LY12超塑性成形有限元分析

基于LY12铝合金超塑性材料属性建立了弹-粘塑性本构模型。利用该本构模型并结合最大等效应变速率控制压力变化算法对LY12铝合金板超塑性圆杯成形进行数值模拟，得到圆杯变形过程中的应力应变分布、板料厚度变化及所需成形时间。根据模拟获得的优化压力时间曲线对圆杯进行超塑性气压胀形加载实验，制件厚度分布与模拟结果非常接近。     

板材超塑性胀形过程的数值仿真

板料超塑性胀形成形是一种全新的金属成形工艺.用Pare-Stamp2G板料成形数值模拟软件对一个实际成形件的超塑性胀形过程进行了数值仿真,分析了超塑性胀形成形变形过程中成形件的应力、应变、摩擦和厚度分布,研究了超塑性胀形过程中金属变形规律和工艺参数对成形过程的影响.结果表明,Pam-Stamp 2G板料成形数值模拟软件是超塑性胀形成形工艺应用到实践中的有效分析工具.     

一种耦合晶粒长大的超塑性本构及数值模拟

本文基于弹粘塑性有限元技术 ,将经过修正的晶粒长大模型耦合到材料粘塑模型中 ,得到一个考虑晶粒行为的超塑材料本构模型。利用所建立的考虑晶粒效应的本构模型和经典的Backofen本构模型 ,分别对Ti 6Al 4V圆杯进行超塑性成形模拟 ,其厚度分布结果表明 ,新本构能很好地描述晶粒敏感型材料的超塑性能。     

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。     

板料超塑性拉伸失稳研究

基于板料超塑性变形的特点，本文将超塑性变形全过程分为稳定变形、准稳定变形、应变路径漂移和集中性失稳发展四个阶段，依据增量理论，用数值方法建立了一普遍适用的失稳模型。然后在此基础上，依板料发生集中性失稳（ｄε＿２＝０）为许用变形程度的极限，预测了板料超塑变形时的成形极限曲线。对铝合金ＬＹ１２ＣＺ和半硬态黄铜Ｈ６２的超塑性实验研究表明：用本文提出的失稳模型预测的超塑性板料的成形极限与实验结果具有较好的一致性。     

板材超塑性拉延过程的数值模拟

板料超塑性成形是一种全新的成形方法。用刚塑性有限元法对Zn-22Al合金U形拉延过程进行了数值模拟，分析了变形过程中工件的应力、应变、摩擦和厚度分布，揭示了成形过程中金属的性变形规律，为成形工艺设计提供了有效的分析工具。     

一种适用于率相关晶体塑性模型的准隐式积分算法

参考经典的切线系数法,采用向前梯度法对修正的超弹性晶体塑性模型进行本构方程积分,提出了一种新的准隐式积分算法。该算法采用基于中间构型的超弹性晶体塑性模型,无需更新晶粒取向相关的状态变量;采用修正的超弹性框架,无需进行由Green-Naghdi材料共旋引起的旋转变换。这种准隐式积分算法兼有超弹性模型和切线系数法的优点。通过对铝合金筒形件拉深的模拟表明,该晶体塑性模型能有效地预测不同初始织构产生的不同制耳现象,同时具有很高的计算效率。     

塑性有限元模拟技术在金属板料成形中的应用

板料塑性有限元模拟技术是冲压工程中的一项新技术，在我国还较落后。本文论述了板料塑性有限元模拟技术的优点及其力学特点，归纳总结了此项技术在国外的发展历史。本文旨在使国内同行了解国外的研究状况，以尽快缩短与国外的差距。     

金属塑性成形过程的计算机模拟

综述了金属塑性成形过程的计算机模拟基本理论，它包括基于不同材料的本构关系的基本方程，动态边界接触问题的数学模型，网络重划技术等，同时对其软件系统的总体设计和应用进行了阐述，并指出了该领域的发展方向。     

材料超塑性研究的现状与发展

对20世纪90年代以来国内外超塑性的研究工作进行了介绍和评述.主要介绍了新的超塑材料的开发及超塑性的应用,概述了国内外超塑性研究的最新进展,并对超塑性研究的热点问题进行了评述,重点评述了用超塑成型方法制作大型铝合金汽车零件、用分子动力学模拟超塑变形中的晶界滑动、新材料和纳米材料的超塑性开发及超塑微成形的研究等国内外超塑性研究的新进展.展望了超塑性的发展趋势,指出应开发材料的低温或高速超塑性,重视超塑性流动过程的理论研究,进一步拓展超塑性的应用领域.     

Constitutive Equation with Varying Parameters for Superplastic Flow Behavior

In this study, constitutive equations for superplastic materials with an extra large elongation were investigated through mechanical analysis. From the view of phenomenology, firstly, some traditional empirical constitutive relations were standardized by restricting some strain paths and parameter conditions, and the coefficients in these relations were strictly given new mechanical definitions. Subsequently, a new, general constitutive equation with varying parameters was theoretically deduced based on the general mechanical equation of state. The superplastic tension test data of Zn-5%Al alloy at 340 °C under strain rates, velocities, and loads were employed for building a new constitutive equation and examining its validity. Analysis results indicated that the constitutive equation with varying parameters could characterize superplastic flow behavior in practical superplastic forming with high prediction accuracy and without any restriction of strain path or deformation condition, showing good industrial or scientific interest. On the contrary, those empirical equations have low prediction capabilities due to constant parameters and poor applicability because of the limit of special strain path or parameter conditions based on strict phenomenology.     

Ti－6Al－4V及Ti－10V－2Fe－3Al合金超塑性变形中各向异性研究

对Ｔｉ－６Ａｌ－４Ｖ挤压管材和厚板以及Ｔｉ－１０Ｖ－２Ｆｅ－３Ａｌ合金板材进行了拉伸和压缩实验，以考察其超塑性变形中的各向异性。这些钛合金超塑变形中的各向异性主要体现在以下几个方面：（１）超塑拉伸或压缩中圆试样横截面变为椭圆形状；（２）由材料不同方向截取的试样在超塑拉伸或压缩中应力一应变速率关系不同；（３）横向试样超塑拉伸中试样表面凹凸不平并逐渐发展为多颈缩。这些各向异性表现，主要与材料原始显微组织及其在变形中的演变相关。本文并对已有的描述各向异性超塑变形的本构方程进行了修正。     

Ti－6Al－4V及Ti－10V－2Fe－3Al合金超塑性变形中各向异性研究

对Ｔｉ－６Ａｌ－４Ｖ挤压管材和厚板以及Ｔｉ－１０Ｖ－２Ｆｅ－３Ａｌ合金板材进行了拉伸和压缩实验，以考察其超塑性变形中的各向异性。这些钛合金超塑变形中的各向异性主要体现在以下几个方面：（１）超塑拉伸或压缩中圆试样横截面变为椭圆形状；（２）由材料不同方向截取的试样在超塑拉伸或压缩中应力一应变速率关系不同；（３）横向试样超塑拉伸中试样表面凹凸不平并逐渐发展为多颈缩。这些各向异性表现，主要与材料原始显微组织及其在变形中的演变相关。本文并对已有的描述各向异性超塑变形的本构方程进行了修正。     

镁合金超塑性变形的损伤演化效应

研究了AZ31B镁合金板材超塑性变形时的空洞损伤,对拉伸试样在超塑性变形各阶段轴剖面的空洞进行了观察,通过对空洞演化的分析建立了空洞体积分数与变形程度的定量关系,并推导出基于微损伤演化规律及统计细观损伤力学的损伤演化方程,通过试验得到适用于AZ31B镁合金板材超塑性变形损伤演化的特征参数C1、C2和损伤变量临界值DC.     

On the optimization of superplastic blow-forming processes

The superplastic blow-forming process of thin sheets is analyzed, and an optimal stable deformation path that reduces production time is obtained. The analysis is based on an analytical model for the superplastic forming (SPF) of a long rectangular box made of Ti-6Al-4V alloy at 900 °C use of a microstructure-based constitutive equation for the strain rate and grain growth, a stability criterion, and a variable strain rate control. It is shown that by imposing a variable strain rate control scheme derived from the stability analysis, an optimal forming time can be developed while maintaining a stable deformation path. Some other control schemes also show effectiveness in either reducing the localized thinning in the formed sheet or reducing the required forming time. Effects of friction and initial grain sizes on the forming pressure profile and the thickness distribution of the formed sheet are also investigated.     

Superplasticity of fine-grained 7475 Al alloy and a proposed new deformation mechanism

A study has been made to investigate the superplastic deformation mechanisms of 7475 Al alloy in relation to the variation of grain size ranging between 5.5 μm and 13 μm. The strain-rate sensitivity (m) was increased with decreasing grain size in the superplastic deformation regime. Microstructural investigation after tension tests revealed that the dispersoid free zones were produced mostly at the grain boundaries normal to the tensile direction. A new model for describing the deformation behavior of the 7475 Al alloy has been proposed based on the assumption that the grain boundary sliding was accommodated by both diffusional flow and slip. This new model well predicts many aspects of experimental results.     

大型锻件的本构关系

文章简述了大型锻件的锻造工艺特征,并据此给出了大型锻件锻造全程数值模拟对本构关系的具体要求。给出了基于不可逆热力学理论所建立的热粘塑性本构关系的一般框架,详细讨论了各种工况条件下材料流动应力的表达式和内变量的演化方程,后者是正确预报热锻中微观组织演化的理论基础。还特别讨论了考虑3种变形机制的超塑性本构关系,这对发展航空锻件等温锻和超塑性成形具有重要意义。给出了用这些本构关系进行大锻件锻造过程全程数值模拟与晶粒度预测的实际案例,由这些案例可以看出,工艺数值模拟结果对理解和解决实际工程中的技术难题帮助极大。     

Fracture types and thickness distribution in superplastic sheets formed with plastic injection molding

This paper investigates the fracture types and thickness ratio distribution in superplastic Zn/Al sheets formed during a hybrid process combining superplastic sheet forming with plastic injection molding. Three types of sheet fractures, edge cracking, central cracking and combined cracking, are observed. The success of forming superplastic sheets with rib features using injection molding with various parameters, including melt temperature, injection pressure and mold temperature, are investigated. They are presented in the form of a molding area with areas of various fracture types. Central cracks occur when superplastic sheets are formed with injection molding with higher melt temperature, while edge cracks occur with higher injection pressure. When the melt flow is parallel to the sheet rolling direction, the areas of edge crack are enlarged. The sheet thickness ratio distribution is obtained for various injection parameters and rib depths. Observation of the sheet thickness distribution for variation parameters, the tendency of the sheet fracture type can be generalized.     

微细薄板尺度依赖的材料本构模型的构建(英文)

通过表面层理论和金属晶体塑性变形原理解释微细薄板材料在塑性变形中产生尺寸效应的内在机理。引入尺度参数,对经典的Hall-Petch公式进行修正,建立基于表面层模型理论的尺度依赖材料模型。利用所建立的材料模型分析微细薄板厚度及其晶粒尺寸对材料成形流动性能的影响。在晶粒尺寸一定的情况下,随着微细薄板厚度的减小,材料流动应力逐渐降低;晶粒尺寸越大的微细薄板,其流动变形的尺寸效应现象越明显。利用不同厚度的不锈钢和纯铜箔材的微细薄板拉伸真应力-应变曲线对所建立的材料模型进行验证,计算结果与实验结果比较吻合,验证了所建立的材料模型的合理性。