Penetration of laminated Kevlar by projectiles—I. Experimental investigation

Abstract

The response of woven Kevlar/polyester laminates of varying thicknesses to quasi-static and dynamic penetration by cylindro-conical projectiles with an apex of primarily 60° has been investigated. The static properties of the material were obtained by means of standard testing procedures, including in-plane tension, compression and shear, through-thickness compression, fracture toughness and cone indentation. Compressive dynamic results were obtained using a Hopkinson bar at rates up to 2000 s−1. Quasi-static force-indentation behavior for conical indenters was determined for a specimen thickness ranging from three to 10 layers to provide constitutive relations for the corresponding analytical model. These data exhibit a linear rise whose slope and peak values are proportional to specimen stiffness, followed by a plateau that terminates in a rapid reduction to a small, but finite force level when the shank of the penetrator exits. The curves were found to be highly sensitive to the size of the projectiles and the tip angle.Static investigations were also conducted to assess the effect on penetration of specimens subject to special artificial initial conditions. This included a restraint on the global plate deformation; the use of several samples of the same total thickness, but comprised of several assemblies of stacked laminates; and embedment of an artificial dclamination flaw located centrally at the midplane of the plate over approximately half of its diameter.The dynamic tests were executed using both pneumatic and powder guns, mostly with a 12.7 mm barrel diameter. Ballistic limits were determined for these plates and terminal velocities were measured when perforation occurred. Deliberately introduced delaminations and changes in the volume fraction did not result in significant changes in the impact resistance. The damage zone created was square in shape for a 0/90 lay-up and circular for quasi-isotropic specimens. The damage pattern for dynamic loading was, however, quite different from that for the corresponding quasistatic penetration case. Kevlar laminates were found to be very resistant in arresting blunt-nosed strikers in comparison with metals on a specific weight basis.