Advanced T-ray nondestructive evaluation of defects in FRP solid composites

Nondestructive testing technique using T-ray (terahertz ray) receives attention these days as a new field of test engineering. In this study, T-ray time-domain spectroscopy was used for inspecting and evaluating physical property and defect characteristics in FRP composite material. Also, general refraction and transmission mode of this T-ray spectrography was used for finding refraction coefficient (n) and for obtaining T-ray image. First, in order to obtain the terahertz ray refraction index, refractive and transmission mode technique was induced, with which refraction index of GFRP composites, balsa and epoxy of wind turbine blade could be obtained. In GFRP and CFRP composites, T-ray propagation faces hindrance by carbon fiber. Accordingly, the authors have analyzed directional dependence between E-field of T-ray and the carbon fiber. Also, evaluating method of wind turbine blade composites having two (2) saw-blade delaminations integrally inserted was presented in this study. It was found that the time of flight of T-ray using T-ray transmission mode technique coincides well with that using refractive index in the wind turbine blade.