Deformation and Fracture Mechanisms in a SiCw-Al Metal Matrix Composite

Although much work has been carried out to date on the mechanical properties of SiCw/Al metal matrix composites at quasi-static loading rates, comparatively little work has been aimed at understanding their dynamic mechanical behavior, i.e., mechanical behavior at high rates of strain, and this forms the main aim of this research. Experiments were carried out using the Split Hopkinson Pressure Bar at rates of strain from quasi-static to > 1000s−1. The tests consisted of subjecting cylindrical samples of the MMC’s to dynamic compressive loading and studying their response. The stress/strain curves for different rates of strain were obtained. In order to study the effect of specimen geometry on the mechanical behavior, different aspect ratios were investigated. To study the influence of the whiskers on the dynamic behavior of the MMC, unreinforced Al alloys were also tested for comparison. The results showed a significant increase in strength of the MMC’s under dynamic loading conditions as compared with quasi-static loading. However, the toughness was found to decrease concomitantly. The deformation and fracture mechanisms of the tested samples were analyzed by SEM and TEM. The principal feature of the observations was the development of narrow shear bands interspersed with relatively undeformed regions in the composite samples. Ultimate fracture was by a process of microvoid coalescence.