圆盘件镦粗成形过程中摩擦模型对接触区分布的影响

针对圆盘件镦粗成形过程中，接触区不同区域在不同变形程度下的摩擦剪切应力变化复杂的情况，研究了适合于圆盘件锻粗成形的摩擦模型，建立了初始径厚比为5的圆盘件镦粗成形有限元模型，分析了不同摩擦模型在不同变形程度下接触区的分布特点以及制动区半径的变化特点，并与计算结果进行了比较，开展了相关工艺实验验证。结果表明：在圆盘件镦粗成形中，随着变形程度的增加，接触区分布随径厚比的变化而变化，采用修正混合摩擦模型预测的制动区半径变化特点与理论值更接近，其预测精度较高。研究结果为圆盘件塑性成形有限元模拟中摩擦边界条件的设置提供了指导。     

圆柱体镦粗的较精确上限解

根据翁克索夫等人提出的镦粗时接触面上相当准确的摩擦切应力分布规律，利用上限法，求得了圆柱体镦粗时，接触表面为停滞区或与制动区的组合两种情况的单位镦粗力上限解，其解和主应力法解析解完全相同。比通常假设接触面上摩擦切应力为某一常数分布的上限解更为精确。     

基于圆环镦粗法的TC4钛合金热成形摩擦因数测定

为了准确测定玻璃润滑涂层的摩擦因数,通过分析圆环镦粗变形理论,修改传统DEFORM-3D有限元模型并完成TC4钛合金圆环镦粗正交数值模拟,得到3种摩擦因数标定曲线.对比分析了理论解析、传统有限元模型和改进有限元模型数值模拟所得3种摩擦因数标定曲线的差异性和分散度.研究了坯料温度、模具温度、镦粗速度和热传导系数工艺参数对...     

多孔烧结材料锻造镦粗成形致密的特性研究

粉末锻造是一种新型高性能的精密塑性成形技术，但其成形时的特殊性导致目前缺乏完善的、普遍适应的粉末锻造成形理论。通过对还原铁粉烧结多孔体预成形坯锻造镦粗成形致密实验，研究了不同初始相对密度、不同高径比、不同摩擦条件对预成形坯锻造镦粗成形、致密的影响规律。得到了粉末锻造镦粗的断裂极限准则，绘制出了断裂极限应变迹线，并着重分析了初始相对密度、高径比和摩擦因子对镦粗断裂极限的影响，确定了镦粗成形极限工艺参数曲线。实验研究结果为粉末锻造预成形坯与模具的设计、工艺参数的优化奠定了理论基础，并提供了有价值的实验数据。     

镦粗试验中鼓度与摩擦的相关性研究

建立了圆柱体镦粗的刚塑性有限元模型,模拟了高径比为1．5和1．0、当摩擦因子从0.1到1.0之间变化时圆柱体镦粗过程,给出镦粗试验中试件鼓度与接触面上摩擦因子间的定量关系,该关系可用来剔除流动应力试验中的摩擦和测量接触面上的摩擦因子。     

R10系列叶片镦头制坯工艺

由于常规的自由锻制坯方式存在坯料尺寸精度低、效率低、依赖操作工人的水平等缺点，尝试采用镦头的制坯方式，即采用小直径的棒料用模具在摩擦压力机上镦粗，但在镦粗的过程中易出现折叠等缺陷。经控制镦粗比，使得到的坯料无缺陷并尺寸一致，经生产验证，该方案切实可行。     

附加扭矩优化圆柱体镦粗成形的有限元模拟

镦粗时在模具上增加扭矩能将接触摩擦从被动的阻力变成促进金属流动的动力，这样会降低成形载荷，且使变形均匀。本文利用有限元模拟软件DEFORM-3D，模拟材料A12017的圆柱体在室温下的扭压复合加载成形。分析证明，附加扭矩将优化传统镦粗变形。     

圆环在平板间镦粗变形规律的数值模拟

采用有限元模拟软件对圆环在平板间镦粗过程进行了研究,确定了毛坯形状、摩擦因子、变形程度等因素对圆环镦粗成形时金属流动的影响.该数值模拟结果对圆环镦粗时各种因素之间确定了量化的关系,对环形件镦粗提供了科学依据.     

金属大塑性变形数值流形方法的研究

将数值流形方法应用于大塑性变形过程,采用固定的矩形网格作为数学网格,并分别采用零阶和一阶覆盖函数,推导出刚塑性数值流形求解公式。以平砧板镦粗成形为例,分析了流形方法特有的固定边界条件的处理方法和摩擦条件的施加方法,讨论了大塑性变形过程中动态边界问题的处理方法,为大塑性变形过程中应力应变场的计算提供理论基础。     

圆环镦粗过程数值模拟应力场研究

对圆环镦粗过程建立刚塑性有限元对称模型,采用autoforge有限元分析软件对纯铝圆环镦粗过程进行了有限元模拟,获得了镦粗过程应力场的相关信息,揭示了镦粗时金属内部应力分布情况。结果表明:由于变形量、摩擦因子的不同,圆环内部应力场分布也有很大区别。变形量增大,圆环坯料的应力分布呈"Y"形,且有扩大趋势;摩擦因子增大,圆环坯料应力分布趋于不均匀,但坯料的变形方式发生改变。这些结果对制定圆环镦粗时的参数有指导意义。     

Effects of temperature boundary conditions on equiaxed dendritic growth in phase-field simulations of binary alloy

By the phase-field approach, the dendritic growth in binary alloy melt was simulated respectively using two types of temperature boundary conditions, i.e., the constant temperature boundary by which the boundary temperature was fixed at the initial temperature, and Zero-Neumann temperature boundary. The influences of the temperature boundary conditions on numerical results are investigated. How to choose appropriate temperature boundary conditions is proposed. The results show that: 1) when the computation region is limited to a changeless size, the Zero-Neumann and constant temperature boundary conditions lead to the different dendritic growth behaviors, and the Zero-Neumann condition is preferable to the constant temperature condition; 2) when the computation region is enlarged continually with the computational time according to the increasing thermal diffusion scale, the two types of temperature boundary conditions achieve the consistent tip velocities and tip radii, and they both are appropriate choices.     

边界条件对离散位错动力学模拟疲劳Cu单晶位错花样的影响

利用二维离散位错动力学方法，研究了边界条件对计算机模拟疲劳Cu单晶位错花样的影响．结果表明：边界条件在模拟位错花样这类多体问题时是非常重要的；在其它模拟机制均完全相同的情况下，不同边界条件会形成不同的模拟结果,自由空间边界条件是最简单、也是最不现实的边界条件，模拟结果与实验结果相差甚远；而一维最近邻周期性边界条件与二维近邻周期性边界条件的模拟结果基本相同，与Cu单晶早期疲劳位错花样的实验比较吻合．     

盒形件多点成形边界条件的处理

通过采用虚功率增率型原理，建立了多点形时具有材料、几何与非连续性接触边界条件三重非线性的有限元模型，给出了非连续动态接触边界及库仑摩擦边界条件的处理方法；引用经典的J2流动理论研究了盒形件的多点成形过程。     

Evaluation of the BEASY program using linear and piecewise linear approaches for the boundary conditions

The boundary element method (BEM) was used to study galvanic corrosion using linear and logarithmic boundary conditions. The linear boundary condition was implemented by using the linear approach and the piecewise linear approach. The logarithmic boundary condition was implemented by the piecewise linear approach. The calculated potential and current density distribution were compared with the prior analytical results. For the linear boundary condition, the BEASY program using the linear approach and the piecewise linear approach gave accurate predictions of the potential and the galvanic current density distributions for varied electrolyte conditions, various film thicknesses, various electrolyte conductivities and various area ratio of anode/cathode. The 50‐point piecewise linear method could be used with both linear and logarithmic polarization curves.     

空心钢锭芯部换热条件的确定

在空心钢锭凝固过程中,芯子内套筒与冷却介质之间的换热条件对空心钢锭的凝固过程及质量有着重要的影响。该换热条件取决于冷却介质管路结构参数和冷却介质本身的特性。本文从气体动力学及传热学角度确定了空心钢锭芯部的换热条件。     

异种钢焊缝中的Ⅱ型边界组织及其影响

综述奥氏体与非奥氏体异种钢焊缝中的Ⅱ型边界组织及其影响。结果表明,在异种钢焊缝过渡区出现了一种平行于熔合线方向伸展的Ⅱ型边界组织。温度条件和晶体结构条件是Ⅱ型边界形成的必要条件,而转变的驱动力是该组织形成的充分条件,二者缺一不可。Ⅱ型边界是一组弱而近似平面的界面,一旦遭遇充氢,熔合边界上的马氏体就可能产生氢致裂纹。Ⅱ型边界的存在也是这类焊缝发生剥离的必要条件,接头的工况条件等则是剥离的充分条件。对于Ⅱ型边界组织引起的焊接裂纹和焊件剥离,必须搞清裂纹的性质与原因,然后采用针对性的工艺措施。     

Influence of solute segregation and drag on properties of migrating interfaces

Recent models on solute segregation and drag search for steady-state solutions of the diffusion equation in the region of a migrating interface and adjacent semi-infinite grains. Such solutions are limited to model massive transformations, for which the chemical composition of the parent grains and that of the product grains are the same. Simulation of diffusive transformations in transient systems with grains of different chemical composition is a hot issue. In the present model the steady-state solution of the diffusion equation is investigated only in the interface. The coupling with the diffusion equation in the adjacent grains is ensured by proper boundary conditions. For simulation of transient diffusive phase transformations it is very convenient if the interface can be treated as a sharp interface with a known effective mobility and prescribed boundary conditions at the interface. In this paper it is shown that solute segregation and drag can be taken into consideration by the effective mobility of a sharp interface and by proper boundary conditions at the sharp interface. The effective interface mobility reflects Gibbs energy dissipation due to rearrangement of solvent atoms and to trans-interface diffusion and drag of solute atoms in the migrating interface. Trans-interface diffusion and drag of solute atoms are also reflected by the jump of the chemical potential of the solute across the interface, which represents a boundary condition for coupling with the diffusion equation in the adjacent grains. Finally, it is shown that the incorporation of the effects of trans-interface diffusion and drag of solute atoms does not make the simulation more complicated provided that some necessary calculations are performed in preprocessing.     

中间包传热边界对钢液流动及传热计算的影响

以某厂T型中间包为例,建立了中间包内钢液流动、传热数学模型。针对数值模拟中存在的传热边界条件的准确性问题进行探讨,引入了中间包包衬散热计算模型,得出关于中间包包衬结构的热流散失与内壁温度的关系,作为中间包内钢液流动、传热计算的边界条件。利用商用Fluent软件模拟计算,并比较分析了不同边界条件对中间包内钢液流动、传热的影响,结果表明提出的边界条件模型法使计算模拟结果更符合实际。     

A finite element analysis of temperature variation in silicon wafers during wiresaw slicing

Temperature variation during slicing can cause undesirable warp and nanotopography on wafer surfaces, especially for large wafers. In this paper, a finite element model is constructed and presented to analyze and synthesize temperature variation of ingot during wiresaw slicing. The heat flux and natural convection boundary condition arising during slicing have been studied and incorporated in the model as well as the material removal. The model is designed to accommodate time-dependent boundary conditions and geometry which are integral to wiresaw slicing process. The results obtained from the model compare very well with the experimental results available in the literature. A method is proposed in order to obtain a relatively flat profile of temperature during slicing in order to reduce warp due to heat generation by intelligent control of boundary conditions. The method is tested using the model developed. The proposed method can be utilized by practitioners in order to obtain wafers with less warp and improved nanotopography due to thermal aspects in slicing using wiresaws.     

工业纯铁中形变对氢渗透的作用

形变对氢渗透的作用与拉伸过程及实验初始和边界条件有关。当初始条件是样品中未充氢时,形变不利于氢渗透;当初始条件是样品中充满氢时,形变有助于氢向外渗出。当边界条件是维持充氢时,形变不利于氢渗透;在停止充氢的条件下,形变使氢通量衰减速度增加。