The fatigue crack propagation rate and crack closure behavior under repeated two- and three-step loadings at low stress intensity level were investigated on an aluminum alloy A5083-O.
The crack opening point, Kop, was found to be constant and was nearly equal to that for KH in Kmax-Kop relation for constant amplitude loading tests, where KH was the highest K value in repeated multiple-step loading tests.
Based on the effective stress intensity range, ΔKeff, which is calculated considering the above mentioned behavior of Kop, the fatigue crack propagation life can be conservatively estimated by the linear accumulation law of crack propagation length adopting ΔKeff-dl/dn relation for constant amplitude loading tests.