【作者】 伊兴华；

【导师】 甄良；

【作者基本信息】 哈尔滨工业大学 ， 材料学， 2007， 硕士

【摘要】 本文以有限元理论和晶体塑性力学为基础,采用Voronoi图表模拟多晶体微观结构,并对建模过程中的两个主要因素:晶粒尺寸和晶粒取向以及计算过程中的两个主要因素:网格划分和晶粒数目对模型模拟计算结果的影响作了深入的讨论,最终建立了面心立方晶格的多晶体塑性变形模型。从细观层次(主要是指晶粒尺度)模拟研究了多晶体室温单向拉伸变形行为,以工业纯铜和GH4169为例,模拟计算了多晶体塑性变形过程的宏观应力应变响应,与实验结果进行比较,得到如下结论:(1) Voronoi图表通过真实材料的几何学性质和拓扑性质,提供了平面晶格边界,在各向同性和稳定状态生长假设下,不同晶粒之间的边界可以用这些多面体很好的描述,而且它可以与晶核成形和随机生长过程作比较,在模拟多晶体材料中具有很好的可靠性和有效性;(2)晶粒数目和网格划分的影响主要体现在计算精度要求上,晶粒数目的多少及网格划分的疏密代表了计算过程中模型离散点的数量多少,模型离散点数量越多,计算过程中对晶粒变形、转动情况的数学记录和描述数据点越多,模拟得到的结果也越精确,但相应的计算效率会大大降低。实际模拟计算时应综合考虑模拟计算的精度和效率,选取适当的晶粒数目和网格划分方法;(3)晶粒取向对模拟计算的影响主要分为两种情况,对于理想条件下的材料,可选用完全随机分布的晶粒取向;对于含有较多织构的材料,选用织构取向。这两种情况得到的晶粒取向具有广泛的适应性,可用于不同加工状态下的真实材料中特殊晶粒取向的模拟;本文建立的Voronoi多晶体晶体结构模型重点关注于晶体结构对模型模拟结果的影响,而晶粒尺寸在本文模型中的影响很小,可以不考虑;(4)综合上述主要的影响因素,建立面心立方多晶体塑性变形模型,并以纯铜多晶体和GH4169拉伸试验为例,对模拟计算结果进行了验证。验证结果表明,本文建立的面心立方多晶体模型具有较高的可靠性和有效性。更多还原

【Abstract】 The poly-crystal plasticity finite element model at room temperature is set up in this thesis using the Voronoi diagram, based on finite element theories and crystal plasticity mechanics. During the modeling, three primary factors that maybe influence the model are discussed in details. Three primary influence factors are the number of the grains of the poly-crystal, the orientation of the grains and the density of the mesh partition. The model is established by taking into account these factors synthetically. By using the model, this thesis studies the macroscopic stress-strain responses of polycrystalline materials in a simple tensile test at room temperature in the meso-scale. Results of simulation are compared with experiments of the pure copper and GH4169. The following results can be concluded:(i) The Voronoi diagram can be used to describe the microstructure of polycrystalline materials via the geometrical and topological properties in real materials. And it also can be used to compare with the form of crystal core and the growth of crystal randomly.(ii) The influence of the size of the grains is not taken into account in this model. The number of the grains has a biggish influence on the results of the simulation. While increasing the number of the grains, results of the simulation go into better and better. The number of the grains in model should be chosen according to the requirement of the precision.In this thesis, we chose universal type of the mesh and study the affection of the density of the mesh partition. Different density of the mesh partition reflects the amount of the elements that will be calculated during the calculation. Results will be more exact with more discrete elements in the crystal. For the responses of the macroscopic stress-strain, the effect of the density of the mesh partition is very small even if there is only one element for one grain.(iii) Two types of the orientation of grains have been chosen to study the affection of the orientation, random and texture respectively. With different orientations of the grains, the macroscopic stress-strain responses of the poly-crystal have biggish difference. With the increment of the content of texture, the poly-crystal represents its anisotropies mightily. But the difference is not obvious if the orientation of the grains have been chosen random. The choice of the orientation of the grains should be determined by the materials accordingly.(iv) It is showed that the model of this thesis is reliable and effective at simulation of the macroscopic stress-strain responses during plastic deformation of the poly-crystal by comparing with experiments for pure copper and GH4169.更多还原