大型500 kV变压器主密封法兰系统受力分析

利用有限元分析软件ABAQUS对油浸式变压器的主密封界面的螺栓、垫片、法兰系统进行建模,分析预紧状态下法兰螺栓受力及变形情况,探讨接触应力随橡胶垫片压缩率、流体压力、橡胶垫片硬度的变化规律。结果表明:在螺栓预紧载荷作用下,法兰偏转使螺栓受力不均,箱沿连接处为法兰最易损坏位置,可在箱沿与箱体处加额外刚性固定来增加强度;随着压缩率与流体压力的增大,橡胶垫片的接触应力和von Mises应力均增大;橡胶垫片硬度越大,相同流体压力下的接触应力和von Mises应力也越大,因此当密封界面承受较大流体压力时,应选用硬度大的橡胶垫片。     

Impression creep: Effects of slip, stick and cavity depth

The impression creep of a power-law material by pushing a rigid cylindrical punch into an existing cavity of the same diameter as the punch located in the surface of a half-space was studied by using finite element method. For both the slip and stick conditions at the interface of the punch and the half-space, there is a well-defined steady punch penetration velocity after a transient stage. The steady penetration velocity is a power function of the applied load, which has the same stress exponent as by conventional creep tests. It increases with the stress exponent but decreases with increasing cavity depth, and is the largest for all slip condition and the smallest for both stick condition on the circular interface between the punch and the cavity and all stick condition.     

旋转组合密封圈表面结构对密封性能的影响

为研究旋转组合密封圈表面结构对密封性能的影响规律,对方圈表面分别加工单槽和双槽等不同表面结构,利用ABAQUS仿真分析不同表面结构的旋转组合密封圈在完成过盈安装与流体加载后的应力及接触压力分布,并研究油槽宽度变化对组合密封性能的影响.仿真结果表明:在过盈安装与流体加载情况下,O形圈的最大vonMises应力均有所减少,...     

渗氮钢粗糙表面的弹塑性接触研究

利用弹塑性有限元和单纯形法求解弹塑性接触模型，分别模拟了屈服强度呈梯度变化的渗氮钢、未经处理的匀质材料和硬涂层材料粗糙表面的弹塑性接触行为。与未经处理的匀质材料相比，渗氮钢可承受更大接触载荷。在相同载荷作用下，渗氮钢表面粗糙峰接触面积较小，平均间距较大，接触体内材料不易发生屈服，从而显著提高接触性能。和硬涂层材料相比，渗氮钢接触体内等效von Mises应力分布平缓，没有应力突变。最后讨论了渗氮层和硬涂层的厚度对粗糙表面接触特性的影响。     

基于正交法的凿岩机水封Y形圈结构参数优化

凿岩机水封在工作过程中承受旋转和冲击复合作用,易造成Y形圈密封失效和疲劳失效。为提高凿岩机水封性能,综合考虑旋转和冲击2种运动形式,对不同结构参数下的Y形密封圈性能进行有限元仿真;基于正交试验法,以最大接触应力和最大von Mises应力作为密封性能评价指标,通过极差分析得出影响密封性能的主、次要因素,并对Y形密封圈结构参数进行优化改进。结果表明：对最大接触应力有显著影响的因素是唇厚、倒角长度和唇长度,最大接触应力随唇厚和倒角长度的增加呈上升趋势,随唇长度的增加呈下降趋势;对最大von Mises应力有显著影响的因素是唇厚、唇口深度和唇与钎尾夹角,最大von Mises应力随唇口深度和唇与钎尾夹角的增加呈上升趋势,随唇厚的增加呈下降趋势。经过优化改进后,Y形密封圈的最大接触应力和最大von Mises应力分别下降了15%和45%。在保证密封效果的条件上,最大接触应力的下降减少了Y形密封圈的磨损,而最大von Mises应力的大幅下降,大大提高了Y形密封圈的寿命。     

Finite Element Analysis of Localized Plasticity in Al 2024-T3 Subjected to Fretting Fatigue

Fretting fatigue is a combination of two complex mechanical phenomena, namely, fretting and fatigue. Fretting appears between components that are subjected to small relative oscillatory motion. Once these components undergo cyclic fatigue load at the same time, fretting fatigue occurs. Fretting fatigue is an important issue in aerospace structural design. Many studies have investigated fretting fatigue behavior; however, the majority have assumed elastic deformation and very few have considered the effect of plasticity. The main goal of this study is to monitor the effect of different fretting fatigue primary variables on localized plasticity in an aluminum alloy (Al 2024-T3) test specimen. In order to extract the stress distribution at the contact interface under elasto-plastic conditions, a modified finite element contact model was used. The contact model was verified through comparison with an elastic analytical solution. Then, a bilinear elasto-plastic isotropic hardening model with a von Mises yield surface was implemented to simulate the material behavior of the aluminum alloy. The effect of different fretting fatigue primary variables, such as axial stress, contact geometry, and coefficient of friction, on localized plasticity was investigated. Finally, the relationship between the location of maximum localized plasticity and Ruiz fretting damage parameter with the crack initiation site is discussed.     

Effect of Slide-to-Roll Ratio on Interior Stresses Around a Dent in EHL Contacts

The present, study extends the transient EHL point contact model and subsurface stress field calculation model to examine the influence of a surface dent on interior stresses in an EHL point contact under various slide-to-roll conditions. Results revealed that under the pure rolling condition the effect of a surface dent on the stresses is quite negligible. The presence of a shallow surface dent is unlikely to reduce the contact fatigue, life so long as pure rolling motion and good lubrication conditions are maintained. Unfortunately, the same cannot be said of the contact if it is operating in the boundary lubrication regime.

When sliding was introduced, the surface indentation generated significantly high pressure spikes with a strong directional preference. These high-pressure spikes cause severe stress concentrations either below the trailing edge of the dent, if it moves faster than the opposing surface, or below the leading edge of the dent, if it moves slower than the opposing surface. The maximum von Mises stress moved close to the surface and significantly increased in value as compared to the smooth surface solution. For the case of simple sliding, the maximum von Mises stress is even greater than the value calculated for the boundary lubrication case.

In regard to maximum tensile principle stresses, the presence of a dent increased the stresses only marginally over the smooth surface solutions. It is unlikely that surface indentation would significantly reduce the contact fatigue life due to Mode 1-type crack initiation.     

Optimization of carrier morphology in terms of Fourier sine series for chemical mechanical polishing process

To establish a 2D axisymmetric quasi–static finite element model during the chemical mechanical polishing process, revolutions of the wafer and the pad were assumed to be the same, the axisymmetric uniformly distributed pressure form was given, and both the wafer–pad interface and wafer–film interface were considered as contact boundaries. Next, the height of the contact interface between the carrier and the film near the zone of nonuniform von Mises stress distribution of the wafer surface was changed to the form of a Fourier sine series. Finally, a quadratic programming method was utilized to solve the coefficients of the Fourier sine series and then an optimal morphology in terms of Fourier sine series under the condition of minimum nonuniformity of the wafer surface was achieved. The result found that the nonuniformity was reduced remarkably and its improved rate reaches 88.45% under the optimal surface of the carrier.     

Analysis of elliptical Hertz contact of steel wires of stranded-wire helical spring

A stranded-wire helical spring is formed of a multilayer and coaxial strand of several wires twisted together with the same direction of spiral. Because of the multilayer structure, the wear on the local area of the steel wires’ surface is related to the elliptical contact between adjacent wires during working process. Based on Boussinesq potential functions and elastic half-space model, the contact area and surface pressure of elliptical Hertz contact were investigated. Moreover, these surface contact quantities are used to expand the calculation of subsurface stress relevant to elliptical contact. It is found that the greater contact angle of two contact wires, the smaller contact area and greater maximum contact pressure. Meanwhile, the magnitude of subsurface von Mises stress is much higher when the contact angle increases.     

两种密封结构橡胶密封圈密封性对比分析*

以发动机出水口处螺栓预紧橡胶密封结构为例,分别建立橡胶密封圈在三孔和四孔螺栓装配结构下的有限元模型,利用有限元软件ABAQUS对比分析橡胶密封圈在不同螺栓装配结构下在不同工作温度下的密封性能和应力状态。结果表明:随着温度的升高,三、四孔螺栓预紧结构下密封圈的von Mises应力、接触应力、最大真实应变及接触宽度均逐渐增大;各工况下采用三孔和四孔螺栓装配结构时密封圈的密封性能相差不大且均满足密封要求,但采用三孔结构时密封圈具有更小的von Mises应力,有利于提高密封圈的使用寿命。     

水泥环破碎器矩形异形活塞密封性能分析

针对传统圆柱形液压活塞承载力不足问题,提出一种矩形异形活塞,研究其在不同工况下的密封性能。基于Abaqus软件建立异形活塞有限元模型,研究介质压力、密封间隙、活塞运动状态以及摩擦因数对密封性能的影响,并分析异形密封环不同位置处的应力分布和翻转情况。结果显示：静密封时,介质压力越大,密封环的最大Mises应力和最大接触应力越大;密封间隙越小,最大Mises应力与最大接触应力越大;相比静密封,内行程过程中最大Mises应力和最大接触应力都有明显增加,且随摩擦因数增加而增加,而外行程中最大Mises应力和最大接触应力相比静密封差异较小;各工况下应力最大值均出现在密封环圆弧段;在活塞运动过程中密封圈并未发生翻转,只是存在位置的平移情况。研究结果证明了异形活塞的可行性以及良好的密封性能,为活塞结构设计与优化提供了依据。     

基于ABAQUS的变截面橡胶密封条热应力与密封性分析

研究用于发动机油气分离器的乙烯丙烯酸酯橡胶密封胶条在不同温度下的强度和密封性能。借助于大型有限元分析软件ABAQUS建立橡胶密封胶条与配合壳体的有限元模型,采用Mooney-Rivlin模型,对不同温度下的密封胶条进行热应力计算分析,得到橡胶密封胶条在不同温度下的Von Mises应力、压缩率、接触应力和接触宽度。结果表明:随着温度的升高,密封胶条的Von Mises应力和密封胶条与壳体连续接触面上的接触应力逐渐增加,接触宽度基本不变,密封条的压缩率逐渐减小;密封胶条的Von Mises应力远小于橡胶材料的拉伸强度,满足强度要求;密封胶条连续接触面上的接触应力始终大于油气分离器的工作压力且接触宽度符合要求,橡胶密封胶条满足密封条件。     

Stresses in hard coating due to a rigid spherical indenter on a layered elastic half-space

The axisymmetrical contact problem of elasticity connected with an indentation of a rigid spherical indenter in an elastic semi-space covered by an elastic layer is considered. Stress tensor components in interior points of the non-homogeneous half-space by numerical calculation of some integrals was obtained. Detailed analysis of the maximal tensile stress distributions and Huber-von Mises reduced stress distributions produced by contact pressure is presented. The dependence between these stresses and the ratio between the layer thickness and contact area width is explored. The obtained results for stresses are compared with results obtained for half-space loaded by the Hertz pressure.     

Enhancement of a simplified model for maximum stress prediction

A simplified model for rapid estimation of maximum subsurface stress was previously reported by the authors. That model was found to predict the upper bound of the maximum von Mises stress in each layer below any surface with good accuracy. In this work, the model is enhanced by quantifying the difference between the predicted upper bound and the maximum stress for a specific rough surface. This is done by evaluating stress predictions for real rough surfaces, sinusoidal surfaces, ideal textured surfaces, and real rough surfaces with imposed computer generated texture. The difference between the predicted upper bound and the surface-specific maximum stress is found to be related to that surface’s roughness. The origin of this relationship is investigated in terms of apparent contact area. The enhanced simplified model provides an efficient means of estimating maximum stress in rough surface contact.     

Comparison of two sealing coupling geometries for a direct fuel injector

The present paper describes some Finite Elements simulations carried out in order to investigate the contact problem in the sealing region of a direct fuel injector. In particular two different design solutions have been analyzed, both patent pending, one characterized by a conformal contact of two conic surfaces and the other one by a non-conformal contact between a cone and a sphere. Pressure distribution, contact width and von Mises equivalent stress have been calculated and employed as comparison parameters. Two different loading conditions have been considered: nominal loads and nominal loads plus undesired effects. Also deviations from the nominal geometry, obtained from profile detection of 40 samples, have been introduced for considering a real-like case. Numerical results stress the robustness of the non-conformal solution with respect to geometrical tolerances and real loading conditions.     

Analyzing Elastic-Plastic Real Rough Surface Contact in Running-in

A numerical method is presented for evaluating the elastic-elastic contact of real rough surface contacts during running-in. For the surface contact, an elastic-plastic model based on the variational method is applied to analyze the pressure distribution and contact area of worn surfaces during running-in. In conjunction with the classical statistic model of Greenwood and Williamson, the numerical result showed that the plasticity index Ψ was decreased to one in the elastic range as running-in proceeded. In comparison with the Hertzian solution, the influence of the asperities is very significant on the pressure distribution, thereafter causing a higher peak value of contact pressure. For the subsurface, the interior stress from the von Mises criterion was calculated to evaluate the subsurface stress field subject to both normal and tangential forces. In the calculated of the interior stress, the total stress is decomposed into a fluctuating component and a smooth component. The fluctuating part is solved by using FFT from the concept of the convolution theorem while the smooth part is obtained directly by analytical solution. Calculations of contact area and subsurface stress on experimentally produced surfaces whose topography has been determined using an atomic force microscope and friction coefficient front sliding have been carried out. The results showed that asperities and friction coefficient gave rise to stress increase in the near-surface stress field and produced a high stress zone towards the surface. As a result, transverse asperity cracking was produced. The calculations and supporting experimental evidence clearly confirmed that the reduction of peak pressure during running-in decreased the plastic deformation of contact.     

Contact analysis of impact in magnetic head disk interfaces

Three-dimensional finite element analysis of head and disk contact effects induced by impact in magnetic head disk interface (HDI) are presented. Elastic–plastic contact simulations are performed using . The entire contact–impact procedures during head disk collision under the dynamic loading of half-sine pulse acceleration with profiles of 300 and 500 g amplitude and 1.0 ms in duration are described in detail. Simulation results for the contact pressure distribution at HDI, von Mises equivalent stress, and equivalent plastic strain fields are examined and interpreted in terms of impact history. A comprehensive history of head disk relative displacement and von Mises equivalent stresses within contact region are provided and the evolution of plasticity are discussed. It is shown that finite element method can provide the simulation of the contact behavior resulting from the dynamic loading.     

大型起重机回转支承钢轮空心度分析

对大型起重机回转支承的承载钢轮采用平面应变单元建立有限元模型,并进行分析,结合经典的接触理论和曲梁理论,揭示了采用空心化设计的钢轮,不仅可以增加径向柔度、提高支承的均载效果,更能降低钢轮应力,提高支承的承载能力。随着空心度的增加,钢轮中合成应力的峰值点从接触区内部经过外缘向内缘转移,钢轮强度逐步由接触应力控制转化成由曲梁应力控制。     

Elasto-plastic indentation of a half-space by a rigid sphere under normal and torque loading

This work presents a numerical study of a spinning rigid sphere pressed against an elasto-plastic half space under combined normal and torque loading. The von Mises stresses and equivalent plastic strain under different torques are investigated. Results show that the torque shifts the maximum von Mises stress and plastic region in the half space closer to the surface at larger friction coefficient. An empirical formula to predict the contact area is suggested. The evolution of the plastic region in the half space is further examined. The region shows more complex shapes than those only under a normal load.     

Approaching Mixed Elastohydrodynamic Lubrication of Smooth Journal-Bearing Systems with Low Rotating Speed

When a conformal interface is under low velocity and heavy load conditions, solid contact (or dry contact) may occur even in a system with smooth surfaces. This paper presents two approaches for solving steady-state and transient mixed elastohydrodynamic lubrication problems of journal bearings with smooth surfaces under low rotating speed. The first approach uses the reduced Reynolds equation with a combined finite element–backward finite difference scheme and the second applies a zero film thickness equation to describe the mechanical behavior of mating surfaces at solid contact points. The major advantages of these two approaches are (1) no division of the solution domain into a lubricated area and a solid contact area is necessary and (2) the solid contact pressure, lubricant pressure, and eccentricity ratio can be solved simultaneously. Numerical examples are presented for the application of these approaches. For the steady-state cases under low velocity studied in this work, pressure distributions approach those found in a dry contact state. This comparison confirms that the contact treatments are proper. Moreover, a transient case under sinusoidal loading was analyzed with these two approaches, and the results showed good agreement. This comparison further supports the use of these approaches.