抄録
For the detection of fatigue damage before crack initiation in an austenitic stainless steel, SUS304, we investigated the possibility of the fatigue damage detection and evaluation from the change in the magnetization. The changes in the magnetization before the fatigue crack initiation were observed in the fatigue process at several stress amplitude and stress ratio. It was found that the changes in the leakage magnetic flux density B_z were observed before crack initiation and the location, where the maximum changes in the value of B_z observed, coincided with the location of the stress concentration, where the crack was formed. The experimental results obtained by fatigue tests conducted under the stress ration, R, of -1, and 0.1 showed that the change in the magnetization of SUS304 specimen was depended on the stress ratio. Under either stress ratio, the value of B_z rapidly increased just before crack initiation. When no crack was found, increasing rate of B_z decreased with increasing the number of cycles, and the value of B_z was saturated to a certain value. It was found that fatigue damage before crack initiation can be detected from the change in the magnetization in SUS304 steel.
