An Eulerian finite element model for the steady state forming of porous materials

This paper is concerned with an Eulerian finite element analysis for the steady state forming of porous materials, such as nano-grained material manufactured via cryogenic milling. The constitutive relation for such porous materials is different from that for a fully dense matrix. The general form of the constitutive equation for a porous material is derived from the yield functions for the plastic deformation of a porous material, as proposed by Shima, Green, Doraivelu, Gurson, Kuhn, Park, and Lee. Then, that general form is utilized in the Eulerian finite element formulation for the strain hardening, dilatant, and viscoplastic deformation. Initial estimation of the porosity distribution in an Eulerian mesh is obtained from the velocity and scaled pressure fields computed by the Consistent Penalty finite element method for the incompressible viscoplastic deformation of the matrix. Applications of the proposed method to rolling and extrusion are given. The change of the porosity is predicted by integrating its evolution equation along a particle path constructed in an Eulerian domain. Comparisons of the predicted distributions of porosity to those by a Lagrangian finite element method and to those by experiments reported in the literature validate the proposed method.     

不同加载方式下硬质合金应力状态的有限元模拟研究

硬质合金中存在分布不均匀的残余热应力,在承载过程中残余热应力与外加载荷产生复杂的交互作用,影响材料的力学性能。现有的实验和模拟方法均为统计性分析方法,难以在微观组织尺度分析应力分布的细节和特征。本工作利用有限元模拟的方法研究了硬质合金的残余热应力分布特征,分析了不同载荷方式下硬质合金内的应力状态,研究了残余热应力和外加载荷之间的相互作用。基于应力分析,提出了提高硬质合金承载能力的组织结构设计方法和理论依据。该方法也可应用于其他多种多相复合材料的应力分析和微观组织优化。     

Mathematical simulation of a cathodic protection system by finite element method

A computer program was developed, to solve the numerical system generated by the variational formulation obtained by the Laplace bidimensional equation in rectangular coordinates at boundary conditions, Newman's type. The finite element method (FEM) was used to solve the numerical system. Compact support functions were used to simulate inert electrodes under an external current, this support was equal to the electrodes diameter. The validation of the model was corroborated when the results obtained by modeling were very similar to those given by experimentation. Three aspects of interest about cathodic protection were simulated; ? Electrodes distribution in the system. ? Low conductivity irregularities in the electrolyte. ? Different resistivities in the electrolyte.     

C276合金板多层多道焊的静态单元法有限元分析

基于有限元理论的静态单元法,在收敛的情况下通过设置适当的静态单元参数,可以兼顾模拟的精度和效率. 文中在母材中间截面上取三个点,分析了这些点在不同静态单元参数下的最高温度、焊接过程中的应力和最大残余应力. 结果表明,越远离焊缝,静态单元参数对于以上几个参量的影响越大. 当静态单元参数为10-5和10-4时,模拟的结果相对稳定;当静态单元参数为10-3时,模拟的结果与前两个参数模拟出来的值差距较大;当静态单元参数为10-1和1时,差距尤为显著. 同时,软件模拟过程中所需的时间也随静态单元参数的减小而增长.     

Rigid-plastic finite element analysis of plastic deformation of porous metal sheets containing internal void defects

Using rigid-plastic finite element DEFORM-2D and -3D software, this study simulates the plastic deformation of metal sheets at the roll gap during the sheet rolling process. The study focuses specifically upon the deformation of porous metal sheets containing internal void defects. The present numerical analysis investigates the relative density distributions, the void closure behavior, the deformation mechanisms and the stress–strain distributions around the internal voids for various rolling conditions. The influences on the dimensions of the final void of the thickness reduction, the initial internal void dimensions, the friction factors and the relative density are systematically discussed. The critical rolling conditions also investigated. A series of sheet rolling experiments are performed in order to verify the validity of the simulation results. The current numerical results provide a valuable source of reference for the design of pass schedules for porous metals undergoing rolling processes.     

采用热弹塑性有限元方法预测低碳钢钢管焊接变形

用有限元分析软件ABAQUS Code开发了用于模拟焊接温度场、焊接残余应力和焊接变形的热弹塑性有限元计算方法.通过建立三维有限元模型,预测了低碳钢钢管多层焊接时的温度场和焊接变形,并通过试验验证了所提出计算方法的精度和有效性.结果表明,在多层焊接条件下,采用有限元方法计算得到的焊接变形与试验结果十分吻合.     

环件轧制过程的显式有限元模拟分析

用于金属成形模拟的有限元方程的求解方法 ,主要有隐式和显式积分两种方法。对于复杂的三维变形分析 ,如环件轧制 ,隐式方法需要很长的运行时间。而利用显式方法 ,可以达到很好的效果。本文利用Abaqus /Ex plicit通用有限元程序对径向环轧进行了模拟。     

4m斜刃剪切机机架有限元分析

用有限元法对４ｍ斜刃剪切机机架强度进行了分析,为剪切机机架的改造提供了理论依据。     

Die land optimization of section extrusion by finite element method

1　ＩＮＴＲＯＤＵＣＴＩＯＮＩｎｔｈｅｅｘｔｒｕｓｉｏｎｏｆｓｅｃｔｉｏｎｓｗｉｔｈｆｌａｔ ｆａｃｅｄｄｉｅｓ ,ａｓｔｈｅｓｅｒｉｏｕｓｆｒｉｃｔｉｏｎｏｎｔｈｅｍａｔｅｒｉａｌ/ｔｏｏｌｉｎｔｅｒｆａｃｅａｎｄｔｈｅｂｉｇｄｉｆｆｅｒｅｎｃｅｉｎｇｅｏｍｅｔｒｙｂｅｔｗｅｅｎｔｈｅｅｘ ｔｒｕｄｅｄｓｅｃｔｉｏｎａｎｄｔｈｅｂｉｌｌｅｔ ,ｎｏｎ ｕｎｉｆｏｒｍｍｅｔａｌｆｌｏｗｏｃｃｕｒｓｉｎｔｈｅｄｅｆｏｒｍａｔｉｏｎｚｏｎｅ .Ｔｈｉｓｍａｙｒｅｓｕｌｔ,ｄｅ ｐｅｎｄｉｎｇｏｎｔｈｅｃｏｍｐｌ…     

Cup-drawing formation of steel sheet with nickel coating by finite element method

The finite element method （FEM） simulation of deep-drawing of steel sheet with nickel coating based on the solid element and dynamic explicit method was reported. Penalty function method was used to treat the contact algorithm. The friction between the punch and coating sheet was based on a Coulomb formulation. The combination of coating and substrate was defined as tied with failure contact. The results of the simulation illustrate that the steel sheet and the nickel coating do not delaminate at the interface. The stress field of the nickel coating is more complicated thala that of the steel substrate. Furthermore, it is found that the punch-nose radius is the most unsubstantial part for the intensity of the entire deep-drawing part and the thinnest part, it is a dangerous zone for the break. At this zone, the thickness thinning of the steel sheet and the nickel coating are up to 4.8% and 6.7%, respectively. Meanwhile, it is found that the curve of the variable blankholder force （VBHF） designed can improve the formability of sheet.     

Simulation of vertical-horizontal rolling process during width reduction by full three-dimensional rigid-plastic finite element method

Vertical-horizontal (V-H) rolling is an important process during width reduction in the roughing stand of hot strip mill. A simulation of steady-state V-H rolling was carried out by the full three-dimensional rigid-plastic finite element method (3D RPFEM). To consider the shear work rate and cope with a singular point, an extremely thin array of elements was attached before the entry of the roll. The slab shape, the spread, the separating force, and the rolling torque calculated were in good agreement with the experimental values.     

有限元分析和粒子法在搅拌摩擦焊中的应用

国内外学者建立了大量模型来对搅拌摩擦焊过程进行分析。目前最常用的分析方法是基于网格的有限元分析。由于有限元分析采用欧拉方法,在处理方程中的平流项过程中可能会导致数值错误。而在基于拉格朗日的粒子法中,平流项可以直接忽略,从而粒子法能解决有限元无法解决的难题。综述有限分析方法和粒子法在搅拌摩擦焊中的应用及研究现状。     

高强度涂层结合性能的试验研究及有限元分析

采用线切割沿涂层/基体界面切成对称切口,两边粘结后直接拉伸的试验方法对高强涂层抗拉结合强度进行评价.并借助有限单元法对涂层/基体交界面上的应力分布及切口附近的应力集中进行了分析,为正确评价涂层/基体的结合强度提供了理论依据.按此方法对不同工艺参数的热喷涂烧结涂层结合强度进行了评价.结果表明,此方法可对高强涂层与基体的结合强度进行评价.     

Investigation on ductile fracture in fine-blanking process by finite element method

In order to continuously analyze the whole fine-blanking process.from the geginning of the operation up to the total rupture of the sheet-metal,without computational divergence, a 3-D rigid visco-plastic finite-element method based on Gurson void model was developed.The void volume fraction was introduced into the finite element method to document the ductile fracture of the sheet-metal.A formulation of variation of the rigid visco-plastic material was presented according to the virtual work theory in which both the effects of equivalent stress and hydrostatic pressure in the deformation process were considered.The crack initiation of the sheet was predicted and the crack propagation was geometrically fulfilled in the simulation by separating the nodes according to the stress state.Furthermore.the influences of different state-variables on the deformation process were also studied.     

基于自适应有限元相场模型模拟强制流动条件下的枝晶生长(英文)

应用投影算法与相场法相结合的数学模型,采用基于非均匀网格的自适应有限元法求解该模型,并对强制流动作用下镍过冷熔体中枝晶生长行为进行模拟。模拟结果表明,强迫对流的引入导致枝晶生长的不对称性。当流速小于临界值时,流动对枝晶的不对称生长影响较小;当流速达到或超过临界值时,枝晶生长的控制因素逐渐从热扩散过渡到对流。随着流速的增大,流动法向的一次枝晶臂朝逆流方向倾斜角度增大。而枝晶生长对熔体流动具有明显的影响。随着枝晶尺寸的增大,在顺流区域产生涡流效应,涡流区逐渐扩大并在枝晶尖端出现重熔现象。此外,非均匀网格的自适应有限元方法的CPU耗费时间比均匀网格方法降低一个数量级,并且加速比与计算域尺寸成正比。     

极薄带轧制过程的晶体塑性有限元分析

极薄带轧制过程中,当轧件厚度降低到与晶粒尺寸同一量级时,其变形在很大程度上受到晶粒形态和取向等内部组织状态的影响,传统塑性理论不能直接用于微观塑性成形的分析。介绍了采用晶体塑性有限元方法对极薄带轧制过程所做的研究,如轧件厚度和晶粒尺寸对轧制变形的影响、塑性变形时滑移系的激活和运动等。     

Three-dimensional analysis of elastic stress distribution of indented ceramic surface by finite element method

The three-dimensional stress distributions in the area surrounding indentation pattern for three different materials, Al2O3, Si3N4 and SiC were analyzed by finite element method（FEM）. Those theoretical results were also compared with the experimental ones by Rockwell hardness test. The effect of loading stress on the plastic deformation in specimens, surface was investigated on the assumption of shear strain energy theory by Huber-Mises when the materials were indented. The distributions of nomal stress, shear stress, and Mises stress were analysed with variations of loading conditions. It is clear that the analytical results for the stress distributions, the crack length and its density of probability are in good agreement with the experimental results.     

液压机结构设计的有限元法

采用有限元方法对液压机中的主液压缸、横梁和立柱进行结构设计。得到了详细的应 力、应变分布云图及应力集中和最大变形的位置。根据分析结果,优化设计方案,并重新进行数值模 拟,使设计达到要求。