Application of digital image correlation algorithm in evaluation of alkali resistant glass for rubidium atomic clock

Because of the obvious deformation difference for the alkali resistant glass tubes with different internal stress, in this paper, a new method for evaluating the internal stress and annealing quality of alkali resistant glass tubes based on digital image correlation algorithm is proposed. According to the deformation change rate of alkali resistant glass tube that obtained by digital image correlation algorithm, it can directly determine whether the internal stress meets the production standard. The alkali resistant glass tubes which have undergone abnormal(annealing time less than 5 hours and annealing temperature lower than 630 ℃) and normal annealing operation were selected as samples of experimental group and control group. The samples of these two groups were heated to 200 ℃ and then cooled to room temperature. The displacement fields between deformed images and the initial image are calculated by digital image correlation algorithm and the mean values change rate of the displacement fields are regard as the evaluated basis for the internal stress and annealing quality. Since the new method has many advantages such as simple, efficient and non-contact and only two continuous pictures are required in the detection process, it has been applied in the actual industrial production testing. In addition, this method provides a new approach for the internal stress detection of other solid materials.