Abstract
In the procedures of the birefringent coating method, it in not easy to separate the strain differences of the principal strains. Because, to obtain the individual strain component, Laplacian equation must the solved numerically taking into account of the boundary conditions. When a plate with a central hole is subjected to equi-biaxial tension, the separation of principal differences becomes easily due to the symmetry. In this paper, the separation of principal strains is conducted under the assumption that sum of two principal strains are constant in the radial direction. The elastic-plastic calculation by the FEM is shown to testify the assumption.
