To prevent an accident due to the metal degradation of stainless steels, we have previously proposed fatigue evaluation methods (such as the remnant magnetization method using a thin-film flux-gate magnetic sensor [1] and the inductance method using a pan-cake type coil [2]). These two fatigue evaluation methods demonstrated a good correlation between the magnetic sensor output signal and the amount of plane-bending fatigue damage in stainless steels. We developed a stacked-coil type magnetic sensor shown in Fig. 1(a) in order to achieve a magnetic sensor for an accurate fatigue evaluation. This magnetic sensor was composed of two detection coils that are connected differentially, an excitation coil, and a ferrite core. Fig. 1(b) shows the connection of the excitation coil and the two detection coils. Fig. 2 shows the detection result of fatigue and crack using this magnetic sensor. The material used for this specimen was an austenitic stainless steel (SUS304), and plane-bending stress was applied. From Fig. 2, it can be seen that this magnetic sensor detected defects well. The evaluation results of plane-bending fatigue damage distribution will be shown in in detail the complete paper
