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2007-2008 Assessment of the Army Research Laboratory 7 Weapons and Materials Research Directorate INTRODUCTION The Army Research Laboratory’s (ARL’s) Weapons and Materials Research Directorate (WMRD) was reviewed by the Panel on Armor and Armaments of the Army Research Laboratory Technical Assessment Board (ARLTAB) at Aberdeen Proving Ground, Maryland, during June 5-7, 2007, and July 15-17, 2008. The theme of the 2007 review was materials research performed in the directorate; the 2008 review was related to research and development (R&D) performed in the lethality and survivability areas. CHANGES SINCE THE PREVIOUS REVIEW In prior years, the Board had commented that the Weapons and Materials Research Directorate had not appeared to be striking an appropriate balance between experiment and computational efforts, with too little emphasis on computational and modeling areas. However, during this assessment period the panel was briefed on the full scope of WMRD’s programs, and it appears that the balance has improved considerably. A new effort, systems effective modeling (SEM), reviewed for the first time, holds promise. SEM is intended to provide ARL-WMRD with a systematic approach for evaluating the usefulness of existing and new weapons systems during design and development stages. As an example, SEM was applied to the development of a 7.62 mm lead-free round, and its application is accelerating the deployment of lead-free rounds that will provide the same or improved lethality. In its general application, SEM promotes the development of simulation and modeling tools and a series of experimental studies to test the validity of these tools. In an iterative process, the simulation and modeling tools are refined to the point that designers have confidence in the predictions resulting from these models. This is a crucial set of steps, which all modeling efforts should seek to emulate. SEM is an excellent tool that provides a methodology through which to incorporate modeling and simulation productively and thereby to accelerate and reduce the costs associated with design and deployment. It is an essential capability that
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2007-2008 Assessment of the Army Research Laboratory should be expanded to other ARL programs. As an example, SEM might have a profound impact on the programs involving quantum chemical modeling by combining modeling efforts with the problem of identifying experimental programs that will serve to validate and instill confidence in the models. Also newly presented was the development of the Novel Energetic Research Facility (NERF), which led to the development of DEMN, an explosive fill. This effort demonstrates a continued paradigm shift from looking for one magic explosive material to using calculations and experience to suggest a mixture of materials providing tailor-made performance. During the 2006 review, the panel learned of a new program—Soft Tissue Physics and Applications—and offered numerous suggestions for its improvement. During the 2008 review, it was obvious that WMRD had taken those suggestions to heart, and the group is to be commended for its successful effort in refocusing the program, which addresses a national defense priority and now seems to be going in the right direction. The understanding of munitions-induced trauma is of high importance in the design of armor, in the design of armaments (e.g., to reduce the risk of collateral damage to noncombatants), in the design and delivery of effective treatment of the wounded, and in the training of medical personnel. Blunt trauma and traumatic brain injury (TBI) have very high profiles with the public and the Congress; hence, WMRD’s efforts in modeling blast loading are timely. ACCOMPLISHMENTS AND ADVANCEMENTS Materials A very important element of the materials effort in WMRD is the formation of several Materials Centers of Excellence (MCoEs) in which the scientific input of academia is melded with the technology-driven, warfighter-focused programs at ARL. Currently, five MCoEs are being funded—at the Johns Hopkins University, Rutgers University, the University of Delaware, Virginia Polytechnic Institute and State University (Virginia Tech), and Drexel University. Some of their contributions include the following: (1) work on developing phase diagrams for glassy grain boundary phases in grain boundary engineered boron carbide—necessary for improving the consistency of armor protection of this very lightweight ceramic armor; (2) development of magnesium (Mg) as a lightweight metallic armor; (3) nanocrystalline tungsten (W) to replace depleted uranium (DU); and (4) nanocrystalline aluminum having the strength of steel but one-third the density. In addition to their scientific input, the MCoEs have been the source of a number of summer postdoctoral researchers, some of whom have stayed on as staff members. Metals The Microscale Compressive Properties of Metallic Glasses project, undertaken in collaboration with the Johns Hopkins University MCoE, explores new microcompression techniques as a method of assessing the properties of metallic glasses. The goal is to measure physical properties of microconstituents to compare with bulk measurements and to inform the models of metallic glasses and composites in the future. This tie to modeling work was not highlighted by WMRD, but it seems to be the only practical use for the results of this work. Extreme care needs to be taken so that experimental variations (notably alignment) do not dominate the observed results. WMRD is encouraged to leverage these measurements with its multiscale modeling interests, because only through linking the micromechanics to larger length scales can it be hoped that the research described will provide new engineering tools of relevance to Army needs. As this technique continues to be developed and tied to single-crystal and multiscale
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2007-2008 Assessment of the Army Research Laboratory constitutive modeling, in particular at Wright-Patterson Air Force Base, WMRD should seek its own unique niche in the leveraging of this technique to underpin improved science and technology needed to address Army needs. Composites Composite materials continue to play an important role in the Army mission in areas of lethality and survivability. Among the various materials-related research activities within WMRD, those focused on composites appear to be among the strongest. The work on transparent composites, which are needed for use in both combat and tactical vehicles, is particularly impressive. Faceplates, vehicular armor, and different grades of ballistically resistant composites were described, but some discussion regarding the scratch resistance of these transparent materials would have been useful. A significant amount of work has been performed on spinels with Technology Assessment and Transfer, Inc., a Small Business Innovation Research (SBIR) contractor. Large plates about 12 inches square were being produced, and a Department of Defense (DoD) Manufacturing Technology/Cooperative Research and Development Agreement (CRADA) program is being pursued to expand these dimensions to handle windshields and other applications for both the Army and the Air Force. Most current projects are strongly driven by and responsive to the near-term needs of the Army. All appear to have good potential for significant payoff. Many of these projects are Army-specific and would not likely be addressed within other organizations, reaffirming the need to maintain internal expertise in the area. The corresponding MCoE at the University of Delaware is well integrated with the ARL effort and continues to make strong contributions. The composites activity has benefited from a solid group of young, bright, energetic individuals. Evidently, recruitment efforts have met with good success. These efforts should be continued. In addition, in order to retain these individuals and maintain internal expertise in the long run, management should take an active role to ensure that its scientists reach their full intellectual potential. This includes encouraging them to publish the more fundamental work in peer-reviewed journals and providing them with the necessary time and resources; promoting interaction with the broader scientific community through participation in conferences and workshops; and helping them establish collaborations with recognized experts in their fields of work, not only with the MCoE but also other institutions. Transparent Composites The work here emphasized the need to create transparent composites for use in both combat and tactical vehicles. The efforts ranged from making transparent polyurethanes to introducing nanoporous polymers in glass matrices to achieve transparency. The work described was focused toward an immediate Army need and was more in the 6.2 than the 6.1 category. Most of the work described involved empirical experimental approaches based on pure materials selection principles and did not involve any predictive modeling. Residual stress was shown to play a major role in the transparency of the product produced. Approaches using chromophores were minimally successful and should be continued further, as there appeared to be some possibilities for success. A poster on this topic was very comprehensive and much more elaborate and addressed many of the difficult but solvable issues. Electromagnetic Gun Rail Wear The problem of rail wear has been worked on for more than 20 years within the DoD. The novelty of the work described here is in the use of novel materials for substrates and the use of cold spray coatings to reduce the wear and erosion during firing. (Cold spray is a relatively new technique that has been developed within ARL in the past 2 years.) Efforts are being made to deposit tungsten coated with copper to improve the wear behavior. In addition, efforts are being
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2007-2008 Assessment of the Army Research Laboratory planned with tantalum (Ta) and molybdenum (Mo) coated powders so that higher temperatures can be withstood (repeated shots) during firing. However, heat extraction rapidly between firings may become a rate (firing)-limiting step, since many of the materials do not exhibit the excellent thermal conductivity of copper. Additionally, elevated temperature exposure may also result in oxidation of the Ta and the Mo, resulting in wear debris that may be more catastrophic than the base materials. Thermal expansion issues are also very difficult to address in this application, and the rate of heating and cooling may dictate the overall life of the barrel and its effectiveness in target accuracy. This work is empirical and experimental in nature, which is probably justified because modeling these conditions, which are dynamic under firing, is difficult without certain specific start and end data points. Work in this area is of direct relevance to the Army’s desires to produce the next electromagnetic (EM) gun. However, considering the numerous challenges involved, it would appear that this is in the category of a long-term program that may generate a significant amount of information that may eventually lead to the actual fielding of an EM gun. Coordination of this effort with the Navy and the Missile Defense Agency should be encouraged, so that a number of the lessons learned can be captured, documented, and retained for the newer generation of staff dealing with research on this topic. Electromagnetic Rail Gun Composites The project on EM rail gun composites involves the design, materials selection, and construction methods employed in the construction of a prototype rail gun. This project highlighted a variety of complementary techniques used effectively in parallel, including finite element simulations of mechanics and electromagnetics, experimental measurements both in situ and ex situ during the firing of the gun, and empirical design of composites. The flavor of this project is clearly on the empirical side, but it uses state-of-the-art diagnostics and analysis. This project stands out as a prime example of materials technologies transitioning into applications of great relevance to the Army. Ceramics The focus of the WMRD work on ceramics is on trying to develop sintering methods for B4C that are reproducible from batch to batch and also concurrently provide repeatable ballistic performance. Sintering of B4C has not changed in more than 20 years, and much of the current product has been performing less than satisfactorily in the field. The recent discovery of shear banding and amorphization in B4C led to an urgent quest to understand the behavior of these materials at very high strain rates. Grain boundary engineering approaches have been tried on metals for many years, and there has been some extensive modeling that has accompanied heat treatment of materials to improve hardness as well as to improve resistance to effects like hydrogen embrittlement. ARL’s approach is focused on creating a glassy intergranular phase that could wet the grain boundaries and assist in promoting preferred fracture pathways. The materials that are being tried are mostly those that form glassy phases, especially the yttrium aluminum borates. This work may contribute to some good understanding of the interrelationship between the fracture paths and the ballistic behavior. One area that has not yet been addressed is the importance of incoming powder qualities (particle size distribution, particle shape, purity, and vendor variability) of the boron carbide itself as well as the additives. More attention should be placed on these powder characteristics and their effects, perhaps through using a round-robin or other comparison matrix techniques. Modeling is vital for supporting these experimental approaches to microstructure/properties behavior. While glassy grain boundary phases have been effective in some ceramic materials systems (for example, alumina), they have not been effective in others (for example, titanium diboride), and detailed modeling to understand the relationship between
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2007-2008 Assessment of the Army Research Laboratory microstructure and observed failure mechanisms is vital information needed for improving structure/property relationships in the future. The development of phase diagrams for any new grain boundary materials will be important, including careful examination of the effects of unreacted carbon and oxygen content on reaction rates and products. Polymers Polymeric materials are an important investment area, and their support clearly needs to be continued. In general, this program is doing very well, and it has been recently invigorated through the recent starts of two MCoEs. Perhaps a Multidisciplinary University Research Initiative (MURI) Broad Agency Announcement in this area would be warranted in order to spread the investments across national leaders in the field. Many of the WMRD briefings were delivered by postdoctoral researchers. This is a plus in that it shows the success of the personnel development strategy being pursued by this program and by WMRD in general. However, it could be a potential negative if it is indicative that the majority of the 6.1 research is being performed solely by the junior researchers. It is understandable that more senior personnel are involved with 6.2 to 6.4 category research and the transitions to the engineering scale-up of the new technology. Senior personnel need to retain a role in the 6.1 research so that they maintain sufficient knowledge of the cutting edge as well as contribute as mentors to the more junior staff and postdoctoral researchers. The polymer area appears somewhat unique in that it has a strong computational component to support and guide the research. However, the computational polymer science work appears to have been used only to confirm the experimental results. It is suggested that an extension of this effort is needed if the end goal of developing physically based predictive capability is to be achieved. In particular, there needs to be a clear infrastructure for maintaining models, both with respect to their parameterization and their validated regimes. The projects involved with the design of polymeric materials and nano-engineered additives in order to control morphology and segregation are also a strong component of the research effort and clearly of high merit. The two Materials Centers of Excellence (MCoE) involved in the polymers area are discussed below. Materials Center of Excellence—Virginia Tech Because the Virginia Tech MCoE program has been operational less than 1 year, it was difficult to assess. It appears to have a good commitment to outreach and collaboration and is focused on Army needs. This MCoE supports an extensive list of research programs, which in some cases are quite mature. However, the presented research appeared to have been performed using leveraged support provided by other agencies. The research actually supported by ARL’s MCoE needs to be articulated, and clear milestones should be established. Without this, it is at present nearly impossible to determine the impact of MCoE funding on the research at Virginia Tech. The topic of impact resistance of polymers was a particularly potent example of the critical need of integrating a strong modeling component into the program if chemistry, formulation, and mechanical behavior are to be linked in a predictive sense. With regard to the program’s computational effort, it appears that several investigators are active in this regard, but this was not elucidated in the presentation. Materials Center of Excellence—Drexel University Because this program has also been operational less than 1 year, it too was difficult to assess. However a few salient points were evident. The program
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2007-2008 Assessment of the Army Research Laboratory contains promising proposed linkages of synthesis, design, and multiscale modeling and simulation. The list of faculty appears to be dominated by the primary principal investigator (PI) working in conjunction with a few younger PIs. While the PIs are clearly skilled, it was unclear how their various research topics/targets work together with each other. The effort in the computational component needs to be strengthened because it currently contains only one PI involved with only one of the nine research topics. The use of subcontracts to add more expertise could be considered. The center shows good promise as a means of promoting the interaction of graduate students and postdoctoral researchers with ARL. The annual funding level of $500,000 covers nine distinct research topics. This level of support is far too low to expect serious research accomplishments across the several topics. The program needs to focus on a small number of scientific topics encompassing high leverage to WMRD programs and Army needs. Computational Polymer Science The program in computational polymer science is developing a multi-scaled modeling effort that makes use of available software in a standard fashion. The efforts here are the only evidence of serious computational work within this program. The work involves a number of models that span a large range of length and time scales. It is troubling that only one person appears to be working in this effort, because it will likely take a larger commitment to succeed. Some of the work is first rate—for example, the use of density functional theory (DFT) to design chromophores. This program profits from the close interaction between synthetic and computational chemists and from the comparative ease with which the theoretical results can be interrogated experimentally. Much of the modeling at mesoscopic length scales beyond the quantum level is assumed—but not verified—to be correct through the calculation of various macroscale physical properties, for example density. Rigorous experimental interrogation of models should be built into the program as milestones. The integration of these models in the coarse-graining direction seemed ad hoc, and a coarse-graining strategy was not described. This leaves open the possibility that successes are accidental and that one might draw poor conclusions when tackling new areas. The information flow in inverting the coarse-grained projection from large scales to small scales was not addressed or even acknowledged as necessary. This is not entirely surprising, because it is difficult to do well, and few people work in that area. The University of North Carolina may be a valuable resource to tap. That said, the computational polymer science effort is important and should be encouraged in a number of ways. First, there is need to support optimizing these models on available high-performance architectures. Second, this effort appeared to be something of a one-man show. The success of this enterprise hinges on its ability to answer technical problems in a timely fashion (i.e., fast relative to experiment). To do this well and often, simultaneous efforts at parameter tuning, model verification, integration, and system validation are required. To do this on an ongoing basis requires more than one person or a small group. This may call for an unusually large commitment, from the ARL perspective, yet it is necessary for success. Recent Advances in Selectively Permeable Membranes The work in selectively permeable membranes is a good technologically driven effort that could be aided by science-based rationale. For example, one needs to uncover the chemical mechanism through which barium ions operate to improve selectivity. Is it simply a size effect, or are there more subtle aspects to the phenomenon? The science base can, in part, be supported by computation, but only if augmented by carefully defined experiments. This process will prove to be time-intensive but should result in a long-term payoff.
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2007-2008 Assessment of the Army Research Laboratory Nano-Engineered Additives with Self-Stratifying Characteristics Self-stratification of reactive materials on the surface of polymer films supports the desire to achieve spontaneous decontamination of the surface. Two rather clever approaches were presented to control segregation in a composite matrix. The first is a method in which ligands are attached to gold and silicon dioxide particles. The free end of the ligand is designed to undergo a Diels-Alder reaction. This thermally reversible reaction is used to tune the properties of the matrix and the location of the particles by migration. The increased concentration of particles at the surface affords the opportunity to enhance the reactivity, control defects, and change the morphology of the film. The second approach is the use of functionalized hyper-branched polymers to segregate at the surface. By functionalizing the end groups with quat salts, biguanides, alkanolamines, or N-halamines, selective degradation of biological and chemical agents can be achieved. Both of these projects are creative ideas with some potential applications both within and outside the Army. Analysis of Adhesively Bonded Ceramics The study analyzing adhesively bonded ceramics successfully demonstrated that the toughness of alumina/epoxy bonds is enhanced by grit-blasting the alumina prior to bonding. Additionally, the strength of the alumina substrates is not appreciably degraded, despite the surface roughening and the potential for generation of strength-limiting flaws. These results should provide useful guidance for fabricators of armor systems. The presentation clearly suggested that the principal motivation of this research was to provide industrial guidance in support of Future Combat Systems (FCS) and to provide the basis for techniques for quality assurance. The toughness enhancement appears to be the result of blasting-induced surface roughness and the ensuing mechanical interlocking of the epoxy with the alumina during bonding. The effects may be anomalously high in the test configuration used to make this assessment. That is, in the asymmetric wedge test, the crack tip stress field contains a significant mode II component. This component is likely to be largely shielded from the crack tip when crack tortuosity is high. Efforts to measure the mode I toughness may prove useful, since this mode invariably yields the lowest value (relative to those for mixed mode I/II cracks) and is less strongly influenced by roughness. It is understood that finite element modeling (FEM) of the asymmetric wedge test is currently underway in the Survivability program, and WMRD should continue such an effort to facilitate future predictive capability in support of complex composite armor design and testing. Surface Modification of Ultra High Molecular Weight Polyethylene (UHMWPE) This program is examining how the strength and durability of glass-reinforced composites can be improved through manipulation of the texturing of the fiber surface. Enhancement of the strength and energy absorption of the fiber-matrix interface is a critical research area for both glass and polymeric fibers. The atmospheric plasma treatment of both UHMWPE films and fibers clearly suggested potential for improvement, based on oxidation of the surface and its beneficial effects on fiber bonding. Similarly, the plasma treatment and its effects on wettability when silica is deposited on UHMWPE fibers clearly indicate improved adhesion and improved mechanical properties. There are clear signs of scientifically inspired approaches to improving the engineering properties of UHMWPE in composite applications, but WMRD should examine previous R&D on strength/wear/friction research in the biomaterials literature following the use of plasma modification of UHMWPE in implant applications and the use of surface modification.
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2007-2008 Assessment of the Army Research Laboratory Lethality Affordable Precision Munitions The Affordable Precision Munitions program is an outstanding achievement for WMRD. In this program a multidisciplinary design approach is being applied to the development of small, compact, guided munitions. The multidisciplinary approach employs such novel features as the following: (1) virtual wind tunnel tests and virtual fly-outs that allow a much larger range of designs to be explored at a much lower cost than would be the case for real wind tunnel tests; both significantly and surprisingly, results have been achieved in terms of nose and body interactions, jet interactions, and diverter interactions that have permitted avoidance of unstable designs; (2) clever use of piezoelectric actuators that provide guidance control; and (3) even though the Global Positioning System would seem to be the first choice for guidance, some out-of-the-box thinking suggested that in this case space constraints and battery-drain considerations would be better accommodated using magnetometers to provide guidance information. Scalable Technology for Adaptive Response A new-start research effort that shows considerable promise is that of Scalable Technology for Adaptive Response (STAR), which examines the development of weapons that can be tailored to deliver a spectrum of weapons effects, including different yields, controlled fragmentation, selectable fragmentation, and behind-armor and threat effects. The program objective of pursuing the development of single munitions capable of addressing multiple mission capabilities rather than requiring a spectrum of munitions in-theater is an innovative and rational goal. The STAR program entails a synthesis of expertise in shock physics, manufacturing technology development, complex fusing, and selectable material response (such as is possible with shape memory materials). This project embodies a system approach to a warhead development that is to be encouraged within WMRD. Missile Propulsion Modeling WMRD’s missile propulsion modeling efforts are aimed at understanding selectable trajectory control in liquid propellant thrusters. These thrusters apply to control over in-flight projectiles. Hypergolic fuel and oxidizer mix in the combustor under conditions that allow the mix to be pumped as needed by the stage of flight. The work employs a reactive computational fluid dynamics (CFD) model that was developed primarily at ARL. The research group conducting this work has had extensive experience in modeling solid gun propellant combustion and is extending this experience to liquid propellants. On the downside, the codes seem to be very inefficient and are usable because of the massive amount of computer power available. The research group has broad collaborations with industry, universities, and other laboratories and is receiving a positive reaction from the user community. If not already done, it would be wise to review the research that the Air Force Office of Scientific Research supported in the 1980-1995 time frame in the area of instability in liquid propulsion systems. Multifunctional Warheads The program on multifunctional warheads, in its last year as currently configured, is developing a multifunctional munition in which kinetic energy (KE) and behind-armor effects and/or blast are considered. The focus is on how to harness rocket propellant to increase the engagement velocity of a
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2007-2008 Assessment of the Army Research Laboratory munition after ballistic launch against different threats by employing a detonable propellant, specifically a hard target (concrete walls or three-layer brick), and/or to allow munition-threat interaction and thereafter to use the rocket propellant to achieve increased blast and/or increased behind-armor effects. This technical approach, like ARL’s new initiatives in tunable/scalable munitions, represents a future-looking, technically challenging approach to novel munition development and is to be encouraged. A continuation of this project’s technical approach in the future by way of transition to other applications (smaller-caliber threats) and/or through a follow-on project continuing this research direction appears technically warranted and is encouraged. Military Operations on Urbanized Terrain Lethality Munitions directed at typical buildings in urban environments often penetrate walls and produce secondary fragments. These fragments can cause significant collateral damage, including the injury or death of noncombatants. The Military Operations on Urbanized Terrain Lethality program is designed to collect data from the impact of standard munitions on walls typically found in urban contexts (poured, reinforced concrete; concrete block; brick; and other materials). These data are used to inform the development of computational models for predicting the amount and distribution of fragmentation produced by selected munitions interacting with selected building materials. These models can be used to evaluate munition design as well as protective measures for the warfighter who may use urban structures for shelter. This is valuable work that addresses real problems in current and future theaters. The project will also use the results of the soft-tissue modeling effort at WMRD. Collaborations (e.g., with Germany) are ongoing. The project requires a significant amount of labor to collect data; this effort is primarily done by one person. This project is significantly understaffed, especially given the labor-intensive nature of debris field data acquisition. Expanded staff would allow a wider range of munitions and building materials to be investigated. Increased interaction with the soft-tissue modeling effort would be useful to that project as well as to related efforts underway external to WMRD. Sensor, Warhead, and Fuze Technology Integrated for Combined Effects The project Sensor, Warhead, and Fuze Technology Integrated for Combined Effects is a portion of the WMRD’s larger multifunctional warhead and munitions effort, focused on the ability to put sensors on the end and forward surface of a munition to sense the type of target and then to enable selective fusing in order to tailor the munition to that target. The goals of the larger project are to simplify logistics by stocking only a single munition type rather than having to estimate the likely target types prior to loading, to automate target discrimination and fusing, to reduce human error, and to enable more rapid fire by the soldier. The technical challenges include determining the most appropriate sensor types, determining the materials for the end cap and the sensors that can survive initial impact, and developing a selective fuzing methodology. The team performing this work is also assessing possible spoofing threats and whether it is possible to readjust the fuzing in flight as more data are received on the sensors. This work will combine with the scaled effects endeavors in the larger project. The overall project will also be evaluated from a systems perspective to determine that the solution is worth implementing. This is an important and intriguing project, and while it is in its initial stages, it appears to have an appropriate overall project plan.
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2007-2008 Assessment of the Army Research Laboratory Electromagnetic Gun This project for an electromagnetic gun showed great advances in materials manufacturing and complex engineering. Challenges of heat buildup are being addressed with active cooling, and firing demonstrations have been successful. The largest challenge for the Army with this gun is the power supply for a mobile gun. The ARL work needs to be closely coupled to the development of the counter-rotating motor power generation program at the Army’s Armament Research, Development and Engineering Center (ARDEC). This is a high-risk project requiring success in projects at both facilities. It might be appropriate to consider a risk-mitigation strategy if the motor proves insufficient for the task. Close coupling with the Navy’s program is also appropriate, and the investigators seem to be aware of what is going on broadly throughout the nation. The intriguing idea of a hybrid EM and conventional gun (propellant-driven) is also being pursued, and results of the ongoing paper study should prove interesting. DEMN (Explosive Fill) The project on DEMN (an explosive fill) is an example of excellent directed engineering that builds on unique capabilities recently brought online at ARL such as the Novel Energetic Research Facility. The development of an insensitive munitions explosive material, with performance, manufacturability, and cost near that of TNT, is a well-defined goal. The development of DEMN also demonstrates a continued paradigm shift from looking for one magic explosive material to using calculations and experience to suggest a mixture of materials that will provide the needed performance. The demonstration of mild response to sympathetic detonation without barriers was a major accomplishment. The team at ARL is well situated to advance this science, having computational expertise, explosive formulation facilities, and testing capabilities. Also, the investment in the NERF facility is commendable because it places ARL in a unique position to fill a need for formulation and scale-up testing. Challenges remain in monitoring the performance of materials when scaled up at commercial sites, because manufacturing processes can affect explosive sensitivity. This program demonstrates a mix of theory, computation, and experimentation. The largest scientific challenge in the continuation of this type of work is the development of a predictive capability for the transient behavior (ignition and failure) of non-ideal explosives. The fidelity with which the chemistry and physics of reactive wave growth are described is higher for predicting failure diameters than is needed for performance parameters such as detonation pressure and velocity. Related to the property testing of the DEMN insensitive munition is the effort on modeling munition response. The computational work focused on the use of the CTH code to model shock-initiated failure.1 While CTH provided good mechanistic understanding, it was not quantitatively valuable, and the ultimate performance numbers were (appropriately) derived from experimental results. It is clear that very long time failure processes, like slow cook-off, are not yet amenable to predictive modeling. However, the expectations for shock-initiated processes are greater, and the inability of CTH to validate experimental results is of some concern. What seems to be missing is an active feedback loop whereby these computations would inform improvements to the code or constitutive models. Absent this feedback, it is not obvious that the existing modeling capabilities can play a meaningful role in munitions design and characterization. 1 The CTH code, developed by the Sandia National Laboratories, provides capabilities for modeling the dynamics of multidimensional systems with multiple materials, large deformations, and strong shock waves.
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2007-2008 Assessment of the Army Research Laboratory Theoretical Chemistry and Advanced Energetic Materials The goals of the theoretical chemistry and advanced energetic materials effort are projected to be as follows: (1) the development of high-performance computing capabilities necessary to characterize energetic materials, including the identification of fundamental mechanisms for the control of reactions; (2) improved thermodynamic predictions; and (3) the use of computation as a means to discover new ways to store and release energy. Currently, some effort is being made to establish underlying mechanisms controlling shock-initiated chemistry, by targeting molecular energetic crystals and, specifically, effects of pressure on properties, and controlling the associated intermolecular forces that are responsible for the properties being investigated. The use of modeling for the prediction of heats of formation is fairly well established, and while the group performing this work does not give the impression that it works toward development of its own methods, it is clearly consulting or collaborating with top-notch groups that do. In particular, this is enabling the group to benefit greatly from the latest state of the art in density functional techniques, such as those offered by the newest dispersion-enabled functionals and pseudopotentials of Grimme, Truhlar, and Rothlisberger. On the other hand, a search into the literature indicates that there is work going on (also coupled to some long-standing collaborations of experts in the community) in the development of capabilities specifically to characterize energetic materials, emphasizing the prediction of properties associated with the performance and sensitivity of materials. This has involved such key developments as the following: the SRT model, which is constantly being refined and extended, in particular now with the advancements in the density functional theory models; and methods for predicting properties of energetic molecular crystals, which has long been a difficult area but for which there are new methods such as those being explored in this group and, for example, a similar model, PIXEL. However, there are clearly some advantages that the group could gain by fostering its own code-development skills directly as a part of the group’s activities. It appears that the theoretical chemistry and advanced energetic materials group does not take advantage of other computational and theoretical development skills within other groups in ARL. Several discussions suggested the need for improved bridges from the molecular scale. The theoretical chemistry group needs to be given a stronger role in these efforts. At present, it appears that the other efforts are developing their own theoretical chemistry expertise without much engagement of this nature. As the theoretical chemistry group develops such ties, it would presumably build some 6.2 and 6.3 components. Certainly, there is a lot to be gained by such collaborative activity in terms of improving the group’s code-developing skills and having the advantage of being directly tied to the experimental direction, something that appears also to be a weak component of the theoretical group. In particular, there is a need to develop multiscale tools that connect the codes that are being used across ARL, from the molecular to macromolecular scales of the theoretical chemistry group to the materials and engineering scales in the other groups. For example, multiscale molecular dynamics modeling and crystal/molecular packing, using the high-level data offered by quantum mechanics, should be considered for the purpose of analyzing the shock compression and shearing sensitivity of materials under extremes of pressure and temperature. In several cases, gaps in certain parameters at the higher scales described during the presentations could be filled in using quantum mechanics data. Materials for Lethality The current focus areas within WMRD’s program on materials for lethality are tungsten for KE munitions, structural reactive materials, and cold-spray particle disposition. The program centers on novel and/or discovery science and concentrates on addressing more near-term applied engineering problems.
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2007-2008 Assessment of the Army Research Laboratory Replacement of DU munitions with W-based materials remains the central goal of this effort. The pursuit of pure W-based materials manufactured using powder metallurgy or equal channel angular pressing (ECAP), each singularly or followed by postprocessing (rolling), appear to offer promise. The question of scale-up appears to be worthy of consideration in both instances—powder metallurgy or ECAP. A combination of integrated (ballistics) and fundamental characterization (high-rate constitutive and fracture toughness testing) is encouraged as soon as possible during the assessment of these materials. The structural reactive materials (RMs) effort presents a compelling focus on developing and manipulating microstructural aspects of RMs to simultaneously achieve multifunctionality (structural capability and reactivity). The coupling of modeling with experimental efforts is encouraged in addressing these coupled goals. The fabrication of unique and tailored materials not obtainable by other processing routes using cold-spray manufacturing was described. Exploration of this technology to produce near-net shape components, such as rocket nozzles or munitions, offers some intriguing possibilities. Further, the use of cold spray as a fabrication route to the production of powders to support the novel W-based materials or reactive materials projects appears technically productive and a novel route to complex alloy powder production. In the area of cold spray, progress has largely been in new materials (tantalum has been very successful, but molybdenum has oxidation issues; the real goals are tungsten or copper). There has also been progress in terms of heat treatment of the deposited layers and testing to demonstrate wear resistance and adhesion of the cold-spray layers. The researchers did not describe any fundamental understanding of why cold spray works or of what the local microstructure or physics effects might be. It is possible that this fundamental work is underway and simply was not described; if it is not underway, it should be. Materials Under Extreme Pressures The work on materials under extreme pressures is focused on exotic energetic materials, specifically equations of state (EOSs) and phase diagrams using the diamond anvil cell. There is an important interaction with the Carnegie Institution of Washington, where outstanding and successful research at high pressures has been conducted for a long time. The impressive EOS and phase diagram studies are important and useful contributions to fundamental aspects of energetic materials. Caution should be exercised with respect to how the work on exotic energetic materials such as polynitrogen and processes such as structural bond energy release is sold. These latter subjects are provocative and push the extreme of chemical imagination. On the one hand, they risk tying the investigator to the growing list of painful attempts to challenge the laws of nature. On the other hand, proven success in one of these areas assures instant fame, however impractical the result might be. It is important to be mindful that the research is still limited by thermodynamics laws. Reactive Material Energy Release Mechanisms The work on RM energy release mechanisms is focused on the development of modeling tools and experimental chemical measurements directed at understanding the energy release by reactive materials in conjunction with explosives. The approach is to understand how to tailor energy release, to model the macroscale, and to develop appropriate diagnostics. More specifically, modeling of the shock wave/fireball, fragment formation, and the effect of additives is being conducted. Experimentally, laser-controlled initiation, the emission spectroscopy of product species, and unique spatial and temporal thermometry are focal points. Blast enhancement by surrounding the explosive with RMs such as Al and Ni alloys has been observed and is being investigated. Important Army applications include the
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2007-2008 Assessment of the Army Research Laboratory development of thermobaric explosives and RM shell cases. In general, the work fits Army needs and is well done. Reactive Materials Reactive materials can deliver chemical energy far in excess of that available from impact alone. Research in this area is essential to ARL’s mission and will result in greater lethality. Fundamental investigations of RMs will involve the quantum chemistry group, and although there is research going on in this area (quantum chemistry and reactive materials) it does not, on the surface, seem to be influencing the development of RMs. The project encompasses both engineering approaches to deliver near-term product (building on previous work in the Navy and elsewhere) and longer-term research to predict and evaluate the performance of other materials (including original work at ARL). The RMs are not explosive but do, on impact, deliver some degree of energetic output relative to an inert projectile. Many of the challenges relate to the mechanical behavior of the RMs: strength needed for launch and flight, density, and manufacturability. Ongoing research to pursue materials with improved mechanical performance with enhanced reactivity is well directed and seems to include appropriate simulation and experimentation. Survivability Reactive Armor Reactive armor (RA) is a common form of add-on armor, used on many armored fighting vehicles. This is a proven concept first used by the Israel Defense Forces successfully in combat with the Israeli Army M-60s and Centurion tanks in the 1982 War, and later by the Soviet Army in the mid-1980s. The RA concept employs add-on protection modules consisting of thin metal plates and a sloped explosive sheath, which explode when sensing an impact of an explosive charge. The RA enables a significant increase in the level of protection, primarily against conventionally shaped charges and the explosively formed penetrator, a special type of shaped charge designed to penetrate armor effectively at standoff distances. The ARL use of modeling and simulation of RA to help understand the impact of several key variables is excellent. The researchers have made outstanding strides to understand the physics integrated with the ballistics to make the current RA successful. The arrival of ARL-recommended RA kits in-theater will be the ultimate verification and validation of this program and of the current modeling and simulation methodology. ARL needs to ensure that the data and experiences of the soldiers using the RA package are given to the developers, closing the loop. Transparent Armor WMRD’s future-force program is focused on the evaluation of transparent materials and on WMRD’s approach to design solutions to meet the needs for transparent armor, sensor protection, and glazing life protection. The project on transparent armor is specifically focused on the following: materials and laminate design, ballistic design, and ballistic modeling. The current materials under consideration are mostly in-hand materials, and the focus is on increasing protection without an increase in weight. Realization of this objective while balancing the requirements of optics, transmission, ballistics, scratch
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2007-2008 Assessment of the Army Research Laboratory resistance, and solar loading makes this area a challenging one in which ARL clearly has established expertise and vision for the future. Details of the solar loading and challenges in thermal management toward the development of a ballistics specification are experimentally fascinating and show a healthy balance of experimental and modeling focus. The data clearly support conclusions of the importance of needing to quantify transparent armor performance above ambient temperatures. This program evinces experimental and modeling balance coupled with near-term application-driven tasking and a long-term vision of where transparent armor evolution needs to proceed to support future force needs. Ceramic Armor Materials The work on ceramic armor materials is a piece of the larger work on ceramic composite armor. The stated goal is to achieve a fundamental understanding of deformation and failure mechanisms at ballistic conditions. There is a lack of good data and models at these very high shear rates, and it is an important problem to work on. As presented, the experimental work to date seems very empirical and exploratory. It is unclear whether existing literature has been leveraged sufficiently. While it is probably true that data do not exist at ballistic conditions, there is ample literature at slower rates, which could inform the choices of experimental techniques and limits. Composite Ceramic Armor Performance The underlying failure mechanisms occurring in composite ceramic armor components were identified through postmortem analysis of representative impacts, and strategies to rectify these problems through modification of the binder and the rigid components were described. The binder study appeared to be systematic, with the key properties of candidate binders being characterized and well understood. Some innovative changes were proposed for the structural components, and these innovations appear to be very successful. It is not clear that a systematic plan exists for refining these new strategies. Computational approaches were suggested by WMRD, but predictive computational capabilities for such complex, textured composite materials were not demonstrated. Some simulation of fabric modeling alone was presented, but the relevance of this modeling seems directed to manufacturing and appears to be disconnected from the overall composite behavior in impact. Electromagnetic Armor Physics The program on electromagnetic armor physics emphasizes the mechanism by which EM armor addresses jets and the role that computational validation plays in this process. The contrast to challenges presented by explosively formed penetrator devices was described. The Alegra code enhancement and concurrent physics hypothesis testing that resulted from the jet validation work (specifically, air conductivity) are commendable. However, a similar attention to fracture was absent and represents a significant lost opportunity. The need for predictive physics-based fracture models was a recurring theme in the overall WMRD presentations. Tactical Wheeled Vehicle Survivability As in the case of the RA program, which is addressing current Army needs, the Tactical Wheeled Vehicle Survivability program is an excellent example of the duality of ARL’s missions to simultaneously quickly solve in-theater problems to support the warfighter while considering how to effect changes
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2007-2008 Assessment of the Army Research Laboratory in armor materials on future systems. ARL’s innovative and rapid turnaround approach to up-armoring door panels for tactical wheeled vehicles in response to needs from the warfighter is commendable. Not being satisfied with resting on its laurels, ARL is continuing research on new materials for lightweight tactical wheeled vehicle (TWV) armor applications in the future by looking, for example, at the ALCAN aluminum alloy 2139. Both the motivation and the research approach effort are to be applauded as clearly technically driven and forward thinking, with the goal of achieving improved performance in future TWVs. ARL is encouraged to work with program managers and prime contractors to orchestrate the insertion of the new aluminum alloys showing promise into future platforms and as replacement materials for upgrades of existing TWVs. Kinetic Energy Active Protection Systems The program on kinetic energy active protection systems is intended to deploy an explosive projectile that will detonate near incoming KE penetrators and cause them to swerve, missing the intended target. The multimedia demonstrations were excellent and provided a realistic sense of the complexities involved in the design and deployment of an active protection system for KE penetrators. This is primarily an engineering program utilizing sensors to identify the friction-produced heat signature of the incoming KE projectile and then maneuvering to the penetrator. The part of the program involving the identification of the incoming KE round is near completion. There is every reason to expect that an active protection system will be deployable in the near future. Composite Materials Technology for Armor A very detailed model of the fibers, threads, and weave of the fabric for future composite armor components was presented. These models will be very helpful to the future manufacturability of the fabric. Simulations of impact damage were also shown, but the overall project plan (including the requirements and selection of adhesives and matrix materials) was not clearly articulated. Armor Technologies for the Current Force The effort involving armor technologies for the current force is primarily driven by expedients, and the WMRD team appears to be satisfying that need well as well as integrating armor technologies with existing and emerging systems. The group has actively pursued the use of many new materials and engineering designs to improve the efficacy of armor technologies. This is also visible in the products that it has delivered to the field. Although the speed with which this group is exploring new materials makes it very hard to implement them into simulation codes, the group is attempting to do so. This is thus a good case study illustrating the need for the 6.1 materials computing area referred to above to develop transferable constitutive models capable of describing new materials quickly. Pulsed-Power Armor Technologies Future Army technologies will require increased flexibility, function, and extension, as well as support for unconventional weapons and armor systems, such as demonstrated in pulsed-power armor technology. Modular pulsed-power technologies have the potential to be used in many applications and field implementations for defense, making this area crucial to ARL. To meet these requirements, this demonstration showed advancements to support propulsion, continuous auxiliary power, and pulsed-
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2007-2008 Assessment of the Army Research Laboratory power demand for weapons and armor. One question would be whether the power supply needed for these purposes can be supported for general use. Predictive Capabilities for Buried Blast Threats The effort involving predictive capabilities for buried blast threats is focused on experimental results for buried threats, with particular emphasis on the role of burial depth and soil properties. Scaling laws were proposed, and some simulation results were presented that support the experiments. These simulations incorporate new constitutive models developed through academic collaborations. Quantitative modeling of soils is very difficult and seems appropriately targeted as a research avenue. Vertical Impulse Measurement Facility The Vertical Impulse Measurement Facility provided data necessary to tune and validate models simulating the impulsive output of buried charges and the response of targets of interest, particularly the vertical impulse from buried charges weighing up to 8 kg. This is a program that reflects the general ARL philosophy of validating models to the level necessary to provide designers with confidence in the results. This facility is crucial to the ARL mission and has been used productively in support of that mission. Novel Energetic Research Facility The Army has made a wise investment in rebuilding the Novel Energetic Research Facility for the pilot-scale formulation of explosives. The amounts of explosive that can be obtained enable engineering-scale tests to be conducted. The hiring of additional employees to work in this facility is laudable and helps fill a national need. The success of DEMN as an insensitive explosive fill is a useful advance to justify the investment and provides a selling point for additional growth in this area. The scale-up and formulation of explosives are usually the “valley-of-death” for many explosive programs. There has been an overall disinvestment throughout the nation in such facilities, which places ARL in a unique position to fill a critical need for the energetics community. OPPORTUNITIES AND CHALLENGES Predicting High Strain-Rate Properties WMRD presenters noted that in the world of armor protection, scientists and engineers speak of horrendously large forces being applied to materials in microseconds or faster, a phenomenon known as high strain-rate deformation. At these high strain rates, materials properties can be markedly different from what they are at slower rates, such as, for example, when tested in an Instron. Accordingly, when developing new armor concepts it makes little sense to use handbook values of materials properties such as tensile strength, yield stress, or fracture toughness, because these could be orders-of-magnitude different from high strain-rate properties applicable to armor. Fortunately, however, there is a way of obtaining such high strain-rate properties using Hopkinson bar experiments in which flyer plates are accelerated toward small samples using high-pressure gas jets. Unfortunately, the experiments tell nothing about what metallurgical factors control properties under rapid deformation, so there does not exist today any way to design materials having preselected high strain-rate properties. The high strain-rate world therefore differs markedly from the more familiar low strain-rate world in which materials scientists often know
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2007-2008 Assessment of the Army Research Laboratory what is needed to increase the yield stress or fracture toughness of many advanced materials that are to be used in more normal applications. In the world of high strain rates, however, very little, if anything, is known about tailoring the strain-rate sensitivity of potential armor materials, leaving the design engineer in the dark and the ability to design armor for some intended application very difficult. The development of materials for low strain-rate applications has benefited in the past from many years of intensive efforts by materials scientists, but currently as new and more demanding applications appear on the horizon, some reliance is being placed on computational materials science in which techniques such as molecular dynamics simulation and electronic structure calculations are employed to understand how features at the atomic, mesoscale, and microscale levels influence the structure/property relationships.2 Seemingly, no such effort has been made to focus the attention of computational materials science (CMS) on the problem of understanding what factors govern the markedly huge difference between the properties of many materials at high strain rates and their better-known properties at low strain rates. Perhaps the reason is that such a study would have to cover many length and time scales and would have to deal with the dynamics of the situation as well as other factors that undoubtedly control structure-property relationships in the high strain-rate regime. In short, it would not be an easy task. However, a program designed to develop such an understanding should be of great benefit to the armor community in that, if successful, it would for the first time allow these researchers to tailor the all-important high strain-rate properties of a potential armor material to specific armor applications. This would constitute both a challenge and an opportunity for ARL. Computational Materials Science As noted above, the balance between experiment and computational efforts in materials R&D has improved markedly within WMRD over the past 2 years. Nonetheless, the development of CMS must be undertaken within the context of a clear objective. The challenge for WMRD, therefore, is as follows. Typically, the objectives of institutional CMS efforts fall along a continuum. At one end are those that push the computational and theory envelope; at the other are programs that support or are integral to the materials development process. The goals in the first of these extremes is to develop or accelerate computational tools, while for the latter extreme the goal is to explore how existing CMS tools can be used to hasten the materials design and deployment process. Considering finite element modeling (FEM), there is good work proceeding at both extremes: computational scientists are exploring ways to expand FEM to larger systems, while at the same time scientists and engineers are employing these techniques to design new structures and processes. Example programs drawn from across the spectrum of CMS efforts range from those at the California Institute of Technology, which can be classified as pushing the computational and theory boundary, to those at Northwestern University and QuesTek Innovations LLC, which have integrated CMS into their materials design process. In the middle is the group in the Materials and Manufacturing Directorate of the Air Force Research Laboratory at Wright-Patterson Air Force Base. The key differences between these extremes are the skills of the personnel involved. Usually, computational scientists and theorists, who for the most part work independently of experimentalists, staff a program pushing the CMS envelope. At best, these researchers are called on to explain experimental 2 See, National Research Council, National Materials Advisory Board, The Impact of Supercomputing Capabilities on US Materials Science and Technology, Washington, D.C.: National Academy Press, 1988; and National Research Council, National Materials Advisory Board, Integrated Computational Materials Engineering: A Transformational Discipline for Improved Competitiveness and National Security, Washington, D.C.: The National Academies Press, 2008.
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2007-2008 Assessment of the Army Research Laboratory observations. For CMS programs directed at materials development, experimentalists and materials scientists use existing software, much as they now use microscopy or spectroscopic information. Given the resources and other constraints placed on ARL, its mission is best served through the development of a CMS effort patterned more on that of the group at Northwestern University than on the California Institute of Technology group. An effort patterned along the lines of the Northwestern paradigm is “grown locally.” As a materials development program is planned, a redundant modeling and experimental effort is created. As an illustration, if one is exploring the effects of alloying or processing on a well-characterized property, a set of experiments is performed in which the processing parameters or alloying elements are varied and the property is measured. For such cases, a redundant CMS effort should operate in parallel with the experiments. In this way, experimental verification of the models becomes an integral part of the design effort. At the same time, the experimentalist learns how to incorporate CMS results into his or her materials development programs. Over time, the experimentalist will gain confidence in the models just as one gains confidence with experimentally derived information. The work at ARL on chromophore design is an excellent example of this type of research. The modeling and experiment are well integrated, and both are targeted to single property prediction. Soft-Tissue Physics The new program on soft-tissue physics, whose motivation is provided by the need to better understand the interactions of munitions, directly or indirectly, with humans, represents an opportunity for WMRD, since it is in an area of great interest in Congress and among the general public. It also represents a great challenge, because it is unlike any prior programs in WMRD and will therefore have to undergo a somewhat extended learning curve. The primary concerns of the soft-tissue physics program are penetrating wounds from munitions (these may be from projectiles or fragments), blunt trauma, and blast loading (shock wave effects, especially, traumatic brain injury). The current focus is on the development of computational models of soft-tissue response to high strain rates induced by projectiles and shock waves. For empirical input into model development and validation, the program is examining historic data from the United States Army Wound Ballistics Laboratory at Edgewood Arsenal, Aberdeen Proving Ground, Maryland. In addition, WMRD is conducting high strain-rate experiments with tissues using the high-rate split Hopkinson pressure bar and is attempting to design clamping mechanisms to allow strain-to-failure experiments with tissues. Shock physics codes from the Department of Energy are being used (and adapted) to support the modeling of blast loading. Model development is directed at the torso (customer-driven work) and the brain. WMRD’s successful efforts in refocusing this program following the Board’s 2006 review are commendable. There is a national defense priority addressed by this program. The understanding of munitions-induced trauma is of high importance in the design of armor, in the design of armaments (e.g., to reduce the risk of collateral damage to noncombatants), in the design and delivery of effective treatment of the wounded, and in the training of medical personnel. WMRD’s program is a vital component in this national effort. TBI has a very high profile with the public and Congress; hence WMRD’s efforts in modeling blast loading are timely. The problem is large and complex, and many players (from other government agencies, universities, and international partners) are participating in as-yet largely uncoordinated efforts to achieve useful solutions. The historic data from the United States Army Wound Ballistics Laboratory at Edgewood Arsenal are a unique resource that could yield very important (and currently unobtainable) data on trauma. WMRD is uniquely qualified to deal with shock physics and to partner in gathering vital empirical in vitro data for high strain rates in tissues.
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2007-2008 Assessment of the Army Research Laboratory There are concerns: The selection of tissue types to be modeled requires consideration (i.e., in the case of a limb, should the model be limited to bone and muscle, excluding nerve and vascular tissue?). The degree to which individual tissue types can be modeled and then the individual models aggregated to form a system model also needs further consideration (e.g., addressing to what extent one type of brain tissue can be modeled and that model successfully integrated with a complete model of the head that encloses the tissue in a cranium and incorporates vascular tissue and other types of brain tissue). The development of anatomical models using grid geometries may not be optimal for use in all application areas and/or easily integrated with other geometrical models. There is an apparent lack of use of decades of research in attaching tissues to fixtures for mechanical tests in favor of developing these attachment mechanisms anew. There is a lack of WMRD personnel with bioengineering/biomechanical backgrounds (although some WMRD external collaborators do possess such backgrounds). There is need to consult with Human Research and Engineering Directorate biomechanics personnel to improve the modeling being proposed and to work with other biomechanics groups outside the Army. Better cognizance of previous and existing efforts is essential. For example, among projects funded by a Defense Advanced Research Projects Agency (DARPA) program in Combat Casualty Care in the 1990s, one was performed by MusculoGraphics, Inc., which developed a Limb Trauma Simulator incorporating a model of a trauma wound to the thigh.3 Another DARPA effort is, among other activities, developing a high-fidelity heart model. Another example of extensive work in computational models of soft tissues is that of Montgomery and co-authors.4 In addition, WMRD should investigate the biomechanics program at the University of California, San Diego. In the same vein, a deeper cooperation with the brain model program of the Massachusetts Institute of Technology would ensure that WMRD model development is complementary rather than duplicative of that effort. There is need for better coordination of WMRD efforts with those of others. For example, WMRD should consider participation on the Defense Science Board Medical IED (Improvised Explosive Device) Panel. WMRD should develop a systematic approach to data mining the Edgewood data. These data are worthy of a fresh look in light of what is needed and may support validation of development models. WMRD should consider acquisition of some in-house expertise in the form of at least one bioengineering or biomechanics expert. Such an expert, in cooperation with external medical experts, could better guide the selection of tissues to be modeled, the choice of grid geometries, and the validation of those models with existing or future empirical data. Models that simply reflect fixed (i.e., one person’s) anatomy will not be as useful as those that can represent a reasonable range of anatomical variations such as are found in the general population. Developing anatomical models with this capability should be a goal. The review of empirical anatomical wound data and the compilation of tissue mechanical property data should advance prior to the large-scale development of anatomical models (grid libraries). Until it is known which tissues are likely to be most important, it may be wise to defer anatomical model development. Such a deferment would also provide an opportunity for the investigation of the large number of currently available anatomical models. Trauma to in vivo soft tissues may do more than alter the geometry of the tissue. In almost all cases, tissue physiology (and that of organs and the organism) will also be affected. Thus, physiological modeling should be included in the overall effort; however, this type of model development may be best done by other organizations and integrated with WMRD models. 3 See, for example, Richard M. Satava, “Surgical Education and Surgical Simulation,” World Journal of Surgery 25:11 (2001), pp. 1484-1489. 4 See, for example, K. Montgomery, C. Bruyns, J. Brown, G. Thonier, F. Mazzella, S. Wildermuth, S. Sorkin, A. Tellier, B. Lerman, B. Beedu, and J.C. Latombe, “Spring: A General Framework for Collaborative, Real-time Surgical Simulation,” Medicine Meets Virtual Reality (MMVR02), Newport Beach, Calif., January 23-26, 2002.
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2007-2008 Assessment of the Army Research Laboratory Careful examination of previous efforts to clamp or otherwise attach tissues to fixtures for mechanical measurements should be done. Model development should proceed with consideration for the likely integration of WMRD models with those developed by other organizations. Such integration requires a careful documentation of model assumptions, prudent choices of grid geometries, and the provision for data interchange with other models. OVERALL TECHNICAL QUALITY OF THE WORK The Weapons and Materials Research Directorate conducts activities across a very wide breadth and depth. The fact that even in time of war when heavy demands have been placed on WMRD, the directorate has to respond in the short term to serious problems faced by the warfighter (e.g., up-armoring Humvees) and still has been able to maintain an excellent series of R&D programs to ensure that the warfighter of the future will receive the same benefits. WMRD’s slogan, Technology Driven, Warfighter Focused, suggests a top-down organizing principle buttressed by science and technologies derived from internal efforts as well as from various Materials Centers of Excellence at several universities. The interaction of WMRD staff with the MCoEs has benefited the organization by creating a link between the basic research results coming out of academia and the somewhat more applied needs and programs of ARL. MCoEs have also been the source of a number of summer postdoctoral researchers, some of whom have stayed on as staff members. Many of the presenters in the 2008 review were postdoctoral researchers and young staff members who showed the enthusiasm of youth in their presentations. WMRD is encouraged to continue and even to expand these connections to universities. The experimental work and the computational materials, modeling, and simulation work being carried out are, in almost all of the activities, of high quality. For example, the work employing DFT to develop various nonlinear optical materials including chromophores for use as eye and sensor protection films is an excellent example of good research that profits from the close interaction between synthetic and computational chemists. The laudable success of the Affordable Precision Munitions program was due in no small part to its emphasis on multidisciplinary design (MDD). This approach combines capabilities from a number of disciplines that in this case included virtual wind tunnel techniques allowing a wide range of designs to be explored, a novel guidance approach, and special propellants. In this case, MDD has resulted in a highly successful program, and WMRD has employed this technique as a means of accelerating development and reducing risk; it should be considered as a model in the future for use in designing other lethality and survivability systems. The use of virtual wind tunnels and virtual fly-outs allows a much larger range of designs to be explored at much lower cost in much less time. Significant, and surprising, results have been achieved in terms of nose and body interactions, jet interactions, and diverter interactions that have permitted development to avoid costly pursuit of what would be unusable designs. Documentation of model assumptions and ongoing validation of models and virtual wind tunnel and virtual fly-out codes are essential to maintaining confidence in the program results. Continual refinement of models and their use by various personnel require that all model assumptions be carefully documented. Systematic and selected validation experiments must be conducted in wind tunnels and on instrumented ranges to ensure that models and the performance testing codes are sufficiently trustworthy to support decisions on final designs.