金属粉末的粘弹塑性本构方程的研究

【作者】 杨晨晨；

【导师】 郑洲顺；

【作者基本信息】 中南大学 ， 计算数学， 2011， 硕士

【摘要】 高速压制技术是2001年提出的一项新的粉末冶金压制技术,由于高速压制速度快、时间短,粉末的变形特性非常复杂。数值模拟是研究高速压制过程的重要途径,而构造本构关系又是数值模拟必要的部分。本文结合流变学理论,利用流变本构模型的构造方法,构造了一种粉末的本构模型,并在此基础上对金属粉末的变形特性进行了讨论。文中首先介绍了两种有关金属粉末压制的粘弹性本构模型,并在改进模型的基础上,通过引入弹簧元件的热膨胀系数,来反映温度对压制过程的影响,推导出相应的热粘弹性本构方程。对所建立方程的分析显示,在高速压制中由于温度的变化,使得金属粉末出现软化现象,即粉末更容易被压实,从而使压坯零件有较高的密度。其次,高速压制中粉末会发生塑性变形,为了描述这种现象,在改进的粘弹性本构模型的基础上引入理想塑性体,构造了金属粉末的粘弹塑性本构模型,推导出相应的本构方程,并引入弹簧的热膨胀系数来描述温度的影响,得到粉末的热粘弹塑性本构方程。通过对比分析,体现了塑性变形的存在和温度的提高使得粉末应力变化速率减小,从而提高压坯密度。最后分析了高速压制成形中的卸载过程,得到了卸载方程。通过对卸载方程的分析显示,压制中粉末温度升高使得压坯的变形恢复更小,体现了高速压制弹性后效低、脱模压力小的特点。更多还原

【Abstract】 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.更多还原