Hard Object Impact Damage of Metal Matrix Composites

Abstract

The paper presents results on the damage mechanisms in hard object impact and their effect on the residual tensile strength of unidirectional Boron/Aluminum and Borsic/Titanium composites. The ballistic tests were carried out with 0.177" steel spheres impacting at the center of centilever plates over a velocity range of 50 to 4000 ft/sec. The induced ballistic damage and the different failure modes are examined by radiography and SEM, and the post impact residual tensile strength and residual velocity after perforation are studied for both materials. The damage induced in Boron/Aluminum consists mainly of lateral and axial cracks causing large strength degradation, up to 50 percent of the initial strength. Borsic/Titanium, on the other hand, shows much better impact resistance and the ballistic damage consists of localized plastic de formation and formation of a sheared plug causing strength degradation of 20 percent of the initial strength, as is the case with homogeneous titan ium. An analytical model based on fracture mechanics can predict fairly well the damage size and the residual tensile strength. Ballistic limit velocity and residual velocity after perforation are shown to be predictable by a model developed for homogeneous metallic plates.