A failure mechanism based failure theory for laminated composites including the effect of shear stress

In this paper, a new failure theory for laminated composite based on initiating failure mechanism is presented. Unlike the existing failure theories, the present theory is based on biaxial state of normal stresses with and without shear stress. The approach is based on micromechanical analysis of composites, wherein a representative volume consists of a fiber surrounded by matrix in appropriate volume fraction and modelled using 3-D finite elements to predict the strengths. In this paper, different failure envelopes are developed by varying shear stress say from 0% of shear strength to 50% of shear strength in steps of 25% of shear strength. Results obtained from this approach are compared with Tsai-Wu and maximum stress failure theories. The results show that the predicted strengths match more closely with maximum stress theory. Hence, it can be concluded that influence of shear stress on the failure of the lamina is of little consequence as far as the prediction of strengths in laminates.