Improved impact damage characterisation in CFRP samples using the fusion of optical lock-in thermography and optical square-pulse shearography images

Image fusion methods with optical lock-in thermography (OLT) and optical square-pulse shearography (OSS) images are proposed to characterise impact damages in carbon fibre reinforced plastic (CFRP) plates. The samples were damaged with low-energy impacts and inspected using OLT, OSS and the reference ultrasound (US) time-of-flight C-scans. A total of 1113 combinations of decomposition, preprocessing, segmentation and fusion tools were proposed and compared with OLT, US and OSS results using the equivalent diameter criterion and the Matthews' correlation coefficient. The results indicated a reduction of 72.21% in the equivalent diameter measurement error and a metric enhancement of 8.05% when using the fusion, showing that one of the developed image fusion methods can successfully perform improved impact damage inspections.