AMPTIAC is a DOD Information Analysis Center Administered by the 

Defense Information Systems Agency, Defense Technical Information Center 

Special Issue:

Ships Navy Experts Explain

the Newest Material &

Structural Technologies
The issue you hold in your hands has been 14 months in the

making. It began with a simple idea: turn the spotlight on the

age-old art of building ships. We wanted to show the exciting

new technologies that are offering novel materials for ship construction, changing the way ships are built, and indeed creating

one of the most fundamental shifts in Navy combatants since

steel replaced wood.

This simple mission turned

out to be much more complex.

The project underwent a number of different iterations, but

finally settled in and came

together. It has been a labor of

love for yours truly, for I really

do believe that even though airplanes and tanks often grab the

spotlight, Navy ships are still the most challenging structural

and materials engineering systems fielded in today’s military.

Nothing has the complexity, impact, size, and sheer force of a

fighting vessel, nor can many things capture the imagination in

quite the same way.

So here it is, finally, and I am thankful that it is done. Not

just because it is off my desk and I can get on to the next project, but we are proud because AMPTIAC has compiled something that probably has not existed before: an overview of the

newest technologies being incorporated into structures and

materials for use aboard Navy combatants. And the people providing the perspective are the experts at the Office of Naval

Research, NSWC-Carderock, and the Naval Research Lab. You

won’t find this level of detail, variety, and expert content

focused on this subject anywhere else.

That all being said, there is one critical feature of this publication that needs some attention: the DOD center behind it.

Some of you out there have been reading this publication for

seven years now. You undoubtedly remember about two years

ago when we shifted over to our current layout format and full

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publishing these large special issues fairly often. It is all a part

of our mission to bring you the most in-depth, focused, and

technologically exciting coverage of Defense materials and processing advances available anywhere.

But the side effect of the more noticeable and attentiongrabbing Quarterly, is that

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attention. The reality is that the

center has grown with numerous projects, focused reports,

and database efforts over the

past few years, but there are

many out there that may read

this publication and not even

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We want to put more emphasis on the other efforts 

AMPTIAC is involved in, and let our customers and potential

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more than 210,000 DOD technical reports in our library and

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and many more compiling vast amounts of data into handbook-style resources.

The basic message here is to take note of this magazine, read

it, and enjoy. But if you think AMPTIAC is just the Quarterly,

Think Again.

Wade Babcock

Editor-in-Chief

Editorial: 

There’s More to AMPTIAC 

than the Quarterly

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Issue focus: 

Ships Navy Experts Explain the Newest Material & Structural Technologies

Advanced Double Hull Concept Reduces Costs, Increases Capabilities ... 5

Jeffrey E. Beach, Daniel D. Bruchman and Jerome P. Sikora, Naval Surface Warfare Center 

While significant resources have been allocated to further develop traditional structural technologies used in ship construction,

these technological options often increase the cost and complexity of the structure, have limited impact on overall operational capabilities, and are, therefore, only utilized in very weight-critical locations and designs. The Advanced Double Hull (ADH) concept,

however, addresses many structural requirements and offers further benefits in signature reduction and improved survivability. Dr.

Beach and his colleagues describe the ADH concept and how its cellular structure could very well change ship construction “from

the bottom up.”

Friction Stir Welding Advances Joining Technology ... 13

Maria Posada, Jennifer P. Nguyen, David R. Forrest, Johnnie J. DeLoach and Robert DeNale, Naval Surface Warfare Center

Ships that can be quickly deployed, carry larger payloads, and travel safely through harm’s way are the ultimate goal of the scientists and engineers working on advanced materials and the technologies for assembling them. One means of achieving these goals

is through the introduction of metals with higher stiffnesses and lower densities (such as titanium and aluminum alloys, and higher strength steels). Ms. Posada and her colleagues explain how effectively exploiting these advanced materials for ship construction

requires developing new joining technologies, and friction stir welding is an important part of this program.

21st Century Surface Combatants Require Improved Composite-to-Steel 

Adhesive Bonds ... 21

Jenness Simler, Office of Naval Research, and Larry Brown, Edison Welding Institute

Whenever composite structures are employed aboard warships, the issue of how to attach them to underlying steel structures is of

vital importance. The Navy is helping to develop adhesive bonding methods for joining composites to steel structures for the Navy’s

next generation ships. The intent is to develop and demonstrate manufacturing technology solutions for adhesively bonded composite-to-steel joints which address all the pertinent requirements of structural performance aboard a Naval combatant. Ms. Simler

and Mr. Brown illustrate how this program of government, industry, and academic cooperation is coming to fruition. 

Rapid Cure Tank Coatings on the Fast Track to the Fleet ... 27

Arthur Webb, Naval Research Laboratory

In 2001, the US Navy embarked on an ambitious plan to significantly reduce the costs associated with shipboard maintenance and

corrosion control. The development and institutionalization of rapid cure coatings is critical to achieving these goals. Key to the

program’s success is the identification of new rapid cure coating technologies, certifying them, and transitioning them to use in the

fleet. Mr. Webb explains some of the exciting innovations being explored in this developing technology, as well as the process of

putting them to work on ships.

MaterialEASE: The Role of Materials in Ship Design and Operation ... 31

Wade G. Babcock, AMPTIAC, and Ernest J. Czyryca, Naval Surface Warfare Center

Frequent readers of the AMPTIAC Quarterly know that we normally provide a tutorial of some sort in the MaterialEASE feature –

and this issue is no exception. Readers should probably start their examination of Volume 7, #3 here; Messrs. Babcock and Czyryca

have provided a compilation of the most important materials issues faced in building and operating Navy ships. Many of the topics which are expanded upon in the other articles of this issue, are presented here in brief and in context of other considerations.

For the uninitiated or experienced, this issue’s MaterialEASE contains a concise overview of critical materials concerns for Navy

ships not found anywhere else. 
Surface Ships Put Composites to Work ... 37

Patrick Potter, Office of Naval Research

The performance of future Navy warships requires novel and innovative material and structural systems to meet ever increasing

design requirements. The application of composite materials for the primary structure of Navy surface combatants offers the potential to meet these performance goals in the areas of increased payload fraction, reduced life cycle costs and improved survivability.

Mr. Potter demonstrates how composite laminates are being used aboard ships to maintain and improve their stability criteria,

accommodate additional payload or weapons systems, and also increase their speed or range.

Intelligent Processing and Inspection of Naval Composites ... 41

Roger M. Crane, Naval Surface Warfare Center, and John W. Gillespie, Jr., Dirk Heider, Shridhar Yarlagadda, 

and Suresh G. Advani, University of Delaware

Composite materials are being used in increasing amounts in a variety of Navy applications. They offer enhanced physical properties such as stiffness, strength, reduced weight and corrosion, fire and ballistics resistance, as well as signature reduction. Dr. Crane

and his colleagues describe how various new intelligent processing methods combined with integrated health monitoring technologies are increasing the usefulness and applicability of composites throughout the future Navy.

Improving the Fire Performance Characteristics of Composite Materials 

for Naval Applications ... 49

Usman Sorathia, Naval Surface Warfare Center 

As advanced composite materials make steady inroads into Navy platforms, it becomes increasingly important to address the risk

of fire, smoke, and toxic gas evolution these materials may present. Since many of the component materials used to fabricate composite structures are inherently flammable, the task of evaluating the finished materials and devising methods to protect them from

fire and heat are doubly important. Mr. Sorathia describes how these evaluations take place, and the recommendations and requirements that come out of them.

The Best of Both Worlds: Composite/Steel Hydrid Ship Hulls ... 55

Roshdy George S. Barsoum, Office of Naval Research

The vast majority of ship hulls are constructed from common carbon steels which are susceptible to corrosion and create distinct

thermal and electromagnetic signatures easily detectable from long distances. While composite construction offers many advantages, it also presents many challenges. What if the best aspects of these technologies were combined? Can a hybrid ship be built

utilizing the advantageous benefits of steel where it performs best and the unique properties of composite materials where they

excel? Dr. Barsoum explains the benefits and challenges of this exciting merger of technologies.

Meeting the Challenge of Higher Strength, Lighter, Affordable Warships ... 63

Ernest J. Czyryca, David P. Kihl and Robert DeNale, Naval Surface Warfare Center

Modern warships require high strength steel plate in increasing portions of hull structure for weight reduction, better stability,

increased payload, increased mobility, and survivability. Even though the key physical requirements for naval shipbuilding steels are

strength, weldability, and toughness at low temperature under shock events, they must also be affordable to keep ship acquisition

costs down. Mr. Czyryca and his colleagues guide us through the process of selecting and testing common, affordable industrial

steel grades to replace specialized Navy-only steels.
INTRODUCTION

The primary hull structure of a modern surface ship can provide

practical solutions for a multitude of obstacles facing a commercial or combatant design. Acquisition cost, life cycle costs,

detectability, survivability, speed, range and payload are all, potentially, important factors when selecting a platform to perform a

specific mission. For improved performance in many of these

areas, significant resources have been allocated for further development of structural technologies used in both primary and secondary structural applications. Often these technological options

increase the cost and complexity of the structure, have limited

impact on overall ship operational capabilities, and are, therefore,

only utilized in very weight-critical locations and designs.

In the late 1980’s, the Structures and Composites Department

at the Naval Surface Warfare Center, Carderock Division

(NSWCCD) began assessing the feasibility of the Advanced

Double Hull (ADH) concept with attributes that can significantly impact all the areas in the design space. The ADH concept consists of an inner and outer hull, connected by longitudinal web girders. The resulting cellular structure

exhibits increased structural capacity

under typical seaway loads and the opportunity for improved resistance to weapons

effects. The ADH concept is shown in

Figure 1. 

GENERAL BENEFITS OF THE ADH

The ADH structure is unidirectional; all of the shell and deck

material acts in the longitudinal (parallel to the long axis of the

ship) direction. The transverse (perpendicular to the long axis of

the ship) frames (welded stiffeners) have been eliminated and the

transverse bulkheads provide the support for the longitudinal

structure. The elimination of transverse frames in an ADH configuration has a number of positive effects on hull girder cost

and performance.

First of all, the elimination of the transverse framing leads to a

geometric simplicity that produces significant acquisition cost savings. It contributes to an overall reduction in the number of piece

parts, substantially reducing labor costs associated with the cutting

and welding at longitudinal stiffener and transverse frame intersections. Figure 2 and Table 1 illustrate the potential piece-part

reduction of a typical destroyer assembly. The geometric simplicity also lends itself to automated fabrication processes. 

Further, the elimination of transverse frames and the smooth

interior surfaces of the ADH structure greatly facilitate the

installation of distributive systems,

painting, and their associated costs. 

A visual comparison is provided in

Figures 3 and 4 showing the relative

complexities associated with the installation of these systems on a conventionally framed combatant and an ADH combatant, respectively.

The distributive systems added to an

ADH structure would not have to navigate through

and over transverse structure. In fact, a cost comparison was

conducted for electrical, HVAC, and piping systems in a

destroyer. The analysis estimated that the use of an ADH 

configuration would result in a 17.5% labor hour savings in the

electrical craft, a 17.9% labor hour savings in the sheet metal

craft and a 23.6% labor hour savings in the piping craft. 

When combined with other material, labor, and yard costs,

construction expense for an ADH destroyer can be reduced by

$60 million when compared to a conventional ship.[1]

The AMPTIAC Quarterly, Volume 7, Number 3 5

Jeffrey E. Beach, Director 

Survivability, Structures, and Materials Directorate 

Daniel D. Bruchman

and

Jerome P. Sikora, Branch Head 

Design Applications Branch

Carderock Division, Naval Surface Warfare Center

West Bethesda, MD 

Figure 1. Graphic Depiction of ADH Concept (Left) and Traditional

Ship Construction (Right).
6 The AMPTIAC Quarterly, Volume 7, Number 3

Ultimately, cost is most often the metric that governs the

selection of a ship platform. Before a new technology is adopted into a platform’s design, significant acquisition and/or life

cycle cost reductions as compared to existing processes and

designs must be demonstrated. Acquisition cost is easily quantified and readily demonstrated with the ADH concept.

However, life cycle cost reduction potential can be difficult to

demonstrate – particularly for a combatant. Life cycle costs

encompass recurring expenses such as routine maintenance,

painting, corrosion management, structural failures resulting

from typical seaway or combatant operations, military and

political ramifications if a platform cannot complete a mission,

and replacement costs if a ship is lost at sea. The ADH concept

offers a unique solution that significantly reduces costs and

risks throughout the operational life of the ship.

The structural material comprising the transverse frames in

conventional, grillage construction (utilizing both transverse

and longitudinal welded stiffeners) is redistributed into the

inner and outer hulls in an ADH configuration - increasing the

hull girder section modulus. This lowers the primary, seawayinduced longitudinal bending stresses and increases the fatigue

life of the structure. The elimination of the transverse frames

further increases the hull girder fatigue life by significantly

reducing the number of crack initiation sites at the intersections

of longitudinal stiffeners and transverse frames. 

The increased section modulus also gives the ship designer

flexibility to isolate (both acoustically and from shock) internal

decks, because they no longer need to resist primary loadings.

Similarly, ADH technology can be utilized to incorporate modular design capabilities into a ship system. The inherent

Figure 2. Piece-parts Used In Framing a Conventional Destroyer Hull Section.

Number of Basic Structural Pieces

Item ConventionalADH Variance

Design Design < - >

Collars 200 0 <200>

Chocks 120 0 <120>

Panel Stiffeners 40 0 <40>

Access 40 11 <29>

Opening Rings

Chafing Rings 100 20 <80>

Deep 11 13 +2

Longitudinal Girders

Intermediate 6 0 <6>

Shell Longitudinals

Intermediate Inner6 0 <6>

Bottom Longitudinals

Individual 50 0 <50>

Floor Panels

Docking 10 10 –

Keel Brackets

Deep Long'l Girder7 9 +2

Panel Stiffeners

Total Basic 584 63 <521>

Table 1. Comparison of Piece-part Requirements in a

Conventional and ADH Destroyer Assembly.

Collar Plates

Flange & Tangency

Chocks

Panel

Stiffeners

Shell & Inner

Bottom

Longitudinals

& Stringers

Longitudinal

Girders

Longitudinal

Girders

Transverse

Floors

Keel

Brackets 

Panel Stiffeners

Chafing

Rings

Compensation

Rings
The AMPTIAC Quarterly, Volume 7, Number 3 7

strength of an ADH hull form can also allow for large openings

in deck structures, simplifying the removal and replacement of

obsolete systems.

STUDYING THE MECHANICS OF THE ADH

Over the last several years substantial research into the ADH

has documented the structural characteristics and performance

of the concept under a variety of loading conditions. This

research has primarily focused on the performance of a prismatic ADH structure located in the mid-section of the ship

(where the sides are roughly parallel). Research has included

investigations into the stress behavior of prismatic ADH structures [2] (Figure 5) and their ultimate strength (Figure 6). 

Ford, et. al. were able to use the finite element method in

conjunction with rigid vinyl model tests to evaluate the stress

behavior of an ADH structure. It was shown that, for a given

ADH geometry, the stress state of the structure could be predicted using classical strength of material approaches. Further

investigations were conducted to determine the collapse

strength of ADH cellular structures, and are pictured in Figure

7.[3]

Devine tested a series of large 3-cell and 5-cell ADH

columns to collapse under axial loading conditions. A significant amount of scatter was observed in the behavior of the

columns, particularly in the columns with plates having a slenderness ratio (length/thickness) typically used in ship construction. Devine showed that classical plate-buckling equations that did not account for welding-induced residual stresses were somewhat unconservative. There was a significant

reduction in the column collapse strength resulting from the

welding-induced residual stresses, which must be accounted

for in the design process.

The Oil Pollution Act of 1990 was enacted following the

Exxon Valdez tragedy in 1989. This legislation requires newly

built tankers trading in US waters to be fitted with double hull structure. It also set a schedule for phasing out single hull tankers currently in service. Significant assets were, therefore, allocated in the

ADH program to evaluate and improve the grounding and stranding behavior of double hull configurations (Figure 8).[4, 5, 6, 7]

Rodd was able to demonstrate through a series of large-scale

grounding tests, that inner hull rupture occurred at the transverse frames of conventional grillage construction. Removal of

transverse frames in the ADH allowed the structure to

absorb substantially more energy before inner hull failure. Additional crash resistant features were also

developed to further enhance the configuration’s

damage resistance.

In addition to the extensive research to determine the structural characteristics and behavior of

ADH structures under conventional loading conditions, there

has also been substantial research to determine their behavior

under combatant loading conditions. This included analysis of

explosions above the waterline (called AIREX) and below (called

UNDEX) (Figure 9).

NSWC conducted an extensive numerical analysis of an

ADH cruiser subjected to an underwater explosion.[8] Results

indicated that an ADH configuration was better at attenuating

Figure 3. Typical Structure-System Interface on 

Conventional Combatant.

Figure 4. Typical Structure-System Interface on an ADH

Combatant.

Figure 5. Rigid Vinyl and Finite Element Analysis

of Stress Behavior in ADH Structures.

Longitudinals (Typical) Machinery

Platform 

Plate & Beam

Web Frame

Pipe (C)

Pipe (B)

Longitudinal BHD Plating

Plate & Beam

Pipe (A)

Pipe (C)

Pipe (A)

Pipe (B)

Advanced

Double Hull

Smooth

Hull Inner

Plating

Smooth Cored Deck

Machinery Platform
8 The AMPTIAC Quarterly, Volume 7, Number 3

shock on equipment by reducing accelerations and peak velocities during the UNDEX event.

Research to date indicates that, compared to a conventional

grillage type of structure, the ADH is generally stronger and

more damage resistant under the tested loading conditions, with

little increase in weight. Both acquisition and life cycle costs are

reduced in the ADH concept due to geometric simplification,

piece-part reductions and the associated facilitation of painting

and the installation of distributive systems. Furthermore, if the

space between the hulls is properly utilized and the right materials

selected, the ADH concept offers the potential for significant

reductions in IR, acoustic and magnetic signature levels. The extensive research to date has culminated in the development of guidelines for ADH structure design.[9] 

MANUFACTURING/MAINTENANCE ISSUES 

WITH THE ADH CONCEPT

There are significant manufacturing, maintenance and inspection issues unique to the ADH hull form. These issues

generally revolve around the ability to gain access to the 

interior cell spaces and are magnified for smaller ship classes 

as the separation between the inner and outer hulls is reduced

for weight and volumetric considerations. As the distance

between the inner and outer hulls increases beyond about one

meter, more conventional construction, maintenance and

inspection methods can be employed. 

Conventional welding techniques can be used for all aspects of

ADH construction until the inner shell region is welded to the

longitudinal web girders in a design with a hull separation less

than one meter. Then, because of the limited access to the interior space, other welding processes may be required. These

processes may include automated welding techniques and can be

accomplished from either inside or outside the cellular structure.

Laser welding, electron-beam welding, and friction-stir welding

(please see accompanying article in this issue by DeLoach, et. al.)

have all been investigated and are viable options. Most near-term

applications being considered could be effectively fabricated

using manual or mechanized welding techniques.

Maintenance and inspection issues of the small interior cellular structure have been investigated. Robotic technologies have

been studied [10] and proven to be effective means of performing inspections and routine maintenance, such as painting and

minor repairs when necessary (see Figure 10). 

Corrosion maintenance and repair costs of Navy combatants

are estimated to be at least $1.2 billion a year for approximately 360 ships.[11] Material selection, coatings and manufacturing techniques must be carefully evaluated to minimize corrosion. In an ADH combatant, the increased horizontal surfaces

where water can accumulate and the generation of additional

moisture caused by variation in temperature between the inner

Figure 7.

Measuring the

Collapse

Strength of

ADH

Structures.

Figure 6. Test Articles for Ultimate Strength Analysis of

ADH Structures.
The AMPTIAC Quarterly, Volume 7, Number 3 9

and outer cell walls can aggravate corrosion problems.[9]

Several coatings were evaluated for ADH applications to help

minimize corrosion problems. In general, high build epoxies

were the most effective in both long- and short-term exposure

tests [12] and often outperformed the standard Navy F150/151

epoxy system. Pre-coating ADH structural components also

proved effective in reducing coating costs.

STAINLESS STEELS

Budget conditions mandate that ship construction costs be

reduced in future combatant construction. Many technologies

and systems that would improve combatant performance are not

considered because they increase acquisition costs, and the

implementation of stainless steels for hull construction is one

example of this. Although preferable to ordinary steel construction for many reasons, austenitic stainless steels and other nonmagnetic, corrosion resistant materials are not often considered

in combatant designs because of acquisition cost constraints. 

The ADH concept provides a practical solution to the combatant need for a more survivable hull form. It offers a unique

geometry and significant cost savings during construction and

the installation of distributive systems that enable the practical

implementation of many multi-spectral ship signature reduction

options. These options include the use of austenitic stainless

steels, not only for their ability to reduce the magnetic signature,

but also for their high resistance to Charpy impact and explosion

bulge loading. Their high elongation before rupture can also

lower hull girder bending stresses acting on the hull during an

UNDEX event, and significantly increase survivability in these

conditions.[13] In Table 2, the properties of commonly used

magnetic shipbuilding steels are compared with select non-magnetic stainless steels.

There are a number of reasons why the ADH concept is an

ideal platform to introduce non-magnetic stainless steels. The

estimated $60M savings for a 9,000 long-ton ADH combatant

can more than offset the added expense in material and fabrication costs of a comparable stainless steel combatant. Further,

because the ADH concept lends itself to automated welding

processes, fume controls mandated by the Occupational Safety

and Health Administration (OSHA) are less problematic. These

requirements were set forth to protect personnel from the fumes

generated during the welding of non-magnetic steels and nickelbased alloys.[14] Finally, automatic and robotic welding operations enabled by the ADH’s geometric simplifications can ensure

a more consistent, high quality weld than possible with manual

welding techniques. This is doubly important when welding

non-magnetic stainless steels, as the weld quality must be

extremely high in both weld surface condition and the weld

deposit itself.[15]

To identify the costs and benefits of a stainless steel ADH

combatant, a comprehensive research and development program began in the late 1990’s. In this program, several stainless

steels were evaluated based on the following criteria: weldability, welded properties, yield strength, elongation, residual stress

effects, fabrication distortions and crevice and stress corrosion

susceptibility. The materials also had to be non-magnetic. Based

on the selection criteria, the focus of the study centered on

austenitic stainless steels because, although the high nickel and

chromium content makes the alloys expensive, they exhibit

Figure 8. Studying the Grounding Response of ADH

Structures.

Figure 9. ADH Structures in UNDEX and AIREX Tests.
excellent ductility, formability and superior corrosion resistance.

Austenitic stainless steels evaluated include AL-6XN, Nitronic

50, and the 300 series. The material costs for plating ranged from

$1.90/lb for the 300 series, $3.10/lb for the Nitronic 50, to

$4.00/lb for AL-6XN.

Based on the results from the stainless steel research and development program, several performance and cost characteristics

were identified. Of the metals investigated, the 300 series steels

were particularly susceptible to crevice corrosion. In general, the

AL-6XN provided the best corrosion protection and is recommended for the most corrosion-sensitive locations. Both the AL6XN and the Nitronic 50 exhibited yield stresses comparable to

AH 36. The 316L had a yield stress value around 30 ksi.

The stainless steel ADH hull form exhibited excellent multispectral signature control characteristics. The magnetic signature alone was an order of magnitude less than that of an ordinary steel hull. However, this did require special handling and

cutting techniques akin to those used for other non-magnetic

metals such as aluminum. The space between the hulls could

also be designed to significantly reduce the IR signature as well

by the inclusion of active or passive insulators.

CONCLUSIONS AND REMAINING CHALLENGES

The Advanced Double Hull concept can significantly

reduce both acquisition and life cycle costs. The cellular

structure exhibits increased structural capacity under

typical seaway loads, superior fatigue performance, and

the opportunity for improved resistance to weapons

effects. The inherent strength of an ADH hull form also

offers the opportunity to isolate internal decks acoustically and from shock, providing a less detectable, more

survivable hull. Further, the ADH concept is an ideal

platform to construct out of stainless steels, thus providing the opportunity for multi-spectral signature control.

Several issues however, remain to be investigated. ADH technology can’t efficiently be implemented approaching the bow

where the hull form rapidly changes and exhibits flare. Therefore

optimum details need to be identified in the regions where the

ADH structure transitions to a conventional structure. Work has

begun to evaluate the performance of non-prismatic ADH structures, but further research is necessary. When constructing a nonmagnetic, stainless steel ADH, a dedicated yard with special tooling may be necessary. Additionally, there are higher levels of distortion resulting from the welding process of the austenitic stainless steels and flame straightening may be required.

REFERENCES

[1] J. Beach. “Evaluation of Advanced Double Hull (ADH)

Including the Use of Stainless Steels”, Presentation to SC-21

Program Office, April 1997

[2] H. Ford, J.M. Grassman, and R. Michaelson. “Stress

Behavior of Advanced Double Hull Structures”, Paper No. 10.

Proceedings of the Advanced Double Hull Technical

Symposium, 25-26 Oct, 1994, at Gaithersburg, MD

[3] E. Devine, J. Ricles and R. Dexter. “Instability and Collapse

Strength of Advanced Double Hull Structures”, Proceedings of the

Advanced Double Hull Technical Symposium, Paper No. 6,

Gaithersburg, MD, 25-26 Oct, 1997

[4] J. Rodd, with M. Phillips and E. Anderson. “Stranding

Experiments on Double Hull Tanker Structures”, Proceedings of

the Advanced Double Hull Technical Symposium, Paper No. 2,

Gaithersburg, MD, 25-26 Oct, 1994

[5] J. Rodd. “Frame Design Effects in the Rupture of Oil Tanks

During Grounding Accidents”, DERA, Proceedings of the

International Conference - Advances in Marine Structures III,

Table 2. Material Property Comparison of Commonly Used Shipbuilding Steel and Select Non-magnetic Stainless Steels.

Ultimate Yield Elongation Charpy Modulus Density

Material Alloy Strength (ksi) Stress (ksi) (% in 2-in.) Toughness (ft-lb) (x106 psi) (lb/in3)

Shipbuilding AH36/ 71-90 51 22 17 transverse 30.0 0.283

Magnetic DH36 25 longitudinal

Steel (20 °F DH36)

(0 °F AH36)

Non- Nitronic 50 104 57 60 103-110 (75 °F) 

Magnetic 83-88 (-100 °F) 26.2 0.285

Steel AL-6XN 108 53 47 140 (70 °F)

100 (-200 °F) 28.3 0.291

10 The AMPTIAC Quarterly, Volume 7, Number 3

Figure 10. Robotic Maintenance and Inspection of ADH

Structures.
The AMPTIAC Quarterly, Volume 7, Number 3 11

Dunfermline UK, 20-23 May, 1997

[6] T. Wierzbicki, E. Rady, D. Peer and J.G. Shin. Damage

Estimates in High Energy Grounding of Ships, Massachusetts

Institute of Technology, Department of Ocean Engineering,

Tanker Safety Program, Report No. 1, June 1990

[7] T. Wierzbicki, D. Peer and E. Rady. The Anatomy of Tanker

Grounding, Massachusetts Institute of Technology, Department

of Ocean Engineering, Tanker Safety Program, Report No. 2,

May 1991

[8] H. Gray. “Survivability Implications of Advanced Double

Hull Combatants”, Proceedings of the Advanced Double Hull

Technical Symposium, Paper No. 18, Gaithersburg, MD, 25-26

Oct, 1994

[9] J. Sikora, and E. Devine. Guidelines for the Design of

Advanced Double Hull Vessels, NSWCCD-65-TR-2001/04,

West Bethesda, MD: Naval Surface Warfare Center, Carderock

Division, 2001

[10] M. Gallagher, T. Barbera, and M. Bankard. “Inspection and

Maintenance of Advanced Double Hull Cells”, Paper No. 17.

Proceedings of the Advanced Double Hull Technical

Symposium, 25-26 Oct. 1994, at Gaithersburg, MD. 1994

[11] D.D. Thurston. Recurring Fleet Corrosion Issues. Paper

read at CORROSION 97 (NACE International) Group

Committee T-9B (CINCLANTFLT maintenance Technical

Advisor), at New Orleans, LA, March 1997

[12] H. Hack, Holder, A., Clayton, N., Dobias, P., Arazy, C.,

Bowles, C., Brush, N., Vasanth, K., Katilaus, J., and Jean

Montemarano. “Corrosion Control of Advanced Double Hull

Combatants”, Proceedings of the Advanced Double Hull

Technical Symposium, Paper No. 16, Gaithersburg, MD, 

25-26 Oct, 1994

[13] E. Moyer, M. Pakstys, and C. Milam. “The Effects of

Plasticity on the Whipping Response of Surface Ships and

Submarines”, Proceedings of the 62nd Shock and Vibration

Symposium, Vol. II, Springfield, Virginia, 29-31 Oct, 1991

[14] National Shipbuilding Research Program. “Impact of

Recent and Anticipated Changes in Airborne Emission Exposure

Limits on Shipyard Workers”, Report NSRP0463 (March 1996)

[15] Marine Engineers Review. “Corrosion Resistance of

Stainless Steels for Chemical Tankers”, March 1972 

Dr. Jeffrey E. Beach is Director of the Survivability, Structures, and Materials Directorate at the Carderock Division,

Naval Surface Warfare Center where he has been employed since 1969. He earned B.S. and M.S. degrees in aerospace engineering from the University of Maryland and has had additional graduate training in naval architecture and

structural engineering. He earned his doctorate in engineering management at The George Washington University.

Dr. Beach manages a diverse program of exploratory, advanced, and engineering development research aimed at

the advancement and application of materials and structures to marine vehicle systems. He is active nationally and

internationally in professional societies, organizations, and exchanges, and has published and presented numerous

technical papers in the international community. Among his awards are the 1984 American Society of Naval

Engineers Solberg Award for research and the 1998 ASNE Gold Medal Award. 

Daniel D. Bruchman has been employed at the Naval Surface Warfare Center, Carderock Division since 1986 when

he received a BS degree in Civil Engineering from the University of Mississippi. Currently, he is a Naval Architect in

the Structures and Composites Department at Carderock, responsible for the technical analysis and evaluation of

advanced structural systems under consideration for Navy surface ships and submarines. Mr. Bruchman began his

career specializing in the use of numerical methods to analyze conventional and unconventional hull forms. His design

of a ship collapse facility, capable of testing large scale ship structures to collapse under pure moment or momentshear combinations, has contributed to a much greater understanding of the global collapse of vessels under these

conditions. Recently, he has been involved in the development of high strength/lightweight materials and structural systems for high speed ships while also serving as the Advanced Double Hull program coordinator. 

Jerome P. Sikora has been employed at the Naval Surface Warfare Center, Carderock Division since 1969 when he

received a BS degree in Physics from the University of Detroit. Currently, he is the head of the twenty-member Design

Applications Branch within the Structures and Composites Department, a position he has held since 1986. The Design

Applications Branch is responsible for developing structural design criteria and design tools for Navy surface ships

and submarines. Mr. Sikora began his career specializing in the field of static and dynamic optical measurements of

such structural parameters as stress, deformations, and vibration modes. He has been instrumental in the development

of unconventional vessels and offshore structures such as SWATHS, tri-hulled ships, and the mobile offshore base. Over

the past two decades, he has developed probability-based loads criteria for conventional and SWATH ships.

Recently, he has been involved in developing structural design criteria and design methods for the cellular structure of

the Advanced Double Hull. 
12 The AMPTIAC Quarterly, Volume 7, Number 3

AMPT-15 Life Prediction and Performance

Assurance of Structural Materials in Corrosive

Environments (1999)

Life prediction of structural components is vitally important to safe and cost effective operation of any system in

which the materials are susceptible to environmental

degradation. Performance assurance, which is closely

related to life prediction, is equally important to ensure

that the system will operate as per design for the duration

of its life. This report presents a panoramic view of this

field by highlighting the variety of current approaches,

identifying the limitations, and discussing directions for

future efforts. 

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Corrosion Prevention (2003)

The use of the conductive polymer polyaniline as a corrosion preventative coating for metals is a new and

emerging technology. Coating metals with dispersed

polyaniline works to shift the corrosion potential of the

metal towards that of the noble region and to form thin

metallic oxide layers on the metal surface. As a result, it is

many times more difficult for corrosion to attack the

metal, displaying an oxide passivation layer formation

more typical of aluminum. Furthermore, conductive

coatings change the corrosion potential of the entire

metal surface, so damaged areas where the coating has

been worn off, such as scratches, are still resistant to corrosion.

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AMP-248 Corrosion of Metals in Marine

Environments (1986)

This report, a companion volume to AMP-222,

“Corrosion of Metals in the Atmosphere,” provides 

assistance in the selection of materials for equipment or

facilities to be used in the ocean environment. Before

reviewing the corrosion behavior of the individual materials, the factors which affect their behavior in seawater

and in the marine atmosphere are reviewed. The report is

based on a review of selected literature items, discussions

with marine technologists, and information derived from

research programs in the marine corrosion field. Reports

dealing primarily with corrosion results & deterioration

behavior in actual ocean environments rather than in laboratory simulations have provided the most reliable

information. However, numerous references were noted

to studies conducted using 3 to 3 1/2 percent sodium

chloride solutions, particularly those involving stress corrosion cracking and fatigue crack growth. While not

equivalent, for most purposes, these references have been

included.

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Price: $175.00 US

AMPT-26 Blast and Penetration Resistant

Materials (2001)

AMPTIAC compiled the recent and legacy DOD unclassified data on blast and penetration resistant materials

(BPRM) and how they are used in structures and armor.

Special attention was paid to novel combinations of materials and new, unique uses for traditional materials. This

report was sponsored by Dr. Lewis Sloter, Staff Specialist,

Materials and Structures, in the Office of the Deputy

Undersecretary of Defense for Science & Technology.

BONUS MATERIAL: Dr. Sloter also hosted a workshop

in April, 2001 (organized by AMPTIAC) for selected

experts in the field of BPRM and its application. The

workshop focused on novel approaches to structural 

protection from both blast effects and penetration phenomena. Some areas covered are: building protection from

bomb blast and fragments, vehicle protection, storage of

munitions and containment of accidental detonations,

and executive protection. The proceedings of this workshop are included with purchase of the above.

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And You Thought We Only Printed This Magazine!

AMPTIAC offers numerous publications in a wide range of technical areas. For further information or to order,

contact Gina Nash at (315) 339-7080 or via e-mail at gnash@alionscience.com 

Our publications most applicable to ship technology include:

1.315.339.7080

h t t p : // iac.dtic.mil/amptiac/
The AMPTIAC Quarterly, Volume 7, Number 3

INTRODUCTION

Lighter, stronger, faster: This mantra drives structural materials

research and development for Navy systems. Ships that can be

quickly deployed, carry larger payloads, reliably withstand the

assaults of high sea states, and travel safely through harm’s way

are the ultimate goal of the scientists and engineers working on

advanced materials and the technologies for building them. One

means of achieving lighter, stronger, and faster ships and submarines is through the introduction of materials with specific

property improvements including titanium and aluminum

alloys, and higher strength steels. Effectively exploiting these

advanced materials for ship construction requires developing

effective joining technologies, and friction stir welding (FSW) is

an important part of this program.

FSW is a rapidly maturing solid state joining process that

offers significant benefits over conventional joining processes.

Invented by The Welding Institute (TWI) in 1991, FSW uses a

combination of frictional heating and compressive loading to

join metal plates that are butted against each other and tightly

clamped to the anvil of the machine.

The process, shown schematically in Figure 1, is initiated by

rotating a welding tool (consisting of a shoulder and pin assembly) at speeds up to several

hundred revolutions per

minute (rpm) before it is lowered into contact with the

plates to be joined. A vertical force (z-axis load) is applied perpendicularly to the joint line, driving the rotating pin into the

work piece. Frictional heat is generated at the top surface of the

workpiece under the FSW tool shoulder, and in the base material at the interface with the pin. For steels and other higher

melting temperature alloys, a small-diameter hole is pre-drilled

in the joint line to lessen the forces acting on the welding tool

during the plunge. 

After sufficient dwell time to allow for homogeneous heating

and softening of the material, a lateral force (x-axis load) is

applied in the direction of travel. Both z- and x-axis loads act

on the rotating welding tool as it traverses along the joint line,

sweeping the softened material along the periphery of the pin

and depositing it in the tool’s wake. This “stirring” action, along

with the pressure and restraining forces induced by both the

tool and fixturing, creates a heavily deformed region of material which upon cooling defines a strong, metallurgical joint that

is fine-grained with no entrapped oxides or gas porosity.

Characteristics that make solid state joining attractive are

included in Table 1.

Friction stir welding of relatively low-melting temperature

materials, such as alloys of aluminum and magnesium, has

matured significantly and is being adopted by the aerospace

community. For example, NASA’s Marshall Space Flight Center

plans to use FSW for constructing Al-Li external fuel tanks, and

Eclipse Aviation has used FSW in the fabrication of jet aircraft.

The Navy is interested in extending this

technology to shipbuilding and optimizing it for joining naval materials, such as

carbon steels, stainless steels, titanium

alloys and nickel aluminum bronze.

FSW FOR SHIPBUILDING

For future naval construction, emerging

higher strength, stiffness, and toughness

steels and stainless steels are of interest.

High strength, low alloy (HSLA) steels

and AL-6XN are currently being investigated. HSLA-65 steel is an alternative to

DH-36 for aircraft carrier construction.

Maria Posada, Jennifer P. Nguyen, David R. Forrest, Johnnie J. DeLoach

Welding and NDE Branch

Robert DeNale

Metals Department

Survivability, Structures, and Materials Directorate 

Carderock Division, Naval Surface Warfare Center 

West Bethesda, MD

13

a

b

c d

X

Y

Z

Figure 1. Schematic of FSW Process (left) and a Photo of an Actual FSW Tool (right)

(Photo courtesy of University of South Carolina)
With improved property-to-weight ratios, HSLA-65 will theoretically enable thinner-gauge sections to be used, resulting in

lighter weight designs. (Please see the accompanying article by

Czyryca, et. al. in this issue.) AL-6XN is a high-toughness, nonmagnetic, super-austenitic stainless steel being evaluated as a

structural material for Advanced Double Hull (ADH) surface

combatants. (Please see the accompanying article by Beach in

this issue.)

In order to exploit the improved properties of these advanced

steels, advanced joining technologies will also be required.

Conventional welding techniques applied to large steel plates

with thin gauge sections result in unacceptable levels of distortion in the final product that require expensive flame-straightening or rework efforts. For stainless steels, weld distortion is

expected to be even greater than for carbon steels due to lower

thermal conductivity and higher thermal expansion. Costs associated with distortion correction can be high; for the USS

Arleigh Burke (DDG 51)-class ship (Figure 2), flame straightening consumes significant labor costs for each ship constructed.[1] Considering other factors affected by flame straightening

operations, such as material costs, interruption of other trades,

and increased fitting time, the total cost of not controlling distortion can reach approximately $3.4 million per ship for conventional steel construction and is expected to be greater if

austenitic stainless steels are used.

Another significant challenge that FSW should overcome 

is the generation of hexavalent chromium (Cr6+), a known 

carcinogen. Conventional welding technologies used on stainless steel alloys require melting the workpiece, and consequently generate hexavalent chromium in fumes. The Occupational

Safety and Health Administration (OSHA) is planning to

reduce workers’ permissible Cr6+ exposure limit to 0.5μg/m3.

Data collected by a joint Navy/Industry task group showed that

Cr6+ levels generated during arc welding of both carbon steel

and stainless steel exceed the proposed OSHA limit. These

requirements will significantly increase fabrication costs; the

Navy estimated that the cost of complying with the new Cr6+

requirement could reach $80M per year for US Navy ship construction after a one time $30M implementation cost.

THE R&D PROGRAM

In response to these challenges, the Navy is investigating

advanced joining methods, including FSW for joining of carbon

and austenitic stainless steels. The overall program includes science and technology directed toward advanced equipment development, tool design and tool material development, welding

process parameter optimization, and understanding and predicting microstructural and mechanical property evolution during

joining.

As part of these efforts, the Office of Naval Research’s (ONR)

Manufacturing Technology (MANTECH) office investigated

friction stir welding of 2519 aluminum for the Marine Corps’

Advanced Amphibious Assault Vehicle (AAAV).[2] The FSW

demonstration projects successfully met ballistic, productivity,

and distortion requirements that could not be obtained with

conventional arc welding. The initial results of steel FSW trials,

including weld evaluation and demonstration projects conducted, are presented here.

Friction Stir Weld Evaluations

The quality and mechanical properties of steel friction stir

weldments were evaluated through metallography, hardness

measurements, chemical analysis and mechanical testing. The

following paragraphs describe general trends and observations

found in DH-36, HSLA-65, AL-6XN and 304L stainless steel

friction stir welds.

DH-36 Weld Evaluation A typical FSW cross-sectional micrograph and corresponding hardness map are shown in Figure 3. In

general, friction stir welds in most metals have three microstructurally distinct regions: the stir zone (SZ) along the weld centerline, a swirl region within the stir zone, and a heat-affected zone

(HAZ) surrounding the stir zone and extending to the base metal

[3, 4]. In some cases a fourth thermal-mechanically affected zone

Figure 2. USS Arleigh Burke (DDG 51).

14 The AMPTIAC Quarterly, Volume 7, Number 3

Table 1. Characteristics of Solid State Joining.

• Minimization of fume generation since the heat 

generated during this process remains below the 

melting temperature of the material

• Reduced distortion

• The ability to form strong joints without filler wire

• Reduced joint preparation and post-weld clean-up

• Reduced post-weld inspection and rework

• Various inherent user- and environmentally-friendly 

properties, such as the ability to be automated 
(TMAZ) can be present, as indicated in Figure 3. In DH-36,

hardness measurements increase from the base metal through the

HAZ into the SZ. The peak hardness corresponds to the swirl

region within the SZ. While this general hardness profile was

observed for all the conditions studied, specific trends were

observed to be functions of travel speed. As the travel speed

increased (1) the width of the SZ and HAZs decreased, (2) peak

hardness increased, (3) yield strength and ultimate tensile strength

increased, and (4) ductility as measured by percent elongation

decreased.

Figure 4 shows tensile properties as a function of travel speed.

Substantial overmatching was noted within the stir zone of 0.25

inch thick welds, and to a lesser extent in 0.5 inch thick weld.

Ductility in the stir zone was greatly reduced in 0.25 inch thick

plates and toughness values were lower for 0.5 inch thick welds.

Bulk chemical analysis of DH-36 showed a residual amount of

material left behind in the weld region by the pin tool as it

wears. (Numbers indicated {kJ/in} above the tensile strength

data points are a measure of heat imparted during the weld.

Closed diamond and square markers are for tests on 0.25 inch

DH-36; open markers are tests on 0.5 inch HSLA-65.)

HSLA-65 Weld Evaluation Consistent with DH-36, HSLA-65

can be friction stir welded–although the resulting structures

and properties differ. Friction stir welded sections from 0.25

inch to 0.5 inch thick have been successfully produced, at

speeds on the order of 5 inches/minute (ipm). Figure 5 shows

the overall structure of an HSLA-65 friction stir weld (in 0.5

inch plate) compared to that of an HSLA steel conventional arc

weld (in 1.0 inch plate). (Note that the conventional weld

shown in Figure 5 is actually HSLA-100, a different alloy composition but one for which hardness maps were available. [5])

Although both welds have similar gross features (a weld zone, a

heat-affected zone, and the base metal), their microstructures

and properties are very different. Within the stir zone of the

friction stir weld a swirl region shows evidence of vertical flow

Figure 4. Plot Showing Increase in Yield Strength and Decrease in Percent Elongation as a Function of Travel Speed. 

The AMPTIAC Quarterly, Volume 7, Number 3 15

Figure 3. DH-36 FSW Cross-section Showing the Four Microstructurally Distinct Regions and 

Corresponding Hardness Values (Vickers Microhardness).

0 5 10 15 20

Travel Speed (ipm)

120

100

80

60

40

20

0

Plate Yield Strength: 62 ksi

Plate Elongation: 22%

(67 kJ/in)

(69 kJ/in)

(26 kJ/in)

(24.6 kJ/in)

(19 kJ/in)

Tensile Property 

[Yield Strength (ksi) or % elongation]

Yield Strength

% Elongation
of material. The 0.5 inch thick friction stir weld was produced in

two passes; the first on what is now the bottom of the photograph, and the second on the top. The 1.0 inch thick conventional weld was produced using approximately 25 successive weld

passes starting at the bottom of a “V”-shaped notch. (It is possible however, to use fewer passes to complete the weld).

Hardness maps of weld cross sections are shown in Figure 6.

In this case there is a softening of the metal in the HAZ around

the stir zone of the friction stir weld, although this does not

always occur. In general, the stir zone is stronger and harder than

the base metal, but not as tough. There is additional hardening

in the stir zone of the first pass, just outside the HAZ of the second pass. (This can be seen along the bottom of the FSW hardness map in Figure 6 at 15,000 and 29,000 microns.) The conventional weld HAZ is harder than the weld or base metal.

Friction stir welds in HSLA-65 have also been compared with

those in DH-36, an alloy with higher C, Ni, and Cr that has

been used extensively in naval structural applications. The hardness profile of an FSW in HSLA-65 differs dramatically from

that of DH-36 and other typical steels. In this evaluation, the

hardness profile of HSLA-65 softened in the HAZ region and the

peak hardness in the stir zone was not significantly higher than

the base metal hardness. (The difference in hardness from the

base metal to peak hardness was approximately two times greater

in DH-36 than in HSLA-65.) The stir zone’s yield and ultimate

tensile stresses were fairly comparable to the base metal properties

and it maintained good ductility. At strength levels of 94 ksi for

the HSLA-65 and 107 for the DH-36, charpy impact energies of

the HSLA-65 material were significantly higher than those of the

DH-36 (Figure 7).

AL-6XN Weld Evaluation Bulk chemical analysis of AL-6XN welds

showed pin tool material pick-up, particularly in the plunge area.

The hardness profile for AL-6XN was similar to that of DH-36 in

which the hardness increased from the base metal through the

HAZ and into the SZ. The SZ properties significantly overmatched the base metal properties with a significant reduction in

elongation. [6] Centerline sigma phase (a hard, brittle intermetallic phase) was observed in 0.25 inch thick plate and not in the 0.5

inch thick plate (Figure 8). Energy dispersive spectroscopy analysis

Figure 5. Optical Micrographs Comparing the Major Features of an FSW and a Conventional Arc Weld

(Transverse Cross Sections).

Friction Stir Weld Conventional Arc Weld

Figure 6. The Hardness Maps of the FSW and Conventional Welds in Figure 5 Show Significantly Different Patterns.

Friction Stir Weld Conventional Arc Weld [5]

16 The AMPTIAC Quarterly, Volume 7, Number 3

Swirl Region Stir Zone HAZ

Base Metal

HAZ Weld Nugget

10000

7500

5000

2500

0

0 10000 20000 30000 40000

Distance (μm)

Distance (μm)

170 180 190 200 210 220 230 240 250

Vickers Microhardness

Vickers Microhardness

216 326 436
of various regions of the weldment demonstrated that (1) the swirl

region contained tungsten particles (i.e., pin tool material), (2)

banded regions outside the weld area had distinct concentration

differences of Mo, Cr, and Ni (compositional elements of the

sigma phase), and (3) intergranular precipitation of sigma phase

was observed in bands with higher concentrations of Mo, Cr, and

Ni. In the 0.5 inch thick plate, the stir zone exhibited excellent

toughness, equivalent to that of the base metal. 

304L Weld Evaluation Similar to DH-36 and AL-6XN, bulk

chemical analysis showed pin tool material pick-up within the

weld region of the 304L. Its hardness profile showed little variance

in hardness across the various weld regions, and the stir zone properties exceeded both the base metal and weld metal requirements

while maintaining high ductility (~65% elongation). [3]

Technology Development

This series of evaluations have demonstrated the feasibility and

promise of FSW for joining steel plate compositions used in

naval construction. They have also illustrated the challenges that

must be addressed in order to successfully exploit this revolutionary technology. The Navy is committed to understanding,

describing and simulating the myriad technical issues being

addressed by the Navy laboratory and warfare centers, universities and industry. These include specifically the mechanisms of

severe deformation, influences of initial workpiece condition

(compositionally and microstructurally), influences of tool materials and geometries, effects of welding parameters on mechanical

and microstructural properties, and many others.

The initial technological focus was motivated by evolving

Navy warfare requirements and increasingly stringent environmental regulations that create a need for improved welding

processes to fabricate military and commercial structures using

ferrous materials. The focus was expanded to include combined Navy/industry interest in the development for self-reacting FSW tool technology for 2519, 2219, and 2195 aluminum

alloys, as well as AL-6XN and HSLA-65 steels. This expansion

was motivated by three FSW technology related developments.

They were:

• adjustable, self-reacting FSW pin tool capabilities 

patented by MTS [7]

• the emergence of FSW technology advancements with

increasing potential benefits to the near term success of the

Advanced Amphibious Assault Vehicle (AAAV) Program, 

• commercial interest in similar FSW technology advancements for aerospace applications. 

The approach has included advanced equipment development, tool material evaluation, welding process parameter development, mechanical property measurements, and metallurgical

evaluation. Various materials were successfully welded and evaluated namely, 0.125 inch thick A588, 0.25 inch thick 304L

stainless steel, 0.25 inch and 0.5 inch thick DH-36, 0.25 inch

and 0.5 inch thick HSLA-65, 0.25 inch and 0.5 inch thick AL6XN, and 0.320 inch and 1 inch thick 2519, 2219, and 2195

Al alloys. Development of welding process parameters for DH36, HSLA-65, AL-6XN, and the Al alloys as a function of pin

tool type (fixed and adjustable self-reacting) and joining method

(single-sided {welded only from one side of the plate}, doublesided {welded from both sides of the plate}, overlapped plates,

and tapered welds {joining two plates of different thickness})

continues.

Two projects were used to demonstrate the specific applicabilFigure 7. Friction Stir Welds of HSLA-65 Show the Potential of

Significantly Tougher Behavior.

Figure 8. Micrographs Showing (a) Centerline Sigma Phase (Dark Strip) Observed in 0.25 Inch Thick Plate and

(b) No Centerline Sigma Phase Present in 0.5 Inch Thick Plate.

The AMPTIAC Quarterly, Volume 7, Number 3 17

160

140

120

100

80

60

40

20

Charpy Impact Energy (ft-lbs) @ -20 ̊F

0

HSLA-65 weld 1 HSLA-65 weld 2 DH-36 weld

a b
ity of the FSW process. The first was a comparative distortion

study between conventional arc and friction stir welded plates,

and the second was an assessment of shock loading tolerance

(which was also the first reported dynamic fracture test of a steel

friction stir weld).

Post Weld Distortion Study Results HSLA-65 plates with a thickness of 0.25 inch were used for the distortion studies.

Conventional arc and friction stir welded plates were fabricated

at Bath Iron Works and the University of South Carolina,

respectively. All welds used a square butt joint configuration

and were fabricated in the flat position. The conventional arc

welds were fabricated using two distinct welding conditions.

Case 1 consisted of a double-pass, two-sided submerged arc

weld (SAW) and Case 2 consisted of a single-pass, single-sided

gas metal arc weld (GMAW). Comparisons between measurements taken before (baseline) and after welding indicated that

the friction stir welded plates displayed significantly lower

angular distortion as compared to arc-welded plates [8]. Figure

9 shows baseline and post weld measurements for FSW, SAW,

and GMAW plates. 

Shock Hole Test Results A shock hole test panel was fabricated

by friction stir welding two, 0.5 inch thick HSLA-65 plates,

each 26 inches wide and 50 inches long; the longest length 

corresponding to the weld direction. After machining, the 50

inch diameter test panel was bolted to a paddle wheel test fixture (schematically shown in Figure 10) and tested underwater

with an explosive charge. Results indicated that the friction stir

welded HSLA-65 test panel had shock holing resistance equivalent to the base metal HSLA-65 test panel under identical test

conditions. [9] Figure 11 shows the resulting deformation of

both the base and friction stir welded plate after testing.

FUTURE EFFORTS

Friction stir welding is proving to be a viable option for joining

high strength steels. The Navy’s goal is to friction stir weld up to

0.5 inch thick HSLA-65 steel for an uninterrupted length of 80

feet at a travel speed that would make FSW competitive with

current conventional arc welding techniques. However, important technical challenges remain due to the higher temperatures

and forces involved which cause accelerated degradation of tool

assemblies and severely limit productivity. A two-pronged

approach is being used to meet the immediate needs of getting

the process to the shipyard and developing the understanding

that will enable wider, more effective exploitation of this tremendous technological opportunity.

A shipyard implementation plan is under development to

address critical technology areas, including:

• novel methods to improve process efficiency, including

processes such as thermal management to enhance tool life

• joint design optimization, including fit-up requirements and

tool change out methods

• improved modeling capabilities validated for materials of

interest to the Navy

• quality assurance and non-destructive evaluation techniques

to identify common welding discontinuities and confirm that

these discontinuities can be detected by traditional NDE

techniques

• material and structural certification to determine mechanical

properties and fracture performance, fatigue life, structural

performance, and corrosion behavior

• process certification requirements

• production implementation which includes technology transfer and training, performing procedure qualification, and performing operator qualification.

Figure 9. Comparison of Baseline (Grid) and Post-weld (Solid) Distortion Measurements of (a) FSW,

(b) SAW, and (c) GMAW Plates.

18 The AMPTIAC Quarterly, Volume 7, Number 3

HSLA-65 Test Panel

Charge

Figure 10. Schematic of Shock Hole Test Fixture.

a b c Y (inches) Z (inches) Z (inches)

Z (inches)

Y (inches)

Y (inches)
Concurrent with shipyard implementation, important

research and development continues to build the base for understanding and exploiting the critical mechanisms at work in

FSW. This work is aimed at identifying and predicting optimal

processing conditions, including tool design and tool material.

Alloys and microstructures that are most amenable to FSW may

be predicted, then further development will tailor welded joints

for high performance and robust responses to a wide spectrum

of loading and environmental conditions. Emerging simulation

and predictive modeling capability will further guide FSW

developments and enable design engineers to confidently exploit

this revolutionary technology.

SUMMARY AND CONCLUSIONS

Friction stir welding is a transformational, solid state joining

technology offering the potential for high performance and

affordability for naval applications. The initial efforts demonstrating the Navy’s interest and commitment to develop the

practical processes and systems for shipyard implementation of

FSW have been described here. The underlying technology

enabling longer-term payoff for an extended array of materials

and component requirements for FSW has also been demonstrated. The ONR-sponsored Dual Use Science and

Technology program successfully demonstrated the feasibility

of FSW in steels and stainless steels, as well as the utility of selfadjusting pin tool designs. The demonstration projects showed

reduced angular distortion in FSW compared with conventionally arc welded plates and excellent shock holing resistance

(equivalent to that of the base metal) from underwater testing.

Future efforts focus on building the understanding needed to

critically assess the viability of, and gain the maximum benefit

from, FSW.

ACKNOWLEDGEMENTS

This work was sponsored by the ONR Seaborne Structural

Metals Program, Julie A. Christodoulou Program Manager.

REFERENCES

[1] C. Conrardy, and R. Dull, “Control of Distortion in Thin

Ship Panels,” Journal of Ship Production, v. 13, no. 2, pp. 83-92 

[2] T. Trapp and T. Stotler, “Friction Stir Welding of the

Advanced Amphibious Assault Vehicle,” presented at the 2002

American Welding Society International Welding & Fabricating

Exposition, Chicago, IL, March 2002

[3] M. Posada, J. DeLoach, A.P. Reynolds, M. Skinner, and J.

Halpin, “Friction Stir Weld Evaluation of Steel and Stainless

Steel Weldments”, Proceedings of the Symposium on Friction

Stir Welding and Processing, eds. K.V. Jata, M.W. Mahoney,

R.S. Mishra, S.L. Semiatin, and D.P. Field, TMS 2001,

Indianapolis, Indiana, 5-7 November 2001, pp. 159-171

[4] T.J. Lienert, W.L. Stellwag, JR., B.B. Grimmett, and R.W.

Warke, “Friction Stir Welding Studies on Mild Steel”, The

Welding Journal, Research Supplement, v. 82, no. 1, 1s – 9s

(January 2003)

[5] D.W. Moon, R.W. Fonda and G. Spanos, “Microstructure

and Property Evolution in HSLA-100 Steel Welds Fabricated

with New Ultra Low Carbon Filler Metals”, The Welding

Journal, Research Supplement, v. 79, no. 10, 278s-285s (October,

2000) 

[6] M. Posada, J. DeLoach, A.P. Reynolds, and J.P. Halpin,

“Mechanical Property and Microstructural Evaluation of Friction

Stir Welded AL-6XN”, Proceedings of the 6th International

Conference on Trends in Welding Research, eds. S.A. David, T.

DebRoy, J.C. Lippold, H.B. Smartt, and J.M. Vitek, Pine

Mountain, Georgia, 15-19 April 2002, pp. 307-311

Figure 11. Photo of FSW Plate After Testing and Comparative Deformation Plot of Base- and Friction Stir Welded-HSLA-65 Plate.

The AMPTIAC Quarterly, Volume 7, Number 3 19

HSLA-65, FSW: Along Weld

HSLA-65, FSW: Perpendicular to Weld

HSLA-65 Baseplate

Distance Across Diameter (in.)

Deformation (in.)

12

10

8

6

4

2

0

0 10 20 30 40 50 60
20 The AMPTIAC Quarterly, Volume 7, Number 3

[7] J. Halpin and R. Edwards, “Friction Stir Welding

Technology Commercialization for High Strength Structural

Alloys”, Final Report for Agreement N00014-00-3-008 between

The Office of Naval Research and MTS Systems Corporation,

10 December 2002

[8] Campbell et. al., “Welding Head”, US Patent No.

US6,1999,745 B1, dated March 13, 2001 

[9] M. Posada, J. DeLoach, A.P. Reynolds, J. Halpin,

“Evaluation of Friction Stir Welded HSLA-65”, to be published

in proceedings for the 4th International Symposium of Friction

Stir Welding, Park City, Utah, 14-16 May 2003

Ms. Maria Posada is a materials engineer in the Welding and NDE branch at the Naval Surface Warfare Center.

Ms. Posada received her BS in Metallurgical Engineering (1996) and an MS in Metallurgical and Materials

Engineering (1998) from the University of Texas at El Paso. She is currently leading a Navy effort to evaluate the

Friction Stir Welding (FSW) process that may provide an affordable alternative to conventional arc welding of steels

and nonmagnetic stainless steels. Ms. Posada has contributed to numerous technical publications and technical presentations in this area. 

Ms. Jennifer Nguyen is a materials engineer in the Welding and NDE branch at Naval Surface Warfare Center,

Carderock Division. Ms. Nguyen received her BS in Materials Science and the Biomedical Engineering (2002) from

Johns Hopkins University. She is pursing her PhD in materials science at the University of Maryland-College Park. 

Dr. David Forrest is a materials engineer with the Welding and NDE group at the Naval Surface Warfare Center

(Carderock). He is involved with projects relating to the friction stir welding, the laser fabrication of HSLA-65, and the

mathematical modeling of welding. He has been a consultant in advanced materials technology with Baverstam

Associates, and has worked in plant operation and research positions in the steel industry between 1978 and 1999,

with Republic Steel, Bethlehem Steel, and Allegheny Ludlum Corp. He specialized in microstructural analysis, computational and statistical methods for optimizing mechanical properties, and in the mathematical modeling of metallurgical processes. He completed his doctorate degree at MIT and is also President of the Institute for Molecular

Manufacturing, a non-profit organization.

Robert DeNale is head of the Metals Department at the Naval Surface Warfare Center, Carderock Division. His

areas of scientific and engineering interest include welding, nondestructive evaluation and high strength steel casting

metallurgy. He has authored numerous publications and US Navy technical reports. He has been awarded 7 US

patents, edited two books, and made more than 50 presentations at professional society meetings.

Mr. DeLoach is the Head of the Welding & NDE Branch at the Naval Surface Warfare Center. He received his 

BS in Materials Science and Engineering from Brown University and his Masters of Materials Science and

Engineering from Johns Hopkins University. Mr. DeLoach has twenty years of experience in the materials and 

welding areas. He has more than 100 technical contributions (papers, publications, etc.) in the areas of welding,

materials, and nondestructive evaluation. 
The AMPTIAC Quarterly, Volume 7, Number 3 21

Jenness Simler 

Navy Manufacturing Technology (MANTECH) Program 

Office of Naval Research 

Arlington, VA

Larry Brown

Edison Welding Institute 

Columbus, OH

INTRODUCTION

As part of the Surface Strike Affordability Initiative, the Navy

Manufacturing Technology Program (MANTECH) is sponsoring a project to develop adhesive bonding methods for joining

composites to steel structures for the Navy’s next generation

ships. Two of the Navy’s Centers of Excellence have teamed with

Northrop Grumman Ship Systems, General Dynamics – Bath

Iron Works, The Boeing Company, and Penn State University

Applied Research Laboratory to develop and demonstrate manufacturing technology solutions for these adhesively bonded

composite-to-steel joints. The MANTECH Program’s overall

objective is to significantly improve the affordability of Navy systems by engaging in manufacturing initiatives that address the

entire weapon system life-cycle. Moreover, the MANTECHestablished Centers of Excellence provide focal points for the

development and technology transfer of specific new manufacturing processes in a cooperative environment between the Navy

(industrial facilities and laboratories), industry, and academia. 

The Need and Plan to Develop New Composite Joining

Technology

New material systems are required as a result of advanced performance criteria spelled out in the DD(X) (next generation

destroyer) program and other Navy ships. These requirements

call for reducing the weight of ships, especially structures above

the waterline and on upper decks (topside). Thus, there is an

increased demand to use composite materials in the fabrication

of topside structures like helicopter hangers, control rooms, and

mast enclosures. (Examples may be seen in Figures 1 and 2.)

Composites are strong, light weight, and are not susceptible to

corrosion. However, to take full advantage of the benefits offered

by composite materials, industry must develop new joining technologies to couple composite and steel marine structures.

The Navy Joining Center, operated by Edison Welding

Institute, is leading the joining project team, supported by the

Composites Manufacturing Technology Center (managed by the

South Carolina Research Authority.) The initial focus of this

technology will be applications for the Zumwalt-Class land

attack destroyers. The technology developed will have applications extending to other surface combatant ships, including aircraft carriers.

Current methodologies utilize mechanical fasteners to join

composites to steel, and even composites to composites joints 

on Navy ships. These fasteners are expensive, their installation

procedures are labor intensive, and the joints require long-term

maintenance. New processes must be cost effective, while meeting the functional requirements of structures, signatures, and

longevity. Thus, the focus of this project is to identify and maximize the efficiency of key joint manufacturing details and assess

the viability and cost of integrating adhesive bond technology

into ship manufacture. Specifically, the project will target large

composite-to-steel structural joints, where adhesive bonds 

must provide load

continuity. The

technology will be

applicable to both

internal and external bulkhead type

structures.

Although

much work has

been done with

regard to design,

manufacture, and

test of adhesive

bonds in other

industries, existing technology may not translate directly into

shipbuilding applications due to the typically large structural

components, the manufacturing requirements, and the marine

environment. A concurrent engineering approach will be used

Figure 1. USS Arleigh Burke (DDG 51) Forward

Director’s Room.
during this project to incrementally demonstrate through analysis and testing that the functional requirements of the adhesive

bond joint and manufacturing processes are attainable. The

intended results of the project are summarized in Table 1.

Further, these items could be used as templates to implement

composite structures aboard all surface combatants. The “rules

and tools” would need to be set in place so that a standard could

be established. This standard would enable current and future

hulls to implement composites supporting higher performance

weapons platforms, and generally result in a more affordable

Navy. The potential benefits of the resulting technology are summarized in Table 2.

The project is currently in Phase II, with five phases planned.

Phase I (begun in June, 2001) provided an assessment and

review of previously developed composite-to-steel adhesive joint

concepts. Tasks included a review of composite marine programs; definition of loading, functional, and qualification

requirements; initial joint design assessments and trade studies;

development of a material characterization plan; an assessment

of manufacturing practices; and a review of possible nondestructive inspection techniques. The results of Phase I have been published and released.

DESIGN ASSESSMENT

To facilitate the team’s understanding of composite joint requirements in the marine environment, a report was completed on the

following marine applications/joint configurations:

• Arleigh Burke Directors Room (composite structure; Figure 1)

• San Antonio AEM/S (Figure 2)

• Composite Close In Weapons System (CIWS) Maintenance

Enclosure

• Sealift Ships

• USS Radford (DD 968)

AEM/S (Figure 3)

• Maritech Prototype

Deckhouse 

• DDG Flight IIA Composite

Helicopter Hangar 

• Swedish Visby-Class Corvette (Figure 4)

• French LaFayette-Class Frigate 

Moreover, functional and load requirements were defined in a

generic and conservative manner to meet DD(X) requirements.

Requirements were established in the following areas:

• Definitions

• Design

• Performance

• Joint Fabrication

• Joint Assembly

• Unit Assembly

• Environmental, Health, and Safety Issues

Bending moment and transverse shear were found to be the

primary loading modes, but solar loading, preliminary shock

loading, and wave slap loading will also be considered. The fire

requirement is based on an Underwriters Laboratory specification: Structures must retain their fundamental integrity for 

30-minutes post-flashover, while subjected to a standard fire per

Figure 2. USS San Antonio (LPD 17) Advanced Enclosed Mast/Sensor (AEM/S). Figure 3. USS Radford (DD 968) AEM/S.

Figure 4. Swedish Visby-Class Corvette.

22 The AMPTIAC Quarterly, Volume 7, Number 3

Table 1. Demonstration Objectives of the Joining Project.

• Comprehensive analysis of composite-to-steel joint design(s)

• Selection of adhesive material(s) that meets functional

requirements

• Structural integrity demonstration

• An engineered steel-to-composite joint design(s) that meets

functional requirements for Navy surface combatants

• A robust manufacturing process/procedure usable for 

shipbuilding

• Best practice nondestructive inspection method(s) for manufacture and field service use

• Field repair techniques

AEM/S Mast Enclosures

Table 2. Benefits of Joining Technology Advances.

• Reliable integration of composites into surface combatant designs

• Reduction in manufacturing cost by eliminating mechanical

fasteners and intensive labor

• Reduction in long-term maintenance (corrosion)

• Increased weapons system performance

• Reduced signatures

• Established standards for further implementation to all Navy ships

• New adhesive technology for general ship adhesive bonding

applications (equipment mounts, etc.)

• Many supplementary performance benefits of composite materials
The AMPTIAC Quarterly, Volume 7, Number 3 23

UL 1709. The structure will be tested as described in UL 2079.

Finally, a 35-year expected lifetime was utilized for fatigue

assessments.

COMPOSITE-TO-STEEL JOINT ASSEMBLY

An initial assessment of current manufacturing practices was

performed. Typically, composite materials for large marine 

structures have a sandwich construction, fabricated via vacuum

assisted resin transfer molding (VARTM), utilizing low cost

fiberglass and core materials, such as end-grain balsa. Large, flat

bulkhead panels generally have an exterior, tooled surface, as well

as an interior, bagged surface. (i.e., the surface of the composite

part against the tool die, and the opposite surface covered by the

vacuum bag.) Therefore one surface will be smooth, while the

other will likely require light machining to fit a steel joint. (See

Figure 5.)

From the initial design assessment and trade study for the

composite-to-steel adhesive joint, the team concluded that the

single leg design pictured in Figure 6 would result in unacceptably high adhesive stresses at the gussets. However, the double

leg design in Figure 7 results in acceptable uniform adhesive

shear stresses.

The “H”-section, double-leg design is most capable of transmitting structural loads and maintaining the integrity of the

composite-steel joint. Based on these assessments, the steel mating surface would be fabricated. (See Figure 8.)

The third step in the manufacturing sequence, depicted in

Figure 9, involves the actual joining of the composite panel to

the steel H-section. A paste adhesive would be applied to the

steel “shoe”, into which the composite part would be fitted.

Finally, the shipyards may use existing welding techniques to

weld the steel H-section to the deck. Weld points should match

the steel H-section to existing below-deck stiffeners, as shown in

Figure 10. A global view of the composite bulkhead to steel deck

connection may be seen in Figure 11.

The preliminary analyses indicate that an adhesive bonded

joint can be created to meet the initial functional requirements

as outlined by shipyards. As a final check in Phase I, the team

examined core crush strength under nuclear blast loads and

found the adhesive fully effective. Subsequently, Phase I defined

a materials characterization test plan, following a building block

approach. (See Figure 12.)

The team also assessed various manufacturing scenarios, each

of which are depicted in Figure 13. Sequence #1 is ideal for comFigure 5. Composite Panel Preparation.

Figure 6. Single Leg Composite-to-Steel Joint Design.

Figure 7. Double Leg Composite-to-Steel Joint Design.

Composite Panel

Gusset

“Single Leg” Design

Composite Panel

“Double Leg” Design

Figure 8. Fabricated Steel H-section.

Reasonably

Smooth

Surface

Expected

E-Glass Fabric/

Vinyl-Ester Facesheets

Machine Surface

to Fit Steel Scarf

Joint

Machine or Grind Surface

to Mate Steel Joint

Outer

Moldline

Tool

Surface

Tool

Balsa

Core

Paste

Adhesive

Weld from

this Side

Figure 9. Adhesive Joining

of Composite to Steel.

Figure 10. Welding H-section with

Composite Panel to Steel Deck.

Weld from

this Side

Balsa

P

P

Composite

Part

Steel “H”

Section
plex bonding processes, where tight tolerances are required. It has

the least impact to shipyards, in terms of real-estate, environmental requirements/regulations, skills, and capital investment.

Sequence #2 is ideal for simpler bonding processes, in which

less tolerance control is required. At a minimum, it necessitates

shipyard acquaintance with the bonding process. There are

greater real-estate needs at the shipyard, slightly more environmental requirements/regulations imposed upon the shipyard,

more personnel and training needs, and additional capital

investment requirements. Sequence #3 is ideal for processes with

the least tolerance control. Its impact to the shipyard is similar

to Sequence #2.

NDI ASSESSMENT

Lastly, a report was completed on possible non-destructive

inspection (NDI) solutions. Primary indications of failure

include voids, disbonds, and porosity. Two possible failure

modes were identified: the joint may either fail in adhesion

(poor or weak bond between the adhesive and adherend) or

cohesion (poor cohesion or weakness in the adhesive).

Secondary considerations are water absorption and other environment issues which may lead to serious joint degradation.

Possible inspection technologies identified are:

• Acoustic Emission

• Thermography

• Eddy-Current Inspection

• Radiographic Testing

• Microwave Imaging

• Ultrasonic Inspection

• Smart and Adaptive Structures

• Acoustic Holography

• Laser Holography

• Laser Shearography

Figure 11. Composite Bulkhead Joined to Steel Deck.

24 The AMPTIAC Quarterly, Volume 7, Number 3

Deck Removed

for Clarity

Composite

Panel

Complete

“H” Style

Joint

Not to Scale

Note: Web frame sizes are only notional, no analysis to support.

Longitudinal Stiffeners

(0.686m spacing)

Web Frames

(2.438m spacing)

Predict Failure Load,

Mode and Location

Fab and Test

Joint

Adhesive Shear 

Stress Strain Curves

Adhesive Shear 

Stress Strain Curves

Joint Validation

Complete

Determine Mode I, II

Fracture Toughness

Determine Mode I, II

Fracture Toughness

Performance

Requirements

Bonded Lap Joint

Concept Trade-Off Studies

Select Adhesive 

(Screening Tests)

Adhesive Shear 

Stress Strain Curves

Develop Adhesive

Design Allowables

Determine Through

Thickness Properties

Determine Mode I, II

Fracture Toughness

Finalize Joint

Design

Iterate

Predict Failure Load,

Mode and Location

Fab and Test Joint

Adhesive Shear 

Stress Strain Curves

Adhesive Shear 

Stress Strain Curves

Joint Validation

Complete

Determine Mode I, II

Fracture Toughness

Determine Mode I, II

Fracture Toughness

Performance

Requirements

Bonded Lap Joint

Concept Trade-Off Studies

Select Adhesive 

(Screening Tests)

Adhesive Shear 

Stress Strain Curves

Develop Adhesive

Design Allowables

Determine Through

Thickness Properties

Determine Mode I, II

Fracture Toughness

Finalize Joint

Design

Iterate

Test

Double Lap

Tensile Coupon

Thick Adherend

Double Lap

Stepped Double Lap

Interlaminar Shear

Interlaminar Tension

V-Notch Shear

With and Without

Adhesive

Mode I Mode II

Composite

Metal

Composite

Adherends

Composite

Adherends

Bonded Lap Joint Generic Validation

Test Program Flow Chart

Figure 12. Materials Test Program Flow Chart.
The AMPTIAC Quarterly, Volume 7, Number 3 25

CONCLUSION

Phase II expands on each of these areas of investigation and

broadens the scope to include joint repair techniques. The team

has worked closely with DD(X) design agents to insure implementation. Both Bath Iron Works and Northrop Grumman

Ship Systems have agreed to incorporate the joining technology

into the DD(X) design and subsequent manufacturing processes where feasible, cost-effective and beneficial. As DD(X) topside design evolves, so too will the specific requirements for

composite-to-steel joints. Regardless, the vital technology

emerging from this effort will serve as the building block for all

future composite ship design, meeting the needs of the 21st century Navy.

ACKNOWLEDGEMENTS

The author would like to extend their thanks to the following

individuals who have made significant contributions to this

Navy MANTECH project: Raymond Bohlmann and Mark

Bitzes from The Boeing Company, St Louis, MO; Jeff Smith

and Bruce Jackson from General Dynamics, Bath Iron Works;

Darlon Necaise and John Sullivan from Northrop Grumman

Ship Systems; Kevin Koudela and Eric Strauch from Applied

Research Laboratory, Penn State University; George Ritter from

the Edison Welding Institute; and Ivan Snell from the South

Figure 13. Possible Manufacturing Sequences. Carolina Research Authority.

Mr. Larry Brown is a Project Manager for the Navy Joining Center (NJC) at the Edison Welding Institute (EWI) were

his duties include planning, control, and reporting of NJC technology development projects and the Teaching Factory.

Mr. Brown has more than 20 years of aerospace associated experience in materials joining. He has extensive experience in various joining processes including fusion welding, brazing, and solid state bonding. Prior to joining EWI,

Mr. Brown worked for Rolls-Royce Corporation as Senior Materials Joining Development Engineer in the Materials,

Processes, and Lifting Department. Mr. Brown specialized in development efforts for joining of high temperature 

nickel, cobalt, iron-base superalloys, titanium alloys, and titanium aluminide intermetallic materials. Mr Brown received

his Bachelor of Science degree in Welding Engineering from The Ohio State University and has six brazing and 

welding technology patents.

Ms. Jenness Simler is a Program Officer with the Navy Manufacturing Technology Program at the Office of Naval

Research in Arlington, Virginia. She has been with the MANTECH Program since December 2001. Ms. Simler has

an advanced materials background and, as a Contracting Officer’s Representative, is responsible for the activities of

the Composites Manufacturing Technology Center of Excellence, located in Seneca, South Carolina. Prior to joining

ONR, Ms. Simler spent 4 years as a project engineer and later a project manager with the Center of Excellence for

Composites Manufacturing Technology. Ms. Simler received her BS in mathematics from Millsaps College in Jackson,

Mississippi in 1995. She is currently earning a Masters in Business Administration from the Robert H. Smith School of

Business at the University of Maryland.

Sequence #1

Composite Panel

Fabrication

Sequence #2

Sequence #3

Composite Panel

Fabrication

Composite Panel

Fabrication

Joint Assembly

Joint Assembly

Joint Assembly

Steel Fabrication

Steel Shop or Shipyard

Steel Fabrication

Steel Shop or Shipyard

Steel Fabrication

Steel Shop or Shipyard

Composite Shop

Composite Shop

Composite Shop

Unit Assembly

Unit Assembly

Unit Assembly

Unit Erection

Unit Erection

Unit Erection

Shipyard

Shipyard

Shipyard

Invert 

Completed

Assembly

Invert 

Completed

Assembly

Invert 

Completed

Assembly
26 The AMPTIAC Quarterly, Volume 7, Number 3

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 Database

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 7, Number 3 27

INTRODUCTION

In 2001, the US Navy embarked on an ambitious plan to significantly reduce the costs associated with shipboard maintenance and corrosion control. Sponsored by the Office of Naval

Research (ONR) and through the technology transition leadership of the Naval Sea Systems Command (NAVSEA), the

Naval Research Laboratory (NRL) is developing and institutionalizing rapid cure coatings to achieve these goals. The key

to this program’s success is the identification of new rapid cure

coating technologies, certifying them, and transitioning them

to use in the fleet.

In this program, the identification of new technology and

material developments are managed through a cooperative

arrangement between ONR and NAVSEA. Under the direction of ONR, NRL is responsible for naming candidate materials and for the development of new technology products.

Under the role of technology transition, NAVSEA performs a

review of candidate materials and newly developed

products, then issues the directives for proceeding

with laboratory qualification testing. 

The technology of rapid cure coatings has been in

existence for many years, but the materials and application technology were not fully exploited until very

recently. For many years rapid cure coatings were laboratory curiosities and remained in the realm of future

marketing concepts. The research for these coating

technologies has typically focused on two main areas:

application technology and component materials.

Both of these issues will be addressed in this article.

THE NEED FOR RAPID CURE COATINGS

Internal areas of ships are under constant attack from

corrosive elements. Internal tankage areas must be

treated to protect against severe and possibly critical

damage. This is commonly done with any number of

specialized coatings. Figure 1 shows the typical corrosion present inside a seawater ballast tank.

Fully one-half of the time for a ship’s overhaul is consumed

waiting for coatings to cure before work can resume either in

the treated area or in adjacent areas. For example, in any one

day of a ship’s availability, there can be more than 10 to 15 large

scale (>3000 ft2) surface preparation and painting activities in

progress. The scheduling of these operations must take into

account the need to retain access to surrounding areas, as well

as allowing concurrent work to progress in order to minimize

scheduling impacts. Fully three-fourths of these painting and

preservation activities directly affect work in adjacent areas, and

thus careful scheduling is required to minimize conflicts.

Balancing work efforts throughout the ship is extremely time

consuming and constantly changes to reflect items such as

structural repairs, material availability, and personnel scheduling. Perhaps the greatest factor affecting the time required for

maintenance processes like painting is weather. Although

equipment and procedures are available to minimize the impact

of the surrounding environment, painting (especially cure and

drying times) is still clearly affected to a significant degree by

weather conditions. Delays due to unfavorable weather create

subsequent delays in additional tasks, whether they are additional painting, structural repairs, or equipment installation.

One of the most problematic issues of painting in a shipyard

is premature damage to a freshly applied coating. Some examples of these scenarios are included in Table 1. Most of these

premature damage issues stem from the fact that the majority

of coatings require lengthy cure times.

Arthur Webb, Marine Coatings Section Head

Center for Corrosion Science and Engineering

Naval Research Laboratory 

Washington, DC

Figure 1. Corrosion in a Seawater Ballast Tank on the USS Whidbey Island (LSD 41).
28 The AMPTIAC Quarterly, Volume 7, Number 3

Typical solvent-free, high solids-content coatings employed by

the Navy have cure times ranging from 8-12 hours at ambient

temperature (~25 oC). This means that for approximately 8-12

hours the coating system is at the mercy of the environment and

must be protected from every conceivable source of contamination. Many applicators stage quality assurance personnel to

guard the application, however, they must be trained, licensed,

and paid. Having to hire and pay benefits to someone who simply stands and watches a coating dry is not popular within the

industry.

RAPID CURE TECHNOLOGY

A simple solution would be to employ a coating system that

cures much more quickly, and thus not prone to the onslaught

of time-controlled risks associated with slower curing coatings.

At present there is no formalized definition of a rapid cure coating, although the concept can generally be applied to a coating

system that cures either instantly or within 20 minutes of application. Fast cure is a broader term that has been in use for several years; however it usually refers to systems that cure in 3-4

hours. Rapid cure coatings in this program are based on two

types of materials: polyurethanes and polyureas. All rapid cure

coatings still require substrates to be prepared in the same fashion that they are for traditional coatings. 

Polyurethanes

Polyurethanes are versatile materials and are used as coatings, linings, structural resins, sealants, and foams. Since their discovery,

the materials employed to make polyurethane products have

changed significantly. In general, a polyurethane coating contains

a polyol and one or more of the following: a monomeric diisocyanate, a polymeric isocyanate, or an isocyanate prepolymer.

Isocyanates also fall into two types: aromatic and aliphatic. In the

realm of polyurethane coatings, the actual formulation and components used depend on the target end use. Aromatic isocyanates

are generally limited to structural applications, chemical resistant

liners and coatings, composites and foams. They are fast reacting

but exhibit poor exterior weathering performance. Aliphatic isocyanates, on the other hand, are used in exterior applications

where UV resistance is required but they are less chemically resistant and slower reacting.

Traditionally, polyurethane coatings have been employed in

architectural applications where aesthetic properties were the

driving factor. For this reason, their market was limited to niche

applications that focused not on coatings but on structural

applications, namely insulation, foams and composites. The

development of plural component application equipment (to

handle the quick setting foams and sealants) has recently sparked

the creation of rapid cure polyurethane coatings. (In general,

plural component equipment is any style of machine that is

capable of metering and mixing multiple components, and

applying them.) The advances in chemically resistant

polyurethanes for foams and sealants have also led to the slow

but steady development of chemically-resistant polyurethane

coatings

In the case of tank coatings,

systems employing aromatic

polyisocyanates are used for

chemical resistance. Figure 2

shows the seawater ballast tank

from Figure 1 after application

of a polyurethane rapid cure

coating.

Rapid Cure Polyurethanes for

Shipboard Corrosion Control

The focus of this program has

been on the identification,

development and use of rapid cure polyurethane coatings based

on aromatic isocyanates for tank linings. The chemical resistance

and inherent high degree of chemical crosslinking leads to a hard,

resilient and chemically resistant coating ideally suited for shipboard tanks and voids. Thus far, all of the coatings employed

make use of high molecular weight (polymeric) aromatic isocyanates which have a very low vapor pressure. Figure 3 shows a

before and after comparison illustrating the application of a rapid

cure polyurethane coating system.

Polyureas

Early work with polyurethanes resulted in the concurrent discovery of polyureas. Polyurea is the product of the very rapid

reaction between isocyanate and an amine. The reaction is so

rapid that mixing a pure low molecular weight diisocyanate with

a low molecular weight amine is nearly explosive. Their discovery was overshadowed by the successes of polyurethanes, and

therefore polyureas remained a little known corner of the larger

world of isocyanate technology. 

In general, the lack of interest in polyureas remained as a

probable consequence of their inherently rapid cure times, poor

film forming properties, and lack of adequate application technology. Polyurethanes had developed into a relatively mature

technology area with a proven history of success and performance, but polyureas did not enjoy the same exposure. However,

interest in polyureas began to surface when plural component

equipment was introduced. 

Rapid Cure Polyureas for Shipboard Corrosion Control The

focus of this program has been on the identification, development and use of rapid cure polyurea coatings based on aromatic

isocyanates and non-polyether polyamines. The chemical resistance and inherent high degree of chemical crosslinking leads to a

hard, resilient and chemically resistant coating ideally suited for

Figure 2. Seawater Ballast Tank

on USS Whidbey Island (LSD 41)

after a Polyurethane Rapid Cure

Coating is Applied.

Table 1. Examples of Tank Coating Contamination.

• Equipment is reinstalled in a freshly coated tank, only to

have that equipment fail soon thereafter.

• A tank is coated and during a subsequent shift another

repair task creates dust, shavings, or metal chips which are

allowed to enter the tank, embedding themselves in the 

still-curing coating.

• Water from washing of interior decks and passage-ways is

inadvertently allowed to run into a freshly coated tank.

• Sea valves where lines have been removed are accidentally

test cycled resulting in hydraulic fluid being sprayed

throughout the tank.
The AMPTIAC Quarterly, Volume 7, Number 3 29

shipboard tanks and voids. Thus far, all of the coatings employed

make use of high molecular weight (polymeric) aromatic 

isocyanates which have a very low vapor pressure to minimize

hazardous exposure to workers.

MATERIAL PERFORMANCE EVALUATION

The key to success in this program has been the rapid progression from laboratory evaluation of candidate products to shipboard demonstration. At the present time two rapid cure

polyurethane coatings have been fully evaluated at NRL’s Key

West Marine Corrosion Facility. (This consists of performance

evaluation in accordance with MIL-PRF-23236.) Some of the

required performance tests include but are not limited to:

• Cyclical seawater/fuel/air exposure in simulated ballast 

tank conditions,

• 1000 hours condensing humidity,

• Cathodic disbondment, and

• Jet fuel immersion

In addition, a unique test protocol is employed for evaluating

the performance of candidate coatings for collection, holding and

transfer (CHT) tank service. To date, two candidate rapid cure

polyurethane products have passed the rigorous CHT protocol. 

In general, the performance evaluation program is designed to

initiate accelerated testing (based on the tests just listed) immediately upon or shortly after receipt and application of the candidate coating(s). These tests are initiated while further application is performed for the longer-term simulated ballast tank

tests. The scheduling is such that all of the accelerated testing is

completed by the time the simulated tank tests have reached the

six-month mark. NAVSEA is then notified of the results and

allows for satisfactory coatings to be scheduled for sea trials.

The installation of a new coating system aboard an active platform can require a significant lead time (six to eight months),

thus, the candidate coating in many cases has completed the full

MIL-PRF-23236 evaluation in the laboratory before it is installed

aboard ship. In other instances, a rapid insertion may be performed, and thus a candidate coating can actually be applied

before the full scale performance testing has been completed. In

either case however, no coating can be applied until the six-month

performance mark has been achieved.

If a candidate coating has met the six month qualification, has

been successfully installed on an active platform, and has demonstrated a passing grade in the one year test sequence and/or has

demonstrated one year of satisfactory in-service performance aboard ship, the coating then receives

approval for incorporation into the Qualified

Products List (QPL). This is provided that all other

performance, manufacturing, environmental and

health and safety requirements have been met. 

TECHNOLOGY AND PROCESS

DEMONSTRATION

Equipment Requirements

For rapid cure coatings, plural component application

equipment is required which can deliver multiple

components to create a specific formula. The basic 

elements of these systems are a metering or proportioning pump, mixing chamber, and the application

gun. There are other features such as heating, material feed or supply, and material process recordation, but these features may or

may not be necessary for a particular application.

Proportioning Pumps Plural component equipment falls into

two general categories, fixed ratio and variable ratio. As the

terminology implies, a fixed ratio machine requires a manual

changeover of the metering portion of the unit when a proportion ratio change is necessary. In general, the proportioning ratio

for fixed ratio machines is very accurate and is set at the factory

using standards. For variable ratio machines, the proportioning

ratio can be adjusted rather rapidly, but is typically less accurate.

Consequently, this may require the user to perform multiple

ratio checks and make small or fine adjustments to establish and

verify a proper proportioning ratio.

Plural component pumps are typically powered by air,

hydraulics or electricity. Air-operated plural component pumps

dominate the heavy industrial market where solvent-free epoxies

are applied, whereas hydraulic-operated pumps are generally

employed in lower volume markets such as in-situ foam or small

scale, specialized coating applications. The choice of an air- or

hydraulic-operated machine is more of a preference than an

industry norm.

Mixing Chambers or Stations Mixing chambers or stations are

available in two basic types; pump-mounted (also called remote

mixing) and impingement mixing. For pump or remote mixing,

the A and B components of the coating are metered at the correct ratio by pump-mounted proportioner and delivered to the

gun as a mixed material through a single feed line. This type of

configuration is ideal for solvent-free coatings and where coating

working time is greater than 20 minutes. It also works well for

coatings which require a brief dwell time before application due

to slight component incompatibilities in the first few moments

of mixing.

Impingement mixing is different from pump-mounted or remote mixing stations in that the coating components are 

supplied in individual feed lines all the way to the application

gun. When the gun is triggered, the individual components are

mixed in a chamber immediately behind its tip or nozzle. In this

manner, the coating experiences a brief or instantaneous period

of mixing before exiting the gun and making its way to the 

substrate. For impingement mixing, it is imperative that the two

Figure 3. Before and After Pictures of Rapid Cure Coating Application.
30 The AMPTIAC Quarterly, Volume 7, Number 3

components of the coating are as mutually compatible as possible. For fast or instant reacting coating systems, impingement

mixing is the only available mode of application. 

Shipboard Demonstration

During FY02 and 03 there have been four successful application

demonstrations of rapid cure, chemically resistant polyurethane

coatings on active ships.

Three of the four demonstrations occurred on 

1) USS Gunston Hall 

(LSD 44) (one seawater 

ballast tank)

2) Whidbey Island (two 

seawater ballast tanks)

3) USS George Washington

(CVN 73) (one damage 

control void)

A fourth ship, USS Tortuga

(LSD 46) was being prepared for application in June/July ’03

and will host application of two rapid cure, solvent-free

polyurethanes in four seawater ballast and two potable water

tanks. Figure 4 shows pictures of the polyurethane rapid cure

coating technology as applied to seawater ballast tanks on

Whidbey Island.

For the first four demonstrations, the application was 

performed using an air-operated, plural component proportioning pump that was modified by the manufacturer to 

handle rapid cure polyurethane coatings. The pump was fitted

with an impingement mixing gun, having a material delivery

rate of approximately 3 gallons per minute. The configuration

performed satisfactorily, and allowed the applicator to achieve

proper film thickness control. The applicator was able to

progress at a fairly rapid rate yielding a coverage area of approximately 15-20 ft2 per minute.

Although mobility of the gun was limited by physical size

(large compared to a single feed gun), its delivery lines were

more flexible due to lower material pressures. This essentially

granted the same coverage of tight spaces and complex geometries within the demonstration tanks, as would be experienced

using a single feed gun (which requires higher operating pressures resulting in less gun-to-supply-line mobility.) The gun

manufacturer has introduced a smaller gun with a delivery rate

of about 1 to 1.5 gallons per minute. It will be employed on

the next demonstration using a newly approved coating system

for demonstration in combination with a hydraulically-operated, proportioning pump.

Cost Savings 

At present, a cost savings based on time required to complete the

coating application has been demonstrated. However, as with any

new material and process scenario, there is a significant learning

curve. For example, much of the savings from reduced time-to-cure

were quickly consumed with process learning and material control.

However, when compared to the initial costs associated with the

Navy’s successful demonstration of solvent-free epoxy coatings in the early 1990s, the relative increases in preservation

costs or those associated with a

learning curve are similar. 

For the first two demonstrations, the manpower and

maintenance costs were higher than would be expected for

a “traditional” job. However,

much of this was based on

increased quality assurance and control, equipment, material,

surface preparation, and environmental control. The preservation costs were also higher in that there was only one certified

applicator. (This was also the case when solvent-free coatings

were introduced.) Efforts are currently underway to bring in

more certified applicators with materials and process experience;

this will reduce the ultimate job cost significantly. Although the

actual application, which would include equipment preparation

and painting, will be higher for single coat application versus a

single feed or conventional solvent based coating application,

such factors as surface preparation remain the same. The significant cost reductions, however, are in the time critical operations

surrounding coating cure time. These include work stoppage in

adjacent areas, maintaining dehumidification and heating, and

constant rework due to premature damage incurred to a wet or

insufficiently cured coating. 

SUMMARY

The US Navy has recently been identifying, developing and

evaluating rapid cure coatings in order to reduce the costs of

shipboard corrosion control painting. The coatings themselves

will cure in significantly less time than current, traditional coatings; about 20 minutes or less compared to 8-12 hours. While

cost of application and preparation are similar, subsequent savings created from shipboard repair schedulers who no longer

have to “protect” curing coatings, or rework damaged coatings,

will be significant. Additionally, the Navy is streamlining the

processes to get new coatings certified for use in the fleet, thus

putting these materials in ships much sooner.

Figure 4. Seawater Ballast Tanks after Application of Rapid Cure

Coatings.

Arthur Webb has more than ten years of experience in the coatings industry and holds BS and MS degrees in

Chemistry from the California Polytechnic State University, San Luis Obispo. His focus areas were the investigation of

rapid reaction kinetics and polymer chemistry for coatings and composites. Mr. Webb is the head of the Marine

Coatings Section at the Center for Corrosion Science and Engineering, Naval Research Laboratory where he is

responsible for the testing and evaluation of corrosion control and specialty coatings for the US Navy. Mr. Webb is

also actively involved in polymer resin research and development and his team is currently developing rapid cure, solvent free resins for corrosion control and antifouling coatings.
The AMPTIAC Quarterly, Volume 7, Number 3 31

Material EASE

THE ROLE OF MATERIALS IN SHIP DESIGN AND OPERATION

Wade G. Babcock, AMPTIAC Quarterly Editor-in-Chief

The Advanced Materials and Processes Technology Information Analysis Center

Rome, NY

Ernest J. Czyryca

Survivability, Structures, and Materials Directorate

Carderock Division, Naval Surface Warfare Center

West Bethesda, MD

23AMPTIAC

INTRODUCTION

A sport fisherman on a quiet lake or river chooses a shallow draft, flat

bottom boat. A deep sea fishing charter chooses a larger, vee-bottom vessel with lots of power. A cargo company chooses a long, square cross section, boxy vessel. Some vessels are welded steel while others are wood and

still others are made of glass or carbon fiber reinforced polymers. All of

these boats share the same basic principles of keeping their operators or

cargo dry, enabling them to cross a body of water, and accomplishing a

certain task. But the differences in structure, speed, agility, sea-keeping,

and overall abilities are enormous.

It is obvious that the mission of an aircraft carrier is different from

that of a cruiser. But why would a fisherman choose a shallow-draft, flat

bottom boat to go bass fishing in? These questions are factors the designer must consider when building a new ship, and there are many more.

In this issue’s MaterialEASE, we seek to provide a look at some of the

most pressing considerations ship designers face when choosing materials for current and future Navy ships. While there is no way we can tackle all the issues unique to shipbuilding, what we seek to do here is present at least the “first tier” of considerations pertaining to materials that

any ship designer will have to address. The information is compiled here

such that the lay person can gain a basic appreciation for some of the

most important materials issues in shipbuilding.

Not only are there multiple grades of steel used throughout modern

ships, but one can see from the articles in this special issue that there are

efforts underway to change the fundamental materials and structures of

combatants. The next 30 years may see the most dramatic shift in shipbuilding technology since steel replaced wood.

First, take a look at modern ships. Since World War II, welded steel

(so-called monolithic) hulls have almost completely replaced riveted steel

hulls for all ships greater than 100 feet long. All of these structures are fabricated with a network of longitudinal and lateral “T”-shaped structural

members covered with plate to form the hull shape. All joints are welded

together and the grades of steel used typically fall into one of three categories: moderate yield strengths of 35 to 50 ksi, higher yield strengths of

around 80 ksi, and the highest yield strengths of 100 ksi or more.

In the United States, high yield strength Navy steels of 80 and 100 ksi

were specified in the 1950s with compositions separate from those of 

general industrial steels. These “HY” series steels had to meet significant

toughness and weldability requirements, especially at cold temperatures,

and were used in nuclear submarine pressure hulls and critical areas of

surface ships for ballistic protection and as “crack arrestors.” These

requirements were driven by the catastrophic failures incurred in the first

welded ships built from steels common in riveted construction. HY-80

and HY-100 have recently been augmented with even newer industrial

HSLA (high strength, low alloy) grades which will meet the strength,

toughness and weldability requirements, but should be significantly less

expensive. (For more information on HSLA steels, please see the article by

Czyryca, et. al. in this issue.)

Any of the steels used in Navy ships must adhere to certain criteria

demanded by the Navy and shipbuilders. There are fundamental weldability, toughness, and forming characteristics for metals which must be

met in the construction phase. Then there are additional parameters

which dictate the ship’s eventual performance, such as weight, shock

loads, vibration, fracture toughness in environmental extremes, and fire

performance. Since these two phases of a ship’s lifetime are governed by

different needs in terms of material performance, we have chosen to

divide this report along these lines. Neither operation of the ship nor construction can be examined independently however, so care should be

taken to consider each in the context of the other. The first section will

cover the main materials issues of concern during the construction phase

of a modern ship. The second section will discuss the most important

materials considerations during the operation of the vessel.

Most Navy ship hulls are constructed of steel, except for a few special

purpose vessels which have either fiberglass or wood hulls. (These are

used specifically for tasks where reduced magnetic signature is critical,

such as mine clearing.) Many ships have structures above the waterline

(called “topside”) fabricated of aluminum and more recently some use

glass reinforced polymer (GRP) composites. Most of the discussion in this

report will be in relation to steel, except where noted on topics where

other materials have been applied.

SECTION 1: 

MATERIAL ISSUES RELATING TO CONSTRUCTION 

OF NAVY SHIPS

It should be noted again that any material parameters considered 

during the construction phase will impact operational characteristics

downstream. For instance, the time and procedures required to weld a

structure together are major cost points during a ship’s construction.
32 The AMPTIAC Quarterly, Volume 7, Number 3

Material EASE

There is significant pressure to reduce these costs, therefore the weldability of a metal is critical. However, if welds are not done carefully

they are literally a breeding ground for flaws and will thus critically

impact the service performance of the vessel in operation.

Strength

Overall size of any structure is often a function of the strength of its component materials. In the case of ships, high strength steels with yields

stresses ranging from 30 to 130ksi are typically used. In general, most of

a ship’s structure is made from 50 or 80ksi yield stress steel, with critical

areas making use of stronger grades as needed. Less dense alloys of 

aluminum may be used for topside structures, and recently composites

are regularly finding their way onto ships also (mostly for topside 

structures – less commonly for hulls.) The current ultimate load carrying abilities (tensile and compressive) of reasonably cost effective GRP

composites limit all-composite hulls to about 200 feet in length.

A more complicated facet of the overall strength issue is the ability

of a structure to do its intended job. For instance, if a designer calls 

for 0.5 inch thick plate with a yield stress of 50 ksi, it might seem appropriate that a thinner, 80 ksi plate could be substituted. Ship structures

(and most other large structures for that matter) are never that simple.

Plate steel is welded into monolithic structures with interconnecting 

I- and T-cross-section beams. Hull or deck plating is then welded into

place creating “grillage” structure. Thinner plate (even with higher

yield stress) will behave differently, often buckling much sooner than

thicker plate. For this reason, careful attention is paid to buckling modes

of overall structures and thicker plate is often required even when its

specific strength is well overmatched to the task.

Similarly, the overall length of a vessel determines its loading 

characteristics. In a shorter vessel (up to ~150 feet), its structural components must perform well in bending and be stiff. For a hull greater

than 200 feet in length, the ultimate tensile and compressive behavior

of its components takes over. While composites can be made with

extremely high strength capabilities, the cost of their component 

materials and fabrication grows rapidly (especially as more exotic

components are chosen). Steel structure can be fabricated to handle

both loading scenarios (stiffness and ultimate strength, based on

length) at a much more affordable cost.

Weldability

An immense amount of welding is required to build a steel ship.

Thousands of piece parts are cut and assembled, requiring miles of welds

at the joints. Many of these joints require multiple passes to complete. By

far, welding is the most labor intensive portion of constructing a ship.

Welds in a ship structure are also very critical to its overall strength, 

durability, and toughness. Even small defects in weldments can create the

initiation point for considerably larger cracks and eventual failures.

Because of the massive amount of welding required, and its importance to the structural integrity of the vessel, careful welding processes

are stringently adhered to. While HSLA steels require diligent attention to

detail and procedure during welding, the HY-series steels require even

more weld preparation and post treatments. One of the reasons for the

push to replace HY-series steels with HSLA grades in the 1990’s, was the

reduction in labor required for welding. In general, any steel grade meeting the strength, toughness, and other requirements, but which is simpler to weld with a lower predisposition to weld flaws, is desirable. The

cost of alloying steels to increase weldability must be balanced against

the added cost of welding labor associated with a less weldable grade. 

Toughness

In addition to strength and weldability, toughness is one of the most

salient attributes of metallic structures. In shipbuilding, toughness is a

critical feature of the structure and its component materials (both plate

and weld metals), as they must be able to deform plastically to some

extent, and tolerate cracks and flaws while maintaining overall structural integrity. This is obviously complicated by the fact that Navy ships must

be capable of operating in every ocean environment, from the frozen arctic to the steamy tropics.

Steels, however, have a ductile-to-brittle transition in toughness as

temperature decreases. It is a function of temperature, loading rate, and

microstructure of the steel. Below a temperature specific to each steel

grade, the material will have little resistance to catastrophic crack

growth. In the transition regime, the combination of dynamic loading

and cracks or defects in areas of stress concentration, may result in

unimpeded, rapid crack propagation through the material.

For shipbuilding steels, it is imperative to select grades with a low

toughness transition temperature (below the expected operational temperature range). For the higher strength steels used by the Navy, alloying

and processing methods are used to produce grades with very low toughness transition temperatures, but again, this can increase cost and reduce

availability of the grade.

Marine Corrosion

Ocean-going ships are intended for use in one of the most corrosive environments on the planet, and as such, corrosion is considered carefully in

the design phase of any vessel. There are various materials options,

design strategies, coating, and cathodic protection technologies available

to the designer and shipbuilder.

Painting a ship is probably the Navy tradition with the strongest

love/hate relationship. The process is necessary to protect the vessel from

the sea’s corrosive effects, yet it is a never ending task that eats up significant labor resources and time. There is rarely a moment in a ship’s service life when something aboard is not being painted. And these paints are

not the kind of materials you find at a hardware store: there are many
A DVANCED M A TERIALS AND P ROCESSES T ECHNOLOGY

The AMPTIAC Quarterly, Volume 7, Number 3 33

AMPTIAC

different formulations, each specifically engineered to perform critical

tasks around the ship. Many also require very rigorous surface preparation and curing processes which place additional drains on manpower.

From the designer’s perspective, the ship must be built in such a way

as to reduce corrosion (limiting entrapped areas where water can collect

and stand for instance) and also allow for the significant corrosion preventative processes that will go on for the duration of the ship’s life.

Structural elements must allow for periodic and sometimes often recoating, and some elements must allow for replacement if they are particularly susceptible.

There have been efforts to replace corrosion-prone steels with other

metals like aluminum or titanium. These alternative metals offer a lower

density (which can reduce weight) and some corrosion resistance, but

they present their own unique problems which are beyond the scope of

this article. In short, marine grade aluminum (5000-series) is the only

non-ferrous, corrosion resistant metal that has seen widespread use in

Navy ships as topside structure over the past 30 years. This is mainly

because of the availability and relatively low cost of marine aluminum,

a consequence of commercial crew boat and high-speed ferry construction using well-understood fabrication and welding processes.

Formability

Ship hull forms and grillage structures require component steel or

composites to be formed into a multitude of complex shapes. The 

considerable amount of welding required to fabricate steel structures

also imparts a significant amount of residual stress and often unwanted deformation in the finished structure. This combination of initial

forming requirements coupled with post-assembly straightening of

deformed plate, requires that the steels chosen for ship construction 

be amenable to a wide range of forming procedures. The labor associated with these forming procedures must be balanced with the cost 

of alloying or preprocessing of steel plate to increase formability. 

In addition, formability of the grade impacts toughness, weldability,

and strength. 

Composites offer the ability to be formed into much more complex

monolithic shapes, but are not as amenable to assembly of multiple

subsections. Transferring structural loads and accommodating thermal

expansion mismatch is not a trivial endeavor in large structures. In fact,

joining technology (including composite-to-composite and compositeto-steel) is currently one of the most limiting (and potentially the most

promising) area of development. All of these

factors must be balanced carefully in the

selection process.

Availability

About 40-50% of the steel used by DOD is

consumed in Navy ship fabrication. The 

HY-series steels were specific to Navy 

applications, forcing manufacturers to 

divert production from common grades and increasing the lead time

required for production. When combined with their unique alloying

requirements, these factors make HY steels considerably more expensive

than more common industrial grades. Some recent efforts to utilize

industrial-standard HSLA steel grades have helped to increase the effective amount of steel available, as well as lower the cost of procurement.

Affordability

Currently and for the foreseeable future, one of the most pressing factors

in materials selection for Navy ships is affordability. With labor costs

continually rising and often outpacing the increased cost of raw materials, the balance between these must carefully accommodate and anticipate how materials decisions impact construction labor expense. The

long-term costs of maintenance and readiness must also be factored in.

Choosing the cheapest material in the construction phase cannot be a

considered a success if the decision requires a significant increase in

construction labor and/or creates a maintenance nightmare during the

30 to 50 year expected lifetime of the platform.

Traditional steels and newer composite materials each offer specific

advantages. As compared to composite materials, steels are less expensive to purchase, relatively less expensive to fabricate, and potentially

more expensive to maintain. When considering the cost of building a

ship from steel, one must always factor in the long term cost of repeated painting and corrosion mitigation. Composites cost more to fabricate,

but offer the promise of lowered maintenance cost through their corrosion resistance. There are however, questions as to the long-term maintenance of composite joining technologies, environmental attack causing delamination (as simple as water infiltration), and perhaps more

as-yet-undiscovered issues.

SECTION 2: 

MATERIAL ISSUES RELATING TO OPERATION OF NAVY SHIPS

Once a vessel enters the fleet, many of the materials selection decisions

made years before during design continue to impact its day-to-day

operation. 

Weight

In design of air and space craft, weight is the driving force for almost all

materials and structural decisions. Wherever weight can be reduced, it

typically is, no matter what the cost. Lower weight translates to greater

speed, range, and payload capacity, as well as a

generally reduced cost of operation in the form of

fuel requirements.

While not quite as critical as air and space

craft, weight reduction in ships is very important. The same economies of increased payload,

speed, and range translate, as well as a reduction in fuel requirements. There are additional

benefits to reducing topside weight of ship
34 The AMPTIAC Quarterly, Volume 7, Number 3

Material EASE

structure, such as increasing the sea-keeping ability of the ship via

improved stability of the platform in a seaway. (Reduced mass higher

up on the ship keeps the center of gravity low and reduces roll

moments.) While the overall weight of a ship is determined predominantly by decisions made in the design phase, they have the greatest

impact on service performance, including the growth margin critical

for added or improved capabilities over the life of the ship. Therefore we

have chosen to include the discussion in our Operation section.

Many ships currently in use have aluminum topside structures.

While these structures employ modern high-strength alloys, the fabrication methods and design are still very traditional, utilizing conventional

welded grillage construction. Composites have also been used very

recently for some limited topside structures, such as mast enclosures and

compartments. (For more information on composites aboard ships, see

the article by Potter in this issue.)

Most recent research efforts to reduce weight on ships have focused on

using higher yield stress steels to replace those with lower yield stresses.

This enables the use of thinner plate, and thus reduces weight. One cannot replace all structural plate with thinner material however, as buckling

instability becomes an ever increasing issue. Much research and experimentation has gone into studying how ship structure performs with thinner, higher yield stress steel and this work will no-doubt continue.

Other innovations such as the advanced double hull (ADH) seek to

replace conventional construction with new techniques which reduce the

overall number of metal piece parts needed. (For more information on

the ADH concept, please see the article by Beach, et. al. in this issue.)

Composites have been used on hulls shorter than 200 feet long with great

success. The raw material and labor cost to build composite hulls is still

too high for applications without a specific requirement (such as reduced

signature) for composite materials.

Fracture Toughness

As discussed earlier, fracture toughness is a critical property required in

the steels and weld metals of warship hull structure. Structural components’ ability to withstand the day-to-day rigors associated with thermal

extremes, impacts from piers and other boats, maintenance procedures,

sea conditions, and other “normal” events is important. These, however,

are not the most important conditions that impact readiness. Naval 

vessels are also subject to shock loading from hostile weapon effects, such

as air and underwater explosive devices and projectiles require protection

measures against shock, blast, and penetration.

Steels used in ships are formulated and processed to have a greater

ability to withstand fracture and a greater flaw tolerance under shock

conditions than more common structural grades. This allows them to

withstand high intensity loading and remain ductile, sustaining 

damage without rupture or fracture. Similarly, the welding processes 

are carefully engineered to produce very clean and uniform welds that

are also very tough and flaw tolerant. The qualification of Navy steels

involves a progression of fracture toughness testing from small impact

tests to large scale, full thickness explosion tests. These tests demonstrate

the capability of the welded system to sustain gross deformation, in the

presence of cracks and low temperature, without fracture. The specifications for both base metals (plate, forgings, castings, etc.) and welds 

contain toughness test requirements to assure their ability to resist 

fracture and tolerate flaws.

Marine Corrosion

Someone once said that from the moment steel comes from the mill, it is

constantly trying to get back to the earth in the form of rust. This is especially true of Navy steels, which are expected to do their job in one of the

most corrosive naturally occurring environments. Salt water and sea

spray cover every surface of an ocean-going vessel and are constantly

attacking its structure. Not only the structural components, but every system aboard the vessel is being chemically corroded. Galvanic corrosion

(produced by the differences in electronic potential between component

metals aboard a ship electrically connected via the ship’s structure and

ionically conductive seawater) is also a critical concern. In addition, the

ship itself generates combustion products (in turbine and diesel powered

vessels, as well as ancillary combustion engine-powered systems on other

vessels) which are high in corrosive compounds of sulfur and some acids.

Upper structures of the vessel are subject to these airborne pollutants.

There are multiple ways of combating corrosive elements. As mentioned in the first section, there are various materials options, design

strategies, cathodic protection, and coating technologies available to the

designer and shipbuilder. Once the vessel is in service, combating corrosion becomes a major maintenance requirement.

Coatings are used to protect the steel hull (or other substrates) from

attack by salt water and other water- and airborne corrosive compounds. They require a significant amount of care during application

and frequent reapplication to maintain their protection. From simply

scraping, sanding, or grinding a small area, to significant removal,

surface preparation, and reapplication of a coating to a large area,

coating maintenance is a never-ending process. Once there is a discontinuity in the coating, corrosive attack is mitigated by cathodic protection, either by sacrificial anodes or by impressed current systems. The

sacrificial anodes are typically blocks of zinc alloy, electrically coupled

with the steel hull and which preferentially corrode, protecting the

exposed steel. The anodes are positioned about the hull of the ship and

replaced periodically as they deteriorate. Impressed current systems use

permanent anodes on the hull and generate a potential field to counteract the corrosion potential of exposed steel.

Galvanic corrosion (caused when, steel is be connected to materials

of higher corrosion resistance), is mitigated by utilizing coatings or

insulators to help reduce the electrolytic connection enabled by the 
A DVANCED M A TERIALS AND P ROCESSES T ECHNOLOGY

The AMPTIAC Quarterly, Volume 7, Number 3 35

AMPTIAC

seawater, and by sacrificial anodes. (There typically is a concentration of

anodes in the stern, where the bronze propeller, galvanically connected

to the hull via the shaft, would otherwise cause accelerated corrosion of

any unprotected steel.)

Biological Attack

In addition to corrosion protection, the hull coating below the waterline

must posess anti-fouling properties to maintain hydrodynamic performance and fuel efficiency. The most commonly used coatings prevent or

slow the attachment of marine organisms by containing compounds

toxic to the animals, thus preventing them from attaching in the first

place. Another method is to apply a coating whose chemistry or surface

morphology hinders the creatures’ attachment, thus allowing them to be

sloughed off by water flow once the vessel gets underway.

Fire

Fire is probably one of the most dangerous events that can threaten the

safety of a ship and its crew. Shipboard fires must be fought with firefighting systems available on the ship. The crew must fight and defeat

the fire if the vessel is to survive. Crew training in fire-fighting and damage control are critical to ship survival.

Structural steels are vulnerable to annealing and softening with

exposure to fire-generated heat, thus allowing structures to collapse.

Shipboard composites can be a fuel source for fires, thus exacerbating

an already serious situation. In both cases, active and passive fire insulation systems are used to keep structural members protected from heat

and flame for a certain period of time – presumably long enough to get

a fire under control. For composites, great care

is taken to select component materials with

higher levels of fire resistance.

An additional fire concern is the production of smoke and toxic gases from burning

materials. Ships contain many flammable and

non-flammable compounds (liquids like fuel,

oil, greases, paint, etc.; solids like furnishings,

electronics, composite structures, metals, etc.)

which when exposed to either heat or flame

can burn, volatilize, or smolder. The smoke

and gases generated are of just as much concern as the fire itself. First and foremost, they hinder the ability of crew

to get near a fire’s source to extinguish it. Secondly, they can pose a significant threat to large portions of the vessel even if the fire itself is small

and easily controllable.

Naval vessels, given their intention to go into harm’s way, are

designed with materials and structures that meet higher standards of fire

resistance and control. Additionally, active fire suppression systems are

often incorporated into combatants. All of these factors are balanced

against affordability, but given that fire is one of the most dangerous

threats to a surface combatant, more resources are usually allocated to

this area.

Signature

Ships are very difficult to hide on the open water. A ship’s main defense

against detection is to reduce the amount of electromagnetic, acoustic, or

thermal radiation it emits or reflects. In order to do this, ship designers

are employing any number of technologies to absorb and deflect enemy

radar, reduce thermal and acoustic emission, and in general increase the

stealth characteristics of surface combatants.

As mentioned elsewhere, composite structures are being used on the

topside of ships to reduce weight. They also offer the capability of integrating absorbing and reflecting materials into topside structures. By

building composite shrouding around the very reflective metal masts on

current ships, the electromagnetic signature of a ship can be dramatically reduced. Future vessels will use predominantly composite topside

structures to further reduce signatures.

Composite hull forms and new steel double-hull technologies offer

the promise of reduced thermal and acoustic signatures. Composites can

insulate the internal components from the water, while double hull

designs allow for flooded compartments which can act as thermal and

acoustic barriers. Composite and double hull technologies are also

allowing more design freedom to create lower-profile, critically-shaped

hull forms which further reduce all types of signatures, including

reduced wake.

Wave Loading

The structural demands of a Navy ship, and indeed any ship, are characterized by one particular load condition that most other structures will

rarely see. Ships are subjected to a constant low-frequency, high-cycle

fatigue stress induced by wave motion. This is

due to ships not being rigid beams; they are in

fact a structural beam uniformly supported by

hydrostatic pressure along its bottom surface.

As the ship moves through water whose surface

is not flat, often the ends are supported more

than the middle (or vice-versa), creating a

repetitive bending moment in the structure.

There are also repetitive lateral forces exerted

on the structure which create other bending

moments. While these moments are accounted

for in design, the component materials still

acquire damage over the service life of the vessel. The fatigue strength of

a welded steel structure does not increase relative to the strength of the

steel. Therefore, the use of higher strength steels requires detailed design

against fatigue cracking over the life of the ship. Fatigue testing of structural joints and computational techniques are employed in modern ship

design to characterize the fatigue life of the structure.

Vibration

Vibration is a constant companion to any ship. There are hundreds 

of pieces of equipment aboard a vessel chugging away at their individual tasks, each one imparting its own characteristic vibration mecha-
36 The AMPTIAC Quarterly, Volume 7, Number 3

Material EASE

nism into the vessel’s structure. While most large equipment is built 

on vibration-isolating spring mounts, none of these systems is perfect

and always some vibratory load is transferred to the substructure. Even

when large equipment is well isolated, its acoustic noise induces vibrational loading into surrounding structure.

Vibration can induce fatigue, fretting, and other forms of 

degradation into structural materials. It also produces detectable 

noise transmitted through the water and interferes with a ships’ own sonar

system effectiveness. Constant small movements cause surfaces 

to wear, and tiny amounts of elastic deformation may induce fatigue-like

failures over time. Since vibration cannot be eliminated, material and

structure decisions must take these degradation mechanisms into account.

Hull Damage

Ships are always susceptible to hull rupture from collision with fixed

objects (rocks, piers, sea walls, etc) and other vessels. Navy ships also

face the possibility of having explosives detonated close by (hull whipping and blast loading) or being impacted by projectiles and fragments.

Material choices are critical in reducing these threats, or at least reducing the amount of damage. Unlike merchant vessels, Navy ships are

expected to maintain a high level of performance even when damaged.

Therefore component materials’ ability to not only limit damage but

also be quickly repairable is paramount.

Hull survivability is part of the structural design of warships. Grillage

is analyzed and built such as to limit the amount of damage caused 

by perceived threats. New designs such as double hulls (and some 

composite structures) have additional, built-in resistance to hull rupture.

Materials with high fracture toughness are obviously prime choices

to limit damage propagation. Specific materials are often used in critical areas of the hull. The hull structure must be fracture resistant under

high intensity loading at temperatures as low as -40 °F. 

CONCLUSION

Materials play a key role in many aspects of the construction and 

operation of modern ships. For construction of Navy vessels, there are

many standard and traditional procedures that determine most of 

these aspects. While steel is by far the most common, economical 

construction material, there is significant interest in aluminum, 

titanium, stainless steels, and composites for future, high-speed ships.

The Navy is aggressively pursuing improved structures and novel 

construction methods that could serve to dramatically revolutionize

future vessels. They will have significantly different hull forms, be 

fabricated increasingly by automated methods, and will utilize even

more light-weight metal, hybrid, and composite structures than we 

currently envision.

The Navy is evolving its combatant fleet with the introduction of new

materials and new construction methodologies. We have provided in

these pages a brief look at the most pressing issues ship designers 

consider when choosing materials. Future vessels will utilize new 

materials to enable capabilities that far outpace their current sisters, just

as the armored steel, steam turbine powered battleships of the early 20th

century were revolutionary technological leaps ahead of their wooden,

wind-powered predecessors. 

REFERENCES

American Society of Naval Engineers, www.navalengineers.org.

C.R. Crowe, and D.F. Hasson, Materials Trends in Marine Construction.

United States Naval Academy, Division of Engineering and Weapons,

Annapolis, MD (1990)

E.J. Czyryca, Advances in High-Strength Steel Plate Technology for

Naval Hull Construction. Naval Surface Warfare Center, Carderock

Division, Metals and Welding Department, Annapolis, MD

Federation of American Scientists, www.fas.org

T.C. Gillmer, Modern Ship Design, 2nd Edition. Naval Institute Press,

Annapolis, MD (1977)

National Shipbuilding Research Program, Advanced Shipbuilding

Enterprise, www.nsrp.org

Ship and Submarine Materials Block, Navy Exploratory Development

Program FY1991 Block Plan. Naval Surface Warfare Center, Carderock

Division (Formerly David Taylor Research Center), Bethesda, MD (1990)

Carbon and Alloy Steels, ASM Specialty Handbook, Steels for Ships and

Offshore Structures. J.R. Davis editor, ASM International, Materials Park,

OH (1996) pp. 669
The AMPTIAC Quarterly, Volume 7, Number 3

INTRODUCTION

The performance of future Navy warships requires novel and

innovative material and structural systems to meet ever increasing design requirements. The application

of composite materials for the primary

structure of Navy surface combatants

offers the potential to meet these performance goals in the areas of increased

payload fraction, reduced life cycle costs

and improved survivability. 

Fiber/matrix composite laminates as

well as cored, composite sandwich 

systems have consistently been shown, 

in both military as well as industrial

applications, to result in weight savings

of up to 70% compared to traditional

metallic structures. This weight savings

can be used to maintain the necessary

stability criteria as a ship accommodates

additional payload or weapons systems

and increases in tonnage throughout 

its service life. The reduced weight may

also be used to increase ship speed or

mission range. 

The wide-scale use of composite technology on Navy ships is dependent on

affordability. The large size of ship structures requires non-autoclave manufacturing processes that produce consistent,

high-quality parts. SCRIMP® (Seemann

Composites Resin Infusion Molding

Process) and other vacuum-assisted

processes have evolved over the last

decade to deliver the necessary laminate

quality at cost-competitive prices. This

affordability is increased through anticipated life cycle cost savings made possible through the non-corrosive nature of

marine composite resin systems. Unlike

steel, these materials do not rust and are highly resistant to

chemical and environmental effects.

Weight savings and affordability are key considerations for any

ship design. The primary driver for the current interest in composite structures for Navy warships however, is in the area of

improved survivability. The laminated nature of composites provides opportunities for integrated electromagnetic designs that minimize radar cross

section, improve antenna performance,

and enhance the structural integrity from

blast and ballistic effects resulting from

weapons. The combination of these

unique features is simply not achievable

with traditional steel ship designs.

BACKGROUND AND HISTORY

Steel has been the structural material of

choice in Navy warships for the past 100

years. Inserting a new material system

which requires a new structural concept as

well as a totally different manufacturing

process is difficult. It requires overcoming

the resistance to change that comes from a

familiarity and knowledge base developed

through a century of experience with steel

design and performance.

Over the past 15 years, the Navy has

incrementally demonstrated the maturity

of marine composite technology and sufficiently mitigated the risks to the point that

composite structural applications are transitioning into the fleet. These applications

have included the installation of the

Advanced Enclosed Mast/Sensor (AEM/S)

System on the USS Radford (DD 968)

(Figure 1) and the under-construction 

LPD 17-class amphibious assault ships

(Figures 2 and 4). These successful transitions helped Northrop Grumman Ship

Systems (NGSS) to propose an all-composite topside for its DD(X) design (Figure 3). 

The acceptance of composite systems into

the fleet has been made possible through a series of Navyand industry-funded development and risk mitigation programs

which investigated the ability of composites to meet Navy 

Patrick Potter

Ship Hull, Mechanical and Electrical Systems Science and Technology Division

Office of Naval Research

Arlington, VA

Figure 1. AEM/S System Composite

Mast on USS Radford (DD 968).

37

Figure 2. Artist Concept of Composite

Masts on LPD 17-Class Amphibious Ships.

Figure 3. NGSS DD(X) Concept with 

Composite Superstructure.
requirements in the

areas of fire performance, blast and

shock resistance,

electromagnetic

effects, environmental conditions

and a host of other

generic and Navyspecific technology

areas. The scope

and objectives of

these programs has

included applied research targeted at understanding the capabilities and limitations of differing composite applications (such as a

composite version of a traditional mast design) or investigating

various manufacturing processes for composite ship hulls. (See

Figure 5.) More focused development programs have included

composite enclosures as alternatives for existing steel structures on

current destroyers (Figures 6 and 7) as well as advanced technology demonstrations investigating integrated structural and electromagnetic concepts for a low-observable composite stack system.

The lessons learned from these and other demonstration 

programs are the basis for the confidence in the current technology readiness level of composites in the Navy.

BREAKING THE “STEEL” PARADIGM: 

CERTIFYING COMPOSITES FOR USE ON SHIPS

No matter how much benefit composites may represent to the

shipbuilding industry and the Navy, they still have to be certified safe and effective for use aboard ships. These validation

efforts address the most critical issues a Naval ship will face; fire,

explosions, and harsh environments being just a few. The following sections present some of the research efforts which have

endeavored to prove composites’ mettle.

Fire Performance

Standard composite shipbuilding materials will typically burn

and produce smoke and toxic fumes when subjected to large

fires. To offset these characteristics, a systems approach must be

taken that combines fire resistant coatings and insulations as well

as active suppression systems into or on the structure. The Navy

has conducted numerous small and large scale tests to fully characterize these material systems. This testing includes small

coupons in a cone calorimeter to determine heat release rates,

burn through tests to evaluate the insulating capabilities of coatings and insulations, room corner tests to evaluate flame spread,

on up to full-scale structures subjected to multiple fire scenarios.

(For a more in-depth look at fire performance of shipboard composites, please see the article by Sorathia in this issue.)

The structure in Figure 8 is a two-level portion of a composite ship structure that was subjected to fire scenarios ranging

from a small trash can fire up to a 60+ minute UL1709 fire

exposure, representative of a large fuel-spill. These tests have

shown that composite sandwich structures coupled with the

appropriate passive and active systems can meet or exceed Navy

requirements for fire.

Weapons Effects

Navy composite ship designs are unique from the commercial

sector in that they must withstand the severe environments 

associated with weapons effects. The pressure and shock waves

resulting from an air blast or underwater explosion represent 

significant design requirements. Simulated nuclear air blast testing on numerous composite structures have shown protection

levels similar to, or better than, appropriate steel structures with

weight savings up to 50%. Examples of some of the structures

tested over the past ten years are shown in Figure 9. 

38 The AMPTIAC Quarterly, Volume 7, Number 3

Figure 4. LPD 17 with AEM/S System Ready for Christening.

Figure 6. Composite Helicopter Hangar. Figure 7. Proposed Composite Director Room Enclosure.

Figure 5. Half-Scale Composite Mast 

and One-Third-Scale Composite Hull

Demonstration Test Articles.
Underwater explosions result in extremely high acceleration

loading on decks and bulkheads. These inertial loads govern the

design of composite-to-composite joints as well as the foundation methods for outfitting attachment. Research into both of

these phenomena has produced an understanding of the out-ofplane failure modes in the joints as well as development of

design guidelines for equipment mounting techniques. (See

Figure 10.)

Reduced Signatures

The layered configuration of laminated structures allows

opportunities to embed and integrate specialized materials into

the composite lay-up which provide improved electromagnetic

performance. Past Navy efforts have also explored various ways

to enclose, embed or integrate features into the structure that

result in reduced radar signatures. As depicted in Figure 11, the

AEM/S System program developed a composite mast concept

with frequency selective structural panels enclosing the ship’s

rotating antennas.

Other programs have investigated the possibility of embedding planar antennas into structural members. One such effort

to demonstrate large, integrated composite structures (funded by

NGSS) is shown in Figure 12. The need for simple structural

lines and uncluttered flat surfaces in order to meet future requirements will accelerate this type of testing and development.

Electromagnetic Shielding

Surface ships operating in a battle group are subject to elevated

levels of electromagnetic (EM) energy from the many antenna

and sensor systems on modern warships. Fiberglass laminates

do not inherently provide sufficient EM shielding suitable for

this environment. It is necessary to add additional conducting

layers into the laminate or sandwich to reflect this EM energy.

Various materials suitable for this task have been characterized

across a range of frequencies in the mode-stirred testing chamber located at NSWC’s Dahlgren Division. These tests have

demonstrated sufficient shielding levels with standard carbon

mat and metallic-coated mesh products that are easily incorporated into the laminate production process.

Environmental Effects

Extensive quantification of material properties has been performed across the range of environmental conditions appropriate

to surface ships. Standard low-temperature cure composite 

shipbuilding materials are subject to reductions in strength and

stiffness due to both increased temperature and moisture. For

typical resin systems used in the maritime industry, temperature

is especially critical. Navy tests have shown that the combination

of ambient temperature and solar heat flux loading can result in

temperatures in excess of 175  ̊F in typical sandwich structures.

Standard E-glass and vinyl-ester laminate systems are shown in

Figure 13 to lose approximately 25% of their strength at this

temperature, with more rapid losses at only slightly higher 

temperatures.

FUTURE DIRECTIONS

The projects presented here only begin to describe a few of the

multi-disciplinary topics that are needed and have been investigated to promote composites’ transition into the Navy’s future

surface combatants. Further proliferation of composite technology into the surface fleet will use and build on the developments

and knowledge gained over the past 15 years of Navy research

in this area. A challenge to this wider usage is the development

and adoption of standard design and acceptance criteria.

Numerous efforts over the years have greatly increased the

understanding of the design process and sufficiently mitigated

the risks associated with particular composite applications.

However, a process comparable to the design data sheets used

for steel construction does not yet exist. Similarly, the vast experience with aerospace composite procedures and specifications

Figure 8. Full-Scale Multiple Compartment

Fire Testing.

Figure 9. Various Blast Test Articles.

The AMPTIAC Quarterly, Volume 7, Number 3 39

Figure 10. Examples of Full-Scale & Component

Shock Tests.

Full-Scale

Barge Shock

Tests

Full-Scale Modules 

(Hat-Stiffened and Sandwich)

Full-Scale Hat-Stiffened Panel

Half-Scale 

Hat-Stiffened Panels

Quarter-Scale 

Mast Panels

Joint Tests
Figure 11. Conceptual Diagram of the AEM/S System.

Frequency

Selective

Surfaces

Structural

Laminate

Foam Core 

Material

Structural

Laminate

Structural

Laminate

Carbon

Reflective

Layer

Balsa

Core

Figure 14. Evolution of the Surface Combatant.

Patrick Potter is a Program Officer at the Office of Naval Research in the Hull, Mechanical and Electrical Systems

Science & Technology Division. He manages research efforts directed toward improving the performance of future US

Navy surface ships through the Hull Life Assurance Thrust. Prior to joining ONR, he was employed for 12 years as an

engineer/naval architect in the Survivability, Structures and Materials Directorate of the Naval Surface Warfare

Center’s Carderock Division. In that capacity he conducted research in the area of advanced composite structures for

Navy ships. He has a Bachelors of Science degree in Aerospace Engineering from the University of Maryland as well

as a Masters of Science degree in Structures & Dynamics from the George Washington University. He is currently taking classes through the Navy War College in the area of Strategy & Policy. 

do not fully lend themselves to the unique issues and materials

associated with the surface ship side of the Navy. This effort needs

to be tackled by a combined effort of industry and government

initiatives.

A further challenge is that even as current composite applications

become more accepted and standardized in design and 

manufacturing, the underlying technology and threats continue to

move forward. Next generation composite ship structures will need

to provide better performance to meet more severe blast, ballistic,

and electromagnetic requirements than ever before. Achieving this

in an affordable system will require improved resin systems, better

core materials and a total integration of technologies into a true

multi-layered, multi-functional structural system. Incorporation 

of these technologies and many others will forever change the

appearance, design, and performance of the Navy’s future surface

ships, as seen projected in Figure 14.

Figure 12. Demonstration of the Composite

Integrated Structure.

40 The AMPTIAC Quarterly, Volume 7, Number 3

Figure 13. Effect of Temperature on Laminate Strength.

80

70

60

50

40

30

20

10

0

70 85 100 115 130 145 160 175 190 205 220

Temperature ( ̊F)

100

75

50

25

0

Strength (ksi)

Strength (ksi)

Flexural Strength versus Temperature

(Dry, warps parallel 9.6 oz./yd2 woven roving)

Reduced

Signatures

Sensor

Integration

Weight & Speed

Improvements

Damage Resistance 

to Weapons Effect

Affordable
The AMPTIAC Quarterly, Volume 7, Number 3 41

INTRODUCTION

Composite materials are being used in increasing amounts in a

variety of Navy applications based on their stiffness, strength,

reduced weight, and corrosion-free capabilities. Additional properties such as fire and ballistics resistance, signature reduction,

and enhanced communications make them attractive for integrated structures known as multifunctional composite materials

(MCMs) that will be able to address the needs of future Navy

vessels. (The long-term plan for Navy ship evolution is called

“Navy After Next.”)

Processing methods are being developed that can fabricate

large-scale components with built-in, tailored multifunctional

capabilities. Intelligent process control (IPC) is critical to fabricate, integrate and scale-up complex, net-shape, multifunctional

composite materials reliably and in a cost effective manner. The

components of intelligent process control – design and analysis,

modeling and simulation, sensing and control – need to apply a

cradle-to-grave philosophy to address not only fabrication but

also inspection and health-monitoring issues. With the use of

intelligent process control and creation of multifunctional materials, composites represent the key to future ships systems

including DD(X) (Zumwalt-class) destroyer and littoral combat

systems (LCS).

History/Background

Several large-scale composite structures have been implemented in

the US Navy and in other partner countries. The main advantages

of fiber reinforced plastic (FRP) structures include lightweight and

multi-functional capabilities such as reduced signature and nonmagnetic hull sections. The major applications include topside

structures (for example the Advanced Enclosed Mast Sensor

System (AEM/S) and the Director’s Room for Arleigh Burke-class

destroyers) as well as complete hull solutions (Coastal Mine

Hunter [MHC 51], P-960 KNM Skjold, and Visby-class corvette). 

The most significant composite structures manufactured for

the US Navy are the AEM/S System and the MHC 51-class

coastal mine hunter hull. The AEM/S system was installed on

USS Radford (DD 968) in October 1997. This structure is

approximately 95 feet tall and 30 ft. wide at its midsection. This,

the largest topside composite structure aboard a US Navy ship

and weighing some 40 tons, was fabricated using the Seemann

Composite Resin Infusion Molding Process (SCRIMP®) (Figure

1, left). Figure 1, right shows the composite hull section of the

mine hunter fabricated at Avondale Shipyard. This solid and

continuous monocoque structure has a length of 188 ft and a

total displacement of 895 metric tons. 

The Swedish Navy put the Visby-class corvette (seen in 

Figure 2) in service in 2000. The vessel is built of sandwichconstruction carbon/vinyl-ester, which ensures high strength at

low weight with integrated stealth qualities. The total length of

the ship is approximately 236 feet at a displacement of 600 tons.

Skjold is the Royal Norwegian Navy’s first fast patrol craft/

littoral combat ship of the Skjold-class and is currently being

evaluated by the US Navy. The ship is based on a catamaran hull

where lift fans blow air into an air cushion between the hulls.

The structure is built with FRP sandwich using uniaxial glass

fiber and carbon laminates with vinyl-ester or polyester resin.

Polyvinyl chloride (PVC) core material is used in main structural elements below main deck and polymethacrylimide (PMI)

core material is used elsewhere and for the complete superstructure. The total length of Skjold is approximately 157 feet at a 

displacement of 260 tons.

These large-scale composite structures have been built using

liquid composite molding (LCM) techniques. LCM allows the

dry lay-up of the materials in a mold, thus permitting integration

of various functional materials into the structure. The preferred

LCM fabrication method for large-scale application is vacuumassisted resin transfer molding (VARTM, as seen in Figure 3).

Here, a stack of dry fiber reinforcements, usually known as a preform, is placed over a tooling surface and is enveloped and sealed

with a flexible plastic bag by drawing a vacuum through a vent.

This compacts the preform and, as a result, the preform conforms

to the tool surface. The resin is injected and drawn into this

assembly through openings known as gates, due to the vacuum in

the compacted preform, by connecting the resin reservoir to the

tooling. The pressure difference of nearly one atmosphere

between the resin reservoir and the vacuum vent port drives the

resin into the preform to impregnate the empty spaces between

Roger M. Crane, Composite Materials Section Head

Structures and Composites Department

Carderock Division, Naval Surface Warfare Center 

West Bethesda, MD

John W. Gillespie, Jr., Dirk Heider, Shridhar Yarlagadda, and Suresh G. Advani

Center for Composite Materials, University of Delaware 

Newark, DE
the fibers. Flow enhancement networks such as flow runner

channels and distribution media (layers of fabrics with relatively

low flow resistance) are used to accelerate mold filling and saturate the preform before the resin gels. The resin flowfront in

VARTM is three-dimensional; it moves through the thickness as

it spreads through the plane of the part. For complex geometries

and when various functional materials are used the flow front can

become complex and difficult to control. After full infusion, the

resin gels and cures at room temperature creating the final part

geometry. Lower tooling costs and the room temperature cure

make VARTM especially favorable in manufacturing large composite parts such as ship hulls, bridges, and wind turbine blades. 

MULTIFUNCTIONAL COMPOSITE MATERIALS 

AND STRUCTURES

Efforts sponsored by the Office of Naval Research (ONR) are

laying the foundations of an affordable and sustainable fleet for

the 21st Century. As a result, the Navy After Next will consume

less fuel per hour, require fewer operating personnel, and spend

less time in dry dock for maintenance than any fleet before it. It

is even expected that procedures undertaken by personnel to primarily check-out systems will be increasingly replaced by “condition-based maintenance” in which sensors report on the

integrity of machines and materials and provide sufficient data

for actual hands-on maintenance and repair only when needed.

Advanced surface combatant designs will incorporate and

extend many features currently in experimentation on today’s

ships, such as Radford, USS Yorktown (CG

48), DDG 51, etc. Indeed, once these features

are developed to the application stage, many

of them can be retrofitted to greater or lesser

extent in today’s ships at major maintenance

and overhaul milestones during their service lives to increase survivability, system reliability, and ship service life. Foremost

among the changes in ship design that advancing technology will

permit and encourage is multifunctional composite structures.

The technology of multifunctional composite structures

(depicted in Figure 4) will enable lightweight energy-absorbing

designs for mine/blast and ballistic protection; fire-hardened

sandwich constructions; embedded and conformal sensors and

actuators for communications, health monitoring, and prognostics; as well as material properties and specific shaping capability that will help meet future signature goals. Such structures will

also reduce weight, corrosion, and maintenance requirements, as

well as allow modular design approaches.

Composite structural designs for blast, ballistic, and fire protection are currently being considered for both ground vehicle

structures (Army Future Combat Systems) and ship topside

structures. Co-injection resin transfer molding (CIRTM) -based

processes have been demonstrated for the director’s room of

DDG 51, enabling multifunctionality for structural and fireresistant performance. Fully integrated instrumentation and

automation can be achieved using embedded and distributed

networked sensors, actuators, and microprocessor controls, thus

enabling reduced crew size. Damage control will also be a primary focus of automated systems, as it is a major determinant of

crew size. Composite materials and structures will also enable

specific geometric shaping, treatment, and reflection or absorption characteristics of exposed structure. Introducing composites

will also allow downsizing or elimination of the mast(s); integration with

other topside components such as

low-observable intakes or uptakes; and

fully enclosed small craft handling

equipment, hangars, speakers, lights,

and doors. The aggregate result of

these changes would be a significant

advancement in the capabilities of

future naval surface platforms in an

affordable manner.

Significant research is being conducted in the various desired functionalities, such as ballistics, fire, health monitoring, signature,

etc. The major barriers to implementation in ship structures are the ability to integrate these functionalities into

the structure and the associated manufacturing issues.

Intelligent process control is key to enabling system 

integration and manufacturing, not only to achieve the

42 The AMPTIAC Quarterly, Volume 7, Number 3

Figure 1. Left, The AEM/S System on USS Radford (DD968) and

Right, Composite Hull of MHC 51.

Figure 2. Visby and Skjold During Sea Trials.
The AMPTIAC Quarterly, Volume 7, Number 3 43

desired performance, but also for quality,

repeatability, and affordability. The ultimate goal is an automated intelligent

manufacturing process, where the

desired performance characteristics can

be obtained through a “plug-and-play”

approach within the constraint of liquid

molding process technology.

INTELLIGENT PROCESSING

Multi-functional composite materials

have to be manufactured using 21stcentury techniques based on the VARTM

process, enabling integration of the

desired capabilities into the final part.

Intelligent processing can be defined 

as the cradle-to-grave use of various 

scientific and monitoring tools such as 

science-based numerical simulations, 

sensors to gather information, and actuators to automatically correct for unforeseen disturbances during processing. In addition,

the introduction of automation will reduce labor, improve

repeatability, and increase yield. ONR has established the

Advanced Materials Intelligent Processing Center (AMIPC) at

the University of Delaware whose goal is to adopt and move liquid composite molding processes towards automation and cost

effectiveness by integrating science-based models into the decisions for process control. The center is focused on the development of software and hardware tools and their integration and

implementation to extend the processing science in order to

improve quality and affordability of multifunctional composite

structures for Naval applications. This will be accomplished using

sensors, science-based simulations, and process 

control to advance composite manufacturing with LCM. This

effort can be divided in four categories as shown in Figure 5.

The first component of intelligent process control is process

design to manufacture composite parts with the desired performance in an affordable manner. This requires an understanding and

modeling of the process physics as the basis for virtual manufacturing simulations and new process innovations. Next, an integrated approach to part and mold design, process optimization, and

formulation of control actions is needed. Critical to both process

control and inspection is adequate sensor technology for process

monitoring. Finally, inspection and health monitoring will

ensure the quality and properties of the composite material in

service. Multifunctional requirements will cause changes in reinforcement schemes, resin selection, and integration of various

materials/devices, all of which require virtual manufacturing

simulations to address process design and optimization.

PROCESS DESIGN

The need for process design arises from two main factors. First,

as one moves the injection location for the resin, the flow pattern will change and will influence the time to fill the mold by

orders of magnitude and create scenarios ranging from complete

saturation of the fibers by the resin to large-scale dry spots resulting in scrap. Second, for very large composite structures, multiple inlet gates are required to ensure complete wet-out of the

part prior to gelation of the resin. Selection of the distribution

media, preforms, and gate and vent locations are typically based

on past experience for similar applications. However, analytical

and finite element analysis (FEA) simulations can be used to calculate the parameters (as a function of resin, preform, and distribution media properties) and to optimize sequential injection

spacing and location.

Figure 3. Schematic of the VARTM Process.

Figure 4. Multifunctional Composite

Materials are Key to Meeting the

Needs of the Navy After Next.

Vacuum Bag

Peel Ply

Injection Line 

Connected to Resin Bucket

Vent

Connected to Vacuum Port

Distribution Media

Breather

Preform

Processing Steps

Preform Manufacturing Impregnation Step Cure Step Quality Assurance/Quality Control
44 The AMPTIAC Quarterly, Volume 7, Number 3

With the integration of new materials, the preform flow characteristics can change by orders of magnitude. Advanced infusion schemes such as interlaminar flow media may have to be

applied and the injection spacing has to be adjusted. Simple

design tools (Figure 6) can support the basic decisions currently

made by the expert engineer. The systems can be used to reduce

prototyping efforts and reduce risk if preform material is being

changed. This will allow for faster integration of more affordable

or improved materials.

PROCESS PHYSICS AND SIMULATIONS

Development of a virtual manufacturing platform is one of the

goals of intelligent processing. The key ingredients to creating

such a platform are formulation of process models (based on the

observed physics of the process and relevant assumptions) and

incorporation of such models in a computer simulation (that can

mimic the process reality in an effective and efficient manner).

Under the AMIPC program, the Center for Composite Materials

at the University of Delaware (UD-CCM) has developed simulation tools such as LIMS (Liquid Injection Molding Simulation)

and SLIC (Simulation-based Liquid Injection Control). LIMS

can describe the resin impregnation physics in most liquid composite molding processes and is used to develop the

optimal tool and process design before fabricating the

tool. The simulation also has a user interface, which

allows for easily changing gate locations in the tool or

adding distribution media at different locations in the

VARTM process. This has made it possible to perform

“trial and error” process runs on the virtual platform

which converge toward the best possible process

design. The simulation has been continuously tested

against experiments to validate the process physics as

new phenomena encountered in the process are incorporated into the simulation. Examples include the

injection and resin flow simulations for composite

armor and a composite twisted rudder, as shown in

Figure 7. Numerical efficiency is also a key parameter,

as the simulation tool will be used for design and optimization studies that would require one to explore

many mold filling scenarios before selecting the optimal one as dictated by the criteria. SLIC was developed to allow the computer to search and find the best

solution using the virtual platform and genetic algorithms. SLIC links its design with a common software interface

that directly controls manufacturing, allowing for automation of

the process.

INTEGRATED SENSING

All design and optimization studies assume an “ideal” known

value of preform permeability. In practice, variation in the flow

due to the variability in the preform lay-up and permeability is

observed. These variations in processing occur not only during

filling but also during curing of the composite. Flow sensors are

important to effectively control the flow in spite of this variability. Another concern is monitoring the health of the composite

after it has been manufactured. Hence sensors that can address

these issues are essential to the intelligent processing framework.

Over the years, many sensors have been developed and tested.

One of the earlier successes was the SMARTweave sensor grid,

which comprises two orthogonal sets of conductive filaments

separated by one or more fabric layers placed within the 

composite mold. As resin fills the mold and the gaps between the

filament planes, electric circuits are completed. Associated

instrumentation detects the signals and can determine the resin

location and cure state. The DC-based system can be integrated

into the tool, allowing re-use of the many sensors required for

large parts. The system monitors resin flow well and has limited

resolution for cure monitoring. 

Recently, time domain reflectometry (TDR) sensors have

been developed and evaluated for both resin flow monitoring

and cure. TDR involves sending high voltage step-pulses into 

a transmission line, and detecting reflections returning from the

impedance discontinuities within the line. Any dielectric and/or

geometrical discontinuity in the line changes the characteristic

impedance, and introduces a voltage reflection at a particular

time and magnitude. The system accurately measures distributed

parameters such as the resin flow position and the degree of cure,

and compares favorably to data collected by charge coupled

device (CCD), Fourier transform infrared spectroscopy (FTIR),

and differential scanning calorimetry (DSC). (See Figure 8). The

Figure 5. Key Components of Intelligent Processing Needed for 21st-Century

Manufacturing.

Figure 6. Process Design Tools and Supporting Materials

Databases Enable Virtual Manufacturing for Intelligent 

Process Control

Database Material Selection

Design Interface
The AMPTIAC Quarterly, Volume 7, Number 3 45

transmission line can be embedded into the part or on the surface or integrated into the tooling making it reusable for many

process runs. The system is a non-contact sensor allowing detection through gel coats commonly applied on the mold surface. 

TDR sensors are unique due to the fact that they are lineal

sensors and can be used to interrogate changes along the entire

length of the sensor, rather than at a point (for example: fiber

optic sensors). This reduces the number of sensor lines and associated acquisition hardware. TDR sensors can also be used for

health monitoring since they can be used to measure strain,

observe crack propagation, and detect defects in composites.

This technology provides a true cradle-to-grave solution for

process and health monitoring and is currently being optimized

for ship structure applications.

PROCESS CONTROL, AUTOMATION AND QA/QC

Due to variations in preform permeability, preform lay-up, and

resin chemistry, the filling and curing scenario may vary from

one part to the next in the same batch. Engineering supervision

is required during the resin infusion process to open the injection gates at the right time intervals. Often the only feedback for

the engineer is a visual surface wet-out measurement. In general, during surface injection with a distribution media, the

flowfront at the tool surface lags behind the flowfront at the distribution media surface due to the time it takes to penetrate the

preform. For thick-section composite parts, the distance

between the flowfronts on opposite surfaces can be of the same

size as the typical distance used between sequential injection

gates. As a result, premature opening of an injection port will

result in large dry-spot development under the injection lines.

Delayed opening of an injection line significantly extends the

overall cycle time. New applications where part thickness, resin

properties, or preform characteristics vary may require costly

trial and error process development to optimize the sequential

opening. Under the AMIPC program, UD-CCM has developed

methodologies to introduce control actions in LCM processes.

An automated system, called SMARTMolding, has been developed to completely automate and monitor the process. Injection

gates are opened in sequence when mold-mounted flow sensors

detect the tool-surface flow front at a particular gate. The process

is completely autonomous and does not depend on resin permeability variations, changes in preform characteristics, or other

Figure 7. LIMS Simulates the Filling Stage of LCM Processes for Complex 3-D Structures.

Upper Perform

Ceramic Tile

Vertical Channels

Thin Layer

Holes in the

Rubber

Rubber Layer

Lower

Perform

Figure 8. Time-Domain Reflectometry Sensors Used in VARTM Processing.

Comparison of TDR and CCD Data

Arrival Time(min)

CCD

TDR 

0 100 200 300 400 500 600 700 800

Location (mm)

0 200 400 600 800 1000 1200

Cure Time (min)

5

4

3

2

1

0

TDR, DSC and FTIR

Normalized Data

1.0

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0.0

TDR 

FTIR (dots) 

Dielectric

Constant DSC 

Dielectric Constant (TDR)

3.55

3.45

3.4

3.35

3.3

3.25

3.2

3.15

3.1
46 The AMPTIAC Quarterly, Volume 7, Number 3

processing factors. In addition, the SMARTMolding system does

not require costly trial-and-error development of a conventional

sequential scheme and therefore does not demand the engineering knowledge normally required during resin impregnation.

However, the number of inlets and sensor locations must be specified. The automation capabilities enable monitoring of cycle

times for all processing steps, sensing of the important process

parameters through embedded sensors, and quality

assurance/quality control (QA/QC) of the complete process.

Figure 9 shows one SMARTMolding workcell implemented at

United Defense-York as part of a larger plant setup for automated VARTM production. The different workcells are connected

and the lay-up stations are semi-automated creating a first step

towards a 21st-century composite manufacturing environment.

INSPECTION AND HEALTH-MONITORING

Once a composite structure has been successfully manufactured,

it becomes necessary to have methods to determine the structural integrity of the component during the service life. This is not

a trivial matter. Two characteristics make most conventional 

composite NDE techniques impractical for these structures: size

and environment. In the case of the AEM/S system and similar

masts, each structure has thousands of square feet of surface. In

addition, the construction has typically been a core configuration

with multiple layers, which can have thicknesses of up to several

inches. The thickness issue causes many problems with most

NDE techniques.

A vibration-based inspection method, developed at Carderock

Division, Naval Surface Warfare Center and the United States

Naval Academy, has been successfully used to inspect large-scale

composite structures of both sandwich construction and 

rib-stiffened configurations. This technique is called the

Structural Irregularity and Damage Evaluation Routine, or

SIDER. This vibration-based method is capable of locating 

areas of structural degradation and specific damage in sandwich

and rib-stiffened structures. 

The SIDER inspection has been used on a .5-scale composite

corvette hull section (Figure 10). This structure is a rib-stiffened

configuration with varying sizes of hat stiffeners, multiple composite decks, bulkheads, and cutouts. The structure was about

Figure 9. SMARTMolding Allows Automation of all VARTM Processing Steps.

Figure 10. SIDER Used to Find Damage in Composite Ship

Structures.
The AMPTIAC Quarterly, Volume 7, Number 3 47

30 ft long 19.5 ft wide and about 11 ft high from the keel to the

top deck. The SIDER inspection was performed prior to and

following the shock testing. In general, significant levels of damage occurred. The SIDER testing was able to identify all of the

areas on the structure that contained damage, indicated by the

labeled areas in Figure 10. 

This damage was in the form of delaminations, debonding of

ribs or stiffeners, separation of decks or bulkheads, and laminate

cracking. All of these areas were verified either visually or

through ultrasonic inspection (indicated with lettered callouts in

Figure 10). It should be noted that all of the damage located by

ultrasonic inspection was also identified by the SIDER inspection. Similar inspections using SIDER have been performed on

an all-composite bridge deck since 1997 on an annual basis.

Capabilities to inspect large-scale composite structures now

exist. Continued advances are expected as new internal and external sensors are developed and inspection technology evolves. One

future possibility is that the two functions (health monitoring and

communication) will be broadcast on different frequencies but

share the same fiber connections throughout a ship.

TECHNOLOGY TRANSFER

While there has been considerable investment in basic and

applied research, resources required by the DOD and Navy

Industry base to transition these technologies into practice are in

many cases insufficient. UD-CCM has a strong history of 

collaboration and technology transfer to the industry, having

been associated with more than 200 companies over its history.

The AMIPC program has developed several technologies ranging from an understanding of basic physical principles all the

way to software and hardware solutions that can be implemented at the factory floor. For example, eight industrial beta-sites

with intelligent process control capability (SMARTMolding 

system) have been established since January 2002. Figure 11

shows the current technology transition structure at UD-CCM,

where industry partners benefit from technology advancements

in the AMIPC program. 

LOOKING FORWARD

The application of intelligent process control to multifunctional composite materials is key to meeting the needs of the Navy

for 21st Century shipyards. Concurrent development of new

materials and processes to meet demanding performance

requirements of next generation ship systems will require the following:

• New materials capable of performing multiple functions.

• Rapid insertion of new technologies through concurrent

development of design, materials, and processing to deliver

performance that can be affordable.

• Intelligent processing to develop affordable processes for next

generation multifunctional composite materials.

• New sensor technologies for inspection and health monitoring.

REFERENCES

S.G. Advani and M. Sozer “Process Modeling in Composite

Manufacturing”, Marcel Dekker, Inc., 270 Madison Ave., NY,

NY 10016, (2002)

Department of Navy: Science and Technology Grand

Challenges, http://www.onr.navy.mil/sci_tech/grandc.htm

A. Dominauskas, D. Heider, and J.W. Gillespie, Jr., Electric

Time-Domain Reflectometry Sensor For Online Flow Sensing In

Liquid Composite Molding Processing, Composites Part A, vol.

34(1), pp. 67-68 (2003)

A. Dominauskas, D. Heider, and J.W. Gillespie, Jr., TDR-Line

Sensor for Multifunctional and Distributed Sensing in LCM.

Proceedings of the 48th International SAMPE Symposium, pp.

290-302 (2003).

R.C. Don, K.R. Bernetich, B. K. Fink, M. Louderback, and J.W.

Gillespie, Jr., “Large-Scale Implementation of Flow and Cure

Sensing in a Thermoset Resin Infused Composite Structure,”

Proceedings of the 43rd International SAMPE Symposium, pp.

268-276 (1998)

B.K. Fink, J.W. Gillespie, Jr., E.F. Gillio, and K.R. Bernetich,

“One-Step Resin Transfer Molding of Multifunctional

Composites Consisting of Multiple Resins,” US patent application, April 1997 (ref#08/956,595)

Future Naval Capabilities (FNC), http://www.onr.navy.mil/fncs/

B.K. Fink, S.H. McKnight, and J.W. Gillespie, Jr., “CoInjection Resin Transfer Molding for Optimization of Integral

Armor,” Proceedings of the 21st Army Science Conference:

Science and Technology for Army After Next, Norfolk, VA, 

June 15-17, 1998

Figure 11. Technology Transfer to the DOD Industrial Base.

Fundamental

Science Base

System Development 

and Validation
48 The AMPTIAC Quarterly, Volume 7, Number 3

B.K. Fink, S.M. Walsh, D.C. DeSchepper, R.L. McCullough, R.

C. Don, B.J. Waibel, and J.W. Gillespie, Jr., Advances in Resin

Transfer Molding Flow Monitoring Using SMARTweave Sensors,

Proceedings of the ASME Materials Division, vol. 69-2, pp.

999-1015 (1995)

D. Heider and J. W. Gillespie, Jr., Automated Processing of LargeScale Composite Structures Using Smart-Molding, to be published

in the SAMPE Journal in 2004

J.M. Lawrence, K.T. Hsiao, R.C. Don, P. ˇSimáˇcek, G. Estrada,

E.M. Sozer, H.C. Stadtfeld, and S.G. Advani, An Approach to

Couple Mold Design and On-line Control to Manufacturing

Complex Composite Parts by Resin Transfer Molding, Composites

Part A: Applied Science and Manufacturing, vol. 33(7), pp.

981-990 (2002)

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, pp. 374-380 (1996)

C.P. Ratcliffe and R.M. Crane, A Non-Destructive Test

Procedure for the Determination of the Structural Irregularity

and Damage Evaluation Routine (SIDER) of Composite

Structures, Navy Case No. 83,356, August (2001)

C.P. Ratcliffe, A Frequency and Curvature Based Experimental

Method for Locating Damage in Structures. ASME Journal of

Vibrations and Acoustics, vol. 122(3), pp. 324-329 (2000)

P. ˇSimáˇcek and S.G. Advani, Process Modeling and Simulation

for Liquid Composite Molding, Proceedings of 34th SAMPE

Conference, CA (2003)

P. ˇSimáˇcek and S.G. Advani, LIMS 5.0 and LIMS UI User

Manual, Tech. Report, CCM, University of Delaware, 2002

Technology for the United States Navy and Marine Corps,

2000-2035: Becoming a 21st-Century Force, Volume 6 Surface

Platforms

Dr. Roger M. Crane is currently the Composite Materials Section Head in the Structures and Composites Department

at the Carderock Division, Naval Surface Warfare Center. He received a BS and BA from Loyola College in Baltimore,

MD; an MS from The Johns Hopkins University; and a PhD from the University of Delaware. Since joining the NSWC

in 1980, Dr. Crane has conducted research on composite materials including material formulation, development of 

processing techniques, design and manufacturing of prototype applications, and development of nondestructive 

evaluation techniques. He has authored more than 75 technical publications and has 20 patents in composite 

technology.

Dr. Jack Gillespie has served the University of Delaware Center for Composite Materials (UD-CCM) in several roles

for more than twenty years, achieving the position of Director in 1996. As an educator, Professor Gillespie has established an intellectually stimulating and highly interdisciplinary research environment for graduate and undergraduate 

students and post-doctoral candidates who work at UD-CCM. He has advised more than 60 graduate degree 

students who have gone on to successful careers in academia, government and industry. He was also chosen as the

recipient of the Faculty Advisors Award from SAMPE in 2001.

Dr. Shridhar Yarlagadda has been conducting research on innovative processing and the manufacturing of composites

over the past five years. As the Assistant Director of Research at the University of Delaware’s Center for Composite

Materials (UD-CCM), he works on several DOD-funded programs. Those programs include environmentally friendly

processing, repair and remanufacture, high volume thermoplastic composite processing, resistive and magnetic susceptor design, process optimization, and smart temperature control based on the Curie temperature of magnetic nanomaterials.

Dr. Suresh G. Advani is a Professor in the Mechanical Engineering Department and Associate Director of the Center for

Composite Materials at the University of Delaware. He received his B Tech degree in mechanical engineering from IIT

Bombay in 1982 and his PhD in mechanical engineering from the University of Illinois at Urbana-Champaign in 1987. His

research interests are in rheology, fluid mechanics and heat transfer as applied to manufacturing processes, especially for

polymers, nano composites and polymer composite processing. He has co-authored more than 200 

journal and conference proceeding articles. Dr. Advani is a Fellow of the American Society of Mechanical Engineers and

was recently appointed as the North American Editor for the journal Composites A: Applied Science and Manufacturing. 

Dr. Dirk Heider is the Assistant Director of the University of Delaware Center for Composite Materials (UD-CCM). He

received his PhD in electrical engineering from the University of Delaware in 1998 and holds the equivalent of BS and

MS degrees from the Technical University of Aachen in Germany. Dr. Heider’s research interests include advanced

sensing methods and intelligent process control of composites manufacturing, and he has published more than thirty

papers in these areas.
The AMPTIAC Quarterly, Volume 7, Number 3

INTRODUCTION

Due to their characteristics, advanced composite materials have

been making steady inroads into military systems for the last 40

years. Principle advantages of composites include higher stiffness

to weight ratio (much better than steel or aluminum), endurance

under cyclic loading, and resistance to chemical attack (e.g. corrosion resistance).

Polymer matrix composite (PMC) materials are increasingly

being used in all aspects of our society, from transportation

(trains, autos and airplanes) and civil engineering (bridges, wall

reinforcement,) to electronics and sporting goods. The aerospace

military industry has been using these materials for more than

40 years, principally due to their demand for low weight structures. The maritime industry, historically not constrained by

weight issues, has used steel as its primary structural material.

As a result of recent requirements for faster and more agile

ships, the Navy has been developing and is now starting to use

PMCs in primary and secondary structures. Some examples

include lightweight foundations, deckhouses, and masts;

machinery components, such as composite piping, valves, centrifugal pumps and heat exchangers; and auxiliary or support

items, such as gratings, stanchions, vent screens, ventilation

ducts, and louvers [1]. The growing interest in composite materials is also driven by the directives to reduce maintenance, save

weight, increase covertness and provide affordable alternatives to

metallic components with lower life cycle costs.

Polymer composites are engineered materials in which the

major component is a high strength fibrous reinforcement (typically a fiber made out of carbon, glass or Kevlar) and the minor

component is an organic resin binder (such as epoxy, vinyl-ester

or -imide). Structural composites for US Navy ship applications

are typically brominated vinyl-ester with glass reinforcement

fibers over a balsa wood core. Some recent notable large composite applications include the Advanced Enclosed Mast/Sensor

(AEM/S) System (installed on the USS Radford DD 968), the

LPD 17 AEM/S, the DDG 51 Forward Director Room, and the

Composite Helicopter Hangar Program. Figure 1 shows the current and potential composite applications in Surface Ships. 

A significant concern in shipboard application of organic

matrix based composites is the possibility that an accidental (or

deliberate) fire may ignite the composite material. This may

result in the spread of flames over the composite’s surface, the

release of heat, and the generation of potentially toxic smoke.

Thus, a localized incidental fire may propagate to a larger structural fire involving the composite, which now becomes additional fuel for the growing fire. In enclosed and confined spaces

(such as ships) the growing fire can lead to a flashover condition

in which all combustible materials within the enclosure ignite

and generate copious amounts of potentially toxic smoke. If the

burning composite component is part of a primary critical structure, it may also collapse. 

The US Navy, Naval Sea Systems Command (NAVSEA),

Naval Research Laboratory (NRL), Office of Naval Research

(ONR), and the Naval Surface Warfare Center, Carderock

Division (NSWCCD) have a long history in fire research and in

Usman Sorathia, Fire Protection Branch Head 

Carderock Division, Naval Surface Warfare Center 

West Bethesda, MD 

Figure 1. Current and Potential Composite Applications for

Surface Ships.

49

Sonar Dome

Foundation

Non-Structural Partitions

Decks & Bulkheads

Auxiliary Machinery

Propulsion Shafts

Rudders Propulsors

Life Rails

Hangar Doors

Deck Equipment Enclosures

Doors & Hatches

Exhaust Stack

Intake Louvers & Ducting Deckhouse

Mast

Radomes

Gun

Enclosures Hull & Deck

Machinery
studies of composite flammability. NSWCCD and NRL 

conduct many small, intermediate, and large-scale (e.g. the

decommissioned USS Shadwell) fire tests to characterize materials, systems, and structures, as well as validate the adequacy of

their performance prior to use aboard ships. It is imperative 

to improve the fire performance of these materials if they are to

be used in the fleet without compromising fire safety. This 

article presents some of the programs that the Navy is working

to address this issue.

FIRE PERFORMANCE REQUIREMENTS

Onboard Surface Ships

The Navy recognizes that composites are being considered for

use in the integrated topside design of the next generation of 

surface combatants, such as DD(X). One of the many design

considerations for composites is fire performance. Egress and fire

fighting situations onboard surface ships are different than those

onboard submarines. For example, where fire performance goals

for use of composites in submarines were based on assumptions

that a fire should be extinguished or brought under control

within 5 minutes, on surface ships the assumption allows about

30 minutes to fight the fire. As a result, the requirements used in

MIL-STD-2031 for submarines need not be adopted for composites on surface ships. 

A guide to goals and qualifications for the use of composites

[2] in the DD(X) program was developed under the sponsorship

of the DD(21) program office, and NAVSEA’s Ship Design

Integration and Engineering Office (SEA 05P). It outlines a

series of fire performance goals and standard fire tests for composite structures to ensure they are fire-safe when considered for

use on the topside of surface combatants. These fire performance

goals are based on current US Navy fire fighting doctrine and

the fire safety goals approved by the International Maritime

Organization (IMO) for use of composites in high speed craft. 

In most cases, fire performance goals are based on full-scale

fire tests. Material fire performance goals should be incorporated in conjunction with existing or additional detection, suppression, and fire-fighting systems. 

Fire Performance of Current Materials System

The Navy currently using brominated vinyl-ester resin (Derakane

510A) with glass reinforcement in most surface ship applications.

This resin was selected based on cost, room temperature curing

properties, chemical resistance, and ease of use in large scale processing methods such as vacuum assisted resin transfer molding

(VARTM). Topside structures usually employ a sandwich style

construction with PMC surfaces and a balsa wood core. 

In a recent ONR-sponsored Composite Helicopter Hangar

Program (for more information see related article in this issue by

Potter), this system was extensively tested in accordance with

NAVSEA performance requirements, including blast and fire

resistance. A typical composite construction in this program

included hat-stiffened (structural support strips attached to one

side of the panel, which in cross section resemble a top-hat) sandwich construction with a balsa wood core (9.5 lbs/ft3, 3.5 inches

thick) and glass/vinyl-ester (Derakane 510A) composite laminate

skins (120 lbs/ft3, 0.25 inches thick.) In this configuration, the

sandwich composite construction weighs about 7.8 lbs/ft2. 

The US Navy unprotected standard sandwich composite, as

described above, does not meet all of the fire performance goals for

interior manned applications. For example, in mock-up room corner tests [3], the unprotected sandwich composite (critical heat flux

for ignition ≈ 15 kw/m2, ignition temperature ≈ 384 oC) ignites in

less than 2 minutes. The composite facesheets delaminate from

the balsa core in approximately 11 minutes, and the system exhibited a total heat release rate of close to 1.0 MW shortly after the

burner heat release rate was increased to 300 kW. 

Passive Fire Protection

The major difference between metallic and composite structures

is that enclosed spaces consisting of PMC structures may be

driven to flashover by small fires. Suppression of this demands

either preventing a fire’s heat from getting to the surface of a

composite, or dampening the resin’s inherent response to heat.

Fire suppression systems can be active (sprinklers, chemical dispersion) and/or passive (inherently non-combustible materials,

fire insulation); this article focuses on passive fire suppression

systems.

Fire insulation provides a solution for both the hazard of fire

involvement of the composite (combustible) structure, and for

the threat of structural collapse. A sufficiently thick layer of fire

insulation (~1.25 inches of materials like StructoGard® or

Firesafe®) can keep the temperature of the exposed sandwich

composite below its ignition temperature. This reduces the hazard of fire involvement, as well as keeping temperatures on the

material’s backside below its glass transition temperature for up

to 30 minutes (reducing threat of structural collapse).

For military applications, fire insulation attachment methods

for composite structures should be robust enough to withstand

the effects of blast and shock in addition to rigorous wear and

tear of use in hostile environments. (NAVSEA Drawing

5184182 dictates the parameters for attachment of fire insulation.) Assembly of insulation to composite structures is a labor

intensive process, with total costs (both material and labor) estimated at about $35-50 per sq ft The insulation must also be

shock qualified as Grade A, meaning it must remain intact and

functional. 

The term “fire resistance” is sometimes misused in the context

of glass reinforced polymer (GRP) composite applications.

Historically, this term is used for expressing the ability of building structures to limit the fire’s spread from its origin to adjoining spaces, such as bulkheads and overheads, by preventing

ignition of items on the non-fire side of the bulkhead (backside).

However, the term has been used occasionally in the context of

GRP applications to suggest that they have limited flame spread,

fire growth and smoke production. A more appropriate term for

this is “fire-restricting,” which is also the IMO preferred characterization to imply that materials have low surface flammability,

heat release rate, and smoke production. The phrase “fire resistance” is used in this section to describe fire spread to adjoining

spaces as measured by the temperatures on the backside or the

unexposed side of a panel.

In the Composite Helicopter Hangar program, the sandwich

composite was protected with a covering of 1.25 inch thick

50 The AMPTIAC Quarterly, Volume 7, Number 3
StructoGard®. All fire resistance tests on bulkheads, decks, and

overheads passed the US Navy fire performance requirements for

fire resistance and structural integrity. Sandwich composite protected with 1.25 inch thick StructoGard®” also passed the ISO

9705 room corner fire test. 

NEW RESINS AND CORE MATERIALS

The Navy has long recognized the need for the development of

resins and core materials which can be processed by VARTM

and have mechanical characteristics comparable to vinyl-esters

and balsa wood, but with superior flammability characteristics

comparable to phenolics. To this end, the Navy has invested

more than $10M toward the development of new fire restricting

resins and foams over the last 5-10 years. Most of this investment is made through ONR Small Business Innovation

Research (SBIR), Small Business Technology Transfer Program

(STTR), and Advanced Technology Demonstration (ATD)

projects, as well as internal research programs. This investment

includes the development of products such as phthalonitrile by

NRL, modified phenolics by General Dynamics’ Electric Boat

Corporation and others, epoxy- and cyanate-ester based on

bisphenol C by the Federal Aviation Administration, polyhedral

oligomeric silesquioxane- (POSS®) based resins, nanoclay reinforced vinyl-esters, phosphine oxide based epoxy and vinyl-ester

resins, and carbon foam materials. More detailed descriptions of

some of these products are included herein. 

Phthalonitrile Resin

Researchers at NRL in the 1980’s developed a new class of hightemperature polymers (based on the phthalonitrile {PN} system)

with attractive properties for composites [4]. The fully cured

resin exhibits good thermal and oxidative stability, and possesses

useful long-term mechanical properties up to 371 °C (700 °F).

More significantly, there is no indication of a glass transition or

softening up to 500 °C (932 °F). The uncured resin has a low

melt viscosity that allows it to be used in a resin transfer molding manufacturing process.

Phthalonitrile is on a short list of materials that have met 

all the small scale fire, smoke, and toxic gas requirements as

defined by MIL-STD-2031. (Large scale fire tests have not been

completed.) Figure 2 shows the chemical structure of the

phthalonitrile system, and once cured it forms a triazine network that is known to be very flame resistant. Also, the benzene

rings forming the backbone structure are very stable against fire.

The resin system’s combination of these two properties helps

create composite materials which are very resistant to fire.

Figure 2 also shows an epoxy composite and a phthalonitrile

composite over a Bunsen burner. One can clearly see the epoxy

composite on fire, while the phthalonitrile is not. (The Bunsen

burner flame does not appear on that photo because of the optics

used in the camera.)

One of the shortcomings of this resin system is its relatively

high processing temperature (Tcure = 270 °C) and small processing window (∆T=40 °C). In a recent development sponsored by ONR, the same group of researchers have been able to

modify the backbone chemistry of the monomer in such a way

as to lower the processing temperature to 190 °C and expand

the processing window to 140 °C without affecting the high

temperature performance of the resin system. Figure 3a shows

the formulation of the two new resins, where n=2 or n=4 in the

structure. Figure 3b shows the thermal stability of the two new

monomers (new21 and new32) together with the original

phthalonitrile system (biphenyl). The original phthalonitrile

and the two new formulations (n=2 and n=4) show the same

onset temperature for thermal degradation (around 500 °C). It

is worth mentioning that the char yield is more than 70% in all

cases and more than 80% when n=4. Also shown in the figure

are the glass transition temperatures (represented by the vertical

arrows in the graph) of various structural resin systems which

can be contrasted with the much higher thermal stability of the

phthalonitrile resins (Vinyl, Epoxy [Epx], Bismaleimide [BMI],

and Phthalonitrile.)

POSS® Based Systems

The Navy is investigating and developing new hybrid inorganic-organic chemical feedstock technology materials manufactured by Hybrid Plastics Inc. The technology is based on a class

of chemicals called Polyhedral Oligomeric Silsesquioxanes or

Figure 2. Left, Original Phthalonitrile Structure. Right, A Phthalonitrile Composite vs an Epoxy Composite

Over a Bunsen Burner (the Epoxy has Ignited.)

Phthalonitrile (PN) Monomer

The AMPTIAC Quarterly, Volume 7, Number 3 51
POSS®. POSS® materials are called hybrid due to their combined inorganic (silicon based) and organic (carbon based)

structure and can be viewed as discrete, chemically-modified

particles of silica having dimensions at the nanometer scale (see

Figure 4). As a result, this technology bridges the property space

between hydrocarbon-based plastics and ceramics.

The organic portion of the POSS® molecule provides compatibility with existing resins, thus enabling its incorporation

into conventional organic resins. The inorganic component of

the POSS® molecule (the SiO1.5 cage, as seen in Figure 4) provides the thermal and oxidative stability. POSS®‚ can improve

the thermal, dielectric and mechanical properties of traditional

polymers and is compatible with existing manufacturing protocols. The material releases no VOCs and thereby produces no

odor or air pollution. POSS®‚ nanomaterials can be used both as

direct replacements for petroleum based materials or as low-density performance additives to traditional plastics. They are biocompatible, recyclable, non-flammable, and competitively

priced with traditional polymer feedstocks. 

Carbon Foams

The Navy is investigating a new carbon foam material being

developed by Touchstone Research Laboratory that has shown

exceptional fire resistance. CFoam® is produced by a controlled

coking process utilizing extracts produced from bituminous

coals of low volatile content, such as those found in the eastern

US. These are attractive and inexpensive precursors for carbon

foam. After the coal extract is foamed in an autoclave, the

material can be heat-treated to further dictate its mechanical, 

thermal, and physical properties. When calcined (heated at

high temperatures to remove bound water), the CFoam® resists

ignition, has high compressive strength, impact resistance, and

low thermal conductivity (see Figure 5). Its properties are tailorable on both micro- and macroscopic scales. As such, it

Figure 3. Left, Structure of the New Phthalonitrile Monomers with n=2 and n=4. Right, Thermal Stability Graph of the Original

Phthalonitrile System Superimposed with the New Monomers.

O

O

O O

O

O

O

O

O

O

O

O

Si Si

Si

Si

Si

Si

Si

Si

R

R R

R

R

R X

R

Figure 4. Polyhedral Oligomeric Silsesquioxanes.

52 The AMPTIAC Quarterly, Volume 7, Number 3

0 200 400 600 800 1000

Temperature, °C

Weight Loss (%)

0

10

20

30

40

50

60

70

80

90

100

new21

new32

biphenyl

Vinyl Epoxy

BMI

PN

Nonreactive

organic (R) groups to increase 

solubility and compatibility.

May

possess one or more functional

groups suitable for polymerization 

or grafting.

Thermally

and chemically robust hybrid

(organic-inorganic) framework.

Nanoscopic

in size with a Si-Si distance of

0.5 nm and a R-R distance 

of 1.5 nm.

Precise three-dimensional structure for molecular level

reinforcement of polymer segments and coils.
offers a large design potential for a wide

range of military, aerospace, and commercial applications.

SMALL-SCALE SCREENING TEST

METHODOLOGY

One of the best guidelines for the rapid

development of resins and core materials

is the measurements of heat release rates

in small scale cone calorimeters. Since

1985, NSWCCD has aggressively 

evaluated the fire performance of conventional and advanced glass- and

graphite-reinforced composite materials

at several incident heat fluxes. The

material flammability characterization

was performed to identify composites

that would meet or compare favorably

with requirements specified by MILSTD-2031. Thermoset materials evaluated include vinyl-esters, epoxies, bismaleimides, phenolics, and polyimides.

Thermoplastic materials evaluated

MIL-STD-2031(For comparison) >150 <65 <50 -

Douglas Fir Plywood 22 314 98 75

Glass/VE (brominated bisphenol A 

epoxy vinyl-ester), 1031 81 122 82 1226

Glass/VE (non brominated), 1167 85 276 184 999

Glass/VE (epoxy novolac vinyl-ester), 1169 85 302 198 815

Gl/VE Sandwich Composite (1257) 70 126 93 1063

Glass/Modar (1161) 119 160 91 126

Glass/epoxy, S2/3501-6, (1089) 105 178 98 580

Glass/epoxy, F155, (1040) 18 40 2 566

Glass/epoxy, 7701/7781, (1006) 49 181 108 1,753

Graphite/epoxy, AS4/3501-6, (1093) 94 171 93 -

Glass/Cyanate ester (1046) 58 130 71 898

Graphite/BMI (1098) 110 74 51 228

Glass/phenolic (1101) 210 47 38 176

Glass/phenolic (1014) 214 81 40 83

PE/phenolic (1073) 129 98 83 294

Aramid/phenolic (1074) 163 51 40 156

Glass/polyimide (1105) 175 40 27 170

Glass/Phthalonitrile, (1273) 437 35 24 157

Glass/PPS (1084) 244 48 28 690

Graphite/PPS (1085) 173 94 70 604

Graphite/PAS (1081) 122 24 8 79

Graphite/PES (1078) 172 11 6 145

Graphite/PEEK (1086) 307 14 8 69

Graphite/PEKK (1079) 223 21 10 274

Gl/Vinyl-Phenyl POSS (HP 112) 107 77 23 93

FAA Cyanate Ester (Bisphenol C) Not Ignited Not Ignited Not Ignited Not Ignited

Gl/Geopolymer Not Ignited Not Ignited Not Ignited Not Ignited

Gr/Silicone 415 10 5 -

Figure 5. Carbon Foam, Exposed to a 3000 °F Acetylene Flame, Doesn’t Burn and

Provides Excellent Insulating Properties.

Table 1. Fire Performance Data for Selected Composite Materials at 50 kW/m2.

Ignitability(s) Peak Heat 

Release (kW/m2)

Average 

Heat Release

300 s (kW/m2)

Extinction

Area (m2/kg; 

a measure of 

smoke production)

Material System

The AMPTIAC Quarterly, Volume 7, Number 3 53
54 The AMPTIAC Quarterly, Volume 7, Number 3

include polyphenylene sulfide (PPS),

polyether ether

ketone (PEEK),

polyether sulfone

(PES), polyaryl

sulfone (PAS), and

polyether ketone

ketone (PEKK). 

Data show that

most conventional

and even some advanced composite

materials do not

meet the MILSTD-2031 requirement of >60 seconds to ignition at 100 kW/m2 incident heat

flux. The heat release rates and related data for several composite materials based on conventional and advanced resins at 50

kW/m2 incident heat flux are shown in Table 1.

To facilitate the introduction of new and modified fire tolerant materials, systems, and designs, a small-scale screening test

methodology is used. This methodology involves the evaluation

of new organic matrix-based composite materials for fire

growth. The test looks at heat release rates from small-scale tests

(cone calorimeter, ASTM E 1354, Figure 6) in combination

with a Composite Fire Hazard Analysis Tool (CFHAT).

CFHAT is a spreadsheet-based tool developed for estimating

fire conditions inside a compartment constructed with composite materials, and uses small-scale data from cone calorimeter heat release tests as input. The tool uses a flame spread

model to determine the rate at which the composite system is

involved in the fire and the total heat release rate of the fire in

the compartment. This heat release rate is used by a compartment fire model to determine the gas temperature, visibility and

toxicity levels inside the compartment. Recent tests conducted

at NSWCCD show that solid (no core) composite materials

which have met the MIL-STD-2031 requirements of heat

release rates and time to ignition at all four heat fluxes of 25,

50, 75, and 100 kW/m2, also meet the requirements of room

corner fire test in accordance with ISO 9705. 

SUMMARY

The US Navy currently uses sandwich composite panels with

balsa wood cores covered in glass reinforced, brominated vinylester resin for topside structures. These unprotected sandwich

composites do not meet the fire growth requirements of 

ISO 9705, and as such require fire insulation to reduce the fire

risk. Since installation of fire insulation is an expensive process,

the US Navy has invested $5M over the last 5-10 years in the

development of fire restricting, low-temperature-cure resins.

Recent efforts in the development of phthalonitriles, tough

novolacs, POSS®-based resins, and phosphate modified vinylesters hold good promise and are expected to continue in the

future. These material developments, in conjunction with smallscale test methods, help to facilitate the rapid development and

transition of new resin systems into the fleet. 

REFERENCES

[1] J.E. Gagorik, J.A. Corrado and R.W. Kornbau, “An Overview of Composite Developments for Naval Surface

Combatants,” 36th International SAMPE Symposium and

Exhibition, Volume 36, April 1991

[2] U. Sorathia, T. Gracik and D. Satterfield, “Fire Performance

Goals and Qualification Procedures for Composite Material

Systems used in Topside Structure and Other Topside

Applications in Surface Ships”, August 2002 

[3] B.Y. Lattimer and U. Sorathia, “Thermal Characteristics of Fires

in a Combustible Corner,” Fire Safety Journal, in press (2003)

[4] T.M. Keller and T.R. Price, “Amine-Cured Bisphenol-Linked

Phthalonitrile Resins,” J. Macrmol. Sci.-Chem. A18, 931

(1982)

Figure 6. Cone Calorimeter Test on 

Composite Test Specimen.

Mr. Usman Sorathia is Branch Head, Fire Protection Branch, Carderock Division, Naval Surface Warfare Center.

Carderock’s Fire Protection Branch is the US Navy’s authorized small and intermediate scale fire test facility with

emphasis in material and passive fire safety. Mr. Sorathia has over 20 years of experience in research, development,

manufacturing, and fire safety characterization of plastics, foams, resins, fibers, and composites. He has an MS in

Chemical Engineering from Washington State University and more than 50 publications and 15 patents to his credit.

He is Chairman of the Interagency Working Group on Fire and Materials (IWGFM) and also chairs the Flammability

Committee of the Society of Advanced Materials and Process Engineering (SAMPE). He is also an active member

of ASTM and NFPA. 
The AMPTIAC Quarterly, Volume 7, Number 3 55

INTRODUCTION

Ships are under constant attack, both from the elements of

nature and the enemy. The vast majority of ship hulls are constructed from common carbon steels, which are obviously susceptible to corrosion, but they also create distinct thermal and

electromagnetic signatures easily detectable from long distances.

Additionally, the construction framing of large steel ships is fundamentally the same as that used in wooden ships many years

ago – the main difference being the larger hull size enabled by

the stiffer steel. Both steel and wood hulls alike utilize networks

of longitudinal and transverse framing, sheathed with relatively

thin plates to create the hull form. Current steel construction

and ship design have been standardized over the past 100 years,

and as such, they are very mature technologies, employing wellestablished and time-honored practices. 

Nonetheless, even methods which are staples of the industry

have shortfalls. First, the construction process is very labor

intensive, involving the welding of thousands of steel plates.

Second, all the welding creates numerous heat affected zones,

resulting in areas of stress concentrations. Next, the entire structure, and especially these heat-affected zones, are highly susceptible to corrosion and reduced fatigue life. Lastly, extensive coatings are required to shield the structure from the elements. All of

these factors and more ultimately translate into higher build and

maintenance costs for ships.

For the next generation of ships, the Navy is looking to

stealthier hull technologies, specifically those which create lower

magnetic, acoustic, hydrodynamic, radar, and thermal signatures. One way to accomplish this is by constructing hulls out of

reinforced polymer composite materials. Composites have many

advantages over carbon steel, including a much higher strengthto-weight ratio, lower maintenance requirement, and an ability

to be formed into complex shapes (such as hulls). Composites

hulls also offer a number of stealth benefits:

• They are non-magnetic, making them less susceptible to

mines and torpedoes

• They can be made to absorb radar energy rather than reflect

it, rendering the structure with lower radar cross-sections

(RCS)

• They have significantly lower harmonic resonance, hence

they are markedly quieter in the water

• Their thermal properties allow for considerably lower thermal

signatures.

Beyond the benefits of stealth, composites also have high durability and increased fatigue life.

At the same time, the Navy has also been investigating stainless steel as a material of choice for the next generation ship

hulls. Stainless steels feature all the benefits of carbon steel, but

have the added benefit of being non-magnetic and less susceptible to corrosion. Unfortunately, stainless steels are appreciably

more expensive (per unit weight) than carbon steels. When it

comes to constructing monolithic single hulls, it is very difficult

for stainless steels to compete economically. There are revolutionary new designs however, such as the advanced double hull

concept, which require significantly less labor to construct than

conventional hulls. For the double hull concept, the reduction

in labor cost overcomes much of the price differential between

stainless and carbon steels, thus making stainless steel a more

economically attractive choice. A double hull also increases ship

survivability by making rupture more difficult.

This article addresses the advantages and challenges of introducing new materials, such as composites or stainless steel into

Roshdy George S. Barsoum 

Ship Hull, Mechanical and Electrical Systems Science and Technology Division 

Office of Naval Research 

Arlington, VA
new and emerging 21st century hull technology. It further introduces the concept of hybrid hull construction, which combines

composites with stainless steel to achieve many of the weight and

stealth advantages of composites, while retaining the stiffness and

strength of steel in the ship. This is followed by a review of two

hybrid composite concepts presently being developed for combatant vessels, and examines the various studies underway to address

the basic issues in the construction and design of hybrid hulls.

COMPOSITE MATERIALS FOR SHIP HULL APPLICATIONS

The most compelling reasons to use composite materials in hulls

are stealth, lower total ownership

cost, and weight reduction. Since

construction with composites is

more expensive than with steel,

designers need to show a clear advantage to composites and a means to

achieve cost savings over steels, either

in initial construction costs or in

total life cycle costs. If stealth is the

highest priority, composites (and

stainless steel) would be proper

choices. Composites, as discussed

below, offer other signature advantages that cannot be achieved by

steel. The Norwegian Navy claims

that its composite ships have very

low maintenance (no corrosion),

which results in lower total ownership costs. Lower maintenance

requirements could aid the US Navy

in its evolution of a fleet requiring

less manpower to operate.

The weight reductions a composite hull would afford could result in improved capabilities, such

as increased payload, higher top speed, greater range, and

reduced fuel usage. As mentioned already, another advantage of

composites is the ability to design very complex hull shapes at

very little increase in cost and weight (which is not true for

steel). Hydrodynamic designs which require complex hull shapes

(especially at the bow and stern) for efficiency or other hydroadvantages can be more easily achieved using composites.

In contrast, the fabrication processes for welded steel hulls

introduce large residual stresses, which lead to large deformations

of the individual plates (known as dishing.) Multiple dished

Figure 1. Potential Use of Composites in Naval Structures.

56 The AMPTIAC Quarterly, Volume 7, Number 3

Figure 2. Hybrid Hull Designs.

Composite section

(a)

Stainless Steel Double

Hull Construction

Stainless Steel Frame

(b)

Composite

Skin
plates along the side of the ship are usually referred to as hungry

horse deformation, similar to the exposed ribcage of a starving

horse. The RCS of the hull is increased by the multiple concave

surfaces diffracting radar signals, thus magnifying overall signature. They also reduce fatigue life under repeated cyclic load, also

called panting. Stainless steel hulls are expected to result in much

higher residual stresses and hence dishing deformations will be

larger. The only means to assure tight manufacturing tolerances

is to relieve the residual stresses by heat treatment (which is very

expensive), or to use some advanced welding technology that

could minimize the residual stresses (e.g. laser welding, which is

not yet available at most shipyards). In some steel hulls, designers

resorted to increasing the steel thickness (thus adding weight) to

reduce hungry horse deformation.

Composites represent an excellent alternative to many of the

problems steel hull construction poses. They can be fabricated

to very tight dimensional tolerances with minimal residual

stresses. Therefore, in order to meet various signature requirements while reducing maintenance and total costs, composites

would seem a logical choice. However, composites bring their

own set of drawbacks to the table, which in turn must be

addressed and managed.

Several studies have shown that for hulls longer than about

200 feet, even carbon fiber composites would not provide the

required stiffness and strength required for a hull. Figure 1

shows the usage of composites in ship hulls and where the proposed hybrid (part composite, part steel) hulls could fill the performance gap.

The cost of carbon fiber composite structures is prohibitive

for larger classes of ships (400 ft or larger). Current cost for carbon fiber is $12-18/lb (depending on grade) vs ~$0.45/lb for

high strength steel, and ~$3/lb for stainless steel. On the other

hand, low cost, high performance composite materials (such as

glass reinforced polymer or GRP) using fabrication processes

such as resin transfer molding (RTM), can compete with steel on

a per-weight basis (high-performance composites have superior

strength-to-weight ratios over steel). A variant of the RTM

process (SCRIMP®) is now being used competitively to build

hulls for patrol boats, corvettes, and minehunters. Currently, the Swedish Visby (210

ft) is the largest all-composite hull (carbon

fiber sandwich) in service.

Still, composites lack both the stiffness

and the in-plane strength required for the

larger combatant ship hulls. The structures

of long Navy combatants carry loads by the

alternating axial tension and compression

the hull experiences during hogging (hull

bows up) and sagging (hull bows down)

modes, the result of traversing waves at sea.

Therefore, for long structures the in-plane

strength of the composite becomes the critical design factor. For small ships or boats,

like Visby, the bending strength (and not the

in-plane strength) of the composite is the

critical design factor. The composite sandwich construction technology common in

smaller ships or boats, cannot provide the

necessary in-plane strength for sea loads in long ship hulls.

Composites therefore provide some of the answers to realize

low-signature, low maintenance hulls, but fall short of being able

to handle the massive structural hull loads of large sea vessels. In

contrast, stainless steels possess sufficient strength, favorable

magnetic properties, and are resistant to corrosion, but are more

expensive in large quantities and lack other stealth properties.

These realizations led to the hybrid hull concept, where a hull

might be constructed in part from composites which provide the

signature and maintenance improvements, and in part from

stainless steel which provides the needed structural integrity.

HYBRID HULL DESIGN

In the past five years, several hybrid hull designs have been proposed incorporating many of the aforementioned performance

characteristics, like stealth, stiffness, and strength. It is interesting to note that the aircraft industry (Airbus Industrie for

example with the A380) has started to work on hybrid aircraft

structures for large passenger transport. Their construction

bears a striking resemblance to the hybrid ship hull concepts.

Two hybrid hull designs have thus far been proposed; and are

illustrated in Figure 2. One design (Figure 2a) has a mid-section

of stainless steel advanced double hull and bow and stern 

sections made of single skin cross-reinforced composite or sandwich composite.This design uses the steel in the center of the ship

to achieve the strength and stiffness required for large combatants,

and the composite at the bow and stern to achieve all the weight

reduction, address complex shapes, and provide other stealth 

features. The hull shown in Figure 2b has an all-composite skin

along the entire hull reinforced with stainless steel framing in the

mid-section. This provides the necessary stiffness, and can carry

the hull-girder sea and whipping loads. [*See Note]

Advantages of a Hybrid Hull Design

The hybrid hull design takes advantage of materials where they

perform best:

• Steel is used for stiffness and strength

• Composites are used for light weight, creating complex shapes

The AMPTIAC Quarterly, Volume 7, Number 3 57

Figure 3. UNDEX Whipping Analyses.

HULLWHIP Analytical Model

Bending Moment Comparison Shear Force Comparison

Lumped Masses Beam Elements
58 The AMPTIAC Quarterly, Volume 7, Number 3

with exact tolerances, and reducing signature.

• Hybrid design does not require expensive composites. It relies

on the use of low cost GRP, which has already gained Navy

and shipyard acceptance.

Hybrid design allows for low maintenance, elimination or

reduction of corrosion problems, light weight, ability to use low

cost/high performance composites, as well as embedded sensors

and fiber optics for health monitoring. The hybrid design in

Figure 2b would also reduce repair costs through the use of

removable panels. This type of construction eliminates the problem of an entire hull delamination, which could result from the

ship impacting ice, piers, or other hard objects. (Sandwich construction used in ships like the Visby incorporated special “stoppers” in the hull skin to prevent the entire hull from delaminating.) In addition, combatants with hybrid construction have the

following advantages:

• Superior performance in underwater explosions (UNDEX); 30% reduction in whipping loads.

• The hybrid hull in Figure 2b is perceived to

be less vulnerable to internal explosions,

because the outer skin would allow relief of

internal blast pressure preventing extreme

loading of the structural frame. 

• The use of low density composites saves

weight, allowing for added additional protection systems.

• The steel framing depicted in Figure 2b also

provides options to reduce structural

acoustic signatures.

ANALYSIS AND TESTING 

OF HYBRID HULLS 

Finite Element Analysis (FEA)

Several finite element analyses were performed

to predict and evaluate the performance of a

hybrid hull subject to UNDEX shock and whipping loads

(shown in Figure 3.) Two hulls were used in the analysis; one

using conventional steel construction, and the other using

hybrid construction as shown in Figure 2a. Figure 3 shows a

comparison of the peak bending moments and shear loads (blue

is for conventional construction and red for hybrid construction.) The moments and shear are measured at specific points

along the structure’s length. As shown in the figure, the hybrid

construction results in a 30% reduction in whipping moments

and shear. 

A detailed finite element analysis of whipping (Figure 4)

shows that for a hybrid hull the highest stressed region is at the

joints due to the material mismatch. To study the behavior of

large composite/steel joints, several applied and basic research

activities are being conducted.

Figure 4. FEA of Hybrid Hull under Whipping Moment.

Highest Stressed

Elements at Joints 

Figure 5. Large Scale Hybrid Joint and Hybrid Hull Testing.

ADH Midbody

GRP

Bow

GRP

Stern

Ship Hull Grillage for Bending Test

(Lehigh University)
The AMPTIAC Quarterly, Volume 7, Number 3 59

Large Scale Testing

Figure 5 shows the large, built-up composite-to-steel joints,

which will be tested soon. In addition, a proposed half-scale hull

may be tested in the future to gain more confidence in the analysis of large scale composite/steel joints under complex sea load

and UNDEX conditions. 

Basic Research on Composite

to Steel Joints

The wide application of composites 

in future ships and submarines (e.g.

composite topside, composite mast,

composite sail, hybrid hulls etc.), has

opened a new field of research in

joints. Several studies are underway to

understand the behavior of composite

to steel joints. These investigations

cover three areas: development of joining mechanisms, understanding failure

behavior under cyclic and dynamic

loads, and development of computational tools for joint analysis. Figure 6

hightlights several studies for development and analysis of various joining

mechanisms: bolting, adhesive joining,

composite fasteners, and compliance

matching methods.

Figure 7 shows some of the theories

and experiments related to dynamic

failure and friction laws that should be

considered in the failure analysis of

these large joints. It is imperative that

friction not be ignored along the entire circumference of a hull

(or length of ship topside) after failure of the fasteners and the

initiation of interfacial cracks.

Figure 8, shows some of the analysis and computational techniques under development to allow the designer to predict failure

of interfaces under cyclic fatigue and dynamic loading. They

Figure 6. Development of Joint Concepts, and Understanding Failure Mechanisms.

University of Maine University of California–San Diego

University of California–Los Angeles

Lehigh University

To Instron

E-glass

beam

Steel

beam

Steel FRP Adherent

insert

Figure 7. Theoretical and Experimental Methods for Understanding and Measuring Friction at Interfaces of Composite/Steel Joints.

California Institute of Technology Harvard University

Brown University Brown University

Steel
Figure 8. Development of Analytical Methods for Analysis of Hybrid Ships.

University of California–San Diego

Rensselaer Polytechnic Institute

Figure 9. Concepts of Hybrid Construction in Fast Craft.

Application of Hybrid Hull

Catamaran

Theater Logistics Vessel

Pentamaran

Theater Support Vessel

Trimaran

Surface Effect Ship

Fast Patrol Boat

cover the use of neural networks and expert systems, as well as the

development of multi-scale computational methods (covering the

scale from interface details to the full scale structure.)

APPLICATION OF HYBRID HULL 

The hybrid hull concept was conceived to enable the use of composites in the structure of large combatants. The emerging need

for fast craft in the Navy however, brought about a new possibility for hybrid construction. Fast craft require high fatigue

resistance and the use of low density materials like aluminum or

composites. Where many aluminum alloys suffer from poor

fatigue performance, composites can be made to possess excellent

fatigue resistance, but may lack the stiffness for some of the hull

forms of the proposed fast ships. Figure 9 shows some concepts

of hybrid construction envisioned for fast ships.

60 The AMPTIAC Quarterly, Volume 7, Number 3

Mathematical formulas, 

rules, weight ...

Automatic learning tools

IMPACT LOADING

Global Scale

Component Scale

Material Scale
The AMPTIAC Quarterly, Volume 7, Number 3 61

Roshdy George S. Barsoum, PhD, PE, directs structural mechanics and ship structures programs for the Ship Hull,

Mechanical and Electrical Systems S&T Division of the Office of Naval Research. Prior to joining ONR, Dr. Barsoum

was chief of the Mechanics of Materials Branch at the Army Materials Technology Laboratory, and senior engineer

at Raytheon Missile Systems Division and Combustion Engineering, Inc. He obtained his PhD and MS from Cornell

University. Dr. Barsoum has written/co-written more than 60 publications in ship protection, smart materials and adaptive structures, finite element methods, pressure vessels and piping, elevated temperature analysis, fracture mechanics,

adhesive mechanics, fracture of composites, instability and mechanics of advanced materials. 

CONCLUSIONS

Many aspects of hybrid hulls are currently being investigated.

While the technology has its drawbacks, there are many advantages that make it worthwhile to investigate. Everyone agrees

that the Navy needs stealthier hull technologies for the next generation of ships. These new hulls must have lower magnetic,

acoustic, hydrodynamic, radar, and thermal signatures. Hybrid

hulls fabricated from both steel and composite materials, making use of the best properties of each dissimilar material, could

very well provide many of the advantages needed in 21st century combatant structures.

REFERENCES

M.J. Boone, V. Caccese, R. Bragg and K.A. Berube, “Mechanical

Testing of Epoxy Adhesives for Naval Applications,” UMMACH-RPT-01-03, April 2003

V. Caccese, M.J. Boone and K. Berube, “Adhesive Study,

Bonding and Assembly of the Full-scale Hybrid Composite

Strut Assembly for the AHFID Project,” University of Maine

Department of Mechanical Engineering. Report No. UMAHFID-RPT-01-1, February 2003, 45 

A. Cochard and J.R. Rice, “Fault rupture between dissimilar

materials: Ill-posedness, regularization and slip-pulse

response”, Journal of Geophysical Research, 105, 25,891-

25,907, 2000. 

D. Coker, A.J. Rosakis and A. Needleman, “Dynamic Crack

Growth along a Polymer Composite-Homalite Interface,”

Journal of the Mechanics and Physics of Solids, 51, 425-460

(2003)

J.L. Grenestedt, “Steel to Composite Joints in Hybrid Ships,”

Proc. International Conference of Sandwich Construction, Fort

Lauderdale, March 31-April 2, 2003

J.W. Hutchinson M.E. Mear and J.R. Rice, “Crack Paralleling

an Interface Between Dissimilar Materials”, Journal of Applied

Mechanics, 54, l987, pp. 828-832

Hybrid Ship Hull, US Patent No. 6,386,131

Hybrid Hull Construction for Marine vessels, US Patent No.

6,505,571 

Kerri Piccinich, “Manufacturing and Characterization of

Chemically Joined Polyester Glass Composite and Stainless Steel

Sections,” MS Thesis, Department of Mechanical and

Aerospace Engineering, UCLA, Los Angeles, CA 90095, March

2002

J.D. Melograna, J.L. Grenestedt, "Revisiting a Wavy Bonded

Single Lap Joint," 2001, submitted

J.D. Melograna, J.L. Grenestedt, “Adhesion of Stainless Steel to

Fiber Reinforced Vinyl-Ester Composite,” Journal of

Composites Technology and Research, Vol. 24, No. 4, 2002, pp.

254-260

R. Mewer, S.S. Vel, and V. Caccese, “Detection of Bolt Stress

Relaxation in Hybrid Bolted Connections for the MACH

Program”, “University of Maine Department of Mechanical

Engineering. Report No. UM-MACH-RPT-01-07, April 2003,

p. 78 

K. Ranjith and J.R. Rice, “Slip dynamics at an interface between

dissimilar materials,” Journal of the Mechanics and Physics of

Solids, 49, 341-361, 2001

J.R. Rice, “Elastic Fracture Mechanics Concepts for Interfacial

Cracks,” Journal of Applied Mechanics, 55, l988, pp. 98-103

J.R. Rice “New perspectives in crack and fault dynamics”, in

Mechanics for a New Millennium (Proceedings of the 20th

International Congress of Theoretical and Applied Mechanics,

27 Aug-2 Sept 2000, Chicago), eds. H. Aref and J.W. Phillips,

Kluwer Academic Publishers, pp. 1-23, 2001

J. R. Rice, N. Lapusta and K. Ranjith, “Rate and state dependent friction and the stability of sliding between elastically

deformable solids,” Journal of the Mechanics and Physics of

Solids, 49, 1865-1898, 2001

NOTE

*Whipping loads are created when the length of the vessel 

bends upward and downward repetitively due to an underwater

explosion. The motion resembles grasping a ruler at each end

and flexing it repeatedly up and down. While similar to routine

sea loading, the magnitude of the bending and the rate are much

greater during whipping.
62 The AMPTIAC Quarterly, Volume 7, Number 3

ACerS Glass & Optical Materials 

Div. Fall Mtg

10/12/03 - 10/15/03

Corning, NY

American Ceramic Society

P.O. Box 6136

Westerville, OH 43086-6136

Phone: 614.794.5890

Fax: 614.794.5892

Web Link: www.acers.org

Intro to Polymeric Adhesives 

and Composites

10/12/03 - 10/17/03

Blacksburg, VA

Office of Society Services

1155 Sixteenth Street, NW

Washington, DC 20036

Phone: 800.227.5558

Fax: 202.872.6067

Email: shortcourses@acs.org

Materials Solutions 2003 

Conf & Expo

10/13/03 - 10/15/03

Pittsburgh, PA

ASM International

9639 Kinsman Road

Materials Park, OH 44073-0002

Phone: 440.338.5151

Fax: 440.338.4634

National Conf on Electronic 

Packaging for Homeland Security

10/14/03 - 10/15/03

Gaithersburg, MD

IPC - Assoc. Connecting Electronics Ind.

2215 Sanders Road

Northbrook, IL 60062

Phone: 847.790.5377

Email: Homeland@ipc.org

5th Annual Carbon Foam Conf

10/15/03 - 10/17/03

Morgantown, WV

West Virginia Univ., 

Dept. of Chemical Engng

PO Box 6102

Morgantown, WV 26506-6102

Phone: 304.293.2111 x 2416

Fax: 304.293.4139

World Maritime Technology Conf

10/17/03 - 10/20/03

San Francisco, CA

SNAME

601 Pavonia Avenue

Jersey City, NJ 07306-2907 

Phone: 201.798.4800 x 3033

Fax: 201.798.4975

Web Link: www.worldmaritimetechnology.org

55th Pacific Coast Regional 

& Basic Sci Div Fall Mtg

10/19/03 - 10/22/03

Oakland, CA

American Ceramic Society

PO Box 6136

Westerville, OH 43086-6136

Phone: 614.794.5890

Fax: 614.794.5892

MSS National Military Sensing

Symposium

10/20/03 - 10/23/03

Gaithersburg, MD

Veridian Systems Division, Inc

PO Box 134008

Ann Arbor, MI 48113-4008

Phone: 734.994.1200 x 2821

Fax: 734.994.5550

Email: mss@veridian.com 

Web Link: www.iriacenter.org

Military Fuel Cells - Needs, Initiatives,

Opportunities and Challenges

10/20/03 - 10/21/03

Washington, DC

Technology Training Corporation

Dept. MFC-C

PO Box 722

El Segundo, CA 90245-0722 

Phone: 310.563.1223

Fax: 310.563.1220

Web Link: www.TechnologyTraining.com

SSPC 2003

10/26/03 - 10/29/03

Las Vegas, NV

Contact: Lorena Walker

SSPC: The Society for Protection Coatings

40 24th Street, 6th Floor

Pittsburgh, PA 15222-4656 

Phone: 412.281.2331 x 221

Fax: 412.281.9993

Email: walker@sspc.org;

Web Link: www.sspc.org/events

MS&T ‘03 (Materials Science 

& Tech 2003)

11/09/03 - 11/12/03

Chicago, IL

TMS

184 Thorn Hill Road

Warrendale, PA 15086 

Phone: 724.776.9000 x 243

Fax: 724.776.3770

Email: mtgserv@tms.org 

Web Link: cms.tms.org

International Coatings Expo

11/12/03 - 11/14/03

Philadelphia, PA

FSCT

492 Norristown Road

Blue Bell, PA 19422 

Phone: 610.940.0777

Fax: 610.940.0292

Email: fsct@coatingstech.org 

Web Link: http://ww.coatingstech.org

Tri-Service Corrosion Conf 2003

11/17/03 - 11/21/03

Las Vegas, NV

Contact: Dawn Mayer, Conference

Coordinator

Navmar Applied Sciences Corporation

1450 Edgmont Avenue, Suite 220

Chester, PA 19013 

Phone: 610.619.7440

Fax: 610.874.8250

Email: triservice@navmar.com

Magnesium Conference

11/18/03 - 11/20/03

Contact: Conference Secretariat

Deutsche Gesellschaft fur Materialkunde e.V.

Vera Hausen

Hamburger Allee

Frankfort 60486 Germany 

Phone: +49 69 7917 743

Fax: +49 69 7917 733

Email: magnesium@dgm.de 

Web Link: www.magnesium.dgm.de

ASIP 2003 USAF Structural 

Integrity Program

12/02/03 - 12/04/03

Savannah, GA

Contact: J. Jennewine

Universal Technology Corporation

1270 North Fairfield Road

Dayton, OH 45432-2600 

Phone: 937.426.2808

Fax: 937.426.8755

Email: jjennewine@utcdayton@com 

Web Link: http://www.asipcon.com

Polymer Chemistry:

Principles and Practice

12/07/03 - 12/12/03

Blacksburg, VA

Office of Society Services

1155 Sixteenth Street, NW

Washington, DC 20036 

Phone: 800.227.5558

Fax: 202.872.6067

Email: shortcourses@acs.org 

Web Link: http://chemistry.org/shortcourses

Mark Your Calendar
The AMPTIAC Quarterly, Volume 7, Number 3 63

Certification and Development of HSLA Steels

INTRODUCTION

Modern warships, surface combatants and submarines, require

high strength steel plate in increasing portions of the hull structure for weight reduction, better stability, increased payload,

increased mobility, and survivability. Nearly 50% of the total

Department of Defense requirement for alloy and armor steel

plate is used in naval shipbuilding. In service, naval ship structures are subjected to a complex spectrum of loads and environments, and the structural steels and welding materials used in

hull fabrication must demonstrate high fracture toughness for

these extreme conditions. The routine dynamic loads in service

include wave loading, sea slap, slamming, vibration, thermal

excursions in both tropical and arctic seas, cargo buoyancy, aircraft/helo landing, and weapons reactions. The structural

integrity of the hull must be assured for continuous sea-keeping

in these severe environments, as well as in response to the effects

of hostile weapons. The fracture safety of Navy ships is addressed

through the use of structural steels and welding materials for hull

fabrication that demonstrate high fracture toughness and flaw

tolerance for these extreme service conditions [1]. Thus, the key

requirements for naval shipbuilding steels are not only strength,

weldability, and toughness at low temperature under shock events

(Figure 1), but are also driven by economics, in order to keep an

affordable ship acquisition cost. 

The Groundwork: HSLA-80 & HSLA-100 Steels

In the early 1980’s, steelmakers were producing grades of HighStrength, Low Alloy (HSLA) steel plate with improved weldability, low temperature toughness, and yield strengths of

60,000 to 80,000 psi. The Navy initiated a project to develop

and certify HSLA steels that were weldable with reduced or no

preheat, high strength, high toughness, and high quality weldments equivalent in performance to the High Yield (HY)-series

steels (HY-80 and HY-100). The focus was weight reduction in

CG 47- and DDG 51-class warships with an affordable hull

fabrication cost.

The project demonstrated that a modified ASTM A 710, Grade

A steel plate could meet the minimum yield strength requirement

of 80,000 psi, have a high Charpy V-notch impact energy at low

temperatures, and possess excellent weldability using the processes

and practices for HY-80 without preheat. HSLA-80 steel, then, is

an optimized version of ASTM A 710 steel and was certified for use

in ship construction in 1984 after an extensive evaluation of plate

properties, welding, and fabrication characteristics, including the

construction and destructive test of structural models [2,3]. Cost

savings from $2,000 to $3,000 per ton of fabricated structure have

been estimated for using HSLA-80 in place of HY-80, where

reduced material, labor, energy, and inspection costs are combined.

Through 2001, approximately 40,000 tons of HSLA-80 have been

used in US Navy combatant ship construction. (See Figure 2.)

Following the HSLA-80 project, an alloy development and qualification project commenced resulting in approval of HSLA-100

steel as a replacement for HY-100 to further reduce fabrication

costs. HSLA-100 is also a very low carbon, copper-precipitationstrengthened steel, with higher alloy content than HSLA-80 [4].

The new steel was developed to match the strength and toughness

of HY-100, and be weldable using the same consumables and

processes of HY-100, without its preheat requirements. The program for the development of HSLA-100 consisted of three phases:

(1) alloy design, where the composition of the steel was formulated through a progressive optimization using laboratory-scale heats;

(2) trial plate production at a steel plate mill to an interim specification; and (3) plate production for the certification program in

thickness from .25 inch to 3.75 inches.

HSLA-100 steel plate and weldment certification included the

Figure 1. Naval Shipbuilding Steels Require High Strength,

Weldability, and Toughness at Low Temperature Under 

Shock Loading.

Ernest J. Czyryca, David P. Kihl, and Robert DeNale

Survivability, Structures, and Materials Directorate 

Carderock Division, Naval Surface Warfare Center

West Bethesda, MD
characterization of mechanical, physical,

and fracture properties; evaluation of weldability and welding process limits for

structures of high restraint (those prone

to large amounts of residual stress); studies of fatigue properties and effects of

marine environments; and the fabrication and evaluation of large-scale structural models to validate the laboratorydeveloped welding process parameters

[5]. Based on the properties and weldability demonstrated in the evaluation,

HSLA-100 steel was certified for use in

surface ship structures and ballistic protection, and was selected

to replace HY-100 for fabrication cost reductions in the construction of USS John C. Stennis (CVN 74). Estimated cost savings for fabricated structure in CVN 74 construction ranged

from $500 to $3,000 per long-ton (2240 pounds), depending on

complexity of the structure [6]. Through 2001, approximately

30,000 tons of HSLA-100 steel plate were used in Navy surface

combatant construction - primarily in aircraft carriers. Figure 3

shows the cumulative tonnage of HSLA-80 and HSLA-100 steels

used in ship construction after certification.

HSLA-65 STEEL

The high strength steel (HSS) plate used in Navy surface combatant structures includes HSS (ABS DH/EH-36) of 50 ksi (345

MPa) yield strength, HY-80 or HSLA-80 of 80 ksi (550 MPa)

yield strength, and HY-100 or HSLA-100 of 100 ksi (690 MPa)

yield strength. Although heavier gage plate is required in some

structures, most ship structure, including the hull shell plating,

uses plate in the 6 to 30 mm (.25 inch to 1.25 inches) thickness

range. No high-strength steel plate grade for yield strengths

between HSS (50 ksi minimum) and HY/HSLA-80 (80 ksi minimum) was certified for surface combatant structures, nor have

design criteria been developed. Except for ship protection plating (armor), the use of higher strength steel in a ship structure is

usually a means to reduce weight and is a cost versus benefit

decision. Thinner plate and less weld metal are required for

HY/HSLA-80 structure compared to HSS (DH/EH-36).

However, buckling limits, requiring additional stiffening, may

prevent optimum use of HSLA/HY-80 for weight reduction.

Additionally, plate cost per ton for HSLA and HY steels are

more than double that of HSS and fabrication costs are significantly higher also.

It was evident in the HSLA-80 steel project that a 65 ksi yield

strength steel, based on the “true” HSLA steels developed for

pipeline and offshore applications, could meet the requirements

for shipbuilding plate with improved strength, toughness, and

weldability. These HSLA steels use low carbon and microalloying in conjunction with thermo-mechanical processing techniques instead of expensive alloy additions and heat treatment.

(Compare this to the HY/HSLA-80 steels which rely on high

amounts of alloy elements (Ni, Cr, Mo, Cu) and off-line heattreating (quenching and tempering) to obtain their properties.)

The Naval Sea Systems Command recommended continuation of the steel development program for an HSLA-65 grade.

This was due to design studies (destroyer-type hull) which

showed that the utility of 80 ksi yield strength steel was limited

(due to buckling limits), and a 65 ksi yield strength steel could

achieve similar weight savings. Fabrication costs could be

reduced for most surface ship hull structures by using a 65 ksi

yield strength steel whose material and fabrication costs were

similar to HSS, and simultaneously provide a weight savings.

Candidate steels for the HSLA-65 grade were controlled-rolled,

micro-alloyed, inclusion shape controlled, low C-Mn steels, similar to line-pipe grade API 5LX 65.

Service-life weight and stability

allowances are key performance

parameters for the new aircraft carrier

designs, with 50-year service life and a

hull-form similar to the CVN 68-class,

as seen in Figure 4. Weight reduction

under such constraints is difficult and

expensive, and it is an absolute surety

that improved capabilities and threat

growth over the ship’s life will continually increase its weight. Any measures

that enable increased weight margins

in aircraft carrier construction must

therefore be considered.

The replacement of HSS with higher strength HSLA-65 will result in the

use of thinner plates and thus structur64 The AMPTIAC Quarterly, Volume 7, Number 3

Figure 2. HSLA-80 Steel Plate is Used in Navy Surface Combatant Construction,

Including Cruisers, Destroyers, and Aircraft Carriers.

40000

35000

30000

25000

20000

15000

10000

5000

0

1984 1986 1988 1990 1992 1994 1996 1998 2000

HSLA-80

HSLA-100

Figure 3. Cumulative Tonnage of HSLA-80 and HSLA-100 Steels Used in Ship Construction.
65

al weight reduction estimated to be on the order of 1,500 longtons per ship – the largest weight reduction measure available to

the design. The cost of HSLA-65 steel plate is approximately

equivalent to that of HSS, and HSLA-65 welding processes, procedures, and consumables are the same as for HSS. The smaller

volume of weld metal for thinner plate will also reduce total fabrication costs. Thus, the HSLA-65 system can be a cost-effective

weight saver.

HSLA-65 Development & Welding Optimization

HSLA-65 steel development gained momentum in the early

1990’s when Northrop-Grumman Newport News Shipbuilding

(NNS) sought the implementation of a cost-effective, industrial

specification (ASTM), HSLA-65 structural grade for aircraft

carrier primary structures. NNS estimated significant weight

savings if the steel was used in the construction of CVN 76 and

CVN 77. CVN 69-class vessels had progressively increased in

weight, decreasing lifetime growth margin. An interim standard

specification for a “clean,” low-carbon steel was proposed by

NNS and reviewed through an ASTM subcommittee, with

Naval Surface Warfare Center (NSWC), the American Bureau of

Shipping, and steel manufacturers among the membership. In

1995, ASTM A 945, Standard Specification for High-Strength

Low-Alloy Structural Steel Plate with Low Carbon and Restricted

Sulfur for Improved Weldability, Formability, and Toughness, was

issued in the annual standards. Between 1994 and 2000, several

major projects studying steel and welding were concurrently

conducted on HSLA-65, which provided mechanical, physical,

and fracture properties; evaluation of weldability and welding

process limits; studies of fatigue properties and effects of marine

environments; and the fabrication characteristics. Some of these

programs are summarized as follows:

• The NNS Aircraft Carrier Research Project conducted initial

characterization of HSLA-65 production plate and review of

CVN 77 critical and non-critical structures for potential HSS

replacement.

• Office of Naval Research (ONR) Seaborne Materials projects

evaluated commercially produced ASTM A 945, Grade 65

(HSLA-65) steel plate strength, toughness, fatigue, and weldability, where weldments are fabricated using HSS-type welding. The welding development for HSLA-65 investigated

HSS-class welding consumables to determine performance

requirements, identify consumables of improved toughness

for HSLA-65 welding, and characterize HSLA-65 heat-affected zone toughness under high heat input welding.

• ONR Manufacturing Technology projects characterized

HSLA-65 welding with commercially available consumables

for gas metal arc welding (GMAW), submerged arc welding

(SAW), shielded metal arc welding (SMAW), and flux cored arc

welding (FCAW) using typical shipyard welding procedures

The effects of shipyard HSS fabrication practices (flame

straightening, hot / cold forming, post-weld thermal stress

relief) on HSLA-65 steel and weldments were also examined.

The project focused on optimization of HSLA-65 welding consumables and procedures, weld joint performance analysis, and

verification of HSLA-65 weld joint performance under the

extremes of service performance.

Domestic steel plate mills delivered plate from 0.25 to 1.25

inch thick to ASTM A 945, Grade 65 for these projects. All plate

production methods (controlled rolled, quenched and tempered,

and thermo-mechanical controlled processing with accelerated

cooling) covered by ASTM A 945 were represented in the evaluations. The conclusions of the ONR and NNS projects on

HSLA-65 steel and welding are summarized in Table 1.

HSLA-65 SYSTEM CERTIFICATION

The testing and analyses performed for HSLA-65 steel plate

and weldments using HSS welding processes, procedures, and

consumables have shown that the material system has the

properties and characteristics to meet the performance requirements for combatant ship structure. The material properties

and characteristics developed in these evaluations paralleled

those conducted for HSLA-80 and HSLA-100 and were sufficient to support certification of the HSLA-65 steel system for

Navy ship non-primary structure. However, structural fatigue,

plate buckling, lateral pressure, local instability, stub column,

& grillage tests were required to validate design criteria and

take full advantage of the higher strength of the HSLA-65 

system for application in primary structure. (Grillage structure

commonly refers to plate with attached longitudinal and transverse stiffeners.)

Certifying HSLA-65 for Structures

The testing and evaluation of HSLA-65 steel structural properties and stability focused on six areas of HSLA-65 structural

behavior: (1) welded structure compressive properties, (2) local

stability of stiffener elements, (3) plate buckling, (4) lateral

deformation of plates, (5) fatigue strength, and (6) grillage

strength. Lack of data in these areas currently prevents the efficient use of HSLA-65 in surface combatant primary structures.

The AMPTIAC Quarterly, Volume 7, Number 3

Figure 4. HSLA-65 Steel Plate Will Enable Weight Reduction in New Aircraft Carrier Design.
66 The AMPTIAC Quarterly, Volume 7, Number 3

Because of the critical need for weight reduction in new 

aircraft carriers, a project for complete structural evaluation to

certify HSLA-65 steel for use in primary hull structure of surface

combatant ships was conducted and completed in 2002. The

effort focused on extreme conditions of anticipated use to provide a database and confidence for general structural use certification. This would also minimize the risk in ship design with a

new, 65 ksi yield strength grade. Design criteria for HSLA-65

plate buckling, lateral pressure capacity, structural fatigue, 

stability of structural members, and grillage performance, 

validated by structural testing were necessary for certification

and the HSLA-65 system design for primary structure. Once

certified for surface combatant structure, HSLA-65 has high

potential benefit to the Navy beyond aircraft carrier applications. Future application for DD(X), LPD 17 & LHA(R)

Classes can be anticipated.

An additional weight savings will be derived by replacing 

inefficient HSS rolled shapes with HSLA-65 built-up (welded)

shapes. HSS rolled shapes are not produced to shipbuilding

sizes and are typically oversize, whereas HSLA-65 built-up

shapes can be designed and fabricated to meet strength requirements and thus save weight. In addition, fabrication and installation costs will be reduced by decreasing the large tolerance

variations rolled shapes present which lead to fit problems in

assembling parts cut from the rolled shapes. Design criteria for

HSLA-65 steel built-up tees (two flat plates welded in a “T”-

shaped cross section) are required to proportion the sizes such

that local buckling of flange and web elements is prevented. In

the certification process, specific structural element tests were

conducted representing extreme conditions for built-up shapes

(stub columns and local instabilities) to provide a database and

support design criteria for welded HSLA-65 steel shapes.

Figure 5. Photograph of Satisfactory 1.25 Inch Thick HSLA-65

SMAW Explosion Crack-starter Test after Third Shot.

Figure 6. Photograph of Satisfactory 1.25 Inch Thick HSLA-65

FCAW Explosion Bulge Test after Sixth Shot.

Table 1. Major Findings of the ONR and NNS HSLA-65 Projects.

• All plates from domestic steel mills met the composition, tensile, and impact requirements of ASTM A 945, Grade 65, and all met or exceeded

a minimum impact toughness of 70 ft-lb at –40 °F (transverse) set as a performance requirement for Navy surface combatant structures;

• All plates used compositions and processing based on steels for other commercial applications, (not exclusive to military type plate) such as

HY/HSLA-80 or HY/HSLA-100 steel plate;

• Ship fabrication practices, such as cold forming, flame straightening, and post-weld stress relief, are limited by the same temperature 

restrictions that apply to HSS (DH36) for the same practices;

• Most 70-series welding consumables have specified minimum yield strength less than HSLA-65 (under-matched yield strength welds). 

In practice, however, most provided weld metal yield strength and tensile strength sufficient to result in ultimate failure in the HSLA-65 

base plate;

• The weldability of HSLA-65 is equal to or better than HSS;

• Several classes of 70-series welding consumables (depending on plate composition and welding procedure) showed excellent Charpy V-notch

impact toughness (exceeding 25 ft-lb at –40 °F, set as a performance requirement for Navy surface combatant structures);

• HSLA-65 welded structural element tests for fracture toughness showed ductile behavior, high flaw tolerance, and significant margin against

brittle fracture at –20 °F service temperature (welds with toughness exceeding 20 ft-lb at –40 °F);

• The high-cycle fatigue properties of HSLA-65 butt welds and cruciform joints (whose cross section resembles a Latin cross; see also Figure 9)

were within the bands of scatter for results for HSS and HY-80 as-welded joints;

• HSLA-65 plate welded with 70-series consumables exceeded the reduction in thickness in explosion bulge tests required for HY-80 weldments,

and performed well in crack-starter explosion bulge tests (See Figures 5 & 6).

Tension Side (Side 1)

Compression Side (Side 2)

Tension Side (Side 2)

Compression Side (Side 1)
The AMPTIAC Quarterly, Volume 7, Number 3 67

Structural Property Column Tests The stability of structural 

members under compressive loads is typically quantified by linearelastic formulae which are only valid for stresses within the initial

linear elastic range of the stress-strain curve. Ship structures are 

typically designed against buckling above the proportional limit at

stresses near the yield strength. (The proportional limit defines the

point at which stress is no longer linearly proportional to strain.)

To predict inelastic buckling, the proportional limit and yield stress

are used to correct the linear-elastic buckling formulas and account

for inelastic effects.

A series of compression tests was conducted on very short sections of built-up HSLA-65 I-beams. The flanges and web of the

I-beam were proportioned to preclude local buckling, and the

overall length of the specimen was short enough to preclude

column buckling. With the presence of longitudinal fillet welds

to introduce realistic residual stresses and fabrication-induced,

out-of-plane deformations, the HSLA-65 I-beams were instrumented to measure deformation and then loaded to failure after

significant plasticity had occurred. The recorded load-deflection curves show the point of deviation from initial linearity:

the structural proportional limit. The results were used to correct elastic buckling formulations for inelastic behavior.

Compared to data from similar tests of HSS and HSLA-80 

I-beams, appropriate factors of safety were determined for

HSLA-65 working stress for structural design.

Local Instability Tests The built-up tee-stiffeners of ship steel

structure need flange and web elements of proper width-to-thickness (b/t) proportions to avoid local buckling under compressive

loads (i.e. to prevent buckling of flange and web elements of the

stiffeners.) Neglecting this mode of failure can lead to more serious, global-buckling failures, since the load carrying capacity of

individual members is reduced. Column tests were conducted on

lengths of built-up HSLA-65 I-beam sections, short enough to

preclude column buckling, but long enough to eliminate low

aspect ratio effects, where plate buckling modes dominate. Flange

and web dimensions were designed to have the same stability to

achieve a lower-bound strength; i.e., the flange did not stabilize

the web and the web did not stabilize the flange. End caps were

welded at each end to provide good load transition into 

the beam. 

The columns were instrumented with strain and displacement

gages to ensure even load distribution, as well as define the onset

of buckling and post buckling behavior. (See Figure 7.) Four slenderness ratios (width-to-thickness ratios) were tested, similar to

tests performed for HSS and HSLA-80 steels. The HSLA-65

tests showed structural behavior and ultimate strength as expected for steel with yield strength between HSS and HSLA-80. The

analysis of HSLA-65 structural behavior provided the experimental basis to establish slenderness ratio limits for the design of

HSLA-65 plating stiffeners. 

Plate Buckling Tests Ship structure is composed almost entirely

of orthogonally stiffened plating. Both the plating and stiffeners

must be designed to sustain working loads. Plate panels in the

ship are welded around their periphery to stiffeners or adjacent

panels. The welding introduces residual stresses, which can

adversely affect the strength of the panel. Plate buckling is generally characterized by a plate slenderness parameter, which is a

function of the width-to-thickness ratio, yield strength, and elastic modulus. For design purposes, the edges of the plate panel are

assumed simply supported, and under increasing uniform compressive edge load, the plate will first buckle and then develop

post-buckling strength until ultimate collapse occurs.

HSLA-65 plate panels with welded edges were fabricated with

different widths and loaded in axial compression such that buckling behavior over a wide range of slenderness was evaluated.

The panels were instrumented with strain gages and displacement transducers to determine the inception of buckling and

track the post-buckling behavior of each panel. The results for

HSLA-65 plate panel tests compared favorably with the curves

used for design against plate buckling and ultimate strength in

naval ships.

Lateral Pressure Tests Most plate panels of ship hull structure are

subjected to and designed for sustained lateral pressure loadings

of various magnitudes associated with draft, ballast, fuel, and

flooding conditions. In addition, certain structural members

Figure 7. Left, Welded HSLA-65 Steel I-beam Test Series After Compression Tests for Local Instability and Right, Instrumented I-beam

Under Test.
(such as shells, tanks, and bulkheads) are designed to hold a lateral load, even though it may cause the panel to undergo some

degree of permanent deformation. Design guidance has evolved

which uses correction factors (known as “C-factors”) to determine the maximum slenderness ratio of the panel (width-tothickness), given the aspect ratio of the panel (length-to-width),

and the hydrostatic head acting on the panel.

Tests were conducted for HSLA-65 plates to experimentally

determine the elastic, inelastic, and rupture capacity, as well as

to determine C-factors for the steel using the NSWC Carderock

Division’s pressure tank facility. A cylindrical fixture was fabricated with heavy plate internal stiffening across one end of the

cylinder. The HSLA-65 test plates were welded to both the

internal diameter of the cylinder and the stiffeners. With the

opposite end of the cylinder capped with a heavy circular plate,

the entire test assembly was placed into

the pressure tank, where pressure was

incrementally increased and decreased to

establish the relationship between permanent deformation and applied pressure. Strain gages and displacement

transducers measured the panel’s

response and permanent set. After sufficient data were collected to determine a

C-factor for HSLA-65 plate, the pressure was increased until the ultimate

holding pressure was reached. At this

point, the panel failed by shearing a stiffener weld at a panel edge. Figure 8 shows

views before and after lateral pressure

tests. The C-factors established for

HSLA-65 plate panels under lateral pressure were as expected for a steel of its

yield strength.

68 The AMPTIAC Quarterly, Volume 7, Number 3

Figure 8. Welded HSLA-65 Steel Plate Lateral Pressure

Test, Showing Stiffeners in Cylinder Interior (Top),

Exterior View of Test Plate Prior to Test (Middle), and

Instrumented Plate After Rupture in Test (Bottom).

Figure 9. Cruciform Fatigue Test

Specimens Cut From 

Tee-weldment.

Figure 10. Cruciform Weld

Under Fatigue Test Clamped

in Hydraulic Grips. 

← → 3 3/4”

← → 3 3/4”

←3 3/4”→← → 3 3/4”

←→2”

14”

Weld
The AMPTIAC Quarterly, Volume 7, Number 3 69

Structural Detail Fatigue The use of HSLA-65 steel will result in

lighter gage structure with associated higher stresses than for

HSS. Fatigue strength may become a significant design consideration when the structure is subjected to cyclic stresses in service in both primary and secondary structural applications. The

fatigue strength of welded structural details is determined by

cycling representative weld joints at constant amplitude stress

levels until failure by fatigue cracking occurs. Since the constant

amplitude behavior will eventually be used to predict seaway

loadings, random amplitude loadings were also applied in the

HSLA-65 weld joint evaluation in order to evaluate the accuracy of the fatigue life prediction methodology. Simple tee structures were tested in order to characterize the fatigue strength of

welded HSLA-65 steel. 

The fatigue test joint configuration was flat plate-type with

two side attachments at mid-length, with the full-penetration

fillet welds of the non-load carrying side attachments oriented

perpendicular to the applied axial, fully reversed load amplitude.

(See Figure 9.) This configuration represents a weld detail prevalent in ship structure, and similar tests have been performed on

the same type of specimen using HSS and

HSLA-80 steel, which

offer a basis for comparison. The fatigue tests

were conducted in dedicated machines using

hydraulic grips, as seen

in Figure 10.

The fatigue stress

amplitude levels included tests to determine

fatigue strength at long

lives, which would provide data for design

against fatigue over the

ship’s life. This would

help prevent maintenance problems as the

ship structure ages. The

results indicated that HSLA-65 weldments are comparable

in fatigue properties to HSS and HSLA-80 weldments over

the life range investigated. Results of this testing are shown

in Figure 11. Fatigue strength of weldments is related to the

stress concentration at the toe of the weld (weld geometry)

and not to the yield or tensile strength of the steel. Thus, as 

the strength of the steel and the design stress increases, 

closer attention must be given to fatigue design in order to

obtain adequate structural life.

Grillage Tests As previously noted, ship structure generally

consists of longitudinally and transversely stiffened plating.

The preceding tests addressed the properties of local structural issues, such as the capacity of plating between stiffeners, the proportions of the flange and web elements of

stiffeners, and the fatigue strength of a welded detail.

However, local structural issues like these must be understood before the larger, general structure can be designed. As the

overall structure increases in size, the size, shape, and length of

the members may be limited to control buckling of main loadcarrying members. Due to the complicated nature of buckling

mode interaction and the effects of initial deformations and

residual stresses from

fabrication, the ultimate load carrying

capacity of a large

structure is best determined experimentally. Grillage test structures, containing 

multiple longitudinal

and transverse stiffeners, were evaluated for

catastrophic modes of

buckling failure and

to define margins of safety for design against ultimate failure. (See

Figures 12 and 13.) The grillage test structures were 8 ft wide X

24 ft long containing three bays, and fabricated by NNS.

Instrumentation, out-of-plane deformation, testing, analysis and

documentation were performed by NSWCCD, home to the

unique grillage test facility.

HSLA-65 Steel Design Criteria / Guidance

The HSLA-65 structural testing provided experimental validation for design criteria for plate buckling, lateral pressure 

capacity, structural fatigue, stability of structural members, and

grillage performance. The data support full implementation,

unrestricted use of HSLA-65 for primary hull structure and minimum risk of unanticipated problems in construction and service. The structural tests demonstrated adequate performance of

the HSLA-65 system (both bulk material and welded structure)

to perform as expected under current criteria and guidance.

STEELS FOR THE FUTURE NAVY

The HSLA steel research and development projects provided the

Navy with the opportunity to develop lower-cost alternatives to

the HY steel systems and new high strength welding products

for higher productivity. The Navy’s investment in high strength

Figure 11. Results of Constant Stress Amplitude Fatigue Tests of Cruciform

Weldments of Ordinary Strength (OS), HSS, HSLA-65, and HSLA-80 Steels. 

Figure 13. HSLA-65 Grillage After Test in

Grillage Test Machine. 

Figure 12. Grillage Test Machine with 

High Load Capacity: +/- 5 Million lbs

(Longitudinal), +/- 1 Million lbs 

(Transverse), and 25 psi Lateral Pressure.

HSLA-65 1/2”

HSLA-80 7/16”

HSS 1/2”

OS 1/2”

1.E+03 1.E+04 1.E+05 1.E+06 1.E+07 1.E+08

Cycles to Failure

100

10

1

Applied Stress Amplitude (ksi)
70 The AMPTIAC Quarterly, Volume 7, Number 3

steel research has had a major payoff in providing metallurgical

approaches to obtaining weldable, tough, structural steels not

burdened by the cost and welding limitations of the HY-series

steels of the 1960’s.

Advanced ultra-low carbon steel metallurgical systems and

processing technology previously limited to research or foreign

production are becoming domestically available for commercial

production. The synergism of sophisticated hot metal treatments, microalloying, improved slab production, thermomechanical controlled processing, and accelerated on-line cooling, have the potential for achieving up to 150 ksi yield strength

in an inherently weldable alloy steel plate.

Advanced HSLA metallurgical systems, steel plate processing

technology, and advanced joining methods for high-strength

steel systems will continue to be part of Navy R&D through the

21st century. The performance requirements for the ships of the

“Navy-After-Next” can be expected to increase the demands on

the steel systems. Improved ship protection at reduced weight is

one requirement that will demand alloy steel systems extending

over the 130 to 150 ksi yield strength range for design against

future weapon threats.

ACKNOWLEDGEMENTS

This work was sponsored by the ONR Seaborne Structural

Metals Program, Julie A. Christodoulou Program Manager.

REFERENCES

[1] P.M. Palermo, Structural Integrity Criteria for Navy Hull

Materials, Naval Engineers Journal, October 1976, pp. 73-86

[2] T.W. Montemarano, B.P. Sack, J.P. Gudas, M.G.

Vassilaros, and H.H. Vanderveldt, High Strength Low Alloy

Steels in Naval Construction, Journal of Ship Production, vol.

2, no. 3, August 1986

[3] L.G. Kvidahl, An Improved High Yield Strength Steel for

Shipbuilding, Welding Journal, vol. 64, no. 7, July 1985, pp.

42-48.

[4] A.D. Wilson, High Strength, Weldable Precipitation Aged

Steels, Journal of Metals, March 1987, pp. 36-38

[5] E.J. Czyryca, R.E. Link, R.J. Wong, D.A. Aylor, T.W.

Montemarano, and J.P. Gudas, Development and Certification

of HSLA-100 Steel for Naval Ship Construction, Naval

Engineers Journal, May 1990, pp. 63-82

[6] J.P. Christein, and J.L. Warren, Implementation of HSLA100 Steel in Aircraft Carrier Construction - CVN 74, Journal of

Ship Production, vol. 11, no. 2, May 1995, pp. 97-101

Ernest J. Czyryca is a research project leader in the Metals Department of the Naval Surface Warfare Center,

Carderock Division. He holds degrees in Metallurgical Engineering (Drexel University), Civil Engineering (Johns

Hopkins University), and Engineering Mechanics (Pennsylvania State University). In his 40-year career with the Navy,

he has been involved in or managed R&D projects in naval structural metals, alloys for machinery applications, metals processing, mechanical metallurgy, welding metallurgy, fatigue of metals and structures, fatigue design, fracture

properties and fracture mechanics, and failure analyses. He is author or co-author of more than 150 technical reports

and papers published in professional society journals.

Dr. David P. Kihl is a structural naval architect and has been employed at the Carderock Division, NSWC since 1978.

He received his BS degree in Civil Engineering from the State University of New York at Buffalo, and his MS and DSc

degrees in Structural Engineering from The George Washington University. Over his 25-year career, he has authored

or co-authored more than 100 technical documents, including NSWC reports, journal articles, and conference proceedings, many dealing with life prediction and failure criteria of surface ship structures. Most recently he received the

American Society of Naval Engineers Jimmie Hamilton Award, awarded annually for the best original technical paper

in Naval Engineering. 

Robert DeNale is head of the Metals Department at the Naval Surface Warfare Center, Carderock Division. His

areas of scientific and engineering interest include welding, nondestructive evaluation and high strength steel casting

metallurgy. He has authored numerous publications and US Navy technical reports. He has been awarded 7 US

patents, edited two books, and made more than 50 presentations at professional society meetings.
The AMPTIAC Quarterly, Volume 7, Number 3 71

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