Non-contact detection of impact damage in CFRP composites using millimeter-wave reflection and considering carbon fiber direction

Carbon fiber reinforced polymers (CFRPs) are widely used for various structural materials because of their high stiffness and strength. Detecting damages in CFRP composites is important for structural safety. This study was conducted to detect impact damage in CFRP specimens using the millimeter-wave of 65–67 GHz. The impact damage was artificially produced by impact energies of 3.63 J, 8.89 J and 13.21 J, respectively. Since the CFRP composites are electrically anisotropic materials, reflection coefficients are affected by the angle between the electrical field vector direction of the electromagnetic wave and the carbon fiber direction in the CFRP surface. When this angle was 0°, reflection coefficients on the surface with and without damage were easily distinguished. Accordingly, imaging the CFRP specimens including the impact damage was conducted using changes of the reflection coefficient. In addition, in order to obtain better image, the edge detection image processing technique was applied to the original image, and a more natural image was obtained. The magnitude of impact energy producing damage could also be distinguished through the image.