Abstract
The propagation behavior of a circumferential fatigue crack in cylindrical bars of a carbon steel (JIS SGV410) and a stainless steel (JIS SUS316NG) was investigated under cyclic axial and torsional loadings. The J-integral range was used as a fracture mechanics parameter. When compared at the same J-integral range, the crack propagation rate under mode III was smaller than that under mode I. Parallel markings perpendicular to the crack propagation direction were observed on the fatigue fracture surface obtained under mode III loading. The residual stresses in the radial direction, σr, and in the tangential direction, σθ, were measured for both mode I and mode III fatigue fracture surfaces. For mode I fracture surface, σr was tension, and was almost constant irrespective of the applied J-integral range. σθ was close to zero for both materials. On the other hand, for mode III, σr and σθ were compression. For SUS316NG steel, the compressive stress of σθ increased with the J-integral range. For SGV410 steel, the change of σθ with the J-integral range was small. The breadth of diffraction profiles increased with J-integral range for both mode I and III. The breadth was found to be a good parameter to evaluate the applied J-integral range.
