Low-cycle fatigue of a metal-matrix composite: Influence of pre-straining on the fatigue life

Low-cycle fatigue tests were conducted on an Al2O3 particulate-reinforced metal-matrix composite. Special emphasis was placed on the effect of plastic pre-straining on the fatigue lives of subsequently performed fatigue tests. In all cases of a standard heat-treated material (T6), the pre-deformed samples showed reduced fatigue lives compared to the sample without pre-strain. The cyclic deformation curves showed initial hardening and subsequent cyclic softening for nearly the whole remaining life time. In another test series, specimens were investigated, in which the matrix was not hardened by precipitates. This material was found to be cyclically stable, showing no softening.