High Strain Rate Effects on Two AS4 Graphite Fiber Polymer Matrix Composites

Polymer matrix composites offer excellent mechanical properties such as high specific strength and stiffness which make them attractive for many naval, aerospace and automotive structural components. Although they are candidate materials for many applications where high strain rate loading is probable, little is known of the material responses to shock loading for most composite materials. Because mechanical properties vary significantly with strain rate, the use of static properties in the analysis and design of structures which undergo dynamic loadings can on one hand lead to a very conservative overweight design, or on the other hand can lead to designs which fail prematurely and unexpectedly. The use of dynamic material properties will ensure the design of composite structures which are weight efficient and structurally sound when they are subjected to dynamic loads. In this study, a Split Hopkinson Pressure Bar is used to obtain compressive mechanical properties of two AS4 graphite fiber polymeric matrix quasi isotropic composites. One is an Avimid* K3B polyimide matrix composite; the other involves a shell epoxy matrix. For both the in-plane (i.e. 1 and 2 direction) and the thickness direction (i.e. the 3 direction) the yield stress, yield strain, ultimate stress, ultimate strain, modulus of elasticity, elastic strain energy function and the total strain energy to failure are presented for strain rates varying from 76 sec−1 to 1209 sec−1. The data from 58 tests are statistically analyzed, represented by equations, and discussed in some detail. Comparisons are made between the two composite quasi isotropic materials, each having the same graphite fiber, but one having a polyimide matrix and the other an epoxy matrix.