板料拉深成形数值模拟关键算法的比较

在板料拉深成形过程的数值模拟中显式算法和隐式算法是两种主要的有限元算法.板料拉深成形是一个准静态的变形过程,静力隐式算法是比较合理又相对精确的方法,但计算费时,需要大量的计算机内存空间;动力显式算法计算效率高且占用的存储空间少.本文分别用基于静力隐式算法的软件ANSYS和基于动力显式算法的软件ANSYS/LS-DYNA模拟了板料拉深成形过程,并通过与实验值相比较,验证了模拟结果的正确性.     

半球形凸模拉深过程的动力显式有限元分析

本文基于连续介质力学及有限变形理论 ,建立了用于三维板料成形过程分析的有限元模型 ,开发了动力显式算法的板料成形过程模拟的有限元分析程序DESSFORM3D。采取集中质量矩阵 ,用动力显式积分的方法 ,使位移计算显式化 ,避免了由材料、几何、边界条件等高度非线性因素引起的计算收敛问题。对半球形凸模拉深过程进行模拟计算 ,并把模拟结果与实验结果进行对比 ,验证了软件的计算结果     

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。     

环件轧制过程的显式有限元模拟分析

用于金属成形进行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。文中利用Abaqus／Explicit通用有限元程序对径向环轧进行了模拟。     

数值模拟对薄板冲压成形工艺设计的优化

成形数值模拟是板料冲压加工领域中的虚拟制造技术。通过研究薄板冲压成形数值模拟关键技术(弹塑性本构关系、单元技术以及积分求解策略)，将一个简单零件的拉深模拟所进行成形工艺参数的优化设计，应用在某轿车结构件——风窗横梁加强板，根据数值模拟的计算结果，通过修改坯料尺寸、压边力和拉深模压料面形状等工艺边界条件，来实现复杂拉深件成形工艺参数的优化设计，最终获得符合质量要求的产品拉深件。     

LY12半球形件拉深成形过程的动力显式有限元模拟

基于连续介质力学及有限变形理论，建立了用于三维板料成形过程模拟的有限元模型，开发了动力显式算法的板料成形过程模拟的有限元分析程序DESSFORMM3D。最后，用笔者新开发的动力显式弹粘塑性有限元程序对不同压边情况下半球形件的拉深过程进行分析，并把数值结果与实验结果进行对比，验证了软件的计算结果。     

率相关晶体塑性在有限元应用中的关键技术

率相关晶体塑性在有限元应用中存在数值求解稳定性、精度和效率不能兼顾的问题,这是由于其数值化过程中的诸多关键技术相互的制约所致。文章讨论了这些关键技术,指出了建模采用的变形构形和控制方程的主未知量对求解计算的影响,研究了本构计算的隐式和显式算法及数值技巧,并分析了有限元计算过程对本构求解的影响。基于对这些关键技术的研究及对其处理方法的探讨,简要给出了率相关晶体塑性隐式和显式模型及求解算法示例。圆棒料镦粗和杯形件拉深过程模拟研究表明,这些模型和算法能够较好地兼顾计算的稳定性、精度和效率,而且其结果也表明,文章对这些关键技术问题的处理是合理可行的。     

变薄拉深过程模拟的有限元动力显式算法

为研究变薄拉深工艺中材料流动变形,开发了基于单点积分和粘性阻尼沙漏控制算法相结合的八节点六面体单元的有限元动力显式算法程序.采用粘性沙漏控制算法有效控制了由于单点积分造成的沙漏模式,节省了计算时间.同时,沿厚向划分多层网格、三维的本构关系以及双面接触算法,可以精确获取板料应力应变状态.最后给出了圆筒件的变薄拉深成形模拟实例,通过与实验结果的比较,验证了此实体单元的实用性.     

考虑内禀长度的纯铝L2微拉深过程模拟

结合传统拉深成形工艺过程,采用材料的内禀长度来表征微塑性成形过程中的尺度效应,并在建立的三维有限元分析模型的基础上,对纯铝L2的微拉深工艺过程进行数值模拟与分析,研究了纯铝微拉深的塑性成形过程.试验成形出的微拉深件直径在1.4～1.6 mm之间,纵向深度在1.2～1.4 mm之间,拉深力为2.67 N,微拉深试验结果与模拟结果基本吻合.通过试验结果和模拟结果的对比,说明含内禀长度的微塑性本构方程能够用于微拉深成形过程的有限元数值模拟.     

板料成形模拟中压边力处理的研究

针对弹性压边建立了一个力学模型，用于板料成形的动力显式有限元模拟。以NUMISHEET‘93方盒拉深标准考题为例，模拟了方盒在不同压边力情况下的起皱情况。数值计算结果表明该模型能有效地模拟弹性压边力，并预测工件法兰部位的起皱状况。     

Numerical damage prediction in deep-drawing of sheet metals

This paper presents an efficient damage model based on the strong coupling of both anisotropic elasto-plasticity and isotropic ductile damage. The elasto-plasticity is modeled with mixed non-linear work hardening considering both isotropic and kinematic effects. The developed model is then coupled with the finite element method using ABAQUS finite element code. First, the formulation of the proposed damage model is presented. A comparison between numerical and experimental results is presented, in the context of the square cup deep-drawing benchmark test of Numisheet 1993. The results demonstrate the capability of the model to predict where and when the damaged zones will appear in the workpiece during the forming operation.     

3D finite element simulation of deep drawing with damage development

The elasto-plastic constitutive equation accounting for isotropic hardening coupled with material damage has been implemented in the finite element code ABAQUS. A damage variable, which was defined in meso-scale, was used to reveal the effects of micro-defects within the material. With an explicit integration scheme, deep drawing of a mild steel square cup was simulated using the ABAQUS with a specially designed VUMAT subroutine. The three-dimensional brick element was adopted to build-up the finite element model, and the contact and friction between the blank and tool were taken into consideration. The forming process of deep drawing is a non-proportional loading one, so that the accumulated damage state variable depends on the strain path, or in other words, the loading history. The damage evolution and the wrinkle formation under the influences of Coulomb friction and the blank holding force were analyzed and discussed. Experiments have been conducted to investigate the effect of blank holding force on wrinkling, and determine the position of crack initiation. Experimental results are in good agreement with the predicted ones.     

Failure Analysis of a Sheet Metal Blanking Process Based on Damage Coupling Model

In this paper, a blanking process of sheet metal is studied by the methods of numerical simulation and experimental observation. The effects of varying technological parameters related to the quality of products are investigated. An elastoplastic constitutive equation accounting for isotropic ductile damage is implemented into the finite element code ABAQUS with a user-defined material subroutine UMAT. The simulations of the damage evolution and ductile fracture in a sheet metal blanking process have been carried out by the FEM. In order to guarantee computation accuracy and avoid numerical divergence during large plastic deformation, a specified remeshing technique is successively applied when severe element distortion occurs. In the simulation, the evolutions of damage at different stage of the blanking process have been evaluated and the distributions of damage obtained from simulation are in proper agreement with the experimental results.     

金属板料冲压数值模拟中的宏观硬化模型研究现状

金属板料冲压数值模拟的精度取决于所应用的材料模型是否能够对材料的弹塑性行为提供准确描述。对于考察材料力学响应在变形过程中的变化,采用宏观硬化模型,并将微观结构特征整合在宏观内变量中,是一种合适的方法。文章结合微观结构演化,讨论了对金属材料宏观硬化的4种基本方式(各向同性硬化、运动硬化、旋转硬化、畸变硬化)及其限制;根据对不同应变路径变化下材料性能变化的描述,归纳了近年来较为典型的板料宏观硬化模型研究,并指出其不足之处及需要进一步研究的内容。同时,就金属板料冲压的宏观硬化模型研究需要注意的问题进行讨论。     

Rigid plastic constitutive theory for porous materials including void evolution and mixed hardening effects

A new rigid plastic constitutive model was constructed in the previous research for porous ductile materials based on modified Gurson’s yield function. However, in that model, attention was focused on the effect of isotropic hardening on plastic deformation and damage processes of porous materials. In this paper, that model is further extended to a more general model in which both the isotropic and the kinematic hardening mechanisms of porous materials are incorporated. The characteristics and self-consistency of the extended model are briefly discussed.     

基于3D-FEM的大型钛环热辗扩过程微观组织演变仿真

基于ABAQUS/Explicit软件平台,采用弹性预估-塑性校正策略和隐式积分算法,将Ti-6Al-4V的微观组织演变模型和率相关温度相关各向同性硬化弹塑性本构模型写入子程序VUMAT,实现了微观组织演变与宏观热力行为的耦合模拟。利用Ti-6Al-4V圆柱体等温镦粗实验,对所开发子程序的可靠性进行了验证。将该子程序应用于大型钛环热辗扩过程的热力耦合3D-FE模拟中,研究了微观组织在成形过程中的演变特征及机理。研究发现,沿着成形环件的径向,中间层相对于表层具有较小的β晶粒尺寸和β体积分数。     

板料成形中材料模型的研究进展

介绍了板料成形数值模拟中材料模型的研究进展。将材料模型的理论研究分为屈服准则、强化模型、流动法则、加卸载历史4个方面,并进行简要综述;对材料在循环加载条件下应力应变曲线的实验获取方法进行了探讨,重点介绍了板料压缩、三点弯曲实验确定材料反向加载应力应变曲线的原理和方法;对当前屈服准则、强化模型的研究热点和发展方向进行了分析。     

A Modified Mroz Model for Springback Prediction

A new anisotropic material hardening model is introduced in this study for springback simulation. It is modified from the Mroz multi-yield surface hardening model and incorporated more realistic Bauschinger effect for cyclic loading and anisotropic yield surfaces for sheet metals. The model is targeted for sheet metal forming simulations where the accurate springback predictions are important, and where materials have more rapid hardening characteristics and ability to sustain higher stresses such as so-called advanced high-strength steels (AHSS). The constitutive integration algorithm is derived and it is numerically implemented in the commercial FEA code via a user-material subroutine. The new model is applied to a U-channel forming test with DP600 steel. Experiments are conducted and springback results are compared with numerical prediction to demonstrate the new model’s effectiveness. This article was presented at Materials Science & Technology 2006, Innovations in Metal Forming symposium held in Cincinnati, OH, October 15–19, 2006.     

An orthotropic ductile damage model for visco-plastic materials

Numerical modelling of bulk forming processes has to identify the conditions that may result in unsatisfactory products. In ductile materials, damage may occur with the micro void nucleation at the site of second phase particles and inclusions in the plastic or visco-plastic matrix and then with the micro void growth. In this work an isotropic ductile damage model is extended to load cases with successive tensile and compressive steps and with pure deviatoric stress state. The constitutive equations satisfy the Clausius-Duhem inequality for negative or positive voids volume fraction rate. The constitutive parameters are identified with the Rice and Tracey model modified for a sphere initially filled with a soft or a hard inclusion. Axisymmetric geometries are considered for remote strain fields without distortion. A plane cell and a 3D unit cell are analysed numerically for the deviatoric strain state and various combined deviatoric and volumetric deformations.