汽车铝合金覆盖件成形数值模拟的各向异性屈服准则研究

铝合金作为一种典型的汽车轻量化材料,被越来越多的运用到汽车车身覆盖件中。但由于铝合金具有明显的各向异性特征,为了准确模拟铝合金板的成形过程,选择合适的屈服准则是关键。文章以汽车铝合金油箱的拉深成形为例,采用3种典型的各向异性屈服准则Hill48、Barlat89和YLD2000-2d对成形过程进行有限元模拟,结合实验验证,分析了不同屈服准则对有限元模拟结果精度的影响。结果表明,Hill48屈服准则的模拟结果与实验结果存在较大的差异,故不适用于铝合金板料成形的有限元模拟;Barlat89屈服准则的模拟结果与实验结果接近,但存在一定的偏差;YLD2000-2d屈服准则的模拟结果与实验结果吻合最好,数值模拟的精度最高。     

航空发动机机匣钣金成形及屈服准则

钣金机匣作为航空发动机的主要构成零部件,其结构复杂、材料难于成形,且成形后内部存在不同程度的残余应力,随着计算机的发展,数值模拟成为辅助板料成形研究的主要手段,屈服准则是数值模拟的基础。本文对航空发动机机匣钣金成形性能做以叙述,对各向同性材料屈服准则、各向异性材料屈服准则、先进的各向异性材料屈服准则进行归纳,提出屈服准则应以屈服轨迹、单轴屈服应力、塑性各向异性参数等为选择依据,并提出未来屈服准则可沿新的屈服准则、描述非线性加载情况下的屈服轨迹、创新实验研究方法等方向发展。     

圆筒形件拉深成形的数值模拟研究

采用动态显式有限元方法和目前在板料有限元数值模拟中最常用的Hill各向异性屈服准则对筒形件拉深过程的变形情况进行了分析,得到各种不同的工艺参数对板料成形性能的影响,从数值模拟方面预测各参数对简单筒形件拉深中的变形影响.     

板料拉深过程数值模拟分析系统的开发

采用有限元动态分析技术、HILL屈服准则，模拟板料拉深成形的过程，结合实验拉深进行比较，模拟结果与实验数据符合。应用Visual Basic和ANSYS中的APDL语言进行了二次开发。该系统可以方便有效地模拟实验过程和对参数进行优化。     

各向异性屈服准则对铝合金板成形预测精度的影响

基于板料成形过程的数值模拟 ,研究了不同的各向异性屈服准则 (Hill194 8,BarlatYLD89,BarlatYLD91和BarlatYLD96 )对铝合金板成形过程的影响 ,模拟结果和实验结果进行比较 ,结果表明 ,采用屈服准则 (YLD96 )模拟结果和实验吻合较好 ,而Hill屈服准则的模拟结果和实验差别较大 ,故不适宜用于铝合金板的成形模拟。采用不同屈服准则模拟的应变分布有所不同 ,采用YLD89,YLD91和YLD 96屈服准则预测的起皱和断裂的趋势比Hill屈服准则预测的要高。     

影响板料成形回弹数值模拟精度的因素分析

分析了影响板料回弹精度的数值模拟因素：屈服准则、硬化模式、单元技术及有限元数值计算方法。研究结果表明各向异性屈服准则Barlat89更接近于材料的实际屈服行为；对于具有Bauschinger效应的材料及复杂加载问题，采用非线性混合强化材料模型预测板料回弹量的精度最高；由于实体壳单元具有实体单元和壳单元的优点，预测回弹模拟结果精度高。研究还表明，在时间允许的条件下，采用较小单元尺寸模拟精度高。     

板料冲压过程的数值仿真与参数优化

采用有限元动态分析技术，采用HILL屈服准则，模拟了板料拉深成形的过程．结合实验拉深进行比较，模拟结果与实验数据符合。应用0．618一维搜索优化方法，在数值模拟中对压边力进行了优化，为实验中压边力的确定提供了参考数据。     

工业AA1200铝合金薄板拉伸成形模拟和实验研究(英文)

对工业AA1200铝合金薄板拉伸成形的模拟和实验结果进行比较和评估。采用单向拉伸试验得到模拟所需输入参数。根据von Mises和Hill-1948屈服准则,采用Abaqus/Explicit有限元软件分析成形过程。将冲压力和应变分布的模拟结果与实验结果进行比较和验证。结果表明:在这两种情况下,使用各向异性屈服准则模拟的结果与实验结果更吻合。     

板料成形数值模拟的关键技术及难点

本文结合国内外板料成形数值模拟的最新研究动态，从关键算法、屈服函数、本构方程、有限元列式、接触问题、破裂准则、回弹计算、起皱分析八个方面叙述了板料成形有限元计算的关键技术及主要难点。     

应用韧性断裂准则预测板料的成形极限图

将Oyan韧性断裂准则引入数值模拟预测板料的成形极限图(FLD).讨论了各向异性系数对不同应变状态下准则中各项的影响,通过测定单向拉伸和平面应变拉伸的断裂应变确定了准则中的材料常数.模拟凸模胀形实验得到每一时间步应力、应变值,代入韧性断裂准则预测板料的成形极限.应用Oyan韧性断裂准则预测了铝合金A5182-O和SPCC的成形极限图.模拟结果表明,用韧性断裂准则和数值模拟相结合能成功预测板料的成形极限图.     

Plastic anisotropy in FEM analysis using degenerated solid element

Hill's quadratic, anisotropic yield criterion is implemented to the sheet metal forming simulation FEM code ITAS-3D. Several problems arouse when a constitutive equation with anisotropic yield criterion and related numerical procedures have to be formulated for shell like structures. Strategy to deal with large rotations, anisotropy updating topics and stress updating procedure for degenerated solid element used in ITAS-3D code are presented in our paper. Finally, results of numerical simulation for an anisotropic steel sheet deformed in cylindrical deep drawing process are verified by experiment.     

Characterization of yielding behavior of sheet metal under biaxial stress condition at elevated temperatures

The enhancement of material modeling in fields of sheet metal forming is essential for finite element-based designing of processes and dimensioning of parts. Since new lightweight materials, e.g. aluminum and magnesium wrought alloys show anisotropic and temperature-dependent forming behavior adequate testing methods and evaluation strategies have to be developed to obtain the reliable material data. For that purpose an experimental setup has been designed at the Chair of Manufacturing Technology which enables biaxial tensile testing of sheet metal at elevated temperatures. In this paper, the setup is introduced and the obtained results, i.e. experimentally determined yield loci and subsequent yield loci as a function of temperature are given for the well-known aluminum alloy AA6016 as well as the magnesium alloy AZ31.     

Identification of material parameters from punch stretch test

To accurately describe the mechanical properties of aluminium alloy sheet during deformation, an inverse identification was presented to deal with material parameters from the popular punch stretch test. In the identification procedure, the optimization strategy combines finite element method (FEM), Latin hypercube sampling (LHS), Kriging model and multi-island genetic algorithm (MIGA). The proposed approach is used on material parameter identification of aluminium alloy sheet 2D12. The anisotropic yield criterion Hill'90 is discussed. The results show that the Hill'90 anisotropic yield criterion with identified anisotropic material parameters has a good potential in describing the anisotropic behaviours. It provides a way to obtain the material parameters for FE simulations of sheet metal forming.     

Comparison of Material Models for Spring Back Prediction in an Automotive Panel Using Finite Element Method

Springback is a crucial factor in sheet metal forming process. An accurate prediction of springback is the premise for its control. An elasto-plastic constitutive model that can fully reflect anisotropic character of sheet metal has a crucial influence in the forming simulation. The forming process simulation and springback prediction of an automobile body panel is implemented by using JSTAMP/LS-DYNA with the Yoshida-Uemori, the 3-parameter Barlat and transversely anisotropic elasto-plastic model, respectively. Simulation predictions on spingback from the three constitutive models are compared with experiment measurements to demonstrate the effectiveness and accuracy of the Yoshida-Uemori model in characterizing the anisotropic material behavior of sheet metal during forming. With an accurate prediction of springback, it can provide design guideline for the practical application in mold design with springback compensation and to achieve an accurate forming.     

平面各向异性金属盒形件拉深过程的有限元模拟

在薄板成形过程中需要精确地描述薄板的各向异性特征。本文给出了用三参数Ｂａｒｌａｔ－Ｌｉａｎ各向异性屈服函数有限元数值模拟盒形件拉深过程的结果，给出了各向异性系数Ｒ对耳状法兰边的形状影响及成形高度，厚度变化，薄板法兰边起皱等结果，并与实验结果进行了比较，结果是令人满意的。     

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.     

车用铝合金板材回弹规律研究

在车用铝合金材料的成形加工过程中,回弹是主要的成形缺陷之一并且较难控制。本文对车用6061铝合金板材进行了室温拉伸试验获得其应力-应变曲线并建立改进的Johnson-Cook本构模型。该模型被应用于V形弯曲试验的有限元仿真中,研究不同各向异性屈服准则对板料回弹预测精度的影响,仿真结果表明应用YLD2000-2d屈服准则时其预测精度较高,同时也验证了该模型用于回弹分析的有效性。进一步探究不同因素如变形程度,冲压速度,摩擦条件,压边力等对铝合金板材回弹行为的影响规律,并应用于铝合金发罩内板的冲压成形过程,能够有效减小工件的回弹。     

Anisotropic plasticity model coupled with strain dependent plastic strain and stress ratios

It is necessary to describe properly anisotropic material behavior for realistic numerical analyses of sheet metal forming processes. The implementation of many yield criteria in finite element analysis is very complicated. Various material tests are also required to determine yield function coefficients. Stress ratios and anisotropy coefficients are not constant during forming processes due to deformation induced anisotropy. This paper introduces a yield function using strain dependent plastic strain ratios and stress ratios. The main advantage is to fully utilize the data of uniaxial tensile tests. The described material behavior shows a significantly improved agreement with experimental data.