Variation of Residual Magnetic Field of Defective U75V Steel Subjected to Tensile Stress

Variation of the stress-induced magnetic field of the U75V rail steel under tension was investigated in this research. Various magnetic responses were registered by a magnetometer in the elastic and plastic deformation stages, which can be explained by the microstructural changes in magnetic domains. Two types of defective specimens were also tested to correlate the stress concentration with the magnetic field. It is found that the tangential component of the magnetic field B-x is much more sensitive to local stress concentration than the normal component B-z. The tangential component B-x reaches a peak value at the rupture position, and the peak magnitude is proportional to the concentrated stress caused by the defect. This observation is different from the Q235 steel, whose tangential component B-x and the normal component B-z are equally effective. Such discrepancy might be due to that U75V fails in a more brittle pattern than the Q235 steel. The average value of the B-x along the loading axis can determine the overall stress state of the structure, while the peaks in the B-x curve tell the local stress concentration caused by cracks and dislocation.