ANALYSIS OF MULTIPLE MATRIX CRACKING IN [+/-THETA(M)/90(N)]S COMPOSITE LAMINATES .1. INPLANE STIFFNESS PROPERTIES

In previous work Fan and Zhang1 have proposed the equivalent constraint model (ECM) to predict the effect of matrix cracking on the in-plane stiffness properties of [+/- theta(m)/90n]s composite laminates loaded in tension. The model is based on a two-dimensional shear-lag analysis where out-of-plane shear stresses in the constraining +/- theta-layers are assumed to vary linearly. In the present paper this shear-lag model is further developed to allow partial variation of shear stresses across the thickness of the constraining layers. The effect of non-uniform matrix cracking on the stiffness properties is also examined. Predictions of the new model compare favourably with experimental results for various multiply laminates and the discrepancy is less than that given by other theoretical models.