Modelling low-cycle fatigue life of particulate-reinforced metal-matrix composites

A low-cycle fatigue life prediction model for particulate-reinforced metal-matrix composites (MMCs) is presented. The low-cycle fatigue behaviour of particulate-reinforced MMCs is treated as a localised damage development phenomenon activated by applied cyclic loading. The localised cyclic stress and strain concentration and fatigue damage evolution of microstructural elements within the fatigue damaged zone ahead of the crack tip are considered to dominate the whole low-cycle fatigue processes. In high-strain low-cycle fatigue conditions, the fatigue-damaged zone is described as the region in which the local cyclic stress level approaches the ultimate tensile strength of the composite and within which the actual degradation of the composite material takes place. The fatigue crack growth rate is directly correlated to the range of the crack tip opening displacement. The empirical Coffin–Manson relationship is derived and the model naturally predicts that in strain-controlled low-cycle fatigue tests the MMCs with the higher volume fraction of reinforcement particles exhibit shorter fatigue lives than composites with a smaller volume fraction. The theoretical predictions from this model are in good agreement with the low-cycle fatigue life data of AA6061-T6 aluminium alloy reinforced with 15 and 20 vol.% alumina particles, respectively, for a temperature range between −100 and 150 °C in total-strain controlled mode.