Influence of Friction and Plastic Anisotropy in Cube- and Ring-Compression Test

概要

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An extruded or rolled material such as a bar and a tube naturally possesses plastic anisotropy like a sheet. The property influences the metal flow in bulk forming as well as in sheet metal forming. In this paper, some examples of the anisotropic bulk deformations in a cube- and a ring-compression test were demonstrated. The cube with the edges of 1 mm long, which was cut out of a round bar or a tube, was compressed in z-axis under a well-lubricated condition by applying beef-tallow. After the compression test, the strain ratios of εy to εx were 0.83 and 0.76 for A1050 and A6063 respectively. They showed normal anisotropy, because the ratios of εy/εx keep unity if they are isotropic materials. Furthermore, friction also affects the metal flow for the anisotropic material. The ratios of εy/εx changed when the cubes were compressed under different frictional conditions by using some lubricants such as beef-tallow, VG460, VG100, castor oil, and no lubrication. The anisotropic deformation was restrained by the higher-frictional die-surface. Also the ring-compression test, as another example, was investigated, which is a well-established test to determine the friction coefficients by measuring the change in the inner diameter. Plastic anisotropy and friction influenced the reduction in the inner diameter, so the coefficient of friction must be decided with appropriate diagrams that consider the plastic anisotropy of the material.