Predictive creep response of linear viscoelastic graphite/epoxy composites using the laplace transform method

Abstract

In this research project, creep and stress relaxation tests were run on angle- ply layups of a medium toughness graphite/epoxy system (Hexcel T3T145/F155). The creep and relaxation responses were represented with Maxwell/Kelvin- type models. Using a convolution integral and the Laplace transform method, a predictive creep response formulation was developed following a principle of virtual equilibrium state. Predictions of normalized creep compliance responses from short relaxation tests (based on a pseudo- elastic complementary approach) were compared to normal creep compliance values. As the fiber angles increased (moving farther away from the direction of the applied load), the difference between the compliances increased. This implies that, as toughness is increased, the accuracy of the pseudo- elastic method decreases. With the newer, tougher, resin systems, complementary approaches similar to the one used in this paper may be required.