扁挤压筒的挤压力及应力场的光弹性分析

扁挤压筒是挤压大型铝壁板的重要工具，也是关键技术之一。与圆挤压筒相比，由于扁挤压筒型腔的线型特殊，理论计算相当困难，很难有精确的理论解。同时，非中心对称的型腔使挤压力的分布也不均匀，使得以均匀分布挤压力作为边界条件的数值计算产生了相应的误差，也使理论计算更加困难。本文制作了1：18的环氧树脂扁挤压筒整体模型，用低弹模的环氧树脂材料作挤压材料模拟挤压工况并将应力加以“冻结”，然后通过光弹性实验研究分析了挤压筒挤压时挤压力的分布特点以及筒体内部的应力场情况。结果分析得出：挤压力沿型腔高度大体上是均匀分布的，但沿型腔周向有着明显的变化；并在型腔的长轴位置出现应力集中。该实验结果为扁挤压筒的强度计算及结构设计提供了参考依据，也与数值分析解起到相互佐证的作用。如果把扁挤压筒的受力模型简化成中间带椭圆孔的无限大平面的弹性力学模型，理论最大应力值与实验结果比较接近。     

应用光弹性法分析扁挤压筒应力

扁挤压筒受力情况复杂,采用光弹性法进行应力分析,可了解应力分布情况和应力集中部位.在光弹性实验中,采用软环氧树脂作为加载介质,通过光弹性分析得出应力大小,得到组合式扁挤压筒的应力分布规律,并找出最大应力发生部位以及过盈配合对改变组合式扁挤压筒应力分布的影响,为生产实践中扁挤压筒的设计提供一定的依据.     

预紧扁挤压筒内孔变形和缝隙度Km的影响分析

应用ANSYS有限元分析软件,对受预紧作用的两层扁挤压筒进行了数值模拟。研究了内腔位移分布情况和内孔变形规律,分段对内孔位移做了多项式曲线拟合,并用物理实验加以对比验证。本文还对三层扁挤压筒缝隙度Km对内孔长短轴变形的影响作了分析,拟合出一定条件下内孔位移与Km的多项式插值函数表达式,得出Km的取值范围。为扁挤压筒修模、装配和结构优化提供了依据。     

扁挤压筒的等强度设计

本文仅就扁挤压筒的等强度设计计算方法及测试效果作简要介绍:(一)单层扁挤压筒的应力与变形分析单层扁挤压筒可看作是断面形状如图(1)所示的筒体,其断面外边界为一圆,内边界为两 ...     

宾汉姆流体在两平行圆板挤压流中的理论解

本文对宾汉姆流体在两平行圆板中的挤压流动进行了分析,并用适当的变量代换得到了板内压力梯度分布及压力分布的理论表达式,其结果与 David 的精确解相吻合.利用本文,只需一计算器即可得到与大型计算机相同的结果.     

多跨换热器传热管在静水中的阻尼特性

本文对多跨换热器传热管在静水中的结构阻尼与粘滞阻尼作了分析。通过求解带N—1个同心支承板的管子运动方程,导出计算挤压膜阻尼的公式. 为了验证理论分析结果,对四跨传热管在静水中的挤压膜阻尼进行了实验研究.得出挤压膜阻尼与支承板数、支承板厚度、管子—支承板管孔偏心率、以及管子—支承板间隙之间的关系.在分析实验结果的基础上,得出了计算传热管挤压膜阻尼的改进公式.     

基于发动机主轴轴承异常油膜噪声特征的模拟试验研究

由发动机主轴轴承油膜空穴造成的不规则打字机敲击噪声一直是汽车领域未解决的难题. 为了探究发动机主轴轴承动态载荷性能耦合作用下产生的异常空穴噪声，本文作者利用自行设计的平行板挤压油膜试验机进行模拟噪声试验并探究空穴噪声的特征. 该试验机可同时采集振动、位移、声压、力和空穴图像等五种信号，通过试验探究了不同激励信号、挤压振幅、挤压频率、润滑油黏度等因素对空穴噪声的影响，结果表明在方波、大振幅、使用高黏度润滑剂以及挤压频率为12 Hz的状况下容易产生空穴噪声.      

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通过对套铣筒这种特殊结构钻柱的分析,在现有钻柱力学模型研究的基础上,针对 套铣筒结构特点(大筒径、薄壁筒型钻柱),建立套铣筒与井壁接触力学模型,通过分析套铣 管柱在井下屈曲状态以及与井壁接触压力的计算,对套铣筒进行力学分析以及摩阻力计算.     

油水井取套过程中套铣筒摩擦阻力分析计算

通过对套铣筒这种特殊结构钻柱的分析,在现有钻柱力学模型研究的基础上,针对套铣筒结构特点(大筒径、薄壁筒型钻柱),建立套铣筒与井壁接触力学模型,通过分析套铣管柱在井下屈曲状态以及与井壁接触压力的计算,对套铣筒进行力学分析以及摩阻力计算.     

管道封堵机器人的大变形橡胶筒静态密封特性仿真与试验研究

在管道封堵机器人中大变形橡胶筒是实现密封的核心部件，其在使用中常出现密封失效和撕裂失效等问题.为了明晰上述原因和解决问题，本文中研究了不同橡胶材料以及不同橡胶筒轴向长度、径向长度和倾斜边角等结构参数对管道封堵机器人的静态密封特性影响.基于橡胶材料的高弹性和大变形特性，进行了橡胶筒的多阶段变形力学分析.对橡胶材料进行单轴拉伸压缩试验，得到橡胶材料的本构关系参数.建立管道封堵机器人橡胶筒密封特性分析的有限元计算模型，通过多因素分析方法，获得橡胶筒关键结构参数的最优方案.并设计了室内试验来进一步确定最优橡胶筒材料.研究结果表明集中在橡胶筒肩部的应力直接影响橡胶筒的形变损伤.经过橡胶筒的密封效果对比分析后得出最优的橡胶筒结构为轴向长度180 mm、径向厚度55 mm、倾斜边角28°，橡胶材料硬度为85 HA.     

Measuring small internal pressures along a tube during steady flow

A tube that can accurately measure small strains and pressure profiles during flow of non-Newtonian paste explosives has been designed and strain gaged. Equiangular rosette strain gages were installed along the length of a 6-mm-diam, 0.46-m-long thin-walled aluminum tube. The rosettes were oriented in the classical stress-gage configuration to measure circumferential stress and, hence, internal pressure independent of other stresses. The tube was static calibrated on a floating-piston pressure calibrator. Steady flow calibration was accomplished by extruding a viscous Newtonian silicone oil. Inlet pressure ranged from 0.52 to 2.1 MPa (75 to 300 psi). For the low-pressure 0.52-MPa silicone-oil extrusion, the full-scale strain levels varied from 6 to 53 μm/m. For all eight strain-gage stations, the maximum deviation from a linear pressure profile was equivalent to 0.5 μm/m. A pulsed-current-excitation signal-conditioning and digital data-acquisition system provided the necessary stability and precision to measure these unusually low-strain levels accurately.     

On thermal stresses and displacements in finned-tube panels

The end stresses in a finned-tube panel subjected to transverse temperature gradients are shown to be substantially different than those of a flat plate. Important differences occur due to the local bending of the tube and the extension of the tube beyond the end of the fin. On the other hand, stresses not near the ends and the in-plane deflections of a finned-tube panel are similar to those of a flat plate. These results are obtained by means of a review of flat-plate analysis and comparison with measurements made on two finned-tube panels with a step-transverse temperature gradient.     

Shear of rubber tube springs

Rubber tube springs consist basically of cylindrical rubber tubes bonded on their inner and outer curved surfaces to rigid cylindrical tubes. They are widely used as flexible linkages, for example in vehicle suspensions. Rotation of one rigid tube with respect to the other about their common axis subjects the rubber tube to azimuthal shear. Displacement of one rigid tube with respect to the other along their common axis puts the rubber tube into axial shear. Using FEA, we have calculated the stresses set up in both cases, for a long rubber tube of a non-linearly elastic (neo-Hookean) material. The results are compared for the two modes of deformation, and with analytical predictions where available. For a long tube the shear stresses are substantially independent of the end conditions, but the normal stresses are strongly affected, as found previously for sheared rectangular blocks [A.N. Gent, J.B. Suh, S.G. Kelly III, Mechanics of rubber shear springs, Int. J. Nonlinear Mech. 42 (2007) 241-249]. If the end surfaces are stress-free, unexpectedly large normal stresses are generated, even in azimuthal shear. These high tensile stresses are attributed to restraints at the inner and outer cylindrical boundaries that compensate for the absence of stresses on the end surfaces that would be needed to maintain a simple shear deformation. Thus, the boundary conditions affect the stresses everywhere (in contrast to an “end effect” that would diminish away from the ends). Small departures from complete incompressibility are found to lower the internal stresses markedly, and even cause the sign of the stresses to be reversed.     

Stretching flow instabilities at the exits of extrusion dies

As liquid leaves an extrusion die, the surface layers are rapidly stretched. Stretching flows may become unstable in two ways: by breaking, or in a ductile manner producing an uneven “necked” sample which, in continuous extrusion and drawing, is sometimes called “draw resonance”. There is a quantitative correlation between the extrusion defect known as “sharkskin” and the cohesive failure of polymer melts. By extruding under closely defined conditions, it is possible to introduce a transitory “structure” into the surface layer of the extrudate greatly enhancing its cohesive strength and eliminating this defect. A similar quantitative correlation is established between the uneven coating thickness sometimes obtained during coextrusion of a high viscosity melt on the surface of a low viscosity melt and the tensile drawing instability known as “draw resonance”. Simple criteria are established to avoid this problem in practical flow engineering.     

Photoelastic investigation of a channel cover of bleed condenser

This paper describes the investigation on an epoxy model of a channel cover of bleed condenser, by three-dimensional photoelasticity. The channel cover is a thick plate with two nozzles which are connected on one side to pipes carrying water vapor/water under high pressure. A flat tube plate is connected on the other side by means of sixteen bolts around the periphery with high initial bolt forces. The photoelastic model of the channel cover was made by machining a cast epoxy block (Araldite CT200). The stress distribution along critical sections of the model and the regions of maximum stresses and their values were determined. The prototype stresses were calculated from experimentally obtained values of model stresses, using simiilitude laws.     

冷拔无缝钢管残余应力测量的杂交实验方法

提出了一种数值模拟和实验杂交的实验方法,测量了钢管内表面的残余应力。采用非线性有限元法模拟了冷拔钢管的成型过程,得到了钢管脱模以后的残余应力,通过释放切口处单元的刚度模拟了含有残余应力钢管的切割过程,研究了切割方法对残余应力的影响,数值计算和实验结果表明切割方法对二次残余应力有很大影响。采用X射线测量仪测量了钢管内表面的残余应力。研究结果表明,计算结果基本符合实验结果,误差可以被工程接受。     

精密金属异型挤压塑性成形共形上限解及模腔优化

针对异型材精密挤压塑性成形及模腔建模理论的焦点课题，借助共形映射理论和金属塑性成形理论成果，将异型材截面域的金属挤压三维塑性流动转化为二维轴对称成形问题，建立了金属异型塑性流动的流函数、应变速度场和模具模腔等数学解析模型，应用能量上限原理，以含有对称轴叶形和六边形截面域的挤压型材模腔为例，求解了模腔优化参数，使优化模腔曲面的CAD／CAM一体化技术目标成为可能．     

Photoelastic determination of stresses in the tube plate of a 70-mw steam generator

This article describes the examination, by three-dimensional photoelasticity, of the tube plate of a sodium steam generator. The tube plate is flat on the side of the tube bundle (121 tubes) and spherical (concave) on the other side. The photoelastic model was made by precision casting, there being no glued joints at the points which are important from the point of view of stresses, such as the tube-tube plate junctions. Both the stress distribution along important sections and the stress concentrations in different types of tube-tube plate junctions due to the internal pressure were determined. The investigation described in this article was carried out in the framework of the Association—Euratom TNO/RCN on Fast Reactors, on behalf of the TNO—Neratoom Sodium Technology Project.     

Analysis of surface crack on forward extruding bar during axisymmetric cup-bar combined extrusion process

In this paper, the kinematically admissible velocity field with surface crack on forward extruding bar is put forward during the axisymmetric cup-bar combined extrusion process, in accordance with the results of model experiments.On the basis of velocity field, the necessary condition for surface crack formation on the forward extruding bar is derived, with the help of upper bound theorem and the minimum energy principle. Meanwhile, the relationships between surface crack formation and combination of reduction in area for the part of forward and backward extursions (ε_b,ε_f) relative residual thickness of billet (T/R₀),frictional factor (m) or relative land length of ram and chamber (l_b|R₀,l_f|R₀) are calculated during the extrusion process. Therefore, whether the surface crack on forward exturding bar occurs can be predicted before extruding the lower-plasticity metals for axisymmetric cup-bar combined extrusion process.The analytical results agree very well with experimental results of aluminium alloy LY12 (ASTM 2024) and LC4 (ASTM 7075).