Research On The Uncertainty Analyse And Applications Of Three-Dimensional Digital Image Correlation Method

Digital image correlation(DIC)method has become the most popular non-contact deformation measurement method in experimental mechanics research.Combined with the binocular vision principle,three-dimensional digital image correlation(3D-DIC)method can measure the three-dimensional morphology and deformation simultaneous,and has rich applications.Until now,the research on the measurement accuracy of 3D-DIC method is still insufficient.Only find out the measurement uncertainty in correlation matching,camera calibration,3D reconstruction and strain calculation,can establish the error backtracking process and improve the credibility of 3D-DIC method.The research in this thesis focus on the errors in 3D-DIC method,the interpolation bias in sub-pixel regristration calculation and the camera calibration errors are analyzed.The main contents are as follows.1.The interpolation bias in the presence of strain is studied,and the law of the interpolation bias in the presence of strain are found for the first time.The coupling mechanism of strain and subset size on interpolation bias is discovered and explained.A general form of interpolation bias with strain existing is given.On this basis,a method using pre-deformed reference subset is proposed to eliminate the interpolation bias in DIC method.2.Based on the numerical simulation and real experiment,the error propagation in the camera calibration calculation is studied.The effects of calibration board machining errors and feature point extraction errors on traditional method and fixing 3points method are analyzed,proved the wide applicability and high measurement accuracy of the fixing 3-points method.In addition,the error transfer formula in the camera calibration calculation is deduced,and the coupling between camera parameters is analyzed.3.DIC based lens distortion measurement methods without calibration board are proposed.Designed speckle pattern is displayed on the screen and speckle image with distortion is captured.Correlation calculation between these two images are employed to extract the per-pixel registration results.Constraint equations containing distortion parameters is established and solved.The calibration-free DIC method is explored in this work.Besides theoretical research,two practical applications of three-dimensional digital image correlation method are also introduced.1.A video extensometer system based on single camera 3D-DIC method is developed.Using reflecting mirrors,two views of the specimen is captured by one camera.An optical path analysis method of single camera 3D device imaging based on "virtual object" is proposed.Measured result on tensile testing shows the stability and effectiveness of the video extensometer system.2.A fusion method combining 3D-DIC method and total station prism transfer technology is proposed to measure the three-dimensional morphology and space position of continuous rail support platforms in high speed railway construction.Several reflecting prisms are fixed on the stereo camera system,the moved stereo camera system is aligned with each other by means of the measured prism position using total station.