Effect of loading sequence on fatigue damage under push-pull followed by torsion and torsion followed by push-pull

摘要

Fatigue tests of push-pull followed by reversed torsion (PP-to-T) and reversed torsion followed by push-pull (T-to-PP) were carried out on 0.47percent C steel specimens containing an initial small crack of 400 #mu#m in surface length. The initial small cracks were introduced by a preliminary push-pull fatigue test using a specimen which contained an artificial small hole of 40 #mu#m diameter/depth. Fatigue tests of combined push-bull/torsion followed by push-pull (PP/T-to-PP) were also carried out to investigate the effect of crack geometry, such as branching and kinking from the initial small crack, on cumulative fatigue damage. Different crack growth behaviors due to different loading modes and their sequence complicatedly influence cumulative fatigue damage. Thus, existing fatigue damage theories cannot be applied to the cases presented in this study.