Abstract
The fatigue crack propagation behavior from a tesile pre-crack under cyclic torsion combined with static or cyclic axial loading was predicted on the basis of the maximum tangential stress criterion. The prediction was compared with the experimental results obtained for a medium carbon steel. The direction of fatigue crack propagation follows the direction of the maximum of the total range of the tangential stress, Δσ_<θmax> near the crack tip and then gradually changes to the direction perpendicular to the maximum of the total range of the principal nominal stress. The mode II stress intensity factor range ΔK_<II> quickly gets close to zero after small amount of crack extension. The propagation rate was faster than the uniaxial data as cracks extended a long distance.
