High-Accuracy, High-Efficiency Compensation Method in Two-Dimensional Digital Image Correlation

When measuring plate specimen deformations, traditional two-dimensional (2D) digital image correlation (DIC) often leads to insufficiently accurate results due to out-of-plane motion of the specimen during the measurement. To remove the effects of out-of-plane motion, a compensation method for 2D DIC has been developed by researchers. The method markedly improves 2D DIC measurement accuracy. However, two problems with this compensation method remain to be solved: (1) the compensation-method coefficient matrices are affected by experimental noise and correlation errors, and (2) the coefficient matrices are singular when the specimen deformations are small enough, especially when the specimens remain static. For these reasons, an improved compensation method is proposed in this paper. The proposed method adds an extra single-camera calibration step to determine the distortion parameters so that the coefficient matrices are not affected by deformed images and the compensation results become more stable. To ensure measurement efficiency, virtual extensometers are taken as an example to compare the two compensation methods. Static experiments have been carried out to analyze the effects caused by different measurement parameters. Tensile experiments indicate that the improved compensation method leads to highly accurate results that not only are comparable with those of three-dimensional (3D) DIC, but that also agree with the results measured by a strain gauge. A video extensometer with a high accuracy of 5 με at a rate of 28 fps has been developed as well.