Influence of a static torque on plasticity and asperity-induced closure effects during fatigue crack growth in bainitic steel cylinders loaded in push-pull

Mode I fatigue crack growth with a superimposed static torque was investigated in bainitic steel. The torque had little effect on crack growth kinetics and path. However, the non-singular stress parallel to the crack front, and bending stresses due to eccentric crack growth triggered crack twisting, even in mode I. A progressive increase in crack sliding displacement was due to a rise in elastic torsional compliance, but also to plastic ratchetting at the crack tip, and to a progressive shearing of crack face asperities, which reduced the enhancement of roughness-induced closure by the torque, however shown to enhance plasticity-induced closure.