New digital-image correlation method and its application

In this paper, a new digital-image correlation method----twelve variables gradient method is presented. The influence of second derivative terms of displacement is considered, the directional derivatives of correlation coefficient are obtained and variational step-length search is used in this method. Consequently, the truncation error caused by increasing of subset size and vast computation time are avoided. The measurement precision of displacement and strain are less than 0.011 pixels and 100 muepsilon, respectively. Two test experiments and the application show that this is an efficient and accurate method.