Polarization Characteristic Model Of Infrared Radiation On Metal Surface

Fatigue failure is the main form of mechanical structure and parts failure.In the use of metal components,early fatigue or low-cycle fatigue cracks are prone to occur.Without warning,the sudden brittle fracture may cause casualties.Fatigue failure has no obvious plastic deformation and is difficult to detect and prevent,so the fatigue failure of components will cause huge economic losses and even life-threatening.Infrared thermal imaging technology is an effective way to solve this contradiction,but the influence of surface microstructure on spontaneous emission during fatigue damage is ignored.The surface emissivity of the material is closely related to the surface microstructure,and the infrared thermal imaging test results are pretty sensitive to the surface roughness.Due to the limitations of traditional infrared thermal imaging technology,the measurement of the microstructure of the material surface is based on the overall effect,and it is difficult to make a fine understanding of the local microstructure change.Therefore,this paper introduces optical polarization to study the thermal infrared spontaneous emission of the metal surface from a micro perspective.It mainly studies the construction of the infrared radiation polarization characteristics model of the rough metal surface and the influence of surface roughness and observation geometry on the detection results of metal infrared polarization characteristics.There are the following four aspects:First,Basic theory of polarization thermography.The basic theory of optical wave polarization,the generation of polarized light,the polarization representation method,the calculation of infrared radiation measurement,and the fundamental law of infrared radiation are introduced.Second,Polarization characteristics of the metal surface.By analyzing the reflection characteristics of the fine structure on the metal surface,the scattering of the metal surface is divided into three parts: mirror reflection,diffuse reflection,and volume scattering.Based on the micro-surface element reflection theory,the three-component polarization bidirectional reflection distribution function is constructed to improve the accuracy of the polarization characteristic model of the rough metal surface.The applicability and accuracy of the model for characterizing the reflection information of metal surfaces are verified by simulation and experiment.Third,Polarization characteristics of infrared radiation on the metal surface.According to Kirchhoff’s law,energy conservation law,and three-component polarization bidirectional reflection distribution function,the polarization characteristics model of infrared radiation on the rough metal surface is deduced.The research shows that the surface masking effect is closely related to the characteristic texture parameters such as surface roughness.Therefore,the four-parameter masking function is introduced into the three-component polarization bidirectional reflectance distribution function model to reduce the influence of masking and masking effect between adjacent micro-surface elements on the model accuracy.The simulation results show that the model has a strong characterization ability for the polarization characteristics of rough metal surfaces,and the model accuracy is greatly improved.Fourth.Polarized thermal image of fatigue damage metal surface.The mechanism of metal fatigue damage and the evolution of metal surface morphology and energy dissipation during fatigue damage is introduced.The polarized thermal images of different fatigue cycles during metal fatigue damage are obtained and analyzed by building metal fatigue polarized thermal image observation platform.Compared with the metal infrared polarization images under different fatigue cycles,the metal infrared polarization gradually decreases with the increase of fatigue cycles.The edge becomes more blurred,and the roughness gradually increases.Comparative experiments obtain the thermal infrared intensity image and infrared polarization image.Compared with the infrared intensity image,the metal infrared polarization image can highlight the target contour and improve the contrast.Understanding the light scattering model on the metal surface is further deepened by studying the basic theory of polarization thermography,the distribution function of polarization bidirectional reflectance on the metal surface,and the polarization characteristic model of infrared radiation on the rough metal surface.In this paper,the relationship between the degree of infrared radiation polarization of metal and the observation angle and surface roughness is deeply analyzed.The polarization characteristics model of infrared radiation suitable for the rough metal surface is established.The accuracy and practicability of the proposed model are verified by experiments,which improves the accuracy of the polarization characteristics model of infrared thermography on the rough metal surface,and provides better theoretical support for the real-time evaluation of metal fatigue damage by polarized thermography.Figure[38] table[2] reference[67]...