Development and optimization of THz NDT on aeronautics composite multilayered structures

Abstract

Modern aircraft structures have to comply with severe requirements: they have to be light and safe. These requirements lead to an increased use of composite materials in the aircraft industry. To support the high standards of composite part construction and repair, new non-destructive techniques are necessary to improve the efficacy of composite part inspection. DOTNAC (Development and Optimization of THz Non-Destructive Techniques on Aeronautics Composite multi-layered structures) proposes to develop a NDT using THz waves. The THz spectrum covers a frequency spectrum from the far-IR region to the mid-IR. Over the past several years, there has been a significant interest in the potential of THz detection for imaging: (1) Terahertz radiation is transmitted through most non-metallic and non-polarized media, (2) THz radiation poses no health risk to the system’s operator. Nowadays very little research is being performed using THz radiation for air transport NDT, and little is known on how typical composite material defects such as delamination, porosities and inclusions can be detected by THz waves. The overall approach of the DOTNAC project starts with the knowledge acquisition of the end user NDT requirements and the assessment of aeronautic relevant composite materials and occurring defects. Starting with the THz hardware research, a first process will concentrate on the development of a pulsed THz system using fibre coupling and a second one on a multi-frequency FMCW (Frequency Modulated Continuous Wave) THz system using electrical cable coupling. These two complementary THz systems will be completed with a 3D scanner and appropriate signal and image processing. In a final step the integrated imaging systems will be used to evaluate the potential of a THz NDT, first on calibrated, then on so-called blind samples. By comparing these measurements with the results from UT, RT, IRT, and acoustic tapping on the same samples, the THz-NDT tool can be validated and valorised with respect to the established methods.