Abstract
Fatigue tests of crack propagation from a circular notch in thin-walled tubular specimens made of a stainless steel (SUS 316NG) were performed under cyclic torsion with and without superposed static and cyclic axial loading. The propagation path of mode I fatigue cracks followed the direction perpendicular to the maximum direction of the total range of the normal stress. The propagation rate was faster than the uniaxial data when compared at the same range of the stress intensity factor or the effective stress intensity factor. The negative nonsingular stress induced excessive plasticity ahead of the fatigue crack, which accelerated the fatigue crack. The J-integral range was estimated from the relation between the torsional load and the crack center opening displacement which was obtained by a specially designed extensometer. The J-integral range was proved to be an appropriate parameter for crack propagation with excessive plasticity under combined loading.
