先进高强钢DP780板料的温成形极限预测研究

为准确预测DP780钢板料在温成形条件下的成形极限曲线,将韧性断裂预测模型引入到数值模拟.基于DP780钢板料在温度范围573 K～873 K、应变率范围6.67× 10-4s-1～6.67×10-3s-1的单向拉伸试验结果分析,利用强塑积指标确定了温度为673 K、应变率为3.33× 10-3s-1条件下材料的温冲压成形性能较好.通过该变形条件下的简单拉伸试验和数值模拟,确定了影响DP780钢板料韧性断裂的主要因素.建立了可以预测DP780钢板料在不同应变路径下发生拉伸型断裂和剪切型断裂两种断裂机制的韧性断裂预测模型,并与温成形本构模型、Hill'48屈服准则相结合实现了刚模胀形试验的数值模拟,预测了DP780钢板料在温度为673 K下的成形极限曲线,并建立了成形极限数学模型.结果 表明,利用该方法预测的成形极限结果拥有较好的精度.     

基于连续介质损伤力学的7075铝合金高温成形极限理论预测与数值仿真

开展7075铝合金高温单向拉伸试验和成形极限试验，获得了不同温度和应变率的应力-应变曲线和成形极限曲线。结果表明，在较高的温度和应变率时7075铝合金的强度减小、成形性提高。为描述7075铝合金高温损伤演化过程，提出一种改进的连续介质损伤模型，并建立了耦合损伤的多轴统一黏塑性本构模型。基于试验结果，运用NSGAII遗传算法标定了模型中的参数，标定后的本构模型可以很好地预测7075铝合金的高温热力行为和极限应变。通过有限元软件Abaqus的用户材料子程序VUMAT，该本构模型被编入到Abaqus软件中进行数值仿真计算。结果表明，仿真获得的成形极限曲线和应变场分布与试验和理论结果吻合度好，进一步证明了所建立的耦合损伤的多轴本构模型的正确性及其在高温成形极限有限元仿真中的适用性。     

板料成形极限预测新判据

从控制塑性变形能的角度出发,基于总塑性功的积分形式,建立板料的成形极限预测判据.这种板料成形极限预测判据考虑应变路径变化、材料的硬化指数、各向异性系数及材料的初始厚度等对成形极限的影响.判据中的参数可由常用的单向拉伸极限应变试验确定.由此通过数值模拟可以预测板料在各种不同应变路径下的成形极限,适用于成形极限图的拉-压和拉-拉应变区,从而建立完整的成形极限曲线,可大大减少试验工作量.试验验证表明,这种成形极限预测判据对于钢板和铝合金板的成形极限可做出较为准确的预测.实现了只进行单拉试验即可预测板料在不同应变路径下的成形极限.     

基于Gissmo失效模型的6016铝合金板材断裂行为研究及应用

准确预测金属板材在成形过程中的失效行为是当前面临的挑战。许多试验表明,金属材料的断裂失效行为伴随着强烈的应变路径依赖性。Gissmo失效模型采用非线性方式计算损伤积累,考虑材料的应力状态对断裂失效应变临界值的影响,适用于预测金属材料在不同应力状态下的断裂行为。以汽车用6016铝合金板材为研究对象,设计六种反映材料不同应力状态的试样,通过试验结合有限元仿真对标的方法,校准Gissmo失效模型中的参数。将Gissmo失效模型用于预测铝合金板材汽车发动机罩内板在冲压过程的断裂失效问题,并对数值模型计算结果进行试验验证。结果表明,与传统成形极限图相比,Gissmo失效模型的计算结果与试验结果更加吻合,铝合金汽车发动机罩内板样件均未出现裂纹区域,表明Gissmo失效模型适合用于准确预测6016铝合金板材的断裂行为。     

基于等效模型矿用车零件加工性能优化分析

利用网格应变测量系统,对典型深拉延类零件车门内板成形破裂风险区域的应变状态进行分析;基于AutoForm建立车门内板拉延工序模型,分析不同应变破裂极限类型下,材料的主要性能参数与零件成形安全裕度的关系;根据性能参数与安全域度的对应关系,基于Matlab建立不同屈服强度下性能参数的双响应面选材模型;利用危险点应变状态及应变大小相同,则其经历的极限变形能力相同的原理,提出简单有效地等效选材模型;结合实际车门内板冲压开裂及材料性能优化,对选材模型进行验证。结果可知：车门内板成形破裂风险区域应变属于平面应变;厚向异性指数r值对平面应变类成形安全域度影响要大于硬化指数n值,危险点属于平面应变的应着重考虑提高r值;通过优化材料性能,车门内板原开裂区域减薄率小于23%,安全裕度高于10%,解决了车门内板开裂的问题;实际冲压结果表明等效模型的可靠性。     

高强铝合金热塑性变形本构关系研究现状及发展趋势

高强铝合金热成形工艺条件下的变形行为表征，需要在考虑温度、应变速率及应变影响的基础上结合微观演化行为建立热塑性本构关系。总结了高强铝合金热塑性变形本构关系相关研究成果。研究结果表明：广泛应用的唯象本构模型通过修正模型参数可以充分耦合应变、温度及应变速率作用，并准确地预测不同变形条件下的流动应力，然而缺乏对变形机制的明确解释，使得唯象本构模型对试验温度、应变速率变化范围较大以及试验条件范围外的变形行为预测精度难以得到保证；基于物理意义的本构模型能够模拟位错密度、晶粒尺寸及动态再结晶等微观演化过程，对流动应力进行精确计算，展现了强大的宏微观变形预测能力，是高强铝合金热塑性变形本构关系的研究趋势。     

双相钢的力学性能和对成形极限的影响

对两个来自不同生产线的冷轧双相钢DP780试样的主要力学性能进行比较,发现相同牌号的DP钢产品性能有显著差异。建立拉伸过程的有限元模型,将拉伸试验和有限元仿真相结合,利用材料失效点主应变二次导数的变化规律准确预测DP780在拉伸过程中的缩颈和破裂。研究发现相同牌号的DP钢产品成形极限亦有明显不同。最后从延伸长度和极限应变两方面定量分析应变强化指数n值和强度系数K值的变化对拉伸过程成形极限的影响。发现应变强化指数n值的变化对成形极限影响较大,强度系数K值的变化对成形极限影响较小。增大n值可以提高发生缩颈和破裂时的延伸长度和极限应变。     

一种考虑钢板表面及内部损伤的形成极限预报模型

应用损伤力学的观点,基于对板材成形过程中的表面和内部损伤的研究结果以及考虑影响板材成形极限的基本力学性能、各向异性、初始板厚、表面损伤及内部损伤诸因素的作用,提出了新的极限应变预报模型。采用新的极限应变预报模型计算的盛开极限曲线与实验结果基本吻合。     

考虑成形方向的航空铝合金修正本构模型的构建

为了能够准确地反映材料成形方向对其动态力学性能的影响,利用电子万能试验机及分离式霍普金森压杆（SHPB）装置,对航空铝合金7050-T7451板材沿不同成形方向（法向ND,横向TD,轧向RD）取样,并进行准静态加载试验和动态冲击剪切试验。结果表明：成形方向是影响材料准静态和动态力学性能的重要因素之一,在动态冲击剪切过程中,铝合金7050-T7451表现出一定的应变率敏感性和正应变率强化效应。基于材料的成形方向影响规律,构建包含应变率敏感函数项的修正的Johnson-Cook本构模型,并对比验证修正模型与试验数据的结果,证明了修正的、包含应变率函数项的材料本构模型更适用于描述不同成形方向下的材料动态力学性能,该模型能够为建立精确可靠的各向异性材料仿真模型提供数据支持。     

AZ31镁合金板材成形极限及温热成形应变速度研究

AZ31镁合金板材的伸长率随着温度和高温下应变速度的变化而改变，所以在研究AZ31镁合金板材的温成形性能时，必须考虑温度和变形速度对其的影响。在本文中，在不同成形条件下，对板材进行半球形凸模的拉伸试验和强度测试试验，并结合有限元模型，分析了温度和应变速度对AZ31板材的温成形性的影响。     

铝合金磁脉冲辅助板材冲压技术研究进展

铝合金板材室温下的成形性较差,但在高速变形条件下成形极限大幅提高。为了促进铝合金板材在汽车制造、航空航天及3G领域的应用,需要开发先进的板材成形技术。磁脉冲辅助板材冲压成形技术（EMAS）通过在普通冲压模具中嵌入线圈,能有效控制和改善变形板料的应变分布。针对这些问题,重点介绍和讨论了EMAS技术的国内外研发现状,阐明了开展该技术研究的必要性和重要意义。     

铝合金汽车板性能及其应用的研究进展

系统总结并提出了铝合金汽车板材的七种性能要求,以使铝合金汽车板材的研发具有明确目标;介绍了铝合金汽车板的典型化学成分、力学性能及成形性,论述了影响其性能的主要因素,并重点讨论了预处理工艺的影响及其在保证铝合金汽车板性能上的重要性;还介绍了铝合金汽车板的重点研发内容及其应用情况,最后指出降低铝合金汽车板的成本和价格、做好应用研究是今后扩大铝合金汽车板应用的重要工作。     

利用激光局部硬化效应提高2B06铝合金板材拉深成形性研究

针对2B06铝合金复杂零件成形困难问题,提出了利用激光热处理局部硬化提高板材成形性的思路。在通过激光热处理试验研究了铝合金板的激光硬化效应的基础上,采用数值模拟计算了铝合金板激光热处理过程中激光光斑路径和其周边热影响区域的峰值温度场,并通过实际测温验证了其准确性。提出并构建了耦合性能梯度的差性坯料模型,对激光局部硬化的杯形件拉深成形性进行了模拟和试验研究。结果表明,激光扫描方式可以形成稳定的梯度温度场并对周边非加热区影响较小,且可以通过多道次扫描方式设计不同宽度范围的大梯度差性板材坯料。力学性能试验表明激光热处理可以有效地提高铝合金的局部加工硬化能力,这种效应可以有效抑制杯形件拉深时圆角大变形区的减薄,从而提升了板材的拉深性能。在上述基础上,将激光局部热处理用于2B06铝合金航空复杂口框零件的成形,通过设计激光处理路径和参数,获得合理的局部硬化区域,可有效地避免在加强筋处出现过度减薄导致的破裂,大大提高复杂零件的成形性。     

Development of application technique of aluminum sandwich sheets for automotive hood

Objective of this study was to develop basic techniques in order to apply aluminum sandwich sheets for an automotive hood part. The aluminum sandwich sheet is the material fabricated by adhering two aluminum skins to one polypropylene core. When it has the same bending stiffness as a steel sheet, it is 65% lighter than the steel sheet and 30% lighter than an aluminum alloy sheet. Therefore, it is notified exclusively as good substitutive materials for a steel body to improve the fuel efficiency. Through aluminum sandwich sheet, however, it has relatively lower formability than that of the steel sheet for automotive application. In this study, we developed application techniques of the aluminum sandwich sheet for automotive hood. The various formability evaluations were carried out in order to secure the fundamental data for the measurement of sheet metal forming and the establishment of optimum application conditions of the sandwich sheet. From these results, it was found that the sandwich sheet could reduce the weight and maintain the flexural rigidity simultaneously comparing to the steel sheet.     

铝合金阶梯形件粘性介质压力成形的研究

通过压缩试验得到了粘性介质的应力－－应变关系、压力衰减随冲头加载速率及时间变化的规律。采用有限元软件DEFORM分析了在不同压边力下分别用钢凸模和粘性介质成形铝合金阶梯形件的工艺过程。结果显示，采用VPF可以提高板料的成形性。根据模拟结果，采用VPF成功地制备了阶梯形件，这表明有限元法对VPF试验具有很好的指导意义。     

Process metallurgy design of aluminum alloy sheet rolling by using two-scale finite element analysis and optimization algorithm

Recently, the asymmetric rolling (ASR) process was applied to the aluminum alloy sheet generation to control the micro-crystal structure in order to improve the formability and the strength. Until now, many experimental and numerical studies of ASR process have been carried out, but these schemes have not enough capability to predict the texture evolution at the micro-scale and the sheet formability at the macro-scale. In this study, we develop a process metallurgy design code to analyze and optimize the sheet rolling process. At first, our dynamic-explicit crystallographic homogenized elasto/viscoplastic finite element (two-scale FE) code was applied to analyze ASR sheet deformation and optimized ASR process to generate a high formability sheet metal by employing the response surface method. A texture evolution of ASR sheet metal under an optimum process condition was compared with the experimental results, and the availability of our design code was confirmed. Next, an initial texture for the symmetrical warm rolling was optimized to generate a better formability sheet metal. Consequently, our two-scale FE code combined with the optimization algorithm was verified as a comprehensive tool in the process metallurgy design to predict plastic induced texture evolutions and optimize a rolling process and an initial texture for a high formability sheet generation.     

Analysis of the bulging process of an AZ31B magnesium alloy sheet with a uniform pressure coil

As the lightest metal material, magnesium alloy is widely used in the aerospace, automobile, and consumer electronic industries. However, magnesium alloy sheet has poor formability at room temperature. Electromagnetic forming is a high velocity forming technique that can promote the formability of low ductility materials, improve the strain distribution of workpieces, and reduce their wrinkling and springback. In this work, a uniform pressure coil was used to bulge AZ31B magnesium alloy sheets. The finite element method was then used to analyze this bulging process. The bulging contours and displacements of AZ31B magnesium alloy sheets were consistent with the experiment results. The distribution of the magnetic field intensity and magnetic field forces were found to be better than using a flat spiral coil. The deformation rule of AZ31B magnesium alloy sheet using the uniform pressure coil differed from that using the flat spiral coil. The largest strain occurred at the center of the sheet.     

AA6061铝合金正方形截面管胀形工艺研究

AA6061铝合金挤压管材在常温下强度高但塑性差,难以成形复杂形状零件。基于此,提出了固溶处理+固体颗粒介质胀形+人工时效的工艺流程,通过固溶、淬火和时效等热处理工艺调整铝合金变形前后的力学性能,应用固体颗粒介质胀形技术实现管件塑性成形。以AA6061挤压铝合金管为研究对象,分析了固溶处理工艺参数对合金力学性能的影响,发现管材经固溶温度560℃且保温120min处理后,其延伸率提高3倍以上,强度和硬度也大幅降低,使合金管材的成形性能指标显著提高,具备了固体颗粒介质胀形管件的条件;对合金固溶处理后再人工时效处理的试验研究表明,人工时效温度180℃且保温360min时合金塑性下降,强度和硬度等性能指标均可恢复至初始状态。基于铝合金热处理工艺特征的研究,采用固溶处理+固体颗粒介质胀形+时效处理的工艺流程,成功试制了AA6061铝合金典型的正方形截面管件,其环向最大展长率可达34%。     

Numerical simulation of electric hot incremental sheet forming of 1050 aluminum with and without preheating

Incremental sheet forming (ISF) consists of deforming the sheet, through a spherical punch, punctually and progressively until it reaches the desired geometry. Compared to the conventional process, the ISF can achieve much higher levels of formability. But the stresses and residual strains are often pushed to the limit on the path, producing a piece with brittle behavior, which is not desirable for applications in engineering. To work around this inconvenience, one solution would be to perform the conformation at high temperatures, a process known in engineering as hot forming. This study aims to evaluate the behavior of the state of stresses and strains in the hot incremental sheet forming of 1050 aluminum alloy, with and without pre-heating, using the finite element method. This behavior has been studied by numerical simulation, using the software RADIOSS, which has a suitable formulation for inserting the effects of temperature and strain rate in the material. The results show a decline in the forces for electric hot incremental sheet forming preheated (EHISFP) compared to the electric hot incremental sheet forming (EHISF). Moreover, for these same cases, there was a gain in relation to the geometric precision on average more than 4%.     

Viscous pressure bulging of aluminium alloy sheet at warm temperatures

Improving the formability of aluminium alloy sheet metal by using warm or elevated temperature has become a valid approach. In this paper, viscous pressure bulging (VPB) at warm temperature is proposed. The coupled thermo-mechanical finite element method and experimental method were used to investigate the VPB of aluminium alloy AA3003 at warm temperature. The temperature distributions of sheet metal and viscous medium were analyzed for non-isothermal VPB. The influence of forming temperature on thickness distribution, forming load and failure location of sheet metal were investigated. Research results show the temperature gradient field in sheet metal forms when the initial temperature of viscous medium is lower than that of sheet metal. The formability and failure location of sheet metal changes with initial temperature of viscous medium.