Abstract
We investigated a method to measure deformation using image correlation technique. If we put random pattern on material surface as target marks, we can measure deformation distribution on the surface by comparing two images before and after deformation taken with CCD devices. In this method, searching method of the corresponding points on the two images is important. We considered a method to search quickly and with high accuracy. We employed two-stage method of searching, coarse and fine search to make search in short time. In these search methods, we derived a new iteration method to search corresponding points with sub-pixel accuracy. We investigated the interpolation method for the estimation of gray level using neighboring pixel data with linear, third-order polynomial and fifth-order polynomial functions. The results showed that interpolation is more accurate using higher order polynomials. We obtained about 0.01 pixel accuracy using this interpolation method using fifth-order polynomials. We applied this method for strain measurement on metal plate under tensile test. The result showed that we could measure strain up to 10^<-4> using a normal NTSC CCD camera with VGA resolution.
