Self-resonance eddy-current testing method in noncontact detection of carbon fiber reinforced plastics

Eddy-current testing (ECT) is relatively mature and has gradually become one of the main non-destructive testing technologies of carbon fiber reinforced plastics (CFRP). From the perspective of low conductivity of CFRP, high-frequency ECT technology is considered to be more suitable for such materials with less conductivity. However, high-frequency ECT method is more susceptible to various interference factors and has higher background noise, which will cause great inconvenience to practical applications. Concerning this issue, a self-resonance ECT method in noncontact detection of CFRP was proposed in this paper, and the corresponding ECT system that can detect the defects of CFRP at a low-frequency and keep a relatively high signal-to-noise ratio was developed. The system is mainly composed of a resonant eddy-current probe, a special excitation circuit, and an ECT signal pickup module. Three CFRP samples (orthogonal woven laminate, cross-ply laminate, four-directional angle-ply laminate) were scanned by using the self-resonance ETC system developed in this paper. The scanning results show that the detection effect of the self-resonant ECT system at 500 kHz is similar to that of the traditional ECT system at 10 MHz, and 500KHz is enough to provide good detection results for the above CFRP samples. Therefore, the proposed research is a valuable ECT technology, which has played a guiding role in the application of low-frequency ECT method in CFRP.