Evaluation of defect depth in CFRP composites by long pulse thermography

Long pulse thermography (LPT) is an emerging non-destructive technique that has been used for rapid, cost-effective and accurate damage assessment of composite materials. This paper proposes three analytical models for the in-depth evaluation of defects in a carbon fibre-reinforced plastic (CFRP) specimen by long pulse thermography. The first two models rely on the estimate of the peak temperature-contrast and the peak temperature-contrast slope from the thermal data recorded by an infrared (IR) camera. Both the analytical and experimental results showed that the arriving time of the peak temperature-contrast depends on both the depth and the diameter of defects, whilst the contrast time slope is mainly proportional to the square of the damage depth. The third model here proposed consists of a two-dimensional (2D) axisymmetric heat conduction model based on virtual heat sources. Compared to previously reported analytical models, the proposed 2D one showed higher accuracy on the depth estimation.