Domain nucleation and annihilation in a steel bar subjected to an increasing tensile load

Measurements of magnetoacoustic emission (MAE) and Barkhausen emission (BE) are made on a steel bar under an increasing tensile load. Both MAE and BE profiles possess two peaks. The initial peak is corresponding to domain nucleation while the final peak is due to domain annihilation. The ratios, r_MAE and r_BE, of the initial peak to the final peak in both MAE and BE profiles are used to indicate the relative strength of the nucleation process to the annihilation one. Initially, the value of r_MAE is constantly kept at about 1.3 even the applied tensile load is changing. After the bar is yielded, r_MAE increases up to a value of 1.7. On the other hand, r_BE is greater than 1 when the bar is in the elastic state; it is about unity when the bar begins to yield; in the plastically deformed state, r_BE is less than 1. It is therefore possible to estimate the mechanical condition of the steel components when they are under stress by the MAE and BE techniques. We have also conducted the microhardness test and optical microscopy on the steel bar in order to investigate the effect of microstructure on MAE and BE