An Investigation into the Accuracy of a One-Parameter Nonlinear Model for Unidirectional Composites

Abstract

The nonlinear response of unidirectional composites has often been modeled using orthotropic plasticity theories. Of these, the one-parameter model developed by Sun and Chen is the simplest and hence attractive from the point of view of applications. The range of applicability of this theory is investigated by performing a number of off-axis tension tests on laminae, shear tests on 0°/90° laminates and uniaxial tension tests on +45°/–45° laminates. The theory appears to explain the results of off-axis tension test of laminae, but is unable to accommodate the full range of stress-strain response observed in the case of laminates. This is clearly due to extensive micro-cracking that laminates with orthogonal fiber orientations are able to withstand prior to failure—a phenomenon the single parameter model is not designed to account for. Nevertheless, it appears from the limited number of results presented, that the model if properly calibrated, can be used to predict the behavior of both laminae and laminates with reasonable accuracy.