Fracture Mechanics Studies of Composite Systems.

A combined theoretical and experimental research program for investigating the application of fracture mechanics to composite systems is carried out. Preliminary results are presented which include the development of two fiber reinforced composite crack models, one with a low-fiber volume fraction and the other a high fiber volume fraction, and corresponding experimental data. The qualitative features of the theoretical prediction are in agreement with the experimental data indicating that there exists an optimum fiber volume fraction for which the composite achieves maximum fracture toughness. Tests were performed on uni-directional fiber reinforced composites with the crack running parallel to the fibers. For this arrangement, the current theory of fracture mechanics is shown to apply with good accuracy for FRP/epoxy composites. This is accomplished by performing two independent fracture tests the results of which are checked by an analysis of the crack system. A more elaborate analytical model is required for studying the graphite fiber/epoxy composite. (Author, modified-PL)