Stress-Dependent Magnetic Charge Model for Micro-Defects of Steel Wire Based on the Magnetic Memory Method

Magnetic memory method (MMM) is widely used for diagnosing ferromagnetic material on early stage as a nondestructive technology, but no clear description exists for the influence of stress on MMM signals at the micro-defect position on the surface of steel wire yet. Hence, based on traditional magnetic charge model, a stress-dependent magnetic charge model that combined the Jiles magneto-mechanical constitutive relation was intended to calculate the MMM signals around micro-defect on surface of steel wire. Meanwhile, the Hp(y) signals on surface of steel wire with different defects were measured during the whole tension test. By comparing the results of theoretical model and experiment, some conclusions can be drawn. First, the position of vale-peak on Hp(y) signals curves can be used to determine the micro-defect on steel wire. Secondly, the vale-peak amplitude (Sv-p) and vale-peak width (Lv-p) of Hp(y) signals curves, as two characteristic parameters of magnetic signals, not only can reflect the variations of defect depth and defect width, but also judge the load subjected by specimen. Sv-p has an approximate growth with the increase of defect depth as a whole, but decreases with the increase of loads. And the effect of load on Sv-p increases with defect depth. Lv-p has an approximate growth with the increase of defect width as a whole, but does not change with the increase of loads. Finally, the stress-dependent magnetic charge model can be better to reflect the changing laws of Hp(y) signals around defect and can be used for the numerical analysis of MMM signals on surface of steel wire.