Abstract
The characterization of micro cracks on metal surface plays an important role in the process of manufacturing and using, which has attracted a lot of attention. This is mainly due to the fact that the size of defects is smaller and the depth of defects is difficult to predict compared with metal materials with larger plane, which is still challenging. In order to solve this problem, this paper proposes a characterization method of surface defects based on reflective laser thermography, and designs a laser heating nondestructive testing system based on reflection. The system includes a semiconductor laser to heat the surface of metal cracks, and an infrared imager to record changes in the temperature field of the metal surface. In the process of data analysis, an Otsu adaptive threshold segmentation method is selected to quantify the defect size, which can control the quantification accuracy of defect size within 25%. A derivative analysis method is proposed to quantify the depth of defects, which can control the depth quantification accuracy of tiny defects within 7%.
Highlights
The blades of heavy-duty gas turbines, aero engines, etc. can work under high temperature, high pressure, and high speed environments [1], [2]
Wang Zijun et al compared eddy current pulse thermography technology and long pulse thermography technology, and the results showed that long pulse thermography technology has better advantages in detecting low thermal conductivity materials [20]
The results show that the defect size detection accuracy of this method at different defect depths can be controlled within 25%
Summary
The blades of heavy-duty gas turbines, aero engines, etc. can work under high temperature, high pressure, and high speed environments [1], [2]. When a tiny defect exists, the depth camera cannot collect the details of the tiny defect, so the method in this article has limitations in the characterization of the tiny defect [26] It can be seen from the above research that active infrared thermography technology has made considerable progress. A reflection-based laser thermography system is built and a reflection-based laser thermography method is used to perform quantitative characterization of micro cracks on metal surfaces to evaluate surface micro cracks In this system, the laser is used to heat the vicinity of the defect, and the infrared thermal imager is used to collect the surface temperature field of the material.
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