Defects identification in fiber reinforced plastics using long pulse thermography

Infrared Thermography is a non-contact technique for non-destructive evaluations that has been widely used for inspection of structural materials. The prediction of defect depth is the most obvious advantage compared with other non-destructive techniques. Several thermal signal processing technologies and quantitative measurement methods have been reported in literature. However, most of those methods are only applicable to Pulse Infrared Thermography and Lock-In Thermography. In this paper, Phase Fourier Analysis (PFA) was used to determine the defect location and Logarithm Second Derivative Time (LSDT) was used to calculate the defect depth with Long Pulse Thermography (LPT). The experimental results were compared with numerical simulations of a Glass Fiber Reinforced Plastics (GFRP) panel with predesigned defects. It is found that the thermal signal processing can enhance the defect contrast and the specific characterize time in LSDT has a linear relationship with the square of depth.