Alternating Current Electric Flux Leakage Testing for Defect Detection and Characterization

This paper analyzes the inspection characteristics of the alternating current electric flux leakage (AC-EFL) testing method. Three specimens with different conductivity are prepared, and a series of experiments is carried out to explore the advantages and disadvantages of the AC-EFL method. For metal materials that carry an alternating current (AC), defect detection can be realized using both AC-EFL and electric current perturbation (ECP). However, the signal noise ratio (SNR) from using the AC-EFL method is lower than that obtained using the ECP method according to the experimental results obtained from an aluminum plate. For both the Ni–Zn ferrite specimens with very low conductivity and the carbon fiber reinforced polymer (CFRP) specimens with low anisotropic conductivity, the ECP method failed to detect defects because of the weak disturbed magnetic field that was caused by the defects, whereas the AC-EFL method was able to realize the defect detection. These proof-of-concept experimental results indicate that compared to magnetic field testing method, the AC-EFL is more suitable for inspecting low-conductivity materials.