Accurate depth determination of defects in composite materials using pulsed thermography

•Thermal conduction considering lateral diffusion and sample thickness using pulse thermography is investigated.•Prediction of defect depth is influenced by the defect size and sample thickness in particular situations.•An accurate depth determination method based on the peak slope time is proposed.•The experimental results validate the accuracy of the proposed method in defect depth estimation, especially for small, deep defects. The determination of defect depth is one of the important advantages of pulsed thermography. The existing methods for depth estimation in pulsed thermography are generally established based on the one-dimension heat conduction along the thickness of the sample. However, most of the methods neglect the effects of defect size and sample thickness, which induces additional systematic errors in depth estimation. In this study, simulations are conducted to demonstrate that the accuracy of depth determination of defects is greatly influenced by the defect size and sample thickness in some simulations. By establishing the relationship between the characteristic time and these factors, an accurate depth determination method based on the peak slope time is proposed. The proposed method has been applied to characterize the defect depths of a composite panel with flat-bottomed holes. The experimental results show that the use of the proposed method is able to identify the depths of defects with high accuracy.