339 高強度材料の破壊形態に及ぼす影響因子(OS1-7 疲労特性への影響因子)(OS1 高強度材・表面改質材の疲労と破壊)  [in Japanese] 339 Influence of Failure form for High Strength Steel  [in Japanese]

In order to clarify the influence factors on high-cycle fatigue of high strength steel SUJ2, the fatigue test have been carried out up to 10^8 cycles under rotating bending at room temperature. According to the experimental results, in the case of comparative low-cycle range, the fatigue crack initiates from specimens surface. On the other hand, in the case of high-cycle range, the crack initiates from an internal inclusion. In addition, there exisits transitional zone in the S-N curves between surface failure and fish-eye one. The damage, which means slipping would be accumulated in the specimen's surface under the high stress amplitude during two step stress fatigue. In addition, according to the above phenomena, surface appears in the region of extra-high cycle fatigue. According to the observation results, slip bands are generated in the spoecimen's surface. That is to say, speaking of failure form cause of surface hardness and surface damage.