各向异性屈服准则的发展及应用

各向异性是影响板料成形的重要因素之一。在板料成形的有限元模拟中，正确描述板料的各向异性行为有助于提高模拟精度。近年来，人们对板料的各向异性屈服行为进行了深入研究，研究内容主要有屈服准则的提出、实验验证及其在有限元模拟中的应用3个方面。本文总结了各向异性屈服准则的理论研究及实验验证的发展现状，以及各向异性屈服准则在板料成形有限元模拟软件中的应用，最后提出了各向异性屈服准则研究中今后的研究方向。     

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。     

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。     

材料参数对斜壁矩形盒件多点拉深成形性能的影响

多点成形技术是一种用于三维板类件成形的柔性加工技术.本文采用数值模拟方法研究了三个重要的材料力学性能参数──各向异性指数、应变硬化指数和屈服强度对斜壁矩形盒件多点拉深成形性能的影响.结果表明,与传统的模具拉深成形一样,板料的成形性能参数对多点拉深成形结果有着十分重要的影响;并且在一定的范围内,材料的各向异性指数越大,硬化指数越大,屈服强度越低越有利于斜壁矩形盒件的多点拉深成形.     

航空钣金材料性能参数与工艺知识库

为了解决目前航空钣金研制过程中存在的材料基础性能数据与成形工艺知识不足并无统一管理体系的问题,通过进行常用金属板料成形性能实验获取数据,总结了钣金6种成形工艺的知识内容,将信息录入通过Visual Studio和Oracla平台开发的航空钣金材料性能参数与工艺知识库系统,包括材料性能数据库、钣金成形工艺知识库和管理系统。该数据库可为钣金成形有限元模拟分析提供材料数据,并辅助工程师进行工艺性审查、工艺设计、工装设计和缺陷诊断,支撑钣金零件的整个数字化生产过程,缩短飞机研制周期,节约成本。     

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.     

机匣体毛坯等温挤压工艺的研究

主要研究了机匣体毛坯等温挤压工艺的设计方法。在分析机匣体产品特征的基础上,以Deform-3D数值模拟软件为基础,分析了机匣体等温挤压过程的变形规律。以数值模拟结果为参考对象,详细地阐述了机匣体的工艺制定方法与工艺流程设计,为其他采用难成形材料的同类型零件等温挤压工艺设计提供参考。     

涡扇发动机薄壁焊接支承机匣连续工艺仿真研究

伴随着计算机技术及有限元数值模拟技术的发展,焊接、热处理等模拟仿真技术逐渐得到了广泛的应用。焊接及热处理工艺仿真主要针对温度场变化、残余应力分布、尺寸变形分布等几个方面进行研究,旨在通过优化参数进而达到提升零件制造质量,延长产品服役寿命等目的。相对于传统优化参数的方式,数值模拟分析可很大程度缩短试验周期、降低试验成本,这对于航空发动机零部件的研制是极为重要的。文中利用有限元仿真技术对某涡扇发动机钛合金薄壁钣金支承机匣的焊接及热处理过程进行了数值模拟,并将仿真残余应力结果与实际结果进行了对比分析,得到了准确的有限元模型,利用此模型分析各个工序对零件变形的影响,获得了该类型零件制造过程中的变形规律,确定影响零件关键尺寸的关键工序,并提供了控制零件变形的优化方向。     

SUS430不锈钢自由曲面弯曲回弹的预测和试验研究

金属板料弯曲中,回弹预测与控制是产品精确成形的关键.针对厚度为0.55 mm的SUS430不锈钢自由曲面弯曲回弹问题,采用Hill48、Barlat89和YLD2000-2d 3种典型的各向异性屈服准则对SUS430不锈钢板材自由曲面弯曲成形进行有限元模拟,并结合试验验证,研究了不同屈服准则对自由曲面弯曲成形回弹量的影...     

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.     

一种建立板料成形极限应力图的新方法

基于塑性理论建立了比例加载条件下双向拉伸应力应变关系,结合Swift分散性失稳准则,提出了一种建立板料成形极限应力图的方法。分别应用Hill 48和Hosford屈服准则以及单向拉伸性能参数,建立了铝合金板(r<1)和薄钢板(r>1)两种材料的成形极限应力图(FLSD),分析表明,不同的屈服准则的选取对于成形极限应力曲线有不同的影响,对于不同类型的材料屈服准则的影响程度也不同。与由通常的成形极限图(FLD)转换所得到的成形极限应力图(FLSD)进行了对比分析,结果表明,所提出的方法计算过程更为简便,并能较为准确地建立成形极限应力图,可以作为复杂加载路径下的成形极限破裂判据。     

基于韧性断裂准则的铝合金板材成形极限预测

为了准确地预测铝合金板材成形极限，将韧性断裂准则引入到数值模拟中。在数值模拟获得的应力应变值基础上，采用简单拉伸试验和数值模拟相结合的方法确定了韧性断裂准则中的材料常数，并应用该韧性断裂准则预测了铝合金LYl2(M)的圆筒件拉深和半球形凸模胀形的成形极限。预测结果与实验值吻合较好，该韧性断裂准则能够预测铝合金板材成形极限。     

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。     

On predicting forming limits using hill’s yield criteria

The analysis of localized necking is strongly dependent on the yield function. To predict forming limits, therefore, numerous yield criteria have been postulated to characterize the plastic deformation of sheet materials. Among them Hill’s 1948 and the fourth form of 1979 yield criteria are the most commonly used. A new yield criterion was proposed by Hill in 1993. It uses five independent and easily obtainable material parameters, which makes it flexible in representing the shape of the yield locus for different materials. The present investigation compares these three yield criteria in forming limit predictions based on both the Marciniak and Kuczynski (M-K) approach and the bifurcation analysis. It is observed that the M-K analysis based on Hill’s 1993 yield criterion provides forming limit predictions in agreement with experimental data. The bifurcation analysis based on Hill’s 1948 yield criterion also provides an acceptable prediction of forming limits for aluminum, although they are slightly higher. All three yield criteria are found to provide acceptable predictions for aluminum-killed (AK) steel based on the M-K method. For brass, only the prediction based on the M-K method and Hill’s 1993 yield criterion is close to the trend of experimental data.     

板料成形极限的理论预测与数值模拟研究

本文针对目前板料成形极限的实验、理论计算和数值模拟方法以及成形极限应力图的研究进展 ,进行了综述与分析 ,提出了通过数值模拟方法预测板料成形极限所存在的一些问题。认为找到一种能够尽量减少对外部条件的依赖 ,从而更本质地反映材料性能的方法。     

Evaluation of effect of flow stress characteristics of tubular material on forming limit in tube hydroforming process

The material properties for the analytical and numerical simulation in sheet metal processes, especially in tube hydroforming process, are generally obtained from the uniaxial tensile test of raw sheet material. However, the validation of the formability and reliability of the numerical simulation for the tube hydroforming process arises from the fact that the material characteristics of tubes are different from those of the raw sheet materials. In order to determine the most suitable material property of the tubular material for the evaluation of forming limit on the THF process, the uniaxial tensile test for the specimens of the raw sheet metal and the roll-formed tube and the free bulge test for the roll-formed tubular material are carried out in this paper. The forming limit curves are also derived using plastic instability based on three kinds of necking criteria, which are Hill’s local necking criterion for sheet and Swift’s diffuse necking criteria for sheet and tube, to describe and explain the forming limits for the roll-formed tubular material in the THF process. In order to acquire the informative data on the forming limit curves in the THF process, the loading condition of the free bulge test is controlled. The proper band from nearly necking initiation to nearly bursting initiation has been defined for the roll-formed tubular material in the THF process. It can be concluded that the flow stress of the tubular material should be determined from the actual free bulge test to find the practically valuable forming limit curve for the THF process.     

Formability evaluation for hot-rolled HB780 steel sheet based on 3-D non-quadratic yield function

A common practice to evaluate formability in the typical sheet metal forming process is to measure hardening behavior and a forming limit diagram as separate material properties, and perform numerical forming simulations utilizing various yield functions. The measured forming limit diagram is applied as the failure criterion. However, the performance of material properties such as hardening behavior and yield functions in predicting strain localization in the simple tension and forming limit diagram tests is seldom validated before their application to forming simulation. In this study, a new numerical formability evaluation procedure was proposed, in which not only hardening behavior but also measured forming limit data were employed in characterizing the input data for the hardening behavior and the yield function. Besides, strain localization was directly monitored to determine failure without employing any forming limit criterion. The new procedure was applied for rather thick advanced high strength hot-rolled steel sheet so that 3-D continuum elements were utilized along with 3-D non-quadratic Hosford and quadratic Hill yield functions.     

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.