Method for detecting and locating cracks in aluminum plates based on balanced field electromagnetic technique

Aluminum plates are susceptible to environmental and fatigue loads producing randomly distributed cracks and thus compromising safety performance. This paper proposes a detection and location method based on the balanced field electromagnetic technique (BFET) for the detection of cracks on the upper and backside surfaces. The self-zero nature of BFET and the principle of high-sensitivity crack detection are analyzed. The signal characteristics and variation laws are clarified theoretically. The results show that the amplitude and phase of the upper surface crack signal both vary linearly with the crack depth. The signal amplitude of the backside crack decays exponentially with depth and the phase lags linearly. The two-dimensional amplitude phase diagram is rotated at a fixed angle with increasing crack depth and can locate the crack. BFET can detect cracks below the skin depth and provides a reference to increase the detection penetration depth for other electromagnetic detection methods.