Terahertz Spectroscopic Characterization and Thickness Evaluation of Internal Delamination Defects in GFRP Composites

 Nsengiyumva, Walter, Shuncong Zhong, Manting Luo, and Bing Wang. "Terahertz Spectroscopic Characterization and Thickness Evaluation of Internal Delamination Defects in GFRP Composites." Chinese Journal of Mechanical Engineering 36, no. 1 (2023): 1-21.

Abstract

The use of terahertz time-domain spectroscopy (THz-TDS) for the nondestructive testing and evaluation (NDT&E) of materials and structural systems has attracted significant attention over the past two decades due to its superior spatial resolution and capabilities of detecting and characterizing defects and structural damage in non-conducting materials. In this study, the THz-TDS system is used to detect, localize and evaluate hidden multi-delamination defects (i.e., a three-level multi-delamination system) in multilayered GFRP composite laminates. To obtain accurate results, a wavelet shrinkage de-noising algorithm is used to remove the noise from the measured time-of-flight (TOF) signals. The thickness and location of each delamination defect in the z-direction (i.e., through-the-thickness direction) are calculated from the de-noised TOF signals considering the interaction between the pulsed THz waves and the different interfaces in the GFRP composite laminates. A comparison between the actual and the measured thickness values of the delamination defects before and after the wavelet shrinkage denoising process indicates that the latter provides better results with less than 3.712% relative error, while the relative error of the non-de-noised signals reaches 16.388%. Also, the power and absorbance levels of the THz waves at every interface with different refractive indices in the GFRP composite laminates are evaluated based on analytical and experimental approaches. The present study provides an adequate theoretical analysis that could help NDT&E specialists to estimate the maximum thickness of GFRP composite materials and/or structures with different interfaces that can be evaluated by the THz-TDS. Also, the accuracy of the obtained results highlights the capabilities of the THz-TDS for the NDT&E of multilayered GFRP composite laminates.

THz-TDS and Imaging System

The THz-TDS (TeraView TPS 4000) is used to detect and characterize hidden delamination defects in GFRP composite samples. To measure the optical parameters and characterize the delamination defects of the GFRP samples, the system is configured to perform tests in reflection and transmission modes. These two modes are not simultaneously configured but rather one is configured after the other depending on which mode is needed at the different stages of the study. This THz-TDS system features a scanning range of up to 1200 ps and its resolution can reach 0.1 ps at a rapid scanning frequency of 50 Hz.

Full paper can be seen at

 https://cjme.springeropen.com/articles/10.1186/s10033-022-00829-7