The fundamental problem posed in this study is that associated with the behavior of short surface crack in low-cycle fatigue, which plays a significant role in predicting fatigue life. In the investigation, low-cycle fatigue tests of smooth specimens were conducted under push-pull loading for several materials, and behaviors of cracks on the specimen surface were observed by means of a plastic replication technique. When the growth rate of surface cracks was correlated to J-integral range, the data for cracks longer than about three times grain-size without coalescence growth were found to coincide with the relation obtained for large through-thickness cracks. Other data, even when excluding the results with coalescence, shifted toward the higher-rate region than the large-crack relation. Such an acceleration was suggested to be due to the difference in growth mechanism.
The prediction of fatigue life was investigated on the basis of the J-integral approach, and it was found that some restrictions remained in the applicability of the crack growth law of ordinary fracture mechanics type to the life prediction for smooth specimens under low-cycle fatigue.