基于金属刚塑性/刚粘塑性不可压缩材料的无网格RKPM法

文章将刚塑性/刚粘塑性流动理论与再生核质点方法(RKPM)相结合,提出了基于刚塑性/刚粘塑性不可压缩材料的无网格RKPM法,进一步拓展了无网格RKPM法的应用范围。分别采用边界奇异权法和修正的罚函数法处理本质边界条件和体积不可压缩条件,推导了金属塑性成形过程无网格RKPM法数值模拟的刚度方程,给出了关键算法。对平面应变镦粗过程进行了数值模拟,并将模拟结果与刚塑性有限元体积成形商品化软件Deform 2D计算结果作了比较,二者吻合良好,表明了该文方法的正确性和有效性。     

ANALYSIS OF THREE-DIMENSIONAL UPSETTING PROCESS BY THE RIGID-PLASTIC REPRODUCING KERNEL PARTICLE METHOD

A meshless approach, called the rigid-plastic reproducing kernel particle method （RKPM）, is presented for three-dimensional （3D） bulk metal forming simulation. The approach is a combination of RKPM with the flow theory of 3D rigid-plastic mechanics. For the treatments of essential boundary conditions and incompressibility constraint, the boundary singular kernel method and the modified penalty method are utilized, respectively. The arc-tangential friction model is employed to treat the contact conditions. The compression of rectangular blocks, a typical 3D upsetting operation, is analyzed for different friction conditions and the numerical results are compared with those obtained using commercial rigid-plastic FEM （finite element method） software Deform^3D. As results show, when handling 3D plastic deformations, the proposed approach eliminates the need of expensive meshing and remeshing procedures which are unavoidable in conventional FEM and can provide results that are in good agreement with finite element predictions.     

基于耦合无网格-有限元法的金属成形过程数值模拟

建立刚塑性耦合无网格-有限元法,通过过渡单元将无网格区域与有限元区域相耦合。采用边界奇异核方法对EFG形函数进行修正,直接施加本质边界条件。采用修正的罚函数法约束体积不变条件,避免体积闭锁现象的产生。采用耦合方法分析了局部镦粗工艺,在变形剧烈的区域采用无网格节点,发挥其处理大变形问题的优势;在变形较小的区域采用有限元单元,充分利用其计算高效的特点。数值计算的结果表明,该耦合方法准确、有效。     

任意模具形状的金属三维体积成形过程刚塑性无网格RKPM分析方法

将无网格方法引入三维金属体积成形分析,在给出基于刚塑性流动理论的三维无网格再生核质点方法及其基本理论方程的基础上,为了提高分析系统的通用化和自动化,采用网格法来描述任意形状的三维模具型腔曲面,给出了三维无网格法数值模拟系统中动态接触边界自动处理的非线性接触算法,实现了任意模具形状的三维体积成形过程的无网格法数值模拟。对上模为半球形的三维立方体塑性变形过程进行了数值模拟,并与三维刚塑性有限元体积成形商品软件Deform3D的计算结果作了比较,验证了本文方法的正确性。     

A new energy method analysis of plastic distortion in plane strain compression

This paper describes the use of a realistic admissible velocity field for the analysis of plane strain compression of workpieces in the presence of boundary friction. The velocity field is derived from displacement functions written in the form of trigonometric series. The coefficients of terms in the series defining the velocity field are obtained from considerations of volume constancy and minimisation of the energy function. The method is applied to rigid-plastic materials deformed in non-steady-states between flat rigid tools with an assumed friction factor m at the interfaces. Both loads and distortion at free surfaces are analysed, for various forging conditions. This analytical approach appears to have application to a range of non-steady-state or steady-state processes in which non-uniform deformation results in bulged free surfaces.     

Prediction of the forming limit curves of sheet materials using the rigid-plastic finite element method

An incremental rigid-plastic finite element method is used to predict the forming limit curves (FLCs) of sheet materials. In this analysis, the deforming sheet materials is assumed to obey Hill's anisotropic yield criterion and its associated flow rule. To obtain the critical strain paths in both the positive and negative minor strain regions, simulations are performed using hemispherical punch stretching of a circular blank with various circular cutoffs and various friction conditions at the tool-sheet interface. A critical slope condition derived from the computed load-displacement curve is employed as a criterion to determine the limiting major and minor strains. FLCs of several sheet materials are predicted and the results are compared with the existing experimental data.     

轴对称拉深件多步反向模拟方法研究

针对轴对称拉深件多步反向模拟问题,以理想成形理论为基础,采用直线和圆弧作为基本线素,根据母线对于轴对称拉深件、中问过渡形状以及毛坯进行描述,建立供节点移动的滑移线。根据零件的轴对称性质,采用对数应变以及R.Hill48厚向异性屈服准则对径向、周向、厚向应变以及等效应变进行描述,在此基础上,构建了以初始构形上的节点坐标为基本未知量的有限元方程。通过求解上述有限元方程得到了满足理想成形条件的节点坐标,以及应变分布规律。通过实际应用,该算法简单易行,计算效率高。     

Simulation of bulk metal forming processes using one-step finite element approach based on deformation theory of plasticity

The bulk metal forming processes were simulated by using a one-step finite element(FE)approach based on deformation theory of plasticity,which enables rapid prediction of final workpiece configurations and stress/strain distributions.This approach was implemented to minimize the approximated plastic potential energy derived from the total plastic work and the equivalent external work in static equilibrium,for incompressibly rigid-plastic materials,by FE calculation based on the extremum work principle.The o...     

等径角挤压工艺的无网格数值模拟研究

等径角挤压(Equal Channel Angular Pressing,ECAP)工艺,是一种通过材料的剧烈塑性变形,获得大块超细晶材料的有效方法。采用无网格伽辽金法对等径角挤压工艺进行了数值模拟研究,分析了挤压过程中材料的流动规律,研究了模具圆心角、挤压件与模具间的摩擦状况对ECAP挤压效果的影响。随着模具圆心角的减小,挤压件的等效应变增大并且变得更加均匀,但是模具圆心角越小,挤压载荷越大,严重影响模具的使用寿命;摩擦状况对挤压件的等效应变的影响较小,对挤压载荷影响显著。无网格模拟分析结果与实验结果吻合良好。     

变形热对齿轮冷锻精度影响的数值模拟研究

在有、无变形热产生的条件下,采用刚塑性热力耦合有限元法,对冷精锻直齿圆柱齿轮成形过程进行了模拟,并且完成了直齿轮冷锻模具弹性变形和工件弹性回复的模拟。由模拟结果可知:变形热的产生及热量传导能对齿轮精度产生很大的影响;由于在不同温度下材料的膨胀系数以及弹性模量不同,在有变形热的条件下,成形力有所降低,模具弹性变形和工件弹性回复量增大。     

稳态挤压过程刚塑性无网格伽辽金方法分析

采用刚塑性材料假设,建立了刚塑性无网格伽辽金方法。利用变换法施加本质边界条件;采用反正切摩擦模型描述摩擦力边界,在局部坐标系下施加摩擦力边界条件;采用Newton-Raphson迭代方法求解刚度方程。对于挤压过程而言,当高径比较大时,可被近似为稳态流动。由于口模内速度变化梯度较大,采用最小二乘近似节点控制方法来控制近似效果。根据建立的刚塑性无网格伽辽金方法对正向、反向和复合挤压过程等进行了稳态分析,并与刚塑性有限元软件Deform模拟结果进行了相应的比较,验证了无网格伽辽金方法分析结果的正确性。     

液晶高分子材料PolyesterX7G黏滞系数数值计算方法研究

热致性液晶高分子材料以其优异性能被视为微注塑行业的首选材料,应用广泛,但薄弱的研究基础跟不上应用的需求。针对热致性高分子液晶材料黏滞系数实验获取困难的问题,提出两种数值求解Leslie黏滞系数的方法,理论基础分别为Maier-Saupe理论与Doi-Edwards理论。对典型热致性液晶材料Polyester X7G的微注塑过程进行了数值模拟,并将两种求解黏滞系数的方法嵌入模拟过程。通过与实验结果的对比发现,基于Maier-Saupe理论的黏滞系数求解方法结果更加准确,与实验结果吻合度更高。文中的研究结论丰富了热致性液晶高分子材料的基础研究成果,并为该材料在微注塑行业的更广泛应用提供了参考。     

塑性力学镦粗工艺理论与技术的研究进展

在镦粗工艺理论方面 ,提出了圆柱体平板间镦粗时的刚塑性力学模型的拉应力理论和静水应力力学模型的切应力理论 ,并经定性物理模拟、光塑试验及数值模拟证明 ;设计了锥形板镦粗的新工艺 ;提出了广义滑移线法 ,将经典滑移线理论拓展到能求解所有二维问题和轴对称塑性变形问题 ;发展了主应力法 ,提出了力学分块法。     

分流模结构对连续挤压扩展成形的影响

连续挤压扩展成形是一种先进的铜母线制造方法,而分流模结构是影响成形的重要因素。根据连续挤压扩展成形特点,建立了基于DEFORM-3D刚塑性有限元模型,通过对铜母线连续挤压过程的数值模拟,分析了不同分流模结构下的金属流动规律、流速均方差。结果表明,分流模结构为无过渡面梯形时,金属流动速度差最小,流速均方差为3.11,变形最均匀。通过试验研究验证了数值模拟结果,为连续挤压扩展成形模具优化设计提供了重要的理论指导。     

板带轧制过程的三维耦合有限元分析

对板带轧制过程进行严密的三维分析是研究轧制参数对轧后板带尺寸、板形和机械性能的影响 ,从而实施有效控制的基础。本文简要回顾了板带轧制过程三维数值模拟的研究进展 ,提出了一个分析板带轧制过程的耦合有限元模型 ,其中 ,轧件塑性变形采用刚塑性有限元法计算 ,辊系弹性变形采用弹性有限元法计算。计算实践表明 ,该模型具有良好的精度和较高的效率。     

Rigid-plastic boundaries approach to the analysis of arbitrary profile dies in axisymmetric extrusion

A new theoretical model to analyze arbitrary profiles of extrusion dies is proposed in this paper. In this model, generalized rigid-plastic boundaries with optional variables are used to minimize the power by the upper-bound method. To satisfy the velocity boundary conditions at the entrance and exit, the streamline function is designed in the normal form of r(η, z), which satisfies the flow conditions and the rigid-plastic boundaries. Four sets of profile dies (cosine, elliptic, hyperbolic, and conic) are represented with different slopes at the entrance and exit in order to illustrate this method. Experiments were conducted in order to compare the results with those of the theoretical model. It was found that the predicted load and flow patterns were in agreement with the experimental observation and the results from the literature.     

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.     

利用数学规划的刚塑性成形有限元仿真方法研究

本文建立了金属刚塑性成形问题的数学规划有限元求解模型 ,将体积不变、边界接触条件和体积不变条件处理为数学规划的约束条件。通过构造迭代算法 ,将变形体分为刚性区域和塑性区域 ,并利用罚函数法消去刚性区约束条件 ,把非线性规划问题归结为求解一系列的二次规划问题。以铅柱镦粗作为仿真计算实例来验证算法的有效性。     

汽车用镁合金零件的成形工艺模拟分析

以刚塑性有限元分析为基础,对镁合金零件的挤压成形工艺进行了模拟分析,从模拟中找出挤压成形时模具的最佳尺寸及最佳摩擦系数和最佳变形温度、变形速度,为现实生产提供了有利的依据。     

阻流环及模具结构对大扩展比连续挤压成形的影响

大扩展比连续挤压是制造铜带的一种新技术,阻流环及模具结构是影响扩展成形的重要因素。根据大扩展比连续挤压扩展成形特点,建立基于DEFORM-3D刚塑性有限元模型,通过对铜带连续挤压过程的数值模拟,分析不同阻流环及模具结构下的金属流动规律、流速均方差。实验与数值模拟结果均表明,使用有促流角的圆鼓形阻流环及变定径带模具时,金属流动速度差最小;流速均方差为0.58时,变形最均匀。为连续挤压成形模具优化设计提供了重要的依据。