Linking Theory to Practice: Predicting Ballistic Performance from Mechanical Properties of Aged Body Armor

Abstract

It has long been a goal of the body armor testing community to establish an individualized, scientific-based protocol for predicting the ballistic performance end of life for fielded body armor. A major obstacle in achieving this goal is the test methods used to ascertain ballistic performance, which are destructive in nature and require large sample sizes. In this work, using both the Cunniff and Phoenix-Porwal models, we derived two separate but similar theoretical relationships between the observed degradation in mechanical properties of aged body armor and its decreased ballistic performance. We present two studies used to validate the derived functions. The first correlates the degradation in mechanical properties of fielded body armor to the degradation produced by a laboratory accelerated-aging protocol. The second examines the ballistic resistance and the extracted-yarn mechanical properties of new and laboratory-aged body armor made from poly(p-phenylene-2,6-benzobisoxazole), or PBO, and poly(p-phenylene terephthalamide), or PPTA. We present correlations found between the tensile strengths of yarns extracted from armor and the ballistic limit (V50) when significant degradation of the mechanical properties of the extracted yarns was observed. These studies provided the basis for a validation data set in which we compared the experimentally measured V50 ballistic limit results to the theoretically predicted V50 results. The theoretical estimates were generally shown to provide a conservative prediction of the ballistic performance of the armor. This approach is promising for the development of a tool for fielded armor performance surveillance relying upon mechanical testing of armor coupon samples.

Hydrothermal aging of fire‐protective fabrics

“…A good resistance to repeated domestic launderings was also reported for a Fabric with a similar content as Fabric ME compared to other para‐aramid‐containing outer shell fire‐protective fabrics 32 . On the other hand, PBO has been reported as sensitive to atmospheric moisture in previous studies 48 . This may indicate a difference in the aging behavior of PBO fibers between water immersion and exposure to atmospheric moisture.…”

“…32 On the other hand, PBO has been reported as sensitive to atmospheric moisture in previous studies. 48 This may indicate a difference in the aging behavior of PBO fibers between water immersion and exposure to atmospheric moisture.…”

Effect of Aging on Unidirectional Composite Laminate Polyethylene for Body Armor

“…In contrast, the specimens tested at a slow loading rate had minimum predicted V 50 retentions of 0.957 and 0.945 for the dry and wet conditions, respectively. There is reason to believe that these predictions may be conservative, based on other research [ 32 ], and that the true reduction in V 50 may be even less than that predicted by the Cunniff or the Phoenix–Porwal models.…”

“…The V 50 ballistic performance measure can be calculated from the tensile properties following either Cunniff [ 30 ] or Phoenix and Porwal [ 31 ], as described in [ 32 ]. The predicted V 50 retention is presented in Figure 13 , where mean retention is calculated by scaling the V 50 values at various aging times by the predicted initial V 50 .…”

“…Of key interest is how the V 50 velocity, the velocity at which half of the projectiles penetrate, changes with aging. The V 50 can be related to the tensile strength through empirical research by Cunniff [ 30 ] and theoretical research by Phoenix and Porwal [ 31 ], as detailed in [ 5 , 32 ]. Furthermore, tensile strength was chosen as a relevant metric because it is less complicated to measure than V 50 and requires less material.…”