Predicting the effect of non-uniform ply cracking on the thermoelastic properties of cross-ply laminates

When damage in the form of ply cracks in laminated composites arises during loading, the cracks are in general non-uniformly spaced due to property and geometrical inhomogeneities in the laminate. The objective of this paper is to establish the validity of an approximation that can be made when analysing the stress and displacement distributions in multiple-ply cross-ply laminates having arrays of non-uniformly spaced ply cracks. The approximation assumes that the stress and displacement distributions in the region between the planes containing neighbouring ply cracks are the same as those arising in an identical laminate having uniformly spaced ply cracks of the same separation. The validity of this approach is established by comparing predictions of the thermo-elastic constants of the cracked laminates generated by two distinct stress-transfer models. The first model, that generates the approximations for non-uniform ply crack spacings, is based on a stress-transfer analysis that was specifically developed for uniformly spaced ply cracks while the second model accurately takes account of the effects of the non-uniformity of ply crack spacing on the stress distribution. It is shown, following a comprehensive analysis of various laminate types and crack patterns for both carbon fibre and glass fibre systems, that the approximation suggested provides highly accurate predictions of effective thermo-elastic constants over a wide range of laminate parameter variations.