Full-Field Strain Measurement of Rotating Object Using Digital Image Correlation

Digital image correlation (DIC) is a non-contact and full-field optical measurement method used to measure displacement and strain of object surfaces in numerous fields. In traditional DIC, the local displacement pointwise least square method (PLS) is widely used for full-field strain measurement owing to its high accuracy; however, this leads to a significant error when used for strain measurement of rotating object. To address this issue, a PLS strain calculation method that considers the rotation was proposed herein. By introducing a rotation matrix before and after deformation into the traditional PLS method, the proposed method can eliminate the strain error caused by rotation. Consequently, the proposed method can be used to calculate strain at an arbitrary rotation angle without the loss of measurement accuracy. To verify the high accuracy and validity of the proposed method, two simulation experiments of strain measurement were conducted. One considers the same strain under various rotation angles and the other considers different strains under the same rotation angle. In the two respective experiments, the strain measurement results of the root-mean-square error mean value decreased from 0.00498 to 0.00011 and from 0.00703 to 0.00027 compared with the conventional DIC method. Results indicate that the proposed method can significantly improve the strain measurement accuracy under rotating conditions.