A Novel Fatigue Crack Angle Quantitative Monitoring Method Based on Rotating Alternating Current Field Measurement

Under complicated fatigue loading conditions, cracks initiate nd grow in the arbitrary direction from corrosion pits in the aerospace equipment. The monitoring of crack propagation angle is very important for the safety assessment of the aerospace equipment, which is still a challenge by the conventional structural health monitoring (SHM) method. In this paper, a novel crack angle quantitative monitoring method is presented based on the rotating alternating current field measurement (RACFM). A theoretical model of the crack angle measuring method is established to analyze the perturbation principle of the induced electromagnetic field. The relationships between the angle, length and depth of the crack and the Bz signal are analyzed. The probe and testing system are established, and experiments are carried out. The results show that the phase of the Bz signal has a linear relationship with the crack angle for the same crack, and the amplitude of the Bz signal can correct the crack angle for the different cracks. The angle of fatigue cracks can be quantitatively measured by the Bz phase difference method based on the RACFM.