The Effects of Stress on Magnetic Properties and the use of Magnetic Measurements for Evaluation of Materials

Abstract

A new magnetic imaging system has been developed for non-destructive evaluation of structural and mechanical conditions of magnetic materials. The system produces a multiparameter contour plot of the spatial variations of a variety of magnetic properties such as coercivity, reman- ence, permeability and Barkhausen effect BE) signal. These can then be used for the detection of material conditions such as residual stress or the presence of cracks, since the magnetic and mechanical properties of materials are closely related via the magnetoelastic coupling. An inte-grated sensor probe capable of measuring both magnetic hysteresis and BE signals was developed using magneto resistive devices. For comparison hysteresis loops and BE signals were measured in materials subjected to various tensile and compressive stresses within the elastic limit. A magnetic model has also been developed which provides a self-consistent description of the effects of stress on hysteresis loop and Barkhausen effect (BE) signals. BE signal was calculated based on the hysteretic-stochastic process model of domain wall dynamics, which has been extended to include the magnetomechanical effect.