The metal magnetic memory detection of rotating bending fatigue damage for 45QT steel

In order to research the character of 45QT's rotating bending fatigue before fracture, the theoretical study was conducted based on magnetomechanical effect and the magnetizing analysis of load bearing specimen, and the rotating bending fatigue experiment was carried out on 45QT steel with annular notch. The normal magnetic signals of specimens were analyzed. Theoretical analysis indicates that, the magnetization of specimen will be enhanced and reach saturation with stress and geomagnetic field working together, and the magnetization field will leak outside from the fatigue crack and make surface magnetic field distortion. Experimental results show that, the normal magnetic signals tend to be steady after about 20000 cycles; the steady normal magnetic signal distribution around the notch reflects the location of max fatigue crack source where the signal amplitude is smallest; the normal magnetic signal distribution curve along axis will fluctuate acutely at the notch area before fracture if the measurement line is near the max fatigue crack source. Then the corresponding detection method based on the normal signals around the notch and along the axis is put forward.