307 高強度鋼の疲労破面に及ぼす大気/高真空/材料内部環境の影響(OS1-1 高強度材の超高サイクル疲労(1))(OS1 高強度材・表面改質材の疲労と破壊)  [in Japanese] 307 The Effect of Atmosphere / High Vacuum / Inner Environment of Materials on Fatigue Fracture Surface of High Strength Steel  [in Japanese]

Uniaxial tension fatigue tests of high strength steel, SNCM439, were carried out in air and high vacuum environment. As a result, the following were obtained : (1) Compared with surface fractures in air, the fatigue life of surface fractures in high vacuum tended to be longer. (2) High vacuum environment strongly influenced the fatigue fracture surface in the initial stage of crack propagation. (3) High vacuum environment was similar to inner environment of materials. (4) The formation of Optically Dark Area (ODA) closely related to mean stress.