Finite element analysis on local yield map and critical maximum contact pressure for yielding in hard coating with an interlayer under sliding contact

Micro-crack in the hard coating initiates usually from the local yield position. To prevent the crack to occur, the most important criterion is to satisfy the condition that the von Mises stress is less than the yield strength of material. In this paper, the local yield map showing the yielding position are introduced by using the finite element method and the criterion. The critical maximum contact pressures for yielding at the different positions were calculated by using the coating thickness, friction coefficient and the yield strength, where a critical range of yield strength ratio for the transition of yielding positions was found for 0.40.5. When the yield strength ratio is less than the range, yielding initiates from the interlayer and when the ratio is larger than the range, yielding initiates at the surface for high friction coefficient and in the base for low friction coefficient.     

Finite element simulations of static and sliding contact between a human fingertip and textured surfaces

This paper presents a mechanics study of the variations with position and time of stresses within the dermis and epidermis of a human fingertip when it is loaded and slid over textured surfaces. Its purpose is to examine how fingerprints interact with surface texture to cause stress variations in tune with the sensitivities of Meissner and Pacinian corpuscles through which humans in part interpret tactile sensations. A two-dimensional multilayer elastic finite element model of a fingertip has been created for this purpose. Results show that fingertip’s epidermal ridges have little effect on stress distribution within the fingertip in static loading but significantly increase stress oscillations during sliding over a textured surface. Oscillation frequencies from the sliding simulations are in ranges that should stimulate a fingertip’s Meissner and Pacinian corpuscle nerve endings.     

高速角接触球轴承接触疲劳寿命的有限元分析

首先简述了滚动轴承寿命的基本理论以及传统估算方法.然后根据轴承结构与工作特点,指出了滚动体与滚道的接触疲劳是轴承的主要失效形式,通过总结一般结构疲劳分析方法,提出了滚动轴承采用有限元法进行疲劳分析的方法和步骤.针对实际课题,对给定工况下的角接触球轴承B7005轴承接触疲劳寿命的有限元分析,将分析结果与轴承经典寿命估算结果进行了对比,一定程度上验证了提出的滚动轴承有限元疲劳分析法的合理性.     

Finite element analysis of coating adhesion failure in pre-existing crack field

Abstract

The influence of a pre-existing crack field on coating adhesion failure in a steel surface coated with a 2 μm thick titanium nitride (TiN) coating was investigated by finite element method modelling and simulation. The stress and strain fields were determined in contact conditions with a spherical diamond tip sliding over the coated surface at a loading of 8 N. One crack in or at the coating increased the maximum tensile stresses with six times from 82 to 540 MPa when the crack was vertical through the coating or L shaped and with nine times when the crack was horizontal at the coating/substrate interface. A simulated multicrack pattern relaxed the tensile stresses compared to single cracks. The results indicate that a cracked coated surface needs to have about five to nine times higher adhesive and cohesive bonds to resist the same loading without crack growth compared to a crack free surface. For optimal coated surface design, the strength of the adhesive bonds between the coating and the substrate in the vertical direction needs to be 50% higher than the cohesive bonds within the coating and the substrate in the horizontal direction. The first crack is prone to start at the top of the coating and grows vertically down to coating/substrate interface, and there it stops due to the bigger cohesion within the steel material. After this, there are two effects influencing that the crack will grow in the lateral direction. One is that steel cohesion is normally bigger than the coating/interface adhesion, and the second is that there are higher tensile stresses in the horizontal than in the vertical cracks. Several vertical cracks can stop the horizontal crack growth due to stress relaxation.     

The maximum tensile stres on a hard coating under sliding friction

In the friction of a hard coating the maximum tensile stress in the sliding direction generated at the friction surface is important for predicting crack propagation in the coating. The finite element method is employed to evaluate the stress field in the hard coating and the substrate under frictional loads, and the ratio between the values of maximum tensile stress and the maximum contact pressure is calculated under various contact conditions. Finally, a simple equation is introduced for the calculation of the maximum tensile stress at the friction surface. This equation is a function of friction coefficient, maximum contact pressure, coating thickness, contact width and elastic moduli of coating and substrate, and gives the value of the maximum tensile stress which is affected by the existence of the substrate.     

鼓式制动器的有限元模拟与接触分析

运用ANSYS Workbench平台建立了某鼓式制动器的三维有限元模型,对摩擦衬片与制动鼓之间的摩擦接触进行模拟。通过改变边界条件的施加方式及不同的接触对设置参数,确定了模拟鼓式制动器制动过程的接触分析边界条件及接触对的设置方法。采用三个载荷步加载,分析了制动力矩在制动过程中的变化规律,得出摩擦力矩达到平稳时接触压强的分布特性及制动器的等效应力与变形。为优化制动器结构参数、改善鼓式制动器磨损均匀性和制动效能提供了参考依据。     

FE-simulation of the effects of machining-induced residual stress profile on rolling contact of hard machined components

Compared with grinding, hard turning may induce a relatively deep compressive residual stress. However, the interactions between the residual stress profile and applied load and their effects on rolling contact stresses and strains are poorly understood, and are difficult to measure using the current experimental techniques due to the small-scale of the phenomena. A new 2-D finite element simulation model of bearing rolling contact has been developed, for the first time, to incorporate the machining-induced residual stress profile instead of only surface residual stresses. Three cases using the simulation model were assessed: (a) measured residual stress by hard turning, (b) measured residual stress by grinding, and (c) free of residual stress. It was found that distinct residual stress patterns hardly affect neither the magnitudes nor the locations of peak stresses and strains below the surface. However, they have a significant influence on surface deformations. The slope and depth of a compressive residual stress profile are key factors for rolling contact fatigue damage, which was substantiated by the available experimental data. Equivalent plastic strain could be a parameter to characterize the relative fatigue damage. The magnitudes of machining-induced residual stress are reduced in rolling contact. The predicted residual stress pattern and magnitude agree with the test data in general. In addition, rolling contact is more sensitive to normal load and residual stress pattern than tangential load.     

UG环境下齿轮弯曲强度的有限元仿真

通过理论计算能够得到齿轮齿根弯曲疲劳强度,但理论计算方法未考虑径向压应力对齿根弯曲强度的影响.在UG NX 2环境中建立标准渐开线圆柱直齿轮,在UG结构分析模块中对轮齿进行静态结构分析并得到应力分布图,仿真精度与解算器和网格划分关系密切.理论计算与虚拟仿真结果均满足许用应力要求.该方法在同一软件环境中实现了对象CAD与CAE的结合,能够辅助模型结构的优化设计,有助于提高设计效率和产品质量.     

法兰套接触有限元分析

接触问题是一种典型的边界条件非线性问题,接触体的接触面积和压力分布随外载荷变化而变化。在分析接触问题时,使用Abaqus/standard模块,能正确模拟接触的过程,判断接触状态、输出接触压力、接触面积、能量的变化、局部方向的摩擦剪应力和相对切向滑移。通过对螺钉连接的法兰套和支座的接触分析,得到螺钉、法兰套和支座变形程度和应力大小,以便于正确施加螺钉夹紧力。     

基于ABAQUS的二维金属切削有限元分析

运用大型通用有限元分析软件ABAQUS对金属切削加工过程进行非线性弹塑性有限元分析,讨论了切削模拟过程中切削力、应力场、应变的变化情况,验证了通过剪切失效和单元删除模型实现切屑分离符合切削理论。     

推力球轴承接触问题有限元分析

推力球轴承是被广泛应用的支承机械,用于承受转速较低的轴向载荷.它是由上下座圈、保持架和球体组成的可分离结构,分为单向推力球轴承和双向推力球轴承两种.着重分析了不同尺寸、形状的球形滚动体和橄榄球形滚动体对接触情况下的应力和变形量的影响.使用Pro/E建立实体模型,导入ANSYS进行数值模拟和计算.通过对获得的数值模拟结果和赫兹理论解进行对比,结果表明有限元分析是比较准确而且可靠的.最大接触应力和弹性趋近量取决于滚动体与滚道接触处的主曲率和、主曲率差,与滚动体形状、体积没有直接联系.     

硬X射线调制望远镜准直器的有限元分析

利用有限元方法对硬X射线调制望远镜的关键部件准直器进行了分析与计算。首先，基于有限元软件ANSYS提出一种SOLID单元与SHELL单元自由度连接的方法，并应用此方法建立了准直器的有限元计算模型。然后计算了不同设计参数的准直器在过载情况的应力与应变；最后对准直器进行了模态分析，得到前100阶固有频率与振型。文中的分析结果为准直器的结构设计提供了重要依据。     

单层涂层最佳厚度的有限元分析

采用有限元数值计算的方法对TiN、TiC、Si3 N4及SiC四种材料的硬涂层体系表面下的应力分布进行了模拟分析。结果表明 ,对于TiN材料 ,当涂层厚度与接触半宽之比t/a <0 .3时 ,表面下的最大剪应力分布对提高轴承疲劳寿命较为有利 ;t/a =0 .5时 ,涂层系统的摩擦力学性能最差。涂层厚度较薄时 ,位于赫兹接触中心附近的涂层表层上的最大剪应力要远大于基体内的最大静态剪应力 ;当t/a >0 .1时 ,涂层表面上的最大剪应力对提高轴承疲劳寿命较为有利 ;涂层材料与基体材料的弹性模量之比小于 2 .0时 ,有利于提高涂层系统的疲劳寿命     

激光涂层多冲碰撞疲劳强度的正交分析

对激光涂层零件进行多冲碰撞疲劳试验,并用正交方法对试验数据进行了分析。发现涂层材料对激光涂层的多冲疲劳强度起主要作用,基体材料次之。涂层厚度对疲劳强度的影响随循环次数的增加而减小。     

汽车驱动桥桥壳强度与模态的有限元分析

介绍了汽车驱动桥桥壳结构强度和模态有限元分析的研究背景,论述了ANSYS Workbench软件的有限元分析功能和优点。采用三维CAD软件UG建立了汽车驱动桥桥壳的三维几何模型,然后将其导入ANSYS Workbench软件中进行了结构强度和模态有限元分析。仿真结果表明,汽车驱动桥桥壳的强度满足设计要求,并且具有良好的抗振性。     

Finite element analysis on global and local estimation for thermo-mechanical response of EPL wafer heating

In this paper, an approach is presented for the computation of the in-plane pattern placement error (PPE) caused by the wafer heating during exposure of electron projection lithography (EPL) using the finite element method (FEM), which is one of candidates in the next-generation lithography (NGL) exposure tools. The PPE is the global and local distortion, and is the thermo-mechanical response due to the thermal deformation of the wafer in the lithography process. The prediction of PPE requires high accuracy for NGL exposure tools. The simultaneous estimation of the global and local PPE to the whole wafer of a full three-dimensional FE model using a solid element requires excessive computation time. A novel technique of numerical simulation is developed and proposed, which is the employment of a shell element combined with previously proposed the dynamic meshing technique (DMT), being possible to predict PPE in realistic computation time with high accuracy. Simulations are performed for the wafer heating of EPL effectively using three techniques, that is the equivalent average heating technique and two proposed techniques. The simulation results agree closely with the result of a full three-dimensional FE analysis, and the required computation time becomes 1/16 or much less of that.     

渐开线直齿圆柱齿轮齿根应力的有限元分析

根据啮合原理 ,建立了轮齿齿廓的精确模型。在此基础上 ,建立了整个齿轮平面有限元模型 ,并进行了分析计算。根据计算结果总结出了在对轮齿齿根应力进行有限元分析时 ,模型参数的选取原则 ,并对在该原则下建立的二维和三维模型分别进行了计算 ,将各种模型下的计算结果进行了比较 ,证明了所述原则的有效性     

高速主轴/刀柄联结特性的有限元分析

非线性有限元法可以分析、模拟主轴 /刀柄联结面间的变形、接触应力分布规律 ,为主轴 /刀柄联结的设计和优化提供理论依据。研究表明 ,适当提高轴向拉力和过盈量可以有效地解决上述问题 ,改善联结性能和加工精度。     

Finite element analysis of shot-peening effect on fretting fatigue parameters

Shot peening is widely used to improve the fretting fatigue strength of critical surfaces. Fretting fatigue occurs in contacting parts that are subjected to fluctuating loads and sliding movements at the same time. This paper presents a sequential finite element simulation to investigate the shot peening effects on normal stress, shear stress, bulk stress and slip amplitude, which are considered to be the controlling parameters of fretting damage. The results demonstrated that among the modifications related to shot peening, compressive residual stress has a dominant effect on the fretting parameters.     

润滑油膜压力作用下齿轮应力有限元分析

通过建立直齿圆柱齿轮三维模型,在ANSYS有限元分析软件中进行考虑润滑影响的应力分析。在进行有限元分析时,引入齿轮弹流数值计算的油膜压力作为加载项,通过这种加载方式得到轮齿应力值,与真实工作环境下产生的轮齿应力值之间存在的相对误差是目前计算方法中最小的。研究结果对提高轮齿强度、改进和优化齿轮设计具有一定的参考价值。