Abstract
Non-propagating cracks were formed in sharply notched iron specimens stressed for 107 cycles or more at a stress slightly below the notch fatigue limit. These cracks extended markedly at the retest with the same stress after annealing at 973 K. Tangled dislocations of extremely high density, developed ahead of the cracks, were almost annealed out during the annealing. Cyclic strain-hardening due to these dislocations seemed to relate to the formation of non-propagating cracks in iron specimens. On the other hand, such cracks were not observed in stainless steel showing a high strain-hardening character. From these results as well as the fact that these cracks can be formed in very sharply-notched specimens only, it is concluded that the formation of non-propagating cracks in machined notches is influenced by three factors: (1) the amount of cyclic strain-hardening, (2) the rate of cyclic strain-hardening, and (3) the stress field associated with notch sharpness.
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