Delamination Detection in Glass-Fibre Reinforced Polymer (GFRP) Using Microwave Time Domain Reflectometry

Glass Fibre Reinforced Polymer (GFRP) is an important material that is used in different engineering applications, such as the rehabilitation of structures. However, delamination can occur between GFRP laminates and the metallic surfaces to which they are applied. The existence of such defects can cause major failures and compromise the integrity of the entire component. Hence, delamination detection is extremely important to maintain the integrity of any component that involves GFRP laminate. The unique layered nature of the GFRP material in terms of dielectric properties renders most Non-Destructive Testing/Evaluation (NDT/E) techniques inadequate to detect its delamination. However, microwave NDT/E can be regarded as an excellent choice for such purpose due to the ability of microwave signals to penetrate GFRP structures and detect the changes in their internal structures.This paper proposes a novel microwave NDT/E technique that uses Fourier analysis to analyze the reflections from a GFRP structure in the time domain. By scanning a back-drilled GFRP sample within the frequency range of 18 to 26.5 GHz, the proposed technique has proved to detect delamination thicknesses down to 1 mm. The technology reported in this paper represents a significant advance in the efforts to solve the currently challenging task of inspecting GFRP laminates for defects.