Experimental research on metal magnetic memory characterization of crankshaft fatigue damage behavior

Magnetic charge model for crack propagation was established based on analysis of crankshaft fatigue crack growth characteristics. Bending fatigue test for crankshaft was carried out in test rig and then the law of the vertical component of Metal Magnetic Memory signal from fatigue damage parts was analyzed. Combined with the observation of fatigue fracture morphology from Scanning Electron Microscope, the feasibility of crankshaft fatigue crack growth characterized by Metal Magnetic Memory was discussed. The research results showed that: Crankshaft bending fatigue crack was three-dimensional semi-elliptical crack. Long axis of fatigue crack extended along fillet and short axis of fatigue crack extended to the center of crankshaft journal. The distribution of vertical component of Metal Magnetic Memory signal in different fatigue damage moments was obtained by magnetic probe. Abnormal signal in the distribution of vertical component was stimulated by fatigue crack growth. Abnormal signal area matched long axis of fatigue crack and amplitude of abnormal signal was associated with the size of short axis. The results could lay the foundation for the application of Metal Magnetic Memory for crankshaft fatigue crack growth life evaluation.