Improvement of Moire and Grid Methods of Plastic Strain Analysis and Their Application to Extrusion

Abstract

The authors have proposed a new moire method of measurement of plastic strain. The method is based on the principle that the common tangential direction of two interference fringes coincides with the direction toward which the normal strain vanishes, when the master grid is composed of two families of strainght lines. The authors have also suggested a new technique for the calculation of strain which reduces the errors of the measurement by applying the gridwork method. These two methods are applied to the experimental analysis of the plane strain extrusion and the axi-symmetric extrusion. From the experimental results, it has become clear that the undulations of the distribution of the strain and of the hydrostatic pressure become less with the decrease of the die angle or with the increase of the reduction of area. The experimental results of the plane strain extrusion show good agreement with Hill's solutions concerning the non-hardening material in regard to the velocity field, while the experimental results of the axi-symmetric extrusion also show considerable agreement with the authors' upper bound solutions.