Research On In-situ Testing Of Laser Speckle For High Temperature Deformation Behavior Of Materials

With the rapid progress of China’s aerospace,weapons,and other fields,the use of equipment materials service environment temperature is getting higher and higher,such as aero engines,hypersonic vehicles,and other equipment critical thermal protection components are acting under high-temperature complex load loading,whether these thermal protection components can work safely and stably is directly related to the safe operation of the entire device,so it is necessary to characterize the mechanical behavior of materials and their components under high-temperature environment.The detection of high-temperature deformation is essential to characterize the mechanical properties of the material and its components because it can better represent the damage initiation and progressive damage of the thermal protection components under extreme operating conditions.Although the traditional contact deformation detection method has good applicability and reliability,it is not applicable in high-temperature conditions because the measurement components need to be in direct contact with the parts to be measured and cannot withstand high temperatures.Therefore,there is an urgent need to carry out research on non-contact high-temperature material thermal deformation detection technology to achieve accurate detection of the deformation behavior of thermally protected components under high-temperature complex stress environments.Digital image correlation(Digital Image Correlation)is the most widely used noncontact deformation detection technique for thermal strain detection,which has the advantages of high detection accuracy,high sensitivity,and full-field strain detection,and has a higher temperature detection interval than other non-contact deformation detection techniques.Although a few digital speckle detection techniques based on artificial speckles can detect material deformation in high-temperature environments,they are not universally applicable because of the tedious speckle preparation process and the strict material matching requirements.The traditional DIC technique still has the effect of high-temperature speckle material oxidation and dislodging,strong background radiation interference,etc.,which affects the observation effect and detection accuracy and cannot meet the demand of deformation detection under a hightemperature environment.Therefore,in this paper,we propose a laser speckle in-situ testing technique for the high-temperature deformation behavior of materials,which provides a new method and idea for high-temperature deformation detection,in response to the scientific problems such as unclear mechanical behavior and damage mechanism of materials under high-temperature complex stress environment.The specific research contents are as follows:First,this paper developed a DIC-based strain detection system based on the basic framework of digital image correlation detection,which is widely used nowadays,and conducted comparison tests with the standard electronic extensometer and commercial strain detection system to verify the accuracy of deformation calculation of the selfdeveloped strain detection system.In this paper,a laser speckle detection device based on active laser bilateral irradiation imaging was proposed,and laser speckle imaging tests based on this device were carried out to analyze the effects of various influencing factors such as material surface roughness,camera aperture,laser power and material properties of the parts to be measured on the quality of laser speckle imaging,to facilitate the effective acquisition of high-quality laser speckle images in practical tests.At the same time,a comparative test of laser speckle tensile at room temperature was carried out to verify the accuracy of deformation detection of the laser speckle detection device.Secondly,the theoretical characteristics of strong background radiation and heat flow perturbation of laser speckle detection technology under a high-temperature environment were studied in this paper,and corresponding suppression methods were formulated.The test of high-temperature resistant speckle materials and the test of hightemperature digital speckle in-situ observation were carried out,respectively,and the deformation detection under the high-temperature environment of 1700℃ was successfully achieved,and the maximum strain distribution area of the strain cloud map in the observation area of the specimen and the fracture location of the specimen matched each other,which confirmed the accuracy of digital speckle deformation detection under the high-temperature environment of 1700℃ and provided an accurate comparison for laser speckle deformation detection under high-temperature environment.In addition,the laser speckle imaging test under high-temperature environment was carried out to analyze the influence of temperature on the laser speckle imaging quality,and the in-situ inspection of the tensile deformation behavior of the specimen under different temperatures was carried out to verify the stability of the laser speckle under high-temperature environment.Finally,based on the above research,a comparative test study of C/C composite tensile testing under a high-temperature environment was carried out in this paper.The feasibility of laser speckle deformation detection under a high-temperature environment was compared and analyzed by in-situ deformation detection with digital speckle and laser speckle on both sides of the specimen observation area,respectively.The test results show that laser speckle deformation detection has minor absolute and relative errors with digital speckle deformation detection as the benchmark,which confirms the stable and reliable thermal deformation detection capability of the selfdeveloped laser speckle detection system.