOD technologies.

MCT and QWIP photodetectors require a specific cooling

system to operate at a temperature where they exhibit maximum detection, offer extremely fast refresh rates, much smaller focusing optics, and can have a much higher resolution in

a smaller detector size, see Figure 2. Thermal detectors, however, can operate at or near room temperature, but they require

larger focusing optics and longer exposure times[2]. Most 

legacy photon detectors utilize photoconductive HgCdTe as a

detector material; though, QWIPs composed of III-V (compounds from the third and fifth columns of the periodic table)

semiconductor super-lattices (GaAs/AlGaAs) are also being

actively developed for these same applications.

Although the fabrication costs for QWIP detectors is on par

or less than the cost for thermal detectors, the necessary requirement of cooling brings factors of size, weight, volume, operating

life, maintenance, cost, and reliability into the detector design.

As a result, for many applications where high sensitivities are not

necessary, lower cost, lighter weight thin film pyroelectric detector systems are finding relevance. The development of uncooled

thermal detectors, particularly those based on the use of pyroelectric ceramic materials, currently offer advantages for certain

applications in comparison with the cooled photon detector

technology; though, as cooling technology continues to

improve, this may not hold true for much longer. There is a constant drive within the DOD to improve sensitivity, reliability

and energy consumption and lower cost, weight and size.

PYROELECTRIC BASED INFRARED DETECTORS

According to the September and October 2001 issue of the

Army AL&T, the development of uncooled thermal detectors

has been designated an important technology breakthrough[5].

The article, written by Douglas K. Wiltsie (Technical Director

for Project Manager Night Vision/ Reconnaissance, Surveillance, and Target Acquisition, PM NV/ RSTA) states that

small uncooled thermal sensors offer the Army mediumperformance alternatives that are cost effective, light weight, and

low powered (uncooled FLIRs are specifically either pyroelectric

or microbolometer devices). These sensors are currently applied

in rifle sights and driver viewers, and according to Wiltsie, futuristic applications include the Enhanced Night Vision Goggle

and families of unattended ground imaging sensors. 

Applying new technologies to multiple products will reduce

costs and capitalize on economies of scale in manufacturing.

Wiltsie further states that a major attractive characteristic of the

uncooled technology is the elimination of the need for 

a mechanical scanner and cryogenic cooler, and hence the 

uncooled devices will draw significantly less power [5,6]. 

Figure 1. LWIR and MWIR Images[4].

LWIR MWIR Fused
The AMPTIAC Quarterly, Volume 8, Number 4 113

The primary consequence of this technological advancement has

not been the replacement of the expensive, high performance,

cooled detectors with pyroelectric detector materials, though this

has happened to a certain extent; rather, it has been the proliferation of inexpensive, mid-performance detector materials allowing night vision equipment to become standard issue [6].

The Army continues to investigate a variety of alternative

materials in addition to QWIPs, MCT, and bulk barium

strontium titanate (BST) infrared sensors and bolometers.

Pyroelectric detectors offer the advantage of room temperature

operation and thus do not require costly, heavy, bulky cooling

systems. To further investigate their application to Army

systems, the Army Research Laboratory (ARL) recently completed a collaborative Director Research Initiative involving

the Weapons and Materials Research Directorate (WMRD)

and the Sensors and Electron Devices Directorate (SEDD).

The materials investigated are suitable for small, light-weight

infrared detection systems that are reliable and require minimal

power. While there are ongoing efforts to examine thermal

detector materials like bulk BST, thin film vanadium oxide,

amorphous silicon, and yttrium barium copper oxide,

ARL-SEDD and WMRD have focused much effort

on developing thin film pyroelectric materials for IR

sensors. All of these materials are being evaluated for

room temperature/uncooled applications.

For a given material and area of the detector, the

sensitivity can be increased by decreasing the thickness of the detector. Hence, thin film pyroelectric

materials for IR detectors are expected to be better

than bulk ceramic materials that are currently used

in many applications. In one example of recent

research at ARL, BST based thin films were investigated for use as phase transition pyroelectric thin

film materials. Undoped and doped (Mg, Al, Ta, or

La) BST thin films were fabricated via the

metal-organic solution deposition (MOSD) technique. The metrics of success for all of these materials include low volume specific heat, a moderate

dielectric constant, low loss tangent, a large pyroelectric coefficient, and the system must be single

phase, dense, have minimal defects, a smooth surface and a high film resistivity. As shown in Figure 3,

the absolute metric values were based on achieving a

detectivity material figure of merit value, D*, which is competitive or better than that of the industry standard lead titanate

(PbTiO3) based thin films [3].

A comparison of recent joint ARL-WMRD and SEDD

research shows that the MOSD fabricated BST films designed,

characterized, and optimized in this investigation possessed

low dissipation factors, reasonable permittivities, excellent

insulating properties and a high pyroelectric constant yielding

a high calculated value of D*, competitive with that of Pb

based thin films for IR pyroelectric detector applications.

The MOSD fabricated, undoped BST thin films were determined to be an excellent candidate material for IR pyroelectric

detector applications. Preliminary results also suggest that

the 5 mol% Mg doped BST and 1 mol% La doped BST thin

films are strong candidates for utilization as IR pyroelectric

materials [3].

The accomplishments of this research endeavor were due

to the combined efforts and expertise of the joint ARL

WMRD-SEDD research team. This study examined fundamental research issues while at the same time addressed a current

Army problem in advanced sensor technology.

Figure 2. Cross-Section of a Dewar Containing a Cryogenically Cooled (<77K) QWIP/MCT Photodetector.

Figure 3. Comparison of D* for Conventional and Phase Transition

Pyroelectric Thin Films. The Materials were Deposited by:

1) Sol-gel, 2) Sputtering, 3) MOSD, and 4) PLD.

(†) indicates the results obtained recently by Army researchers [3]

Cold Finger

Detector

Window Cryo Cooler

Focusing Optics

Vacuum Port

Material Figure of Merit, D*. (Cm3/J)

0.00 0.02 0.04 0.06 0.08 0.10 0.12

Phase Change 

Pyroelectrics

Traditional 

Pyroelectrics

PbZr0.54Ti0.46O3 (1)

Pb0.7Ca0.3TiO3 (2)

PbSc0.5Ta0.5O3 (2)

Ba0.60Sr0.40TiO3 + 5wt%Mg

Ba0.94Sr0.06TiO3 + 5wt%MgO (4)

Ba0.94Sr0.06TiO3 + 0.25wt%MgO (4)

Pb0.9La0.1TiO3 (2)

Ba0.60Sr0.40TiO3 (3)†

Ba0.964Sr0.046TiO3 (4)

Ba0.80Sr0.20TiO3 (1)

PbTiO3 (1)
114 The AMPTIAC Quarterly, Volume 8, Number 4

QUANTUM WELL INFRARED PHOTODETECTORS

In the most general sense, QWIPs work by absorbing individual rays of light. In QWIPs, two very similar but slightly 

different materials are placed next to each other. Where the

two materials touch, a “quantum well” is created and this

quantum well can trap electrons. Due to the discrete energy

levels in a quantum well, electrons in the well absorb very 

specific wavelengths. 

In most QWIPs, the well material is Gallium Arsenide

(GaAs) while the barriers are made of Aluminum Gallium

Arsenide (AlxGa1-xAs, where x is the Aluminum mole fraction). Extremely thin layers (nano-scale) make up the structure.

The absorbed light energy (or photon) causes an electron to

become excited to a higher state, where it produces a photocurrent before it falls back to the ground state. By very carefully

engineering the bandgap of a material, it is possible to tune the

sensitivity of a detector to a very specific wavelength. 

Typically, the bandgap tuning is done by changing the

quantum well parameters such as the well thickness and the

barrier height. III–V materials with relatively large bandgaps

(1.43 eV for GaAs, greater than 1.7 eV for AlGaAs) are 

commonly used for QWIP fabrication. The InGaAs/AlGaAs

materials can detect photons between 4 and 20 μm wavelengths, or within the MWIR to VLWIR spectrum. To optimize performance, the interface must be very flat, and the

materials must be exceedingly uniform [2,7].

Thin film detector materials are typically deposited via molecular beam epitaxy, MBE, which is a very precise method of putting down one atomic layer at a time in a controlled manner.

MBE has been shown to be a very effective process for QWIPs

fabrication. Using MBE grown films on high quality substrates

allows for the fabrication of an extremely high 

performance thin film, but it incurs a relatively high cost.

Recent advances have succeeded in lowering this cost by increasing the throughput and the substrate size. However, QWIPs

must still be cooled to a very low temperature (<77K) to achieve

optimum performance, and this further increases the cost.

The GaAs/AlGaAs material system has numerous advantages, including: high bond strength, good thermal stability,

ease of doping, and no need to passivate the surface due to

materials stability, making it ideal for radiation hard (i.e. space)

and harsh environment applications. There is a commercially

viable GaAs industry, which significantly lowers the cost of

device fabrication with these materials. After years of research,

GaAs based QWIPs with all of these advantages have been successfully fabricated and tested. The challenges today facing

QWIP researchers lay not in the fabrication of the base GaAs

system, but rather in modifying it to improve its properties and

lower its cost [7].

One such modification attempted by researchers at ARLSEDD, is the design of multi-chromatic detectors [7]. These

detectors would be able to detect and distinguish between

light of differing wavelengths. Most display technologies (and

the human eye) are tri-chromatic. Traditional infrared detectors, however, are mono-chromatic. The depth of view

humans see is due to the eyes’ ability to detect the different

wavelengths of red, green and blue light. Multi-chromatic IR

detectors, shown in Figure 4, would allow the simultaneous

detection of multiple different wavelengths within the IR spectrum. As different materials emit light at different wavelengths, using a multi-chromatic detector allows for an

increased ability to discern between varieties of threats and 

collect a wealth of new information. These include identifying

buried objects, improved temperature sensing, decoy detection, and material identification [7].

Current methods for fabricating dichromatic detectors

include using a mechanical filter wheel that “chops” the signal,

a dithering system with a striped filter, or using two separate

focal plane arrays (FPAs). None of these methods are efficient

or entirely effective. To overcome this, researchers at ARLSEDD have designed a linear array of quantum grid infrared

photodetectors (QGIPs). The detector material, based on a

binary super-lattice, has a spectral window between 8-14 μm,

where it absorbs photons. The geometrical shape of the grid

Figure 4. Multi-Chromatic QWIP Structure (1-4, G Represents the Electrical Signals from Each Layer[8]).

Relaxed

Buffer

Layer

G

4

2

1

3

IncidentRadiation
The AMPTIAC Quarterly, Volume 8, Number 4 115

then selects specific wavelengths for each photodetector element, allowing multiple wavelengths to be detected from the

same incident light, simultaneously. This makes it ideal for

stand-off spectral analysis for chemical detection. By fabricating the QGIPs into an array, it will be possible to see infrared

images in multiple colors. One such example is a new QGIP

being developed with two QWIPs that allow detection into the

LWIR and VLWIR, where there is a significant amount of

information that was not previously visible. These detectors

have been found to have very uniform stable sensitivities across

the range of operating biases and temperatures [9].

In a parallel effort, based on previous work, researchers at

ARL-SEDD have been working to improve the detection limit

within photodetector materials [10]. In present detectors,

there is a threshold bias voltage, below which no signal is

detected. The threshold is due to the lack of photocurrent generated at the contact layer, which induces a large contact resistance. This decreased efficiency is attributed to the presence of

a large number of defects that exist in the material at the interface between the doped contact layers and the doped quantum

well. To overcome this, a compositionally graded contact layer

has been fabricated. The composition within the new contact

changes atomic layer by atomic layer, from the quantum well

concentration at one end to the contact concentration at the

other end. By grading the composition in this manner, the

ARL-SEDD researchers have been able to completely eliminate the threshold voltage and enhance the low-bias performance of the detectors. This will significantly reduce the power

needed to run these devices, making them smaller and less

expensive [11].

MERCURY-CADMIUM TELLURIDE 

BASED PHOTODETECTORS

The MCT based detector systems are the first photodetector

systems that were widely used and represent a mature thermal

imaging technology being deployed within numerous Army

and DOD systems. They have found applications in many

detectors that require an extremely fast refresh rate, such as missile seekers. In order to achieve this high refresh rate, MCT

detectors have to be cooled to low temperatures, frequently

below liquid nitrogen temperature (77 K), and often as low as

30 K. At these temperatures the films are able to achieve refresh

rates less than a millisecond, and in some cases less than a

microsecond. The currently-deployed MCT based systems

employ HgCdTe films grown by liquid phase epitaxy (LPE) on

a semiconductor substrate. Most of the substrates currently in

use are quite expensive, such as sapphire or CdZnTe. As the

technology is more mature than QWIPs or pyroelectric thin

films, the research effort within the Army has focused on trying to improve the resolution of the system, increase the operating temperature, and lowering the cost.

There are two important elements of any detector unit: the

array of photodetector elements and the array of silicon readout

integrated circuitry (ROIC). Traditionally, HgCdTe detector

elements are grown epitaxially on lattice-matched and optically transparent cadmium-zinc-telluride (Cd0.96Zn0.04Te) substrates, and a complimentary metal-oxide-semiconductor

(CMOS) process is used to produce ROICs. The detector elements are bonded to the ROICs with an indium bond layer to

form high performance infrared focal plane arrays (IRFPAs).

The CdZnTe substrates are very expensive and contribute to

the poor reliability of large IRFPAs. Currently, the size of IRFPAs is limited because the indium bond breaks with repeated

cycling of temperature between room temperature and operating temperature (77 K). Recent research at ARL-SEDD and the

Communications and Electronic Research, Development and

Engineering Center’s Night Vision and Electronic Sensors

Directorate (CERDEC-NVESD) has indicated that this is

caused by the difference in thermal expansion coefficient

between the ROIC-Indium-CdZnTe [12].

To fabricate larger, more reliable IRFPAs two different solutions have been investigated within the Army: (1) growing the

detector material on a silicon substrate that is then indium

bonded to the ROIC, and (2) integrating the HgCdTe detector

material directly onto the ROIC without an indium bond.

Both solutions require a significant redesign of the material’s

microstructure at the atomic level, and for this MBE is ideally

suited. Buffer layers and doping must be used to minimize

defects that will inhibit the device’s performance and lifetime.

Army researchers have recently designed a successful MWIR

photovoltaic test structure on a silicon substrate, as shown in

Figure 5 [13]. One of the major innovations that has allowed

this advance to take place is the growth of a CdTe buffer layer

on the silicon substrate. The proper orientation of the crystallized CdTe allows for the minimum Hg to be used during

MBE growth of the HgCdTe. It has proven very challenging

to grow properly oriented CdTe, but with a thin ZnTe layer on

{111} (crystallographic plane) silicon, it has been achieved.

When scaled to full production levels, this structure will

enable much larger IRFPAs (i.e. greater resolution) at a lower

cost [14].

This work has been accomplished with a collaborative effort

between ARL-SEDD and CERDEC-NVESD. While examining some of the fundamental science questions behind the 

Figure 5. Hg1-xCdxTe P-N Double Layer Heterojunction 

Photovoltaic Diode Structure for MWIR[15].

Metal Contact

CdTe passivation

CdTe Buffer Layer

ZnTe

{111} Silicon Substrate

HgCdTe (x=0.380)

n type: HgCdTe (x=0.323)

p type: As
116 The AMPTIAC Quarterly, Volume 8, Number 4

performance of the MCT systems, the collaborative research

effort was able to significantly improve the quality, performance, and reliability of the systems being delivered to the soldiers in the field, and should significantly reduce the cost.

CONCLUSIONS

The advances in infrared materials technologies described here

characterize the effort being put towards developing the next

generation of Army technologies across the entire spectrum of

electronic materials research. While these efforts and many

more have been underway to develop the next generation of

electronic materials based systems, there have also been parallel

endeavors where Army researchers are producing advancements

in electronic materials for the generation after next. Some of

the recent successes in this area include:

• There has been significant work at ARO, focusing on

improving the efficiency and effectiveness of Light Emitting

Diodes from spin-loss effects, white light emitters, nitrogen

defect structure, InGaN/GaN quantum well emitters, and

doping of erbium and europium into nitrides. This work will

have future applications in a wide variety of amplifiers,

focused light, lasers, and illumination technologies [16,17].

• There have been some significant advances at ARL-SEDD

and CERDEC-NVESD on Schottky Diodes from AlGaN

and Cd/CdTe materials. Electron transport measurements

have been made and surface treatments were examined to

help design better diodes on silicon substrates [18].

• Some of the most promising work occurs where multiple disciplines overlap. The Army Research and Development

Command has recently assisted in developing an extremely

small ultraviolet (UV) source for detection of biological particles. By decreasing the size of the UV source, the entire

detector becomes small enough, inexpensive enough, and

light enough to be easily and rapidly deployed for a variety

of applications [19].

• Once IR detector materials are developed there is still a significant amount of materials research that needs to be done

before a device can be fielded. Recent work at the Army

NVESD has focused on exactly this obstacle. They have

made recent advances adapting devices and materials for

multiple roles to both simplify the devices and reduce their

cost, while also improving the overall performance [20].

• Extremely exciting are the potential discoveries being examined in molecular electronics within an ARL-WMRD and

ARL-SEDD collaboration. This technology promises construction of electrical circuits out of individual molecules.

Individual circuit elements have been demonstrated, and

current research is focusing on methods for engineering molecules so that they self-assemble into device structures [21].

These are but a few of the examples of research being undertaken at the Army research facilities focusing on electronic

materials for potential applications in the Future Force.

ACKNOWLEDGEMENTS

The authors would like to gratefully recognize the contributions and assistance that Dr. Kwong Kit Choi of ARL-SEDD

has made to this article.

REFERENCES

[1] M.W. Cole, W.D. Nothwang, C. Hubbard, E. Ngo, and 

T. Garvin, Alternative Detectors for Infrared Army ApplicationsFinal Report, 2003

[2] M.Z. Tidrow, Material Science and Engineering, B74,

2000, 45-51

[3] M.W. Cole, P.C. Joshi, M. Ervin, M. Wood, Compendium

of FY01 DRI Final Reports, 2002, 33 - 45

[4] 2004 Project Sheets, (http://www.arl.army.mil/sedd/index.

html)

[5] D.K. Wiltsie, Army AL & T, 22, Sept/Oct 2001

[6] E.H. Biass and S. Gourley, Armada International, 28-36, 5-

2001

[7] Goldberg, S.W. Kennerly, P.N. Uppal, and M. Sundaram,

Proc. 1998 Meeting of the IRIS Specialty Group on Infrared

Materials, 1998, 1

[8] R. Soref, L. Friedman, M. Noble, D. Schwall, and R. RamMohan, AFRL Horizons, SN-99-07

[9] A.R. Ellis, Amlan Majumdar, K.K. Choi, J.L. Reno, and

D.C. Tsui, Appl. Phys. Lett. 84, 2004, 5127

[10] M.Z. Tidrow, J.W. Little, R.P. Leavitt, A.C. Goldberg, S.

W. Kennerly, P.N. Uppal, and M. Sundaram, Proc. 1998 Meeting of the IRIS Specialty Group on Infrared Materials, 1998, 1

[11] J.W. Little and R.P. Leavitt, Appl. Phys. Lett. 84, 2004,

3010

[12] Dhar C.E.C. Wood, A. Gray, H.Y. Wei, L. SalamancaRiba, and J.H. Dinanl, J. Vac. Sci. Technol. B14 (3), May/Jun

1996

[13] N.K. Dhar, J.P. Zanatta, P. Ferret, and A Million, Journal

of Crystal Growth, 201/202, 1999, 975-979

[14] Y. Xin, S. Rujirawat, N.D. Browning, R. Sporken, S

Sivananthan, S.J. Pennycook, and N.K. Dhar, Appl. Phys. Lett.

75, No. 3, 1999, 349

[15] N.K. Dhar, M. Zandian, J.G. Pasko, J.M. Arias, and J.H.

Dinan, Appl. Phys. Lett. 70 (13), 1997, 1730

[16] J.M. Zavada, S.X. Jin, N. Nepal, J.Y. Lin, H.X. Jiang, P.

Chow and B. Hertog, Appl. Phys. Lett. 84, 2004, 1090 

[17] W. Mason, L.A. Almeida, A.W. Kaleczyc, and J.H. Dinan,

Appl. Phys. Lett. 85, 2004, 1730

[18] A. Motayed, A. Sharma, K.A. Jones, M.A. Derenge, A.A.

Iliadis, and S.N. Mohammad, Journal of Applied Physics. 96, 6,

2004, 3286-3295

[19] J.B. Cabalo, R. Sickenberger, W.J. Underwood and D.W.

Sickenberger, Proceedings of SPIE, 5417, 2004, 73-81

[20] J. Kostrzewa, W.A. Terre, J. Frank, R. Malmberg, L.

Switzer, W. Antesberger and G. Newsome, Proceedings of

SPIE, 5406, 2004, 541-549

[21] R. Pati and S.P. Karna, Phys. Rev. B, 69, 2004, 155419
The AMPTIAC Quarterly, Volume 8, Number 4 117

Dr. William D. Nothwang is a senior researcher in the Electronic Materials Research Group of the Multifunctional

Materials Research Branch, within the Materials Division at Aberdeen Proving Grounds, MD. He has significant

research expertise in bulk and thin film ferroelectric materials for applications in such areas as microwave communications, actuations, device integration and reliability, pyroelectric detectors, and power storage. 

Dr. Melanie Cole has been a research scientist with the US Army Research Laboratory [ARL] for 16 years. She currently serves as the Team Leader and Principal Investigator of the Active Materials Research Group. Her work focuses on fundamental and applied research in the synthesis, properties, and processing science of thin film materials

for use in next-generation electronic, microwave, and opto-electronic devices and circuits. She has published 76 articles in peer reviewed scientific journals, 108 manuscripts for conference proceedings, and has given numerous talks

at national and international symposia. She has also authored 10 patents/disclosures. Approximately 1,100 citations appear in the scientific literature relevant to Dr. Cole’s research.

Dr. Arnold Goldberg holds a BS in physics from the University of Maryland, a MS in applied physics from Johns

Hopkins University, and a PhD in physics from the University of Maryland. He was employed as a scientist in the

Advanced Infrared Technologies Department at Martin Marietta Laboratories from 1981 to 1995. Since 1996, he

has worked at the U. S. Army Research Laboratory in Adelphi, MD as the leader of the Passive IR imaging team in

the EO/IR Technology Branch of the Sensors and Electron Devices Directorate. The principal focus of his work is

multispectral infrared imaging. Dr. Goldberg has published several refereed journal articles; and a book chapter on

IR imaging using QWIPs, as well as comparisons of the various IR detector technologies.

Overworked? Overloaded? 

Could you use some materials engineering help? 

AMPTIAC can provide answers to materials-related technical questions. 

Here’s how it works: You contact our inquiry manager with the problem. The

inquiry manager discusses the problem with you to make sure we understand exactly what

you need. He then assigns the task to an AMPTIAC technical expert with knowledge and

experience of the discipline in question. 

AMPTIAC maintains the DOD’s knowledge base in advanced materials; nearly 220,000 technical reports addressing

all classes of materials. Our database contains information on properties, durability, applications, processes, and more.

Plus if we don’t find it in our resources, we also have direct access to NASA and DOE databases. With this tremendous

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The resultant data book provided the contractor with valuable information they needed in their effort to design a satellite structure. 
118 The AMPTIAC Quarterly, Volume 8, Number 4

INTRODUCTION

The Army and the DOD have been moving towards using

polymer matrix composites (PMCs) in their current set of

vehicles, ships, and equipment because of their combination 

of light weight and good mechanical properties. Programs have

been initiated to replace steel components with composite parts

on the high mobility multipurpose wheeled vehicle

(HMMWV), the Apache Longbow helicopter, (Figure 1), as

well as many other army vehicles. For instance, composite rotor

blades have already replaced metal blades in the Apache Longbow. Furthermore, future classes of vehicles and ships will use

significantly higher amounts of composite materials, making

these vehicles lighter, faster and more maneuverable.

Fabrication of composite materials can, however, produce

large amounts of volatile organic compounds (VOCs) and

hazardous air pollutants (HAPs). VOCs are materials that

readily vaporize under ambient conditions while HAPs are

defined by the 1990 Clean Air Act Amendments (Section 112)

as chemicals that require emissions limits. Sources of pollution

from PMCs include disposal of hazardous polymer ingredients, solvents used for viscosity reduction, gases evolved during and after processing, and disposal of contaminated scrap

materials. Through implementation of the Clean Air Act and

Clean Water Act, the Environmental Protection Agency (EPA)

has established regulations limiting the amount of VOCs,

HAPs, and heavy metals that can be used in the fabrication of

composite materials. 

The Army has developed a number of potential solutions to

these problems that may impact the Department of Defense

(DOD) and commercial composite manufacturers. High VOC

containing solvents such as styrene and methyl methacrylate

have been partially replaced with low VOC plant-derived fatty

acids. Modified resins are used which allow curing methods

other than autoclave curing which produces nitrous oxide

(NOx) HAPs. The result is environmentally friendly PMCs

with properties comparable to current commercially manufactured PMCs.

FABRICATION PROCESSES

Liquid molding, depicted in Figure 2, is used to manufacture

many thermoset PMC parts, such as automobile components

and furniture. Vacuum Assisted Resin Transfer Molding

(VARTM) is among the most common manufacturing

processes to produce composites. In all of these processes, a

liquid resin is injected into a mold containing fibers, such as

glass or carbon fibers. It is important that the resin have a low

viscosity (resistance to flow) so that the resin fills the gaps

between fibers. Otherwise, defects will be present, significantly reducing the mechanical properties of the part. The high

viscosity of thermoplastic polymers, like polycarbonates, is

John J. LaScala

James M. Sands

Weapons and Materials Research Directorate

Army Research Laboratory

Aberdeen Proving Ground, MD

Giuseppe R. Palmese

Department of Chemical Engineering

Drexel University

Philadelphia, PA

Figure 1. Current and Future

Uses of Composite Materials in

the Army Include Component

Replacements in the HMMWV

and the Apache Longbow.
The AMPTIAC Quarterly, Volume 8, Number 4 119

why these materials cannot be used to a large extent in 

composite manufacture. Once injected into the mold, the

thermoset resin is then cured (i.e. reacted to form a solid) 

at room temperature or at elevated temperatures. Unlike thermoplastics, thermoset resins cannot be melted and reprocessed

once cured. 

The most commonly used thermoset resins for making composite materials are epoxy resins, unsaturated polyesters (UPE),

and vinyl esters (VE). Reactive diluents in UPE and VE resins,

such as styrene and methyl methacrylate, are used to reduce the

resin viscosity to enable liquid molding. However, these diluents are VOCs and HAPs that can produce adverse health

effects including headache, fatigue, depression, irritation, and

cancer and are damaging to the environment. 

VOCs evaporate at substantial rates at room temperature

and could potentially produce smog-promoting ozone as well

as long-term and acute health effects. VOC/HAPS are emitted during all of the phases of composite fabrication and even

after fabrication (Figure 3). Emissions occur during the mixing of diluents, catalysts, and initiators into the system. Composite parts typically have very large surface to volume ratios,

which allows up to 20% loss of diluent content during the

molding stage. The elevated temperatures increase the vapor

pressure of styrene and thus increase the rate of VOC emission. Unfortunately, even after cure during the lifetime of the

part, VOC emissions can be substantial. 

Studies have shown that up to 50% of the styrene in vinyl

ester resins is unreacted after cure [1]. These unreacted

monomers (simple compounds which react to form a part of a

thermoset polymer) evaporate as VOCs, giving the composite

an unpleasant odor and possibly leaching out into the water

supply during the lifetime of the part. Studies have shown that

although the composites industry only consumes 9% of the

styrene, it produces 79% of the styrene emissions [2]. For

these reasons, by means of the Clean Air Act, the EPA has

enacted the Reinforced Plastic Composites National Emissions

Standards for Hazardous Air Pollutants (NESHAP) to limit

styrene emissions from composite manufacturing[3]. This 

legislation could have a significant impact on the use of composite materials in military as well as commercial applications

unless methods for mitigating VOC emissions during composite processing, curing, and fielding of the composite part

are developed. Current resins typically contain approximately 

40-50% VOC content. The new regulations require the VOC

content to be effectively about 30%, resulting in emissions

reduction of approximately 8000 tons per year. Although some

commercial resins have as little as 30% VOC content, these

resins suffer from inferior properties.

Autoclave processes are used to cure PMCs and adhesives at

elevated temperatures and high pressure. Global heating in an

autoclave requires the application of pressure on the entire

part. Nitrogen is used to provide the pressure and leads to the

generation of high amounts of NOx emissions, which is also

regulated as a HAP under the Clean Air Act. NOx emission is

Figure 2. General Resin Transfer Molding Process.

Figure 3. VOC Emissions are Liberated During All Stages of Composite Production.

The fiber preform is placed into the mold. The resin is injected into the mold.

The resin is then cured, after which the composite part is demolded.

Fiber Preform Tool (Mold) Injection Cure Demold

Mixing Molding Curing and Post-curing In Service

Resin

VOC Evolution

VOC Evolution

VOC Evolution

VOC Evolution
120 The AMPTIAC Quarterly, Volume 8, Number 4

conservatively estimated at 2% of the resin or adhesive mass

[4]. The DOD produces approximately 30 million pounds of

composites per year, of which half is processed in an autoclave

resulting in about 150,000 pounds of HAP emissions per

year. NOx emissions generated from adhesives amount to

approximately 90,000 lbs/year. As a result, there is a large

push in the DOD and composites industry for “moving out

of the autoclave.”

Resins used for repair of PMC components for DOD applications produce significant amounts of hazardous emissions

[4]. In addition, spoilage of these resins results in large

amounts of hazardous waste a year. Estimates show that resin

spoilage amounts to 20% of composites resulting in roughly 5

million pounds of hazardous waste per year, and 40% of adhesives materials resulting in 22 million pounds per year. Furthermore, many PMC components have been designed using

existing technologies that fail to provide for practical and

affordable component repair. These systems will generate large

amounts of waste; and therefore, it is important to develop

affordable and environmentally friendly PMC repair technologies, resins, and adhesives with longer shelf-lives.

UNSUCCESSFUL ENVIRONMENTAL SOLUTIONS

An obvious solution to reducing diluent emissions is simply to

reduce the reactive diluent content in resins. There are a number of problems with this approach. First, the resin viscosity

increases exponentially as the diluent content is decreased,

making it impossible to use liquid molding techniques to produce composite parts. In addition, properties such as the

strength and toughness decrease significantly as the diluent

content is reduced. Lastly, reducing the styrene content increases the resin cost because vinyl ester/unsaturated polyester

monomers typically cost double that of inexpensive diluents

like styrene.

Various petroleum-based monomers, such as vinyl toluene

with VOCs lower than that of styrene, have been used as

styrene replacements [5]. However, these styrene replacements

still produce significant VOC emissions, and are regulated by

the EPA [3]. In addition, few monomers yield resins with performance comparable to styrene-based resins, and even fewer

can match the low cost of styrene.

Vapor suppressants have been used to reduce emissions from

vinyl ester resins. These suppressants are typically a surfactant

or paraffin wax that segregates to the air interface and reduces

the styrene evaporation rate [2]. Unfortunately, these suppressants also tend to segregate to the resin-fiber interface, which

decreases fiber-matrix adhesion and the mechanical properties

of the composite.

Another possible solution is to trap the VOC emissions during resin processing, composite production, and painting applications. These trapping devices need to absorb most of the

VOC emissions and then efficiently remove the emissions from

the air before exhausting to the atmosphere. Trapping devices

fail in two major aspects. First, their use is not feasible in the

production of large scale structures. Large scale structures are

typically fabricated outside or in covered shelters, and building

a device to trap a significant portion of the emissions is cost

prohibitive. Secondly, although such devices would remove the

VOCs from the atmosphere, the workers, due to their proximity to the structure being fabricated, would still be subjected to

emissions and the associated health risks.

NOx emissions can be eliminated by using an inert gas, such

as argon, to generate the pressure required for autoclave

processes. However, the cost of switching to argon is not economically feasible. Electron beams have been used as a mechanism to cure thermoset polymers. E-beams are a source of ionizing radiation that can generate ionic species, free-radicals, and

molecules in excited states capable of initiating and sustaining

polymerization. They can be used to reduce VOCs and NOx

emissions by cationic polymerization of epoxy monomers. Yet,

the photoinitiators (compounds which cause polymerization

upon the absorption of light) designed for E-beams are very

expensive, and the initiator is easily poisoned by nitrogen and

alcohols. Furthermore, cationically cured epoxies suffer from

poor interfacial strength. 

Resin suppliers have been trying to improve the shelf-life of

resins and adhesives through the use of new inhibitor packages.

The shelf-life has been improved but is still less than one year

for most resin systems, and large amounts of spoiled resins are

still produced annually.

SUCCESSFUL ENVIRONMENTAL SOLUTIONS

We have developed three solutions to reducing the VOC emissions from UPE and VE based composite resins. These solutions involve replacing conventional reactive diluents with

plant oil derived monomers, altering the molecular structure of

the cross-linking agent and reducing the styrene content in

these resins. This also allows the use of environmentally friendly repair techniques, such as E-beam curing (Figure 4) which

decreases cure time and temperature and reduces hazardous

waste generation and NOx emissions. These methods are currently in the process of being patented [6].

Fatty Acid Monomers

Triglycerides are the main component of oils derived from

plant and animal sources. Triglycerides are three fatty acids connected by a glycerol center (Figure 5). Triglycerides are simply

broken down into fatty acids using industrial processes, such as

acidolysis and saponification. A number of synthetic routes

have been established for making fatty acid-based monomers.

These synthetic routes can either use the acid group of the fatty

acid or the functionality along the fatty acid backbone to attach

Figure 4. Photograph and Schematic of E-beam Curing 

Equipment [7].

Composite

Structure

Electron

Source
The AMPTIAC Quarterly, Volume 8, Number 4 121

functional groups that can polymerize. The resulting

monomers have fairly high molecular weight and are nonvolatile, making them excellent alternatives to styrene in liquid

molding resins. Due to the low cost of fatty acids and the simple modifications to produce fatty acid monomers, these

monomers are inexpensive, with an estimated cost only slightly above that of styrene. Although plant oils have been used to

make polymers for years, the use of fatty acid monomers as

reactive diluents is a novel concept [6].

Ideally, all of the styrene in UPE and VE resins could be

replaced with fatty acid-based monomers; however, the resulting resin and polymer properties are poor relative to commercial resins. Good performance can be realized by partially

replacing styrene with fatty acid monomers. Styrene contents

ranging from 10 wt% to 20 wt% (55-78% reduction in VOC

content relative to commercial resins) were used resulting in

good resin and polymer properties. The resin viscosities were

far below the threshold for liquid molding processes and have

been successfully used to produce defect free composite parts at

high production rates. The glass transition temperature (Tg),

the temperature at which a material transitions from hard and

rigid to soft and rubbery, was similar to commercial resins, and

the toughness was twice that of commercial resins. On the

other hand, the stiffness and strength were a bit lower than that

of commercial resins. Fortunately, we have found a number of

methods for improving the stiffness of fatty acid-based polymers. The first involved using fatty acid monomers with shorter chain lengths. Experiments have shown that the resin viscosity decreases while the stiffness and Tg increase as the fatty acid

chain length decreases. In addition, slightly modifying the VE

chemical structure offers promise for improving the strength

and stiffness by altering the polymer morphology.

A number of composite materials were made using VE resins

with both styrene and fatty acid monomers as the reactive diluents. To prove that these resins can be used to produce large

scale structures, a composite hood for an M35-A3 truck (Figure 6) was fabricated using a low VOC resin containing 15%

fatty acid monomers and only 20% styrene. The resin infused

very quickly for such a large structure (7 ft x 7 ft) and cured

well to produce a fine composite structure. Therefore, successful low VOC resins are not merely a concept, but instead are

reality.

Bimodal Blends of Vinyl Ester Monomers

The molecular structure of VE monomers can be used to alter

the polymer properties and reduce the styrene content in these

resins. Simply reducing or increasing the molecular weight of

vinyl ester monomers does not provide a means for both

decreasing styrene emissions and maintaining resin and polymer properties. Low molecular weight VE monomers have

poor fracture properties because of their high cross-link densities. High molecular weight VE monomers yield resins with

high fracture properties because of reduced cross-link density

(i.e. matrix toughening). A mixture of low and high molecular

weight VE monomers (i.e. bimodal blend) could be used to

maintain low resin viscosities and low styrene contents while

achieving high fracture toughness [6].

Figure 5. Methods to Reduce VOC Emissions in Thermoset Resins.

Continued on Page 124

Standard Vinyl Ester

Monomer (Cross-linker)

Styrene

Monomer

Electron

Beam Cure

Soybeans

Low VOC Composite

Triglyceride

Commercial Resins 

Produce Large Amounts 

of VOC Emissions

Methacrylated

Fatty Acid

(Stryrene Substitute) Low Styrene 

Content

VOC

VOC

Bimodel Blends and Other Chemical Modifications
122 The AMPTIAC Quarterly, Volume 8, Number 4

Coatings are used to prevent corrosion and damage to vehicles and structures, while also providing camouflage. Prior to the application of coatings, the metal surfaces are usually cleaned with

solvents and treated with chemicals, such as lead and hexavalent chromium, to promote adhesion

and corrosion resistance of the coating. Chemical agent resistant coatings (CARCs) contain polymer binders that provide the required performance level of the product, pigments that provide the

desired color and gloss, and solvents/additives that control the viscosity and aid in film formation

[1]. An aliphatic polyurethane binder provides the chemical agent resistance while the camouflage

properties are provided by an appropriate selection of tinting pigments for visual color and nearinfrared reflectance, plus extender pigments for gloss control. 

In a typical solvent-based urethane system, polyol reacts with polyisocyanate to form

polyurethane, see Figure 1. If designed properly, crosslinking (bonds between polymer chains) 

in this system provides high-performance coatings. CARCs must display resistance to alkali,

hydrocarbons, and acids. The coating must also exhibit high flexibility and mar resistance (i.e.

high ability to resist damage). Lastly, the coating must have a very low gloss for camouflage

requirements. This usually requires high pigment contents, which tend to have an adverse effect

on the coating’s performance. 

The use of organic solvents to clean surfaces prior to coating has been affected by the Environmental Protection Agency mandated Reinforced Plastic Composites National Emissions Standards

for Hazardous Air Pollutants and harsher regulations imposed by local governments. Typical cleaners, such as isopropanol and tetrachlorethylene, are volatile organic compounds (VOCs), materials

that readily vaporize under ambient conditions, and/or hazardous air pollutants (HAPs) as defined

by the 1990 Clean Air Act. The use of lead or chromium pre-treatments are regulated under the

Clean Water Act because heavy metals accumulate in organisms and can cause blindness, autoimmune disorders, and cancer among other health problems. CARCs require a solvent to reduce

the viscosity for painting and film formation. Previous CARCs use organic solvents that produce

large amounts of VOCs and HAPs during application and drying. The Clean Air Act and its

amendments has set the VOC limit for the CARC topcoat at 3.5 lbs/gal, but local governments

have set this limit as low as 1.8 lbs/gal. Therefore, new environmentally friendly CARC systems,

cleaning solvents, and primers are necessary.

The Army has developed a number of solutions to reduce the overall environmental impacts 

of surface preparation and coating processes (Figure 2). Low VOC solvents for cleaning, dry 

(no water) metal coating processes, and low VOC CARCs are all excellent methods leading to cost

efficient, good performance coatings. The systematic approach to developing alternative processes and materials has resulted in methods that have a very beneficial cumulative impact. 

A few low vapor pressure solvents were identified that can be used to effectively clean composites prior to repair [2]. Exxsol D60 and Isopar G, both developed by Exxon Chemical, clean

surfaces as well or more effectively than conventional solvents, such as isopropanol and acetone.

Furthermore, these solvents are similar in cost. Because these alternative solvents have substantially lower vapor pressure, they produce less VOC/HAP emissions and are less flammable.

Different materials and approaches can be used to increase the part-life rather than using a high

VOC/HAP chemical treatment. Tantalum coated gun barrels that protect the bore surface from the

hot propellant gases were developed to eliminate the need for hexavalent chromium processing [3].

Furthermore, the tantalum coating was deposited using an environmentally friendly method called

Figure 1. Chemical Reaction to Produce Polyurethane.

Army Develops New

Environmentally

Compliant Coating

Technologies

H O

l ll

R—OH + R’—N=C=O R’—N—C—O—R

polyol polyisocyanate polyurethane
The AMPTIAC Quarterly, Volume 8, Number 4 123

Cylindrical Magnetron Sputtering (CMS) that does not

generate heavy metal-based hazardous wastes. CMS is a

magnetically enhanced sputtering system that is capable of

providing high deposition rates over large areas while

maintaining low substrate heating levels. In fact, the

resulting gun barrels exhibit superior corrosion and wear

resistance relative to chromate treated barrels. In cases

where CMS cannot be used, the Army has also developed

lead-free and acid-free solid rocket motor propellants

reducing the need for lead and chromium treatments [4].

ARL developed a water dispersible CARC as a “drop in”

replacement for the previous solvent-based CARC that

can be applied and stripped using existing equipment [5].

The patented (US patent #5,691,410) water-based system

eliminates HAPs and ozone depleting chemicals entirely,

along with 4 millions lbs/year of VOC emissions, a 50%

reduction, thereby meeting the new emissions requirements. The binder is still a mixture of polyisocyanates and

polyols that cross-link to form polyurethane. While there

is still competing reaction occurring with water, the chemical kinetics, raw materials, and a large excess of isocyantes

to hydroxyl groups (5:1) were used to ensure good coating

performance. Polymeric beads were used rather than

siliceous-based pigments. This allowed for lower pigment

contents to produce the same low gloss coating, while 

further improving the coating’s performance.

The water-based system was found to be a better CARC

than the solvent-based system because of its superior 

flexibility and durability, and it requires one-third less paint [5]. This improved performance increases the time between 

finishing and reduces damage to the structure resulting in less coating maintenance. Furthermore, the cost per square foot

per year of service for the environmentally friendly CARC is actually less than that of the previously used solvent-based 

system even though the water dispersible CARC costs more per gallon. In addition, dry abrasive blasting was successful in

removing the environmentally friendly CARC, rather than using solvent-based paint removers. For these reasons, the Army

has switched almost completely to the environmentally friendly CARC. More recently, the Army has conducted an extensive

investigation of coatings and their degradation mechanisms, thereby improving coating durability even further and generating less VOC emissions [6].

The Army recently developed a universal ammunition coating (UAC) for munitions systems [7]. To improve the overall

coating performance for munitions, a new class of corrosion-inhibiting pigments was incorporated into a durable fastdrying alkyd (drying oil modified polyester) polymer system. In addition to meeting the requirements for emissions, substrate adhesion, and long-term storage with energetic materials, the UAC provides improved corrosion resistance, eliminates

the primer coats on certain munitions, and is a drop in replacement for existing coatings. After extensive evaluations, the

UAC was qualified for Army use.

REFERENCES

[1] J. Duncan, Demonstration/Validation of Low Volatile Organic Compound (VOC) Chemical Agent Resistant Coating (CARC),

Final Report, ESTCP 200024, November 2003

[2] D. Helfritch, T. Miller, V. Champagne, S. Grendahl, W. Ziegler, Evaluation of Alternative Cleaners for Hand Wipe Cleaning of Composite Materials, Report to the US Army Aviation and Missile Command, Huntsville AL, May 2002

[3] M.J. Audino, Tri-Service ‘Green’ Gun Barrel, Final Report, SERDP PP-1074, March 2003

[4] M.G. Feathers, Elimination of Toxic Materials and Solvents from Solid Propellant Components, Final Report, SERDP PP1058, January 2001

[5] B. Lacovara, Reducing Emissions with Styrene Suppressants, CFA, 1999

[6] W.E. Kosik, Mechanisms of Military Coatings Degradation, Final Report, SERDP PP-1133, August 2003

[7] P. Smith and K. Chesonis, Recent Advance in Ammunition Coatings, Proceedings of the American Chemical Society,

Philadelphia PA, August 2004

Figure 2. Methods for Reducing VOC/HAP Emissions and Heavy

Metals in Surface Preparation and Coating Processes Include

Low VOC Solvents for Cleaning, Dry Metal Coating Processes,

and Low VOC CARCs.

VOC/

HAP

Standard Surface

Preparation

Water Hazard

Environmentally

Friendly Surface

Preparation

VOC/

HAP

VOC/

HAP

VOC/

HAP

CCI2=CCI2

CH3-CHOH-CH3

(High VOC Cleaners)

5 RCNO + 1 ROH +

Polymeric Bead Pigments

+ Water + Less Solvent

(Low VOC CARC)

1 RCNO + 1 ROH + Siliceous Pigment + Solvent

(Standard CARC)

ISOPAR G, EXXSOL D60

(Low VOC Cleaners)

Metal Deposition via CMS

(No Heavy Metal Waste)

Pb or Cr6+ Based Primers

(Heavy Metal Waste)
124 The AMPTIAC Quarterly, Volume 8, Number 4

Experimental results showed that the styrene content of these

bimodal blends can be reduced while still maintaining low

enough viscosity for composite liquid molding processes. The

viscosity was found to be dependent on the number average

molecular weight of the bimodal blends of VE monomers. As a

result, the styrene content can be decreased to as low as 30-37

wt% while maintaining good resin processability. Although not

a severe reduction in styrene content, this does amount to

~20% reduction in VOC emissions relative to commercial

resins. The modulus and strength were also comparable to

commercial resins. But most importantly, bimodal blends substantially improved the toughness relative to commercial resins.

Therefore, the concept of bimodal blends of VE monomers can

be used not only to reduce VOC emissions, but also improve

the composite properties.

Composite Repair

E-beam curable resins were developed that can be used in

VARTM applications [4]. These resins consists of di-epoxy,

tetrafunctional amines, di-vinyl monomers, and monomers

with both epoxy and vinyl functionality. The liquid monomeric resin has a low enough viscosity for VARTM, whereby it can

be injected into a mold containing glass or carbon fibers and

properly wet the fibers. When the resin mixture is cured at

room temperature, the epoxy-amine forms a network, while the

vinyl functionality remains unreacted inside the network. This

gelled mixture is then irradiated with an E-beam to form a second network by cross-linking the vinyl groups, which are subsequently linked to the epoxy network. The Tg of the resulting

polymers are high (250-350°F) with fracture toughness values

above that of other E-beam resins. Furthermore, the shelf-life

of the resin was found to be nearly infinite, with no chemical

change occurring as a function of time until the two-part system is mixed together. This resin has been commercialized as

Prepreg T-17 by YLA, Inc. in Benicia, CA for E-beam/VARTM

applications.

Environmentally friendly E-beam adhesives were formulated

in a similar fashion [4]. However, blends of mono- and multifunctional amines and epoxies were used to prevent gelation of

the epoxy-amine network. Instead, when these components

completely react, the resin viscosity increases to that of a paste.

The paste can be applied to join sections of a composite, fill in

holes, etc. and then be completely cured via E-beam. These

resins were toughened through the addition of a functionalized

rubber that phase separates into rubbery domains during cure.

The resulting polymers have high Tg and excellent adhesion

strength that far exceeds previously developed commercial Ebeam resin systems.

The most common bonding methods for repairing composites are the use of convection ovens, thermal blankets, and radiant heaters. All of these processes heat the entire part and do

not target just the repair zone. This requires long process times

and exposes large areas of the composite structure to excessive

heating, which could have detrimental effects on the composite’s performance. Induction heating occurs when magnetic or

conductive materials, like carbon-fiber composites, are subjected to a high frequency electromagnetic field (Figure 7). For

parts not using carbon-fibers, metal wire meshes are impregnated with resin/adhesive at the point of repair or the repair resins

are formulated with 20-30% magnetic particles by volume [8].

Induction heating can achieve thermal powers necessary for

high temperature and rapid heating. This achievement is not

trivial and has been made possible only though the development of high frequency (>10 MHz) self-tuning induction

power supplies. Furthermore, induction heating can be used

with both thermoset and thermoplastic resins.

Both E-beam and induction heating processes eliminate the

need for autoclave processing, which completely eliminates

Figure 6. Photographs of a) the Unpainted Composite Hood and b) the Hood Affixed on an M35-A3 Truck. 

The Blue Stripes are PVC Foam Stiffeners that are Fabricated into the Part.

Figure 7. The Coils Magnetically Induce the Resin Cure by 

Heating the Composite Material.

a)

b)
The AMPTIAC Quarterly, Volume 8, Number 4 125

NOx emissions. In the cases where thermoplastic resins can be

used to replace thermoset resins for repair, VOC/HAP emissions can also be eliminated using the induction heating technology. Even for thermoset systems, emissions are reduced by

50% through the use of E-beam cure because of the rapid cure

associated with E-beam. In addition, the E-beam curable resins

were designed to have nearly unlimited shelf-life, thereby

reducing the amount of hazardous waste produced by DOD

and industry in terms of spoiled resins. Overall, a conservative

estimate of the annual savings for the DOD is a substantial

$220 million on top of the large environmental benefit associated with these technologies.

CONCLUSIONS

The military and commercial industry has a large need for high

performance composite resins with reduced VOC emissions.

Previously developed solutions to the emissions problem are

not acceptable because the resins still produce large amounts of

VOCs or performance is severely reduced. The Army’s solutions to these problems involve modifying the molecular structure of the cross-linker molecules, using plant derived fatty acid

monomers as styrene substitutes, using epoxy/amine/vinyl Ebeam curable resins, and induction curing techniques. These

solutions allow for severe reduction in VOC and NOx emissions and reduction in hazardous waste, while producing resins

and coatings that have comparable, and in some cases, superior

properties to commercial polymers. Therefore, these solutions

will help enable the Army and the entire DOD to produce the

next generation of lighter, more efficient, and environmentally

compliant vehicles, ships, and structures.

REFERENCES

[1] S. Ziaee and G.R. Palmese, J. Polym. Sci. B: Polym. Phys.,

37, 725, 1999

[2] B. Lacovara, Reducing Emissions with Styrene Suppressants,

CFA, 1999

[3] Environmental Protection Agency, Federal Register, 68,

19375, 2003

[4] J.M. Sands, Non-Polluting Composites Repair and Remanufacturing for Military Applications, Final Report, SERDP PP1109, December 2002

[5] T.W. Smeal and G.L. Brownell, US Patent 5,292,841, 1994

[6] G.R. Palmese, J.J. La Scala, and J.M. Sands, Vinyl Ester

Monomers to Reduce Emissions and Toughen Polymers, US Patent

Disclosure, April 2004

[7] http://www.ms.ornl.gov/researchgroups/composites/new%

20orccmt %20pages/pages/ebwhat.html

[8] D. Helfritch, T. Miller, V. Champagne, S. Grendahl, 

W. Ziegler, Evaluation of Alternative Cleaners for Hand Wipe

Cleaning of Composite Materials, Report to the US Army 

Aviation and Missile Command, Huntsville AL, May 2002

Dr. John LaScala is a postdoctoral scientist from the Oak Ridge Institute for Science and Education (ORISE), 

working with the Army Research Laboratory for the past two years. He has seven years of experience in composite materials and materials from renewable sources. Dr. LaScala holds a PhD in Chemical Engineering from the 

University of Delaware and a BS in Chemical Engineering from the University of Virginia.

Dr. James M. Sands is currently the Leader of the Transparent Materials Technology Team in the Survivability 

Materials Branch of the Weapons and Materials Research Directorate at Aberdeen Proving Grounds, MD. 

Dr. Sands began his research career at the US Army Research Laboratory in 1998, working as a contractor, 

until joining as a civil servant in 2000. He earned his doctorate in Materials Science and Engineering from the 

Pennsylvania State University; and a BA degree in Chemistry and Mathematics from Augustana College (SD). 

Dr. Sands has more than 20 combined refereed publications, conference proceedings, and Army technical reports

to his credit.

Dr. Giuseppe R. Palmese is Department Head of Chemical Engineering at Drexel University’s School of Engineering; where he continues to a run a research program in nanocomposites, standard composites, and materials 

from renewable resources. He has twenty years experience in composite materials and eight years experience 

in materials from renewable resources. Dr. Palmese holds a PhD in Chemical Engineering from the University of

Delaware, and a BS in Chemical Engineering from Princeton University.
126 The AMPTIAC Quarterly, Volume 8, Number 4

INTRODUCTION

Future Army helicopters will be able to fly farther and carry

more payload thanks to the advanced material systems being

developed by scientists and engineers at the Army Research

Laboratory (ARL). Current gas turbine engine components,

mainly the combustor and turbine, are made of heavy metal

alloys that depend on significant amounts of air to cool and

maintain them at or below their maximum use temperature of

about 1100°C. Major efficiency gains can be made if the cooling air is dramatically reduced, completely eliminated, or the

operating temperatures of components can be increased. The

cooling system does not produce the primary work function,

propulsion; therefore it is viewed as a penalty or inefficiency to

the operation of a gas turbine engine. Turbine engine operational efficiencies can be increased through the use of ceramic

matrix composites and ceramic thermal barrier coatings.

TURBINE ENGINE MATERIALS DEVELOPMENT

During the evolution of gas turbine engines, there have 

been great improvements made to the design of the combustor

liners, turbine vanes, and blades (Figure 1). Those improvements have made more efficient use of the cooling air, resulting

in significant cooling system reductions and efficiency

improvements. However, the material operational temperatures

have not been increased and are preventing further improvements in fuel efficiency (Figure 2). 

Ceramic materials have the potential of operating at temperatures greater than 1100°C with minimal or no cooling, which

will produce a variety of performance advantages. ARL, in collaboration with NASA, has been working on the development

of fiber-reinforced ceramic matrix composites (CMCs) for

potential use in combustor and turbine vanes and blades.

CMCs are capable of higher operating temperatures, are about

Waldo A. Acosta

Ramakrishna T. Bhatt

David N. Brewer

Dongming Zhu

Vehicle Technology Directorate

Army Research Laboratory

Cleveland, OH

Figure 1. Gas Turbine Engine Components.

a) CMC Combustor Can b) CMC Turbine Vane Coated with a Thermal Barrier Coating
The AMPTIAC Quarterly, Volume 8, Number 4 127

30 to 50% lighter than the metallic alloys currently in use,

exhibit the necessary toughness needed to operate in the 

turbine engine environment, and provide at least the same

level of safety and operability. There are several key factors that

need to be met to apply CMCs with success. Achieving a

CMC system with the required thermal and structural properties will depend on the ability to design and process the CMC

so that it achieves the proper microstructural features.

Our efforts have been centered on the development of a 

silicon carbide (SiC) fiber-reinforced SiC matrix composite

system (SiC/SiC), which was initially developed under

NASA’s Enabling Propulsion Materials (EPM) Program [1].

The goal of the EPM Program was to develop a SiC/SiC 

system capable of operating for many hundreds of hours at

temperatures up to 1200°C. The current goal is to develop a

SiC/SiC system capable of operating at 1427°C for hundreds

of hours and at the same time retaining the thermal and structural properties required by the particular component. This

Table 1. Key Constituent Material and Process Data For NASA/ARL-Developed CMC Systems.

CMC System N22 N24-A N24-B N24-C N26-A

Upper Use 2200°F 2400°F 2400°F 2400°F 2600°F

Temperature (1204°C) (1315°C) (1315°C)) (1315°C) (1427°C)

Fiber Type Sylramic Sylramic-iBN

(Dow Corning) (Dow Corning + N)

Interphase Coating CVI Si-doped BN CVI Si-doped BN

(GEPSC) outside debond

(GEPSC + N)

Matrix CVI SiC – low content CVI SiC – CVI SiC –

(GEPSC) medium content medium content

(GEPSC + N) (GEPSC)

SiC slurry infiltration PIP SiC (Polymer 

(GEPSC) Infiltrate and Pyrolysis)

(Starfire + N)

Silicon melt infiltration

(GEPSC) Silicon melt infiltration

(N)

N = NASA/ARL Processing

GEPSC = GE Power Systems Composites

Figure 2. Present and Future Army Helicopter Systems will Benefit from Advances in Gas Turbine Engine Technology.
128 The AMPTIAC Quarterly, Volume 8, Number 4

requires the optimization of many factors within the SiC/SiC

microstructure, including the fiber type, fiber coating material, fiber architecture, and matrix structure. The selection of a

few first-order property goals facilitated this task including a

high tensile proportional limit stress after processing, high

ultimate tensile strength (UTS) and strain after processing,

high UTS retention after interphase (region between the fiber

and matrix) exposure at intermediate temperatures in wet

oxygen, high creep resistance at upper use temperature under

high tensile stress, long rupture life (greater than 500 hours)

at upper use temperature under high tensile stress, and high

thermal conductivity at all service temperatures [2].

Various CMCs developed by NASA/ARL are shown in Table

1 [2]. In addition to the organizations listed, these CMCs have

been processed at other organizations resulting in material systems with similar properties. Recently, two types of hybrid

SiC/SiC composites with no residual silicon were fabricated:

the first using a combination of polymer infiltration and pyrolysis (PIP) and chemical vapor reactive (CVR) process; the second using a combination of chemical vapor infiltration and

PIP. Preliminary results indicate both types of hybrid SiC/SiC

composites are very promising for high temperature applications, up to 1450°C. However, additional studies are needed to

optimize processing and properties of these composites. Figure

1 indicates that at a stress level of 69 MPa, Sylramic-iBN

hybrid SiC/SiC composites fabricated by a combination of

CVI and PIP methods show a creep rupture life greater than

300 hours at 1500°C in air. At 103 MPa, the same composite

fails at about 60 hours (Figure 3).

Residual silicon in a SiC matrix has significant influences on

the upper temperature capability of SiC/SiC composites. The

SiC/SiC composites without any residual silicon show creep

rupture lives greater than 300 hours, whereas those containing

residual silicon rupture in less than 100 hours (Figure 4).

THERMAL AND ENVIRONMENTAL BARRIER COATINGS

Ceramic thermal and environmental barrier coatings

(TEBCs) have the potential to increase further the efficiency

of gas turbine engines by providing them with the ability 

to operate at higher gas temperatures while reducing cooling

requirements. Figure 5 shows that the development of revolutionary ceramic coatings results in a step increase in combustor and turbine vane and blade temperature capability. As

shown in the figure, advanced TEBC systems will withstand

higher surface temperatures and larger thermal gradients than

current coating systems. This will require the development of

advanced ceramic coatings with lower thermal conductivity to

allow the use of a thin layer coating while achieving a larger

temperature gradient across the coating, thereby enabling

reductions in cooling requirements since a lower substrate

temperature will be maintained.

ARL researchers, in collaboration with NASA, have been

developing advanced thermal barrier coatings (TBCs) for

metallic turbine airfoils and TEBCs for thermal barrier coatings

SiC/SiC combustor applications. The incorporation of multicomponent, paired-cluster rare-earth oxide dopants into conventional zirconia-yttria (ZrO2-Y2O3), and hafnia-yttria

(HfO2-Y2O3) oxide systems to develop the advanced oxide

coatings has been shown to achieve low conductivity, high temperature stability, and improved durability [3]. We synthesized

TBC systems containing ZrO2-Y2O3-Nd2O3(Gd2O3,

Sm2O3)-Yb2O3(Sc2O3) oxide clusters and investigated their

Figure 4. Creep Behavior of Melt Infiltrated SiC/SiC (With Silicon)

and Hybrid (Medium CVI +PIP) SiC/SiC Composites (Without 

Silicon) at 69 MPa, 1450°C in Air.

Figure 5. Potential Benefits from the Development of Advanced

Barrier Coatings.

Figure 3. Effect of Stress on Creep Behavior at Constant 

Temperature (1500°C) for Sylramic-iBN Hybrid SiC/SiC 

Composites Fabricated by CVI and PIP.

0 100 200 300 400

Time, Hrs 0 100 200 300 400

Time, Hrs

0.6

0.5

0.4

0.3

0.3

0.2

0.1

0.0 Tensile Creep Strain, %

1.4

1.2

1.0

0.8

0.6

0.4

0.2

0.0

Total Tensile Creep Strain, %

103 MPa

69 MPa

Melt 

Infiltrated

SiC/SiC

CVI + PIP

SiC/SiC

TEBC Surface

Ceramic Matrix Composite

Single Crystal Superalloy

1st Generation

3rd Generation

2nd Generation Current Commercial

4th Generation

Year

Temperature Capability

Increase in ∆T

Across TEBC 
The AMPTIAC Quarterly, Volume 8, Number 4 129

thermal conductivity, sintering behavior, and cyclic durability

at high temperatures. Figure 6 shows the advanced low conductivity electron beam - physical vapor deposited (EB-PVD) 

turbine airfoil thermal barrier coating demonstrated more than

200 hot-hour high-heat-flux, high-thermal gradient cyclic

durability at 1360°C (2480°F).

Under the wet oxidizing conditions encountered in the combustion gases, silica (SiO2) formation on the surface of unprotected SiC/SiC reacts with water to form volatile species, giving

rise to paralinear oxidation kinetics and a gas velocity-dependent degradation of the Si-based materials [4]. Advanced thermal and environmental barrier coatings for SiC/SiC combustor

liner and turbine vane applications will extend operating temperatures up to 1650°C while protecting the SiC/SiC substrate

from the wet oxidizing combustion environment. 

Figure 7 shows an advanced coating design concept for the

1650°C TEBC system for CMC combustor applications. The

top layer is a high-temperature capability ceramic thermal barrier coating, designed to provide the major thermal protection

for the sub-coating systems and CMC substrate. It also acts as

the first-stage radiation barrier by reducing the transmission of

infrared thermal radiation from the combustion gas environment. The energy dissipation, secondary radiation barrier and

environmental barrier layers will also be incorporated into the

coating system to provide strain tolerance, further reduce radiation energy penetration, and ensure environmental protection

functions.

HfO2-based oxides have been developed as a potential candidate for a 1650°C coating material for advanced thermal/environmental barrier top coating applications. Figure 8 shows the

1650°C sintering and cyclic behavior of a multi-component

HfO2-Y2O3-Gd2O3-Yb2O3 coating that was deposited on a

mullite (3Al2O3-2SiO2) based environmental barrier coating,

Si buffer layer, SiC substrate. The advanced multi-component

HfO2 coating had a relatively low conductivity increase during

the first 20 hour steady-state testing, and also showed essentially no cracking and delamination during the subsequent 100

cycles where the specimens were subjected to 30 minute exposure to 1650°C, indicating its excellent sintering resistance and

cyclic durability as compared to the baseline coatings. This

coating system recently demonstrated 300 hour long-term

1650°C sintering and cyclic durability on SiC/SiC under thermal gradient cyclic testing, far beyond the current state of the

art baseline ZrO2-Y2O3 coating capabilities.

LIFE ANALYSIS

The structural integrity of any material system, whether metal or

ceramic-based, cannot be guaranteed to be 100 percent safe.

Many factors come into play that can introduce uncertainty.

Among them are the uncertainties of the properties of the in-situ

material, limitations in the analysis, both human and analytical;

and last but not least the actual load conditions under which the

Figure 6. Advanced Low Conductivity EB-PVD Thermal Barrier

Coating Demonstrated Cyclic Durability.

Figure 7. Advanced Coating Design Concept for 1650°C CMC

Combustor.

Figure 8. Sintering and Cyclic Behavior of a Multi-Component

HfO2-Y2O3-Gd2O3-Yb2O3 Coating.

High temperature capability

Thermal and radiation barrier

Energy dissipation and 

chemical barrier interlayer

Secondary radiation barrier

with chemical barrier interlayer

Environmental barrier

Ceramic matrix composite

(CMC)

Coating Concept

Cycle Number

0 500 1000 1500 2000 2500

Tsurface=2480°F (1360°C)

Tinterface=2020°F (1104°C)

Low Conductivity EB-PVD 

Turbine Airfoil Coating

HfO2-15mol%Y2O3 Coating (15YSHf)

HfO2-5mol%Y2O3 Coating (5YSHf)

30 Min Cycle Exposure

SteadyState

5YSHf Advanced HfO2

After Testing

15YSHf

Advanced Multi-Component 

HfO2 CoatingSystem

6 Min Heating, 2 Min Cooling Cycles

Thermal Conductivity, W/m-K

0 50 100 150 200 250 300 350

Time, hours

1.6

1.4

1.2

1.0

0.8

0.6

0.4

Normalized Thermal Conductivity k/k0

0 20 40 60 80 100

Time, hours

2.0

1.5

1.0

0.5
130 The AMPTIAC Quarterly, Volume 8, Number 4

structure will ultimately be placed. Safety factors are used during

the design process to account for those uncertainties; nevertheless it is a requirement that the probability of failure be within an

acceptable range for each particular application.

A turbine vane made of SiC/SiC was designed, fabricated,

tested, and analyzed to demonstrate the performance increases

that result from these new advanced composite materials.

Because of scatter in material property data and uncertain load

conditions, a formal probabilistic analysis and reliability assessment of the vane was conducted in order to calculate the probability of failure to meet design requirements [5]. Two cases

were studied. The first had four random variables that were

material property related. The second case added two random

variables that were load related. The study found that there was

a 1.6% probability that the material system would not meet the

requirements for which it was designed. The importance of this

methodology is, in addition to providing a quantifiable risk

assessment; it also provides a tool that would allow specific tailoring of the structure’s design for a specific reliability.

CONCLUSIONS

The research and development of ceramic matrix composites

and ceramic-based coatings for use in turbine engines components has the potential to achieve increased levels of efficiency

and push the performance of Army vehicles to new heights.

The use of ceramics as opposed to metals allows higher operating temperatures and little to no cooling requirements. These

material technology improvements can transition the Army

into becoming a more mobile and effective force.

REFERENCES

[1] D. Brewer, HSR/EPM Combustor Materials Development

Program, Materials Science and Engineering, A261, pp. 284-

291, 1999

[2] J.A. DiCarlo, H-M. Yun, G.N. Morscher, and R.T. Bhatt,

SiC Fiber-reinforced SiC Matrix Composites for Thermostructural

Applications to 1200°C and Above, in Handbook of Ceramics

and Glasses

[3] Dongming Zhu, and Robert A. Miller, Thermal and Environmental Barrier Coatings for Advanced Propulsion Engine Systems, NASA TM-2004-213129, ARL-TR-3263, August 2004

[4] J.L. Smialek, R.C. Robinson, E.J. Opila, D.S. Fox, and

N.S. Jacobson, SiC and Si3N4 Recession Due to SiO2 Scale

Volatility under Combustor Conditions, Adv. Composite Mater,

8 [1], 33-45 (1999)

[5] P.L.N. Murthy, N.N. Nemeth, D.N. Brewer, and S. Mithal,

Probabilistic Analysis of a SiC/SiC Ceramic Matrix Composite

Turbine Vane, NASA Technical Memorandum, April 2004

Mr. Waldo A. Acosta is Chief of the Engine Components Division of the Army Research Laboratory Vehicle Technology Directorate. Mr. Acosta is responsible for planning, coordinating, and directing division activities involving

basic and applied research of fluid mechanics, heat transfer, combustion processes, and propulsion materials; all of

which are fundamental to advanced vehicle propulsion systems. Mr. Acosta holds a BS in Chemical Engineering

from the University of Puerto Rico, a MS in Chemical Engineering from the University of Toledo, and a MS in Industrial Engineering (with a concentration in Engineering Management) from Cleveland State University.

Dr. Ramakrishna T. Bhatt is a Senior Materials Research Engineer at the Army Research Laboratory, Vehicle Technology Directorate. His research interests include processing of monolithic ceramics and fiber reinforced ceramic

matrix composites; structure/property correlation; NDE; and microstructural characterization. Dr. Bhatt has authored

and co-authored more than 120 peer-reviewed scientific publications for journals, handbooks, and national and

international conferences. He holds two patents and has two other patents pending. Dr. Bhatt obtained his BE and

ME degrees in Metallurgical Engineering from Indian Institute of Science, Bangalore, India; and a PhD in Materials Science and Engineering from Pennsylvania State University.

Mr. Dave Brewer is a Materials Research Engineer at the Army Research Laboratory, Vehicle Technology Directorate. He is the Advanced Materials manager for Highly Loaded Compressors and Turbines under NASA’s Ultra

Efficient Engine Technology project. He has 13 years experience in the development of CMC components for gas

turbine applications. Under NASA’s High Speed Research program, Mr. Brewer led characterization, analysis, and

life prediction for CMC material systems. He later led the CMC combustor liner material development effort under

the Enabling Propulsion Materials Program. Dave holds a MS in Mechanics of Materials from Case Western

Reserve University.

Dr. Dongming Zhu is a Materials Research Engineer at the Army Research Laboratory, Vehicle Technology Directorate. His expertise covers the areas of thermal conductivity, lattice defects and transport, and mechanical behavior of ceramic coating systems, with an emphasis on experimental investigation and analytical modeling of processing, thermal fatigue and failure behavior of ceramic coatings and composites. His major contributions include the

development of low conductivity thermal barrier coatings for turbine airfoil applications, 1650°C thermal/environmental barrier coatings for SiC/SiC ceramic matrix composite (CMC) turbine vane and combustor liner applications, and the development of high-heat-flux testing techniques for advanced ceramic coatings. He earned his PhD

in Chemical Engineering and Materials Science from the University of Minnesota.
The AMPTIAC Quarterly, Volume 8, Number 4 131

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& SPECIAL FUNCTION MATERIALS

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Naval Research Laboratory

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Email: murday@nrl.navy.mil

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Alion Science and Technology Personnel

Bruce was a highly accomplished

man – whether as an engineer, scholar,

manager, or soldier; he served his country, his profession, his peers, and his

community with distinction; having

risen rapidly in each forum, with the

trust and respect of those around him.

His entire adult life was a testament of

his drive to excel. A complete listing of

his achievements would require many

more pages than are available here. At best, we can provide the

reader with a brief portrait of the man. 

Upon his graduation from college Bruce was commissioned

into the US Army as a regular officer. While on active duty, he

served 10 years as a Combat Engineer Officer, and also earned

both his MS and PhD degrees. He eventually left active service

after attaining the rank of Major, and having won many awards

and commendations. 

Bruce’s civilian career at ARL spanned over 10 years, where

he conducted research in numerous fields, such as the processing and modeling of composites, lightweight structures, armor,

and the integration of materials and structural design. He was

instrumental in establishing a new way of approaching materials research so that it was more focused on the soldier; a necessary part of meeting the goals of the Current and Future Force.

He rose through the ranks quickly. In his capacity as Chief of

the Materials Division of ARL’s Weapons and Materials

Research Directorate, he was responsible for reorganizing the

Materials Division along functional rather than discipline lines.

This remains the Division’s current structure, leaving his signature on the organization. He earned more than 30 different

technical awards; including the Paul Siple Award for the best

paper at the Army Science Conference, and the US Army

Research and Development Achievement Award. He was a 

prolific author and speaker, and was the originator of several

patents. During his career, he also served as an adjunct professor at the University of Delaware and Tuskegee University.

Bruce was a very important member of the greater technical

community, having served leadership and advisory roles in

such organizations as the National Science Foundation, the

Military Handbook 17 Committee, and the National Materials

Advisory Board.

Bruce was an energetic and vital individual who was an integral part of the DOD materials community. Bruce was not only

a dynamic and creative leader, but also an empathetic and

thoughtful man who easily and almost invariably crossed the

boundary between colleague and friend. He will be missed not

just within the Aberdeen and Army Research communities, 

but throughout the DOD and the national and international

materials and defense research and engineering arenas. 

Beyond the professional man was one who was deeply committed to a greater sense of community. He was highly active 

in his church, directing and supporting a number of his congregation’s efforts. Always eager to pitch in, he also served the

greater community in a variety of roles, large and small. Such

consummate gentlemen are rare in this world. His loss will be

felt by us all. - Editor

In Memoriam: Bruce K. Fink

It is with great sadness and a heavy heart that we announce the recent passing of one of this issue’s principal sponsors, Dr. Bruce K. Fink

of the Army Research Laboratory (ARL). This issue of the AMPTIAC Quarterly was already on press when we received word of 

his tragic death. The cover of the quarterly had not yet gone to print, which presented the opportunity to insert this announcement 

and tribute.
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