The Study Of Algorithm For Deformation Measurement Based On DIC And Designing The Dynamic Link Library

The thesis is supported by National Science and Technology Ministry project whichresearches key scientific problems of mechanical performance test for nano-materials,one of main research contents is the measurement of material deformation and strain.This thesis title selected from the project, and studied the algorithm and dynamic linklibrary design of material deformation based on digital image correlationDigital Image Correlation (DIC) has been an important testing technique in the fieldof modern optical measurement mechanics. Although the algorithms are relativelymature, the complete encapsulation for material deformation measurement algorithmshas not been done. The aim of this paper is to design a dynamic link library softwaremodule by comparing and choosing an algorithm, which has better accuracy andtimeliness to provide a convenient measuring tool for the realization of measuringmaterials deformation and strain. This research has a certain scientific significance topromote the study of material deformation and strain measurement based on DIC andthe commercialization of the instrument.The main research work as follows:First studied the mathematical model of digital correlation algorithm, chosecovariance correlation function as the main measurement algorithm by comparing thesensitivity of different mathematical model; Using hill climbing algorithm as the searchalgorithm by investigating the searching efficiency; The sub-pixel search method hasbeen studied in order to improve measurement accuracy; The principles and algorithmsfor camera calibration are studied, all of these theoretical research work laid thefoundation for the software development.Second, a dynamic link library based on DIC deformation measurement has beendeveloped by using VC++6.0and OpenCV, and the function of camera calibration hasbeen realized. The calibration function of a single pixel volume after removingdistortion and the encapsulation of digital correlation algorithm deformationmeasurement function has been achieved, too. Through the development of deformationmeasurement application software, the dynamic link library module has been provedreliable.At last, based on the constructed material deformation measurement system, dynamicdeformation measurement link library is used for the camera calibration test, specimens’ rigidity moving measurement test and tensile mobile measurement test. Both theinternal parameters of the camera and the pixel equivalent have been obtained. Themeasurement results which are close to the values of tensile deformation test have beenachieved as well. Finally the factors influencing the measurement accuracy wereanalyzed, and the improvement methods were put forward.