Use of transmission mode of induction heating assisted eddy current testing at near resonance frequency for detection of delamination in CFRP

Abstract

This paper presents an eddy current-based approach for detection of delamination in carbon fiber-reinforced plastics (CFRPs). It has been difficult for conventional eddy current testing to detect delamination because delamination is parallel to eddy current paths. The authors proposed induction heating assisted eddy current testing (IHAET) for delamination detection. In IHAET, surface of the material under test is heated by induction heating coil to cause temperature difference between intact zone and delamination zone. Delamination can be detected by electrical conductivity measurement of eddy current testing utilizing the temperature dependence of conductivity. In this paper, heating and temperature measurement of materials was carried out in transmission mode to reduce the lift-off effect. In addition, surface temperature of CFRP was measured by eddy current testing probe at near resonance frequency to improve sensitivity of thermo-sensing. Experimental studies prove that sensitivity of thermo-sensing can be improved by using a resonant probe compared to our previous work. We found that measurement of reactance of thermo-sensing coil offers higher sensitivity due to the resonance frequency shift caused by variation of material’s conductivity. Furthermore, 10 mm wide delamination 2 mm away from the surface of 4 mm thick CFRP could be detected by the proposed method.