In this work, we developed novel ultrasonic guided wave testing technique for carbon-fiber reinforced plastic (CFRP) based on magnetostriction and HTS-SQUID gradiometer. As magnetostrictive sensor, nickel and Fe-Co-based magnetic alloy thin plates were used. In case of using the nickel thin plates, conventional pre-magnetization and magnetostrictive method to transceive T(0, 1) mode ultrasonic guided waves was utilized. In case of using the Fe-Co-based alloy thin plates, new magnetization method using permanent magnets was tested to transceive the T(0, 1) mode guided waves. The T(0, 1) mode guided waves were generated on the CFRP plate, which attenuation coefficient is much greater than those of metals, thus the guided waves decay quickly, using the two different plates and the propagated waves were converted to magnetic signals on the nickel or the alloy plates. The magnetic signals were measured by the HTS-SQUID gradiometer, which was set above the plates. In the both cases, multipoint measurements using the gradiometer were carried out. In the both measurement results, a reflection wave at a slit defect on the CFRP plates, which was located 150 mm away from the receiver, were clearly detected on the measured magnetic signal images due to the propagated T(0, 1) mode guided waves. Signal intensity of the waves obtained using the alloy plates were about 1.5-2 times stronger than those using the nickel plates. Signal waveform of the reflection wave at the defect was confirmed using an ultrasonic wave simulator, and the waveform in the measurements was roughly agreed with that in the analyzed result using the simulator.

Keywords: HTS-SQUID gradiometer, Fe-Co-based magnetic alloy, T(0, 1) mode ultrasonic guided wave, carbon-fiber reinforced plastic