A THEORETICAL AND EXPERIMENTAL-STUDY OF ALTERNATING-CURRENT STRESS MEASUREMENT UNDER DIFFERENT LOADING MODES

This paper presents some experimental studies on the inverse magnetost riction effect that were recently conducted at University College Lond on (UCL) by the authors. A form of alternating current field measureme nt (ACFM) instrumentation, which was developed to detect and size surf ace defects in ferromagnetic components, was used in the present study to induce a low alternating magnetic field near the surface of a mild steel specimen and to pick up the influences of applied stresses on t hat field. The mild steel specimen was tested both in four-point bendi ng and uniaxial tension to investigate the response under different st ress modes within the elastic region. Consistent and repeatable result s have been obtained under both bending and tension loading modes when different probe types with different inducing frequencies are used. I n the present paper, the mathematical model of half-space electromagne tic induction which was recently developed at UCL has been combined by the authors with the previously published fundamental relationships b etween stress and magnetization. The combination gives a new model, wh ich has been introduced here to demonstrate that stress will alter the magnetic field. This suggests that ACFM technology can be further dev eloped into that of alternating current stress measurement (ACSM) for industrial applications.