FEM-assisted shearography with spatially modulated heating for non-destructive testing of thick composites with deep defects

This study aims at improving shearography non-destructive testing (NDT) of deep defects in thick composites with thermal loading. Instead of conventional global heating (GH), the core idea is to apply novel spatially modulated heating (SMH) for shearography NDT. In this paper, the finite element method (FEM) has been used to advance shearography towards a quantitative inspection tool for thick composites. Both GH and SMH have been performed experimentally and modelled in Abaqus to evaluate the corresponding efficacies in the detection of deep defects. SMH was achieved by using a halogen lamp with a Fresnel lens. The heat flux distribution on the specimen surface was taken into consideration for defect detection, a factor which is rarely reported in shearography inspection. Besides, the influence of different reference states on shearography NDT of deep defects in thick composites has also been studied by looking into the defect-induced phase maps from shearography. The results indicate that the proposed SMH can improve deep defect detection with shearography in thick composites by 2 to 3 times that of GH. It should be addressed that a similar and defect-free reference sample is currently necessary to compare with a defective one.