Research on Composite ACFM and EMAT Nondestructive Testing Technology

Alternating current field measurement（ACFM） is a kind of nondestructive testing（NDT） technology with high sensitivity for surface defects, but it is difficult to detect subsurface defects due to skin effect. In order to realize the simultaneous detection of surface and subsurface defects, a hybrid NDT method of ACFM and electromagnetic acoustic transducer（EMAT） is proposed. The composite simulation model of ACFM and EMAT is established to analyze the quantitative relationship between magnetic field distortion signal, ultrasonic echo signal and defect size. The composite experimental system of ACFM and EMAT is built to test the artificial defects of aluminum plate. The simulation and experimental results show that the composite NDT technology of ACFM and EMAT can detect and classify the surface and subsurface defects of aluminum plates with high sensitivity. Additionally, the extracted characteristic signals Bx, Bz and echo signal have quantitative corresponding relationship with the defect size, the system has the ability to quantify the defects.