Chapter 3.9 - Prediction of failure envelopes and stress/strain behavior of composite laminates

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This chapter presents failure envelopes for unidirectional composites and multilayered composite laminates, which have been predicted by linear laminate theory. There are three major failure modes in composites—namely, fiber failure, matrix failure, and fiber/matrix interfacial failure. Because, in general, the stresses in the fiber and matrix are different; their respective failures are determined by different stresses and have different failure mechanisms. Thus, a lamina failure criterion that separates matrix failure from fiber failure, such as the Hashin–Rotem criterion, is mechanistically more appropriate. The ply-by-ply discount method with parallel spring stiffness reduction model is used in the prediction. Laminate ply-by-ply failure analysis is performed on the basis of the 2-D stress field in the laminate. The stress/strain behavior of four laminates under uniaxial or biaxial loading is predicted by considering both material nonlinearity and progressive matrix cracking. Material nonlinearity is considered by using a one-parameter plasticity model for fiber reinforced composites. Progressive matrix cracking and the corresponding stiffness reduction are predicted by the use of a simplified shear-lag analysis and finite element analysis.