Magnetostatic determination of variations of internal stress in magnetic steels

This paper explores the possibility to measure changes in internal stress in ferromagnetic steels using magnetostatic methods. The device consists of a permanent magnet placed close to the steel piece and a magnetic probe between both elements. The magnetostatic field measured by using the probe is partially due to the magnetization of the steel piece. Internal stress variations in the steel alter its magnetic permeability due to the magnetoelastic effect, varying the magnetostatic field measured by using the probe. For the device we present here, the relative variation of the measured magnetic field is of the order of 1.7 × 10-5/MPa of internal stress.