Heat Induced Damage Detection by Terahertz (THz) Radiation

Abstract

Terahertz (THz) and sub-terahertz imaging and spectroscopy are becoming increasingly popular nondestructive evaluation techniques for damage detection and characterization of materials. THz radiation is being used for inspecting ceramic foam tiles used in TPS (Thermal Protection System), thick polymer composites and polymer tiles that are not good conductors of ultrasonic waves. Capability of THz electromagnetic waves in detecting heat induced damage in porous materials is investigated in this paper. Porous pumice stone blocks are subjected to long time heat exposures to produce heat induced damage in the block. The dielectric properties extracted from THz TDS (Time Domain Spectroscopy) measurements are compared for different levels of heat exposure. Experimental results show noticeable and consistent change in dielectric properties with increasing levels of heat exposure, well before its melting point.

Nondestructive Testing of Polymers and Polymer–Matrix Composites

“…Thus, terahertz testing can be applied in transmission or reflection as well as in scanning or imaging mode (201)(202)(203)(204). It has been applied to aircraft components (205), impact damage characterization (206), damage detection (207), fiber orientation (208), thickness measurement by terahertz pulsed imaging (209), and surface profiling by phase sensitive terahertz holography (210)…”

Applications of Terahertz Spectroscopy in the Field of Construction and Building Materials

“…Based on this knowledge, THz technology has been used as a nondestructive tool for inspection of voids and delaminations within the lightweight polyurethane sprayed-on foam insulation (25,27,31). THz beams have also been used for detection of the heat-induced damage in porous polymer pumice stone (44) due to the changes in dielectric properties, which decrease when the material is exposed to high temperatures. In addition to defects, properties such as material density (13,22) and IR radiation absorption on nanoadditives (22,30) can be probed by THz waves.…”

Terahertz detection and identification of defects in layered polymer composites and composite coatings

“…That allowed them to detect mentioned defects. Heatinduced damage evaluation of polymer foam tiles was also considered in [10] by Rahani et al The same authors in [12] used the finite element numerical analysis of dispersive materials to improve the detection of mechanical damages in polymer materials. Numerical study was also presented in [11] to detect voids in sprayed on foam insulation material.…”