Strain Measurement and Stress Visualization Using Global Digital Image Correlation

Abstract

  The basic principle of the 2D displacement/strain measurement using global DIC and a method for obtaining stresses from the measured strains are described. In this method, a finite element mesh is defined so that it overlaps the measurement target in the image, and all nodal displacements of the mesh can be determined simultaneously by using the correlation of gray value distributions. After determining the nodal displacements, the strains in the elements are computed using the displacement-strain relationship. If the strain is small, the strains can be obtained from the displacement gradient. If the strain is not considered small, the strains are obtained from the deformation gradients based on finite deformation theory. After calculating the strain, if the material properties and constitutive equation of the object to be measured are known, the stress distribution can be obtained. As examples of stress visualization, stress concentration around a circular hole and stress distribution near a crack tip are shown. The evaluation of fracture mechanics parameters for the crack example is also presented.