Fatigue crack growth behavior in stainless steel under cyclic torsion

Crack growth tests were conducted under cyclic torsion on circumferentially pre-cracked round bars of an austenite stainless steel. The crack growth rate decreased with crack extension because of the sliding contact of the crack faces. After the initiation of microscopic flat facets from circumferential pre-crack of the specimen, the crack face began to twist, and then the crack propagation rate started to decrease because of the crack face sliding contact under cyclic torsion. The crack growth rate declined continuously with crack extension and the crack arrested at last when torsional load less than some value. The crack growth rate without the influence of crack surface contact was determined by extrapolating the relationship between the crack growth rate and the crack extension to the zero crack length. The applied stress intensity factor (SIF) range was divided into two parts: one was the effective value responsible for crack growth and the other was the shielding value dissolved by crack surfaces contact. The fatigue limits for crack initiation and fracture were predicted and the predicted values agreed well with the experimental results.