Fatigue Crack Propagation from Pre-Crack under Cyclic Tortional Loading

摘要

Fatigue tests of crack propagation from a pre-crack in thin walled tubular specimens made of a medium-carbon steel were performed under cyclic torsion with and without superposed static tension. The direction of fatigue crack propagation follows the direction of the maximum of the total range of the tangential stress, DELTA sigma_(theta max) near the crack tip and then gradually change to the direction perpendicular the maximum of the total range of the principal nominal stress. The mode II stress intensity factor range DELTA K_(II) quickly gets close to 0 after crack extension. The propagation rate was faster than the uniaxial data when cracks extended a long distance.