塑性成形有限元模拟六面体网格划分和再划分技术

总结了使用三维六面体单元有限元技术模拟塑性体积成形时的网格自动划分技术和自适应网格再划分技术,并分析了各种技术的优缺点。     

金属塑性成形有限元六面体网格自动划分

六面体网格具有计算精度高、网格数量少等特点 ,是工程三维有限元分析一种重要网格。本文提出了一种基于栅格的六面体网格自动划分方法 ,它首先采用栅格法生成核心网格 ,然后把核心网格与模型边界拟合 ,为克服由于边界拟合造成的表面网格质量下降 ,采用包络表面网格的方法生成零厚度表层网格 ,通过表面网格平滑和内部节点位置平滑处理 ,最终生成具有较高质量的全六面体网格。网格划分实例说明 :该法具有原理简单 ,算法可靠 ,编程方便 ,划分网格质量高等特点。最后还对该算法进行了讨论。     

基于模型特征的新型有限元网格划分方法研究

开孔构件的开孔形式各异,增加了其网格划分难度.另外,全六面体网格划分一直是有限元网格划分中的难点之一,实现开孔构件的全六面体网格划分具有重要的现实意义.文章基于开孔实体的参数化特征模型思想,提出了一种非自由边界分割有限元网格划分方法,可以针对开孔实体的几何特征和力学特征,对多种类型的开孔构件进行全六面体网格划分,生成的网格质量均匀、局部加密方便且疏密过渡合理.经实例应用表明,此种网格划分方法具有通用性强、简单、实用、高效等特点.     

金属塑性成形有限元模拟中的六面体单元再划分技术研究进展

系统分析比较了各种六面体单元网格再划分方法的具体技术思路和优缺点 ,及其在模拟三维金属体积成形过程中的应用。结论指出 ,基于在任意几何形状的三维实体上实现全自动生成满足要求的六面体网格的通用算法非常复杂和困难 ,涉及许多具体的特殊问题的处理 ,而且基于畸变后边界节点生成满足拟合精度的几何实体也是如此。本文提出基于畸变网格的质量优化和局部网格加密 /稀释是最佳的解决方法 ,既可以保持初始网格的拓扑结构 ,还可以有效地避开网格再划分问题     

铝型材挤压流动模型的网格划分算法研究

根据铝型材挤压流动模型的特点,提出了一种适用于有限体积法铝型材挤压数值模拟系统的六面体网格划分算法。该算法可以依据模型的几何尺寸定义相应的网格尺寸和疏密程度,实现用尽量少的单元捕捉和拟合模型的所有几何特征,保证了网格数量和网格质量的平衡。最终,利用开发的六面体网格划分算法,对方孔铝型材挤压系统模型进行了网格划分,与Hypermesh的网格划分结果相比,网格单元数由88079减少为20126,从而有利于提高数值计算效率。     

锥齿轮结构化网格生成方法与参数化建模仿真

针对渐开线锥齿轮建模与数值仿真的复杂性、结构化六面体网格划分困难等问题,提出渐开线锥齿轮建模与网格划分参数化方法,编程搭建锥齿轮建模与网格划分参数化仿真分析专用软件平台。运用C++语言编写参数化主程序,进行图形界面可视化设计,搭建锥齿轮主参数输入模块。通过渐开线数学模型和锥齿轮的主参数精确建立插值点位置坐标,提出锥齿轮齿廓渐开线及三维实体结构的分块化合并六面体网格生成法,实现渐开线锥齿轮精确建模、正确规整高质结构化六面体网格生成和有限元分析全过程的参数化。此平台具有渐开线直齿锥齿轮建模速度快和结构化光滑六面体网格精度高、动力学分析操作快捷方便等优点,为解决锥齿轮的有限元结构化六面体网格划分和动力学分析提供一种参数化建模与仿真平台。     

四边形有限元网格划分方法——二分法的改进

提出了一种自动的四边形网格生成法,其实质是把被划分区域无限地分割,直到整个区域全部由四边形单元组成。文中对关键技术最优分割线确定作了改进。实例表明该方法适用性强,可以用于有限元网格的初始划分和网格重分。     

栅格法三维六面体网格自动生成算法与优化

提出了以栅格法六面体网格生成为基础方法,基于实体模型几何特征的六面体网格自适应生成算法,首先对模型进行识别,根据实体模型几何特征建立加密源点信息场,并进行相容性控制,采用栅格法生成核心网格,然后进行核心网格与模型边界的拟合,为克服该方法在实体模型表面网格质量较差的缺点,采用节点位置平滑和拓扑关系优化对网格质量进行优化,生成质量较高的六面体网格。网格划分实例表明,该方法实用性强,效果良好。     

塑件成型模拟分析中网格划分的技巧与参数优化

介绍了塑件成型模拟分析中使用Moldflow软件进行网格划分的一些技巧、方法及参数设置。使用3D软件或CAD Doctor对塑件模型进行适当的处理后,再导入Moldflow中进行网格划分可以提高网格的质量,缩短网格的修补时间,提升工作效率。合理设置塑件模型网格划分的参数也直接关系到网格划分的质量,从而保证分析结果的准确性。     

金属三维挤压成形过程数值模拟的若干关键技术

推导了采用六面体等参单元网格划分的金属三维挤压成形过程数值模拟中的摩擦力功率泛函在局部坐标系的一阶和二阶偏导数的表达式 ,提出了有效的三维六面体网格划分和网格质量控制技术处理方法。以此为基础 ,建立了三维刚塑性有限元数值模拟系统和六面体网格再划分系统。方坯料反向挤压过程数值模拟的结果与实验非常吻合 ,验证了所推导的公式和开发的系统 ;圆坯料侧向挤压过程的模拟验证了提出的网格质量控制技术的第三种方法。     

COUPLED SIMULATION OF 3D ELECTRO-MAGNETO-FLOW FIELD IN HALL-HEROULT CELLS USING FINITE ELEMENT METHOD

Two full 3D steady mathematical models are developed by finite element method （FEM） to calcalate coupled physics fields. the electro-magnetic model is built and solved first and so is the fluid motion model with the acquired electromagnetic force as source body forces in Navier-Stokes equations. Effects caused by the ferromagnetic shell, busbar system around, and open boundary problem as well as inside induced current were considered in terms of the magnetic field. Furthermore, a new modeling method is found to set up solid models and then mesh them entirely with so-called structuralized grids, namely hex-mesh. Examples of 75kA prebaked cell with two kinds of busbar arrangements are presented. Results agree with those disclosed in the literature and confirm that the coupled simulation is valid. It is also concluded that the usage of these models facilitates the consistent analysis of the electric field to magnetic field and then flow motion to the greater extent, local distributions of current density and magnetic flux density are very much dependent on the cell structure, the steel shell is a shield to reduce the magnetic field and flow pattern is two dimensional in the main body of the metal pad.     

Changes in the potential and vibrational energies upon the formation of vacancies in the oxygen-alloyed cores of crystallite-conjugation regions of polycrystalline Cr, Cu, and Ir

The changes in the potential and vibrational energies upon the formation of vacancies in the oxygen-alloyed (OA) cores of crystallite-conjugation regions (CCRs) in polycrystals of d transition metals Cr, Cu, and Ir have been determined. The potential energy increases upon the formation of vacancies (upon the formation of complexes of vacancies with oxygen atoms) in the OA cores of CCRs in the polycrystalline Cr, Cu, and Ir. However, the vibrational energy decreases upon the formation of vacancies in the OA cores of CCRs in these polycrystals, as in the OA cores of CCRs in polycrystals of the 4d and 5d transition bcc metals Mo, Ta, and W. The volume of the OA cores of CCRs in polycrystals of Cr, Cu, and Ir decreases upon the formation of vacancies. The changes in the interatomic interactions and dynamic properties in the regions of vacancy localization in the OA cores of CCRs coincide with analogous changes introduced into the lattices of metals by split interstitials.     

Two decades of change in graduate education in metallurgy/materials—A perspective

It is now almost a decade since the introduction of massive federal support to universities for graduate education and research in the materials field. Accordingly, it is appropriate to examine the changes in the nature and activity of the field which have occurred during this period, both in the universities themselves, and in professional practice in industry and government, and also the implications of such changes for graduate education in metallurgy and materials science in the future.The present paper examines the growth of relevant university activities in the field over the past 10 years in comparison with that during the preceding decade and with the growth of engineering, science and advanced education in general in the United States, i.e., the question of the supply of new personnel with advanced training in the materials field. While it is appreciated that the nature and quality of education must be of prime importance, this paper deals principally with the numerical aspects of graduate education in materials, rather than with the philosophy, as a necessary first step in the broader study which is advocated.     

高通量方法在钎焊领域的应用现状

高通量方法作为"材料基因组技术"三大核心要素之一,在材料成分设计、组织分析、性能优化、过程模拟等方面起着关键性作用.钎焊技术作为焊接与连接领域的重要分支之一,是现代制造业中材料连接应用最广的方式.首先对高通量方法在钎焊领域的应用研究进行概述,其次主要对近5年有关高通量制备钎料、软钎焊和硬钎焊领域高通量计算方面的最新研究...     

DISTRIBUTION OF SULFUR IN HIGH TEMPERATURE PHASES OF CAST IRON

The distribution of subversive element sulfur in high temperature phases during solidificationof cast iron was investigated by means of liquid quenching method and autoradiography.Theresults show that in grey cast iron,sulfur is concentrated in the liquid,flake graphite and in theperipherial area of D-type supercooled graphite eutectic cells,but less sulfur is in austenite.Besides,the content of sulfur in A-type graphite is higher than that in D-type graphite,andsulfur content in eutectic austenite is a little higher than that in primary austenite.While,innodular graphite cast iron less sulfur is in liquid and austenite,but more in nodular graphite.The blackness of the spots on the emulsion film corresponds to the atomic percentage ofradioactive substances located on the surface of the specimen.     

非对称通道内亲疏水结构影响下的纳米气泡滑移效应

目的 研究非对称性通道中亲疏水表面结构影响下纳米气泡特征与边界滑移之间的关系,以实现良好的流体减阻效果.方法 采用二元体系分子动力学方法,研究纳米气泡在通道流动中产生的滑移减阻效应.首先建立上下壁面非对称微通道模型,通过考虑微通道流动传热过程,探究纳米气泡影响下的微通道界面速度滑移现象.结果 保持亲水下壁面高度以及上下...     

丹酚酸对大鼠骨骼肌缺血再灌注损伤的保护

目的：分析丹酚酸通过AKT/mTOR/p70S6K信号通路对骨骼肌缺血再灌注损伤小鼠细胞自噬及凋亡的影响。方法：选取SPF级雄性大鼠45只,随机数字表法分为假手术组、模型组、丹酚酸组,模型组、丹酚酸组制备骨骼肌缺血再灌注损伤模型,丹酚酸组分别在开始实验前72 h、48 h、24 h及再灌注前15 min,腹腔注射剂量为30 mg/kg的丹酚酸溶液1 mL,假手术组和模型组大鼠腹腔注射生理盐水1 mL。观察各组大鼠腓肠肌组织病理形态,血清肌酸激酶（CK）、乳酸脱氢酶（LDH）含量,腓肠肌组织Akt、p-Akt、p70S6K、p-p70S6K、mTOR及p-mTOR蛋白表达及腓肠肌组织内Bcl-2、Bax表达。结果： 再灌注0 h、4 h及24 h时模型组大鼠腓肠肌湿/干重（W/D）比值较假手术组升高,丹酚酸组腓肠肌W/D比值较模型组降低,差异有统计学意义（P<0.05）;再灌注0 h、4 h及24 h时模型组大鼠血清LDH、CK含量较假手术组升高,丹酚酸组大鼠血清LDH、CK含量较模型组降低,差异有统计学意义（P<0.05）;模型组大鼠腓肠肌Akt蛋白表达较假手术组降低,p-Akt蛋白表达较假手术组升高;丹酚酸组大鼠Akt、p-Akt、p70S6K、p-p70S6K、mTOR及p-mTOR蛋白表达较模型组升高,差异有统计学意义（P<0.05）;光密度值（IOD）量化腓肠肌细胞内Bax、Bcl-2蛋白表达,模型组Bcl-2 IOD数值、Bcl-2/Bax比值较假手术组降低,Bax IOD数值较假手术组增加;丹酚酸组Bcl-2 IOD数值、Bcl-2/Bax比值较模型组升高,Bax IOD数值较模型组降低,差异有统计学意义（P<0.05）。结论：丹酚酸可维持骨骼肌缺血再灌注损伤大鼠骨骼细胞Bax与Bcl-2动态平衡,抑制细胞凋亡,其作用机制可能和激活AKT/mTOR/p70S6K信号通路有关。     

水钢100 t转炉出钢过程回磷分析与实践

转炉出钢过程常伴有钢水回磷现象,导致钢水磷含量上升甚至出格,影响钢材成品质量和经济技术指标。为有效控制转炉出钢过程回磷,通过现场取样、数据采集、模拟试验及FactSage软件分析了出钢过程钢水回磷机理,研究探讨了渣中FeO、SiO₂、出钢温度、钢包渣碱度对回磷的影响。研究结果表明,出钢过程下渣,渣中FeO含量与出钢温度过高,钢包渣SiO₂含量与碱度不在合适范围均会增大钢水回磷率,最高达41%。结合水钢生产实践,出钢温度控制为1 625~1 640 ℃、转炉终渣FeO质量分数为15%、钢包渣碱度为3.6~4.1、控制含硅合金加入、控制出钢过程下渣量的条件下,可高效调节出钢过程回磷,将回磷率降低至15%以下。通过控制出钢温度、终渣FeO、碱度等,可有效降低因下渣导致的回磷。     

面向制冷行业在线应用的铝铝感应钎焊

铝管由于其熔点低,在焊接的过程中很容易烧破,致使管壁减薄或管路泄漏。所以,制冷行业的铝铝管路基本采用洛克环进行连接,洛克环连接的成本较高,并且洛克环在本质上不属于焊接,在安装工艺不成熟时也会存在较大比例的焊漏率;铝铝感应钎焊在工艺成熟的前提下可以实现铝管的低成本连接,并且焊接效果稳定,降低焊漏率。针对铝铝管的感应钎焊进行研究,并探究铝铝感应钎焊的在线应用条件,推动感应钎焊在制冷行业铝铝管路连接中的应用和发展。     

Recent developments in the study of hydrogen embrittlement: Hydrogen effect on dislocation nucleation

In this paper, the intrinsic complexities of the experimental examination of hydrogen embrittlement are discussed. On the basis of these complexities, an experimental approach, in situ electrochemical nanoindentation, is proposed and performed on different materials. This technique is capable of registering the onset of plasticity in extremely small volumes, namely perfect crystals in hydrogen-free and charged conditions. It is shown that hydrogen reduces the required stress for the onset of plasticity, i.e. homogeneous dislocation nucleation by reduction in the shear modulus, dislocation line energy and stacking fault energy. The change in the shear modulus can be related to reduction in crystal cohesion whereas the reduction in dislocation line energy and stacking fault energy are explained by the defactant concept, i.e. reduction in the defect formation energy in the presence of hydrogen. Thus, neither hydrogen-enhanced decohesion nor hydrogen-enhanced plasticity, but the reduction in the cohesion and defect formation energy are responsible for hydrogen embrittlement.