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Past Issues

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V6N1

Feature Article: Accelerating Materials

Insertion By Evolving the DoD Materials

Qualification-Transition Paradigm

TechSolutions 19: Blast Resistant

Fenestration Design and Testing

3rd Article: Clean Fire Extinguishants

for DoD Applications

V5N4

Feature Article: US Army Builds

Degradation Resistant Bridges

TechSolutions 18: Polymer Matrix

Composite Manufacturing Induced Defects

3rd Article: NDE for the Process Control

of PMC Fabrication

V5N3

Feature Article: Manufacturing Readiness Levels

TechSolutions 17: Toolkit for DoD Manufacturing

Engineers

3rd Article: Joint Defense Manufacturing Technology

Panel

V5N2

Feature Article: Automating Aircraft Inspections: Time and Cost

Saving Measures for the Inspection of Large Area Aircraft Surfaces

TechSolutions 16: Selecting a Nondestructive Testing Method, Part VII: Acoustic Emission Testing

3rd Article: New Technical Resource for Scientists and Engineers: Handbook on Visual Testing

V6N1 2011

V5N3 2010

V5N4 2010

V5N2 2010
The AMMTIAC Quarterly, Volume 6, Number 2 3 http://ammtiac.alionscience.com

Today’s Army faces extreme challenges at home and abroad, and

meeting these challenges has forced the Army to take a hard look at

all the materials used in vehicles and in construction. One material

dominates this discussion, both for the US Army as well as the rest

of the industrialized world: steel. Steel has been used by mankind

for about four centuries. There is a tendency, even within engineering circles, to think of steel as an old, fully developed technology.

When design engineers are looking to utilize improved materials,

they often overlook significant improvements that can be obtained

using enhanced steels.

The reason that steel has endured as the material most associated

with economic development is its value. Steel is cheap to make and

provides a wide range of properties for applications in vehicles, construction, the industrial base and consumer products. It is the most

widely recycled material, and

is generally easy to repair.

Think of the average automobile, or truck – what would

be left if you removed all the

steel? A similar relevant question can be asked about most

commercial construction –

what would be left if you

removed the steel rebar, steel

beams, and steel joists? We

know that today’s and tomorrow’s Army will be dominated

by steel, whether in combat

vehicles, support vehicles and

equipment, or in the construction of military buildings, hangars, bases, etc. The

Army has a huge on reliance

on steel, with large quantities

of advanced and powerful

weapons all over the world. Ground vehicles, usually made of steel,

are the backbone of the Army’s fleet for sustainment and mobility.

Today, the Army has over two hundred thousand ground vehicles in

the fleet. So what can we do to get better value from steel as we

move toward the future? Make it stronger! And that’s where vanadium is able to play an important role.

Vanadium can be added in small amounts during the steelmaking process to provide significant increases to the strength of the

steel produced. Most of the vanadium used within the United States

steelmaking is itself a “reused” product, derived from spent catalyst

used in chemical operations. When added in small amounts to steel,

the steel is referred to as microalloyed, or “low-alloy” steel. High

Strength, Low Alloy steels with vanadium additions (HSLA-V)

show improved strengths of 50-100% as compared to traditional

low-carbon steels. Adding this strength adds value. Adding a small

amount of vanadium to steel, produces a high-strength, low-alloy

vanadium (HSLA-V) steel while reducing weight, energy and production costs. Why? Because many applications are strength dominated, and in these cases we can use less steel to accomplish the same

mission without impacting performance. Therefore, it’s simply a

better use of our resources.

CONSTRUCTION APPLICATIONS

Studies have shown that HSLA-V steels produce weight and cost

savings for use in long-span joists, rebar-reinforced concrete, and

bridging applications. Detailed experimental, computational and

design studies showed that long-span joists and girders can be

reduced in weight by up to 25%, allowing structures to reduce their

overall steel usage in girders

and joists by 17% (see Figure

1).[1] The Army should care

about lightweight construction, primarily for sustainability. Doing the same job

with less steel means that less

energy was used to produce

and transport that steel, saving money and reducing the

environmental footprint of

the building. HSLA-V rebar

can provide the same benefits

in reinforced concrete structures: less steel for the same

mission. Alternatively, it can

provide enhanced capabilities, whereby an identical

quantity of HSLA-V steel can

provide more protection to

the structure. Studies performed by the US Army Engineering Research and Development

Center (ERDC) in Vicksburg, Mississippi have demonstrated that

the use of high strength rebar can build structures with increased

blast resistance.[2] In a similar approach, the high strength rebar

also enhances the earthquake resistance of the structure.

TRANSPORTATION APPLICATIONS

Lightweight materials pay dividends over the entire life cycle of

vehicles and transportation equipment, as weight reductions are a

proven means to save fuel. Furthermore, the logistics of getting fuel

to remote battlefields magnifies those savings and makes weight

reduction a priority for our forces. A case study completed by a producer of high strength steel and a flatbed trailer manufacturer has

shown that the use of HSLA-V steels can reduce the weight of

John H. Beatty

US Army Research Laboratory

Weapons and Materials Research Directorate

Figure 1. The use of HSLA-V steels in long-span joist-girder construction can

reduce the total amount of steel required by 17-25%.
The AMMTIAC Quarterly, Volume 6, Number 2 4 http://ammtiac.alionscience.com

conventional steel trailers by 21% (see Figure 2).[3] Weight savings

will reduce fuel usage every time a trailer rolls out on a mission.

There are materials even lighter than HSLA-V steels that can

further reduce fuel consumption, (e.g., aluminum, magnesium, and

polymer composites) and the use of these materials will also continue to expand as fuel prices increase. However, HSLA-V steels still

represent great value to the engineering designer and to the Army.

In many cases HSLA-V steels can be substituted for low carbon

steels with minimal redesign. The manufacturing processes (e.g.,

forming, welding, etc.) remain essentially the same. Finally, the cost

of components produced using HSLA-V steel remains about the

same, since any increase per pound to use HSLA-V steel is directly

offset by the fact that less steel is used. All in all, HSLA-V steels

represent a great overall value to the Army.

EXPANSION OF THE USE OF HIGH STRENGTH, LOW ALLOY

STEELS

All HSLA steels, including HSLA-V steels, are not new materials,

though they remain underutilized. This is primarily an education

challenge. Engineering designers throughout the Army’s acquisition

community need to be made aware of the availability and properties

of HSLA steel products. The vanadium industry has recently

launched a database of products available from many steel producers online at www.hsla-v.org. This database provides engineers with

HSLA steel options and product forms both with and without vanadium additions.

Full acceptance within standard-setting societies is another barrier to HSLA implementation that must be addressed. Current efforts

are underway to expand the use of HSLA steels in established professional design guidelines from the American Concrete Institute

(ACI) and the Steel Joist Institute (SJI). Additionally, recent changes

to the American Society for the Testing of Materials (ASTM) grades

of rebar (ASTM A706/706M) that include new high strength rebar

products should facilitate increasing the availability and utilization

of high strength steel products.

SUMMARY

The value that vanadium brings to steel comes from increased

strength, and that increased strength transfers directly into benefits

for the Army too. The Army acquisition community must press for

more value from all of the materials used in Army materiel. Since

steel is a big part of today’s Army, improving the value of all the steel

that the Army continues to procure should be a priority. This is

where HSLA-V and other HSLA steels can play a vital role.

REFERENCES

[1] An Experimental Study of the Behavior of Trusses Fabricated with HighStrength Low-Alloy Microalloyed Vanadium Steel, Ron Mayes, Simpson

Gumpertz & Heger Inc. Technical Report for work performed under cooperative agreement DAAD 19-03-2-0036 with the US Army Research

Laboratory, 17 October 2008

[2] Vanadium Rebar Case Study, Beverly P. DiPaolo, Bradley W. Foust,

Edward F. O’Neil, Photios Papados, and Stanley C. Woodson Technical

Report for work performed under Cooperative Research and Development

Agreement (CRADA-04-GSL-02) U.S. Army Corps of Engineers,

Engineer Research and Development Center, Vicksburg, MS

[3] Use Of Vanadium High-Strenght Low-Alloy Steels in Trailers, Jan Eckerlid,

Mikael Åsell, and Anders Ohlsson, The Steel Company Tunnplåt,

Borlänge, Sweden, 2004

Figure 2. The use of HSLA-V steels in tactical trailer applications can reduce weight by up to 21% compared to conventional steels.

Dr. John H. Beatty received his bachelor’s degree in Mechanics from the Johns Hopkins University in 1984 and his PhD in Materials Science

from the University of Virginia in 1988. Since receiving his doctorate, Dr. Beatty has continually served the US Army, both as a commissioned

officer and as a Department of Defense civilian for 23 years. Currently, he works for the Weapons and Materials Research Directorate of the US

Army Research Laboratory at Aberdeen Proving Ground, where he is the Acting Division Chief of the Materials and Manufacturing Science

Division. He serves in various capacities for the Army Environmental Quality Technology program, Army and DoD Corrosion Programs, the DoD

Strategic Environmental Research and Development Program (SERDP) and the Environmental Security Technology Certification Program (ESTCP)

technical panels for Weapons and Platforms. His research has included studies on metallic armor, adiabatic shear, and corrosion/erosion problems of US Army Materiel. Dr. Beatty has published over 40 technical articles and presented his work more than 100 times at related conferences

and technical symposia.
The AMMTIAC Quarterly, Volume 6, Number 2 5 http://ammtiac.alionscience.com

Direct metal deposition (DMD) is an advanced additive manufacturing technology that enables repair and rebuild of worn/damaged

components, as well as manufacture of new components. The technology is an extension of rapid prototyping, however, in contrast to

most rapid prototyping processes, DMD produces fully dense,

functional metal parts. Parts are made directly from the computeraided design (CAD) drawing by depositing metal powder pixelby-pixel utilizing laser melting and a patented closed-loop control

system to maintain dimension and quality).[1] The same process is

extended for remanufacturing of damaged components, such as

gas turbine blades and stator vanes (see Figure 1).[2, 3] Besides

remanufacturing, DMD can build wear-resistant coatings and

other features on complex, high-value components. With its closedloop feedback system and six-axis deposition capability, DMD can

coat and rebuild parts with a very complex geometry.[4] This article presents an overview of the DMD process and a few case studies

involving remanufacturing of used parts, as well as manufacturing

of new parts. It also discusses benefit of such technology insertion

in DoD.

PROCESS OVERVIEW

Direct metal deposition is a proprietary laser aided manufacturing

(LAM) process that originated at the University of Michigan and is

being further developed and commercialized. Although LAM has

played a key role for repair of aerospace components for more than

a decade, DMD provides a major advancement of the technology.

The preliminary work on

direct metal deposition of

aluminum has been demonstrated to provide metal

properties equivalent to

those of wrought material,

thus making it potentially

useful for the direct fabrication of parts.[1] Since then,

the technology has been advanced significantly and has been applied

to a wide range of alloys and components.

An industrial laser beam under computer numerical control

(CNC) is focused onto a workpiece, producing a melt pool. A small

amount of powdered metal is injected into the melt pool, building

up the part in a thin layer. The beam follows a toolpath generated

based on the CAD data, tracing out the part layer by layer.

DMD machines are equipped with a three or five-axis head with

an additional rotary axis on the work table that allows deposition of

almost any geometry. Large DMD workstations have been developed for hardfacing and repair of large components, dies, and

molds. Smaller and more compact machines are available for building or cladding smaller parts and pursuing materials research, (see

Figure 2). Recently, a robot-based system, shown in Figure 2 has

been developed, enabling repair/cladding applications in the field.

Bhaskar Dutta

Shiva Palaniswami

Joohyun Choi

Jyoti Mazumder

The POM Group, Inc.

Auburn Hills, MI

Figure 1. Component remanufacturing using DMD process.

Figure 2. (a) Robotic

DMD system, and (b)

compact DMD system.
The AMMTIAC Quarterly, Volume 6, Number 2 6 http://ammtiac.alionscience.com

Some of the main features of the system include:

• Co-axial nozzle design gives full five-axis deposition capability

versus side powder-feed systems, which can only deposit linearly

in motion along with local shielding by inert gases

• “Moving optics” capability allows processing of large, heavy parts

• Patented closed-loop optical feedback system monitors and controls the melt pool in real time, resulting in a near net shape

part[6]

• Proprietary tool path software translates CAD data into the nozzle motion for six-axis deposition

• Multiple powder delivery system allows deposition of different

materials simultaneously or consecutively at specified locations,

enabling production of on-the-fly alloys/composites

• Deposits are fully dense and create a true metallurgical bond with

the substrate/part. DMD has been used successfully on a broad

range of materials, including, tool steels, stainless steels, high

speed steels, and alloys of nickel, cobalt, titanium, aluminum, and

copper.

• Multi-functional software for normal production jobs and for

research and development activities

• Inert chamber atmosphere for deposition of reactive materials,

such as titanium, tantalum, molybdenum, etc.

Feedback System

The DMD closed loop feedback system is the key tool for producing a near net-shape product. The system consists of high-speed

sensors with optics looking at the melt pool (see Figure 3). The

sensors collect the melt pool image, which is then directly fed into

a dedicated controller. The controller extracts the melt pool

dimensional data from this signal.

A software algorithm processes the data, and controls the laser

power in order to maintain a consistent melt pool. Tight control of

the laser power means tight control of the layer thickness, and this

results in the near net shape of the final product. The feedback system also allows control of heat input by controlling melt pool

dimensions. This in turn leads to minimal heat-affected zone and a

better microstructure with superior properties.

Deposition Software

Six-axis deposition software (DMDCAM) for additive manufacturing builds a CAM tool path directly from CAD data. It includes an

integrated direct metal deposition database with process recipes as a

part of the software. Contour, surface, and volume deposition paths

are provided in three dimensions, and multi-layer deposition paths

can be prepared in a single operation.

Simulation and collision-detection modules are included for a

“Ready to Use” deposition path. They detect any possible collision

of the processing head and the part while creating the deposition

tool path. The modules enable the user to search for alternate tool

path strategies.

Vision System

The vision system has been developed for deposition on small parts

with fine features, such as turbine blades. When a part is placed on

the machine table, cameras take an image of the area of deposition

and the image coordinates are translated to machine coordinates.

This eliminates manual part pick-up, which is practically impossible for very small components with fine features. Intermittent imaging can even allow inspection and adjustment of tool paths for

required part geometry.

The vision software also has in-built tool pathing capability

that allows direct-deposition path creation from the acquired

image for simpler geometries. This is particularly useful for

remanufacturing applications in which CAD data of a damaged or

worn out part is no longer available. Figure 4 shows an example of

a turbine blade image taken by the vision system. This was followed by an automatic edge detection and subsequent tool path

generation with or without offsetting the edge, as required by the

user. Vision system software is capable of having different processing parameters at different points, as shown in Figure 4. This is

Figure 3. Schematic showing closed loop feedback system.

Figure 4. Left: Demonstration of DMD vision system capability, Right: As deposited turbine blade squealer tip in DMD system.

Final Focus Optics

To Powder Feeder

Laser Beam

Nozzle Shielding Gas

Workholding Fixture

Feedback Sensor 1

Substrate or Die Preform

Solid Free Form

Shape by Direct

Deposition

Feedback

Sensor 2

Blade Picture

Modify blade profile and

set point process parameter

(Development mode)

Automatic NC file

generation with

point wise process data
The AMMTIAC Quarterly, Volume 6, Number 2 7 http://ammtiac.alionscience.com

critical for components with vast geometry variations, such as turbine blades in which the trailing edge can be very thin compared

to the rest of the component.

DMD MATERIALS

As-deposited material is fully dense, and its mechanical and physical properties can be as good as or better than those of comparable cast or wrought materials. Table 1 shows tensile and hardness

data of some typical materials, such as IN625, Stellite 31, and

Ti-6Al-4V. The table compares DMD materials with wrought or

cast materials. Note that the DMD materials can be fully stressrelieved, heat-treated, and aged to alter the microstructures for

specific applications and to improve ductility or toughness.

DMD has been successfully applied in a wide range of materials

including, various, steels, Ni-alloys, Co-alloys, Ti-alloys, Alalloys, Cu-alloys, refractory metals, such as Ta, and cermets (i.e.,

metal-ceramic composites).

APPLICATIONS

DMD is suitable for a broad range of applications covering industries from defense to aerospace, from automotive to oil and gas,

from injection molding to medical, from tool and die to

mining/construction. Examples of applications, include:

• Repair and restoration of expensive components, such as, gas

turbine components

• Building of near net shape parts/features for new part fabrication, such as aerospace components, medical components, etc.

• Wear or corrosion resistant coatings on parts/dies/tools etc. for

longer life

• Conformal cooling for higher productivity in plastic injection

molding/die casting

• Tool reconfiguration for engineering changes to production

tooling

REMANUFACTURING

One of the areas best suited for DMD is remanufacturing of worn

out and/or damaged components. DMD can rebuild worn out or

corroded surfaces by adding the same or similar metal to the damaged part. The concentrated heat of the laser source limits the size

of the heat affected zone (HAZ) and minimizes microstructural

damage of the parent part. This ensures that the integrity of the

repaired part is good.

Damaged turbine components including, blades/vanes, bearings, seals, bearing housing are great candidates for DMD repair.

The DMD vision system plays a significant role in remanufacturing of the worn out turbine vanes. Easy and precision part pickup

helps in reliable and rapid remanufacturing of these high value

components. Closed-loop feed back system controls the heat

input into the part, and results in a quality product that requires

minimal post grinding. Figure 5 shows the cross-section

microstructures of the DMD area of a repaired turbine blade.

Excellent process control leads to a fully dense microstructure, as

observed in the vertical cross-section along with a small heat

affected zone.

DMD can also be used to repair cracked components. Figure 6

shows a case study of a large casting from a stamping press that

developed cracks upon extended service due to constant fatigue

loading of the component. The cracked area was machined to

Figure 6. Large component remanufacturing using DMD. Right

bottom shows a cracked area machined back. This was filled back

using DMD deposited steel.

Figure 5. Macro (a) and microstructures (b-d) of DMD deposited

Ti-6Al4V, and (b) the clad, (c) the interface and (d) the base material.

Table 1. DMD vs. conventionally fabricated nickel, cobalt, and titanium alloys.

Material Condition Tensile Yield Elongation, Hardness,

Strength, Strength, % HRC

MPa MPa

IN 625 DMD As deposited 795 598 14 13

IN 625 Wrought 927°C Annealed 897 483 40 16

Stellite 31 DMD As deposited 1182 903 6 40

Stellite 31 Cast As cast 662 386 10 33

Ti-6Al-4V DMD As deposited 1163 1071 8 38

Ti-6Al4V (V) Wrought Annealed 950 880 14 36

(a)

(c)

(d)

1 mm

20 μm

20 μm

200 μm

HAZ 300 μm

(b)
remove the crack completely, rebuilt

using DMD process, and re-machined

to final specification. The component

has been back in service and performing

successfully. A significant cost saving

was obtained due to high value and long

lead time of the new castings. This

demonstrates the ability of DMD to

repair and remanufacture large components without sacrificing their

integrity.

Figure 7 shows microstructure

and mechanical properties of

DMD deposited 4340 steel for

such a component. A metallurgical bond with no defects and a

short heat affected zone (HAZ)

are observed in the microstructure (see Figure 7a). As a result of

fast cooling during DMD, the

cladding exhibits a martensitic structure.

Figure 7(b) shows tensile properties of

the as deposited material and compares

it with the substrate 4340 steel. Results

show that the DMD material is substantially stronger than the wrought 4340

steel. To estimate the strength of a DMD

repaired component, a sample was prepared in which half of the material was

4340 wrought steel and half of the sample was built using DMD. This sample

exhibits similar strength as wrought

4340 steel. Fracture surface investigation

also shows that failure occurred through

wrought 4340 steel. These data conclusively prove that the DMD repaired

material has excellent strength and can

be successfully used for remanufacturing

applications.

FREE FORM FABRICATION

Very intricate and complex features and

parts that contain such features are possible with DMD. An example of this is

shown in Figure 8, in which a mirror

housing (see Figure 8a) was built from

scratch under a NASA sponsored project. The closed-loop feedback control

system allowed uniform build-up with

no intermediate machining step.

The part was conventionally built

from a solid piece of metal by electrodischarge machining (EDM), which is a

slow process that generates a significant

amount of waste. Figure 8(b) compares

the efficiency of the DMD and EDM

processes in terms of material, energy,

and time. Clearly, DMD requires only

about a third as much material as EDM,

and this results in a huge savings, especially for expensive aerospace materials,

such as nickel-base super alloys. In terms

of process time and energy, DMD consumes only 4% and 80%, respectively as

compared to a conventional process.

Besides its ability to build complex

geometries, DMD can build a single

part with multiple materials to provide

functional properties at different segments/surfaces of a part.

Multiple hopper capability of

DMD systems makes this feasible, and easy while maintaining

productivity.

BENEFITS TO DOD

Maintaining battle readiness for

the armored vehicles, fighter

jets, naval vessels, while managing inventory costs has been a

constant challenge for the DoD. Long

lead-times and high costs of procuring,

inventorying and transporting replacement parts has resulted in a reduction of

equipment readiness rates, while DoD

operation and support costs have

increased. Insertion of additive manufacturing technologies, such as DMD can

benefit the DoD. DMD can either

remanufacture damaged parts, or replace

them by creating new parts from CAD

data. Field deployable DMD systems that

can be carried with mobile Army units or

Aircraft carriers and used for spare part

manufacturing have been built.

Ground vehicles, such as tanks and

automobiles, have numerous parts that

undergo extensive wear and tear due to

the aggressive operational environment.

The components are expensive, and spare

parts are sometimes in limited supply or

not available. In order to maintain the

force readiness, it is essential to have the

parts replaced as needed. In case of the

Navy, the severe sea water corrosion is the

main cause for damage and failure of

submarine or other vessel components.

DMD has been applied successfully to

salvage some of these damaged parts, and

it has been demonstrated that a proper

insertion of such a technology can effect

significant savings for the Navy. For the

Air Force stringent safety requirements

demand that remanufactured parts are as

good as new, or better. DMD has the

capability of meeting these challenges

due to its superior process control as

compared to other open loop processes.

The AMMTIAC Quarterly, Volume 6, Number 2 8 http://ammtiac.alionscience.com

Figure 8. (a) A mirror housing built by DMD

process. (b) Comparison of DMD and EDM

process efficiency for building the housing.

100%

90%

80%

70%

60%

50%

40%

30%

20%

10%

0%

EDM

DMD

Process Process Process

Volume Time Energy

(a)

(b)

Figure 7. (a) Microstructure of laser deposited

4340 steel, and (b) tensile properties of DMD

4340 steel, wrought 4340 steel for comparison,

and a sample with half wrought 4340 and half

DMD 4340 steel.

100 μm
The AMMTIAC Quarterly, Volume 6, Number 2 9 http://ammtiac.alionscience.com

To comment on this article, email: ammtiac@alionscience.com

Dr. Bhaskar Dutta, Chief Operations Officer of POM Group, has a M.E. and a Ph.D in Metallurgical Engineering. He has more than 20 years

of experience in academia and industry. Dr. Dutta has more than 40 technical publications.

Shiva Palaniswami is the Vice President Business Development at POM Group. He has a M.S. in Mechanical Engineering and a Masters in

Business Administration, with 20 years of experience in the manufacturing industry.

Dr. Joohyun Choi is the Director Engineering at POM. He has a M.S. and a Ph.D in Mechanical Engineering. Dr. Choi has more than 25 years

experience in additive manufacturing and laser processing, both in academia and industry.

Dr. Jyoti Mazumder is the Chief Executive Officer of POM Group and Robert H. Lurie Professor of Mechanical Engineering in the University of

Michigan. He is one of the founders of the POM Group and inventor of Closed Loop Direct Metal Deposition technology. Dr. Mazumder has a

D.I.C. and a Ph.D. in Metallurgy. He has more than 325 technical papers, co-authored 2 books, edited 9 books and awarded 16 patents, all in

the field of laser materials processing.

DMD-based part restoration practice will also offer the DoD an

opportunity to demonstrate its commitment for more environmentally friendly processes. DoD depots currently use a chrome plating

process to refurbish damaged components. This process produces

hexavalent chromium as a by-product, which is a well-known carcinogen. The DoD is undergoing an effort to minimize this process.

An additive manufacturing technology, such as DMD, can offer an

alternative to the use of hexavalent chromium. Moreover, the additive nature of DMD technology leads to material and energy savings

compared to a subtractive machining process.

DMD technology can be used to improve wear, corrosion,

fatigue resistance, and other mechanical properties of expensive

DoD components. Based on the damage pattern of high cost DoD

components, selective deposition can be applied on new parts to

obtain significant life enhancement in these critical parts. This can

lead to improved vehicles and armor components.

REFERENCES

[1] Koch, J. L., and J. Mazumder, “Rapid Prototyping by Laser Cladding,”

ICALEO (ed. by P. Denney, I. Miyamoto and B. L. Mordike), Vol. 77,

1993, pp. 556-565.

[2] Gao J., J. Folkes, O. Yilmaz, and N. Gindy, “Investigation of a 3D

Noncontact Measurement Based Blade Repair Integration System,” Aircraft

Engineering & Aerospace Technology, Vol. 77, No 1, pp 34-41.

[3] Dutta B., H. Natu, and J. Mazumder, “Near Net Shape Repair and

Remanufacturing of High Value Components Using DMD,” TMS Annual

Conference, February 2009.

[4] Dutta B., “Surface Modification by Direct Metal Deposition Process:

Technical Challenges, Opportunities and Performance Benefits,” Proc. Mat

Sci.Tech., October 2008.

[5] Koch J. and J. Mazumder, US Patent #6,122,564.

AMMTIAC Success Story

Diversifying The Energy Supply:

The DoD Energy Handbook

The Department of Defense (DoD) faces the challenge of reducing its total

energy footprint by minimizing its dependence on traditional fuels, enacting

greater operating efficiencies, and turning more to renewable energy

sources; all while decreasing operating costs and lessening environmental

impact. A great deal of information on renewable and alternative energy

technologies already exists, but is scattered through a number of disparate

sources. What is required is a one-stop reference that provides both the

guidance and technical information necessary to assess and formulate power and

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The AMMTIAC Quarterly, Volume 6, Number 2 10 http://ammtiac.alionscience.com

INTRODUCTION

Corrosion is a gradual and cumulative process that leads to shortterm maintenance and long-term system reliability problems. Too

often the deleterious effects of corrosion affect critical weapon systems platforms, particularly those located in areas of high relative

humidity (RH). Humidity plays a critical role in forming and accelerating the rate at which corrosion progresses. Nonetheless, it has

been well documented that the corrosion of metals can be prevented by reducing the RH to a level below 45%.[1]

To achieve reduced humidity levels in the field, the US Army

has deployed fixed and mobile dehumidification (DH) units.[2] Although the system

documentation claims that these systems

effectively reduce the humidity level, measuring their effectiveness has proven difficult. As a result, wireless sensors were

developed for the Army Aviation and

Missile Command’s (AMCOM) Corrosion

Program Office (CPO) using Small

Business Innovation Research funding.

The developed sensors provide a method

for validating DH technologies since they

are able to measure and record temperature

and humidity data over time, record the

data on board, and transmit the data when

queried by the developed software. This

article details the successful use of wireless

sensors for the validation of dehumidification units deployed to

the field.

Wireless sensors have been deployed to Hunter Army Airfield

(HAAF) and Kadena Air Base, Okinawa, Japan, to validate the

effectiveness of the already present DH units. These two locations

are well known for their corrosive environments. At HAAF, a fixed

DH unit is being used for the gross area dehumidification of a storage facility that houses critical aviation components. The DH unit

employed here has been operating since mid-2008. At Kadena Air

Base, the 1-1 Air Defense Artillery (ADA) utilizes mobile DH units

to control humidity when radar systems undergo maintenance or

are placed in storage. Figure 1 shows a self-contained DH unit connected to a PATRIOT radar system at this location.

DEHUMIDIFICATION THEORY AND TECHNOLOGIES

Dehumidification technologies seek to eliminate the corrosion of

metal surfaces by reducing the amount of water in the air and ultimately preventing the atmospheric conditions that form condensation. The formation of water (condensation) on a surface is a complex thermodynamic process that occurs when moist air is cooled, at

constant pressure, to its dew point temperature* (Tdp).[4] When the

temperature of a regular thermometer (drybulb temperature (Tdb)) is the same as the

Tdp the air is said to be saturated. In other

words, the relative humidity is 100%.

Although condensation readily occurs when

the RH is near 100%, the surface structure,

surface temperature, atmospheric pressure,

and atmospheric impurities (pollutants) can

cause water to condense on a surface at a

humidity level below 100%.[5]

Atmospheric pollutants such as chlorides

from marine environments and sulfur dioxide (SO2) from volcanic activity and industrial power production magnify the corrosive

properties of an electrolyte. Evidence indicates that these pollutants can produce an

electrolyte between 35 and 60% RH.

Atmospheric humidity levels are commonly reduced by mechanical refrigeration. This method cools the atmospheric air to its dew

point, removing water via condensation. This process requires a

substantial energy input and is most efficient when the required

humidity level is 50% RH or higher. Even though this process produces cool, comfortable air that is adequate for most residential and

commercial applications, it is insufficient for corrosion prevention

and control.

For applications where the only requirement is that the RH be

below 45%, with no cool air requirement, desiccant dehumidification systems are most efficient. This is the best choice for military

Steven Harrigan, PE

US Army Aviation and Missile Command, Corrosion Program Office

Redstone Arsenal, AL

Figure 1. A desiccant DH unit connected to

a PATRIOT radar system at Kadena Air Base.

These DH units are intended to increase the

mean time between failures (MTBF) and to

provide savings in material and labor costs.

The three most common forms of corrosion are general corrosion, concentration cell and galvanic corrosion. In all cases, corrosion can be reduced by controlling the amount of electrolyte

present.

General corrosion (also known as uniform corrosion) is the decay of a metal surface in the presence of an electrolyte such as standing water.

Concentration cell corrosion occurs when two or more areas of a metal surface are in contact with different concentrations of the same solution. The electrolytic solution causes the interface between two metals (faying surface) to corrode.

Galvanic corrosion occurs when two dissimilar metals are electrically coupled in the presence of an electrolyte.[3]
The AMMTIAC Quarterly, Volume 6, Number 2 11 http://ammtiac.alionscience.com

equipment since the water is removed directly from the air and energy is not wasted cooling it. As a result, these systems lower annual

operating costs.

Although a significant emphasis has been placed on humidity, it

alone cannot describe the amount of water vapor in air. To define

this a parameter known as the humidity ratio (W) is required.[4]

Rarely, however, are both parameters specified when reading

requirements. The humidity ratio, calculated using Equation 1, is

the mass ratio of water vapor to dry air, expressed in grains of water

per pound of dry air (7000 grains = 1 pound). This parameter can

also be calculated using the partial pressure of water vapor in the air

or through the use of a psychrometric chart. Table 1 illustrates the

effect of increasing atmospheric temperature on the water content

of air at a fixed relative humidity. The data in this table validate the

claim that humidity alone cannot accurately describe the amount of

water vapor in air.

Equation 1

WIRELESS SENSOR DEVELOPMENT AND VALIDATION

The acquisition of data from the dehumidification space is required

to determine the effectiveness of DH technologies. Although adequate weather data exists for virtually every military installation in

the US and overseas, localized data in and around the installed

equipment is often unavailable. To overcome this barrier, wireless

sensors were developed (as shown in Figure 2).

The sensor (also known as a mote) is composed of a low-power

Wi-Fi (802.11 wireless standard) radio, a flash memory chip, an

antenna, and sensors that record both temperature and humidity

data. The self-contained device is powered by a single lithiumhydride (LiH) battery that has an estimated life of more than three

years. The mote is similar in size to a deck of cards and, when sensing at a rate of once per minute, can store approximately six months

worth of data. This wireless system can be configured to store and

forward data to a portable laptop computer via a wireless router and

can be configured to operate through a broadband cell card with

continuous monitoring through a web-based application. The data

are accessible to users from any web portal via a secure login.

Laboratory Testing and Data Analysis

Laboratory testing was conducted by the Corrosion

Program Office (CPO) using several motes, to confirm

their capabilities for accurately detecting, storing, and

transmiting temperature and humidity data. During

testing, the motes were subjected to temperature and

humidity variations from 14°F to 140°F (-10°C to

60°C) and 25% to 85% RH, respectively. The motes

were set to record data at one minute intervals and tested in an environmental chamber for approximately 48

hours. This data acquisition rate is equivalent to 30 days

using 15 minute sensing intervals, or 120 days sensing every hour.

This test was within the manufacturers specified storage capacity of

10 days, with 60 second sensing periods. The resulting temperature

and humidity data are shown in Tables 2 and 3, respectively.

The temperature data, shown in Table 2, are consistent with the

chamber’s settings. Since the chamber has a tolerance of +/- 9°F, all

mote temperature readings are within the chamber’s tolerance. The

humidity data in Table 3 show standard deviations greater than

those calculated from the temperature data.This difference is a direct

result of the large fluctuations in the wet bulb temperature readings

within the chamber, which indicates that the chamber had reached

its operational mechanical limit. Refrigeration and heating were

occurring simultaneously at the various humidity settings. Overall,

the data confirm the motes’ ability to accurately detect, record, and

transmit data, thus providing a practical method for obtaining temperature and humidity data from the dehumidification space.

DEHUMIDIFICATION UNIT VALIDATION

Hunter Army Airfield

Test Set-Up & Data Collection

A 96,000 cubic foot parts storage warehouse at Hunter Army

Airfield, Savannah, Georgia, was selected for the installation and

testing of a desiccant DH system since it stores high value critical

W= ––– mw

ma

Table 1. The effect of temperature on the water content of air under fixed humidity

conditions.

Temperature Relative Humidity Ratio Location

°F (Tdb) Humidity (%) (grains of water/

pound dry air)

50 40 22 Yuma, AZ, January 2009

65 40 37 Huntsville, AL, March 2009

85 40 72 Washington, DC, April 2009

100 40 117 Abu Dhabi, July 2009

Table 2. Temperature data collected by the motes during their validation testing.

Chamber Motes Average Motes Standard Remarks

Temperature (μ) Deviation

Setting °F ( )

140 140 0.38 5 motes tested, aggregate

figures (1000 data points)

77 78 0.30 5 motes tested, aggregate

figures (1000 data points)

14 16 0.68 4 motes tested, aggregate

figures (800 data points)

Table 3. Humidity data collected by the motes during their validation

testing.

Chamber Motes Average Motes Standard Remarks

Humidity (μ) Deviation

Setting (%RH)† ( )

85 86 5.29 5 motes tested, aggregate

figures (1000 data points)

65 68 13.46 5 motes tested, aggregate

figures (1000 data points)

45 53 8.70 5 motes tested, aggregate

figures (1000 data points)

25 32 3.50 5 motes tested, aggregate

figures (1000 data points)

Figure 2. The wireless

sensor designed to aid

in DH unit validation.

† Based on temperature difference as humidity is controlled by wet bulb temperature.
The AMMTIAC Quarterly, Volume 6, Number 2 12 http://ammtiac.alionscience.com

aviation components, and is subject to extreme temperature and

humidity conditions. At this location, the relative humidity exceeds

45% for approximately 89% of the year, resulting in an estimated

7,796 hours of required dehumidification per annum.[6] The

HCUc-6020AAD DH unit was installed in the warehouse to maintain 75°F (Tdb), 45% RH conditions. In addition, a small computer, wireless access point, and broadband cell card were installed to

enable continuous access to the World Wide Web.

Data Collection

Two motes were placed within the warehouse, while a third mote

was placed outside the facility. The outdoor mote readings closely

resembled the National Weather Service data for HAAF.[7] The

mote data that were obtained outside the storage facility are shown

in Figure 3 for the period from 15 November 2009 to 4 May 2010.

Figure 4 presents the mote data that were obtained from within the

climate controlled storage facility over the same period. Figure 4

demonstrates the DH unit’s effectiveness in reducing the RH to a

level below 45% and maintaining a fairly consistent 75°F dry-bulb

temperature. Table 4 lists the average internal and external temperature and humidity for each month throughout the data collection

period. This data was used to calculate the humidity ratio.

Data Analysis

Rather than relying upon a subjective evaluation of the data, statistical hypothesis testing was used to compare the monthly humidity

ratios using the paired t-test.[8] Statistical hypothesis testing is an

experimental, data-based methodology that aids in the decision

making process assuming the data follow a normal distribution.[9]

To perform a statistical hypothesis test, null and alternative

hypothesis statements must be created to compare two different

variables The standard null and alternate hypotheses statements are

shown in Equations 2 and 3, respectively. For the statistical test carried out in this work, μ1 represents the average monthly external

humidity ratio and μ2 represents the average monthly internal

humidity ratio.

H0: μ1=μ2 Equation 2

H1: μ1 μ2 Equation 3

To test the hypothesis, a test statistic must be calculated and

then used to reject or fail to reject the null hypothesis. This computational approach requires a p-value, which denotes the critical

or rejection region. The p-value is the smallest level of significance

that would lead to rejection of H0. Stated another way, any p-value

less than 0.05 (p<0.05) results in a rejection of the null hypothesis.

Figure 3. The mote data obtained outside the HAAF parts storage

facility from 15 November 2009 - 4 May 2010.

Dec 2009 Jan 2010 Feb 2010 Mar 2010 Apr 2010 May 2010

Time

100

95

90

85

80

75

70

65

60

55

50

45

40

35

30

25

20

15

10

5

0

80

75

70

65

60

55

50

45

40

35

30

25

20

15

10

5

0

Humidity [%]

Temperature [°F]

Humidity Temperature

Figure 4. The mote data obtained from within the storage facility at

HAAF as recorded from 15 November 2009 - 4 May 2010.

Dec 2009 Jan 2010 Feb 2010 Mar 2010 Apr 2010 May 2010

Time

52.5

50.0

47.5

45.0

42.5

40.0

37.5

35.0

32.5

30.0

27.5

25.0

22.5

20.0

17.5

15.0

12.5

10.0

7.5

5.0

2.5

0.0

80

75

70

65

60

55

50

45

40

35

30

25

20

15

10

5

0

Humidity [%]

Temperature [°F]

Humidity Temperature

Table 4. Psychrometrics by month at HAAF.

Month Year External Internal External Internal External Internal Difference in

Temperature Temperature Relative Relative Humidity Humidity Humidity

(°F) (°F) Humidity Humidity Ratio (W) Ratio (W) Ratio (W)

(% RH) (% RH) (grains/lb) (grains/lb) (%)

July 2009 81 76 *76 39 121.8 52.6 -56.8

August 2009 81 76 *76 41 121.8 55.5 -54.4

September 2009 77 76 *74 41 103.6 54.5 -47.4

October 2009 72 74 43 42 50.7 53.1 4.7

November 2009 59 73 76 43 57.5 51.9 -9.7

December 2009 55 69 76 40 49.3 42.8 -13.2

January 2010 49 75 67 29 34.9 37.8 8.3

February 2010 49 77 67 27 35.1 37.5 6.8

March 2010 58 76 66 33 47.7 44.1 -7.5

April 2010 69 76 68 38 72.2 50.0 -30.7

May 2010 76 77 75 40 102.6 54.7 -46.

Average 66 75 69 38 72.5 48.6 -33.0
The AMMTIAC Quarterly, Volume 6, Number 2 13 http://ammtiac.alionscience.com

For this report, the null hypothesis is that no difference exists

between the humidity ratio outside the dehumidified space and the

humidity ratio within the dehumidified space. This is shown by

setting the two variables equal to one another as in Equation 2.

To satisfy the assumption that the test data follow a normal

distribution, normality tests were performed on both the internal

and external humidity ratios using statistical software. Upon completion, it was determined that the data followed a normal distribution. The p-value was then calculated to be 0.020.

Since this value was less than 0.05 the null hypothesis that there

is no difference between the external and internal humidity ratio

was rejected. Therefore, the data infer that the dehumidification

technology installed at HAAF is effective at reducing the relative

humidity, and water vapor in the air, to the desired level.

Testing at Kadena Air Base

Test Set-Up & Data Collection

The 1-1 ADA at Kadena Air Base, Japan is utilizing DH units on

their PATRIOT Missile Defense Systems when removed from the

field for maintenance. Kadena Air Base is located on the tropical

island of Okinawa, Japan where the annual daytime temperatures

average between 68 and 90°F (Tdb); the relative humidity is typically above 69%. The PATRIOT Missile Defense Systems have a number of critical electronics and are often subject to elevated numbers

of corrosion-related problems at this location. Since continual readiness of this defense system is of great importance, it was an excellent

candidate for DH testing. Testing was conducted using PROTEC

Model 150 Desiccant Dehumidifiers.

Temperature and humidity data were collected within and outside the radar shelters using the motes, a laptop computer (with

installed software), and a USB-powered wireless router. Since the

system is battery-powered, it did not require any external support.

The testing lasted 3 days, beginning 26 October 2009 and ending

29 October 2009. The sensors were turned on at approximately

1430 hrs local time on 26 October 2009 and allowed to gather data

while the DH unit was turned off to establish the baseline conditions. The DH unit was turned on at approximately 2040 hrs local

time on 27 October 2009 and turned off at approximately 0640 hrs

local time on 28 October 2009. The monitoring continued until 29

October 2009.

The local weather station data (International Civil Aviation

Organization indicator RODN) for Kadena Air Base, Figure 5,

show a relatively constant humidity ratio on a day to day basis.

Meanwhile, the temperature increases as the humidity decreases,

and vice versa. The increased humidity ratio on 26 October was the

result of two rain events that occurred at about 1400 and 1900 hrs.

The temperature, humidity, and humidity ratio data for the sensors placed outside the radar system are shown in Figure 6; this data

closely resembles the weather data in Figure 5. The average value

data from the five sensors placed within the radar shelter are shown

in Figure 7. Tables 5 and 6 show the differences in the ambient conditions between each of the sensor locations at the start of the testing and in the ambient conditions at the point of the lowest humidity ratio reading within the shelter (28 October 2009 at 0550 hrs),

respectively.

Data Analysis

The collected data reveal insignificant differences between the temperature readings, but significant differences in both the relative

humidity and the humidity ratio. To assess the significance of the

relative humidity and humidity ratio differences statistical hypothesis testing was utilized. The null and alternative hypotheses were the

same as those used to assess the HAAF data. In this case, the data

were compared by hour during dehumidification to determine

whether differences did in fact exist.

Normality testing was conducted to determine if the paired ttest could be used. In this instance, it was determined that the data

did not follow a normal distribution, requiring the use of an alterFigure 5. Local weather data collected near Kadena Air Base, Japan. native method for non-normal data. The method used was the

1400hrs 0000hrs 1000hrs 2000hrs 0600hrs 1600hrs 0200hrs

 26 Oct 27 Oct 28 Oct 29 Oct

100

90

80

70

60

50

40 Temp (°F)

RH (%)

W (grains H2O/lb dry air)

Variable

Day

DH On @ 2040hrs DH Off @ 0640hrs

Figure 6. Sensor readings from outside the radar shelter.

1400hrs 0000hrs 1000hrs 2000hrs 0600hrs 1600hrs 0200hrs

 26 Oct 27 Oct 28 Oct 29 Oct

100

90

80

70

60

50

40 Temp (°F)

RH (%)

Variable

Day

DH On @ 2040hrs DH Off @ 0640hrs

W (grains H2O/lb dry air)

Figure 7. Average of the sensor data collected from within the radar

shelter.

1400hrs 0000hrs 1000hrs 2000hrs 0600hrs 1600hrs 0200hrs

 26 Oct 27 Oct 28 Oct 29 Oct

100

90

80

70

60

50

40

30

Temp (°F)

RH (%)

Variable

Day

DH On @ 2040hrs DH Off @ 0640hrs

W (grains H2O/lb dry air)
The AMMTIAC Quarterly, Volume 6, Number 2 14 http://ammtiac.alionscience.com

Kruskal-Wallis test.[10] Using this method, the p-value was calculated to be 0.000.

This p-value strongly suggests the rejection of the null hypothesis. Therefore, it is inferred that the dehumidification technology is

effective at reducing water vapor in radar shelters.

CONCLUSIONS

Sensor technologies were used to verify the effectiveness of dehumidification technologies using statistical hypothesis testing. The

desiccant dehumidification units employed at Hunter Army Airfield

and Kadena Air Base effectively reduced the relative humidity to

levels below 45% RH, as required. With the reductions in humidity provided by these DH systems, it is expected that the corrosionrelated costs will decrease.

RECOMMENDATIONS

It is recommended that a dry-bulb temperature be included

when specifying criteria for environmental operating and storage

conditions for military resources as proper moisture control is

dependent on both temperature and humidity. In addition, future

demonstration and validation efforts of DH technologies should

require temperature and humidity measurements for at least oneyear to allow for the inclusion of seasonal effects. By analyzing

seasonal changes, it may be possible to determine periods in which

DH technologies may not be required.

It is further recommended that an investigation of the ambient

pollutants be conducted since it is known that the critical humidity level varies with the material under attack (e.g., iron, copper,

aluminum, etc.), and with the type of pollutant (e.g., sulfide,

chloride, nitride, etc.). Local environmental data could be combined with the known atmospheric data to create a comprehensive

pollutant database algorithm and, subsequently, a corrosion forecasting model.

REFERENCES

*Sensor data was not available; therefore, this information is based on the

historical average.

[1] Van Droffelaar, H., and J.T.N. Atkinson, Corrosion and its Control: An

Introduction to the Subject, 2nd Edition, NACE International, 1995.

[2] Cocoon, Inc., “Dehumidification,” http://cocoon-inc.com/products/

dehumidification/, accessed 21 January 2010.

[3] Korb, L.J., and D.L. Olson, “ASM Handbook, Volume 13: Corrosion,”

ASM International, Fifth Printing, March 1996.

[4] Lindeburg, M. R., Mechanical Engineering Reference Manual for the PE

Exam, 10th Edition, Professional Publications, Inc., 1998.

[5] Jones, D.A., “Principles and Prevention of Corrosion,” 2nd Edition,

Prentice Hall, 1996.

[6] PROTEC Project #3056, Summer–Fall 2007, PROTEC, Inc (now

DBA Cocoon Inc.)

[7] National Oceanic and Atmospheric Administration, “National Weather

Service,” http://www.weather.gov/, accessed 4 May 2010.

[8] “Paired Difference Test,” http://en.wikipedia.org/wiki/Paired_

difference_test, accessed 7 June 2010.

[9] Montgomery, D.C., Design and Analysis of Experiments, 6th Edition,

John Wiley and Sons, 2005.

[10] Rice, J.A., Mathematical Statistics and Data Analysis, 2nd Edition,

Wadsworth Inc., 1995.

To comment on this article, email: ammtiac@alionscience.com

Table 5. The initial conditions at the test start of the Kadena Air Base

testing.

Variable RODN External Internal Percent Difference

Sensor Sensors (greatest and least)

Relative Humidity (%) 61 65 68 10

Temperature (°F) 81 80 80 1

Humidity Ratio

(grains of water/lb 97 100 105 8

of dry air)

Table 6. Ambient conditions within the radar shelter at the minimum

humidity ratio.

Variable RODN External Internal Percent Difference

Sensor Sensors (greatest and least)

Relative Humidity (%) 60 74 35 -53

Temperature (°F) 72 66 70 6

Humidity Ratio

(grains of water/lb 72 71 51 -28

of dry air)
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