2021 年 87 巻 901 号 p. 21-00196
It has been shown that fatigue damage is brought about by crack initiation and growth and fatigue life can be predicted by crack growth analysis. This study approximated the fatigue life of S45C carbon steel and its change due to the mean stress and loading history effects according to the proposed LDC model (fatigue Life Determined by Cracking model). The equation for the fatigue life approximation was derived assuming the fatigue life was equivalent to the number of cycles for a small crack to grow to a critical size for specimen failure. According to the LDC model, it was shown that the fatigue life and fatigue limit for various mean stresses could be predicted using the effective strain range, which accounted for the crack mouth closure. To confirm the applicability of the LDC model to the loading history effect of carbon steel, the overload fatigue tests were conducted, in which cyclic compressive over strains were applied. Also, non-propagating cracks were observed to investigate the correlation between the fatigue limit and crack arrest phenomenon. It was shown that the fatigue life was reduced by applying the cyclic overloads and the magnitude of the reduction could be predicted using the effective strain range. A procedure was shown to predict reduction of the fatigue life due to mean stress and loading history conservatively. Finally, it was shown that the LDC model was useful to deal with effects of various factors such as mean stress, loading history, specimen size, surface finish and environment in a unified way.
