Thermomechanical similarity between Van Aken plasticine and metals in hot-forming processes

Abstract

In this study, compression tests are conducted to determine the strain, strain rate, and temperature sensitivities of Van Aken plasticine at elevated temperatures. A true stress—true strain relationship is presented in the form of the Norton—Hoff viscoplastic model. The plasticine is most sensitive to the deformation rate and temperature. At low strains, the material hardens with increasing strain, but strain hardening is negligible above a logarithmic strain of approximately 30 per cent. The shear friction factor for a plasticine—metal interface with and without lubrication is estimated using ring compression tests. Without lubrication, the shear friction factor approaches 1.0; however, lubrication with Vaseline considerably reduces friction. In addition to the mechanical properties of the plasticine, thermal conductivity and specific heat capacity are measured. The thermal conductivity is independent of temperature, and the heat capacity varies only slightly with temperature. A discussion on plasticine and metal similarity is presented in detail. It is shown that mechanical similarity is possible between the Van Aken plasticine and many steel and aluminium alloys. For thermal similarity in a hot-deformation process, the product of the Prandtl and the Eckert numbers, the Peclet number, and the thermal boundary conditions must all be matched. Thermal similarity is extremely difficult to achieve exactly; however, it might be possible to satisfy approximately such that the physical model is valid qualitatively.