In long fibre composite cross-ply laminates submitted to shear loading, matrix cracking appears in both 0° and 90° layers. The number of such cracks increases throughout both quasi-static and fatigue tests. A 2-D shear lag analysis for progressive damage in composite laminates is then developed to model this crack geometry. A general governing equation is derived for [0_m/90_n]s laminates that involves only in-plane stresses in both layers. Stress distributions, elastic constants and strain energy release rate are obtained as functions of the crack densities in 0° and 90° layers of the laminate. Experiments give the critical value of the strain energy release rate associated with damage initiation.
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