高速压制成形中金属粉末本构方程的研究

【作者】 岳书霞；

【导师】 郑洲顺；

【作者基本信息】 中南大学 ， 应用数学， 2008， 硕士

【摘要】 高速压制成形(HVC)技术以高效率、高性能、低成本等优点成为近年来压制成形研究的热点。为了研究金属粉末的变形特征,得到一个封闭数学方程组,本构方程是必不可少的。本文在综述高速压制成形研究现状、特点的基础上,详细介绍了经典的压制方程、损伤力学等相关理论。首先根据高速压制的压制机理,将压制过程分成硬化和软化两个阶段。由于金属粉末在硬化阶段压制力和密度呈线性关系,所以用heckel模型进行模拟,利用黄培云应变双对数计算公式,推导出硬化阶段的本构方程。第二阶段考虑到高温引起软化效应,同时应力-应变表现为非线性,对ZWT模型进行修正,去掉低应变率项,加入粘塑性项,得到此软化阶段的本构方程。数值模拟表明对硬化和软化两阶段分别建立本构方程是合理的,与试验的结果基本一致。其次,利用损伤力学原理分析高速压制过程的损伤现象,将金属粉末看成柔度矩阵与弹性模量有关的E材料和柔度矩阵与剪切模量有关的G材料的复合体,在热力学第二定律的基础上,得到了金属粉末各向异性弹性损伤本构方程、相应的有效柔度矩阵以及损伤能量释放率。最后,考虑金属粉末损伤过程的体积变形特征和软化效应,构造合适的塑性耗散势函数,构造高速压制成型金属粉末的弹塑性各向异性损伤本构方程。更多还原

【Abstract】 High velocity compaction (HVC) technology became a hot research topic because of its efficient, high-performance and low-cost. In order to get closed mathematical equations in studying the deformation characteristics of the metal powder, constitutive equation was essential. Based on HVC theories, the classical suppress equation and damage mechanics were introduced.At first, according to the relevant principles of HVC, the compaction process was divided into two stages: softening and hardening. The Heckel model was used for stimulation in the first stage because of its pressure and density e was a nearly linear relation. And the constitutive equation was deduced by using Huang’s double logarithmic strain formula. The ZWT model was adopted in the second stage so as to reveal the nonlinearity. The item of low strain rate was eliminated, but the viscoplastic item was added. Thus the constitutive equation was established for the hot softening viscoelastic-plastic of HVC. It was proved reasonable to deduce the constitutive equation apart by the numerical simulation.Secondly, the principles of damage mechanics were applied to analyze the damage phenomena in HVC process. According to the complex characteristics of the deformation of the metal powder, the metal powder is considered as a compound of two categories of materials. The flexibility matrix of one category of material (E material) is only relevant to the modulus of elasticity of the metal powder, while the flexibility matrix of the other category of material (G material) is only relevant to the shear modulus of the metal powder. In light of the second law of thermodynamics, the constitutive relation, the corresponding effective flexibility matrix and the damage energy release rate of the damage model of anisotropic elasticity of the metal powder were established.Ultimately, according to the characteristics of the volume deformation of the powder, an appropriate dissipation potential function was selected to construct a constitutive equation of the Elastoplastic anisotropic damage of HYC powder.更多还原