An improved speckle method for measuring in-plane displacement and strain fields

An improved speckle method which can measure in-plane displacements to an accuracy of 2 mu m is presented, provided that the distance between two pixels in an image corresponds to 0.1 mm. The algorithm developed to obtain the displacement field uses the usual assumption that the displacements within each sub-element of the image are constant and evaluated at the center of the sub-element. In the present work, instead of moving the entire sub-element in each loop of the algorithm, a fraction of the subelement size is adopted to generate a family of overlapping sub-elements, resulting in an enhanced resolution of the resulting displacement field.