Effect of Matrix Plasticity on Ultimate Strength of Composite Laminates

Abstract

Prediction of ultimate strength of a multidimensional composite laminate subjected to arbitrary load condition is difficult in nature. A fundamental reason is that the load share by each lamina in the laminate depends on the lamina instantaneous stiffness matrix which is not a constant throughout in most cases. The lamina nonlinear response is mainly caused by the inelastic deformation of the matrix material in the lamina. The primary objective of the present paper is to investigate the effect of matrix plasticity on the progressive failure process in the laminate. The study is based on a recently developed micromechanics model, the Bridging Model, which provides the instantaneous stiffness of the lamina at any load level using its constituent properties and the fiber volume fraction only. Another purpose of this paper is to compare predictive capability of different failure criteria for the laminate ultimate strength. Two typical failure criteria, i.e., the Tsai-Wu criterion applied to the lamina level and the maximum normal stress criterion applied to the constituent level, are incorporated in this paper. It is found that the matrix plasticity affects heavily the laminate strength if the laminate does not have 0 lamina plies in the loading direction or if the stiffness of the matrix does not differ significantly from that of the fibers. It is also found that the maximum normal stress criterion is generally more efficient for composite failure analysis.