A concise and accurate model for the magnetomechanical effect

Stress concentration and microscopic defects inside a component can cause the failure of equipment and mechanical structures, and traditional non-destructive testing (NDT) methods are not able to completely solve this problem. The magnetomechanical effect organically combines the magnetic field and stress, making it an important approach for detecting stress concentration and microscopic defects in a component. The magnetomechanical model proposed by Jiles can explain the non-linear relationship between stress and magnetic induction, but it fails to explain the asymmetry in the change of magnetisation under the conditions of tensile and compressive stress. A general nonlinear magnetomechanical model proposed by Shi can more precisely explain the magnetomechanical effect, but with complex equations. Using a more precise equation for magnetostrictive strain and taking into account the effects of the demagnetising field and a linear stress-dependent term on the magnetomechanical effect, this paper proposes a concise and accurate model based on the merits of the two methods. This theoretical model can demonstrate the magnetomechanical effect more accurately than Jiles' model and is easier to solve and apply than Shi's model. This model offers the possibility of quantitative measurement of stress concentration by magnetic measurements.

Detection of Magnetomechanical Effect in Structural Steel Using GMR 2nd Order Gradiometer Based Sensors

The magneto-mechanical behaviour of structural steel specimens stressed up to the plastic deformation stage was investigated using a 2nd order gradiometer based on Giant Magneto Resistive (GMR) sensors. The correlation between the gradient of the magnetization and the dislocation density before the crack initiation inside the test material was reported. The capability of the GMR scanning sensor to detect the residual magnetization due to the tensile stress with a non-invasive technique was demonstrated.