Shearography with thermal loading for defect detection of small defects in CFRP composites
Topic(s) : Experimental techniques
Co-authors :
Nan TAO (NETHERLANDS), Andrei ANISIMOV (NETHERLANDS), Roger GROVES (NETHERLANDS)Abstract :
Composite materials, e.g., carbon fibre-reinforced polymers (CFRPs), have been increasingly adopted in safety-critical structures in the aerospace, marine and wind energy sectors. Numerous types of defects and damage including delaminations, fibre breakage and impact damage can occur in composite structures. Non-destructive testing (NDT) and defect detection of these composites are therefore critical to ensure structural integrity and safety. A key demand for NDT is to detect the presence of defects and early-stage damage to avoid future failure. Hence, it is important to advance the capabilities of NDT of composite materials towards small defects, e.g., in mm and sub-mm size. Among different NDT techniques, digital shearography is a non-contact and full-field optical method that has received considerable interest in various industries, particularly, for the inspection of aerospace and marine composite structures. Shearography NDT methods can offer effective solutions for the detection of both manufacturing and in-service defects in composites. However, its efficacy in detecting small defects of mm and sub-mm scale is not fully characterised yet.
The objective of this study is to improve the detection of small defects in composite materials using shearography with thermal loadings. One major issue is that fibre-related deformations, which arise from the difference in thermal conductivity and thermal expansion coefficiency between fibre and resin, can affect significantly the efficacy of defect detection, especially when detecting small defects and deep defects (Figs. 1(a, c)). Although the selection of a certain shearing direction may help reduce fibre-induced phase noise (e.g., for UD composites), however, it is not suitable for composites with layups such as [0/90] and [0/45/90/-45], which are more commonly used in different industrial sectors. In this study, a new approach of a corresponding shearography pair has been developed through the analysis of fibre-induced deformation, where optimal shearography pairs of reference and signal speckle interferograms are determined for reliable defect detection (Figs. 1(b, d)). A FEM model was established in Abaqus to assist shearography inspection. This FEM assistance is capable of evaluating different thermal loading schemes for defect detection. Besides, the efficacy of various well-known signal processing methods including Fourier transform and principle component analysis have also been investigated and compared with the proposed shearography approach. The results show that the new approach of the corresponding shearography pair can minimise the effect of fibre-induced deformation in composite materials (Figs. 1(a, b)). This approach enables the detection of mm and sub-mm defects in CFRP. These detection results are one of the smallest defects detected with shearography and reported in literature. This research was performed as part of the Horizon Europe COMP-ECO project (grant agreement 101079250)
The objective of this study is to improve the detection of small defects in composite materials using shearography with thermal loadings. One major issue is that fibre-related deformations, which arise from the difference in thermal conductivity and thermal expansion coefficiency between fibre and resin, can affect significantly the efficacy of defect detection, especially when detecting small defects and deep defects (Figs. 1(a, c)). Although the selection of a certain shearing direction may help reduce fibre-induced phase noise (e.g., for UD composites), however, it is not suitable for composites with layups such as [0/90] and [0/45/90/-45], which are more commonly used in different industrial sectors. In this study, a new approach of a corresponding shearography pair has been developed through the analysis of fibre-induced deformation, where optimal shearography pairs of reference and signal speckle interferograms are determined for reliable defect detection (Figs. 1(b, d)). A FEM model was established in Abaqus to assist shearography inspection. This FEM assistance is capable of evaluating different thermal loading schemes for defect detection. Besides, the efficacy of various well-known signal processing methods including Fourier transform and principle component analysis have also been investigated and compared with the proposed shearography approach. The results show that the new approach of the corresponding shearography pair can minimise the effect of fibre-induced deformation in composite materials (Figs. 1(a, b)). This approach enables the detection of mm and sub-mm defects in CFRP. These detection results are one of the smallest defects detected with shearography and reported in literature. This research was performed as part of the Horizon Europe COMP-ECO project (grant agreement 101079250)