Nondestructive evaluation of forced delamination in glass fiber-reinforced composites by terahertz and ultrasonic waves

Abstract

a b s t r a c tGlass fiber-reinforced composite laminates in polyetherimide resin have been studied via terahertz imaging and ultrasonic C-scans. The forced delamination is created by inserting Teflon film between various layers inside the samples prior to consolidating the laminates. Using reflective pulsed terahertz imaging, we find high-resolution, low-artifact terahertz C-scan and B-scan images locating and sizing the delamination in three dimensions. Furthermore, terahertz imaging enables us to determine the thicknesses of the delamination and of the layers constituting the laminate. Ultrasonic C-scan images are also successfully obtained; however, in our samples with small thickness-to-wavelength ratio, detailed ultrasonic B-scan images providing quantitative information in depth cannot be obtained by 5 MHz or 10 MHz focused transducers. Comparative analysis between terahertz imaging and ultrasonic C-scans with regard to spatial resolution is carried out demonstrating that terahertz imaging provides higher spatial resolution for imaging, and can be regarded as an alternative or complementary modality to ultrasonic C-scans for this class of glass fiber-reinforced composites.

A Survey of Scrutinizing Delaminated Composites via Various Categories of Sensing Apparatus

“…(d) Electromagnetic testing: In NDE electromagnetic testing, composite laminates undergo a process in which the internal anomalies are inspected in terms of electromagnetic responses utilizing electric currents or magnetic fields induced. As shown in Figure 6, radiography, computed tomography, terahertz (THz) spectroscopy, and the electrical resistance change-based method may be included in electromagnetic testing [107][108][109][110][111][112][113][114][115][116][117][118][119][120]. In addition, thermography, as explained above, is a part of electromagnetic testing.…”

“…In the immersion testing process, a liquid couplant is employed to establish direct contact between a transducer and the composite specimen. Most of the research effort in the technical literature searched regarding the ultrasonic C-scan testing has been focused on either verification of other NDE techniques with ultrasonic C-scan as a reference standard [35,47,89,91,109,112,126] or yielding supplementary information [26,38,105,117,127].…”

Application of Ultrasonic Coda Wave Interferometry for Micro-cracks Monitoring in Woven Fabric Composites

“…Thanks to their advantages of light weight, design flexibility, and high specific stiffness and strength, composite materials have been widely used for several years as structural materials in a number of industrial sectors ranging from aviation, automotive [1,2], civil construction, and the sport industry [3][4][5]. Nondestructive testing and inspection of composite structures, both for manufacturing quality assurance and for in-service damage detection, has, over the last years, prompted the development of a number of techniques including water-and air-coupled ultrasound, bond testing, thermography, shearography and terahertz imaging [6]. A review of the mentioned methods is given by Gholizadeh [7].…”

Terahertz Pulse Detection Techniques and Imaging Applications

“…(iii) TPI and THz-TDS are also explored to identify features such as coating, pores and cracks in polymer materials [92]. Another study employs TPI to study glass iber-reinforced composite laminates in polyetherimide resin [93]. (iv) Relective pulsed THz tomography can be a tool to monitor oil pollution.…”