THEORY OF STRESS TRANSFER IN A 0-DEGREES-90-DEGREES-0-DEGREES CROSS-PLY LAMINATE CONTAINING A PARALLEL ARRAY OF TRANSVERSE CRACKS

TWO NEW analytical methods have been developed that can predict the stress transfer between the 0 and 90-degrees plies in a 0-degrees-90-degrees-0-degrees cross-ply laminate containing transverse cracks. Account is taken of thermal residual stresses arising from a mismatch in thermal expansion coefficients of the 0 and 90-degrees plies. The first method is based on a 2-D model which assumes that generalised plane strain conditions prevail. The theoretical approach retains all relevant stress and displacement components, and satisfies exactly the equilibrium equations. the interface conditions, and other boundary conditions involving stresses. The stress-strain-temperature relations are satisfied either exactly or in an average sense. The 2-D representation can be used to predict the stress and displacement fields for a laminate containing parallel transverse cracks. In this paper the solutions are used to estimate the dependence of the longitudinal values of Young's modulus, Poisson's ratio, and thermal expansion coefficient on the density of transverse cracks. The second analytical method extends the 2-D model so that it can apply to 3-D problems which arise, for example, when edge effects or orthogonal cracking are to be taken into account. For the special case of very large laminate widths the 2- and 3-D models predict results which are very close to each other for both glass fibre/epoxy and carbon fibre/epoxy laminates. It is shown how the 3-D model can be used to predict the transverse Young's modulus and thermal expansion coefficient. Theoretical predictions of the dependence of Poisson's ratio on transverse crack density indicate that experimental measurements can be sensitive to the strain measurement technique used, and to specimen width when using a transverse extensometer. Theoretical predictions, for glass fibre/epoxy and carbon fibre/epoxy laminates, of the dependence of Young's modulus and Poisson's ratio on the crack density are compared with some experimental results.