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 at Aberdeen Proving Ground, Maryland, during June 14-16, 2011, and May 7-9, 2012. The theme of the 2011 review was warfighter protection; the 2012 review was focused on lethality research and development (R&D).

The Army Research Laboratory is the corporate laboratory underpinning the operational commands for the U.S. Army, and its WMRD serves as the locus of the fundamental science and technology (S&T) research on materials issues supporting warfighter protection and lethality. The presentations to the reviewing panel outlined the breadth and scope of WMRD’s research efforts during 2011-2012, which span the gap between basic research that improves the understanding of scientific phenomena and technology generation that supports weapon and protection system developments and fielded system upgrades. The directorate executes its mission of leading the Army’s research and technology program to enhance the protection and lethality of the individual soldier and advanced weapon systems.

CHANGES SINCE THE PREVIOUS REVIEW

WMRD’s focus has significantly changed. The quality of its research is greatly improved, and its interactions with other laboratories, both governmental and academic, have developed into active collaborations. WMRD is to be commended for these improvements. For example, several past reviews observed that computation did not often play a key role in research accomplishment. Now there is a clear commitment to transforming materials computation into a reliable predictive tool, as evidenced by a new thrust toward multiscale modeling and toward model validation, verification, and uncertainty quantification.



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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 at Aberdeen Proving Ground, Maryland, during June 14-16, 2011, and May 7-9, 2012. The theme of the 2011 review was warfighter protection; the 2012 review was focused on lethality research and development (R&D). The Army Research Laboratory is the corporate laboratory underpinning the operational commands for the U.S. Army, and its WMRD serves as the locus of the fundamental science and technology (S&T) research on materials issues supporting warfighter protection and lethality. The presentations to the reviewing panel outlined the breadth and scope of WMRD’s research efforts during 2011-2012, which span the gap between basic research that improves the understanding of scientific phenomena and technology generation that supports weapon and protection system developments and fielded system upgrades. The directorate executes its mission of leading the Army’s research and technology program to enhance the protection and lethality of the individual soldier and advanced weapon systems. CHANGES SINCE THE PREVIOUS REVIEW WMRD’s focus has significantly changed. The quality of its research is greatly improved, and its interactions with other laboratories, both governmental and academic, have developed into active col- laborations. WMRD is to be commended for these improvements. For example, several past reviews observed that computation did not often play a key role in research accomplishment. Now there is a clear commitment to transforming materials computation into a reliable predictive tool, as evidenced by a new thrust toward multiscale modeling and toward model validation, verification, and uncertainty quantification. 103

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104 2011–2012 ASSESSMENT OF THE ARMY RESEARCH LABORATORY The WMRD armor technology program has undergone a major change in focus during the past 2 years. At the time of the last review (2009) the WMRD armor program was primarily focused on developing and demonstrating armor technologies that could meet Army Future Combat Systems (FCS) requirements and on meeting urgent Army needs for upgraded combat vehicle armor for use in Iraq and Afghanistan. Since then, the Army has cancelled the FCS program, announced plans to initiate a new Ground Combat Vehicle (GCV) development and acquisition program, and fielded a number of combat vehicles with improved protection that employ WMRD-developed armor technology. These develop- ments have provided WMRD with an opportunity to restructure its armor S&T program to better meet long-term Army protection needs. WMRD has taken advantage of this opportunity by developing plans to support GCV armor requirements and by following a new back-to-basics approach that has led to the establishment of longer-term, ARL grand challenges in protection. The restructuring of the WMRD armor technology program will help the Army to ensure that new and improved armor technologies are available to address all currently projected and future emerging threats. WMRD has streamlined its core armaments technology programs to make them consistent with the Army’s current “squad-centric” focus aimed at increasing the combat effectiveness of small units. New efforts have been established in four areas: (1) low-cost, hyper-accurate munitions technologies; (2) dis- ruptive energetics and propulsion technologies (disruptive technologies are those that provide significant improvements over current technologies, often through sudden innovation); (3) lethal and scalable effects technologies; and (4) soldier lethality technologies. Efforts in advanced propulsion technology now place more emphasis on small caliber munitions and less emphasis on artillery and tank cannon propulsion. WMRD has established a solid armaments technology program that will likely be capable of providing improved technologies to meet future Army needs for advanced weapon systems. WMRD technical staff continue to show tremendous enthusiasm for their work and awareness of the importance of the solutions being generated through research. They have universally embraced the need to marry experimental and empirical protocols, long established at ARL, with the emerging multiple- scale modeling efforts. Early-career staff lead these efforts, aided by mentoring from the more senior staff. Likewise, the practical aspects of the ARL mission are repeated everywhere, and it is important that actual military vehicles and weapons remain a part of the underpinnings. A passion for timely solutions is well demonstrated, which provides urgency to the research. WMRD’s efforts address fundamental and pressing Army needs, and so any means to accelerate progress is of great national importance—a message that is clearly embedded in the program’s scientific staff. Networking is evident, but fostering of relationships with outside speakers and visitors would be beneficial. External reviews and emerging new university linkages are encouraged. ACCOMPLISHMENTS AND ADVANCEMENTS The connection between ARL and the Army Research Office (ARO) is working well. ARO staff have developed strong connections with ARL personnel and programs and have cleverly incorporated ARL interests into the ARO-sponsored programs. A number of recent examples of links between ARO-­ sponsored projects and ARL interests were described, including projects that involve exchange of per- sonnel (in both directions), use of facilities, transfer of expertise, ARO-sponsored students who became staff at ARL, and seminars and workshops on various topics. In addition, there have been important examples of technology transfer from the ARO-sponsored projects to ARL programs. The researchers’ excitement for their work is contagious, and investments in human talent of the past several years have produced exceptional results. Interactions with universities in the region have

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WEAPONS AND MATERIALS RESEARCH DIRECTORATE 105 resulted in long-term relationships with appropriate faculty and advanced degrees for ARL personnel. WMRD staff has revealed a strong and healthy environment for creative interdisciplinary interactions. Protection WMRD’s progress over the past 2 years in the development and integration of modeling and simula- tion is impressive. In several cases, the integration of simulation and experiment has yielded results not possible with either of these approaches alone. The 2011-2012 reviews revealed a new commitment to transforming materials science computation into reliable predictive tools, as evidenced by new thrusts for multiscale model development, validation, and verification, and for capturing variability through uncer- tainty quantification. These developments are reminiscent of the Department of Energy’s maturation of computation for the purpose of stockpile stewardship, the results of which have been transformative. There is evidence of quality research programs that allow “out-of-the-box” investigations leading to new discovery, or better yet, to applications beyond initial intent. For example, the study to character- ize ceramic microstructure via capacitance measurement and then to correlate to ballistic measures is one clear example of out-of-the-box thinking, because it recognizes the statistical characteristics of the measurements and cleverly uses Bayesian methods to extract dominant ballistic behavior. Efforts in materials chemistry reflect high-quality work spanning the range of science to engineering. Combinatorial chemistry and property modeling of the behavior of individual molecules uses state-of- the-art chemical selection as pioneered by the pharmaceutical industry, where there are hundreds of millions of possible molecules to synthesize and combinatorial chemistry down-selects a small number of best candidates for experimental trials. At the other extreme, off-the-shelf materials with careful selection of ligands and surface activity are used to develop cost-effective coatings that can be adapted rapidly to a wide range of specific threats. In the future, the merging of the combinatorial chemistry and science with the surface engineering of coatings should provide a strong foundation for future important contributions. Furthermore, fundamental studies of polymer networks and tunable microstructures, combined with use of dynamic mechanical testing, diffusion properties, mechanical properties, and morphology studies to understand these crystalline and amorphous microstructures, will add value to the entire materials knowledge base. Many of the armor technology efforts reviewed were impressive. For example, the kinetic energy (KE) armor technology effort illustrates how a back-to-basics approach can potentially provide a signifi- cant, long-term payoff for the Army. Some of the initial WMRD KE armor research employed very high quality, small-scale, reverse ballistic experiments. The early experimental results led to the unexpected discovery of a new KE projectile defeat mechanism. During the initial phases of this research, it was not clear that this new defeat mechanism could be scaled up and used in full-scale designs of practical armors. The experimental results were combined with multi-dimensional computational modeling to better understand how this defeat mechanism worked and how the armor technology could potentially be improved and/or optimized. This effort eventually led to a multi-year, applied R&D effort focused on further maturing and demonstrating this new KE armor technology in practical armor designs. This WMRD work has recently resulted in full-scale prototype KE armors that show significant tactical potential for use in GCV and other applications. All of these developments illustrate how a high-quality, well-thought-out experimental and computational modeling approach can improve understanding and thus help meet future Army protection requirements. SiC tiles for passive ballistics protection have been developed through an integrated experimental and statistical analysis project. Recent experimental advances have provided the capability to measure

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106 2011–2012 ASSESSMENT OF THE ARMY RESEARCH LABORATORY a broad variety of tile properties via dielectric spectroscopy, leading to detailed spatial profiles of their electrical and mechanical properties for large numbers of tiles. Current work now focuses on the con- nection of these properties to ballistics measurements. Data analysis is based on information theory, genetic algorithms, and Bayesian analysis, with results suggesting that combining these measurements can lead to a successful correlation. These results may change tile specifications and thereby lead to more uniform and effective passive protection components. A practical route for the fabrication of large-area panels of nanostructured AZ31-Mg alloys, suitable for lightweight armor applications, has been demonstrated. Specifically, using equal channel angular extrusion, it has been shown that the grain size of polycrystalline material can be reduced to 300-500 nm, doubling the tensile strength while maintaining 15 percent elongation. It is anticipated that further reductions in grain size to the 10-20 nm level could yield even greater improvements in mechanical properties, and thereby armor performance. A similar development is expected in Al and its alloys. The polymer work is exemplified by well-defined project objectives, well aligned with WMRD objectives. The projects extend process-structure-property relationship studies to new regimes—for example, very high strain rates, balance of functional and mechanical properties by control of chemistry and processing, and definition of three-dimensional (3D) damage to high and low modulus polymers by well-defined projectile physics and impact characteristics (such as size and speed). The close integra- tion of experimental and computational techniques within project teams is synergistic and positively affecting progress. The engineering science work is impressive. A variety of diagnostics have been used to characterize fundamental armor mechanisms. Flash x-ray, proton radiography (at Los Alamos National Laboratory), polarized imaging, shadowgraph (back lighting), and other techniques are used. The WMRD experi- ments are complex and have been conducted quite well. The researchers were enthusiastic and spoke competently about their techniques. All of the programs embrace modeling. The integration over multiple lengths or timescales via efforts to simulate bulk properties linked to atomistic-scale attributes is a very challenging topic in materials engineering. The research team is making progress, and the current efforts are likely to mature in the next few years. In the mechanics of materials research there is a strong effort to advance transparent armor. The research team is very enthusiastic, mission-focused, and rightfully proud of its contributions. The team is more than adequate for the tasks, with an excellent marriage of a range of disciplines. In the work, the effects of composition on toughness are linked to the atomistic defect structure, and in turn processing parameters are evaluated in light of the desired properties. A key development is in the impurities that facilitate the reaction and sintering with microstructure control. This work reflects an impressive com- bination of modeling, processing, and examination of linkages to performance and uses both modeling and practical experiments. Although details of the models were not addressed in the short discussions, still the overview seemed to convey sophistication and an effective team. No information was provided on the specific modeling tools, software, hardware, or needs, so it is assumed the combination is more than adequate and properly supported. Integration with external suppliers was evident, but no comment was offered on the relationship to possible system vendors. Penetration of armor is a fundamental issue for the Army, leading to much research on high-strain- rate fracture. A large body of testing is required to construct accurate models, which is a significant barrier in terms of number of samples, testing time, and expense required to hone the predictions. Atten- tion to minimum testing to validate and refine existing models is required to expedite future efforts. The balance between experiment and statistical analysis is appropriate. The research on penetration is well aligned to critical issues. Some comparable testing is being performed in other federal laboratories; for

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WEAPONS AND MATERIALS RESEARCH DIRECTORATE 107 example, the National Institute of Standards and Technology has considerable prior work in prediction of failure for brittle systems (ceramics) that might be relevant. Research on lightweight aluminum alloys is important and has directed much attention to how technical gains can be propagated quickly to the field. Features such as grain size or differences in grain boundary segregation or internal porosity need to be understood. Scale-up issues are inherently part of this research and will eventually be addressed. For example, the relative merits of a monolithic cast- forged structure versus assembled pieces (most likely by welding) will eventually need to be considered with respect to the possible vendor base (apparently limited at this time), property differences, and overall unit cost. The team is qualified and working in an area where there are essentially no peers. There are external vendors to advance the work, so there is no apparent limitation in terms of internal capabili- ties. It is unclear whether the team is properly linking early with existing manufacturability capabilities. Other examples of high-quality research endeavors include the following: • Textile composite armor. The multiscale modeling has reached a mature level and provides not only answers to 30-year-long performance questions about protective textile composite materi- als, but also a framework for successful design of lightweight textile armor of the future. The work is both systematic and unparalleled outside of ARL. • Aluminum oxy-nitride. The senior ceramics personnel are mentoring researchers in several areas of simulation; they meet, discuss, and exchange progress. Although AlON is a commercial product, this research may produce unexpected benefits in determining more suitable means to synthesize, consolidate, or otherwise fabricate the material. At the same time, there could be tremendous gains if new compositions or microstructures are discovered to increase the plasticity of the system. Pressure-induced phase transformation can yield nano-scale grain size. • Modeling high-strain rate behavior of glasses and crystal plasticity. Formalisms combined with computational implementation for single crystal and multi-grain forms are well conceived and executed. Care is taken to explicitly account for high-pressure states involved in impact conditions. • Armor physics. The experimental work on armor physics and testing is outstanding as a whole. Within this work two efforts stand out as being of especially high quality, both concerning diag- nostics of jets. The jet temperature measurement technique is unexpected in its simplicity, and it has already shown value in validation of plasticity models. Likewise, the imaging is providing important new insight into penetration and mitigation physics that will be vital for both design and validation. • Layered nano-materials manufacturing capitalizes on in-house expertise in larger area pro- cessing of polymer sheets—for example, fabrication of polymer-supported carbon nano-tubes, grapheme sheets, and even nano-diamond film—as a means to provide reinforcement as protec- tion materials. • The polymer research programs for the mission that ARL is undertaking are very good. The experimental and computational collaboration within the polymer research programs is out- standing. The fundamental understanding of the structure-property-processing relationship for the polymer systems being studied in polymer networks and tunable microstructure properties is excellent. The combined use of dynamic mechanical testing, diffusion properties, mechanical properties, and morphology studies to understand the crystalline and amorphous microstructures will add value to the entire materials understanding.

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108 2011–2012 ASSESSMENT OF THE ARMY RESEARCH LABORATORY Lethality There is a developing continuum of work, coupled to Army-specific needs, from basic research through applications. Real barrier problems are being approached with the fundamental science neces- sary to achieve revolutionary advances. One notable example is the work in new forms of energetic materials. The development of new high-energy-density materials has led WMRD to renew its interest in ballistics phenomena with a clear commitment to address issues of both internal and external ballistics. The specific work on extended solids and nano-diamonds for structural bond energy release is techni- cally high risk and potentially high payoff. The 885A1 system successes in lethality and in reduction of environmentally sensitive materials are particularly noteworthy. Deployment of the system without complete laboratory validation has proven to be a wise and timely choice. WMRD deserves significant credit for its support of dedicated facilities for advanced energetics development. This was an investment of several millions of dollars, and although the various aspects are not unique, the combined facilities form a capability to synthesize, characterize, formulate, and test new materials in a state-of-the-art facility. Other laboratories are moving away from this technology capa- bility that is critical for the warfighter. In addition, the work on extended solids and nano-diamonds for structural bond energy release is technically high risk and potentially high payoff. These experimental efforts are supported by computational work. The extended solids work builds on work at the Lawrence Livermore National Laboratory and is motivated by a project of the Defense Advanced Research Projects Agency (DARPA). The accomplishments to date are encouraging, and if the work can be scaled for full characterization, then the results will be very interesting. The cold spray capabilities continue to show great promise for applications. This work has demon- strated that reactive materials can be used to tailor the lethality profile of the fragments as a function of distance with a density high enough to compete with conventional inert fragments (7 g/cc). It was found that processing challenges exist in making homogeneous materials (i.e., density gradients) using cold spray. Would composite particles (pre-mixed by milling) result in more homogeneous samples, as well as in tunable reactivity? The development of low-cost hyper-accurate munitions is one of WMRD’s grand challenges. The purpose of this program is to develop precision munitions that will operate in a global positioning system (GPS)-denied environment with the use of flight control algorithms for mortars and artillery rounds by understanding and utilizing the aero-mechanics. Current ballistic rounds are costly to replace (about $1,000 per round) but are relatively low performance compared to an Excalibur-type round, which is a high-performance precision munition. Achieving the Excalibur-type performance with a target cost of $10,000 per round is the goal of the Very Affordable Precision Projectile research program. The high-pressure polymerization of CO and N is very interesting and cutting-edge work in the polymer field. In this work it is important to characterize Poly CO and Poly N as polymers with their properties such as molecular weight and glass transition temperature. The goal of producing 1 gram of polymer this year may not represent enough to characterize these polymers. These characterizations are important for validating the computational data on the various species being predicted. Other examples of work of good technical quality include the following: • The application of commercial off-the-shelf microelectronics for guidance, navigation, and control (GNC) systems has resulted in development of these competencies within WMRD. The addition of on-board intelligence in GNC to achieve accuracy at acceptable cost is noteworthy. • The crosscutting study of small caliber projectile design, which correlates design parameters with projectile damage and then further correlates damage with the ability to incapacitate an enemy, has led to a sophisticated understanding of projectile effectiveness and has translated

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WEAPONS AND MATERIALS RESEARCH DIRECTORATE 109 into the adoption of more effective ammunition for use by combat troops. Overall, this work represents an impressive success. • The polymer work on mechanical properties of soft materials demonstrates a high-level under- standing of the issues. • Low-cost hyper-accurate munitions technology offers considerable potential, and is greatly needed by the Army. WMRD’s technical approach is very sound. • The research on technology to improve the performance of small arms against hard and soft tar- gets is clearly aligned with improving capabilities of small units and individual soldiers. WMRD can do a good job is this area, taking advantage of its integrated capabilities and providing a big payoff for soldiers. • The work in the computational fluid dynamics (CFD) simulation of the combustion and flow processes in the hypergolic pulse engine is very important and useful to the Hellfire missile program. The work is highly commendable. WMRD’s approach is organized in logical fashion by considering a detailed chemical kinetic mechanism, developing a reduced mechanism, and performing fluid dynamic simulation of combustion processes of IRFNA and TMEDA-DMAZ impinging jet-induced spray.1 Further consideration and treatment of the dense spray behavior will help to refine the existing model and solution. • The work on CFD simulation of interior ballistic and muzzle blast phenomena is commend- able. Using the modified NGEN code, the researchers were able to predict the shot start process being initiated by the intragranular stresses transmitted through the compressed aggregate of propellant grains. WMRD has demonstrated its findings for both large (XM829E4) and small (5.56 mm) calibers to industrial companies. WMRD researchers have appropriately extended their interior ballistic calculations to the muzzle blast zone. The suppression of muzzle flash is an important area to address in detail. Collaboration with Banat Laboratories in this research area could accelerate progress. OPPORTUNITIES AND CHALLENGES Materials by Design ARL seeks to develop the capability to design, optimize, and fabricate lightweight protection mate- rial systems exhibiting revolutionary performance. The approach is to realize a “materials by design” capability by establishing a new Collaborative Research Alliance (CRA) focused on Materials in Extreme Dynamic Environments (MEDE). The focus of the CRA is to advance the fundamental understanding of materials in high-strain-rate and high-stress regimes. The CRA is intended to create a collaborative environment that enables an alliance of participants from academia, government, and potentially industry and/or nonprofit organizations to advance the state of the art and assist with the transition of research to enhance the performance of protection materials of interest to the Army. With an award ceiling of $89.9 million, this effort is clearly a major undertaking that will likely require a new approach and level of management both within ARL and in the management of the multi-university consortium to ensure success. 1IRFNA and TMEDA-DMAZ are types of fuels and propellants. IRFNA is inhibited red fuming nitric acid, TMEDA is tetramethyl-1,2-Ethylenediamine, and DMAZ is dimethylaminoethylazide .

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110 2011–2012 ASSESSMENT OF THE ARMY RESEARCH LABORATORY The ARL multiscale material modeling program is a very ambitious effort. It relies on university partnerships to provide and develop many aspects of multiscale materials science. Excellent partners with strong and appropriate backgrounds in these areas have been identified. This is a noble effort if the university partnerships can be coordinated under ARL leadership. These new university programs, especially MEDE given its large number of participating universities, will require effective management on both the university and WMRD sides of the relationship to ensure success. However, no clear man- agement framework has been identified for this purpose. Several areas are not currently well developed. For example, the methodology to bridge scales (particularly coupling to the continuum level for system- level modeling) is still a research area in the general material science community. Most importantly, the approaches to assess the accuracy of material physics require a deep understanding of validation. Key to that is linking to experimental studies that probe the scale of intent. Continuum-level experiments and techniques are often insufficient for validation at reduced scales. Furthermore, many uncertainties will be encountered in these assessments, and uncertainties propagate across scales. Quantifying these uncertainties is an important aspect of validation. The Department of Energy (DOE) sponsored an Advanced Simulation and Computing Academic Strategic Alliance Program to address these same issues. ARL should review this DOE program, because the university partners are perhaps several years ahead in uncertainty quantification, and their model for university interaction bears close examination. Also, in the effort to incorporate computations, modeling, and simulation in the research, it is important to sustain the commitment to leading-edge experimental methods and validation at all scales. Examples of needed leading-edge facilities include electron microscopy with atomistic resolution; ballistic measure- ment facilities that provide three-dimensional, digital kinetic information with innovative, state-of-the- art measurements systems; and innovative validation at scales consistent with the multiscale analyses. “Materials by design” is a grand challenge that pushes the high-performance-computing envelope, and its attainment will require a significant commitment of time and resources. In principle, accurate and efficient multiscale modeling will replace costly and time-consuming experimentation to discover process-structure-property relationships; it proceeds from a set of desired properties (or performance criteria) in a systematic way to identify material structures that display the desired properties. Gener- ally, the systematic aspect of the design process utilizes process-structure-property relationships, which reflect the control a process places on structure and the control that structure places on properties. The current limited ability to design materials stems from an incomplete knowledge of all of the process- structure-property relationships. Furthermore, because design is the inverse of multiscale modeling, ARL’s solution to this problem will only be found through a systematic search of materials structure space for desired properties and performance. Solving the inverse problem has taken on a mathematical definition in recent years, although the principle remains the same—to work systematically from proper- ties to structure. In addition, extension of mature multiscale modeling to manufacturing considerations will ensure that materials or designs remain in the window of practical solutions. Much more progress is needed to integrate this competency with manufacturing and affordable solutions. Rather than use phrases such as “multiscale modeling” and “materials by design,” the programs should use the phrase “integrated computational materials engineering,” while still encouraging multiscale modeling. In this way, the emphasis would shift to materials engineering, which is where ARL’s emphasis should be. The programs in materials and manufacturing science for lethality identified the following current and future themes: materials by design—a multiscale approach; materials in extreme dynamic environ- ments; field effects in materials; emerging materials; life prediction of materials; and enabling agile manufacturing science During the past few years, WMRD has expanded efforts aimed at materials modeling, as evidenced by the first-principles density functional theory (DFT) analyses on interface properties in rare-earth

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WEAPONS AND MATERIALS RESEARCH DIRECTORATE 111 modified silicon nitride (Si3N4) for ceramic armor, and the research on chemical kinetics and reactions paths that provides input for computational fluid dynamics models for rocket propulsion. In addition, crosscutting efforts build on other computational expertise within ARL, notably on survivability with the Survivability/Lethality Analysis Directorate.   A higher level of the WMRD organization has goals for multiscale modeling, materials by design, and integrated computational engineering. A more detailed strategy for the development of a suite of modeling capabilities along with validation and verification plans is needed for continued success in this area. Developing this strategy is important in light of managing the new MEDE program. An approach that has been successful in other DoD-oriented organizations involves the selection of one or two foun- dational problems that address a system or subsystem (e.g., a medium-caliber weapon) and motivate the development of a suite of complementary computational and experimental tools. WMRD should clearly define the classes of computational tools needed to solve important foundational problems and should articulate a timeline for their development, validation, and application to problems. The role of external organizations, including DOE and universities, should also be considered carefully. Computational and Experimental Tools The development of a complementary suite of computational and experimental tools is expected to permit WMRD to respond to the needs of the soldier at the unit level with unprecedented speed. Development of this infrastructure will require new investments in state-of-the-art characterization and testing capabilities, particularly in the areas of microscopy and spectroscopy, in order to validate models across all length scales and to rapidly explore the design space. The work on detonation characteriza- tion is an example in which development of small-scale experimental tools, combined with modeling, enables more rapid exploration of novel, insensitive energetic materials. In the area of characterization, strategic partnerships will be critical for success, because no single institution can maintain all classes of advanced instrumentation. Integration over multiple length or timescales is a very challenging topic in materials engineer- ing and the simulation of bulk properties linked to atomistic-scale attributes. The extension of mature multiple-scale modeling to manufacturing consideration will ensure that materials or designs remain in the window of practical solutions. Little attention has been directed to identifying the needed attri- butes for the testing or forming equipment. It may be impossible to attain the desired combinations of pressure, temperature, time, strain rate, or other manufacturing attributes. Polymers decompose, metals melt, diffusion occurs, and stress or temperature-induced phase transformations occur, and these bound- ary conditions have to intersect with tooling constraints (strength, for example), loading rates (press design), and practical limitations. WMRD made repeated mention of cost, and although some of the novel penetration-resistant materials are of great importance, the researchers did mention the inability to lower cost. Extension into the arena of cost is yet another aspect of multiscale modeling. That is, are the materials simply too costly (aluminum alloyed with silver, for example), or is the fabrication window too narrow, incurring an excessive cost? There has been good progress, but still much more is needed to integrate the materials into manufacturing and affordable solutions. The research program is broadly based on sound conjectures and relies on contemporary tools. The research tools are adequate, but with limited technicians one would expect to see more automation in the experimental tools. However, practical aspects are elusive at times, and the solutions offered sometimes can be at odds with statements about cost considerations. For example, gradient microstructures are commonplace in sintered tungsten carbides, requiring only an atmosphere adjustment during sintering, but the early trials with cemented carbide projectiles lacked appreciation of this dimension. Indeed the

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112 2011–2012 ASSESSMENT OF THE ARMY RESEARCH LABORATORY early materials were taken from lower quality materials. Partnerships should be formed with leading teams in technologies for which WMRD is not up to date. In the case of the cemented carbides, it is most appropriate that teaming agreements be made with leading firms such as Kennametal. Overall, although partnerships exist for several projects, the critical participation of leading partners is missing. WMRD can benefit from more active outreach to experts and from broader involvement by experts in individual programs. WMRD researchers mentioned that joint publications were discouraged, but such collaboration should be encouraged. Nanoscale materials can be consolidated by new combinations of temperature-pressure-time. Multiple-scale modeling will identify the combinations of greatest merit, which will likely lead to lower processing temperatures and a need for much higher consolidation pressures. Higher pressure consoli- dation and shaping of materials (e.g., polymers, metals, ceramics, and composites) is a very desirable new research direction for WMRD. The work should anticipate pressures in the 2 to 5 GPa range and simultaneous temperatures in the 1,400 °C range. Short cycles are of great merit. Modeling and Simulation Challenges Because many physicochemical processes, simulated by ARL researchers, involve multiscale, multi- dimensional, and multiphase flows with heat and/or mass transfer under dynamic conditions, numerous challenges exist in the modeling work as well as in numerical simulation of these processes. Because of the complex physical and chemical processes described above, scaling laws are expected to be very difficult to develop for armor penetration process. There are multiple pathways for material to respond to its physical contact with the impacting or penetrating projectile and to the combustion- induced environment variations. For example, the material used in the armor plate can go through mechanical fracture process. The instantaneous contact surface(s) between the high-temperature ­ opper c jet depend upon many detailed interactions between the hot penetrating materials and the deformed armor plate components. To understand the potential heterogeneous reactions between the gas-phase chemical species and the instantaneous surface of the condensed phase materials, one has to consider the nanoscales in terms of active reaction sites, the microscales for chemical kinetics, the mesoscales for species mass diffusion across the layer with strong concentration gradient, and the integral scale in the processes associated with jet penetration, convective heat transfer in the flow channel, conductive heat- transfer process, and mechanical deformation in the condensed phase. Besides the matter of different reaction paths, the armor material may evaporate and react with the ambient penetrating gas mixture. Some combustion products may also adsorb on the surface. Some metal plates may have molten layer on their surfaces. High-speed flow may introduce Kelvin-Helmholtz instability associated with surface wave breakup and droplet formation. Turbulent multiphase reacting flow also requires consideration of a broad range of length scales, from smallest Kolmogorov length scale to the integral scale. Surface roughness and/or contour variation with time should also be considered, because armor components usually do not consume at high rates. The timescale for their deformation and consumption usually dif- fers from the short timescale for chemical reaction and jet penetration. The influence of protruded edge of damaged armor plates may induce vortex shedding phenomena and therefore influence the mixing process between the fuel-rich and oxidizer-rich species. These are some of the important processes to be considered in the model formulation. From the numerical simulation point of view, wide ranges of scales are present in the armor pen- etration processes that differ by orders of magnitude because of both turbulent and multiphase reacting processes. Therefore, massive computational resources are required to reasonably resolve those scales. A large-eddy simulation (LES) approach can be applied in this problem, for which adequate subgrid

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WEAPONS AND MATERIALS RESEARCH DIRECTORATE 113 scale models need to be developed. The direct numerical simulation (DNS) approach is expected to be far from suitable for any of the armor plate penetration simulations at the present time. Because this problem involves liquid-gas interface, liquid-solid interface, and time-varying diffusion flames in the gas phase zone, interface capturing (or tracking) becomes an important requirement to achieve. Thus, a level set technique should be considered for treating time-varying interfaces. The Disruptive Energetics Program The “disruptive” energetics program conducts leading-edge research in new material design largely based on state-of-the-art molecular modeling toward developing new energetic materials that surpass the energy densities of current materials. Several WMRD researchers in this area are well recognized in this field. However, the focus on energy density as the metric of performance may be too restrictive. The manufacturability and stability of these meta-stable materials are important aspects to consider for practical application. The desired energetic materials also have to readily convert stored chemical energy almost directly into PdV work (refers to expansion work) rather than into just heat (thermal energy) if it is to be used in fragmenting or blast munitions. Determining these transformation proper- ties usually requires material quantities that are much greater than those associated with the atomistic scales. Although the laboratory uses the traditional experimental methods to assess heat of formation and density, these techniques may be insufficient to determine appropriate energetic material character- istics. To complement the developing simulation capabilities, some research should consider developing experimental diagnostics (i.e., ultrafast laser or line-Visar) that can probe the smaller scales appropriate for assessing the atomistic, subgranular, and mesoscales. The diagnostics may be necessary to deter- mine the bridging of scales (particularly linking to the continuum scale), but it is currently lacking in the research portfolio. WMRD has initiated a new disruptive energetics technology effort with very aggressive goals for developing new types of high energy density materials (factor of 10+ greater than current materials) suitable for use in Army weapon systems. This is an extremely challenging problem, and the WMRD staff needs to ensure it is taking advantage of all of the related work that has taken place elsewhere, both in the United States and overseas. The goal WMRD has set of being able to provide the power of 155-mm artillery in a significantly smaller volume (i.e., 40-mm-size to 80-mm-size munition) is an extremely challenging problem. The high risk inherent in extended solids and nano-diamonds as energetic materials can be mitigated by the development of new theoretical and experimental tools that are applicable to energetic materi- als in general. To this end, WMRD needs to complement the traditional experimental characterization methods by collaborating with other university and national laboratory experimental programs using advanced diagnostics for assessing the atomistic, subgranular, and mesoscales, specifically, the local electrode atom probe at Iowa State University, Colorado School of Mines, and Northwestern University; the ultrafast laser at Lawrence Livermore National Laboratory and Los Alamos National Laboratory; and the hot stage scanning electron microscopy at Lawrence Livermore National Laboratory. Investing in advanced detonation diagnostics such as line-Visar, available at Sandia National Laboratories, would benefit both high- and low-risk efforts (e.g., DEMN—a type of explosive). The nano-diamond work is interesting, but additional work, some of which is planned, is needed to make measurements beyond temperatures. A question to ask is: Would a detonating system be expected to yield measureable effects? In the study and development of poly-CO, WMRD uses systematic approaches to explore the proper- ties of this new energetic material, whose energy density is higher than those of conventional explosives (e.g., RDX, HMX, and CL-20). The estimated heat of explosion (∆Hexp) of poly-CO is around 8,130 J/g,

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114 2011–2012 ASSESSMENT OF THE ARMY RESEARCH LABORATORY which is higher than that of RDX (5,700 J/g) and CL-20 (6,344 J/g). In addition, the estimated mass density of this new material is 2.46 g/cc, which is also higher than that of RDX at 1.8 g/cc and CL-20 at 1.96 to 2.04 g/cc. WMRD’s systematic approaches include: • Verifying the stability of the poly-CO using hysteresis characteristics of this material after compressing it to 10 GPa and then dropping the pressure to lower levels; • Studying its phase diagram and establishing boundaries between delta, alpha, beta, epsilon, and fluid phases; • Determining its decomposition temperature around 650 K, which is higher than those of RDX and CL-20 at 435 and 468 K, respectively; and • Studying the deflagration emission enhancement of RDX/nano-diamond mixture from pure RDX, using pulse jet laser with a wavelength of 1.06 µm. However, this material’s effectiveness for propulsion and detonation application is not clear. First, the heat of explosion (∆Hexp) is not as high as the teams believe, around 8 to 10 times that of RDX and/or CL-20. It is only 1.28 × ∆Hexp of CL-20. Second, because of the relatively high atomic weight of both carbon and oxygen, the molecular weight (Mw) of the combustion product of poly-CO will not be low enough to become highly attractive. This is based on the fact that both specific impulse (Isp) for rocket propulsion and impetus (Im) for gun propulsion are dependent on the following equations, where Tf refers to the flame temperature: Tf Isp ∼ and Im~Tf/Mw Mw The group should consider evaluating the propulsive performance of poly-CO using the thermochemistry computation with NASA-CEA Code, Blake Code, or Cheetah Code before putting further effort into its development. Third, the amount of material is only available in micrograms, which is too small for any accurate material characterization purpose. A more economic method for its scale-up production in gram quantities would be helpful. The ARL Sensors and Electronic Devices Directorate (SEDD) has been a major contributor to a DoD and Army multi-year advanced power and energy research and development initiative. The results of this initiative should be reviewed to determine if any new, low-cost technologies for producing and/or storing energy can power novel advanced protection systems and help to improve vehicle and/or soldier protection. Human Models Development of improved human models is both challenging and controversial. Not only are there multiple scales, both temporal and spatial, in the modeling of the brain subjected to primary blast, but also it is not clear how to relate the stress-strain history calculated at the continuum level to physiological and cognitive damage. The subscale damage may not be modeled directly. Instead, careful measurements of the damage of insulted biological materials should be correlated with prescribed insult levels. However, the use of continuum modeling techniques of complex structures such as the brain (neuronal networks, highly vascularized) or extremities (hard material connected to soft material by connective tissues of intermediate properties), in a way that the data can be translated to actual injury, is highly ambitious, If successful, however, this work would make an extraordinary contribution to the understanding of such injuries and ultimately to the development of protection strategies.

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WEAPONS AND MATERIALS RESEARCH DIRECTORATE 115 Collaborations and Other Interactions with the Professional Community Given the complexity of multi-scaling research, ARL should consider using an interagency approach. Many other government agencies internal and external to DoD are attempting to understand similar prob- lems, and ARL can take advantage of synergies to fast track its computation and computation method programs. ARL can assume the leadership role in this research area by organizing an interagency confer- ence focused on multi-scaling research. Understanding what the laboratories at DOE, other parts of the Army, Air Force, Navy, Federal Aviation Administration, and the academic community have attempted in this area would be very beneficial. Although the phrase “low cost” was mentioned repeatedly by WMRD staff, no consistent description of cost analysis or cost-benefit tradeoffs was provided, and some of the researchers seem to be moving into very expensive processes to lower material cost. There have been attempts to disrupt prior thinking and to find disruptive solutions. However, it is difficult to be disruptive from an insider position. It will be important to properly construct and empower programs so they can be truly disruptive. Often, those with nothing to lose, that is, outsiders, can be most effective in constructing and empowering programs so they can be truly disruptive, which suggests that parallel organizations, Small Business Innovation Research (SBIR) contracts, or maybe even university teams could take on this role. The SBIR program is inconsistent with regard to assisting with the research mission. In a few instances SBIR programs provided visible contributions, but overall this seemed to be ignored. Although there was considerable discussion on filling out the tool box for the investigators, there was no mention of maintaining that array of tools. As computational platforms, researchers, and software change, it will be important to frequently revisit the tool box to ensure that the packages are operable and adequate. The once robust SBIR program has been de-emphasized. Proposal review may be a contributing factor, but this trend should be examined. Similarly, proposal evaluations of the Director’s Strategic Ini- tiative (DSI) and the Director’s Research Initiative (DRI) programs, which allocate funds for innovative projects, should be streamlined to reduce the burden on the senior members of the staff. Researchers are not routinely attending scientific meetings to interact with peers and share unclas- sified work. One example is the APS shock compression meetings, but there are numerous professional meetings where ARL personnel could benefit from exchanges with their peers. The unclassified work could be presented at such meetings. Because effort, time, and funding are expended on basic research, the talented ARL researchers should be encouraged and supported to interact with their peer researchers, to benefit their classified work and the scientific community. Leadership should encourage archival pub- lication of the experimental results, as well as the computational results. The Journal of the Army, Navy, NASA, and the Air Force (JANNAF) could be considered if the work is considered limited distribution. The goal of assembling a world-class research staff in WMRD will require a sustained effort. The recession of 2007 may have contributed to the surge of excellent personnel joining ARL, but as the recovery of the economy progresses and the DoD budget is reduced, there will be a need to retain the human talent pool responsible for the progress in recent years. One suggestion is to develop a program like the Truman postdoctoral fellowship of Sandia. Additionally, the need to develop programs to mature and mentor junior staff is essential. To enhance the recruiting of highly talented staff, ARL should consider offering a special fellowship that may attract exceptional new researchers to ARL. The DOE national laboratories offer special fellowships (Truman Fellowship at the Sandia National Laboratories, Oppenheimer Fellowship at Los Alamos National Laboratory, and Lawrence Fellowship at Lawrence Livermore National Laboratory) that typically bring in approximately 50 applicants. Formal proposals and letters of recommendation are requested and evaluated by a committee of senior scientists. One or two of these fellowships are offered per year. These fellowships have brought to the national labora-

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116 2011–2012 ASSESSMENT OF THE ARMY RESEARCH LABORATORY tories exceptional researchers who often later become permanent staff members. They are offered as a postdoctoral position with equivalent staff salary and with additional funding that supports self-directed innovative research of their own origin. Perhaps ARL can consider developing a similar fellowship program to attract exceptionally talented researchers that will showcase research capabilities at ARL. OVERALL TECHNICAL QUALITY OF THE WORK The overall scientific quality of WMRD’s work is comparable to that of comparable national labo- ratories. WMRD should be commended for its investment in advanced energetic material investments. Many other laboratories are generally moving in the opposite direction with respect to investments in energetic material research, unfortunately. Generally, the WMRD programs reflect a broad understanding of the science and engineering underlying their work. There is generally a strong interaction between experiment and simulation. WMRD has appropriate laboratory equipment and numerical codes and models. Generally, the laboratories are well supplied and state of the art. In particular the shock physics laboratory is impressive. Computational tools are used extensively, but use of characterization equip- ment could be expanded, and in some cases WMRD could adopt additional numerical codes and models from outside ARL. The research staff is well qualified, enthusiastic, and knowledgeable. WMRD’s work reflects understanding of the Army’s requirement for research or analysis, and in many cases there is a clear focus on the Army’s needs—for example, in the development and fielding of the new bullet. WMRD uses an appropriate mix of theory, computation, and experimentation, as exemplified by the interaction of the grain modeling that predicted the dislodging of the bullet by bed compaction and experimental verification. Also, the balance between 6.1 and 6.2 research and the ratio of customer funding to internal funding are appropriate. The enthusiasm of the WMRD staff appears impressive. The number of WMRD staff members hold- ing advanced degrees, particularly Ph.D.’s, has been steadily growing. The staff’s technical qualifications are impressive, reflecting hiring from many universities. The research staff’s skill set is diverse, reflect- ing hiring from many universities. Recent hires show great capability in contemporary simulation tools. However, the knowledge base is missing certain critical components, such as a connection to the nation’s research infrastructure and the practical observations that should predate simulations. These limitations are offset by the researchers’ enthusiasm. More linkages are needed, and hiring is not coordinated and planned to bring in top talent. As the science and engineering markets recover, ARL will need to be more proactive in its early identification of talent. Because fewer hires will be possible in future years, care should be taken to ensure that top talent is added. The research tools are adequate, but the limited number of technicians makes automation in the experimental tools a necessity. The WMRD efforts are focused on critical aspects of improved armor and munitions. The improve- ments in protection and penetrators create a perpetual contest. The lethality of the new ammunition is well demonstrated and requires a responsive escalation in protection. The cadre of early-career technical hires is maturing and sustaining focus on topics with likely impact, and management allows projects to reach maturity. How decisions on project termination are made is unclear, so a more formal case might be appropriate to show the decision points. The WMRD armor protection technology and prototype combat vehicle armor development are internationally recognized as best-in-class, as evidenced by the half dozen or so allied countries that maintain active collaborations with WMRD in the armor technology area, as well as by Army near- reliance on WMRD-developed combat vehicle armor technologies. Compared with most of the Army, Navy, Air Force, and DOE laboratories performing weapons-related research, as well as a number of weapons laboratories in foreign countries, the integrated capabilities that WMRD has in the armaments

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WEAPONS AND MATERIALS RESEARCH DIRECTORATE 117 and lethality areas are among the best anywhere. WMRD is not the best in everything it does, but its integrated interior, exterior, and terminal ballistics, lethality, materials, experimental, computational modeling, and systems analysis capabilities are very impressive and considered to be among the best worldwide. WMRD continues to conduct high-quality armament-related research that is leading to new weapon system concepts and products offering advanced capabilities that make a significant difference to soldiers. The quality of WMRD’s lethality research also is impressive. The lethality mission is very impor- tant to the Army, and WMRD continues to conduct lethality-related research that is leading to weapon system concepts and products that can make a significant difference to the soldiers. WMRD has a good understanding of the Army needs in this area. WMRD has streamlined and focused its core lethality technology to make it more consistent with the Army’s current “squad centric” focus aimed at increas- ing the combat effectiveness of small units. WMRD’s solid lethality technology program will be able to deliver new understanding and many new products to the Army over the coming years. WMRD is doing an excellent job.