1. Material thermal property parameter detection

Compared with other temperature measurement technologies, infrared thermal imagers can quickly and accurately measure the temperature of a large area, and the temperature measurement range is wide. Therefore, when it is necessary to accurately measure the temperature boundary conditions in a large range, infrared thermal imagers have incomparable advantages over other temperature measuring instruments.

Researchers from Harbin Institute of Technology studied the change of the heat transfer coefficient of the material in the welding temperature field with the increase of temperature, proved the feasibility of the inversion algorithm of the thermal conductivity coefficient in the welding process, combined infrared thermal imaging with thermocouples to measure the welding temperature field of the LY2 aluminum alloy fixed TIG spot welding process, and obtained the curves of the thermal conductivity coefficient changing with temperature in the heating and cooling processes by calculation.

The research on the inverse problem of heat conduction has a wide range of engineering application prospects. In recent years, many research results have been achieved in the identification of thermal property parameters, boundary shape, boundary conditions, heat source and other aspects. When conducting research on inverse heat transfer problems, the temperature map of the research object is measured by infrared thermal imaging technology, which can quickly and easily solve the problem of measuring the temperature boundary. This method has been widely used in the research of inverse problems of heat conduction.

2. Detection of internal structural damage and material strength

Currently, the structural damage research using infrared thermal imaging technology includes concrete internal damage detection, concrete fire damage research, weld fatigue crack detection, carbon fiber reinforced concrete internal crack detection, etc. Due to the change in the thermal conductivity of the damaged part, the temperature of the damaged position in the infrared thermal image is abnormal. Compared with conventional flaw detection methods such as X-rays and ultrasound, infrared thermal imaging technology has the advantages of not requiring physical contact or coupling agents, simple and convenient operation, and no radioactive hazards.

Researchers at Tongji University used infrared thermal imaging technology to conduct experimental research on concrete fire damage, and obtained the curve of the average temperature rise of infrared thermal images of fire-damaged concrete over time, and the regression equation between the average temperature rise of infrared thermal images of concrete and its fire temperature and strength loss. The application of infrared thermal imaging technology to fire concrete detection is an international first, breaking through the traditional detection mode and creating a new way to evaluate concrete fire damage. However, there are still many problems to be solved when this method is applied to actual engineering detection, such as the influence of concrete strength grade, carbonization depth, gradation, fire type, etc. on the reliability of detection results, as well as heating measures during detection.

In recent years, ultrasonic infrared technology developed on the basis of photothermal infrared technology has played the advantages of infrared technology and ultrasonic technology. This method uses ultrasonic pulses as the excitation source. When the ultrasonic pulse propagates in the specimen and encounters defects such as cracks, the defects cause additional ultrasonic attenuation and local temperature rise, so that these crack defects can be detected using infrared thermal imaging technology. Researchers at Nanjing University combined infrared thermal imagers with ultrasonic transmitters, used ultrasonic transmitters to input heat into aluminum alloy specimens with fatigue cracks, took infrared thermal images, and compared them with computer simulation calculation results. The test showed that ultrasonic infrared thermal imaging technology is very sensitive to crack defects, uneven structures and residual stress.

3. Application of detection in building energy conservation

In terms of building energy conservation detection, Sweden began to use infrared thermal imaging technology to detect building energy conservation and insulation as early as 1966. Researchers in many countries such as the United States and Germany have also conducted research in this area. In my country, with the increasing requirements for building energy conservation, building energy conservation detection is imperative. At present, the detection of heat transfer coefficient of building envelope structure in my country mostly adopts on-site measurement of building thermal engineering method, and infrared thermal imaging technology is only used as an auxiliary means to comprehensively evaluate the thermal insulation performance of buildings by detecting heat transfer defects of envelope structure. At present, the research of infrared thermal imaging technology in the field of energy-saving detection in my country is still in its infancy, and there is no definite indicator to quantitatively evaluate the energy saving of infrared thermal images of buildings. Due to the diversity of building facade forms and finishing materials, the compilation of special image analysis and processing software and the establishment of a basic database of emissivity of internal and external wall finishing materials have become an important part of this research.

4. Application in building leakage detection

The leakage of buildings includes leakage caused by water supply pipes and rainwater leakage caused by cracks in roofs or exterior walls. Since the moisture content of the leakage part is different from that of the normal part, the temperature of the two parts is different during the heat conduction process. Therefore, the infrared thermal imager can be used to take infrared thermal images of the wall surface with abnormal humidity, and the location of the leakage source can be found by comparing and analyzing with the direct observation results on site.

Conclusion

The application prospect of infrared thermal imaging technology in non-destructive testing is very broad, and the corresponding research work has also achieved preliminary research results, and gradually moved from qualitative research to quantitative research. However, in general, it is still in its infancy, and there are not many research results that can be applied to actual projects. Most of them are qualitative conclusions and lack corresponding operating specifications. Therefore, quantitative research should be strengthened to improve the processing ability of infrared thermal images.