This chapter discusses the notion that the body armor testing community should retain and improve on the current body armor testing methodology that has evolved from the early work of the Prather and other studies as the way into the future. It describes the four main body armor community stakeholders: the users; the technologists; the medical researchers; and the production testers. It also describes how the current methodological basis for testing can be improved by aligning the body armor testing community stakeholders and by developing a common understanding of the dynamics and measurements of behind-armor phenomena to link medical research to product testing criteria.
Chapter 3 described the original “Prather study” (Prather et al., 1977) and subsequent work that formed the underpinning of modern body armor testing. Mr. Prather told the committee that the original work of his team was intended to provide a quick turnaround process that could be the starting point for conducting soft body armor testing by the Army. It was never intended to become the body armor testing gold standard for military and police forces nationally, especially not for hard body armor.65 Nonetheless, it has in fact evolved into a standard approach internationally even though the character of the threats as well as the composition and construction of body armor have changed.
The original work in the late 1970s provided an efficient method for testing body armor without live animals using a surrogate that allowed determining the adequacy of a given soft body armor to prevent a certain magnitude of backface deformation (BFD) that would cause serious harm to warfighters or law enforcement personnel.
Perhaps the greatest accomplishment of this test approach as used currently is the assertion by the Army Program Executive Office Soldier (PEO Soldier) that no soldier is known to have died on the battlefield as a result of the penetration of body armor by
65Russell Prather, Survice Engineering Company, “The Lightweight Body Armor Program - A History,” presentation to the committee, August, 10, 2010.
rounds the body armor was designed to defeat. Owing to the limited basis for the Prather work, however, essential trade-offs of protection with weight are unknown. At the present time and for the next few years this methodology needs to be retained and the incremental improvements and refinements over the past three decades need to continue until an acceptable alternative method can be introduced for both development and testing of new armor for realistic threats.
Finding: The committee finds that the current body armor testing methodology that has evolved from the early work of Prather et al. (1977) should be retained and improved on while investigating alternative methods.
Chapter 3 concluded with a summary of strengths and weaknesses of the Prather approach, which is repeated here as Table 9-1. The committee focused on retaining the strengths while providing insights into overcoming the weaknesses.
|Ease of use
Relatively low cost
Large historical database of results
Apparent success in field for soft body armor
Apparent success in field for hard body armor
|Clay constituents have changed considerably since original study
Clay variability (handling, thixotropy, temperature effects, etc.)
Current methodology requires elevated clay temperatures
All variability in testing results is assumed to be design flaws in the armor
Method has limited medical validation for soft body armor
Method has no medical validation for hard body armor
In Chapter 4 the report discussed and provided findings and recommendations for mitigating the weaknesses associated with the variability of clay and its formulations, especially important for production testing. The road map of the Chapter 4 findings and
recommendations is reiterated as Figure 9-1. It includes immediate actions to improve the current clay methodology and longer term activities to develop techniques for optimizing body armor development and testing manufactured vests that are alternatives to the clay surrogate testing methods.
FIGURE 9-1 Road map showing suggested near-term actions, medium-term research needs, and a long-term goal to develop a more consistent backing material and a more reliable process for evaluating hard armor. The color coding shows “highest priority” items in red text with “high priority” actions in orange.
To overcome the weaknesses of the Prather methodology, Chapter 5 provides findings and recommendations on the instrumentation to measure indents in the clay recording medium. This understanding should lead to refinements to the current body armor testing process and provide a platform for evaluating new body armor designs to defeat future threats while minimizing the ergonomic penalties of vest bulk and weight.
Chapter 8 described how related medical studies of blunt force trauma should be performed to better understand the interactions between the armor and the back face, including the amplitude and speed of back-face displacement, so that body armor can be perfected that minimizes physical injury. The road map of the Chapter 8 findings and recommendations is recapitulated in Figure 9-2.
FIGURE 9-2 Flow chart showing suggested near-term and medium-term research needs, and a long term goal to provide the fundamental medical basis for injury risk assessment behind helmets and hard body armor.
Medical researchers and production testers have adopted the original Prather approach as a conceptual basis for medical experimentation and for body armor testing. However, each community has evolved different processes to create and measure behind-armor phenomena.
Figure 9-3 shows a schematic view of the conceptual approach that is used by both testers and researchers. The figure depicts a projectile impacting normally onto the body armor in front of a recording medium surrogate for a human body. A is a hard armor (typically, a ceramic), B is a soft armor, and C is the human surrogate (animal, cadaver, or sensor-based simulator in medical research or modeling clay in production testing). Note that A, B, and C do not necessarily touch and that the lateral dimensions of A, B, and C are large compared to the projectile diameter. The production tester’s BFD or the medical researcher’s behind-armor blunt trauma (BABT) in C is the final outcome of the localized damage due to the ballistic load imparted by the projectile on the front face of A.
FIGURE 9-3 Schematic of conceptual approach used by both testers and researchers showing a projectile impacting normally onto hard body armor (A), soft body armor (B), and a recording medium surrogate for a human body (C).
The motion or deformation of the B/C interface can be considered in two parts:
- An early-time motion, and subsequent dynamic deformation, due to the stress wave that originates from the point of impact at front of the hard armor and propagates to the B/C interface, followed by various wave reflections from different interfaces and boundaries.
- A late-time, or final, BFD due to the transmission of the projectile itself through the hard armor (A) and the soft armor (B), but without perforation through the soft armor.
The following simple exercise can be used to determine the characteristic times associated with each of these two parts.
In the latter expression, half the projectile velocity is used because the projectile comes to rest within the armor. As such, half the projectile velocity is a good estimate of the average projectile velocity.
During the time between TW (microseconds) and TP (milliseconds), the interface B/C and the human surrogate C are subjected to dynamic forces and deformations that depend on several factors: projectile velocity, area of impact, and thicknesses of A and B.
Establishing a correlation between BABT and BFD is crucial and requires that two key issues be addressed. First, the impact conditions (projectile mass and velocity) in the medical research and the production testing efforts need to be identical and to reflect the actual threat faced on the battlefield. Second, the motion and stress at the B/C interface, which correspond to BABT and BFD, need to be measured and correlated as a function of time (microseconds to milliseconds). Without addressing both these issues, it will be difficult to make a meaningful comparison between test results in medical research and production testing.
The practical issue facing the body armor community is that since the medical-research and production-testing stakeholders use different projectiles and different recording media (C) as human surrogates, their base data for BABT and BFD are not easily comparable. Some ideas on aligning the two different processes will be discussed below.
Aligning Recording Media Data
The committee appreciates that medical researchers and production testers have different goals. Medical researchers are trying to develop very specific insights in how behind-armor forces cause trauma to a specific organ, groups of organs, or other localized portions of the human body. Higher cost recording media such as electronic sensors or organ surrogates are the norm in this type of research. Production testers are concerned with holistic approaches that can test many plates or helmets in a short period of time. Since the Prather study, production testers have used inexpensive modeling clay as a recording medium. Ideally, both the medical and production testing community would use the same object C. That may be possible in the long run, as described in Chapter 4, with the development of better alternatives to modeling clay, including inexpensive, disposable sensors. However, the realities of the different levels of detail needed by these two stakeholder communities as well as the practical aspects of cost and time make it likely that at least for the short to medium term the different recording media currently used will persist.
As a result of these practical differences, the recording medium C that stands in for a human being (Figure 9-3) will be different for medical research (a large animal, cadaver, or sensor-based simulator) and for production testing (a clay box). Therefore, the dynamic motion and deformation at the B/C interface discovered by the two efforts will be different. Better correlation between the two can probably be best accomplished by monitoring in real time (with the requisite time resolution) the motion and deformation at the B/C interface in the two cases, using yet-to-be-realized identical sensors.
One possible near-term way to obtain valuable information on this BFD using the current clay methodology was recommended in the Phase II study report (NRC, 2010, p. 24) as follows: “To better understand and measure the forces that create the backface deformation, the Army should experiment with inserting microscopic temperature and displacement sensors into the clay near the site of the backface deformation.” One possible idea is a set of microscopic sensors embedded in a frangible wire grid system on thin paper, as shown in Figure 9-4. A sensor grid system such as shown in the figure could be placed immediately behind armor at the B/C interface and immediately ahead of medical recording sensors for medical research. A similar grid could be placed immediately behind armor and immediately ahead of modeling clay during production testing.
As behind-armor forces contact the wire grid, regardless of its makeup, the wires sequentially break and the dynamic contact area can be measured using resistive, conductive, or capacitive methods at high rate. In principle, the data can be recorded at 1 MHz or greater. An approach such as this could allow common near-term measurement of behind-armor forces and could compensate largely for the variability inherent to the recording media. It would also allow medical researchers and production testers to document that they are in fact creating comparable behind-armor displacements—even if the latter are using rifled firearms and the former are using smooth-bore or rifled gas guns to launch projectiles.
Considering the inherent variability of the clay, the application of a thin layer of sensors is unlikely to have a significant impact on BFD formation. Assuming that experiments with sensors on clay using medical recording media confirms this to be the case, a practical application of measurements derived by this method could be a better correlation between BABT injury data developed in the medical community and BFD criteria used by production testers.
The author of the Prather study stated that the original BFD criterion of 43 mm was very conservative for typical lower-rate deformations behind soft body armor.66 That is, it would almost certainly require a dynamic force significantly greater than that which produces a 43-mm BFD to cause serious injury to a human. Prather and colleagues (1977) did not address higher-rate deformations behind hard body armor.
It is possible that if medical researchers used dynamic measurements as described above, they might be able to better determine the balance between increasing levels of BABT and the risk of human injury. The behind-armor impact that produces an acceptable risk of human injury could be replicated in clay by the production testers. Such research could lead to the adoption of a less conservative BFD criterion for production testing. A less conservative BFD could, in turn, allow the technology community to develop armor for soldiers that provides adequate survivability but is lighter, enhancing soldier mobility.
Finding: Recording medium data from medical research and production testing need to be correlated using identical sensors having the requisite time resolution. The results need to be shared among the stakeholders.
This could be a significant practical improvement that results from better alignment of stakeholder communities, including users, technologists, medical researchers, and production testers.
Recommendation 9-1: The Director of Operational Testing and Evaluation should take the lead in aligning the production testing, medical research, and body armor/helmet technology development communities so that the data outputs from their various processes can be easily correlated. This will lead to a better understanding of the relationships among body armor testing performance, human/animal survivability, and
66Russell Prather, Survice Engineering Company, “The Lightweight Body Armor Program - A History,” presentation to the committee, August, 10, 2010.
other trade-offs. Specifically, two policies should be adopted and applied: (1) specify acceptable ranges for projectile weights and velocities used to generate behind-armor dynamic forces during testing and research and (2) investigate the use of standardized sensors behind armor to measure the amount of dynamic force that is produced during testing and research.
The recommendation means relating data from comparable projectiles and recording media used in production testing and medical research as well as relating the use of recording media such as animals, cadavers, or sensor-based simulators to the use of modeling clay for production testing. The data should be shared among stakeholders to promote a more detailed understanding of the relationship between body armor performance, human survivability, and other trade-offs. Importantly, implementation of this recommendation will provide data- based evidence for adopting credible BFD pass/fail testing criteria for body armor and helmets. As stated in the Phase II report (NRC, 2010), the 1977 Prather study with its BFD criteria has to its credit resulted in the fielding of successful—but almost certainly heavier than necessary—body armor. The current pass/fail testing criteria, based on the early Prather work, should be retained until Recommendation 9-1 has been completed and reviewed by all stakeholders.
The actions contained in Figures 9-1 and 9-2 require the coordinated activities of the entire body armor community. Stakeholders include not only the at-risk warfighters and law enforcers but also the organizations and individuals involved in fabrication design, fabrication technology, materials testing, production quality assurance, performance criteria development, and performance verification, as well as those involved in linking medical damage thresholds to body armor performance. The stakeholders and some of their interactions are shown in Figure 9-5.
The principal stakeholders are the warfighters and civil servants at risk for gunshot wounding who need protection with limited ergonomic or other penalties. The
stakeholders also include military and civilian medical personnel as well those who test the adequacy of fielded vests against evolving threats.
One of the reasons body armor has been so successful on the battlefield is that body armor manufacturers and government acquisition agencies have been actively involved in research and development of materials that improve body armor performance. This collaboration has resulted in currently fielded body armor products that provide adequate survivability against specific threats at relatively light weights. The principal members of this stakeholder group, for which the Army has the Department of Defense (DoD) lead, are the acquisition community (to include the Army’s PEO Soldier and the Marine Corps’ Program Manager Infantry Combat Environment), the research community (including the Army Research Laboratory), and industry, such as body armor and helmet manufacturers, defense munition experts, and materials manufacturers (the companies that produce the base materials that are subsequently manufactured into hard armor, soft armor, and helmets).
Medical and other researchers continue to push the boundaries of quantifying and correlating BABT forces with injury data collected from experiments with animals, cadavers, and simulators. Importantly, medical research conducted by government, academic, and industry researchers can focus on the different levels of injury that the same behind-armor forces might inflict on humans of different sizes, genders, and ages. These data can lead to insights on what injury BABT force is likely to cause on various humans. Important members of this stakeholder group include medical research organizations such as the U.S. Army Medical Research and Materiel Command and the Armed Forces Institute of Pathology; university research organizations; and industry contract researchers.
The production testers take the body armor items that have been provided from industry or researchers and test them following prescribed processes and standards to ensure they are effective and suitable for military use. The products are tested to determine if they meet basic specifications and to learn how they function while worn by the soldier in a simulated or actual battlefield environment. Production testing is based on practical, cost-effective, and accurate processes. These processes need to ensure that the armor being tested will prevent specified threat rounds from penetrating it and keep the measured BFD below the level that could cause serious injury for the soldier while achieving the lowest practical weight burden. The organizations that have been doing this type of testing include DoD organizations such as the Office of the Director, Operational Test and Evaluation (DOT&E) and the Aberdeen Test Center; the National
Institute of Justice (NIJ) and the National Institute of Standards and Technology, which have developed the national standards for testing procedures; NIJ-certified commercial testing facilities; and the military organizations of U.S allies that have adopted U.S. standards for testing their own armor.
As stated above, each of the four stakeholder groups has worked hard to improve its part of the body armor community. However, the committee feels that faster advances could be made if there was better coordination and communications among the stakeholders.
The Phase II report (NRC, 2010) recommended that the ad hoc clay working group be empowered and adequately resourced to gather information, influence research, and develop working-level consensus across body armor testing organizations. The report recommended that, after the clay working group had reached a reasonable consensus, DOT&E and NIJ should convene a nationally recognized group to review all appropriate considerations and develop recommendations that could lead to a single national body armor testing standard to achieve more uniform testing results.
The committee observed that the clay working group has made reasonable progress in developing working-level consensus but that not all stakeholders are participating. A nationally recognized coordination committee, as recommended in Phase II, would facilitate the alignment of activities among the stakeholders.
Members of such a military-industry-academia committee would be drawn from the stakeholder groups and would facilitate the passing of information to all stakeholders. It could also assist in rationalizing priorities for research and allocating responsibilities among the more senior organizations. It could provide an efficient means for informal feedback on policy and procedures that are related to two or more of the stakeholders. It could also oversee the development and modification of national standards that could unite various stakeholder groups.
The proposed military-industry-academia coordinating committee could, as appropriate, host occasional conferences to bring interested parties together to present papers and otherwise share ideas on topics of interest to multiple stakeholders. Subcommittees could be set up by the coordinating committee to communicate among the production testing community, NIJ-certified commercial testers, manufacturers, acquisition experts, and others to quickly provide feedback on proposed changes to testing procedures. This could ensure that all testers, government and commercial, as well as product manufacturers and end users are able to provide feedback that will minimize unintended consequences from proposed changes and ensure uniformity in the procedures once adopted.
The coordinating committee could also be used to coordinate biomedical and biomechanical research or to organize conferences from time to time, assuring more of a systems engineering framework for body armor technology and standards development. Members of the coordinating committee would be cognizant of relevant international efforts—in particular, the North Atlantic Treaty Organization-organized working groups. The overall need is for the coordinating committee to provide oversight and facilitate the exchange of information between stakeholder groups.
Finding: The nationally recognized coordination committee recommended in the Phase II report is needed to align and accelerate efforts of technologists, production testers, and biomedical researchers in behind-armor blunt trauma/ backface deformation - related research for both body armor and helmets.
The Phase II report (NRC, 2010) provided insights into some of the problems arising as a consequence of not having uniform standards. For example, the NIJ, with assistance from the National Institute of Standards and Technology, has developed requirements for the conditioning and validation of the clay box used in body armor testing. Those requirements are described in the NIJ body armor standard. However, in many cases the requirements are general and not prescriptive in that they do not define the methods, tools, materials or details involved in building clay blocks, ensuring that the blocks are uniform, conditioning the clay blocks, and measuring deformations resulting from the validation drop tests or the tests of the armor.67
The NIJ standard is used by DoD testing organizations to guide the development of their procedures for clay handling and deformation measurement. These procedures are used in the testing program to determine if various types of body armor are adequate for military applications. Other non-DoD and private testing laboratories also use NIJ standards to guide their procedures to test the body armor used by police forces and other organizations throughout the country. These standards have also been adopted by the military forces of some other countries to guide their body armor testing.
Over time, the NIJ standard has undergone multiple revisions, and depending on the circumstances, different versions of the standard have been adopted by various testing organizations at different times in their histories. As a result, it is possible at this time that identical body armor plates tested by different organizations could achieve dissimilar and not easily comparable results. In the extreme case, a plate could be deemed acceptable at one testing facility and unacceptable at another. It would therefore be a considerable improvement to have one standard or only a few, so that identical plates would be likely to achieve the same test results regardless of the test facility.
The NIJ standards offer a broad set of procedures that will evolve over time owing to changes in technology and other considerations. The Aberdeen Test Center has made decisions on specific procedures and refinements to be used in the testing of body
67NIJ requirements were originally developed to support independent civilian law enforcement organizations. Those organizations wanted maximum flexibility to allow decentralized procurement for various types of body armor on the market. The NIJ philosophy was to permit the various testing laboratories flexibility in technical approaches as long as the standard was met. Civilian law enforcement has long since adopted the NIJ approach. The military subsequently adopted the NIJ standards for body armor testing but felt that the large quantities of body armor that were being purchased in a centralized manner could benefit from more prescriptive requirements. Ideally, there is a middle-ground solution where the NIJ standard(s) could (1) meet the needs of both civilian law enforcement and the military and (2) facilitate reproducibility of results at different laboratories by addressing more detail than was originally envisioned.
armor plates in an effort to standardize both commercial and government production testing.
Eventual adoption of fewer standards—or even a single national standard — would require detailed analysis of key issues such as the threats that are being protected against and the rationale for differences in testing processes. Ideally, developing consensus across all the organizations involved in body armor testing will be more effective than simply mandating national standards.
As an important step in this process, the committee agrees that the ad hoc clay working group approach that was started by and is currently chaired by DOT&E can serve as organizational nucleus and a way ahead for DoD. The working group began as an assembly of individuals with expertise in clay properties, clay calibration, clay working techniques, and future efforts in body armor testing. Two efforts in particular could help lead to a single national body armor testing standard:
- Collaborating on and investigating clay properties, formulation, calibration, and working techniques.
- Collaborating on alternatives to the existing test procedures and standards.
Reducing the number of national standards for body armor testing requires examining issues other than just the recording medium. An encompassing standard for testing would include the following:
- Rationalization of instruments and procedures to achieve consistency in measuring the indents in backing materials.
- Application of statistics and other mathematical tools to improve standardization, such as determining test sample size.
- Alignment of body armor and helmet testing procedures.
Finding: The original ad hoc clay working group could be expanded to form Department of Defense’s portion of the national body armor testing standardization committee that was recommended in the Phase II report.
The mission for an expanded working group would include not only the group’s original tasks but also the areas touched on above. Membership would consist of experts from each stakeholder group. Examples of the tasks to be performed by the standardization committee include these:
- Gather and document information that defines and explains the reasons for the different testing procedures used by various organizations.
- Determine areas where alignment of processes among organizations makes sense.
- Determine areas where different missions, customer requirements, resources, and other organizational considerations provide a reasonable rationale for different testing procedures to be retained, at least in the short term.
- Oversee additional analysis that is required to make recommendations on procedure and process changes. (It would be useful here to design
- experiments, gather data, and perform analyses that would lead to informed recommendations to the chains of command of the participating organizations.)
- Achieve consensus from all stakeholders that will, ideally, lead to the drafting of a single national testing standard or at least fewer such standards.
Once the testing standardization committee achieves a consensus, it should take actions to gain ratification of the appropriate national standards for the testing of body armor and helmets for both military and police forces. After ratification, the committee could conduct a periodic review to determine if existing standards need to be updated.
Recommendation 9-2: The Director of Operational Test & Evaluation and the National Institute of Justice (NIJ), in collaboration with the military services, unified commands, government testing organizations, NIJ-certified testing laboratories, medical researchers and governmental and commercial material developers should convene a national body armor testing standard committee to review all appropriate considerations and develop recommendations that could lead to updated national body armor configurations and testing standards for body armor and helmet testing.
This final recommendation is conceptually the same as Recommendation 15 in the Phase II report (NRC, 2010). However, it has been expanded to include helmet testing. Since helmets and body armor plates have different requirements, there will likely be different testing standards for them for the foreseeable future.
NRC (National Research Council). 2010. Phase II Report on Review of the Testing of Body Armor Materials for Use by the U.S. Army. Washington, D.C.: National Academies Press.
Prather, R., C. Swann and C. Hawkins. 1977. Backface Signatures of Soft Body Armors and the Associated Trauma Effects. ARCSL-TR-77055. Aberdeen Proving Ground, MD: U.S. Army Armament Research and Development Command Technology Center.