In this paper the equivalent constraint model (ECM) proposed recently by the authors in references (1-2) has been used to model the multilayer ply cracking in a glass fiber reinforced epoxy [0 / 90 /± 45]_s laminate subjected to cyclic tensile loading. It was observed in reference (3) that the ply cracks develop extensively in the 90°-ply as well as in the 45°-and -45°-plies. The effect of the ply cracking in each individual layer, 90°-, 45°- and -45°-plies, on the degradation of the elastic constants of the laminate was evaluated by analyzing a respective model laminate, so-called the ECM laminate. The crack interactions from layer to layer were taken into account. The model's predictions are in a good agreement with the experimental E-modulus data under fatigue.
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