The interfacial failure sequence during fiber pushout in metal matrix composites

Fiber pushout tests have been used widely in both metal- and ceramic-matrix composites as a means of measuring the fiber-matrix interfacial shear behavior. The tests have a significant experimental appear in their apparent simplicity. However, experimental analysis of fiber pushout data from metallic matrix composites, MMCs, is complicated by a combination of large thermally induced residual stresses and (often) a strongat the fiber matrix interface. This combination results in the necessity of push-out tests of thin slices of composite so that large fibers can be displaced at loads less than that at which the indenter fractures or the fiber crushes. For example, room temperature fiber pushout testing of sapphire or SCS-6 SiC-reinforced MMCs with ∼125 microm diameter fibers is usually restricted to thin slices of specimens of less than approximately 0.7 mm thick. The purpose of this communication is to present experimental evidence which indicates that, even in the absence of specimen bending, the interfacial failure process initiates at the specimen backface, during fiber pushout in MMCs. Based on laser profilometry measurements of the fiber displacements at the specimen backface as well as the topface, the interfacial failure process is examined as a function of increasing indenter load for fiber pushout of sapphire fibers in a NiAl matrix, as well as sapphire fibers in two TiAl matrices