Prediction of the non-linear viscoelastic response of unidirectional fibercomposites

A methodology for predicting the nonlinear viscoelastic behaviour of unidir ectional fibre composites is proposed. The prediction, which is based on a modified Schapery formulation, is easy to apply by using a combination of a nalytical formulations and numerical procedures. In addition a generic func tion is developed for the description of the stress dependence of the creep -recovery response over the whole stress range examined. All the parameters included in the proposed generic function used for the prediction of the n onlinear viscoelastic behaviour of unidirectional fibre composites, such as the stress threshold of nonlinearity and the ultimate tensile strength of the material, have a clear physical meaning. The accuracy of both the gener ic function and the numerical technique is checked by creep-recovery tests on 90 degrees unidirectional carbon-fibre/epoxy-matrix composites in which predicted response is compared with measured response. Good-to-reasonable a greement between experimental and analytical results is observed. The metho d is presented in a generalised manner and could be applicable to a large c lass of UD fibre composite systems. (C) 1999 Elsevier Science Ltd. All righ ts reserved.