Low-cycle impact fatigue of SiC_w/7475Al composite

Abstract

Important uses in the future for metal-matrix composites are in aerospace, weaponry, and high-speed power plants in which the inertial force produced by great acceleration is a load of high strain rate. Therefore close attention is given to the mechanical behavior of a composite at high strain rates. This paper reports a study of the behavior and mechanisms of a SiC _w /7475 composite in low-cycle impact fatigue (LCIF). The LCIF and impact tension tests were conducted by using the push-pull impact fatigue apparatus developed by the authors, in which the loading assembly was actually a combination of a Hopkinson’s pressure bar and an extension bar. In the apparatus the trapezoidal stress wave loads were produced. The strain rates in specimens may reach 400 s ^-1 .The results show that for a SiC _w /7475 composite, the strain-rate effects on yield stress, ductility, cyclic hardening and softening, δ _e /2-N _f relation, and transition life were slight. In low-cycle impact fatigue the cracks often initiated within or near the SiC particles, which mingled in the composite. The SiC _w /7475 composite was found to be less ductile than its alloy matrix; in low-cycle fatigue brittleness appears. Therefore great attention must be given to the behavior of the composite when it is used as a structural material.