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Terminal Effects

INTRODUCTION

On November 14–17, 2022, the National Academies of Sciences, Engineering, and Medicine panel charged to conduct the 2022 assessment of the terminal effects competency, which focuses on the sciences and applied research of weapon–target interactions, met at the Aberdeen Proving Ground to review information presented by the U.S. Army Combat Capabilities Development Command (DEVCOM) Army Research Laboratory (ARL). The focus of this year’s review was to assess the four core competencies that make up the terminal effects competency, specifically (1) armor mechanisms and countermeasure; (2) mechanisms for human injury and protection; (3) mechanisms for lethal target interactions; and (4) terminal effects mechanics, modeling, and simulation.

There have been many transformations affecting ARL as it restructures within the Army Futures Command to pivot to the pursuit of material solutions to support army mission needs—current and future. Per ARL’s mission, the focus on “operationalizing science”¹ as a guiding force in its terminal effects programs to enabling the objective of delivering solutions at the speed of relevance are well thought out. Integrating science toward supporting the Army needs of 2040 through utilizing intramural and extramural programs clearly requires focused attention on continuous improvement in building future talent, managing equipment, updating and developing new research facilities, while evolving ARL’s research and engineering culture. This focus was evident and demonstrates that ARL’s leadership understands both the state of the art in the science and engineering underpinning terminal effects science and technology (S&T), as well as the need to invest in coupling theory, modeling and simulation, and numerical analysis tied to both small-scale experiments as well as integrated platform-specific tests and evaluation. Continued building of linkages within ARL’s programs with emphasis on the ties between processing-structure-properties-performance (PSPP) is seen as a powerful pathway to improvements in the terminal effects overall portfolio and a driving pathway to the development of physically based predictive models to support future design and performance capabilities. As increasingly more complex physics is introduced into ARL’s design and performance simulation computer codes, continued efforts to include quantification of uncertainty, margin, and errors in both experiments and modeling is to be strongly encouraged toward improving predictive tools.

The overall level of science and engineering across the breadth of the terminal effects portfolio was excellent in its scope, prioritization, staffing, and utilization of facilities. It was difficult to assess the overall balance of the terminal effects programs given the evolving adversary transition from engaging against a third world to a first world adversary environment. Consideration of how ARL’s terminal effects portfolio needs be balanced against the evolving threats, which are changing in terms of speed, energy, and range of engagement (e.g., a movement from body armor and rigid bullets to defending against antitank guided missiles) was clearly a driving force in ARL’s program development and resource prioritization.

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¹ The U.S. Army Combat Capabilities Development Command (DEVCOM) Army Research Laboratory’s (ARL’s) mission is to “Operationalize Science for Transformational Overmatch.” See DEVCOM ARL, “Who We Are,” https://www.arl.army.mil/who-we-are, accessed December 20, 2023.

The challenges facing the Army in weapon–target interactions in the current era of fighting in multi-domain environments, where the environment is both dynamic and where munitions and countermeasures have fleeting effectiveness, is well understood by ARL and is central to ARL’s terminal effects strategic planning. Furthermore, the challenge to defend against a battlefield awash with threats spanning rigid projectiles against the warfighter to high-velocity, explosively formed projectiles (EFPs), and shaped-charge jets (SCJs) where inertial effects are dominant, is arduous.

While it is beyond the scope of this assessment to comment on the relevance of terminal effects projects to the Army’s mission, better delineation of ARL’s high-level strategy governing the balance between the Army Research Directorate (ARD) and the Army Research Office (ARO) programs during future National Academies’ reviews of ARL’s terminal effects programs would provide future ARL assessment panels and committees with helpful insight that may inspire ideas on both partnership and technical opportunities, and is encouraged.

The next chapter presents the publicly releasable assessment of the technical quality, opportunities, and challenges; the portfolio of scientific expertise; and an assessment of the facilities and resources for each of the core competencies within ARL’s overall terminal effects competency, specifically (1) armor mechanisms and countermeasure; (2) mechanisms for human injury and protection; (3) mechanisms for lethal target interactions; and (4) terminal effects mechanics, modeling, and simulation.

TECHNICAL QUALITY OF THE CORE COMPETENCY RESEARCH

Armor Mechanisms and Countermeasure Core Competency

Research Portfolio Challenges and Opportunities

The armor mechanisms and countermeasure core competency focuses on the discovery and advancement of techniques to minimize or eliminate lethal effects at minimum space, weight, and power.² The presentation “Architectured Materials for Controlling Dynamic Behavior” focused on a new Multidisciplinary University Research Initiative (MURI) on graph topology and network science–enabled design of irregular or disordered metamaterial structures for manipulating stress, which aims toward controlling dynamic behavior through architecture materials. There is an opportunity to start early and link these very fundamental studies with terminal effects requirements, thereby guiding the outcome of the MURI toward terminal effects benefits that could bear fruit in the next decade. If they are not already doing so, the MURI principal investigators (PIs) need to be encouraged to focus on defining realistic values for stress regimes that determine if the material should be ordered versus disordered. Another area for synergy is for machine learning (ML) expertise to flow from extramural PIs on this diverse and scientifically top-notch MURI team to the intramural terminal effects teams.

Broader opportunities for the core competency include:

• Machine Learning: As the core competency develops its ML capabilities, it would be important to note that ML is a staggeringly fast-growing field. There are now new adaptive algorithms that incorporate human experts in the loop to bring in their physics knowledge as an extra layer in addition to experiments and simulation data. The thinking here is that human expert knowledge is also data, and its significance needs to be carefully weighted in circumstances where machines are used to learn and make predictions.
• Data Management: The terminal effects competency has a tremendous amount of valuable legacy data on ballistics that is unique and irreplaceable to the Department of Defense (DoD).

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² DEVCOM ARL, “Foundational Research Competencies and Core Competencies,” document for the Army Research Laboratory Technical Assessment Board, received March 30, 2022.

Generating new data can be expensive and time consuming, which calls for planning beyond just a data-driven ML approach. One first step could be the incorporation of materials science databases. Discussions with ARL scientists revealed their interest in learning more about existing materials databases. While there exists no single database that can serve as the model for the Army’s efforts (especially considering the security challenges), there are some good examples to start with—if ARL is not already using them. The following list came out of the Materials Research Society Artificial Intelligence Staging Taskforce meetings. This voluntary group (academia, industry, and government.) is exploring how the materials community uses, stores, and shares data to understand how it might meet the emerging needs of materials researchers. The list includes:

• REMI: Resource for Materials Informatics is an indexed repository for (scripting) notebooks using Jupyter,³ Matlab LiveScripts, etc., for collecting, pre-processing, analyzing, and visualization of materials data.⁴
• The Materials project is a materials data repository in coordination with the Materials Genome Initiative. This open web-based resource offers access to information on known and predicted materials as well as powerful analysis tools to design novel materials.⁵
• Materials Resource Registry helps the materials community to search for and find information about materials. This National Institute of Standards and Technology–developed, web-based registry operates as a centrally located service, allowing users to register materials data sets and other resources, bridging the gap between existing resources and end users by making all registered information searchable and available for research to the materials community.⁶
• nanoHUB is a website that provides open access to simulation as well as new ML tools in nanotechnology and materials science for research as well as education and training purposes.⁷
• The Cambridge Crystallographic Data Centre is a compilation of crystal structures and perhaps the best and widely used example for a materials data repository. They represent the largest database for small-molecule organic and metal-organic crystal structures, worldwide.⁸

Finally, it is important to craft data management plans that are compliant with Findability, Accessibility, Interoperability, and Reusability (FAIR) principles. The FAIR standards deal with digital object identifiers for publishing data, tagging the data with appropriate metadata, and finding the right repositories for ease of access and relevancy. The Department of Energy’s (DOE’s) Office of Science provides a comprehensive summary of these requirements for scientific data management.⁹ ARL’s intramural and extramural programs need to pursue the assurance that FAIR principles are followed as they craft their data management plans.

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³ See the JUPYTER website at https://JUPYTER.org, accessed December 5, 2023.

⁴ National Institute of Standards and Technology (NIST), “REMI: Resource for Materials Informatics,” https://pages.nist.gov/remi, accessed December 5, 2023.

⁵ See The Materials Project website at https://materialsproject.org, accessed December 5, 2023.

⁶ NIST, “NIST - Materials Resource Registry,” https://materials.registry.nist.gov, accessed December 5, 2023.

⁷ NanoHub, “NanoHub - Resource Tools,” https://nanohub.org/resources/tools, accessed December 5, 2022.

⁸ See the Cambridge Crystallographic Data Centre website at https://www.ccdc.cam.ac.uk, accessed December 5, 2022.

⁹ See Department of Energy, “Statement on Digital Data Management,” https://science.osti.gov/Funding-Opportunities/Digital-Data-Management,” accessed December 5, 2022.

Mechanisms for Human Injury and Protection Core Competency

Research Portfolio Challenges and Opportunities

The mechanisms for human injury and protection core competency focuses on developing a quantitative understanding of the mechanics and physics that affect human structure and function as well as the fundamental understanding of human injury to high-intensity loading (i.e., ballistic and blast). The exploitation of this understanding is to protect or degrade soldier function.¹⁰ The meeting presentations for this core competency focused on mitigation of critical tissue and organ damage (i.e., damage that is fatal or near fatal). The research areas that were highlighted included skull fracture, lung damage, and armor penetration.

ARL is leading in simulations of lung mechanics. However, challenges that need addressing include generating simulations that can recreate the physics from the experiments (e.g., blast loading) to mitigate over- and under-correcting the simulation results. Addressing these challenges will require engaging more outside collaborators that perform experiments using animal models to advance the lung mechanics-modeling field. This is an opportunity for ARL to become one of the leaders at linking lung mechanics with local injury.

Additionally, there is an opportunity to advance the development of ARL’s surrogate lung model by using the data from ARL’s high-speed X-ray videos of lung deformation for validation. The benefits of this surrogate model to understand lung mechanics needs to be clearly defined. For instance, damage severity for a surrogate lung model used for prediction and mitigation needs to be defined at various length scales to facilitate a comparison of the results between theory, simulation, and experiments involving animal models and cadavers.

Mechanisms for Lethal Target Interactions Core Competency

Accomplishments and Advancements

The mechanisms for lethal target interactions core competency is defined by the discovery and advancement of weapon and target interactions to maximize the effectiveness and efficiency of munitions to provide lethal overmatch across all calibers and platforms.¹¹ The research methodology within this core competency appeared to have a heavy emphasis on experiments, although modeling to guide experimental investigations was seen in some areas. The overall scientific quality of the experiments is high, with the methods and diagnostics comparable to research conducted at other top academic and government facilities.

Research Portfolio Challenges and Opportunities

The balance of this core competency’s research portfolio is skewed toward experiments. State-of-the-art modeling capabilities are being applied within the other core competencies, which creates an opportunity to connect with and leverage those efforts here. Extension of the current program of record may present a risk in obtaining the insights necessary to explain some of the observed phenomena relating to armor performance. Balancing the portfolio with modeling creates an opportunity for hypothesis-driven experimentation and a better path forward for understanding the underlying physics.

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¹⁰ DEVCOM ARL, “Foundational Research Competencies and Core Competencies,” document for the Army Research Laboratory Technical Assessment Board, received March 30, 2022.

¹¹ Ibid.

Terminal Effects Mechanics, Modeling, and Simulation Core Competency

Accomplishments and Advancements

The terminal effects mechanics, modeling, and simulation core competency focuses on developing a quantitative understanding of structural and material response due to ballistic, blast, and highly energetic events. It also looks at high-fidelity experimentation closely coupled to development and validation of theory, algorithms, and computational techniques that enable the reduction of the problem space related to technology concepts for protection and lethality.¹²

This core competency could be considered as the development platform for providing the scientific foundation and the tools for the work carried out in the other core competencies within terminal effects, with the presentations and posters representing the impressive interdisciplinary breadth of work undertaken under the umbrella of the competency. The main scientific thread running through this core competency is the study of fracture and failure of materials with the objective of developing predictive capabilities to further the process of materials selection and design. This is being accomplished through development of an understanding of the underlying unit processes and then enriching the tools as needed with the appropriate physics. For example, the characterization of the fiber and film-based ultra-high-molecular-weight polyethylene failure and deformation behavior project utilizing both innovative experiments and modeling was seen as an excellent example of coupling innovative experimental technique development with carefully focused modeling. Probing the transverse tensile behavior and delamination of the composite plies with careful quantification of the single fiber properties as a function of strain rate was seen as very innovative and world-leading research.

ARL’s programs in terminal effects, as far as their understanding of mechanics, modeling, and simulation from both the standpoint of munitions and protection, lead DoD across the domains of small arms to vehicle protection technologies. The projects presented in this year’s terminal effects review both highlighted ARL’s leadership in the science and engineering in this area but also their deep understanding of the evolving threat environment facing the United States around the world. ARL’s programmatic space needs to cover the physics of protection from small-arms munitions, where material strength mostly dominates, to high-velocity threats for vehicle protection, where the response may primarily be controlled by inertial physics or hydrodynamics. The physics, chemistry, and engineering controlling ARL’s terminal effects from a munition’s vantage needs to similarly span a regime challenged to arm the warfighter with technologies to confront adversaries one on one or to hold adversary platforms at risk.

Research Portfolio Challenges and Opportunities

There is strong evidence across the terminal effects portfolio of close coupling among experiments, modeling, and simulation. Continuing this synergy is crucial if the goal of developing physics-based predictive capability to support munition and armor design and performance is to be achieved.

A concern about the use of different codes emerged from the presentations of many different simulation platforms. These ran the gamut from commercially available canned codes to more sophisticated multi-physics codes that are export controlled. The commercial codes are largely being exercised in extramural projects, while internally the scientists tend to use codes developed by DOE’s National Nuclear Security Administration (NNSA) national laboratories. To have confidence in the outputs there needs to be a benchmarking exercise on a common problem between the commercial and NNSA codes. This will also allow a determination of the physics or numerical gaps in each platform and, in addition, point to which code is most suitable for a particular task. A similar problem is faced by the NNSA national laboratories, and a common validation exercise is seen as the best path forward to enable constructive cross-talk across experimental and computational platforms.

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¹² Ibid.

COMPETENCY PORTFOLIO OF SCIENTIFIC EXPERTISE

The scientific expertise across the terminal effects competency was found to be very impressive. Suggestions and comments on the individual core competencies are detailed below.

The mechanisms for human injury and protection core competency has at least one external collaborator for each of the projects. Some of the extramural scientists are well known and highly qualified to support the goals of this core competency. Others did not seem to be doing mechanics at the leading edge that could advance the technical goals of the overall competency. The inclusion of a panel consisting of medical experts in the project assessing injury severity as a function of skull fracture was advantageous. All ARL projects that involve the development of injury risk or damage severity would benefit from such panels to increase accuracy of the predicted results from simulations or experiments. For this core competency, it was found that the investigators within ARL were well qualified but there was a lack of evidence of actual teamwork in some projects. Although not articulated explicitly, one exemplary example of mentoring of a junior investigator by someone who is more established exists within this core competency. Replicating this type of relationship to enhance the career trajectories of the junior investigators and produce future high-quality research can be beneficial to the goals of the overall competency.

The scientific expertise of the presenters within the mechanisms for lethal target interactions core competency was impressive. It was encouraging to see that a number of early-career scientists have been recruited to work in this core competency area. The core competency would benefit from seeing the stakeholder requirements for improved performance in the various research areas being pursued, in order to help judge the significance of the technology gap and whether additional staff or resources need to be recommended for work in the area.

The overall level of scientific and engineering staff across the breath of the terminal effects mechanics, modeling, and simulation core competency within ARL’s overall terminal effects portfolio (both ARD and ARO) was excellent in its caliber of personnel, their productivity, and their vision driving the direction of their projects. ARL’s expertise in this area is well recognized across the other branches of DoD and NNSA national laboratories and the level of expertise evident in the projects presented within the mechanics, modeling, and simulation portions of the terminal effects project agenda was very impressive.

COMPETENCY FACILITIES AND RESOURCES

Suggestions and comments on the facilities and resources that support the individual core competencies may be improved are detailed below.

The armor mechanisms and countermeasure core competency briefings illuminated its ballistics data, which has been developed over several decades. These data are unique and are a big advantage over adversaries. Additionally, there is availability of excellent materials characterization systems, theater-based assessment tools, and performance evaluation and testing facilities.

ARL appears to have outstanding facilities and resources to support the mechanisms for human injury and projection core competency. It is not clear, however, if individual investigators or projects are limited by inadequate resources or a lack of access to them. The lung project did not seem to be utilizing internal computational resources to the extent needed to adequately support simulating the available experimental test data. Some of the most intriguing experimental data on lung deformation ever acquired is completely underutilized.

Within the mechanisms for lethal target interactions core competency the researchers are leveraging modern experimental facilities both internal and external to ARL. Internally, the impact facilities are being well utilized for quality experiments coupled to high-fidelity diagnostics. Externally, there is impressive immersion in state-of-the-art facilities such as the Dynamic Compression Sector at the Advanced Photon Source and the proton radiography facility at Los Alamos National Laboratory. The

complementary simulation resources leveraged in the other core competencies do not have a significant footprint within the mechanisms for lethal target interactions core competency and better utilization of these capabilities is possible.

It is likely that computing resources within ARL will need to be used in order to enable the ARL modeling and simulation teams to transition from the two-dimensional simulations that currently constitute the bulk of their analyses to full three-dimensional simulations that can greatly improve the confidence level of the predictions.¹³

For the terminal effects mechanics, modeling, and simulation core competency the level of expertise evident in the modeling, and simulation projects within the terminal effects agenda, in terms of both the intramural and extramural staff and in the facilities, was excellent and displaying strong innovation in developing new equipment and facilities. Continued attention to quantification of margin and uncertainty in the experimental, modeling, and simulation portions of all intramural and extramural projects is encouraged.

OVERALL SCIENTIFIC QUALITY OF THE COMPETENCY

The overall quality of ARL’s research and development, both fundamental and applied, in the terminal effects portfolio is excellent. There is a need, as realized by ARL management, to continue to balance fundamental and applied research that will underlie future innovations and developments in terminal effects addressing evolving Army needs. ARL’s existing S&T in the terminal effects area is very well served by the current Aberdeen Proving Ground’s infrastructure and facilities as well as the facilities leveraged through the ARO extramural programs. There was clear evidence of the speed of response to changing needs to support the warfighter with innovations in ballistic lethality and warfighter protection. ARL’s experimental programs concerning threats is quite detailed and demonstrates commendable knowledge of the evolving threat environment and the immense challenges this presents. The spectrum of science and technology, as well as modeling and simulations applied to both armor design and ballistic development, demonstrated a broad array of technical approaches and flexible and rapid response to a very rapidly evolving threat environment facing the warfighter.

Continued building of linkages within ARL’s terminal effects programs with emphasis on the ties between PSPP is seen as a powerful pathway to improvements in the terminal effects overall portfolio, across all four core competencies, and a driving pathway to the development of physically based predictive models to support future design and performance capabilities. As increasingly more complex physics is introduced into ARL’s design and performance simulation computer codes, continued efforts to include quantification of uncertainty, margin, and errors in experiments, modeling, and simulations is strongly encouraged as a way to improve predictive capability.

ARL’s staff is clearly motivated and competent, and the staff members articulated a clear and well-defined line of sight from their research, whether more fundamental or applied S&T, to the mission of ARL and to the challenging needs of the warfighter. All the briefings and poster presentations were well represented by the researchers. For the majority of research presented, the work was state of the art when compared to research at other institutions.

Specific examples of research presented that was particularly noteworthy as examples of excellent research include:

• For the mechanism for human injury and protection core competency, the armor simulations presented during the review were outstanding, particularly the polymer composite which has been well characterized. These high-rate experiments, component level characterization, and multi-physics simulations represent an area where ARL is truly shining.

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¹³ The text here and throughout was modified after the release to the sponsor to clarify that ARL has existing resources that can be used by the ARL simulation and modeling teams to transition from 2D to 3D simulations.

• “The Role of Grain Size and Microstructure in the Shock Response of Metals” results suggesting an ability to suppress shock hardening in a material via processing to manufacture nanocrystalline materials germane to SCJs and EFPs.