Laser scanning infrared thermography for metal microcracks inspection based on thermal signal spatial quasi-static reconstruction

Active infrared thermography has been demonstrated to offer a wide range of applications in the domain of non-destructive testing, thanks to its multiple advantages. However, when applied to the detection and identification of minute defects on the surfaces of metals and other highly thermally conductive materials, the performance of conventional active infrared thermography is suboptimal. In this paper, a quasi-static reconstruction method based on spatial domain feature reconstruction is proposed to solve this problem. Combined with miniaturized detection equipment, this method enables reliable detection of cracks as narrow as 2 µm on titanium alloy surfaces, offering a novel approach for detecting microcracks on alloy surfaces. Based on the three-dimensional simulation model, the thermal response characteristics caused by crack defect are analyzed to provide theoretical support for the quasi-static reconstruction method proposed for different scanning methods. To verify the reliability of this method, a TC4 specimen containing cracks of various widths is prepared and a mobile laser scanning infrared thermography system is established, which demonstrates the potential for miniaturization and integration, broadening its applicability in industrial in-situ inspection endoscopic inspection. Comparative experiments demonstrate that an appropriate combination of scanning method and reconstruction method can effectively suppress background signal interference caused by surface reflections, allowing for the reliable detection and identification of cracks with widths down to 2 µm. Analysis indicates that the signal-to-noise ratio(SNR) is positively correlated with crack width, and feature extraction algorithms demonstrate a significant contribution to the improvement of SNR for cracks with a width of 2 µm.