Deformation Measurement Of High Temperature Materials Based On Digital Image Correlation Technique

The measurement of high-temperature material deformation is an important parameter for evaluating material properties.With the development of science and technology,hightemperature materials have been widely used in the military and defense fields such as aero engines,aircraft shells and other basic manufacturing industries,so the deformation testing of high-temperature materials is becoming more and more important.The digital image correlation method(DIC)used in this paper is a non-contact optical measurement method,which has the characteristics of full-field measurement,high accuracy,and low environmental requirements,and meets the requirements of high-temperature environment for material deformation testing.According to this method,a complete high-temperature environment measurement system was established.The thermal expansion coefficient of high-temperature materials was successfully measured under high-temperature environments,and rigid body displacement and tensile strain were measured.Finally,it was fused with an infrared thermal imager to simultaneously measure the strain of the material.Field and temperature field.The specific research content includes the following aspects:1)The main principles of digital image correlation methods are introduced.It is proposed to locate the displacement point through the whole pixel search algorithm and the sub-pixel solution method.Analyzed and compared the accuracy and efficiency of different algorithms in the whole pixel and sub-pixel positioning,and finally determined the improved artificial fish school algorithm as the whole pixel search algorithm,and the surface fitting method as the subpixel solution method.2)The basic principles of binocular vision imaging are studied,including the imaging model,the epipolar constraint relationship and the conversion of different coordinate systems of the imaging system.It is proposed to use Zhang Zhengyou's checkerboard calibration method to calibrate the camera,and it is proposed to use an infrared thermal imager and a traditional CCD camera to collect the pictures of the calibration board synchronously to achieve joint calibration.3)Several key problems of DIC testing in high temperature environment are studied.Firstly,the thermal radiation interference is eliminated by adopting the filter system based on active lighting.The interference of hot air flow is reduced by adding gray average to controllable fan.Finally,the problem of how to adjust the exposure time of the camera in high temperature environment is analyzed.4)Through the establishment of high temperature DIC experimental system.At the highest temperature of 1200?,the thermal expansion coefficient of the material was measured to verify the feasibility of the experimental system.Then the high temperature rigid body displacement experiment was carried out at 1000?,and the measured rigid body displacement was in accordance with the setting of the gradient displacement of 100 um,and the error was within10 um.Subsequent high-temperature stretching and necking experiments were conducted to obtain the strain values of the specified lines at different moments.Finally,the temperature field and strain field of the specimen at 200? were measured synchronously by fusion with the infrared thermal imager.