Preliminary Study on Improving DIC Analysis Using Optical Flow to Reject Outer Images

Using the digital image correlation method for on-site measurement, limited by continuous operation conditions and environment, two inevitable challenges are introduced. First, the reference images at the balanced positions needed for DIC analysis are always unknown; and environmental disturbances contaminate the continuously recording images and distort the measurement results. To overcome the two challenges, a preliminary attempt is to adopt the optical flow algorithm to redefine the reference image and reject the outlier video images to suppress the possible significant departures introduced by unknown reference images and environmental disturbances on the DIC-determined dynamic displacement and strain field. In this study, the balloon inflation experiment evaluates the improvement by adopting the optical flow method. The results show that the optical flow can provide additional information that helps redefine the reference image and reject unwanted image frames. After adopting the redefined reference image for DIC calculation, the averaged displacement and strain intuitively show that the balloon is in extension. Meanwhile, the overall frames' averaged displacement and averaged strain can conduct a 3.6% difference for displacement and 5.6% for strain in magnitude as the redefined one is used. According to the results, selecting reference images needs further study to improve the measurement accuracy, particularly for continuous displacement and strain measurement using DIC.