Internal Defect Inspection of Composite Material Using Non-Contact UT

Abstract

The NAUT technique allows non-contact ultrasonic testing in air. If the NAUT technique can be applied, not only ultrasonic testing in air with no couplant would be possible, but also the stable transmission and reception of ultrasonic waves, which would thus enable ultrasonic testing of hot or cold materials, or rough surfaces of specimens that could not be tested with conventional-contact ultrasonic testing techniques. By trying NAUT for CFRP (carbon fiber-reinforced plastic) specimens, the applicability of NAUT in these areas was observed, and the results from the waveforms of parts of the specimens were analyzed. To verify the usefulness of NAUT, first, artificially defective specimens were tested to investigate the defect detection ability of NAUT; and second, a test was conducted to select the test conditions, the ultrasonic propagation characteristics, and the mode conversion by the material thickness. Both the spot welding and CFRP specimens showed good applicability of NAUT. For the spot welding specimen, the ultrasonic transmittance was highest at the spot-welded part, regardless of the thickness and location of the specimen. For the CFRP specimen, the waveforms of a defective part and a defect-free part were compared, and the existence of delamination was discovered through the increase and decrease in the amplitude. These findings confirmed the practicality (usefulness) of NAUT.