About the Cover: An F-15 aircraft fades off to the left of its future replacement, the F-22 Raptor. The image not only represents the transition of fighter power, but it also represents the advancement of materials and manufacturing technology and the progression toward making composites more widely used on aircraft.

This past year, the C-141 Starlifter was retired from service bythe US Air Force. This storied cargo aircraft flew missions thatnot only spanned the globe, but also spanned many decades

and several generations. Likely themost famous C-141, which was best-known as the “Hanoi Taxi”, was thelast Starlifter to be retired from serv-

ice. At the end of the Vietnam War in 1973, this aircraft – tailnumber 66-0177 – flew several missions to Hanoi in NorthVietnam where it picked up American POWs and returnedthem to freedom on US soil. Overall, the C-141 fleet flew 51missions to Hanoi to repatriate 567 American soldiers thatwere held in North Vietnam prison camps. [1] More thanthree decades later the same “Hanoi Taxi” flew aid missions inthe aftermath of Hurricane Katrina.

The “Hanoi Taxi” was only one in a fleet of Starlifters,which over the years served many purposes and flew severalfamous missions. For instance, the Starlifter was the first jet toland in the Antarctic. It also retrieved the Apollo 11 astro-nauts after they returned from their journey to the moon. Inmore recent missions during the last months of its service, C-141s were evacuating wounded American troops from Iraqand Afghanistan.

Over the past decade the C-141 Starlifter was phased out ofservice by the Air Force, and many of its duties were takenover by the C-17 Globemaster III, which was entered intoservice in June 1993. As newer systems replace older ones,technological advances become much more apparent. Assuch, the progression of materials technology can be observedas newer aircraft are phased into service to replace older air-craft. For example, the C-141 was entered into service in1964 and was built with a primary airframe structure com-posed of high strength aluminum and steel alloys (mostly7075-T6, 7079-T6, and 4340 steel).[2] These structuralmaterials were joined with steel, mechanical fasteners, and theaircraft had very few composite components. The C-17 onthe other hand was manufactured with approximately 16,000pounds worth of composite parts, which are used for some of

the control surfaces and secondary structural components.[3]Although this was a step in the right direction, 16,000 poundsis a small percentage of the 277,000 pound aircraft.

It is well-established that composites can enhance the per-formance of an airframe in terms of improving the strength-to-weight ratio and the corrosion resistance. However, sincecomposites have been in development for decades, whyhaven’t they been used to a greater extent on current aircraft?Traditionally, there have been a few barriers which haveobstructed the use of composites; primarily cost and the risksassociated with using newer materials have limited the use ofcomposites in aircraft. The slow advancement of compositesfor aircraft has become even more apparent on systems newerthan the C-17.

The feature article in this issue of the AMMTIAC Quarterlyfocuses on an effort that was spearheaded by the US Air ForceResearch Laboratory to address some of the concerns relatedto the inhibited advancement of composites technology. Thearticle presents an overview of the Composites AffordabilityInitiative, which was set up to help overcome the barriers thathave hindered the transition of composites into airframestructures. Certainly the next generation cargo aircraft thatreplace the C-17 will benefit from the successes of this initia-tive. And perhaps the last Starlifter, which now resides in theNational Museum of the United States Air Force at WrightPatterson Air Force Base, will not only be a marvel for its rolein history, but will be also be a time capsule for the era of air-frames built with monolithic alloys and mechanical fasteners.

Ben CraigEditor

REFERENCES:[1] M. Novack, “The Lockheed C-141 #66-0177 The ‘Hanoi Taxi,’”American Aviation Historical Society Journal, Vol. 51, No. 3, Fall 2006, pp. 162-173.[2] L.D. Griffin and D. Latterman, “C-141A Service Experience –Materials and Processes,” SAMPE Journal, March/April 1978, pp. 9-16.[3] “C-17 Globemaster III,” GlobalSecurity.org.

Editorial: The Last Starlifter

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INTRODUCTIONIn the mid-1990’s, the Air Force Research Laboratory (AFRL) rec-ognized that despite the potential of advanced composites to drasti-cally reduce aircraft structural weights compared to conventionalmetal structures, the aircraft industry was reluctant to implementthem in new aircraft. Although composites were used on the F-15,F-16, and F-18 in small percentages, data showed that compositeapplications had reached a plateau. For example, despite early pro-jections of the F-22 airframe being 50% composite by weight, it set-tled back to 25% [1]. As a result, AFRL launched the CompositesAffordability Initiative (CAI) to address the perceived risks and bar-riers. What resulted was a team consisting of personnel from theAFRL Materials and Manufacturing Directorate (AFRL/ML) andAir Vehicles Directorate, the Office of Naval Research-ManTech,Bell Helicopter Textron, The Boeing Company, Lockheed MartinCorporation, and Northrop Grumman Corporation. Ultimately, a$152M, eleven year effort was performed to attack the problem.

What Needed to be Done?The CAI Team found that the key to affordability in compositestructures was to reduce assembly costs. State-of-the-art aircraftstructures have thousands of parts and hundreds of thousands of fas-teners (Figure 1). In addition, drilling holes and installing fasteners

has been and still is a major source of labor and rework in aircraftstructures. If the number of fasteners is reduced substantially, struc-tural assembly costs and cycle time could be drastically reduced. TheCAI team pursued part integration and structural assembly throughbonding parts together to achieve this goal. As a result, CAI’s objec-tive was to “establish the confidence to fly large integrated andbonded structures”. To meet this objective, the technical programwas structured to ensure that Department of Defense (DoD) struc-tural integrity goals were met (see Figure 2). This required a multi-disciplinary approach: maturation of materials and processes, anunderstanding of the structural behavior of bonded joints, qualityassurance and nondestructive evaluation to ensure bonded jointsremain bonded throughout an aircraft’s service life, and the approvalof DoD aircraft certification authorities.

The CAI business strategy was intended to maximize leveragingof knowledge and funding as well as improve the transition of “gamechanging” technologies. CAI was a collaborative effort among allparties, each sharing data equally for core technology efforts anddelaying data release on specific technology applications (transitiondemonstrations). The industry partners agreed to a 50% cost sharewith the government, which increased the leveraging and also creat-ed an internal company incentive to realize an acceptable return onthe investment by using the CAI technologies in their products.

Technology transition demonstration projects(“T”-programs) were also a key feature of CAI.These T-programs focused the development oflarge integrated and bonded structures technolo-gy tailored to specific needs for several DoDweapon systems. Demonstrations were per-formed for several aircraft, including the X-32(Boeing JSF prototype), F-35, X-45, and C-17. Akey feature of these T-programs was that the inte-grated product teams (IPTs) were staffed withpeople from the DoD laboratories, industrydevelopment personnel, DoD program officepersonnel, and industry program personnel.Having representatives from each type of organi-zation greatly improved the lines of communica-tion and ensured the technology being deliveredmet the needs of the customer.

http://ammtiac.alionscience.com The AMMTIAC Quarterly, Volume 1, Number 3 3

John D. RussellAir Force Research Laboratory

Materials and Manufacturing DirectorateWright-Patterson Air Force Base, OH

Figure 1. Composites Affordability Initiative’s Technical Approach.

• Reduce Part & Fastener Count• Reduce Direct & Indirect Costs

• 11,000 Metal Components• 600 Composite Components• 145,000 Fasteners

• 450 Metal Components• 200 Composite Components• 6,000 Fasteners

Today

Design for Affordability

TECHNICAL ACHIEVEMENTSIn light of CAI’s goal to “establish the confidence to fly large inte-grated and bonded structures”, the primary technology pursued forintegrated structures was Vacuum Assisted Resin Transfer Molding(VARTM). Bonding was enabled by the pi-joint bonded primarystructure design and robust manufacturing processes. These tech-nologies, along with the supporting tools and methods used to makecertification possible, are described in the following sections.

Vacuum Assisted Resin Transfer MoldingFor integrated structures, a nonautoclave process for making largeyacht hulls was transitioned to the aerospace industry. VARTM is aprocess that uses a pressure that is less than atmospheric (typicallyfull vacuum) to pull a liquid resin into a fiber bed. It was madefamous in the boatbuilding industry with the advent of theSCRIMP process (Seemann Composites Resin Infusion MoldingProcess). There are two key advantages of VARTM over convention-al autoclave curing. First is that an autoclave is not needed, unlikethe conventional processes used for fabricating composite aerospaceparts, resulting in reduced capital equipment costs. Furthermore,removing the need for the autoclave provides industry with a muchlarger supplier base for part fabrication. Second is that the typicalVARTM resins cure at a low enough temperature to enable the use

of inexpensive tooling such as medium density fiberboardrather than the typical invar tooling used for 350ºF(177ºC) curing autoclave materials. This also reduces system development costs.

While the aerospace industry dabbled in VARTM overthe years, CAI has demonstrated its viability as a valid pro-duction method for aerospace parts up to 160 ft3 (5.4 m3).As shown in Figure 3, several parts were demonstratedincluding a replica X-32 one piece cockpit tub (top left)*,a C-17-like fuselage skin with integral stiffeners (bottomleft), and a C-17 nose landing gear door (right). CAI’sVARTM efforts resulted in fiber volumes and per plythickness comparable to typical autoclave cured aerospacecomposite parts. In addition, the process worked with sev-eral resins, including EX-1510, SI-ZG-5A, and VRM-34.†

Further use of the VARTM process would be enabledthrough the development of toughened resins with prop-

erties similar to the 977-3 resin‡.Overall, VARTM has enabled reduced part counts (up to 80%),

reduced fastener counts (up to 100%), and lower part fabricationcosts as compared to conventional structures (30% to 50%). CAIhas demonstrated the VARTM process to be versatile in the parts itcan create, while achieving acceptable quality and validating itsrepeatability. VARTM is a production ready process for the aero-space industry.

Adhesively Bonded StructuresWhile bonded primary structural joints are currently in service onDoD aircraft, including the F-18 and Global Hawk, there contin-ues to be an unease in the DoD airframe certification communitywith regard to bonded structures. That community has a legitimateconcern based on past research programs intended to broaden theuse of bonded structures. The inability to discriminate between agood bond and a “kissing” bond (intimate contact between adhesiveand structure without adhesion) has been the key roadblock to fur-ther use of bonded structures. Despite this unease, bonded struc-tures have tremendous potential for aircraft structures. If designedcorrectly, bonded aircraft structures have greatly reduced part countand fastener count and also greatly reduced structural assemblytimes. The CAI attacked each barrier to increase the confidence tofly bonded primary structures.

The AMMTIAC Quarterly, Volume 1, Number 34

Figure 3. Aerospace VARTM Demonstration Parts. Figure 4. Cross Section of the Pi Joint.

Allowables

Process Scale-Up

Process Development

MaterialScreening

Material Development

Accept/RejectCriteria

• Element• Subcomponent• Repairability

• Maintainability• Reliability

• Analysis• Structural

Testing

Evaluation ofProducibility

ManufacturingMethods Development

FacilityAssess-

ment

II. Producibility: Manufacturing Scale-Up

I. StabilizedMaterials and Processes

StructuralIntegrity

V. SupportabilityIV. Predictability ofStructural Performance

III. CharacterizedMechanical Properties (Start of EMD)

Figure 2. Structural Integrity Areas.

Pi JointThe first area to be addressed was design of the bonded joint.CAI’s bonded structures work centered on the “pi” joint (Figure4); this stiffener, shaped like the Greek letter π, can be co-cured orco-bonded to the skin. The pi joint has several advantages. First, itprovides structural redundancy. The pi joint acts as two independ-ent bondlines, and the joint is stronger than a double lap shearjoint. When used with EA 9394 adhesive§, the pi joint takesadvantage of the inherent properties of the material. EA 9394 hasexcellent shear properties and performs better in shear than in ten-sion loaded bonds. It also paves the way for much reduced assem-bly times by providing a determinate assembly feature. Tensionloaded bonded structures typically have the adhesive spread overthe skins and/or spar/rib caps prior to assembly. This leads toadhesive out time** issues. They also may require several verifilmcycles to ensure the correct tolerances to get the adhesive thicknessrequired by the designer. Conversely, out time is minimal with thepi joint. It takes much less time to apply the adhesive into the cle-vis of the pi, and much less surface area is exposed to the air beforebonding takes place.

The CAI Team spent considerable energy in analyzing and veri-fying the design and manufacture of the pi joint. Testing has shownthat the joint is very robust and has predictable performance. A keyfinding from the CAI pi joint studies is that the room temperaturepaste-bonded pi joint has three to five times more strength than theco-cure joint of the pi stiffener to the skin. Thus, the pi joint willnot be the weak link in a primary structural applica-tion. It is tolerant of several defects including: thickbondlines; a canted blade; a blade skewed to one sideof the clevis; and typical manufacturing defects, such asvoids and peel plies that were not removed prior tobonding. This robustness was proved by a series of suc-cessful tests ranging from coupons to full scale airframecomponents (examples are given in Table 1).

The X-45A wing carry through and the X-45C wingwere structurally tested to design limit load, designultimate load, and finally to failure. Both articles failedjust above the predicted design ultimate load. Thesestructural and ballistic tests show that bonded struc-tures can meet structural requirements for military air-craft. In addition, these structural demonstrationsshowed that assembly times are drastically reduced. Byfilling the pi joints with adhesive rather than mating,drilling, deburring, remating, and installing fasteners,assembly times can be reduced from 50 to 80%depending on the article, translating to a cost savings of20 to 50%.

Enabling Tools for BondingBesides the validation of robust designs and manufacturing process-es, several key supporting tools and technologies had to be maturedand validated to make the application of bonded primary structuresa reality. These included more accurate analysis tools which tookinto account peel as well as shear stresses in a bonded joint, tools toevaluate damage progression, nondestructive inspection for the pro-duction and maintenance of bonded primary structures and finallyan acceptable certification approach.

Analysis ToolsConventional analysis methods for bonded joints were found to belimited in their capabilities and accuracy. For instance, A4EI, a com-puter code for bonded joint analysis, is only applicable to adhesivefailures in shear-loaded joints and does not account for peel stressesor for potential adherend failures. To date, the only alternative tothese limitations has been to develop detailed finite element modelsof a joint. This approach is time consuming and requires great skilland care by the analyst to ensure stresses and strains in critical loca-tions of the joint are properly quantified. Small errors in modelingcan lead to substantial errors in joint performance prediction.

To alleviate these problems, the CAI team implemented improve-ments to the StressCheck®†† P-version finite element software,including the incorporation of a strain invariant failure theory. TheStressCheck® tool handbook function was used to expertly modeltypical joints, thereby developing reusable joint models including:single lap shear; double lap shear; scarfed lap shear; and step lapjoints for in-plane loading; as well as a pi and back-to-back anglejoints for out-of-plane loading. These handbooks are parameterizedso that similar joints in the future can be modeled by simply updat-ing geometric parameters of the existing model. StressCheck® willthen automatically remesh the model, calculate results, check forconvergence problems in the new joint configuration, and evenpost-process the results.

Durability and Damage Tolerance Analysis MethodsUsers are also concerned about how the damage would progress inorder to understand the full impact of damage and the durability

http://ammtiac.alionscience.com The AMMTIAC Quarterly, Volume 1, Number 3 5

Table 1. Full-Scale Structural Testing of Pi-Joints.

Test Article Testing Performed

F-35 replica wing Static and ballistic tolerance(Figure 5, upper left)

F-35 replica vertical tail Static, damage and fatigue(Figure 5, upper right)

X-45A replica wing carry Staticthrough (Figure 5, lower left)

X-45 wing (Figure 5, Static, damage and fatigue lower right) (2 lifetimes)

Figure 5. Full-Scale Bonded Structure Demonstration Articles.

The AMMTIAC Quarterly, Volume 1, Number 36

Dr. John D. Russell is a Senior Materials Engineer with the Air Force Research Laboratory’s Materials and Manufacturing Direc-torate. He has a Bachelor of Chemical Engineering degree and a Master of Science degree in materials engineering fromthe University of Dayton, and a Doctor of Science degree in chemical engineering from Washington University in St Louis, Mis-souri. At AFRL, Dr. Russell began his research in the processing of advanced composite materials, and in particular, the pro-cessing of polyimide composites and dimensional control of composite parts. Since 2000, he has been the government’sprogram manager for the Composites Affordability Initiative (CAI), where he leads a consortium of aircraft manufactures toreduce the cost of composite airframes through the use of large integrated and bonded structures.

of the structural design. Software based on a novel implementationof the Virtual Crack Closure Technique (VCCT) was developedunder the CAI program and was being applied to the evaluation ofdelaminations and disbonds in composite structures after the onsetof initial failure. VCCT plays an important role by providingunprecedented capability for the design of aerospace structuresinvolving composites. Boeing has filed a patent application for thisinterface fracture analysis software and ABAQUS, Inc., will marketan enhanced version of the technology commercially.

Quality AssuranceOne major hurdle inhibiting the application of bonded primarystructures has been the lack of a nondestructive technique to assessthe strength of a bonded joint. Boeing, a CAI team member, ledthe quality assurance technology effort and has developed a laserbond inspection technique (patent pending).

High peak-power, short-pulse-length laser excitation generatesstress waves that can be used to discriminate between kissing, weak,and strong bonds in graphite-epoxy composite-to-composite bond-ed structures. The technique is able to discriminate between varia-tions in surface preparation techniques, levels of surfacecontamination and/or changes in paste adhesive mixing. In morethan 3000 laser stress wave experiments this approach has beenfound to be repeatable and reliable in the detection of weak versusstrong bonded joints. Such an approach offers a potentially costeffective method to be certain of a minimum predetermined load-carrying capability of a bonded joint after manufacture or in-serv-ice. A production floor laser bond inspection device is beingdeveloped and optimized in two Small Business InnovativeResearch programs with LSP Technologies sponsored byAFRL/ML.

CertificationThe CAI team worked with certification authorities from the AirForce, Navy and FAA to understand and eliminate the barriers toadvanced bonded structures. The CAI team prepared certificationplans for three structures, each with increasing levels of innova-tion. The plans started with a secondarily bonded rib to askin/stringer interface. Next up was a vertical tail featuring 3-D pipreforms and z-pinning‡‡. The final plan featured a bonded wingthat carried fuel with 3-D pi preforms and z-pinning. These plansincluded the use of CAI-developed analysis tools and their valida-tion, CAI-developed process controls for bonding and guidelinesfor advanced processes, as well as advanced bondline inspectiontools. These tools and technologies, along with a sound certifica-tion plan of analysis supported by test, provided the certificationauthorities with enough confidence that they believe the methodswere sound enough to certify an actual structure. This is a majorbreakthrough to realizing the cost, cycle time and durability ben-efits of advanced bonded structures.

TECHNOLOGY TRANSITIONCAI tools and technologies have transitioned across the industrialbase. AFRL is currently aware of 22 companies and organizationsbenefiting from CAI-derived technologies. Technologies includeVARTM, pi-joints, laser bond inspection, StressCheck® and crackpropagation analysis tools, and certification plans. Bonded struc-tures are flying on the F-35 AA-1. StressCheck® and crack propaga-tion analysis tools have become standard industry practices and arebeing used to design and analyze DoD and commercial aircraft. TheC-17 landing gear door (Figure 3) will be fabricated by a first tiersupplier for future C-17’s and as a preferred spare. This article onlycovers a portion of the technologies developed under CAI. Othertools include an improved cost model for composites. This costmodel is being used by over 10 organizations worldwide. A processmaturation database capturing the entire CAI database with a com-plete pedigree of processing data, environmental exposures, etc., ishosted on AMMTIAC’s National Materials Information System(NAMIS) website (https://namis.alionscience.com/CAI/). Anexhaustive set of guidelines has been prepared to provide potentialusers with clear understanding for advanced materials, designs,analysis tools, process controls, fabrication and assembly processes,quality assurance and repair. All of the CAI technologies, reportsand data are open to the DoD and DoD contractors.

SUMMARYThe Composites Affordability Initiative was a huge technical suc-cess. CAI matured technologies for large integrated and bondedcomposite structures across the fixed and rotary-wing industrialbase. Through this program technology advancements were acceler-ated and structural performance and cost effectiveness exceeded thecurrent state-of-the-art. Furthermore, technology applications areincreasing and are anticipated to continue to expand, as a result ofthis initiative.

NOTES & REFERENCE* This piece was designed/manufactured with the Boeing’s X-32/JSF con-cept in mind, but did not include all features required by the program.† EX-1510 is a cyanate ester resin; SI-ZG-5A and VRM-34 are epoxy resins.‡ 977-3 is an epoxy resin.§ EA 9394 is a structural paste adhesive.** Out time is the working life of the substance, and is an issue consideredwhen applying epoxy adhesives and composite prepregs. If they are leftexposed at room temperature for a finite time before the resin cures toomuch, they can become unusable.†† StressCheck is a registered trademark of Engineering Software Researchand Development, Inc. (ESRD).‡‡ Z-pinning is a method of orienting fiber bundles in the z-direction andplacing them through gaps in a two-dimensional fiber weave. This methodis intended to provide enhanced interlaminar strength.1. F-22 Raptor Materials and Processes, GlobalSecurity.org, http://www.globalsecurity.org/military/systems/aircraft/f-22-mp.htm.

techsolutions 2

http://ammtiac.alionscience.com The AMMTIAC Quarterly, Volume 1, Number 3

INTRODUCTIONVisual inspection is by far the most common nondestructivetesting (NDT) technique [1]. When attempting to determinethe soundness of any part or specimen for its intended application, visual inspection is normally the first step in theexamination process. Generally, almost any specimen can bevisually examined to determine the accuracy of its fabrication.For example, visual inspection can be used to determinewhether the part was fabricated to the correct size, whether the part is complete, or whether all of the parts have beenappropriately incorporated into the device. [2]

While direct visual inspection is the most common nondestructive testing technique (Figure 1), many other NDTmethods require visual intervention to interpret imagesobtained while carrying out the examination. For instance,penetrant inspection using visible red or fluorescent dye relieson the inspector’s ability to visually identify surface indications.Magnetic particle inspection falls into the same category of visible and fluorescent inspection techniques, and radiographyrelies on the interpreter’s visual judgement of the radiographicimage, which is either on film or on a video monitor. Theremainder of this article provides a summary of the visual test-ing method, which at the minimum requires visual contactwith the portion of the specimen that is being inspected.

In arriving at a definition of visual inspection, it has been

noted in the literature that experience in visual inspection anddiscussion with experienced visual inspectors revealed that thisNDT method includes more than use of the eye, but alsoincludes other sensory and cognitive processes used by inspec-tors [3]. Thus, there is now an expanded definition of visualinspection in the literature:

“Visual inspection is the process of examination and evaluation of systems and components by use of human sensory systemsaided only by mechanicalenhancements to sensoryinput as magnifiers, dentalpicks, stethoscopes, and thelike. The inspection processmay be done using suchbehaviors as looking, listen-ing, feeling, smelling, shaking, and twisting. It included a cognitive component wherein observations are correlated with knowledge of structure and with descriptionsand diagrams from service literature.” [3]

PHYSICAL PRINCIPLESThe human eye is one of mankind’s most fascinating tools. Ithas greater precision and accuracy than many of the mostsophisticated cameras. It has unique focusing capabilities andhas the ability to work in conjunction with the human brain sothat it can be trained to find specific details or characteristics in a part or test piece. It has the ability to differentiate and distinguish between colors and hues as well. The human eye iscapable of assessing many visual characteristics and identifyingvarious types of discontinuities*. The eye can perform accurateinspections to detect size, shape, color, depth, brightness, contrast, and texture. Visual testing is essentially used to detectany visible discontinuities, and in many cases, visual testingmay locate portions of a specimen that should be inspectedfurther by other NDT techniques.

Many inspection factors have been standardized so that cat-egorizing them as major and minor characteristics has becomecommon [4]. Surface finish verification of machined parts haseven been developed, and classification can be performed byvisual comparison to manufactured finish standards. In the fab-rication industry, weld size, contour, length, and inspection for

Selecting a Nondestructive Testing Method, Part II: Visual Inspection

This edition of TechSolutions is the second installment in a series dedicated to the subject of nondestructive testing. TechSolutions 1, published in Volume 1, Number 2 of the AMMTIAC Quarterly, introduced the concept of nondestructive testing and provided brief descriptions of the various nondestructive testing techniques currently available. This article continues the series and focuses in on the mostcommon nondestructive testing technique: Visual Inspection. The next TechSolutions article in this series will delve into detail about another common nondestructive testing technique: Eddy Current Testing. Once the series on nondestructive methods is complete, we will combine all of the articles into a valuable desk reference on nondestructive testing. - Editor

7

George A. MatzkaninTRI/AustinAustin, TX

Figure 1. Visual Inspection of a Torpedo Tube Aboard a NavyAttack Submarine (Photo Courtesy of the Department of Defense;Photo Taken by JO3 Corwin Colbert, USN)

The human eye is one ofmankind’s most fascinating

tools and is capable ofassessing many visual

characteristics and identifying various types

of discontinuities.

techsolutions 2

The AMMTIAC Quarterly, Volume 1, Number 38

surface discontinuities are routinely specified. Many companieshave mandated the need for qualified and certified visual weldinspection. This is the case particularly in the power industry,which requires documentation of training and qualification of the inspector. Forgings and castings are normally inspectedfor surface indications such as laps, seams, and other varioussurface conditions.

INSPECTION REQUIREMENTSRequirements for visual inspection typically pertain to thevision of the inspector; the amount of light falling on the spec-imen, which can be measured with a light meter; and whetherthe area being inspected is in anyway obstructed from view. In many cases, each of these requirements is detailed in regulatory code or other inspection criteria [2].

Mechanical and/or optical aids may be necessary to performvisual testing. Because visual inspection is so frequently used,several companies now manufacture gages to assist visualinspection examinations. Mechanical aids include: measuringrules and tapes, calipers and micrometers, squares and anglemeasuring devices, thread, pitch and thickness gages, levelgages, and plumb lines. Welding fabrication uses fillet gages todetermine the width of the weld fillet, undercut gages, anglegages, skew fillet weld gages, pit gages, contour gages, and ahost of other specialty items to ensure product quality.

At times direct observation is impossible and remote view-ing is necessary which requires the use of optical aids. Opticalaids for visual testing range from simple mirrors or magnifyingglasses to sophisticated devices, such as closed circuit televisionand coupled fiber optic scopes. The following list includesmost optical aids currently in use [2]:

• Mirrors (especially small, angled mirrors)• Magnifying glasses, eye loupes, multilens magnifiers,

measuring magnifiers• Microscopes (optical and electron)• Optical flats (for surface flatness measurement)• Borescopes and fiber optic borescopes• Optical comparators• Photographic records• Closed circuit television (CCTV) systems (alone and

coupled to borescopes/microscopes)• Machine vision systems• Positioning and transport systems (often used with

CCTV systems)• Image enhancement (computer analysis and enhancement)

Before any mechanical or optical aids are used, the specimen should be well illuminated and have a clean surface.After the eyeball examination, mechanical aids help to improvethe precision of an inspector’s vision. As specifications and tolerances become closer, calipers and micrometers becomenecessary. The variety of gages available help to determinethread sizes, gap thicknesses, angles between parts, hole depths,and weld features.

As it becomes necessary to see smaller and smaller discontinuities, the human eyes require optical aids that enableinspectors to see these tiny discontinuities. However, theincreased magnification limits the area that can be seen at onetime, and also increases the amount of time it will take to lookat the entire specimen. Mirrors let the inspector see aroundcorners or past obstructions. Combined with lenses and placedin rigid tubes, borescopes enable the inspector to see inside

specimens such as jet engines, nuclear piping and fuelbundles, and complex machinery. When the rigidborescope cannot reach the desired area, flexible bundles of optical fibers often are able to access thearea. Figure 2 shows visual inspection using a fiberoptic borescope. Some of the flexible borescopes havedevices that permit the observation end of the scopeto be moved around by a control at the eyepiece end.Some are also connected to CCTV systems so that alarge picture may be examined and the inspectionrecorded on videotape or digitally. When the videosystems are combined with computers, the images canbe improved which may allow details not observablein the original to be seen.

PRACTICAL CONSIDERATIONSVisual inspection is applicable to most surfaces, but ismost effective where the surfaces have been cleanedprior to examination, for example, any scale or loosepaint should be removed by wire brushing, etc. Visiontesting of an inspector often requires eye examinations

Figure 2. An Inspector at Tinker Air Force Base Gets a Magnified View of anEngine’s High-Pressure Turbine Area with a New Digital Fiber-OpticBorescope. (Photo Courtesy of US Air Force; Photo taken by Margo Wright)

with standard vision acuity cards such as Jaeger, Snellen, andcolor charts. Vision testing of inspectors has been in use forabout 40 years. Although many changes in NDT methods havetaken place over the years and new technologies have beendeveloped, vision testing has changed little over time. Also littlehas been done to standardize vision tests used in the industrialsector. For those seeking certification in the area of visual testing, the ASNT Level III Study Guide and Supplement onVisual and Optical Testing provides a useful reference [5].

SELECTED EXAMPLESTwo major studies of visual inspection thathave been carried out in recent years providea great deal of insight into the reliability of visual inspection. Since visual inspection isthe predominant NDT technique used forbridge inspection, the Federal HighwayAdministration (FHWA) NondestructiveEvaluation Validation Center (NDEVC) conducted a comprehensive study to examinethe reliability of the visual inspection methodfor highway bridges [6]. Performance trialswere conducted using 49 state bridge inspec-tors to provide overall measures of the accura-cy and reliability of routine and in-depthinspections. One of the objectives was tostudy the influence of several key factors inorder to provide a qualitative measure of theirinfluence on the reliability of routine and in-depth inspections. Figures 3 and 4 showroutine and in-depth inspections at a SafetyTesting and Research (STAR) facility.

Among the findings is that vision testingof inspectors is almost nonexistent, with onlytwo state respondents indicating that theirinspectors had their vision tested. From theroutine inspections it was found that theinspections were completed with significantvariability in the results. This variability was most prominent in the assignment ofcondition ratings, but was also present inexamination documentation. From the in-depth inspection tasks it was observed that in-depth inspections were unlikely tocorrectly identify many types of specific discontinuities forwhich this inspection is frequently prescribed. As an example,only 3.9 percent of weld inspections correctly identified thepresence of crack indications.

As a result of this study, it was recommended that the accuracy and reliability of both routine and in-depth inspections could be improved through increased training of inspectors in the types of discontinuities that should be identified and the methods that would frequently allow identification to be possible. Also, additional research is neededto determine whether ensuring minimum vision standardsthrough vision testing programs (with corrective lenses, if

necessary) would benefit bridge inspection. Additional detailsare fully documented in the two-volume final report [6].

In the second comprehensive study of visual inspection,experiments were performed at the Federal Aviation Adminis-tration’s (FAA’s) Aging Aircraft Nondestructive Inspection Validation Center (AANC) to provide a benchmark measure ofthe capability for visual inspection performed under conditionsthat are realistically similar to those usually found in major airline maintenance facilities [3]. More than

80 percent of inspections on large transportcategory aircraft are visual inspections. Small transport and general aviation aircraftrely on visual inspection techniques evenmore heavily than do large transport aircraft.Visual inspection, then, is the first line ofdefense for safety-related failures on aircraftand provides the least expensive and quickestmethod for assessing the condition of an aircraft and its parts [3]. Therefore, accurateand proficient visual inspection is crucial to the continued safe operation of the air fleet and it is important that its reliabilityshould be high and well-characterized. Theexperiments at the AANC were conducted ona Boeing 737 aircraft test bed, as well as on a sample library of well-characterized flaws in aircraft components or simulated compo-nents. Figure 5 shows visual inspection insidean aircraft.

Results showed substantial inspector-to-inspector variation. For example, on a specific task of looking for cracks frombeneath rivet heads, the 90 percent pro-bability of detection (percentage of cracksexpected to be detected) crack length for 11 inspectors ranged from 0.16 to 0.36 inch,with the 90 percent probability of detectioncrack length for a twelfth inspector being0.91 inch. Also noted was a high variabilityfrom one inspection task to another as performed by the same inspector. Results ofthese experiments have paved the way forother organizations to better understand theintricacies of visual inspection in developing

laboratory and field visual inspection protocol.

CONCLUSIONSDespite advances in other NDT technologies, visual inspection will likely remain the first inspection method usedin many field applications. As new mechanical and optical aids become available, the reliability of visual inspection willincrease to more acceptable levels. It is expected that additionalvisual inspection standards will be developed to provide guidance in applying visual inspection for nondestructive testing. Visual inspection will continue to be an importantNDE inspection approach that will often identify areas

http://ammtiac.alionscience.com The AMMTIAC Quarterly, Volume 1, Number 3 9

A D VA N C E D M AT E R I A L S , M A N U FA C T U R I N G A N D T E S T I N GAMMTIAC

Figure 3. Part of a RoutineBridge Visual Inspection [6].

Figure 4. Part of an In-DepthBridge Visual Inspection Using a Man-Lift [6].

Figure 5. Visual InspectionExperiment inside a Boeing 737.(Photo Courtesy of the FederalAviation Administration)

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of structures or components where more advanced NDE methods need to be applied.

REFERENCES[1] Nondestructive Testing Handbook, Volume 8: Visual and OpticalTesting, Technical Editors M.W. Allgaier and S. Ness, American Society for Nondestructive Testing, Columbus, OH, 1993.[2] F.A. Iddings, Visual Inspection, Materials Evaluation, Vol. 62, No. 5, May 2004, pp. 500-501.[3] F.W. Spencer, Visual Inspection Research Project Report on Benchmark Inspections, U.S. Department of Transportation, FederalAviation Administration, Washington, DC, 1996.[4] S. Kleven and L. Hyvarinen, Vision Testing Requirements for Indus-try, Materials Evaluation, Vol. 57, No. 8, August 1999, pp. 797-803.[5] ASNT Level III Study Guide and Supplement on Visual andOptical Testing, American Society for Nondestructive Testing, Columbus, OH, 2005.[6] Reliability of Visual Inspection for Highway Bridges, PublicationNos. FHWA-RD-01-020 and FHWA-RD-01-021, June 2001.

NOTE & GENERAL REFERENCES* In general, as described in the literature of the American Society for Nondestructive Testing, inspectors determine the presence orabsence of indications of “discontinuities”. Whether or not a discontinuity is a defect is based upon the design criteria, and is generally not up to the inspector.[1] S. Endoh, H. Tomita, H. Asada, and T. Sotozaki, “Practical Evaluation of Crack Detection Capability for Visual Inspection inJapan,” Durability and Structural Integrity of Airframes: Proceedings ofthe 17th Symposium of the International Committee on AeronauticalFatigue, June 9-11, 1993.[2] J.W. Shoonard, J.D. Gould, and LA. Miller, “Studies of VisualInspection,” Ergonomics, Volume 16, No. 4, 1993, pp. 365-379.[3] E.D. Megaw, “Factors Affecting Visual Inspection Accuracy,”Applied Ergonomics, March 1979, pp. 27-32.[4] J.N. Riley, E.P. Papadakis, and S.J. Gorton, “Availability of Training in Visual Inspection for the Air Transport Industry,” Materials Evaluation, 1996, pp.1368-1375.

Visual Inspection Summary

Discontinuity types • Cracks(e.g., what types can the method detect) • Holes

• Corrosion• Blisters• Impact damage• I.e., most discontinuities that are surface breaking or result in a

deformation at the surface

Size of discontinuities • Approximately 0.25 inches and larger

Size of system that can be inspected • Any, i.e., Large (e.g., aircraft skin), Medium (e.g., structural support), Small (e.g., electrical circuitry)

Field portable method? • Yes

Inspection restrictions • Surface areas only• Some internal and inaccessible areas can’t be inspected visually.

Inspector training (level and/or • Recommendedavailability – e.g., who provides training) • Commercial training schools available

Equipment • None• Optical aids optional except where internal surfaces require

borescopes or small television cameras, etc.

Certification required • Depends on application• Certification available through the American Society

for Nondestructive Testing (ASNT)

Relative cost of inspection • Low(i.e., compared to other methods) • Equipment cost can range from nothing to a modest price,

but this method can be labor intensive

Probability ofDetection for NDE

NDE CapabilitiesDatabook

http://ammtiac.alionscience.com The AMMTIAC Quarterly, Volume 1, Number 3 11

INTRODUCTIONThe High Temperature Polymeric Laminate Workshops (a.k.a.High Temple), which were initiated in 1982 by a Tri-Service/NASA steering group, are a series of workshops thatcover the areas of design, development and application of hightemperature reinforced polymeric composites. The primary pur-pose of High Temple is to communicate ongoing high tempera-ture polymer composite research among DoD, NASA, othergovernment agencies, industry and universities. Over the years,interdisciplinary teams were formed to advance and implementhigh temperature polymer composites in many applications,such as advanced engine and aero-structure components. Theseteams continue to make significant advances in composite relat-ed technologies, such as fiber-resin interfaces, new chemistriesthat enhance thermal oxidative stability,high temperature test methods, design-material databases, and low-cost and intel-ligent processing techniques.

In today’s world of “better, faster, cheap-er,” many long-lasting relationships, whichstarted at High Temple workshops, gener-ate technical advances and enable the pro-duction of light weight, low cost polymercomposite hardware. Many of the originalHigh Temple Workshop contributors areno longer active participants, yet the themeof High Temple remains the same. Today,government overviews of federally-spon-sored high temperature composites research serve to create anawareness in both the public and private sector. Active participa-tion from both large and small businesses report on theiradvances. Similarly, university researchers describe their effortsto advance high temperature polymer composites. Many of thesenew applications and much of the knowledge was generatedfrom key information taught at High Temple workshops. Newmonomer and polymer chemistries continue to be introduced atHigh Temple, often before they are published in peer-reviewedjournals. Newer technical subjects, such as electron beam curing,low-cost processing and coatings are some of the topics that con-tinue to make High Temple one of the premier composite tech-nical meetings.

HISTORY OF HIGH TEMPLEThe first High Temple Workshop was co-sponsored in May of1982 by the Joint Army Navy NASA Air Force (JANNAF)Structures and Mechanical Behavior and the Propulsion CostsSubcommittees and hosted by the NASA White Sands TestFacility in New Mexico. The purpose of the workshop was todetermine the state of development of high temperature poly-meric composites and to establish an understanding of futuretechnology needs and service requirements. Emphasis wasplaced on basic polymer chemistry, materials development, andmaterials applications.

The success of the initial workshop led to a second workshophosted by University of Dayton Research Institute (UDRI) and held at the Dayton Mall Holidome, in Dayton, Ohio,

December 1982. Emphasis was on theprocessibility and producibility of hightemperature polymeric composites fromboth a lamination and filament-woundapproach.

The third workshop was hosted byUDRI and held at the Dayton MallHolidome in October 1983. Emphasiswas focused on the art and science of test-ing and evaluating polymeric compositesthat are designed to be used in a temper-ature range of 600°F to 1400°F. Extensivediscussions covered the topical areas ofrequirements, material system usage cri-

teria, candidate screening tests, structural element and full-scaleverification test methods, physical and mechanical propertiestest methods, chemical characterization, and material systemacceptance criteria.

Workshops four through twenty-six were general topic work-shops covering the area of design, development, testing, andapplication of high temperature reinforced polymeric compos-ites. Presentation materials were published during the workshopsfor distribution to all attendees.

HIGH TEMPLE PROCEEDINGS DATABASEThe first effort to provide the high temperature composites com-munity with the accumulated data from the High Temple Work-

The AMMTIAC Quarterly, Volume 1, Number 312

shops began in 1996 when a High Temple Task Group publisheda list of keywords associated with the presentations previouslypresented at High Temple Workshops. In 1999, AMMTIACestablished a web-based searchable database containing all thebriefings from the High Temple Workshops. This databaseincluded an updated keyword library based on the original key-word list developed by the High Temple Task Force. This web-based database has been continuously updated after each HighTemple Workshop since inception in 1999 and is located athttp://namis.alionscience.com.

HIGH TEMPLE XXVII12-15 February 2007 Hilton Sedona Spa and Resort -Sedona, Arizona The purpose of the High Temple Workshop is to review and dis-cuss the latest technological developments in high-temperature

polymer matrix composites with the aim of providing Govern-ment and Industry with the necessary technical data to effective-ly utilize these materials in aerospace applications.

The material to be presented and discussed at the Workshopsessions may contain information covered under the Interna-tional Traffic in Arms Regulation (ITAR) or the Export Admin-istration Regulation (EAR). Because of this, attendance islimited to U.S. and Canadian citizens or registered aliens (greencard holders). Further, all non-government employees must bepreregistered with the Defense Logistics Service Center (DDForm 2345, Military Critical Technical Data Agreement).

For more information about High Temple,including registration information,

visit http://namis.alionscience.com/ or contact Mr. Dan McCray, UDRI, 937.656.6009.

TEMS Update

In Volume 1, Number 2 of the AMMTIAC Quarterly, an articleproviding an overview of the Defense Technical InformationCenter’s (DTIC’s) Total Electronic Migration System was pub-lished. Since publication of that article in October 2006, there

has been significant progress in the development of the system.As of December 2006, TEMS had approximately 111,700 full-text documents available and more than 1,016,700 citations forreference or further request.

TEMS allows DTIC users to access and search the scientific and technical knowledge base of DoD’sstate-of-the-art InformationAnalysis Centers (IACs).Through sophisticated software and search engine technology, users can locate, read, and download reports, andassemble bibliographies and indexes.

Go to http://www.dtic.mil/dtic/registration/ and follow the instructions.Once registered, visit https://tems-iac.dtic.mil/ to log in to TEMS.

To get started

Textile Preformsfor Composite Material TechnologyThis publication is the first and only one of its kind – A panoramic and thorough examination of fiber/textileperform technology and its critical rolein the development and manufacture of high-performance composite materials. This product was prepared in collaboration with Drexel Universityand authored by Dr. Frank Ko, theDirector of Drexel’s Fibrous MaterialsResearch Center. Dr. Ko is one theworld’s foremost authorities on fibrouspreforms and textile technology.

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Blast and Penetration Resistant MaterialsThis State-of-the-Art Report com-piles the recent and legacy DODunclassified data on blast and penetra-tion resistant materials (BPRM) andhow they are used in structures andarmor. Special attention was paid tonovel combinations of materials andnew, unique uses for traditional mate-rials. This report was sponsored byDr. Lewis Sloter, Staff Specialist,Materials and Structures, in the Officeof the Deputy Undersecretary ofDefense for Science & Technology.

BONUS MATERIAL: Dr. Sloter also hosted a workshopin April, 2001 (organized by AMPTIAC) for selectedexperts in the field of BPRM and its application. Theworkshop focused on novel approaches to structural pro-tection from both blast effects and penetration phenom-ena. Some areas covered are: building protection frombomb blast and fragments, vehicle protection, storage ofmunitions and containment of accidental detonations,and executive protection. The proceedings of this work-shop are included with purchase of the above.

Order Code: AMPT-26 Price: $115 US, $150 Non-US

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P RP R O D U C T SO D U C T SOur complete product catalog is available online athttp://ammtiac.alionscience.com/products

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National Materials Information System (NAMIS)NAMIS is a compilation of high-value materials information featuring:

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PACE 2007, Paint and Coatings Expo02/11/07 - 02/14/07Dallas, TXContact: Annette S. DeLorenzoCMP; DirectorPACE Meetings and Expositions537 Stanton-Christiana Rd, Suite 111Newark, DE 19713 Phone: 302.998.6550Fax: 302.234.4608Email: delorenzo@pace2006.comWeb Link: www.pace2007.com

2007 Army Corrosion Summit02/13/2007 - 02/15/2007Clearwater Beach, FLContact: Claire LesinskiConcurrent Technologies Corporation7935 114th AveLargo, FL 33773-5026Phone: 727.549.7013Fax: 727.549.7010Email: lesinskc@ctc.comWeb Link: http://www.armycorrosion.com/

U.S.Air Force T&E Days02/13/2007 - 2/15/2007Destin, FLContact: Customer ServiceAmerican Inst. of Aeronautics and Astronautics1801 Alexander Bell Dr, Suite 500Reston, VA 20191-4344Phone: 703.264.7500Fax: 703.264.7551Email: custserv@aiaa.orgWeb Link: www.aiaa.org

TMS 2007 136th Annual Meeting and Exhibition02/25/07 - 03/01/07Orlando, FLContact: TMS Meeting Services420 Commonwealth DrWarrendale, PA 15086Phone: 724.776.9000 x243Fax: 724.776.3770Email: mtgserv@tms.orgWeb Link: www.tms.org/AnnualMeeting.html

uv.eb WEST 200703/06/07 - 03/07/07Los Angeles, CAContact: Mickey FortuneRadTech - The Association for UV & EB Technology6935 Wisconsin Ave, Suite 207Chevy Chase, MD 20815Phone: 240.497.1243Fax: 240.209.2337Email: mickeyfortune@jangomail.comWeb Link: www.uvebwest.com

Components for Military and SpaceElectronics Conference & Exhibition(11th International CMSE Conference)03/12/07 - 03/15/07Los Angeles, CAContact: Leon HamiterComponents Technology, Inc.904 Bob Wallace Ave., Suite 117Huntsville, AL 35801 Phone: 256.536.1304 Fax: 256.539.8477Email: lhamiter@cti-us.com Web Link: www.cti-us.com/

SPIE Smart Structures and Materials &Nondestructive Evaluation and HealthMonitoring 14th International Symposium03/18/07 - 03/22/07San Diego, CAContact: The International Society for Optical EngineeringPO Box 10Bellingham, WA 98227-0010Phone: 360.676.3290Fax: 360.647.1445Email: spie@spie.orgWeb Link: www.spie.org

3rd International Conference and Exhibition on Device Packaging3/19/2007 - 3/22/2007Scottsdale, AZIMAPS-International Microelectronics and Packaging Society611 2nd St, N.E.Washington, D.C. 20002Phone: 202.548.4001Fax: 202.548.6115Email: imaps@imaps.orgWeb Link: www.imaps.org/devicepackaging

38th Structures and Mechanical Behavior Subcommittee, 25th RocketNozzle Technology Subcommittee,and 16th Nondestructive EvaluationSubcommittee Joint Meeting03/20/07 - 03/22/07Newport, RIContact: Debra S. EgglestonThe Johns Hopkins University, CPIAC10630 Little Patuxent Pkwy, Suite 202Columbia, MD 21044-3204Phone: 410.992.7300Fax: 410.730.4969Email: dse@jhu.edu

2007 Air Force Corrosion Conference04/06/2007 - 04/09/2007Macon, GAContact: Beverly DillardPhone: 478.926.0558Email: afrlmls.olr.scorr@robins.af.milWeb Link: http://afcpo.com/

Aging Aircraft 200704/16/07 - 04/19/07Palm Springs, CAContact: J. JennewineUniversal Technology Corporation1270 North Fairfield Rd Dayton, OH 45432 Phone: 937.426.2808Fax: 937.426.8755Email: jjennewine@utcdayton.comWeb Link: www.agingaircraft.utcdayton.com

AIAA/ASME/ASCE/AHS/ASC Structures,Structural Dynamics, and MaterialsConference4/23/07 – 4/26/07Honolulu, HawaiiContact: American Institute of Aeronautics and Astronautics, Inc.1801 Alexander Bell Dr, Suite 500Reston, VA 20191-4344Phone: 703.264.7500Fax: 703.264.7551Email: custserv@aiaa.orgWeb Link: www.aiaa.org

IMAPS/ACerS 3rd International Conference and Exhibition on Ceramic Interconnect and CeramicMicrosystems Technologies (CICMT)4/23/07 – 4/26/07Denver, ColoradoContact: IMAPS-International Microelectronics & Packaging Society611 2nd St, N.E.Washington, D.C. 20002Phone: 202.548.4001Fax: 202.548.6115Email: imaps@imaps.orgWeb Link: www.imaps.org

International Conference on Metallurgical Coatings and Thin Films 4/23/07 – 4/27/07San Diego, CAContact: Mary S. GraySuite 136, 14001-C Saint Germain DrCentreville, VA 20121Phone: 703.233.3287Email: icmctf@mindspring.com Web Link: www.tms.org/Meetings/Meeting.asp

AISTech 2007 05/07/07 – 05/10/07Indianapolis, IN.Contact: Association for Iron & Steel Technology186 Thorn Hill RdWarrendale, PA 15086-7528Phone: 724.776.6040Web Link: www.aist.org

Mark Your Calendar

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AMMTIAC DirectoryTECHNICAL MANAGER/CORDr. Lewis E. Sloter IIAssociate Director, Materials & StructuresODUSD(S&T)/Weapons Systems1777 North Kent Street, Ste 9030Arlington, VA 22209-2110(703) 588-7400, Fax: (703) 696-2230Email: lewis.sloter@osd.mil

DEFENSE TECHNICAL INFORMATION CENTER

(DTIC) POCMelinda Rozga, DTIC-I8725 John J. Kingman Road, Ste 0944Ft. Belvoir, VA 22060-6218(703) 767-9122, Fax: (703) 767-9119Email: mrozga@dtic.mil

AMMTIAC DIRECTOR (ACTING)Christian E. Grethlein, P.E.201 Mill StreetRome, NY 13440-6916(315) 339-7009, Fax: (315) 339-7107Email: cgrethlein@alionscience.com

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