Defect characterisation using pulsed eddy current thermography under transmission mode and NDT applications

Pulsed eddy current (PEC) thermography has been successfully applied to detect cracks in metal alloy and carbon fibre reinforced plastic (CFRP) in previous works. In these applications, an inductor and infrared camera are on the same side of components, named reflection mode. In this work, the transmission mode, where the inductor and infrared camera are on opposite sides of component is investigated for defect characterisation through the analytical analysis and experimental studies. The studies show that the detection mechanisms for impact and delamination in CFRP are totally different. Carbon structure can be observed on the early stage of heating phase and impact leading to decreasing conductivity can be also detected in heating phase. However, delamination can be characterised using late stage of cooling phase. Combing the detection mechanisms, principal components analysis and independent components analysis, image reconstruction method is used to improve the sensitivity.