Metal Powder Stick Elastoplastic Constitutive Equations

High velocity compaction technology which was put forward in 2001 is a new powder metallurgy compaction technology. Because of high speed and short time, deformation characteristics of metal powder are very complex. Numerical simulation is of great importance in the research of deformation characteristics of metal powder. And the constitutive equation is necessary to the numerical simulation. In this article, combining with rheological theory, constitutive model of metal power is constructed. Based on the model, the deformation characteristics of metal powder are discussed.At first, two kinds of viscoelastic constitutive model of powder compaction are introduced. In order to reflect the influence of temperature in the compaction, the spring element's coefficient of thermal expansion is introduced, and the corresponding thermo viscoelastic constitutive equation is derived based on the improved constitutive model. Because of the increasing of temperature during high velocity compaction, the metal powder is softened and easy to compact. As a result, the density of compacting components is increased.Second, to explain plastic deformation during high velocity compaction, viscoelastic plastic constitutive model is constructed by introducing the ideal plasticity element and the spring element's coefficient of thermal expansion. The corresponding constitutive equations are derived. By comparative analysis, the influence of plasticity and temperature on the compaction of metal powder can be observed.At the end, the unloading equation is derived by analyzing unloading process in compaction. The equation shows that the increasing of temperature makes the elastic aftereffect lower. The characteristics of high velocity compaction can be observed that elastic aftereffect is low and ejection pressure is small.