Research On Impact Mechanism Of Material Surface Emissivity And The Variation Reducing Methods In Thermography Testing

The advance of modern science and technology improves the quality and safety requirements about mechanical equipment and major structure becoming higher and higher. As a new non-destructive testing technology, infrared thermography has played a more and more important role in device security and product quality. However, the surface emissivity of the material is significant in the infrared thermography testing.The non-uniform of the surface emissivity will lead to the false phenomenon of the“high and low temperature” in thermal image, which would impact the results of thermal imaging detection seriously. By now many scholars have payed attention to reducing the influence of the surface emissivity, but the essential reason of non-uniform surface emissivity impacts thermal imaging is often overlooked. Therefore, in this paper,the mechanism of surface emissivity affecting thermal imaging was studies, and on the base of the impact mechanism, the methods of the effective reducing non-uniform emissivity were discussed.Based on the thermal imaging nondestructive testing, in this paper the affecting mechanism of the thermal emissivity was studied by the theoretical analysis, the numerical simulation and the experimental validation. Then, the methods of the reducing non-uniform emissivity were discussed in three aspects. In this paper, the abnormal targeting method based on the area information extraction was detailed, and its feasibility was verified by the experiments. The experiments showed that the method can not only effectively reduce non-uniform surface emissivity, but also reach the goal of the enhancing flaw feature. The main contents were followed by these:(1) Study the basic theory of thermal imaging nondestructive testing system, the conception of surface emissivity and it’s affecting form to thermal imaging. According to the theoretical basis of infrared thermography, the testing flaw detection principle of the infrared thermal imaging nondestructive testing technology was analyzed. In terms of the theoretical and experimental results, the influence forms on the thermal imaging from the surface emissivity were studied.(2) Establish finite difference model of heat transfer and discuss the mechanism of surface emissivity impacting thermal imaging. The heat transfer model was established by using the finite difference method and the transfer heat theory. By employing theestablished heat transfer model, numerical simulation and experimental verification, it demonstrates that the influence of the surface emissivity on surface temperature can be ignored. Then the essence of the surface emissivity affecting the thermal imaging is obtained. In other words, it concludes that the surface emissivity affects the thermal detecting by the form of the amplitude and it doesn’t change the fluctuation rule of signal.(3) Explore the reducing non-uniform surface emissivity method in thermal imaging detection. Based on the relationship between the surface emissivity and surface temperature, methods for reducing non-uniform surface emissivity in three terms including the separation of the surface emissivity from the temperature, the curve shape similarity and the area information extraction were discussed in this paper. Because other methods has many shortcomings, such as low efficiency and losing amplitude message of original signal, this research focuses on the abnormal targeting method,which is a new thought for reducing the surface emissivity affection in the field of the area information extraction. The experiment demonstrates that the abnormal targeting method can not only achieve the effect of reducing non-uniform surface emissivity, but also reach the goal of enhancing flaw feature at the same time.