Research Of High Temperature Materials Mechanical Properties Measuring System Based On DIC

Digital Image Correlation(Digital Image Correlation,DIC)is a non-contact,full-field optical measurement method based on visual images.This method performs correlation calculations between two images before and after deformation to achieve measurement of full-field displacement,deformation,and strain.This method has been widely used in various fields such as machinery,materials,and automobiles after years of research and development.In recent years,this method has been gradually used to measure the mechanical properties of materials at high temperatures.However,there are still many problems when this method is used at high temperatures.This thesis focuses on the key issues of digital image correlation methods in high temperature applications,and a high temperature digital image correlation measurement system is set up and a high temperature measurement experiment is conducted to verify the performance of the system.The specific research work is as follows:(1)This thesis analyzes and introduces the basic principles and concepts of digital image correlation methods,studies and compares several different integer pixel search and sub-pixel search algorithms,and the search algorithm to be used in this system is selected;(2)The effect of blackbody radiation at high temperature is analyzed and studied.The optimal imaging method at high temperature is found by comparing lighting different speckles with different light sources and filtering with corresponding filter;(3)The influence of thermal disturbance on the measurement accuracy at high temperature is studied.The method of combining the gray average algorithm with the image inverse filtering algorithm is proposed to process the images to reduce the influence caused by the thermal flow;(4)The evaluation function of speckle in the measurement of digital image correlation method is studied.A speckle evaluation function based on the regional average grayscale feature is proposed to judge the image quality.(5)A high-temperature digital image correlation measurement system is set up.Conducting the rigid body displacement at room temperature,tensile test at room temperature and tensile test at high temperature to verify the accuracy and feasibility of this system.Analyzing the error sources of this system then taking corresponding methods to reduce the measurement errors.