Quantitative evalutation of stress distribution in magnetic materials by Barkhausen Effect and magnetic hysteresis measurements

The feasibility of determining surface stress distribution in magnetic materials by magnetic measurements has been studied using a newly developed magnetic imaging system. The results indicate that magnetic measurements can be usefully used for detecting stress concentration in magnetic materials nondestructively. The system measured hysteresis loop and Barkhausen effect signal using a surface sensor, and converted the data into a two-dimensional image showing spatial variations in magnetic properties. The sample used in this study was a nickel plate machined into a shear stress load beam configuration. When compressive stresses were applied along the neutral axis of the sample, the image of magnetic properties such as coercivity exhibited patterns which were similar to the stress distributions calculated using finite element model (FEM). For direct comparison with FEM results, stress distributions were determined empirically from the measured coercivity values using experimental calibration of the stress dependence of coercivity. The stress patterns derived from the measured magnetic properties were found to closely resemble those calculated using FEM.