Detecting mechanical stress in ferromagnetic materials using magnetic measurement techniques

Abstract

Abstract

The magnetic properties of ferromagnetic materials are highly sensitive to stress (amplitude and direction), and their measurements have already been employed in industrial setups for non-destructive testing purposes. Magnetic measurements are usually carried out by wrapping or surface coils that convert the magnetic flux variation into an electrical voltage. Previous works have shown that the wrapping coil can, in some cases, be replaced by a needle probe setup, in which two conductive probes measure the voltage at the surface of the sample. This setup can be used to measure variations in magnetic induction along several directions and in samples with complex shapes. This work evaluates the interest of the needle probe setup for non-destructive evaluation applications by comparing its measurements with those obtained using several magnetic measurements: magnetic Barkhausen noise and magnetic induction measurements via a wrapping coil. Measurements are carried out on a ferromagnetic sample under a non-uniform mechanical stress (uniform tension/compression combined with bending). Measurements show that the needle probe technique gives accurate signals that are strongly sensitive to the applied mechanical stress. For the chosen material, the most sensitive indicators are the coercive field, the remanent field and the magnetic permeability.