Spall Strength of S2-Glass Fiber Reinforced Polymer Composites

Abstract

The utilization of layered heterogeneous material systems in the development of armor provides a potential for a great improvement in ballistic performance in a variety of lightweight armor applications. Some of the notable recent examples demonstrating the success of synthetic heterogeneous material systems include composite materials with organic matrices reinforced by glass fibers to achieve lightweight and enhanced ballistic resistance. In the present study, a series of plate impact experiments were performed on two S2-glass fiber reinforced polymer composites (GRP) with different resin content for their promising potential in future combat vehicle defense system. GRP has excellent strength along its fiberglass directions, however, the cohesion between fiberglass layers and its resin matrix is not strong and spall usually occurs during a typical impact process. The objective of the present study is to investigate: (a) dispersion and attenuation of shock-waves in two GRP composites; (b) the spall (delamination) strength of the two GRP composites both under compression and pressure-shear shock wave conditions. The GRP specimens were shock loaded by utilizing A1 7075-T6 flyer plates to around 2 GPa; the thickness of flyer and target for each experiment was carefully designed to produce a state of tension near the center of the GRP target plates. Normal plate impact, and combined pressure and shear experiments with skew angles ranging from 12o to 20o, were performed to study the effects of normal compression and combined compression and shear on the GRPs' spall strength. The measured spall strength as a function of the applied shear strain and the normal stress was used to develop a 3-dimensional failure surface. The results indicate that the spall strength of GRP decreases with increasing compressive stress; the addition of shear stress was found detrimental to the spall strength of GRP.