Characterisation and quantification of multiple crack growth during low cycle fatigue

The collective growth of multiple microcracks (or short cracks) during low cycle fatigue of polycrystalline Cu–30%Zn, 316L and Fe–26Cr–1Mo is investigated. Scanning electron microscopy is employed to study the evolution of surface microcrack populations, as well as the growth of individual cracks, on smooth specimens cyclically deformed at constant plastic strain amplitudes. The damage accumulation process is quantified by construction of so-called damage accumulation (DA) profiles, which reveal important information about crack growth mode, crack initiation rates, strain localisation and crack coalescence. In addition, experimentally measured microcrack growth is quantified in terms of general crack growth relations. The uniformity of these relations for different materials indicates that growth barriers dictate the main differences in fatigue microcrack growth.