Near threshold fatigue crack growth behavior in stainless steel under cyclic torsion

Near threshold fatigue crack growth tests were conducted under torsion on circumferentially pre-cracked round bars of a stainless steel. The crack growth rate was decreased with crack extension because of the sliding contact of the crack faces. 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 range is divided into two parts: one is the effective value responsible for crack growth and the other is 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.