Research on the optical video extensometer with large field of view and high accuracy

Abstract

Optical video extensometer has been widely used in the field of strain measurement because of its features of noncontact, large range, high precision, being suitable for special environments and materials. A new optical video extensometer with the large field of view and high accuracy was designed in this paper. The hardware includes dual telecentric lens, CCD camera, ring light source, tripod, slide rail and some supporting fixtures. This integrated hardware has the advantages of low cost and high imaging quality. Also, the supporting software is developed. By sub-pixel tracking of selected markers, it can automatically calculate the data of transversal and longitudinal strain values. Poisson's ratio of the material can also be obtained. The measured results of the video extensometer are proven to be correct and accurate by experimental verification. Compared with strain gauges, the maximum strain error of the optical video extensometer is about 15με, and the standard deviation error is 8.38με. This optical video extensometer can be used for high-precision strain measurement of large size samples of metal, polymer, film and large deformation materials.