Magnetic domain-informed selection of magnetisation direction in magnetic-acoustic emission for stress evaluation

Magneto-acoustic emission (MAE) is widely used to measure the stress status of steel components and structures. The sensitivity of residual stress measurement depends on the orientation of the excitation field. It is imperative to have some understanding of the selection of magnetisation direction for stress characterisation in MAE technique. In this work, the dependence of the sensitivity of stress evaluation on the magnetisation direction was investigated. The relationship between the stress and MAE signal in different magnetisation directions was established. The sensitivity coefficient of stress detection along the different orientations of the excitation field was obtained. It is shown that the highest sensitivity for stress evaluation occurs when the magnetisation direction is oriented at an angle of 45 degrees to the stress direction. Subsequently, the variation of magnetic microstructure under different stresses based on a magneto-optical imaging system was studied, providing a physical explanation for MAE signal variations. We show that the combined effects of stress-induced anisotropy and magnetic field-driven magnetic domain rearrangement influence the characteristics of the MAE signal. The results of the sensitivity analysis and sensitivity coefficients provide constructive suggestions for selecting the magnetisation direction for stress characterisation. The microstructural observations provide physical insight into macroscopic magnetic non-destructive testing for stress detection.