基于数字图像相关的光学引伸计应变测量精度研究

Study on strain measurement accuracy of optical extensometers based on digital image correlation

基于数字图像相关(DIC)方法的光学引伸计在应变测量领域有着广泛的应用。为了提高数字图像相关方法的测量精度,本文采用二维DIC与三维DIC的光学引伸计、基于双45°反射镜成像的二维光学引伸计以及电测法,对单轴拉伸试验中不锈钢试件的应变进行同时测量,比较分析了各个光学引伸计在测量轴向与横向应变方面的优劣以及误差产生的原因。实验结果表明:试件离面运动的存在大幅降低了普通二维光学引伸计的应变精度;基于双45°反射镜成像的二维光学引伸计可以有效消除离面刚体位移对测量结果的影响,其应变测量精度(尤其是横向应变精度)高于其他光学引伸计,且测量结果与电测法的测量结果高度吻合;三维DIC光学引伸计的横向应变精度明显不如轴向应变精度。

Although optical extensometers based on Digital Image Correlation（DIC）method have widespread applications in strain measurement,there is a lack of systematic research on the strain measurement accuracy.For the uniaxial tensile test,testing equipment including the traditional 2D DIC optical extensometer,three-dimensional digital image correlation（3D-DIC）optical extensometer,2D -DIC optical extensometer equipped with dual-reflector imaging capability,and strain gauge were employed to measure the strain of stainless steel simultaneously.The results of axial and transverse strain measurement using different optical extensometers were compared,and the corresponding sources of measurement error were analyzed.The experimental results revealed that the traditional2D -DIC optical extensometer yields low measurement accuracy because of the presence of out-of-plane motion.The 2D -DIC optical extensometer equipped with dual-reflector imaging capability can eliminate the effect of out-of-plane rigid body displacement and thus,ensure higher measurement accuracy,especially for transverse strain measurement,compared to other optical extensometers.Notably,the strain measurement results obtained using the 2D -DIC optical extensometer equipped with dual-reflector imaging capability were in good agreement with those obtained using a straingauge.The measurement accuracy of transverse strain using 3D-DIC optical extensometer is apparently lower than that of axial strain.