板料网格应变显微测量系统应用研究

综合分析了国内外网格应变测量的研究情况以及应变测量对于FLD的重要性及意义,设计了专门的网格应变用显微测量仪,并选择了合适的CCD和图像采集卡,构成了板料网格应变显微测量的桌面系统.针对不同形式的应变网格,分析了不同网格印制方法的特点,研究了不同的图像处理测量方法,完成网格应变显微测量系统软件的开发及应用研究.     

数字图像处理技术进行方形网格应变测量

针对板料成形中应用的方形网格系统,运用图像处理对变形网格进行参数测量和应变分析。运用邻域平均法进行滤除噪点,采用动态阈值法对拍摄的方形网格图像进行增强等像质改善处理;并通过细化算法得到网格线的简单线条,在分析方形网格交点的图像特征后,设计出相应的算法提取出方形网格的特征点,最后由特征点的空间坐标计算出方形网格的几何参数和应变,得到工件表面的应变分布。对球面胀形件进行了具体分析,并将测量结果与手工测量数据进行比较,结果表明,该方法可以达到一定的精度。     

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。     

弹塑性大应变双重非线性问题分析的再生核质点法研究

再生核质点法是一种新型无网格方法,只需质点信息而无需划分网格,在大变形大应变分析中能够方便适应计算中网格畸变。在大应变情况下引入Jaumann应力率和应变速率来表征材料的弹塑性本构关系,并将再生核质点法的插值方法引入虚位移原理,推导了弹塑性大应变再生核质点法计算控制方程,给出了方程计算格式。通过对具体算例的分析研究表明了,此方法对弹塑性大应变分析的有效性。     

基于应变非接触测量的裂纹拼接

使用基于图像处理的非接触网格应变测量法绘制板料成形极限图,通常选取裂纹边缘网格测量应变,测量值较理论值偏小,甚至相差较多。本文使用图像处理方法,分别建立了基于多目视觉和显微测量镜头的裂纹拼接算法,可对难变形件裂纹处网格进行拼接测量。试验结果表明,两种拼接算法均满足精度要求,前者误差为1.5%,后者为1%,对于改进成形极限图的测量方法、提高成形极限图的测量精度具有一定的参考作用。     

轿车侧围零件冲压开裂网格应变分析

网格应变测量系统是专用于测量汽车车身用钢在冲压过程中变形的分析设备.以某国产轿车侧围零件为例,选择ARGUS网格应变测量系统为工具,通过网格应变分析,找到了冲压开裂的原因,并从模具和材料两个方面提出了优化方案,在实际生产中得到了较好地验证.     

板料成形三维全场应变摄影测量快速检测系统研究

针对目前板料成形过程中应变测量的实际问题,提出了一种新的测量方案,通过采用近景工业摄影测量与坐标网格分析法相结合的方法,可以高效地实现板料成形后表面全场应变的精确测量。基于以上方法设计并开发出了可以应用于实际的板料应变检测系统XJTUSM。通过对某些型号的钣金零件表面应变的测量,验证了本文方法的有效性。     

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。     

便携式板料应变测量系统GMAS

本文介绍了自行研制的板料应变非接触网格测量系统GMAS,并对GMAS的工作原理和关键技术进行了探讨,通过与国际上流行的美国ASAME网格测量系统的比较,验证了GMAS系统在测量精度和操作简便快捷以及界面的美观方面都已达到国际先进水平,是研究板料成形过程中应变路径和变形分布的重要工具.     

光学应变技术在QP钢成形极限试验中的运用

采用光学网格应变分析技术对QP钢进行成形极限试验,评价两种QP钢的成形性能,并与传统的DP钢进行比较。结果表明,和原有的测量方式相比较,光学网格应变分析方法可靠性高,测量较为准确,能够消除人工测量产生的差异;和传统的高强钢DP980相比,第三代汽车用高强钢QP980和QP1180具有较好的成形性能。     

Recent developments in a vision-based surface strain measurement system

The vision-based measurement method is capable of determining three-dimensional (3-D) coordinates of all the intersecting points of a square grid pattern located on the surfaceof a deformed sheet-metal part. These 3-D coordinates are used to determine the surface strau]n over the area. To measure the coordinates of such a surface, multiple video photographs are usually taken over the measurement area. Methods to improve the overall accuracy of the vision-based strau]n measurement system are outlined and the possible ultimate accuracy that can be attau]ned by the use of such a measurement method is discussed.     

Post-processing analysis in sheet-metal forming simulation

This article describes the use of finite-element analysis computer simulation to assess the feasibility of stamping sheet-metal autobody panels at the design stage. Using this methodology, proposed product designs can be tested without the need for expensive and time-consuming prototyping. Post-processing transforms simulation results into stress and strain color-coded or contour plots that can be related to a number of stamping problems and are the key to interpreting product quality and integrity.     

盲孔法测残余应力中应变释放系数的修正方法

应变释放系数A、B是影响盲孔法测试精度的主要因素．常规方法都是通过标定试验来得到具体的A、B值；在前人工作的基础上，本文采用有限元软件，通过建立三维有限元模型，数值模拟了应变释放系数的测试试验．并对随形状改变比能参量S变化的应变释放系数塑性修正公式进行了推广。采用该公式来计算应变释放系数，能够大大提高计算精度，并可以省去标定试验，既节省时间，又方便经济，具有很重要的应用价值。     

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     

Application of laser stereolithography in FE sheet-metal forming simulation

This paper describes a new method developed by authors, by which the results of FE simulation in sheet-metal forming operations can be output as 3-dimensional substantial objects, where previously it could only be done with computer graphics. The system employed in this method is a kind of laser stereolithography system added with interface software to FE data. This method is being used to confirm the design of dies and to analyze successfully problems that may arise during the forming process.     

Improvements in finite-element simulation for stamping and application to the forming of laser-welded blanks

During stamping-die design, the formability in sheet-metal forming process has been evaluated by the geometrical functions in ‘Die-Face CAD’, which has been developed and improved by Toyota Motor Corporation. When evaluation by these functions is difficult, formability has been estimated by performing experiments using test dies in which the forming defects are similar to those in the actual process.

A numerical method has been developed in order to substitute numerical analysis for experiments using test dies for the accurate prediction of defects in sheet-metal forming. The elastic-plastic FEM with the commercial code ‘JNIKE3D’ has been improved in the areas of: (1) the material constitutive equation; (2) the consideration of the pressure distribution on the blank-holder; and (3) the evaluation of breakage initiation. Using the improved method, the square-cup drawing process and the hemming process have been analyzed. Numerical results for strain, breakage initiation, and hemming deflection were in good agreement with experimental results. The formability of laser-welded blanks and the most efficient process to form them were evaluated also using the improved method.     

Efficient control of metal-forming machines with an automated load and measurement device

The properties of metal-forming machines influence the quality of the produced sheet-metal components. To investigate the implication of machine characteristics on quality the components, an automated load and measurement device (LMD) has been developed. This equipment simplifies the investigation of machine properties and increases the reproducibility of the results. Furthermore, it enables the study of other factors like warming-up effects on machine behavior which are not enough researched.     

Optimization of sheet-metal forming processes using the special-purpose program AUTOFORM

Optimizing the parameters of sheet-metal forming processes requires an efficient and accurate simulation program that is able to handle real-world problems and which can be operated by a non-finite-element specialist. The program AUTOFORM is limited to the sheet-metal forming process, and fits the requirements of this process optimally. Not only is the program's technical overhead reduced to a minimum, but also the program is largely vectorizable and parallelizable and allows the use of specially developed algorithms: the number of computational degrees-of-freedom is reduced by decoupling the determination of the sheet-metal form from the flow of metal within this form. The algorithm is not only capable of taking into account the relevant bending effects but also enables more efficient iterative solvers to be used. In addition to appropriate algorithms for material behaviour, friction, blank-holder and drawbeads, the necessary accuracy is attained by using the implicit method and by adaptive mesh refinement algorithms, which allow a very fine discretization of the geometry. Using AUTOFORM, the forming processes of two real-world automotive body parts and other sheet-metal forming parts have been optimized recently by adapting parameters such as blank geometry, material, time variable blank-holder forces, and the location and geometry of drawbeads.