A Study of Cumulative Fatigue Damage Under Variable Loading‐mode Conditions

The accumulation of fatigue damage was investigated by studying deformation processes and the kinetics of short crack initiation and propagation under variable loading‐mode conditions. Fatigue tests were carried out under push‐pull and torsion, both separately and sequentially, that is specimens were subjected to push‐pull loading prior to torsion. The results show that specimens tested in push‐pull followed by torsion have a much longer fatigue life than virgin specimens. The mechanisms of this phenomenon were explored by experimental observations and theoretical analyses of crack initiation and propagation. The effect of stress state on cumulative damage is described in some detail.