Fatigue softening and hardening in mild steel detected from Barkhausen noise

The measurement of Barkhausen noise is used to follow the fatigue process in a mild steel. The variation in the root-mean-square (rms) value of the noise with bending stress during single-strain cycles and in unloaded samples is determined at several stages of fatigue life. The fatigue softening and hardening are found to be sensitively revealed by specific changes in the shape and area of the noise versus stress loops and also in the variation in the noise in unloaded samples, corresponding to changes in the residual stress state. The high sensitivity of the magnetic measurement technique is emphasized.