Damage initiation and progression in notched unidirectional composites

This paper summarizes our recent research in a theoretical and experimental investigation of damage initiation and progression in unidirectional graphite/epoxy composites containing a central circular hole subjected to off-axis uniaxial tension. Theoretically, a newly developed damage constitutive equation model, together with a modified nonlinear finite element procedure, is applied to analyze the inelastic behavior of the composites with respect to material damage initiation and accumulation. A set of failure criteria is proposed and used to predict the threshold condition of failure and to identify different failure modes. Experimentally, to provide a validation analysis, the Moiré interferometry method with a computerized image processing system is employed to monitor deformation fields and failure characteristics of the composites. Results obtained from the tests are collated with those from analyses to gain a better understanding of the parameters affecting progressive damage in the composites.