Research On Video Extensometer Based On Digital Image Correlation Method

The performance of new materials is different,the service environment is complex,and the material performance test faces new challenges.The extensometer is one of the important tools for testing the mechanical properties of materials,and it provides strong data support for the practical application of materials.Traditional contact extensometers are complicated to install and are restricted by the use environment;non-contact extensometers have low measurement accuracy and unstable tracking algorithms.This article aims to achieve high-precision and high-efficiency strain and displacement measurement.Starting from the calculation accuracy,calculation efficiency and hardware design of the video extension algorithm,the calculation process and iterative strategy of the matching algorithm are optimized,and the hardware for stable imaging is designed and built.system.The main research contents and conclusions of this paper are as follows:1.A fast zero-mean normalized cross-correlation function(ZNCC)is proposed to increase the speed of the whole pixel matching method by calculating the parameters related to the reference sub-region in advance.The results show that the fast ZNCC algorithm can reduce the calculation time by 90%?95% compared with the traditional point-by-point method.2.A sub-pixel matching method for initial value estimation based on polynomial fitting is proposed,and a variety of sub-pixel gray-scale matching algorithm formulas are established by taking the first-order shape function as an example.The simulated speckle verification results show that compared with the traditional matching algorithm,the matching efficiency of this method is increased by 20%,and the deformation measurement accuracy is increased by 30%.3.Designed a set of video extensometer hardware system suitable for high temperature,ambient light interference and other working conditions that can stabilize imaging;developed video extensometer software based on MATLAB,visualized image acquisition and processing,and automatically output displacement and strain Curve and Poisson's ratio.4.The measurement accuracy and stability of the video extensometer are verified by rigid body displacement tracking,dog bone sample stretching and large deformation stretching experiments.The results show that the difference between the obtained strain and the result of the electronic strain gauge is within ±10??;the tracking of large deformation(20000??)has good stability.