1989 年 38 巻 426 号 p. 280-286
Fatigue crack propagation tests were conducted using thin-walled tubular specimens of pure copper under combined in-phase axial-torsional loadings. In large scale yielding situations, the crack growth behavior under biaxial stresses was investigated based on the elastic-plastic fracture mechanics. The crack morphology was found to be a bent-type in the combined loadings and a branch-type in the torsion case. Cracks were found to propagate in such direction that the Mode II component of the stress intensity factor was minimized. By using a devise to detect the opening and sliding displacements at the center of crack, the deformation behavior of bent-or branch-cracked specimens was also examined to evaluate the crack opening point. It was noted that tails were observed near both tips of the hysteresis loop in the case of torsion. The correspondence between these tails and the crack closure was discussed in the relation with the opening and closing behaviors of ideally elastic cracks. The effective stress intensity factor ΔKIeff of Mode I was calculated by taking account of experimental observations mentioned above. When ΔKIeff was employed to correlate the growth rate, good correlation was not seen because of gross plasticity. A tentative procedure to estimate the J-integral range ΔJ was proposed for the bent crack. The growth rate of bent crack was correlated very well with ΔJ estimated by the proposed procedure.