高温における引張・圧縮サイクリック・クリープ破壊に及ぼす弱真空雰囲気の影響

抄録

The effects of both vacuum environment and shape of stress wave of “cp” and “cc” as shown in Fig. 2 on push-pull cyclic creep fracture of SUS 316 stainless steel were examined experimentally in both vacuum of 0.1Torr and 1 atmosphere at 600°C.
(1) The cyclic creep failure time of the material tested was remarkably dependent on environment and shape of stress wave. The time to failure under cp stress wave with tensile creep hold in 0.1Torr was shorter than that in air. On the contrary, the failure time under cc stress wave with both tensile and compressive creep hold in 0.1Torr was larger than that in air. The latter fact was also revealed under pc stress wave with compressive creep hold.
(2) The above behavior under cp wave resulted from both early crack initiation and fast crack propagation in tension cycle in 0.1Torr, and the latter effect under cc wave resulted from late initiation and slow propagation of crack in 0.1Torr.
(3) The crack propagation rate of the material tested was well represented by a single curve on the basis of modified J integral, independent of stress levels, shapes of stress wave and environments.
(4) The variations of both crack initiation time and crack initiation time and crack propagation rate of the metal under vacuum environment of 0.1Torr seemed to result mainly from the variation of macroscopic creep rate of the specimen. It was considered that the increase of creep rate under cp wave in 0.1Torr resulted from the increase of dislocation density as in the case of static creep of the metal in 0.1Torr, and also that the decrease of creep rate under cc wave in 0.1Torr was analogous to the deformation and fracture behavior of high-temperature low-cycle fatigue of the metal.