Monitoring fatigue damage in materials using magnetic measurement techniques

Measurements of hysteresis and Barkhausen effect (BE) have been made on 0.1 wt % C Fe–C alloys subjected to strain-controlled fatigue at various strain amplitudes. A relationship between the fatigue lifetime and strain amplitude was observed. The hysteresis properties of the samples cycled at different strain amplitudes were found to vary systematically with expended fatigue life. These properties showed significant changes in the initial and final stages of fatigue, while between these stages they remained stabilized. In the stable stage the remanence was found to decrease, whereas the coercivity increased with increasing strain amplitude. Variations in BE signal during fatigue were found to be closely related to the microstructural changes observed on the sample surface. These results are interpreted in the context of the changes in microstructure caused by fatigue damage, and the effects of the formation and propagation of fatigue cracks on the field distribution and domain structure in the vicinity of the cracks