Study On High Precision Measurement Method Of In-plane Displacement Based On DIC

Digital Image Correlation Method(DICM)is a non-contact optical measurement Method used to measure the total field displacement and strain.It is based on the basic optical theory,takes the mechanical experiment as the main Method,and combines a multi-disciplinary technology.With the rapid development in recent 30 years,digital image correlation method has undoubtedly become one of the indispensable and widely used optical measurement methods in modern experimental mechanics.Domestic and foreign researchers start from the principle of calculation,and continue to innovate and optimize the method,its computational efficiency,computational accuracy and robustness has been gradually improved,the application field has become more and more extensive,in an increasingly important position.According to the characteristics of digital image correlation methods,this paper makes a systematic analysis of them.Firstly,several commonly used correlation coefficient functions are sorted out.Through comparative analysis,it is concluded that the normalized zero mean correlation function is not sensitive to the change of light intensity and light deviation,and has high reliability and anti-interference.At the same time,the calculation principle of several common integer pixel search algorithms and the method of solving strain field based on local least square fitting of displacement field are introduced.Secondly,the computing accuracy,computing time and anti-noise ability of surface fitting method,gradient method of constant gray level mode and n-r method are compared,and the performance and characteristics of each algorithm are summarized.In view of the fluctuation of illumination in the experimental environment,the linear gray gradient method is proposed.Compared with the constant gray gradient method,the method has lower requirements for illumination and other environmental conditions and higher robustness.Thirdly,the zero mean normalized correlation function was optimized,and the computational efficiency was significantly improved after optimization.A path search method based on correlation coefficient is proposed,which has higher reliability.Combined with the characteristics of the linear grayscale gradient method and the surface fitting method,a sub-pixel hybrid search algorithm based on the linear grayscale change mode is proposed.The experimental results show that the algorithm has a computational accuracy of 0.01 pixel,a high noise reduction ability,and is more suitable for practical measurement.Meanwhile,the interpolation process of the improved algorithm is optimized to improve its computational efficiency.Finally,the feasibility and accuracy of the improved algorithm are tested by quasi-static compression experiment,and the experimental results show that the calculation results of the improved algorithm are reliable.At the same time,DIC technology was used to analyze the design parameters that affect the structural stability of multi-cell materials.