Modelling of translaminar cracks in cross-ply composite laminates

An approximate model is developed for the reduced thermoelastic constants of cross-ply laminates containing an array of parallel equally spaced translaminar cracks. The crack lengths under consideration range from short tunnel cracks parallel to the fibres in the 90° plies to long cracks not only covering the full width of the 90° plies, but also cutting into the neighbouring 0° plies. No crack bridging is assumed in the 0° plies. Approximate closed-form expressions for the thermoelastic quantities of the cracked laminate are derived from the application of solutions for the crack opening displacements for an array of cracks in a homogenous orthotropic body. Asymptotic values of the discussed properties valid for infinite crack densities are also computed. The displayed expressions solely contain ply material properties and information about crack spacing and crack length. The presented method yields conservative estimates of the thermoelastic properties of cross-ply laminates containing bridged cracks. Comparisons between the present model and finite element results are presented for two types of material systems exhibiting different degrees of orthotropy. It is seen that the expressions obtained for the E-modulus and the shear moduli are in good agreement with the finite element results for a wide range of crack densities and crack lengths. The expressions for the Poisson's ratios and thermal expansion coefficients are less accurate.