Microscopic and Macroscopic Measurements of Poisson's Ratio of ASTM B557M Using Digital Image Correlation and Local Search Algorithm

We have developed a local search algorithm to enhance the computational efficiency of digital image correlation (DIC). This work examined the biaxial strain and Poisson's ratio of a deformed ASTM B557M specimen using a modified model of DIC. We have also developed a model to enable the precise cropping of large images in order to reduce the numerical cost associated with pattern searches within an image stack. The proposed DIC system produces time-displacement curves based on pattern tracking as well as time-strain curves through numerical differentiation. In the region of elastic deformation, the system provides results consistent with those obtained using strain gauges and material testing systems (MTSs). Local deformation at the microscopic scale is captured using a newly developed DIC program, which outputs raw data corresponding to the vertical and horizontal directions. The proposed DIC system yields clear images with 4K resolution (4096 x 2160 pixels) and high spatial resolution of 1.9 mu m based on a program that uses a numerical gradient to locate peaks in correlated results. Specimen preparation is simple, requiring only the application of speckle on the surfaces of featureless objects. The experimental setup requires only one laptop computer and one or more digital cameras from many manufacturers. The proposed DIC program can be embedded within a variety of MTSs, providing precision measurements for a wide variety of applications.