板材成形模拟的研究和应用

介绍了板材成形数值模拟技术的研究和应用在国内外发展的概况,并从基本算法、单元模型和网格划分、材料模型、接触摩擦、起皱问题、破裂问题和回弹计算等方面介绍了弹塑性有限元的基本原理、关键技术和主要难点,结合在工厂实际生产中的使用情况和存在的问题,展望了板材数值模拟技术今后的发展方向.     

不锈钢棒材无模成形温度场有限元模拟

采用有限元法对不锈钢棒材无模成形温度场进行了研究,并利用有限元分析软件对其进行了模拟,该模拟结果很好地反映了拉伸件在整个变形过程中的温度分布规律,为无模成形的进一步研究提供了可靠的依据.     

PEMFC金属双极板冲压成形数值模拟与实验

目的 研究金属双极板冲压成形过程中各工艺参数和模具结构参数对成形质量的影响。方法 采用Dynaform有限元分析软件对SS304双通道蛇形流道双极板冲压成形过程进行模拟。研究模具圆角半径、模具锥度、压边力、拉延筋等因素对双极板成形质量的影响。结果 增加模具圆角半径和模具锥度可防止双极板破裂。适当增大压边力能有效消除起皱缺陷,设置拉延筋能有效改善坯料流动情况,必要时需设置多重拉延筋使零件成形完全。当模具圆角半径为0.25 mm,模具锥度为0°,拉伸深度为0.5 mm,压边力大小为60 kN,并采用双重拉延筋的情况下,所成形的金属双极板质量良好,无破裂、起皱、成形不足等缺陷。结论 模拟结果与实验结果一致,验证了模拟结果的正确性,可见采用冲压工艺成形金属双极板是可行的。     

摩托车油箱冲压成形数值模拟分析

应用PAM-STAMP软件对摩托车油箱的拉延成形过程进行了详尽的有限元模拟分析,通过对模拟分析和实际冲压结果的比较,验证了摩托车油箱拉延成形模拟分析建模的合理性和模拟结果的准确性.并简要分析了模拟结果和实际冲压结果产生差异的原因.结果表明,采用PAM-STAMP数值模拟软件可准确分析摩托车油箱的冲压成形过程.     

板材软模成形数值模拟研究现状

分析了板材软模成形数值模拟的特点,对目前主要采用的软模成形数值模拟方法进行了阐述和评价,并对三类典型软模成形(液压成形,橡皮成形及粘性介质压力成形)过程数值模拟应用进行了综述,最后对板材软模成形数值模拟发展趋势进行了展望.     

Cartesian网格结合无网格法处理的二维柱体

本文发展了基于四叉树数据结构的网格生成和二维流动的N-S方程数值求解器及动边界问题的Euler方程求解方法。采用压力梯度或者密度梯度的绝对值作为网格自适应的控制参量,同时采用基于最小二乘法的无网格方法处理对于一般Cartesian网格难于处理的物面边界条件。文中采取了绕方柱流动和绕圆柱流动的经典算例对所发展的方法进行了验证。计算的结果验证了所发展的方法在处理绕流流动时的合理性和有效性。采用Naca0012翼型的几种工况验证了所发展的动网格技术在处理无粘流动的合理性和可行性。从而为数值模拟具有复杂几何外形的流动提供了一种网格布局合理、高效,边界处理简单易行的新思路。     

数值模拟锻造成形的关键技术及应用

介绍了锻造成形数值模拟中的刚(粘)塑性有限元法的基本理论,对模具型腔信息描述、网格划分、边界条件处理等数值模拟中的关键技术做了全面系统的总结,分析比较了处理上述问题的各种方法.并通过实例介绍了应用模拟中的关键技术解决实际锻造问题的情况.     

无网格法模拟复合型疲劳裂纹的扩展

本文提出了用无网格Galerkin法模拟构件在复合变形作用下疲劳裂纹扩展路径并预估其疲劳寿命的方法。该法能够自然模拟疲劳裂纹的扩展,不需要网格重构,避免了裂纹扩展过程中的精度受损。应用无网格数值结果计算了J积分和应力强度因子K_I和K_Ⅱ;按照最大周向应力理论获得了裂纹扩展偏斜角。基于最小应变能密度因子理论,确定了裂纹扩展量Δa,并能获得疲劳载荷的循环周数ΔN。文末对数值模拟结果和实验拟合结果进行了对照。     

镁合金板料温冲压成形数值模拟技术

用板料成形的方法对变形镁合金进行加工可以制造更薄更轻的零件,符合轻质化的发展趋势.利用有限元数值模拟的方法可以对实际的冲压过程进行模拟,达到改进工艺与模具的目的.对于板料加热状态下的数值模拟,为了使结果准确,最重要的就是要建立正确的材料本构关系模型,这一材料模型需给出应变、应变率、应力与温度之间的关系.在经典的塑性成型计算中,材料模型包含两方面的内容:①初始屈服表面的确定,②流动法则和加工硬化模型的建立.总结了经典屈服模型和材料本构关系模型以及国内外学者在经典理论基础上建立起来的镁合金材料模型;探讨了板料成形有限元数值模拟技术以及目前常用的模拟软件;并在此基础上综述了镁合金冲压变形的热-机耦合的数值模拟的研究进展.     

数值模拟金属靶抗侵彻中的网格密度影响研究

在数值模拟中,有限元网格的数量对计算结果和计算成本都有较大的影响。采用MSC.Patran建立了弹体侵彻金属靶板的计算模型,并利用MSC.Dytran对所建模型进行了计算;结合相关的理论,对不同网格密度划分的有限元模型的计算结果进行了分析,并和实验进行了对比,得到了数值模拟弹体侵彻金属装甲中靶板的最佳网格数量。当网格无因次量μ=0.10时,所得到的数值模拟结果与实际吻合得较好：当厚度方向的网格数取为12个时,文中所采用的模型能较好地模拟弹体对靶板的侵彻效果。     

金属体积成形的无网格Galerkin模拟

为避免金属体积成形有限元法模拟中网格畸变造成网格重划和模拟精度降低,采用无网格法模拟金属体积成形.利用无网格法近似位移场,建立金属体积成形的无网格法连续性控制方程,采用罚函数法施加本征边界条件和体积不变条件,基于Markov变分原理推导了金属体积成形的无网格Galerkin求解列式.用数值计算法求解该列式,实现金属体积成形的无网格模拟.数值结果表明,无网格法能有效处理金属体积成形中出现的大变形,避免了网格畸变和重划,具有较高的模拟精度.     

Parallel computation of meshless methods for explicit dynamic analysis

A parallel computational implementation of modern meshless methods is presented for explicit dynamic analysis. The procedures are demonstrated by application of the Reproducing Kernel Particle Method (RKPM). Aspects of a coarse grain parallel paradigm are detailed for a Lagrangian formulation using model partitioning. Integration points are uniquely defined on separate processors and particle definitions are duplicated, as necessary, so that all support particles for each point are defined locally on the corresponding processor. Several partitioning schemes are considered and a reduced graph-based procedure is presented. Partitioning issues are discussed and procedures to accommodate essential boundary conditions in parallel are presented. Explicit MPI message passing statements are used for all communications among partitions on different processors. The effectiveness of the procedure is demonstrated by highly deformable inelastic example problems. Copyright © 2000 John Wiley & Sons, Ltd.     

Finite cloud method: a true meshless technique based on a fixed reproducing kernel approximation

We introduce fixed, moving and multiple fixed kernel techniques for the construction of interpolation functions over a scattered set of points. We show that for a particular choice of nodal volumes, the fixed, moving and multiple fixed kernel approaches are identical to the fixed, moving and multiple fixed least squares approaches. A finite cloud method, which combines collocation with a fixed kernel technique for the construction of interpolation functions, is presented as a true meshless technique for the numerical solution of partial differential equations. Numerical results are presented for several one‐and two‐dimensional problems, including examples from elasticity, heat conduction, thermoelasticity, Stokes flow and piezoelectricity. Copyright © 2001 John Wiley & Sons, Ltd.     

高强钢板热冲压成形热力耦合数值模拟

为研究高强钢板的热冲压成形性,采用ABAQUS软件对高温下22MnB5高强钢板沟槽形件冲压成形进行了数值模拟研究.建立了基于热力耦合的弹塑性有限元模型和热成形下的材料模型,通过对沟槽形件热成形进行数值模拟,考察了压边力、模具间隙和凹模圆角半径等工艺参数对热成形时温度分布和回弹的影响,给出了热成形中产生回弹的机理,确定了合适的工艺参数,通过热成形试验验证了数值结果的可靠性.     

薄板类件多点成形过程的数值模拟

以希尔关于弹塑性材料唯一性的充分性条件为理论基础,采用虚功率增率型原理,建立了多点成形的有限元模型,探讨了板材厚度、材质及弹性介质等因素对成形结果的影响,通过数值模拟找出参数合适的弹性介质,并对薄板类件的多点成形过程进行了实验验证.研究表明,通过使用参数合适的弹性介质,可以有效抑制压痕现象的产生,并能保证工件的成形精度;实验验证表明对马鞍形件多点成形过程中压痕现象的模拟是合理的.     

An improved hybrid particle-element method for hypervelocity impact simulation

An improved hybrid particle-finite element method has been developed for hypervelocity impact simulation. The method combines the general contact-impact capabilities of particle codes with the true Lagrangian kinematics of large strain finite element formulations. Unlike some alternative schemes which couple Lagrangian finite element models with smooth particle hydrodynamics, the present formulation makes no use of slidelines or penalty forces.     

Orbital debris impact simulation using a parallel hybrid particle-element code

Simulations of three dimensional orbital debris impact problems, using a parallel hybrid particle-finite element code, show good agreement with experiment and good speedup in parallel computation. The simulations included single and multi-plate shields as well as aluminum and composite shielding materials, at an impact velocity of eleven kilometers per second.     

Adaptive multiple scale meshless simulation on springback analysis in sheet metal forming

Springback is one of the major considerations in the design of part shape, die geometry and processing parameters of sheet metal forming. In this study, an adaptive multiple scale meshless method is developed to predict the amount of springback, which occurs after unloading in sheet metal forming. A two-dimensional meshless continuum approach is applied to the bending deformation of plate/shell structures. The meshless method called reproducing kernel particle method (RKPM) is modified to develop the springback analysis algorithm using two scales. The effective strain is decomposed into two scales, high and low. The two scale decomposition is incorporated into non-linear elasto-plastic formulation to obtain high and low components of effective stresses. The high scale component of effective stress indicates the high stress gradient regions without posterior estimation. Enrichment nodes with a proper refinement scheme are inserted/deleted in those high stress regions to exactly calculate the stress distribution and thus accurately predict the amount of springback. The simulation results show that the algorithm can effectively locate the high stress gradient regions and can be utilized as an efficient indicator for the adaptive refinement technique for non-linear elasto-plastic deformation. The comparison of the amount of springback via the processing parameters between experiment, FEM (ABAQUS), meshless method and adaptive meshless method shows that the adaptive meshless solutions are the closest to experiment results.     

多点成形中压痕的数值模拟及极限成形力的分析

压痕是多点成形中特有的成形缺陷之一,对压痕形成过程进行模拟时,采用实体单元比壳单元计算更准确.但是板料较薄时,采用实体单元划分的有限元很多,计算时间极长.为获得最佳的计算效率及模拟结果,对不同材料和不同厚度的球面和马鞍面样件进行了对比的数值模拟.结果表明,当板厚与板宽的比值小于0.015时,采用壳单元模拟压痕也能得到比较准确的结果,而当比值大于0.015时,则应采用实体单元.在此基础上,对不同板厚、不同曲率半径下的马鞍面和球面件出现压痕时的极限成形力进行分析,得到了厚向压应变为1%和5%的压痕对应的成形力极限图.