基于配点型无网格法的金属挤压过程数值模拟

阐述了配点型无网格法的基本原理,及其用于求解偏微分方程的步骤和方法,对Al在挤压成形过程中的塑性变形情况进行了三维无网格法模拟。该方法避免了有限元法因网格畸变需要重新划分网格的问题,同时解决了伽辽金型无网格法计算效率低的问题。计算实例表明,配点型无网格法可以利用初始节点完成全部计算,得到与有限元法相吻合的结果,是模拟金属塑性变形过程的一种有效的新方法。     

Analysis of microbending of CuZn37 brass foils based on strain gradient hardening models

Microbending experiments of brass foils were conducted and demonstrated clear size effects, i.e., the normalized bending moment increased with the reduction of foil thickness. The experiments were modeled using the classical plasticity model and three strain-gradient plasticity models. A modified Nix-Gao model was proposed to consider the number of twins across the thickness direction in strain hardening. It was found that the proposed model could better predict the normalized bending moment for both fine-grain and coarse-grain foils and the proposed equation for material intrinsic length could better capture the physics of material deformation. Furthermore, micro-hardness distributions in the bending area were measured and obvious lower-hardness region was found in the middle layer of fine-grain foils instead of coarse-grain foils. This indicates that the modified Nix-Gao model and the assumption of fully plastic bending worked better for coarse-grain foils than for fine-grain foils.     

螯合剂亚氨基二琥珀酸四钠（IDS）在纸浆H2O2漂白中的应用研究

以桉木浆和蔗渣浆为原料,研究了亚氨基二琥珀酸四钠(IDS)作为螯合剂在纸浆H_2O_2漂白中的应用。通过单因素实验,以及在此基础上设计的正交实验,分别得出了IDS作为桉木浆、蔗渣浆H_2O_2漂白预处理段螯合剂的最佳使用条件。结果表明,IDS作为桉木浆H_2O_2漂白预处理段螯合剂的最佳使用条件为:温度60℃,时间50 min,IDS用量0.3%;IDS作为蔗渣浆H_2O_2漂白预处理段螯合剂的最佳使用条件为:温度70℃,时间60 min,IDS用量0.8%。在本实验IDS螯合最优条件下,与EDTA对比发现,IDS的螯合效果与EDTA相当,且IDS易生物降解,无二次污染,具有一定的优势。     

曲轴TR锻造三维CAD／CAPP系统开发

针对曲轴TR锻造装置开发了一套CAD／CAPP系统。该系统能进行曲轴锻造工艺分析和锻模设计。系统以Visual Basic为开发工具,Solidworks为平台实现锻造工艺和模具的三维设计,CAD图纸输出,TR装置参数计算等功能,大大减少了曲轴锻造工艺设计阶段开发时间,提高了设计质量     

塑性成形过程摩擦测试的研究进展

摩擦是影响金属塑性成形及其过程有限元模拟的重要因素 ,因此有必要对其测试方法进行研究。本文介绍塑性成形过程摩擦测试研究方法和测试技术的研究现状与进展 ,并对模拟试验法和直接测量法各自的特点进行了分析。作者设计出一种新型的探针传感器 ,开发出了铝合金板料温成形过程摩擦在线检测系统 ,并对铝合金板(5 182 )圆筒形件温成形过程进行了摩擦测试。     

Rapid Finite Element Analysis of Bulk Metal Forming Process Based on Deformation Theory

 The one-step finite element method (FEM), based on plastic deformation theory, has been widely used to simulate sheet metal forming processes, but its application in bulk metal forming simulation has been seldom investigated, because of the complexity involved. In this paper, a bulk metal forming process is analyzed by using a rapid finite element simulation method based on deformation theory. The material is assumed to be rigid-plastic, strain hardening. The constitutive relationship between stress and total strain is adopted, whereas the incompressible condition is enforced by penalty function. The geometrical non-linearity in large plastic deformation is taken into consideration. Furthermore, the force boundary condition is treated by a simplified equivalent approach, considering the contact history. Based on constraint variational principle, the deformation finite element method is proposed. The one-step forward simulation of axisymmetric upsetting process is performed by this method. The results are compared with those obtained by the traditional incremental FEM to verify the feasibility of the proposed method.     

Improved Formulation of One-Step approach suitable for initially non-flat configurations and forward simulation

 In the traditional one-step formulations using shell elements, the computations of the curvature variation and bending stiffness matrix are simplified by omitting the rotational DOFs on the basis of initial flat blank and fully known final configuration. They are highly efficient but not suitable either for the forming processes with non-flat initial configurations, or for one-step forward and multi-step analyses. Thus a one-step formulation based on the rotation-free BST (Basic Shell Triangular) element is presented here. In this formulation, the following improvements are made: 1) the curvature variation can be calculated exactly and efficiently resorting to a patch of four elements without rotational DOFs, which makes the formulation suitable for non-flat initial configurations, one-step and multi-step forward or inverse analyses, 2) The penalty method, instead of traditional sliding constraint, is employed to treat contacts in the forming processes, which makes it possible to inspect some deformation defects such as wrinkling et al directly. To verify the improved formulation, a program has been developed, and the bending process of a rectangular tube is simulated, with particular attentions paid on cross-sectional distortion. The numerical results of the one-step simulation agree with those of incremental analysis and experimental values.     

基于不同强化模型的GTN损伤模型及其在板料回弹有限元分析中的应用

为了进一步提高板料成形中的回弹预测精度,分别建立了基于Ziegler 线性随动强化模型、Lemaitre-Chaboche 非线性随动强化以及非线性混合强化模型的Gurson-Tvergaard-Needleman(GTN)细观损伤本构模型,并给出有限元数值积分方法。通过用户自定义材料子程序VUMAT 将损伤模型嵌入到有限元软件ABAQUS 中,以NUMISHEET’93 板料U 型弯曲考题为例,应用显隐相结合的方法模拟分析了不同材料强化模型和损伤对板料回弹量的影响。结果表明:在相同GTN 损伤模型情况下,线性随动和非线性随动强化模型预测得到的板料回弹量较小,等向强化预测的板料回弹量偏大,非线性混合强化预测的板料回弹量介于它们之间。材料模型在考虑损伤因素后,预测的回弹严重程度比无损伤情况时略小,与实验值更相近。