Elastic-plastic stress analysis for notched tensile specimens is carried out experimentally by means of reflective photoelastic coating method. An incremental law of the Prandtl-Reuss stress-strain relation and knowledge of stress-strain curve of material obtained from a uni-axial tensile test are used to the evaluation of plastic stress. Concepts of secant modulus and equivalent stress are introduced to obtain the elastic-plastic stress-strain relation. Elastic-plastic boundaries based on the Tresca yield criterion can be found employing the isochromatics of the photoelastic stress pattern in birefringent coatings. As the load increases, stress concentration factors are found to be constant in elastic state, but they gradually decreased to a certain constant value in plastic state. Reflective photoelastic method can be used to observe the elastic-plastic boundary and utilize elastic-plastic stress analysis.
