Long-gauge-length and high-accuracy optical extensometer based on field-of-view splitting

Limited by the resolution of the camera and the effect of rigid-body out-of-plane displacement, the strain measurement accuracy of an optical extensometer based on two-dimensional digital image correlation (2D-DIC) is often not high. To address the problem of insufficient camera resolution, a field-of-view (FOV) splitting device was proposed. The device used a right-angled optical prism and two mirrors to split the camera's continuous FOV into two independent fields separated by a certain distance. This device considerably increased the gauge length of the optical extensometer, thus effectively reducing the strain error caused by insufficient camera resolution. Moreover, a telecentric lens was adopted to reduce the effect of out-of-plane motion on the 2D-DIC extensometer. Static tests and uniaxial tensile tests were conducted to verify the feasibility of the proposed extensometer. Experimental results demonstrate that the root mean square errors of corresponding strain results are all within 6 με. The proposed optical extensometer based on FOV splitting is a high-accuracy strain measurement technique. © 2020, Science Press. All right reserved.