Non-destructive Measurement of Stress in Steel by Magnetic Sensor Acting under High Biasing Field

A magnetic sensor acting under high biasing field was developed to measure stress in steel nondestructively, based on the linear dependence of reversible permeability on stress, and it was applied to measure uniaxial tensile stress. It was found that the product of reversible permeability and measured area changed linearly with stress. This result was explained by the magnetostriction theory under high field amplitude. In order to extend the applicability of this method to the measurement of plane stress, the relationship between the measured value of the product and the stress in the transverse direction was examined. Fundamentally, a linear relation was found between them, but some problems, such as hysteresis due to loading and the boundary effect on the test piece, remained to be solved.