韧性断裂准则在高强钢板料成形中的应用

 针对板料成形中的韧性断裂准则预测成形极限的方法,进行了综述和分析,提出了利用韧性断裂准则能够较好地预测塑性差的板料成形极限,而且还能考虑应变路径的变化．将Cockroft和Latham准则应用到高强度钢板DP590的成形预测中．对高强钢DP590进行了单向拉伸试验,获得了相应的物性参数．同时对该高强钢进行了方盒件成形试验,并进行了相应的有限元模拟．通过对高强钢的极限试验,利用有限元模拟获得了该材料的Cockroft和Latham准则常数．最后利用该常数对方盒件的拉深过程进行了缺陷的预测,模拟结果和试验结果完全吻合．表明韧性断裂准则是可以应用到高强度钢板的成形中的．     

基于Oyane韧性断裂准则的板料成形极限预测

本文基于Oyane韧性断裂准则,结合数值模拟方法,预测板料不同应变状态下的极限应变.准则中的材料参数通过单向拉伸和平面应变拉伸试验确定.在模拟胀形试验获得每一时间步应力、应变值的基础上,应用韧性断裂准则预测板料的成形极限.模拟结果表明用韧性断裂准则和数值模拟相结合的方法能成功获得板料的成形极限图.     

一种韧性断裂损伤力学建模方法及其应用

基于连续损伤力学理论,综合考虑变形历史（温度、应变速率）对损伤的累积演化和临界损伤值的影响,提出了一种新的韧性断裂预测方法。建立了相应的韧性断裂准则,准确地预测了钛合金的热锻成形、镁合金的温热冲压成形和不锈钢板的液压成形过程中的破裂行为,表明该方法可以很好地用于存在变形历史的体积成形和板成形的成形极限预测。     

非线性路径下板料拉深成形过程中破裂预测

在优选模型参数和简化孔洞形核规律的基础上,采用Gurson-Tvergaard (GT) 多孔材料本构模型分析圆筒件拉深过程;根据金属成形工艺特点,综合考虑拉伸型和剪切型2种不同韧性断裂机制,提出一个统一的韧性断裂准则形式.对于未经过预变形和经过预变形的圆筒件拉深试验和数值模拟进行了比较,结果表明:相对于成形极限图,新的韧性断裂准则可以更加准确地预测非线性路径下圆筒件的拉深破裂.     

基于韧性准则的金属板料冲压成形断裂模拟

该文基于Rice-Tracey韧性失效准则,探索金属板料冲压成形的断裂数值模拟方法。首先设计两种试验,并结合有限元分析结果确定双相钢板料的材料失效参数;然后,基于Abaqus软件的显式模块Explicit,编写采用Rice-Tracey韧性失效准则的用户自定义材料子程序VUMAT;最后对双相钢薄板深拉成形过程中的断裂行为进行数值模拟,并进行了试验验证。结果表明,数值模拟结果与试验结果吻合较好。可见,Rice-Tracey韧性准则可用于金属板料冲压成形的断裂预测。     

基于GISSMO断裂准则的6016铝合金断裂行为研究

目的 研究零部件在成形与碰撞过程中,6016铝合金在不同应力状态下的断裂行为。方法 通过准静态拉伸实验,获得了6016铝合金的基本力学性能。利用Nakajima成形极限实验,获得了6016铝合金材料的断裂成形极限曲线。设计了7种涵盖成形及碰撞过程中应力状态的断裂极限测试试样,采用数字图像相关技术(DIC)记录了试样在变形过程中的全场应变。利用实验-有限元反求方法标定了6016铝合金的GISSMO断裂准则的参数,并用帽形件三点弯曲实验验证了模型的合理性。结果 相比于传统断裂成形极限图的预测结果,基于GISSMO断裂准则的仿真结果与实验具有更好的一致性。结论 所建立的GISSMO模型可以用于预测6016铝合金在复杂应力状态下的断裂行为。     

利用最小厚度准则预测高强热轧钢板的FLC曲线

为更便捷地获得成形极限图(FLD)中的成形极限曲线(FLC),用最小厚度准则,通过少量成形极限试验结合数值模拟来预测FLC.采用Barlat1989屈服准则对QStE340TM、SAPH370、ZStE260P三种高强度热轧钢板进行成形极限模拟,并以最小厚度准则作为极限判据,根据数值模拟结果绘制FLC图.计算结果表明,采用平面应变路径下的成形极限实验数据作为最小厚度准则的已知参数时,数值预测结果与实验结果能较好吻合.故采用平面应变路径下的成形极限实验数据,结合最小厚度准则和数值模拟,即可得到材料完整的FLC曲线.     

镁合金塑性成形性能实验与数值模拟研究

对ME20M镁合金板料进行了热拉深成形性能实验与数值模拟.研究表明,ME20M镁板热拉深成形极限高度随实验参数的不同而不同,其塑性成形性能随温度的升高明显改善;数值模拟可以很好地预测不同实验参数下镁合金板料热拉深成形极限的高度.对热拉深成形件传力区部位进行金相实验得知,合理控制热拉深实验参数能保证镁合金塑性成形件微观组织,进而保证成形件质量.     

5182-O铝合金塑性成形性能表征

目的 结合复杂加载状态试验、塑性和损伤断裂本构模型及有限元应用,实现AA5182-O铝合金在复杂加载状态下塑性变形和损伤断裂行为的精确表征。方法 通过拉伸、剪切等试验,研究5182-O在剪切、单向拉伸、平面应变拉伸等复杂应力状态下的力学性能,应用pDrucker方程来表征其复杂加载状态下的塑性变形和损伤断裂特性。采用逆向工程方法实现pDrucker屈服方程和pDrucker断裂准则的精确标定。将标定后的塑性本构模型和损伤断裂准则应用到ABAQUS/Explicit中,预测不同试件的塑性变形和损伤断裂情况。结果 通过有限元模拟与试验结果的对比,发现有限元仿真准确预测了5182-O在复杂加载状态下的力-位移曲线和损伤断裂情况。结论 有限元模拟与试验结果的对比表明,pDrucker方程可以实现5182-O铝合金在复杂加载状态下塑性成形性能的精确表征。标定的pDrucker方程可应用于5182-O冲压成形过程的有限元分析、模具设计和工艺优化中。     

金属韧性断裂准则的数值模拟和试验研究

对不同外形的45钢试件进行了拉伸、压缩和扭转等材料试验,对工程中常用的5个韧性断裂准则的适用范围进行了对比研究,并采用Gurson-Tvergaard(GT)多孔材料本构模型对试验过程进行了数值模拟.指出目前使用的断裂准则都不可能对材料在多种变形条件下给出一个固定临界值.根据金属成形工艺特点,综合考虑拉伸型和剪切型2种不同韧性断裂机制,提出一个统一的韧性断裂准则形式.试验和数值计算结果证明了该准则的有效性和普适性,进而利用单向拉伸和扭转试验确定的材料常数合理地预测压缩过程中的韧性断裂现象.     

温成形中铝合金板成形极限图的预测研究

在铝合金板温成形数值仿真中,成形极限图是判断材料颈缩失效和评价温冲压成形能力的基础.提出了一种温成形条件下铝合金板成形极限图的理论预测方法.采用曲线拟合方法建立了Al5083-O铝合金板应变硬化指数、应变率硬化指数随成形温度的变化规律;采用M-K理论模型,结合Logan-Hosford屈服函数计算获得温成形条件下铝合金板的成形极限图.计算结果与实验数据吻合较好,证实了温成形条件下铝板成形极限图的理论预测方法是正确的.     

左前门防撞梁冲压成形数值模拟研究

采用数值模拟技术可以在模具设计初期预测产品的成形质量,从而优化工艺参数以便获得高质量的成品。以eta/DYNAFORM有限元分析软件为平台,对某轿车左前门防撞梁不同工艺参数下的拉延成形过程进行了数值模拟,得出了相应的成形极限图。重点探讨了压边力和拉延筋的设置对起皱和未充分拉深区域的影响,得出了较好的解决方案。     

板厚对08Al薄板单点渐进成形中成形极限的影响

目的 针对渐进成形中成形极限测量难的问题,提出一种新的评定成形极限方法.方法 选用08Al为实验材料,通过模拟和实验相结合的方法,研究不同板厚下成形极限角和减薄率的关系,提出利用成形极限角和最大减薄率2个参数组合的方法判断薄板的成形极限,并通过数控实验验证提出方法的准确性,分析板厚对单点渐进成形工艺成形极限的影响.结果...     

Formability prediction of high-strength steel sheet using experimental,analytical and theoretical analysis based on strain and stress forming limit curves and its application to automotive forming parts

In this work, the high-strength steel (HSS) sheet dual-phase 440 (DP440) were conducted to establish the forming limit curve (FLC) and analytical forming limit stress curve (FLSC) obtained from experimental forming limit curve. First, the Nakajima stretch forming examination was carried out to obtain forming limit curve of investigated sheet. Afterwards, the theoretical Marciniak–Kuczinsky (M–K) model was developed and calculated to evaluate localized necking limits both in strain and stress spaces combination with anisotropic yield criteria. Then, the analytical forming limit stress curves were plastically calculated by using experimental forming limit curve data combination with Swift hardening model and anisotropic yield criteria namely, Hill’48 and Yld2000-2d for representing anisotropic plastic deformation behavior on examined steel sheet. Finally, automotive stamping parts were performed in order to verify an applicability of all developed curves. It was observed that the analytical forming limit stress curves could more precisely predict the formability of automotive parts better than the forming limit curve based on strain. Particularly, the one based on Yld2000-2d predict better than the one based on Hill’48. Simultaneously, the experimental forming limit curve and analytical forming limit stress curve were also evaluated comparing with the theoretical calculated forming limit curve and forming limit stress curve using the Marciniak–Kuczinsky model. It should be noted again that the experimental forming limit curve and analytical forming limit stress curve are the best one. Therefore, the Yld2000-2d yield function better represented the anisotropic behavior of the high-strength steel sheet dual-phase 440 than Hill′ 48 yield function, and can suitable be used for the analysis prediction and design of bumper automotive parts under forming processes.     

Path-independent forming limit models for multi-stage forming processes

Many practitioners of the metal forming community remain faithful to the idea that strain metrics are useful for formability assessment. However, it is only valid when deformation occurs along linear strain paths. Current simulations of multi-stage sheet forming processes for rigid-packaging and automotive components result in higher rejection rates due to the inaccuracy of forming and fracture limit models. In this work, we establish a new approach considering path-independency in forming limits based on the stress-based forming limit and polar EPS (Effective Plastic Strain) diagram which appear to be an effective solution for nonlinear effects. The related theory has been implemented into a user material model in commercial software.     

Effect of annealing on formability of aluminium grade 19000

Forming limit diagrams are used by the stampers to solve sheet metal forming problems. In practice, sheet metals have been subjected to various combinations of strain. Necking during sheet metal forming, sets the limit to which the sheet metal can be formed. Forming limit diagram is an effective tool to evaluate the formability of sheet metal in various strain conditions. The information upon the formability of the sheet metal is important for both sheet metal manufacturers and users. In this work, a study has been made on the formability of aluminium 19000 grades annealed at three different temperatures namely 160 °C, 200 °C and 300 °C for sheet thickness of 2.00 mm. The tensile properties and formability parameters were experimentally evaluated and they are related to forming limit diagram. Strain distribution profiles obtained from the forming experiment have been analyzed. The fractured surface of the formed samples were viewed using scanning electron microscope (SEM) and the SEM images were correlated with fracture behaviour and formability of sheet metal. The sheet which is annealed at 300 °C has been found to possess good drawability and stretchability compared to other two annealed sheets.     

Multi-objective Optimization of Sheet Metal Forming Die Using Genetic Algorithm Coupled with RSM and FEA

Present study describes the approach of applying response surface methodology (RSM) with a Pareto-based multi-objective genetic algorithm to assist engineers in optimization of sheet metal forming. In many studies, finite element analysis and optimization technique have been integrated to solve the optimal process parameters of sheet metal forming by transforming multi-objective problem into a single-objective problem. This paper aims to minimize objective functions of fracture and wrinkle simultaneously. Design variables are blank-holding force and draw-bead geometrical parameters (length and diameter). RSM has been used for design of experiment and finding relationship between variables and objective functions. Forming limit diagram has been used to define objective functions. Finite element analysis applied for simulating the process. Proposed approach has been investigated on a fuel tank drawing part and it has been observed that it is more effective and accurate than traditional finite element analysis method and the “trial and error” procedure.     

渐进成形不同热辅助工艺对制件微观结构影响的研究进展

渐进成形作为一种先进的柔性成形技术获得了当今学者的广泛关注,然而传统渐进成形工艺难以对室温环境下整体延展性较差的板料进行加工成形,研究人员提出的不同类型热辅助工艺可以通过提高板料温度环境进而有效改善上述问题。对热辅助渐进成形体系进行了简要概述,按照渐进成形加热方式的不同将热辅助工艺分为热介质加热、电辅助加热、热辐射加热和其他方式加热4个大类,在此基础上综述了不同学者在热辅助渐进成形工艺方面的学术成果,并基于不同类型的热辅助工艺,结合微观层面总结了温度对板料成形性的影响。在热渐进成形加工过程中,材料处在多场耦合作用的复杂情况下,其中热场是导致板料微观组织变化的主要原因,辅助工艺提供的额外热源有利于材料组织发生演变,最终显著改善了材料的成形性,进而提高了零件的成形极限。最后,针对不同类型的热辅助方式在供热范围与温度均匀性等工艺方面不尽相同的问题,作出了简要评价。