Creep modeling in functionally graded rotating disc of variable thickness

Creep behavior of rotating discs made of functionally graded materials with linearly varying thickness has been investigated. The discs under investigation are made of composite containing silicon carbide particles in a matrix of pure aluminum. The creep behavior of the composite has been described by threshold stress based creep law by assuming a stress exponent of 5. The effect of imposing linear particle gradient on the distribution of stresses and strain rates in the composite disc has been investigated. The study indicates that with increase in particle gradient in the disc, the radial stress increases throughout the disc, whereas the tangential and effective stresses increase near the inner radius but decrease near the outer radius. The steady state strain rates in the composite disc, having gradient in the distribution of reinforcement, are significantly lower than that observed in a disc having uniform distribution of reinforcement.     

Prediction of dimensional instability resulting from layer removal of an internally stressed orthotropic composite cylinder

When a layer of cylindrical composite component containing an axisymmetric residual stress state is removed from the inner or outer surface, the dimension of the remaining material changes to balance internal forces. Therefore, in order to machine cylindrical composite components within tolerances, it is important to know dimensional changes caused by residual stress redistribution in the body. In this study, analytical solutions for dimensional changes and the redistribution of residual stresses due to the layer removal from a residually stressed cylindrically orthotropic cylinder were developed. The cylinder was assumed to have axisymmetric radial, tangential and axial residual stresses. The result of this study is useful in cases where the initial residual stress distribution in the component has been measured by a non-destructive technique such as neutron diffraction with no information on the effect of layer removal operation on the dimensional changes.     

Reliability analysis of stainless steel/carbon steel double-layered tube on the basis of thermal deformation behavior

The thermal expansion of pipes depends on both the temperature of the pipe and the expansion coefficient of the piping material at the operating temperature. In the case of a double-layered tube consisting of two different tube materials, the thermal deformation behaviors are dependent on the relative tube sizes, thermal expansion coefficients, and the mechanical properties of the inner and outer tubes. For the safe and reliable application of double-layered tubes that are fabricated by hydroforming, the thermal stress in circumferential direction and the gap between the inner and outer tubes need to be analyzed over a wide range of temperatures (?50°C～200°C). As it is difficult to measure the thermal stress and the gap between tubes at operating temperature, this study has analytically investigated the thermal deformation behavior of a double-layered tube. From the analytical model, the effect of hydraulic pressure, residual stress, and the relative sizes of the inner and outer tubes on the resultant thermal deformation, such as the circumferential thermal stress and the gap between inner and outer tubes, has been analyzed. The analytical results provide a theoretical basis for determining the reliable operating temperature of double-layered tubes.     

Elastic–plastic stress analysis of an orthotropic rotating disc

In this study, the elastic–plastic stress analysis of a curvilinearly orthotropic rotating annular disc is investigated analytically for strain-hardening material behavior. To be able to see the separation of the plastic region, a few angular velocities are taken into consideration for such an analysis. Radial and circumferential stress components are obtained to increase angular velocity. It is seen that the magnitudes of the circumferential stress components are higher than those of the radial stress components. The magnitudes of the residual stress component of the circumferential stress and plastic flow are the highest at the inner surface. The radial displacements in both the elastic and plastic solutions calculated analytically have higher values at the inner surface than those of the outer surface for all the angular velocities.     

基于 ABAQUS 的角接触球轴承动力学仿真分析

为研究角接触球轴承在不同转速下温度及位移变化,基于 Palmgren 摩擦生热理论,综合考虑轴向载荷、切向摩擦和法向摩擦等边界条件,在 ABAQUS 软件中建立了轴承完全热力耦合模型。对轴承外圈施加固定的轴向载荷,并对内圈加载不同的转速,使用显示求解器求解轴承在不同转速下各部件温度和轴承内圈位移变化。仿真分析表明,该模型能够准确地反映轴承的温升以及轴承内圈位移情况,为轴承选取合适工作转速区间提供理论支撑。     

Plastic Deformation Mechanism in Double-Roller Clamping Spinning of Flanged Thin-Walled Cylinder

Double?roller clamping spinning(DRCS) is a new process for forming a thin?walled cylinder with a complex surface flange. The process requires a small spinning force,and can visibly improve forming quality and production e ciency. However,the deformation mechanism of the process has not been completely understood. Therefore,both a finite element numerical simulation and experimental research on the DRCS process are carried out. The results show that both radial force and axial force dominate the forming process of DRCS. The deformation area elongates along the radial direction and bends along the axial direction under the action of the two forces. Both the outer edge and round corner of the flange show the tangential tensile stress and radial compressive stress. The middle region shows tensile tangential stress and radial stress,while the inner edge shows compressive tangential stress and radial stress. Tan?gential tensile strain causes a wall thickness reduction in the outer edge and middle regions of the flange. The large compressive thickness strain causes material accumulation and thus,an increase in the wall thickness of the round corner. Because of bending deformation,the round corner shows a large radial tensile strain in addition. The inner edge of the flange shows small radial compressive strain and tensile strain in thickness. Thus,the wall thickness on the inner edge of the flange continues to increase,although the increment is small. Furthermore,microstructure analysis and tensile test results show that the flanged thin?walled cylinder formed by DRCS has good mechanical properties. The results provide instructions for the application of the DRCS process.     

High thermal diffusivity materials for railway brakediscs

Two high thermal diffusivity brake discs have been worn againsta metallic pad, a composite pad and a new ceramic pad. Thesediscs are composed of a friction track made of molybdenum orCu-2.5% Be alloy. Molybdenum was used in the form of a coatingsprayed on an aluminum-based disc or as a thin solid disc mechanically clamped onto an aluminum-based stand disc. Coatingadherence, friction coefficient, surface temperature and wearthickness loss were determined for a set of reduced-scale steelbrake discs during a continuous braking simulation. It is shownthat the solid molybdenum disc tested against the composite padinduces significant surface temperature decreases as opposed tosliding against the bare steel disc. The friction coefficient isstable and wear damage acceptable. However, the molydenumcoating performs unsatisfactorily as the large difference inthermal expansion coefficient between molybdenum and aluminuminduces disbonding and crazing of the coating. The aluminumtitanate pad/Cu-2.5Be disc brake system has demonstrated remarkable tribological performance, with a steady frictioncoefficient, a pad surface temperature about 60°C lower thanthat of a steel disc and low pad wear.     

Residual stresses due to a moving heat source

An analytical model based on finite element method is presented for determination of the residual stresses of thermal and mechanical origin due to surface grinding process. The temperature field within the workpiece is determined as the quasi-steady state temperature distribution due to the moving heat source. An iterative procedure is employed for evaluation of the step-by-step movement of the temperature field and the force, in order to simulate the movement of the grinding wheel over the workpiece. Computation of the elastic-plastic stress history culminates in the residual stress state of the workpiece. Influence of the magnitude of mechanical force, the rate of heat input and the speed of movement of workpiece on the residual stress distribution, are discussed.     

轴承套圈磨削热损伤的形成与预防探讨

在轴承套圈磨削加工中，磨削热损伤是困扰人们的一个典型问题。通过对轴承套圈磨削过程中表面层金相组织的变化、内外圈滚道残余应力的产生与分布的分析，找出磨削热损伤的形成机理，探讨预防磨削热损伤的方法。     

平面型非金属阀瓣截止阀的密封性能

应用有限元分析软件建立平面型非金属阀瓣截止阀密封副的简化模型,对变操作工况下密封副的接触应力分布和变形情况进行分析。对比相同工况下不同结构阀瓣的接触应力分布和位移变化的差异,比较其性能,并采用试验进行验证。结果表明:密封接触面上应力分布关于密封面中径呈对称分布,在接触面内外径处应力最大,并从两端向密封面中径方向减小。阀瓣结构中,密封垫径向有约束的阀瓣较密封垫径向无约束的阀瓣密封性能好。     

金刚石砂轮刀片划切过程仿真研究

对金刚石砂轮刀片进行力学分析,得到砂轮刀片切向应力与径向应力。应用有限元分析软件ANSYS建立砂轮刀片模型,分别对应8000～32000r/min不同转速下的砂轮刀片,应用第三强度理论,得到不同转速下砂轮刀片的等效应力云图。由仿真结果可以看出,砂轮刀片切向应力大于径向应力,切向应力的最大值发生在砂轮刀片孔壁处,随着转速的提高,砂轮刀片的最大等效应力呈增长趋势。本文为研究划切时金刚石砂轮刀片的性能打下基础。     

温度梯度对热障涂层影响的模拟

采用热弹塑性有限元法,对热障涂层在不同温度梯度作用的过程中,由于材料系数不匹配而引起的应力和位移进行了模拟分析.结果表明,等效应力的大小随温度梯度的大小单调递减;界面最大位移随温度梯度单调递增.同时也发现,模型在不同温度梯度下存在一个最小位移;当材料属性和载荷一定时,将存在一个最佳涂层厚度,使得涂层总的位移最小.该结果对分析涂层寿命及失效机制有指导意义.     

An experimental study on the thermal performance of a concentric annular heat pipe

Concentric annular heat pipes (CAHP) were fabricated and tested to investigate their thermal characteristics. The CAHPs were 25.4 mm in outer diameter and 200 mm in length. The inner surface of the heat pipes was covered with screen mesh wicks and they were connected by four bridge wicks to provide liquid return path. Three different heat pipes were fabricated to observe the effect of change in diameter ratios between 2.31 and 4.23 while using the same outer tube dimensions. The major concern of this study was the transient response as well as isothermal characteristics of the heat pipe outer surface, considering the application as uniform heating device. A better performance was achieved as the diameter ratio increased. For the thermal load of 180 W, the maximum temperature difference on the outer surface in the axial direction of CAHP was 2.3°C while that of the copper block of the same outer dimension was 5.9°C. The minimum thermal resistance of the CAHP was measured to be 0.04°C/W. In regard to the transient response during start-up, the heat pipe showed almost no time lag to the heat source, while the copper block of the same outer dimensions exhibited about 25 min time lag.     

热障涂层在多次热循环作用下残余应力的模拟

采用热弹塑性有限元方法,对热障涂层多次热循环降温过程中由于热梯度和材料参数不匹配而产生的残余应力进行了数值模拟,分析了平面和曲面的界面形貌对界面残余应力的影响.结果表明,在相同材料参数情况下,陶瓷层与粘接层的界面形状对残余应力及结构稳定状态有显著的影响,凹凸不平的界面将会使界面残余应力发生突变,不利于增强界面结合强度和涂层结构的热稳定性.该结果对分析涂层寿命及失效机制有指导意义.     

螺栓法兰接头用碟形弹簧压缩回弹性能研究

为研究螺栓法兰接头用碟形弹簧压缩回弹性能,建立碟形弹簧力学性能分析的弹塑性有限元模型,并通过试验验证其可靠性。应用ABAQUS软件对碟形弹簧压缩回弹过程进行分析,讨论碟簧外内径比、倾角和厚度对碟簧压缩回弹性能的影响。结果表明:碟簧的压平载荷随厚度、倾角的增加呈上升趋势,随外内径比的增加呈下降趋势;回弹率随厚度、倾角、外内径比的增加均呈下降趋势。基于正交试验分析方法,结合量纲分析,建立螺栓法兰接头用碟形弹簧压平载荷和回弹曲线的预测模型,并验证其可靠性。     

Thermal behavior of full and ventilated disc brakes of vehicles

Braking is a process which converts a vehicle’s kinetic energy into mechanical energy which must be dissipated in the form of heat. During the braking phase, the frictional heat generated at the interface of the disc and pads can lead to high temperatures. This phenomenon is even more important than the tangential stress. The relative sliding speeds during contact are also important. The prediction of surface temperature for a brake rotor is regarded as an important step in studying brake system performance. The frictional heat generated on the rotor surface can influence excessive temperature rise which, in turn, leads to undesirable effects such as thermal elastic instability (TEI), premature wear, brake fluid vaporization (BFV) and thermally excited vibrations (TEV). The objective of this study is to analyze the thermal behavior of the full and ventilated brake discs of the vehicles using computing code ANSYS. The modeling of the temperature distribution in the disc brake is used to identify all the factors and the entering parameters concerned at the time of the braking operation, such as the type of braking, the geometric design of the disc and the material used. The results obtained by the simulation are satisfactory compared to those of the specialized literature.     

Experimental investigation of residual stress distribution in pre-stress cutting

This paper presents an analysis and experimental study on the formation and distribution of machined surface residual stress in pre-stress cutting. In the first component of the paper, the mechanical and thermal effect on residual stress is analysed. The results show that machined harden layer and cutting heat transfer conditions are crucial to form residual stress in a machined surface. Residual stress has three kinds of distributions in different mechanical and thermal conditions: tensile stress, compressive stress and tensile–compressive stress. If pre-stress is applied, it would facilitate residual compressive stress in the machined surface effectively; its action is analysed with an experimental study. The experiment is carried out by hardened 40Cr alloy steel turning with different tool rounds and pre-stress loading; the results obtained in this study indicate that the tool round would redound to generate residual compressive stress in the machined surface and affect the residual stress distribution significantly, whilst pre-stress load can affect the magnitude of residual stress actively, but does not for its distribution. It is found that the experimental results of residual stress distribution are consistent with the theoretical analysis.     

通风制动盘结构参数对制动抖动的敏感性

针对某通风制动盘制动抖动情况,采用正交试验设计方法,得到了通风制动盘各结构参数的最优水平组合。采用有限元法模拟制动盘15次循环制动,对比分析优化前后制动盘的热变形差异,得到各结构参数对制动盘热变形影响的敏感性,并利用台架试验验证了仿真分析的有效性。结果表明：通风制动盘各结构参数对制动抖动的影响敏感性由高到低顺序为盘厚、盘帽高度、颈部角度、制动盘外径、制动盘内径、颈部半径;盘厚、盘帽高度、颈部角度越大且制动盘外径及制动盘内径越小,制动抖动越小。     

Suppression of thermal deformation of machine tool spindle using TiC-Fe composite

The minimization of error generation in machine tool spindle is important because high-speed and ultra-precision machining are extensively utilized in industrial fields. The thermal deformation of the machine tool spindle generated by the frictional heat between the outer and inner bearings can deteriorate the machining accuracy. In this study, a TiC−SUS431 composite was fabricated using the liquid pressing infiltration method to suppress thermal deformation, and its thermal properties were obtained by thermal characteristic tests. For the transient thermal analysis with finite element analysis, the parameters of the machine tool spindle-bearing model were selected, and the boundary conditions were calculated. The temperature and thermal deformation of the analysis model were compared by applying SCM415 and TiC−SUS431 to the material of the machine tool spindle and changing the rotation speed. From the analysis results, it was demonstrated that the TiC−SUS431 machine tool spindle can improve the machining accuracy by minimizing the spindle thermal deformation.

     

相似离心通风机内部机械效率间的关系

讨论了离心通风机叶轮前后盘外壁面与空气摩擦损失的功率、理论功率、内部功率和内部机械效率,并总结出了相似离心通风机内部机械效率之间的关系式.