Testing of Body Armor Materials for Use by the U.S. Army—Phase II Letter Report (2010) / Chapter Skim
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of the National Academies established the Committee to Review the Testing of Body Armor Materials for Use by the U.S. Army to assess the methodologies used for body armor testing.
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These actions are urgently needed to achieve greater part-to-part consistency in the ballistic clay, to analyze BFD dynamics, to determine possible replacements for modeling clay, to achieve a national clay standard for testing body armor, and to implement statistically based protocols. The overarching recommendation is as follows: Overarching Recommendation: The committee applauds DOT&E for assuming a national-level leadership role in bringing the body armor test community together.
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Convene a Nationally Recognized Group to Establish a Single National Standard for Handling and Validating Clay Implementing Statistically Based Protocols 16. Compare the Proposed Statistically Based Protocol with the Existing USSOCOM Protocol 17.
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Phase II Committee Expertise At the conclusion of Phase I, the Phase I Committee felt that greater consistency in the oil-based modeling clay could reduce variability in the body armor test and give more consistent and precise results. More precise results, in turn, could allow certifying with a high degree of confidence lighter weight armor plates that achieve the same survivability for a soldier.
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filled with modeling clay is subsequently referred to in this report as a "clay box" or as a "part" when discussing part-to-part variations. 2 The appliqué is an additional layer of clay that has been molded to the shape of the specific armor plate to be tested.
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(1977) study, there is a correlation between the depths of penetration as a function of time into various media, including the modeling clay Roma Plastilina #1, and the probability of lethality when the same penetrator enters a human surrogate (goat)
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Live Fire Test and Evaluation, "DoD in brief to the National Research Council study team," Presentation to the committee, on November 30, 2009. 4 James Zheng, Chief Scientist, Program Executive Office–Soldier, "Ballistic protection for warfighters," Presentation to the committee, on November 30, 2009.
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The Phase I report also asked the committee to address the oil-based modeling clay medium in which the BFD is formed. Specifically, the committee was asked to provide interim observations on the Army's column-drop performance test used to 5 Faro® Quantum Laser Scan Arm and Geomagic® Qualify® for Hard and Soft Body Armor.
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Medical Study Basis for Use of Modeling Clay in Testing Body Armor The use of clay as a recording medium for body armor testing dates from a 1977 study that correlated the depth that a 200-g, 80-mm hemispherical missile, impacting at approximately 55 m per second (Prather et al., 1977) , penetrated live animal tissue and other media.
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Modeling clay provides an approximation of the actual BFD. It does not record maximum displacement since the clay may exhibit some elastic recovery, nor does it record the rate of deformation.
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Recommendation 1: The Army's medical and testing communities should be adequately funded to expedite the research necessary both to quantify the medical results of blunt force trauma on tissue and to use those results as the updated mathematical underpinnings of the back face deformation (BFD) body armor testing methodology.
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In practice, the term "clay body," which contains multiple constituents formulated in industry, is often shortened to "clay." Roma Plastilina #1 is an oil-based modeling clay that is not designed to be fired, such as is often done by artists to produce a densified ceramic part. This prescription allows the manufacturer to formulate the clay to obtain a given set of rheological (or flow)
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13 These include pigments or colorants, antioxidants, and other minor materials as well as an intentional blending of multiple sources of, for example, the microcrystalline wax to dampen out lot-to-lot variations from individual suppliers. It is perhaps useful to point out that minor constituents can affect the behavior of modeling clay in the context of armor testing in other indirect ways.
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Short-Term Development of a Standard Clay Formulation for Ballistic Testing The Army's protocol for ballistic testing of soft and hard body armor specifies Roma Plastilina #1 as the backing material (DoD, 2008)
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This would put the burden on the Army to specify the properties that are most important to the application but would seem to be the best approach to meet the Army's need for a consistent backing material. Recommendation 2: The Army should develop ballistic testing performance specifications and properties that will lead to a short-term, standard replacement for the current Roma Plastilina #1 oil-based modeling clay.
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The Roma Plastilina #1 clay composition currently in use is proprietary but is known to include a multicomponent organic phases(s) , a kaolinite filler, and two other inorganics, sulfur and zinc stearate.
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These observations are consistent with a 1994 NIST report on the rheological properties in torsional shear of an earlier formulation of Roma Plastilina #1, which found that the material was highly nonlinear and time dependent, and that the shear properties of kneaded and "melted" (i.e., raised to a temperature of 90oC) clay at a fixed test temperature were different (NIST, 1994)
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. Third, if the modeling clay is equilibrated at a temperature significantly higher than the ambient room temperature (as is current practice)
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23 It is the standard used throughout the body armor testing community and the process for calibrating the clay for use in ballistic testing of armor. Several versions of the drop test are in use.
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It was related by Army personnel that the drop test was introduced specifically to account for the complexity of conditions leading to a given consistency. That is, whereas heating to between 105°F and 110°F was necessary to achieve a drop test penetration in the desired range for undisturbed modeling clay, the same result was achieved at a significantly lower temperature when the clay had been "recently worked." This indicates an understanding that both thermal history and shear history affect consistency.
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SOURCE: Scott Walton and Shane Esola, ATC, "ATC perspective on clay used for body armor testing," Presentation to the committee, on March 10, 2010. Recommendation 6: Since oil-based modeling clay is time and temperature sensitive, a post-drop calibration test is needed to validate that the clay remains within specification at the end of a body armor test.
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Given the confounding effect of box geometry, the Aberdeen Test Center should perform a systematic set of column-drop performance tests as experiments to assess the consequence of variation due to the shape and size of the frame that defines the clay box. These tests should determine if a circular box of approximately the same area as the current box reduces the spatial variation that affects ballistic testing, or if a larger box area eliminates the clay edge effects that affect ballistic testing.
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The latter will help to provide information of use in the statistical analysis of armor testing results. Specifically, statistical analyses of the test protocols require quantification of how much of the observed variation in BFD is due to the clay medium (and the test protocol in general)
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A flash x-ray source available at ATC has been proposed for studying BFD dynamics as the plate deforms into modeling clay. Calculations by the committee indicate that during a single flash of the proposed flash x-ray cineradiography system, the number of x-rays that will penetrate the clay box and impinge on a resolution element (i.e., a pixel)
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. Also, as discussed earlier, the Army is looking at short-term modeling clay formulations alternative to Roma Plastilina #1 that have better thermal and other properties for body armor testing.
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Other possible considerations in the use of ballistic gelatin are the need to modify standard test procedures to include gelatin and to modify acquisition contracts to allow the Army to purchase armor that has been tested with standard ballistic gelatin. Recommendation 12: The Army should conduct rheology and other studies on ballistic gelatin as a mid-term alternative to modeling clay due to its properties, which include the ability to directly record BFD using high-speed photography and the elimination of the effects of shear history, time, and temperature on the response of the backing material.
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ACHIEVING A COMMON NATIONAL TESTING STANDARD FOR HANDLING AND VALIDATING CLAY The NIJ, with assistance from the NIST, has developed technical standards for clay handling and validation for body armor testing. These standards are used by DoD testing organizations to guide clay procedures and processes that in turn determine if various body armors are adequate for military applications.
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Random location sampling is best way to determine bulk clay block properties 24 Shane Esola, ATC, "ATC perspective on clay used for body armor testing: NRC Phase II Vandiver Inn brief," Presentation to the committee, on March 9, 2010. 25 Mike Riley and Amanda Forster, NIST, "Handling and validation of clay for NIJ–0101.06 tests, current practice and limitations," Presentation to the committee, on March 9, 2010.
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wood or according to the range backing plywood backing capability of the facility at which testing is Clay conditioning "Actual conditioning performed and the temperature temperature and customer requirements have recovery time between changed over the years uses will be determined by the results of the validation drop test." SOURCE: Shane Esola, ATC, "Major clay calibration technique differences," Presentation to the committee, on March 10, 2010. The committee agrees that it could be helpful if there were one national standard for all body armor testing.
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and the National Institute of Justice (NIJ) , in collaboration with the military services, unified commands, other governmental organizations, NIJ-certified laboratories, and appropriate nongovernmental and commercial organizations 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.
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It concludes with recommendations on involving stakeholders and performing due diligence before formally adopting a set of statistically based protocols. Uncertainty and Variation Drive Overdesign Larger and/or thicker body armor insert plates provide additional survivability but at the cost of more weight.
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To the extent that uncertainty and variation in manufacturing and testing are minimized, body armor with the desired level of performance may be achieved with greater certainty and perhaps at lower weight. Statistically based protocols are designed to quantify variation.
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test personnel collaborated to develop a statistically based protocol, the proposed Standard for Hard Body Armor Ballistic Testing, which DOT&E disseminated for review and comment. The proposed standard would establish a statistically based protocol that sets minimum requirements for tests that will result in a decision to qualify a design for fullrate production and FAT.
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26 The design matrix and the assessment requirements are hereinafter defined as the "proposed statistically based protocol." The 60-plate design matrix is given in Table 2. This design matrix is replicated for each threat.
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For the second shot, the one-sided 80 percent upper tolerance limit with 90percent confidence for BFD must be less than 44.0 mm. TABLE 3 Statistical Analysis Requirements First Shot Second Shot Resistance to penetration Analysis required 90 percent no penetration 80 percent no penetration with 90 percent confidence with 90 percent confidence Backface deformation Analysis required 90 percent upper tolerance 80 percent upper tolerance limit with 90 percent limit with 90 percent confidence confidence SOURCE: Staffing document for review and comment of the DOT&E-proposed Standard for Hard Body Armor Ballistic Testing.
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The committee commends the Army and DOT&E statisticians and ATEC testing personnel for their constructive collaboration in defining the new statistically based protocol. Just as body armor design requires making an explicit trade-off between weight and protection, test-sampling design requires making trade-offs between the precision of the estimates and the number of items tested.
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Requirement Risk Risk 15 0 0.98 0.86 0.206 0.261 22 0 0.98 0.90 0.098 0.359 40 1 0.98 0.90 0.080 0.190 60 2 0.98 0.90 0.053 0.119 60 2 0.99 0.90 0.053 0.022 60 2 0.92 0.90 0.053 0.868 300 9 0.98 0.95 0.000 0.082 6,000 134 0.98 0.975 0.000 0.092 Recommendation 16: Before adopting the proposed statistically based protocol, the Department of Defense Director, Operational Test & Evaluation, (DOT&E) should explicitly compare the risks of the proposed protocol and those of the existing Army and U.S.
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b) 10% variance 0.2 0.2 0.0 0.0 3.0 3.5 3.0 4.5 5.0 3.0 3.5 3.0 4.5 5.0 Standard deviation of hard body armor Standard deviation of hard body armor FIGURE 6 Risk comparisons for BFD assume that the manufacturer's true mean BFD is (a)
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In particular, the statisticians involved with developing and implementing the statistically based protocol should be involved with the experimentation recommended in Recommendations 2-8. It would be helpful for statisticians to be part of the process of understanding and quantifying test system variation.
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The committee feels that DOT&E is making a good faith effort to follow the DoD IG guidance in its development of the proposed statistically based protocol. Many thousands of body armor plates have been produced and sent to soldiers on the battlefield.
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Second, the committee wishes to avoid the misperception that the proposed statistically based protocol accepts a higher death rate for soldiers wearing body armor. In particular, there must be no inadvertent public misperception that U.S.
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concerning the statistically based protocol. This feedback, as well as the results of the experiments and analyses proposed in this report, should be used as due diligence to carefully and completely assess the effects, large and small, of the proposed statistically based protocol before it is formally adopted across the body armor testing community.
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The importance of body armor testing, as well as the life-or-death nature of body armor itself, require that such a large number of recommendations be acted on in a concerted fashion. Both DOT&E and the Army will recognize the issues addressed by the recommendations and have initiated or proposed several projects that move in the same or similar directions toward essential improvements.
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Convene a Nationally Recognized Group to Establish a Single National Standard for Handling and Validating Clay Implementing Statistically Based Protocols 16. Compare the Proposed Statistically Based Protocol with the Existing USSOCOM Protocol 17.
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10-2 210 Ballistic Testing of Hard Body Armor Using Clay Backing. Aberdeen Proving Ground, Md.: Aberdeen Test Center.
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2009. Phase I Report on Review of the Testing of Body Armor Materials for Use by the U.S.
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1992. Police Body Armor Standards and Testing, Volume II: Appendices, OTA-ISC-535.
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