Fiber/Matrix Interaction Effects on Fracture Toughness of Structural Composites.

The object of the study was to relate the effects of fiber, matrix and interface to the fracture toughness of fiber reinforced plastic composites. The initial part of the study employed a model composite system to determine the resistance to crack propagation normal to the fibers. Laminates suitable for projectile impact tests were also used to determine the resistance to interlaminar crack propagation between plies. Subsequently, a series of projectile impact tests were conducted on the laminates at AMMRC. After some delay, another series of fracture tests were conducted at M.I.T. on the systems which showed extremes in projectile impact resistance. This last series of tests was designed to determine the resistance to crack propagation normal to the fibers for laminates representative of those used in the projectile impact tests, as distinct from the earlier tests on model systems. The results of the program indicate that fiber and matrix properties bear a clear relationship to the model composite toughness, while the effects of changes in the interface also are important in some cases. Correlations between the fracture toughness and projectile impact resistance are tenuous in most cases. Author