First Order Analysis of Stiffness Reduction Due to Matrix Cracking

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Abstract
In this paper the reduction in effective elastic constants of composite lami nates due to matrix cracking is considered. A general easily applicable theory valid for two- and three-dimensional analysis of thin as well as thick laminates is presented. The theory is based on the change of elastic energy in a laminate at the appearance of a matrix crack in one layer. This information combined with a dilute approximation , i.e., different matrix cracks are considered not to interact with each other, is utilized to estimate the re duction of elastic constants for a certain crack density. The theory is asymptotically exact for nk « 1, where nk is the number of cracks per unit thickness of the cracked ply and a correct value of the slope of the stiffness reduction crack density curve is obtained at nk = 0.