The Study of Relationship Between Crack Direction and Self-transmitting Magnetic Signal Under Axial Load

The crack direction is one of the key factors affecting the crack growth rate, and then determines the crack growth life of the structure. Therefore, it is very important to determine the crack direction when evaluating the structure safety. Aiming at the problem that it is difficult to determine the crack direction accurately by Magnetic Nondestructive Testing Technology, this paper first analyzes the basic law between the crack direction and the magnetization direction based on the crack magnetic charge model. On this basis, the specimens with four groups of cracks of different directions were designed, and four levels of axial tensile load were applied to the specimens for test verification. During the test, the self-emission magnetic signals of cracks were collected and the signal characteristics were analyzed. The theoretical and experimental results show that the vertical component of the self-emission magnetic signal corresponding to the cracks in different directions has typical characteristics of positive and negative peaks. The gradient of positive and negative peaks changed greatly. The axial tensile load can enhance the magnetic field. The peak-to-peak value of each crack increases with the increase of axial tensile load. When the crack direction is perpendicular to the axis of tensile load, the peak-to-peak value is the largest and the speed of peak-to-peak is the fastest. There is a strong correlation between the crack angle and the gradient of the distorted magnetic field signal.