板料变形三维数字散斑应变测量分析系统研究

针对板料变形中应变检测的常规方法和传统方法存在的不足,通过数字散斑相关方法、计算机双目视觉理论和材料力学理论分析了试件表面变形前后的散斑图像,来动态跟踪试件表面上几何点的运动并得到三维位移场,在此基础上计算得到试件的三维应变场.基于此原理开发了XJTUDIC三维数字散斑动态应变测量分析系统.应用带孔铝质制件进行了单向拉伸实验.测量结果表明,该系统能较好的反映板料变形过程中的三维应变状态,较好的测量试件表面的三维轮廓,直观再现工件表面的变形场、应变场和成形极限图(FLD),对于需要测量的关键点可以实现重点跟踪,动态测量出该点在任意时刻任意位移的应变.该系统可以应用到不同的力学测量现场.     

板料应变视觉测量系统研究

介绍了板料应变视觉测量系统结构和基本原理。该系统运用立体视觉技术对板料成形物理模拟中的圆形坐标网格系统进行测量，获得变形板料的应变分布。实验结果表明，该系统可以较为迅速地完成各种成形工艺的板料件应变参数的测量与分析，并取得比较理想的精度。     

板料渐进成形极限图测试方法研究

成形极限图是判断板料成形中是否会发生失效的重要依据。渐进成形中的板料成形极限图和传统冲压成形极限图有显著不同。板料传统冲压成形极限图测试方法已较为完善,而对于渐进成形尚没有形成统一的标准。本文在已有的测试方法基础上,提出了通过渐进成形圆弧沟槽、十字交叉圆弧沟槽直至板料端部破裂后,测量破裂位置最大和最小主应变以获得板料渐进成形极限图的新方法。通过数值模拟研究,分析了采用该方法对板料进行渐进成形时板料局部的应变状态,表明该方法可行;并使用该方法得了0.9mm厚工业纯铝1060板料的渐进成形极限图。     

工业纯铝板料渐进成形极限图研究

板料渐进成形极限图和传统成形极限图有显著不同,到目前为止尚未有统一的测试方法.提出了一种测试板料渐进成形极限图的方法,成形工具分别沿往复圆弧和交替往复圆弧轨迹运动,对0.9mm工业纯铝板进行渐进成形.板料破裂后,获得了主应变和次应变,建立了该种板料渐进成形极限图.通过板料渐进成形分别成形了一些零件,测量了零件的主应变和次应变并绘制了它的渐进成形极限图.结果表明,所获得的工业纯铝渐进成形极限图能较为准确地预测渐进成形中板料的破裂,测试方法适用于渐进成形极限图的建立.     

基于立体视觉的坐标网格分析法

坐标网格分析法作为一种物理模拟技术 ,已在金属塑性成形的生产中被广泛应用 ,但传统的手工测量方法存在工作量大和精度低的缺点。该文针对板料成形中常用的三维圆形坐标网格系统 ,提出一种新的基于图像处理和立体视觉技术的网格应变自动测量分析方法 ,并开发了相应软件 ,成功地测绘出变形工件的应变等值线图和板料成形极限图。实验结果表明 ,该方法可以使板料应变的测量速度和精度均得到提高     

大型工件成形快速应变测量技术

针对目前大型工件在成形过程中应变测量的实际问题,提出了一种快速视觉测量方案,在采用近景工业摄影测量与坐标网格相结合的基础上,进行基于公共点的三维测量数据拼接可以高效地实现大型工件成形后表面全场应变的快速测量,通过对某汽车顶盖冲压零件表面应变的测量,验证了该方法的可行性和有效性。     

数字图像相关法的板料成形极限研究与应用

为了克服现有板料成形极限测定方法的不足,采用XJTUDIC三维数字散斑应变测量系统,实现了一种基于数字图像相关法的板料成形极限测定新方法。首先,将测量系统架构在杯突试验机上,记录从试验过程初始到破裂的一系列图像,实现应变在线、全场测定。然后,通过对破裂前的最后一张图像进行截线,拟合数据,对颈缩区域插值得到极限应变,从而绘制成形极限曲线图。最后,通过对SPCC36型号碳钢材料板料件成形极限的测量,验证了本文方法的可行性和有效性。     

辊压成形板材表面微结构数值模拟研究

微结构辊压成形技术是耦合了传统的辊压技术与微挤压成形技术的一种新型成形技术,该技术将所需微结构复制到辊表面,然后将辊上的微结构再复印到板材表面。通过有限元对板材微结构辊压成形过程进行数值模拟,对成形阶段及温度在90,120和150℃等条件下对成形力的影响进行分析,结果表明:整个辊压阶段,板料发生剧烈塑性变形的范围只集中在板料表层,应变的最大值总是分布在凹槽的底面,板料中间至底部几乎没有应变;同时随着温度升高,稳定成形阶段的载荷值呈降低趋势。通过实验进行了验证,给出了实验结果的局部测量值。     

数字图像相关法的板料成形极限研究与应用

为了克服现有板料成形极限测定方法的不足,采用XJTUDIC三维数字散斑应变测量系统,实现了一种基于数字图像相关法的板料成形极限测定新方法.首先,将测量系统架构在杯突试验机上,记录从试验过程初始到破裂的一系列图像,实现应变在线、全场测定.然后,通过对破裂前的最后一张图像进行截线,拟合数据,对颈缩区域插值得到极限应变,从而绘制成形极限曲线图.最后,通过对SPCC36型号碳钢材料板料件成形极限的测量,验证了本文方法的可行性和有效性.     

汽车背门口左右角板的冲压成形分析

结合BUP板料成形试验机和ARAMIS三维光学材料应变测量系统,测量DC53D的成形极限曲线,通过试验得出DC53D成形极限最低点应变值为36.4%。利用网格应变分析技术对汽车部件背门口左右角板进行冲压成形分析,得到冲压件的主应变最大值31.2%,最大厚度减薄25%,以及特征截面线上的主应变变化曲线。同时将冲压件的主应变与DC53D的成形极限曲线对比分析发现:汽车部件背门口左右角板的大部分变形为拉延变形;冲压板料DC53D具有良好的冲压成形性能;冲压件对应成形极限曲线最低点的主应变为24.3%,网格应变分析结果可以作为成形件失效分析和模具调试与修整的依据。     

Comparison of different analysis models to measure plastic strains on sheet metal forming parts by digital image processing

The principal strains of sheet metals and their limitations while forming can be obtained by using a strain measurement system. A strain measurement may employ one of two different approaches: namely the total least square optimization method or the multiple regression analysis (MRA) method. With both methods plastic strains of deformed parts are calculated based on the non-deformed reference configuration designated by a circle and the deformed configuration, which is a curve-fitting ellipse. In the MRA method, the mathematical formula is simpler reducing the required computations than that of the total least square optimization method. While the formula has a greater margin of error, this margin proves less than significant in the practical application of the method’s results.Information from the results of a strain measurement system can be used to determine the sheet metal’s formability and strain path allowing engineers to determine at which point, the sheet metal will crack. They can then change the thickness and the material of the sheet metal, or modify its shape accordingly to maximize the metal’s efficiency. Strain measurement systems possess practical advantages in their actual application; they improve the quality of sheet metal being produced by minimizing defects in sheet metal during production. One industrial case study of fine stamping electronic part is discussed to demonstrate the proposed methodology.     

板材成形中的曲面拓展方法

曲面拓展是曲面造型中的一项重要内容 ,研究曲面拓展的方法在板类件设计中有着十分重要的意义。针对板类件成形中板类件与压边面之间的过渡曲面的设计 ,本文提出一种基于非均匀有理B样条 (NURBS)的曲面拓展造型的新方法 ,通过曲面构造、曲面拼接完成曲面拓展 ,生成零件与压边面之间的过渡曲面。这种算法简单、便于应用。在成形用于医学工程中的曲面片时 ,得到高质量的成形件。     

金属板材剪切变形全过程的模拟

应用韧性损伤力学模型以及刚塑性有限元法，分析了金属板材剪切断面变形的全过程。根据损伤变量的变化，采用单元消除法分析了剪切裂纹的扩展，并得到了剪切各个阶段的金属流动、应力应变以及损伤变量分布。模拟得到的断面变形情况与实际十分吻合，说明该方法是可行的。     

A new experimental approach for obtaining diffuse-strain flow stress curves

A new experimental approach for determining the sheet metal flow stress curve for diffuse necking deformation through the hydraulic bulge expansion (HBE) test is introduced. For this approach, a flat sheet of metal is bulged under the load of hydraulic pressure within the confines of a rigid binder/die tool set of circular die opening. The hydraulic pressure and volume flow rate of the pressurized water entering the die cavity are recorded in real time. Operating under the assumption of thin-walled pressure vessel behavior, the real time data are used to compute the flow stress curve for the material type considered. The novel aspect of the proposed technique is the use of water volume measurement for determining the radius of curvature of the expanding dome. An example flow stress curve for 1.0 mm thick DDQ cold rolled sheet steel is shown to be in good agreement with the flow stress curve obtained through the standard uniaxial tension test. One key advantage of this proposed method is that the analyst may determine the diffuse necking portion of the flow stress curve without employing cumbersome techniques associated with uniaxial tensile test methods. Two disadvantages of the proposed method are the uncertainty associated with having to assume a yield surface, and the error associated with having to assume membrane behavior in the work piece. The introduction of this new method will increase researchers’ access to practical methods for obtaining sheet metal flow stress curves.     

基于响应面法的挡风梁冲压回弹预测模型

以5182铝合金挡风梁成形后的回弹为研究对象,通过单向拉伸试验,获取了5182铝合金板料在不同轧制方向及应变速率条件下的真实应力应变曲线,并将其引入数值模拟模型,研究了板料成形速度、模具间隙、摩擦系数对5182铝合金挡风梁成形回弹的影响规律并分析了其形成原因。然后根据响应曲面法建立了5182铝合金挡风梁回弹预测模型,进而通过不同条件下的实验对比,对该预测模型进行了验证。研究结果为铝合金板料回弹的分析提供了新的思路。     

板料成形极限理论与实验研究进展

成形极限是板材成形领域中重要的性能指标和工艺参数。文章在阐述成形极限在板料成形中的意义的基础上,综述并分析了成形极限在理论和实验方面的研究进展。成形极限图受应变路径的影响,给工业生产应用带来极大不便。以极限应力构成的成形极限应力图不受应变路径的影响,作为复杂加载路径的成形极限判据更加方便和实用。FLSD研究与FLD相结合,成为精确地确定破裂判别准则的主要途径之一,是近来研究的热点。十字形双向拉伸是实现复杂加载路径有效实用的试验方法。最后对成形极限应力图和十字形双向拉伸试验需要解决的关键问题作了阐述。     

3D-surface parameters and their application on deterministic textured metal sheets

In sheet metal forming the surface structuring of steel sheets is applied by several methods during skin pass rolling. The function of the surface is to lower the friction in the forming process and to achieve a high glossiness of the finished product after painting. In the past, two technologies have been developed to texture the rolls with a three dimensional deterministic structure: the laser texturing surface and the electron beam texturing surface. Due to their deterministic feature such topographies are totally different from those usually applied and thus, they require adequate methods to characterize them. Appropriate parameters can be derived from the so called mechanical-rheological model which is about to be developed at the LFT. Basic parameters are the material area ratio as well as the open void area ratio and the closed void area ratio. In the present paper the theoretical background of the new surface parameters as well as the method of measurement and the program SAM (Surface Analysis Module) will be explained. To demonstrate the capabilities of the method, different kinds of surfaces are characterized using the newly developed parameters. For practical use in industrial application the change of the surface in a cold rolling process for the manufacturing of steel sheets was investigated. It can be shown by the new parameters that there is a strong influence of the mill's wear process on the structure of the rolled steel sheet. Another application concerns the surface deformation in a deep drawing process.