| The measurement of displacements and displacement gradients (strains) has always been an important topic for mechanical engineers. In the last decade, a cross-correlation technique utilizing two digitized images, which were captured before and after the deformation of an object, has been successfully developed and applied in the measurements of displacement and strain. By utilizing the concept of digitization, one can characterize the image by different levels of light intensity. With this, the technique can be applied to correlate the images, and to render the subtle difference between them.To overcome these problems, the present work proposes a "Fast and Simple" (FAS) algorithm by searching the displacement fields without considering the pattern distortions. A different mapping strategy was chosen to bypass the subpixel interpolation. Therefore, the required computational resources were reduced. Uniform and non-uniform tests were performed to validate the FAS algorithm. The experimental results show an enhancement in computational speed up to 200 folds with reasonable accuracy. Error analysis shows that this new algorithm is applicable for strains ranging from 0.3% to 5%.Original approach developed at the University of South Carolina was to adapt the Newton-Raphson method with partial differential corrections integrated into the search scheme. Their mapping model proved to be capable of considering the effect of pattern distortions. The technique also rendered satisfactory detection accuracy. Although it is convenient, the method has two main disadvantages. Namely, high computational cost and the requirement of guesses for initial input. These factors have prevented its widespread use. |
