Dynamic failure mechanisms in a 6061-T6 Al/Al2O3 metal—matrix composite

Abstract

The dynamic failure of an alumina particle-reinforced 6061-T6 aluminum alloy composite has been studied using a tension Kolsky bar, and the process of fracture has been investigated using scanning electron microscopy. The failure of a 6061-T6 aluminum alloy was also studied for purposes of comparison. The composite was found to fail in a macroscopically brittle manner in tension, with a failure strain that increased with the nominal strain rate. Differences in hardening rate that are observed in dynamic tension and compression are ascribed to the development of internal damage within the composite in the form of particle cracking. Examination of the fracture surface of the monolithic alloy after dynamic failure shows a ductile failure through void nucleation, growth and coalescence, with substantial void sheet formation. Examination of the fracture surface of the composite after dynamic failure shows microscopically ductile failure in the matrix following brittle cracking of the particles. The dynamic failure process is hypothesized to consist of: (a) cracking of the reinforcing particles; (b) partial debonding at the particle—matrix interface resulting in the nucleation of voids within the matrix; and (c) the growth and coalescence of voids in the matrix to form the final failure surface. The failure process itself quickly localizes within the specimen, so that only a small part of the specimen is affected by all of the damage processes of particle cracking, interface failure and void growth.