High strain rate characterization and modeling of polymer composites

The nonlinear rate dependent behavior of two class of polymeric composites, the unidirectional S2 Glass/8553 and the woven E Glass 7781/F155 fabric are investigated in the strain rate range from 0.0001/S to 1000/S. Uniaxial tension tests were conducted on a servohydraulic testing machine at strain rates of up to 1/S, based on which a two parameter overstress viscoplasticity and a three parameter total form of the constitutive equation were developed to predict the rate dependent behavior of these material systems. Both these models were subsequently validated by predicting the rate dependent behavior of various off axis specimens. The three parameter viscoplasticity model was subsequently used to develop a 2D viscoplasticity code to investigate the viscoplastic response of various laminates with different symmetric stacking sequences, in the low strain rate regime of up to 1/S. The material models that were developed was also used to study the rate dependent response of graphite/glass hybrid composites. High strain rate experiments were then conducted using the Split Hopkinson Pressure Bar in which strain rates of the order 1000/S were achieved. Three dimensional incremental equations of viscoplasticity were developed and implemented into a finite element code. Finite element predictions show that the proposed viscoplasticity model adequately models the high strain rate response of these material systems over a spectrum of strain rates.