The post failure analysis of symmetric E-glassJEpoxy and GraphiteJEpoxy (T300/934) laminates are presented in this paper. The main thrust of this research was to predict the progressive fracture mechanisms of composite laminates under load. Several composite laminates were tested under the three-point-bending configuration to observe and record the subsequent failure events. On the other hand, an analytical computational procedure based on lamination theory, Tsai-Hill failure theory, and an assumed stiffness reduction scheme was developed in an attempt to predict the failure mechanisms.
In general, a composite laminate does not fail catastrophically but rather in a progressive manner. In other words, the final fracture of a composite laminates always occur after a sequence of ply failures. It is believed that a clear understanding of the potential failure mechanisms of composite laminates under designed loading will allow an in depth risk assessment. To accomplish this, an analytical scheme for analyzing subsequent ply failure of composite laminates must be established. In addition, the subsequent failure analysis can even provide a database whereby a field inspection engineer can use them to evaluate the state of integrity of a composite structure when failure events are sited. At present the subsequent failure analysis procedures that involve in characterizing the failure mechanisms of actual structural components are still lacking. Petit and Waddoups [11 introduced a negative tangent method to characterize the non-linear stress-strain behavior (produced by the ply failure process) of composite laminates. Chiu [2] introduced a stepwise stiffness reduction scheme to determine the post failure strength of composite laminates. Craddock £3] made a comparison among three stiffness reduction schemes, stepwise stiffness reduction, total stiffness reduction, and negative tangent method on their predictive capability on the stressstrain behavior of composite laminates.
