无网格伽辽金方法在钢筋混凝土梁开裂问题中的应用分析

在固体力学计算过程中,混凝土裂缝处理一直是一个非常关键的问题。无网格方法在处理混凝土裂缝时,无需单元网格,因此非常易用。本文将混凝土裂缝处理分为宏观裂缝和微观裂缝两个方面,在处理宏观裂缝时,引入了无网格伽辽金方法,其调整节点分布时具有非常方便的特点,可以通过增加裂缝面的边界和裂缝节点的方法处理混凝土裂缝;在处理微观裂缝时,采用的方法依然是传统的弥散裂缝模型。     

基于无网格法的反向器拓扑优化设计及性能测试

为了满足柔性机构的大变形特性,该文将无网格伽辽金法和拓扑优化理论相结合,提出了反向器的拓扑优化设计方法,并对按设计结果加工的机构进行了性能测试。在优化过程中,利用无网格法进行反向器的结构响应分析和敏度分析,从本质上满足了柔性反向器的非线性要求。根据设计结果制造了线性和非线性两种反向器,并对其进行了性能测试,测试结果表明,基于非线性无网格法的优化方法优于基于线性的优化方法。     

波纹夹层板线性弯曲分析的无网格伽辽金法

提出了一种求解波纹夹层板结构线性弯曲问题的无网格模型。将波纹夹层板看成两侧平板和中间波纹板核的复合结构,用正交各向异性板等效近似波纹板核。先基于一阶剪切变形理论,由无网格伽辽金法建立各板的刚度方程,再通过位移协调条件将各板刚度方程叠加,以得到整体刚度方程。采用全转换法处理位移边界。算例表明：该文所提出的无网格模型分析波...     

热锻件晶粒变化的预测

开发了金属成型的热力耦合刚粘塑性有模拟系统，具有塑性变形和传热过程的耦合分析及模拟热锻变后工件内部微观组织变化的功能。     

面向叶片精锻过程的三维有限元模拟

对刚粘塑性有限元用于模拟分析叶片精锻过程的基本原理进行了论述 ;对模拟中需解决的关键问题提出了相应的算法和处理技术 ;开发了考虑工模具间的摩擦的三维刚粘塑性有限元模拟分析系统 .采用该系统 ,对航空发动机压气机简单叶片和带阻尼台叶片精锻过程进行了三维有限元模拟分析 .模拟过程中对榫头和叶身过渡处采用圆角连接 ,改善了金属的流动性和充填性 ,使叶片锻造三维有限元模拟的建模与分析更接近于实际过程 .结果表明 :采用作者所提出的基于边界构形的网格重划方法 -内缩法 ,进行畸变网格的重划是可行的 ;采用作者所提出的动态边界条件的处理方法以避免模具死锁问题是有效的 ;所开发的软件系统是可靠的 .     

用无单元伽辽金法求解几何非线性问题

用无单元伽辽金法(EFGM)求解了几何非线性问题。无单元伽辽金法采用移动最小二乘函数近似试函数,并用罚函数法施加本质(位移)边界条件,是一种与单元划分无关的无网格方法。在求解几何非线性问题时,采用了增量和修正的Newton-Raphson迭代分析的方法,并在整个分析过程中所有变量的表达格式都采用全拉格朗日格式。算例表明:EFGM在求解几何非线性问题时仍具有很好的精度。     

改进EFG法用于旋转梁的刚柔耦合动力学研究

采用全域插值广义移动最小二乘(IGMLS)的改进无网格伽辽金(EFG)法,对旋转中心刚体-柔性梁系统的刚柔耦合动力学特性进行研究。利用考虑了柔性梁横向变形引起的非线性耦合项的一次近似耦合模型,根据Hamilton原理和EFG离散方法得到刚柔耦合系统的无网格动力学离散方程。在大范围运动未知的情况下,采用数值方法对刚柔耦合系统进行动力响应的仿真计算,并对EFG法的主要影响因素进行了讨论分析。通过与有限元法的数值计算结果对比,验证EFG法用于刚柔耦合系统动力学研究的有效性及可行性,并为无网格法用于更复杂的柔性多体动力学的研究提供了理论依据。     

无网格伽辽金法求解轴对称问题

将无网格技术用于求解轴对称问题,通过加权余量法导出了无网格伽辽金法计算公式,考虑了不同介质的影响,编制了相应的计算程序,并对钢筋对混凝土管性能的影响进行了弹性和粘弹性的计算分析,与其它解相比,得到令人满意的数值结果.在粘弹性问题求解过程中,采用一种时间域自适应精细算法,给出了的径向位移与环向应力误差收敛速率曲线.     

基于随机无网格伽辽金法和蚂蚁算法的结构可靠性分析

 用摄动随机无网格伽辽金法(PSEFGM)求解随机结构的响应,然后采用蚂蚁算法对结构可靠性进行了分析。摄动随机无网格伽辽金法具有不需要划分单元和精度高等特点。蚂蚁算法是一种智能型随机搜素优化算法,对目标函数没有任何可微甚至连续的要求,可有效克服经典算法易于陷入局部最优解的常见弊病。数值实例表明,在随机结构可靠性分析方面,随机无网格迦辽金法与蚂蚁算法比经典算法具有明显的优势。     

无网格彼得洛夫伽辽金法在大变形问题中的应用

将无网格局部彼得洛夫伽辽金(MLPG)法推广应用于大变形问题。导出了非线性局部子域对称弱形式,通过对该弱形式进行线性化得到了用于非线性计算的MLPG格式,并对MLPG的计算速度进行了优化,使MLPG成为一种复杂度为O(N)的算法。几何非线性和几何与材料双重非线性的数值算例表明,相对有限元方法,MLPG在处理此类大变形问题时收敛性好,精度高,并能减小有限元分析中易遇到的网格畸变带来的困难。     

Development of severe plastic deformation by various asymmetric rolling processes

Rolling is the most appropriate process to produce a severe plastic deformation in the sheet or plate type of materials. Compared to symmetric rolling, asymmetric rolling is more efficient in producing plastic deformation since it develops additional shear strain for a given reduction in thickness. In the present investigation, various asymmetric rolling processes were analyzed by the rigid-viscoplastic finite element method. The results of the analyses were compared to each other in terms of plastic deformation: effects of asymmetries due to the differences in size, rotational speed and frictional condition between upper and lower rolls. Rolling pressure distribution, rolling force and rolling torque were also compared.     

空洞敏感型超塑材料充模胀形的有限元模拟

本文采用大变形刚粘塑性有限元模拟，研究了空洞敏感型超塑材料的充模胀形过程，模具为轴对称任意倾角锥形模。采用轴对称薄膜环单元，由修正的Ｌａｇｒａｎｇｅ法建立包含摩擦项的泛函并在此基础上形成有限元列式。通过对基体厚度耦合迭代和由修正的Ｇｕｒｓｏｎ方程导出的空洞长大模型来计算空洞发展。     

Metal flow behaviour of wide flat bar in the spreading extrusion process

Abstract

To examine metal flow behaviour experimentally in the spreading extrusion process, a round billet is spread by means of a spread ring and extruded through a die opening wider than the internal diameter of the container. In spreading extrusion, the extrusion load is reduced by about 30% in comparison with basic extrusion. However, the metal flow balance in spreading extrusion worsens, because of the high frictional force generated at the interface of the billet and spread ring during the filling process. When the profile is wide or when spread ring height is low, the geometry of the plastic deformation zone on the die face changes from an ellipse into a figure of eight at the wide zone at both ends of the die opening. As a result, the metal flow balance markedly worsens, due to an increase in the size of the plastic deformation zone and frictional resistance acting on the spread ring wall.     

双金属复合材料固相结合数值仿真研究

基于大变形弹塑性有限元理论,采用ANSYS有限元程序,通过建立合理的有限元分析模型,对Cu/Al双金属复合材料静液挤压固相结合的非稳态过程进行了数值模拟研究,得到了变形体在挤压过程中的等效应力、应变分布及相对滑动量随摩擦系数的变化情况,揭示了组元金属在静液挤压成形过程中的流动规律,指出在一定的变形量条件下,增大内外层金属之间的摩擦系数是较好实现内外层金属固相结合的主要方法.     

浅谈深筒锥形件温挤压成形工艺技术

采用温挤压加工7A04铝合金深筒锥形件替代原有棒料车制的加工方法,大幅度提高了原材料利用率。通过设计正挤压与反挤压相结合的复合挤压成形工艺。在1套模具、1次机床行程中实现2个或多个基本变形过程。使用有限元的计算方法对金属塑性成形过程进行模拟,大幅度地缩短产品研发周期,节约人力物力,为复杂形状有色金属异形零件的成形提供了指导。     

A continuum Lagrangian sensitivity analysis for metal forming processes with applications to die design problems

A continuum sensitivity analysis is presented for large inelastic deformations and metal forming processes. The formulation is based on the differentiation of the governing field equations of the direct problem and development of weak forms for the corresponding field sensitivity equations. Special attention is given to modelling of the sensitivity boundary conditions that result due to frictional contact between the die and the workpiece. The contact problem in the direct deformation analysis is modelled using an augmented Lagrangian formulation. To avoid issues of non‐differentiability of the contact conditions, appropriate regularizing assumptions are introduced for the calculation of the sensitivity of the contact tractions. The proposed analysis is used for the calculation of sensitivity fields with respect to various process parameters including the die surface. The accuracy and effectiveness of the proposed method are demonstrated with a number of representative example problems. In the die design applications, a Bézier representation of the die curve is introduced. The control points of the Bézier curve are used as the design parameters. Comparison of the computed sensitivity results with those obtained using the direct analysis for two nearby dies and a finite difference approximation indicate a very high accuracy of the proposed analysis. The method is applied to the design of extrusion dies that minimize the standard deviation of the material state in the final product or minimize the required extrusion force for a given reduction ratio. An open‐forging die is also designed which for a specified stroke and initial workpiece produces a final product of desired shape. Copyright © 2000 John Wiley & Sons, Ltd.     

Formability Limit in Containerless (Open Die) Extrusion of Commercial Purity Titanium Rods and Tubes

Containerless extrusion requires far less forces compared to conventional direct extrusion of rods and tubes due to the elimination of container wall-billet friction. But the strains that can be imparted are less in the former due to the unsupported billet which gets upset first if the axial stress exceeds yield stress of the billet material. If this stress is equal to yield stress, it corresponds to the limit of the process of pure containerless extrusion. It is found that this limit strain as predicted by theory is far less compared to what is observed experimentally. This discrepancy is explained on the basis of heating that takes place in the deformation zone due to ideal, frictional, and shear work done in carrying out the extrusion process.     

Simulation of liquid infiltration and semi-solid extrusion for composite tubes by quasi-coupling thermal-mechanical finite element method

As a new metal forming technology, the liquid infiltration and semi-solid extrusion process can produce various composite parts, such as tubes, bars, and shaped products, in a single process. In this paper, the liquid infiltration and semi-solid extrusion process for forming a composite tube is simulated by means of thermal rigid-plastic quasi-coupling FEM method. The key technologies such as the handling of liquid phase zone, the transition between liquid and solid phase zones, the grid re-meshing method and the establishment of the boundary condition have also been studied. Based on the FEM simulation software developed by the authors and the grid re-meshing technology, the distribution of stress field, strain field and deformation force in the liquid infiltration and semi-solid extrusion process for forming composite tubes are obtained. The deformation force simulation results accord with the experimental data, indicating the reliability of the system. Therefore, the present research is theoretically valuable in the product quality control and the process parameter choice.     

塑性加工法制备各向异性稀土永磁材料的研究进展

塑性加工是一种可制备各向异性材料并可实现近终形成形的方法,已有一系列尝试将其应用于制备高性能各向异性稀土永磁材料的研究报导.介绍了用于制备各向异性磁体或磁粉的塑性加工方法,包括热压、模压、轧制、正挤压、反挤压、等径角挤压等,和用各种塑性加工方法提高永磁材料性能的基本原理、效果,以及工业化应用进展.     

A finite element analysis of damage propagation during metal forming process

In this paper damage propagation during metal forming process is investigated with the concept of continuum damage mechanics. An isotropic damage model based on the theory of materials of type N is adopted to describe the damage process of a ductile material with large elasto-viscoplastic deformation. To solve the finite elasto-viscoplasticity problem, a reasonable kinematic strain measure for largely deformed solids is used and the damage constitutive equations based on thermodynamical framework are developed. The stiffness degradation of the loaded material is chosen as a damage measure. An extended interior penalty method is used to impose the contact condition on the boundary. The highly nonlinear equilibrium equations are reduced to the incremental weak form and approximated by the total Lagrangian finite element method. The displacement control method along with the modified Riks' continuation technique based on displacement parameter is used to solve the incremental iterative equations. As numerical examples, upsetting, backward extrusion and punch problems are simulated and the results of damage propagation and J₂ stress contours with and without damage are presented. For punch problems, spring back and residual stresses are also presented.