Influence of terahertz waves on the penetration in thick FRP composite materials

Abstract

Fiber reinforced plastics (FRP) are increasingly utilized in engineering structures because of their performance and fabrication advantages. With this increased utilization, a technique to gage quality and further characterize the materials would be beneficial. The nondestructive applications for Terahertz (T-ray) methods have also experienced increased utilization for evaluating engineering materials and will be reported on here in applications for the inspection and characterization of FRP materials used in wind energy components. First, refraction and transmission T-ray modes are used to determine the refractive index (n) of a glass fiber reinforced plastic (GFRP) reference sample, and extended for calculating the refractive indices for a sample of GFRP, balsa and epoxy. Additionally, carbon fiber reinforced plastic (CFRP) samples were evaluated with respect to fiber directions versus T-ray electric field polarization direction to evaluate the level of penetration of T-ray energy due to the fiber orientation dependent conductivity of this composite material. Finally, an evaluation of T-ray data was made to evaluate resonance effects, where the resonance frequency was found to agree with that expected from reflections from individual plies in thick GFRP laminates.

Application of Terahertz Nondestructive Testing Technology in the Detection of Polyethylene Pipe Defects

“…Peters et al analyzed and calculated the THz time-domain spectrum of PE samples and obtained their stratified thickness without knowing the sample refractive index. Im et al studied the THz transmission of thick fiber-wound composites, analyzed the obtained time-domain spectrum in detail, and verified the feasibility of THz-TDS and imaging for nondestructive testing of composite materials. Wietzke et al carried out a number of studies in the field of nonmetallic nondestructive testing and used the THz continuous imaging system to detect internal defects in nonmetallic materials, such as PE.…”