50 巻 (1984) 452 号 p. 737-743
The growth behaviors of small surface cracks, of which growth process occupied the great part of the fatigue life, were experimentally examined in low carbon steel under rotating bending fatigue. The growth rate of these cracks, furthermore, were analyzed in terms of J integral range, ΔJ evaluated in elastic-plastic manner by assuming that the crack tip was open even under the compressive stresses during fatigue. The growth rate was represented by a linear band with the smaller amount of a scatter against ΔJ than against the stress intensity factor range, ΔK in the log-log plot. The linearity was also held good up to the region of the lower growth rate against the former than against the latter. The equation of ΔJ=ΔKσ2/E, in which Δσis substituted by E·Δε, where Δσ, Δεand E and stress range, strain range and Young's modulus, respectively, could also be a good parameter equivalent to the above ΔJ for the evaluation of the crack growth rate.