Nondestructive evaluation of hidden multi-delamination in a glass-fiber-reinforced plastic composite using terahertz spectroscopy

In this study, a terahertz time-domain spectroscopy (THz-TDS) imaging system was devised to detect hidden multi-delamination in a glass-fiber-reinforced plastic (GFRP) composite laminates. Shapes, thicknesses and locations in the z-direction of each delamination among the overlapped multi-delamination were analyzed considering the interaction between the pulsed THz wave and the GFRP composite. THz wave power and phase were discussed by the analytical calculations and the experimental results with the evaluation of hidden multi-delamination. Then, the THz image results were compared with those of the ultrasound wave inspection method. Finally, hidden multi-delamination in the GFRP composite laminate was successfully detected and imaged using the THz-TDS imaging system, showing that this system can be widely utilized to evaluate the reliability of composite structures as a nondestructive evaluation method.