Microscopical Study of a Multilayer Nylon Body Armor Panel After Impact

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Abstract
A body armor panel consisting of twelve identical layers of 2 X 2 basket weave nylon fabric was investigated after impact by a fragment simulator .22-caliber steel missile in the range of 330-420 m. sec. (1100-1400 ft. sec.) striking velocities. The kinetic energy of the projectile was either slightly higher or lower than that the panel could absorb (706,000 g.-cm.). Completely and partially penetrated holes were investigated. The area surrounding the bullet holes was studied to learn about the various types of deformations and damages in each layer. The microscopic observations were obtained at various magni fications (5, 10, and 200 X) from cross sections of the panel and from individual layers removed from the panel. Cross sections at various levels were made in three directions, either perpendicular or parallel to the panel surface. In these sections the distortion of the fabric pattern, alignment of extended, unravelted. and broken yarns into the direction of bullet move ment, compression of yarns, softening, heat relaxation, fusion, decomposition, and fibrillation of nylon filaments were observed. It was recognized that the permanent damage was localized to a small area close to the path of the fast-moving missile. After separating the panel into individual layers, the stoppage of the projectile was studied. A slight dissipation of the stress was observed in those layers which were exposed to the bullet after it was stowed down. Some damages to nylon filaments were caused by the transient and localized heat generated during the impact of the missile. Fibrillation indicates the vigorous movements of filaments which took place in the panel during penetration. The restriction of permanent deformations and defects to small regions was explained by the presence of cross yarns. They prevent the propagation oi the stress from the impacted spot to any considerable length along the yarns.

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