Accuracy of Measurement of the Infinitesimal Deformation in Digital Image Correlation and the Intelligent Hybrid Method
The displacement obtained from the experiment is including large error and it is impossible to evaluate the stress and the strain with high accuracy using raw displacement data. The 2-D intelligent hybrid method was applied in order to evaluate the 2-D stress field. In the infinitesimal deformation within elastic region of steel or an aluminum alloy, the quantity of displacement is less than 1 pixel, and analysis accuracy deteriorates. We need the system which can analyze the displacement more exactly in sub-pixel field. Hence, the Newton-Raphson method was applied after obtaining the displacement at any point of the image. On uniform deformation field, the infinitesimal strain was estimated with less than 0.01pixels of an error by DIC by taking into consideration only the 1st deformation gradient in the Newton Raphson method. On nonuniform deformation near the crack tip, it was estimated with about 0.018pixels error by taking the 2nd deformation gradient into consideration.
Yu Zhou, Shan-Tung Tu and Xishan Xie
K. Machida and K. Okazaki, "Accuracy of Measurement of the Infinitesimal Deformation in Digital Image Correlation and the Intelligent Hybrid Method", Key Engineering Materials, Vols. 353-358, pp. 3096-3099, 2007