Effects of matrix cracking on the sitiffness of composite laminates were investigated. Laminate stiffness reduction caused by matrix cracking was predicted by a finite element model, and the prediction was compared with some existing analytical models and available experimental data. The effective moduli of a cracked layer in a composite laminate were studied. It was found that normalized crack density (thickness of the cracked layer/crack spacing) is a more critical parameter to characterize matrix cracking damage; location of the cracked layer in a laminate has negligible effect on its effective moduli; and orientation of the constraining sublaminate has considerable influence on the effective moduli of the cracked layer. An experimental method to investigate effective shear modulus of a cracked layer was also presented, and the test results were compared with predictions by the finite element model and other existing models.
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