Testing of Body Armor Materials Phase III (2012) / Chapter Skim
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3 Historical Basis for Current Body Armor Testing
3 Historical Basis for Current Body Armor Testing
Pages 34-45
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From page 34... ...
It included an injury assessment methodology developed using animal tests and the correlation of animal chest deformation response with the response of simulant materials at velocities that are typical of rounds used to test soft body armors. A diagram of this process is shown in Figure 3-1.
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From page 35... ...
Additional requirements included protection from bullet penetration, blunt trauma mortality risk of less than 10 percent, and sufficient protection to allow the wearer to walk away from any shooting incident. Note that these last two requirements are not necessarily contradictory, because overall mortality risk might involve -35
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From page 36... ...
Materials investigated included high-tenacity nylon, nylon felts, high-tenacity rayon, graphite yarns, XP (an experimental plastic developed by Phillips Petroleum) , Monsanto fibers, and DuPont Kevlar 29 and 49.
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were developing blunt trauma correlation models formulated from experimental data sets obtained from tests on unarmored animals, where the physical characteristics of the impacting projectile (mass, velocity, diameter) were known.
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From page 38... ...
Although none of the materials duplicated the thoracic response, Roma Plastilina #1 clay had a deformation depth response similar to that of gelatin and was considered to be a suitable tissue simulant that was easy to use, inexpensive, and repeatable and that required no high-speed photography.11 The clay and the ballistic gelatin were generally softer and less resistant than the goat thorax to the impactor at the testing velocity of 55 m/sec. Blunt impactor data on goats were used to link this deformation response with fatality using a logistic regression model (Clare et al., 1975)
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From page 39... ...
time of candidate materials in a goat thorax using a blunt impactor at 55 m/sec. SOURCE: Prather et al., 1977.
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From page 40... ...
A further caveat is outlined in Prather's original study on the injury regression shown in Figure 3-4: Attempts have been made using the original blunt impact data to correlate deformation depth with the probability of lethality. A depth of penetration greater than 50 mm is associated with a probability of lethality of approximately 15%.
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From page 41... ...
They also showed that the behind-armor deformation profiles for this soft body armor were similar to those derived under the original program. Limited goat studies demonstrated injuries similar to those incurred in the seven-ply tests.
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From page 42... ...
For example, .50-cal antipersonnel threats to helicopter pilots were assessed in animal models, but there were no recommendations generated concerning risk assessment methodology for generic body armor BABT. Work Performed after the Prather Study To assess the risk of injury using clay at rifle round velocities, a series of tests was performed using human cadavers.
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From page 43... ...
Velocity (m/sec) FIGURE 3-7 Variation of clay penetration depth with velocity for behind-body armor deformation (7.62-mm NATO round, UHMWPE body armor)
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From page 44... ...
Finding: Existing research raises concerns regarding the correlation of the damage measured in the clay with the bodily injury at the very high rates typical of backface deformations caused by rifle rounds in hard body armor. CURRENT STANDARD Strengths and weaknesses of the current Prather methodology are displayed in Table 3-1 and discussed extensively in Chapter 9.
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From page 45... ...
TABLE 3-1 Strengths and Weaknesses of the Prather Methodology Strengths Weaknesses Ease of use Clay constituents have changed considerably since original study Immediate results Clay variability (handling, thixotropy, temperature Relatively low cost effects, etc) Large historical database of results Current methodology requires elevated clay temperatures Apparent success in field for soft body armor All variability in testing results is assumed to be design flaws in the armor Apparent success in field for hard body armor Method has limited medical validation for soft body armor Method has no medical validation for hard body armor Pass/fail criterion -45
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