On Predicting Dynamic Compressive Properties of Some Composite Materials

Abstract

Abstract A need exists to employ high strain rate mechanical properties of composite material systems when designing or structurally analyzing products and vehicles that are subjected to dynamic loadings. This is due to the fact that for many materials some properties vary by factors of two or three from the static mechanical properties which are so often used in design. The result is that some structures may be significantly overweight from what they could be if dynamic material properties were used in their design, while in other instances unexpected failures can occur which are difficult to diagnose if the high strain rate properties of the materials involved were unknown. An ultimate goal might be to develop the capability to predict high strain rate properties from static material properties, but that capability does not exist today. However, it is helpful to develop the capability to predict the needed high strain rate material properties over the entire strain rate range of interest from a minimum number of dynamic tests performed, because high strain rate property testing is time consuming, expensive, and requires sophisticated equipment. From the testing of numerous polymer matrix composite materials in compression utilizing a Split Hopkinson Pressure Bar, repeated patterns have emerged involving yield strength, yield strain, ultimate strength, strain to failure, modulus of elasticity, elastic strain energy density and strain energy density to failure. These are the properties needed for proper design, structural analysis and materials selection. By studying these patterns, a procedure is suggested by which these properties can be obtained through performing a minimum number of tests.