Abstract
Fatigue crack propagation tests were performed in thin-walled tubular specimens with a hole made of a stainless steel (SUS 316NG) 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 of the total range of the normal stress including the compressive component of the stress. The propagation rate was faster than the uniaxial data when compared at the same range of the stress intensity factor. Even when compared at the same value of the effective stress intensity range, the crack propagation rate was faster under combined loading than under uniaxial loading because of excessive plasticity ahead of the fatigue crack. The J-integral range determined from the relation between load and displacement was proved to be an appropriate parameter for crack propagation with excessive plasticity under combined loading.
