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This report explores the possibility that heat plays a role in the penetration of cloth ballistic panels by 0.22 caliber projectiles. We postulate that heat is generated by friction between the surface of the projectile and the yarns, between yarns, and between filaments within a yarn in advance of and in the path of the projectile. Evaluations by light microscopy, polarized light microscopy, and scanning electron microscopy show heat- induced damage in fibers in the path of and several layers preceding the layer at which a 0.22 caliber projectile comes to rest. Polarization microscopy of impacted yarns reveals differences in birefringence within the fibers close to the hole made by the projectile compared with the same fiber at a greater distance from the hole. Heat is an energy sink, and depending on how, when, and where it is generated, can degrade the ballistic performance of the yarns. The quantitative importance of heat in affecting ballistic panel performance is elusive: consequently, the discussion presented here is largely qualitative.

The main purpose of this report is to present an analysis of the ballistic behavior of the fragment-simulating projectile (FSP)-nylon cloth system. For a set of Vc determinations, plots of Vr versus Vs can be adequately represented by hyperbolas. The energy lost by an FSP after complete passage through a nylon ballistic panel of L layers is virtually constant, independent of the striking velocity. The hyperbolas lie on a portion of the surface of a hyperbolic paraboloid with Vr, Vs, and L as axes. The minimum penetration velocity of a missile that has reached the plane of the Lth layer is practically equal to the Vc (or V50) for L layers. The work of penetration per interior layer is essentially constant. For the interior layers, the average force and average deceleration per layer are approximately 1.03 times 104 N and 9.34 times 106 m/s2, respectively. This behavior holds for bonded (laminated) nylon ballistic panels, for the FSP-Kevlar system, and for the right-circular-cylinder missile/nylon system so far. Response surfaces are given for the FSP-nylon and FSP-bonded nylon systems relating ballistic performance to the diameter of the FSP, the firing obliquity, and the number of layers of cloth in the panel. The associated three-dimensional plots are also provided.