弹塑性有限元法在非轴对称挤压变形研究中的应用

本文对用弹塑性有限元法研究三维非轴对称零件的挤压变形问题作了探讨。开发研制了三维弹塑性有限元程序,并利用该程序对所选典型件在挤压变形时的应力、应变分布及金属流动等进行了理论计算,计算结果表明该程序具有实用价值。     

铝合金铸件凝固过程热应力数值模拟

通过铝硅合金准固态力学行为和流变性能的测试，获得了该合金铸件凝固过程应力应变本构方程。并在此基础上开发了考虑材料高温力学性能，分析三维轴对称铸件凝固过程热粘弹塑性问题的热应力模拟程序，对带热节铝硅合金铸伯的计算表明，计算结果与实验吻合较好。     

铝合金铸件凝固过程效应力数值模拟

通过铝硅合金准固态力学行为和流变性能的测试，获得了该合金铸件凝固过程应力应变本构方程。并在此基础上开发了考虑材料高温力学性能，分析三维轴对称铸件凝固过程热粘弹塑性问题的热应力模拟程序，对带热节铝硅合金铸件的计算表明，计算结果与实验结果吻合较好。     

铝合金点焊预压接触分析

利用有限元弹塑性接触理论,建立二维轴对称弹塑性有限元模型,对铝合金点焊预压过程的力学特征进行分析,得出了锥台形电板和球面形电极条件下,工件与工件之间和电极与工件之间的接触压力分布及工件变形状况,为后续的电场分析及热场分析打下了基础.     

数值计算模拟工艺参数对管道环焊缝残余应力的影响

以热——弹塑性理论为基础,建立了厚壁管环焊缝残余应力的二维轴对称有限元模型,利用ANSYS有限元程序分析了三种焊接工艺参数对管道环焊缝残余应力的影响,计算中考虑了材料热物理性能参数和力学性能参数的温度相关性.结果表明,管道内表面焊缝和近缝区的轴向和环向残余应力均为拉应力,而管道外表面焊缝和近缝区的轴向残余应力和环向残余应力均为压应力;接头内表面应力水平高于外表面;残余应力的最大值均位于距管道外表面一定距离处,其数值接近于材料的屈服应力;随着焊接热输入的增加,残余应力峰值变化不大,塑性变形区宽度增加.     

钛合金WSS图中的应力应变循环

焊接热弹塑性应力应变过程全图从宏观上描画了焊接热弹塑性应力应变过程,全图中每一区域内应力应变关系是该图的重要组成部分.取钛合金薄板上距焊缝中心不同距离的点来定量分析各自的焊接热弹塑性应力应变关系,以此给出焊接过程中任一时刻试件上某一点的应力应变状态.在此基础上,给出焊接热弹塑性应力应变过程全图任一区域中点的应力应变关系,定量描述该图,使得对全图的理解更加完整.结果表明,钛合金焊接热弹塑性应力应变过程全图中各区域的纵向应力应变循环曲线不同,在冷却过程中钛合金焊缝和近缝区处于卸载状态.     

12CrMo钢F+M双相组织对两相内应力应变分布影响的有限元分析

本文用弹塑性大应变轴对称有限元程序,较详细地分析了12CrMo钢F+M双相组织的显微结构(马氏体体积分数,尺寸,基体相)变化时两相内局部及平均应力应变分布形态,特别是对两相材料微观断裂机制有重要作用的水静应力和最大剪应力的分布与变化.由计算的应力应变分布形态所展示的亚微观断裂性质与实验观察相符.     

INFLUENCE OF FERRITE-MARTENSITE MICROSTRUCTURE ON STRESS AND STRAIN DISTRIBUTIONS IN TWO PHASES FOR 12CrMo STEEL ANALYSED WITH FINITE ELEMENT METHOD

本文用弹塑性大应变轴对称有限元程序,较详细地分析了12CrMo钢F+M双相组织的显微结构(马氏体体积分数,尺寸,基体相)变化时两相内局部及平均应力应变分布形态,特别是对两相材料微观断裂机制有重要作用的水静应力和最大剪应力的分布与变化.由计算的应力应变分布形态所展示的亚微观断裂性质与实验观察相符.     

基于Visual-Weld的汽车钢圈焊接残余应力数值模拟

焊接残余应力是影响钢圈尺寸稳定性的重要因素。本文运用焊接有限元分析软件Visual-Weld,通过建立轴对称的非线性热弹塑性计算模型,对某型号汽车钢圈进行了焊接残余应力数值模拟,获得了焊接温度场及焊接残余应力的分布规律,并利用X-350A射线残余应力测定仪对钢圈试验件进行焊接残余应力检测。结果表明,数值计算值与实测结果基本吻合,从而验证了有限元分析模型的准确性,为后续的模型改进及优化焊接工艺提供了理论依据和参考。     

带材拉伸弯曲矫直变形仿真模型的建立

分别在理想弹塑性平面应变假设和线性强化弹塑性平面应变假设条件下,考虑任意初始板形缺陷(初始残余应力)的影响,推导出不同应力分布型式的中性层偏移量以及中间层纵向应变的计算公式,分析其应力分布的边界条件。建立了拉伸弯曲矫直过程的仿真模型,对仿真结果分析表明,该仿真模型符合生产实际。     

A finite element analysis of residual stresses in stretch turning

An analytical method has been proposed in this paper to determine the residual stresses in stretch turning. This is done using the thermal elasto-plastic finite element method to determine the transient temperature distribution, followed by thermal elasto-plastic stress analysis. An attempt to explain the mechanism of stretch turning is made, and the effects of stretch level on residual stresses are also discussed.     

An advanced model of designing controlled strain rate dies for axisymmetric extrusion

This paper presents an advanced model for the design of stream-lined axisymmetric extrusion dies based on a prescribed strain rate variation. This is vital to the preparation of the workpieces with mechanical properties that are very sensitive to the strain rate distribution during a manufacturing process. The proposed model, which incorporates Tresca’s yield criterion and velocity field with the die angularity, can give an accurate prediction of the die shape. Influences of the interfacial friction and the ram velocity on the die geometry are also studied. As a verification of the proposed model, an updated Lagrangian formulated, elasto-plastic finite element program was developed to analyze the axisymmetric extrusion process. A clear derivation of the load-correction matrix, which is in dispensable for the surface traction rate equilibrium in the updated Lagrangian formulation, is described for the application of the finite element simulation. A friction-correction matrix based on a constant shear law is used to solve the interfacial friction. From the comparison of the resultant strain rate distribution, it verifies that the advanced model can determine the surface angularity and friction force in the extrusion process.     

短纤维增强金属基复合材料拉伸变形的屈服行为的理论研究

运用空间轴对称弹塑性有限元方法的混合律模型,推导出应力应变分配系数的解析表达式。并由此提出了一种新的定义复合材料比例极限和屈服强度的方法,进而研究了材料参数（纤维长径比、纤维体积分数、纤维根间距和基体应变硬化指数）对短纤维金属基复合材料拉伸变形行为的影响。     

GTAW电弧温度场与流场数值模拟

基于自由燃烧的钨极氩弧焊电弧建立了二维稳态的轴对称模型，研究了电弧的传热和流体流动，计算了电弧温度场和速度场的分布。方程的求解采用以SAMPLE算法为基础编写的通用热流计算软件——PHOENICS(Parabolic hyperbolic or elliptic numerical integration codes series)斟算的条件为电弧电流200A，弧长10mm，氩气作保护气体。计算得到的电弧温度、流体速度和电势分布与文献报导的测量结果吻合良好。     

颗粒增强金属基复合材料的屈服行为

运用空间轴对称弹塑性有限元方法和混合律模型，给出了应力应变分配系数与复合材料的弹性模量，屈服强度以及切线模量之间的定量关系式，并由此提出了一种新的定义颗粒增强金属基复合材料比例极限和屈服行为的方法，进而研究了颗粒形状（球体，正圆柱体以及椭球体）和材料结构参数（颗粒体积分数和颗粒根间距）对颗粒增强金属基复合材料拉伸变形行为的影响。研究表明，通过研究应力应变分析系数及其二阶导数来确定复合材料屈服行为的方法不仅适用于短纤维增强金属基复合材料，而且也适用于颗粒增强金属基复合材料。该方法可以较好地反映出颗粒形状和材料结构参数对复合材料屈服行为的影响，预测的比例极限与已发表的实验结果吻合较好。     

NUMERICAL SIMULATION ON RING COMPRESSION──A New Approch to Determine Calibration Curves of Friction Coefficient

本文采用大变形弹塑性有限元理论，八节点四边形单元，准确的摩擦边界处理技术和反映材料在热加工过程中真实应力－应变的本构关系曲线，用ＡＮＳＹＳ５．１软件对尺寸为外径：内径：高度＝６：３：２的圆环在不同摩擦系数条件下的镦粗过程进行了数值模拟研究，并根据模拟结果绘制了金属热加工成形过程中测量摩擦系数的理论标定曲线，该曲线比经典方法的结果具有更高的精度。     

Large deformation finite element analysis of strain localization in fine-blanking process

In this study, an updated Lagrangian large deformation finite element method is developed for solving the metal forming problems with an incrementally objective mid-interval integration algorithm. A numerical simulation of fine-blanking process is hence performed to predicate the strain localization and to investigate the failure mechanism of fine-blanking process. Using the numerical result, The stress and strain fields developed in the fine-blanking process as well as the large deformation elasto-plastic finite element implementation for solving axisymmetric strain localization problems are discussed.     

筒形件正旋时位移分布规律的研究

本文根据弹塑性有限元模拟结果，给出了正旋时旋压件不同截面上的位移分布，其结果反映了正旋时的金属变形流动特点，该研究为实际生产中控制旋压件尺寸精度，提高产品质量提供了理论依据。     

Numerical modeling and simulation of metal powder compaction of balancer

1 Introduction “Cold” compaction, which is operated at room temperature, is currently the most generally used compacting method in powder metallurgy industry. Under this circumstance, metal powder is often considered a kind of time-independent, elasto-…     

A verification of the thermal stress analysis,including the furan sand mold,used to predict the thermal stress in castings

The restraint exerted on a casting by a furan sand mold on the casting and the contraction of the casting during cooling was dynamically and simultaneously measured using a device that we developed. The measurements were compared during cooling with thermal stress analyses. The thermal stress analyses were based on the representative mechanical models for the furan sand mold, i.e., the elastic and elasto-plastic models used in previous studies. The comparison demonstrated that the elasto-plastic model simulates the restraint force more accurately than the elastic model. In the thermal stress analysis, it was important to describe the development of inelastic deformation and the fracture of the sand mold. However, the simulated restraint force was still twice as large as the measured force even in the elasto-plastic model. This error is most likely attributable to using the temperature-independent mechanical properties of the furan sand mold and the mechanical model of the casting alloy, which neglected the viscoplasticity at high temperature in the thermal stress analysis.