含多粗糙峰涂层等效应力的有限元分析

研究刚性平面与含粗糙峰涂层在二维与三维模型下的弹性接触问题,采用有限元法分析涂层弹性模量比、涂层厚度、粗糙峰间距、刚性平面压下深度对涂层粗糙峰表面、涂层/基体界面分布及基体等效应力分布的影响。计算结果表明压下深度对三维涂层粗糙峰表面最大应力的影响最大,涂层厚度、涂层/基体弹性模量比、粗糙峰间距的变化对应力值影响逐渐减小;增大涂层厚度、减小压下深度和粗糙峰间距、降低弹性模量比会使得三维接触模型最大等效应力值显著降低;增加涂层粗糙峰数和涂层厚度、同时降低涂层弹性模量有助于提高涂层/基体界面结合强度。相对于二维接触模型来说三维接触模型在粗糙峰表面的等效应力增大,造成这种变化的主要原因是由于涂层表面粗糙峰之间的等效应力叠加引起的。该研究为涂层粗糙峰及涂层/基体界面强度的应力分析提供依据。     

固体润滑滚子轴承的接触表面应力分析研究

为获得固体润滑滚动轴承滚动体与滚道处的接触应力,通过固体润滑滚子轴承拟动力学分析并考虑涂层的影响,获得了滚子轴承稳定运行过程中滚动体的力载分布。通过建立带涂层接触的平面应变问题的力学模型,将涂层与基底两种材料的特性等效为一种材料来求解滚子与接滚道触应力分布情况,并与轴承的拟动力学分析相结合,获得了滚子轴承中滚动体与固体润滑膜接触表面的接触变形、接触半径与外加载荷之间的关系,讨论了不同涂层的弹性模量以及不同涂层厚度对接触界面应力分布的影响。当涂层弹性模量比基底大时,涂层的存在使得接触半宽减少,最大名义接触应力增加;涂层弹性模量比基底小时,则与之相反。当涂层的厚度<0.01mm时,涂层的存在对固体润滑滚子轴承的接触表面应力分布影响较小;在一定范围内,当涂层的厚度逐渐增大时,涂层对轴承接触表面应力分布的影响增大。     

齿轮涂层接触应力场分析及应用

涂层的机械力学性能对于涂层的应用尤为重要,涂层/基体系统的失效和破坏与涂层表面及界面接触应力密切相关.基于赫兹接触理论,应用有限元法对齿轮涂层接触应力场情况进行模拟.先在没有涂层的系统上对模型的精确性进行检验,然后通过改变涂层的弹性模量比和厚度,探究应力分布规律.结果表明:当涂层/基体弹性模量比Ec/Es＜2、涂层厚度/接触半径对t/a=0.05齿轮涂层应力分布最为有利 ;研究结果为齿轮涂层技术的应用提供了科学的理论依据.     

带有硬涂层的球轴承应力场分析

在建立名义点接触问题有限元模型的基础上，计算了不同涂层厚度下6309深沟球轴承的亚表层应力场，首次提出了一个涂层膜厚的无量纲参数ξ。结果表明，当涂层厚度参数ξ小于0．035时，接触区内的Mises应力和最大剪应力的最大值及其所在深度较之无涂层时无显著变化；与无涂层的情况不同，涂层体系表面接触中心处的Mises应力不为零；涂层／基体界面上的Mises应力的最大值出现在接触中心处，最大剪应力在偏离接触中心处出现。     

一种新的结合面微观接触模型

为研究粗糙表面中微凸体变形和基体变形对表面动态接触特性的影响,利用GW模型和Hertz接触理论推导出微凸体的接触刚度和基体的接触刚度,通过耦合刚度提出了一种新的结合面微观接触模型。通过新模型与Hertz模型、有限元分析结果的对比发现,微凸体和基体材料弹性模量比值κ=0.60.8时,新模型计算得到的解更加趋近于有限元分析结果,在这个范围内新模型更优于Hertz模型,微凸体/基体系统的接触情况只与微凸体和基体材料弹性模量比值κ有关,与微凸体形状大小、微凸体材料和基体材料的弹性模量没有太大关系。     

基于不同微观固体接触模型的轮轨表面变形特性分析

针对轮轨表面接触变形问题,采用不同的统计型微观固体接触模型,即Greenwood-Williamson （GW）模型,Chang-Etsion-Bogy （CEB）模型和Zhao-Maietta-Chang （ZMC）模型,研究轮轨接触表面变形特性。利用Newton-Raphson方法对微观固体接触模型公式进行求解,并同时求解间隙方程和载荷平衡方程。考虑不同粗糙度和不同塑性指数下各微观固体接触模型的压力分布情况,以及接触半径随载荷的变化情况。并将不同微观固体接触模型的结果和Hertz模型结果对比,结果表明弹塑性微观接触模型（CEB,ZMC）比弹性模型（GW）有着更小的接触压力以及更宽的接触半径,最大压力均小于最大Hertz接触压力,接触半径均大于Hertz接触半径。     

梯度结构对氧化铝陶瓷涂层接触应力的影响

采用幂指数描述"三明治"式梯度结构形式,建立镍基氧化铝梯度陶瓷涂层在静态接触集中力载荷作用下有限元模型,分析静态接触集中力载荷作用下涂层的Mises应力分布,以及梯度层的厚度、中间层数及结构形式对涂层的Mises应力分布及最大Mises应力发生位置的影响。结果表明:梯度结构对接触区Mises应力大小及分布影响不大,但影响最大Mises应力发生位置;合理的梯度结构能避开最大Mises应力发生在表面强化区及梯度区中,防止陶瓷涂层在接触载荷作用下疲劳脱落。制备层状结构梯度陶瓷涂层时,采用氧化铝层厚度20μm、线性梯度层厚度80μm、8层中间层,可改善Mises应力,适当避开最大Mises应力发生在梯度区。     

双层滚珠轴承的载荷分布研究

针对双层滚珠轴承载荷分布问题进行了研究。由于传统理论计算方法中关于刚性套圈的假设和Hertz接触理论半无限空间的边界条件并不完全符合实际情况,因此计算结果与实际情况有一定的误差。基于有限元分析方法,提出了对滚珠进行映射网格划分以及对接触区域网格进行局部加密的方法,分析了在一定载荷作用下滚珠与套圈沟道的接触应力以及弹性变形,并将有限元法分析结果与Hertz理论求解结果进行了比较,最后对计算结果进行了实验验证。     

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     

两种型面轮轨滚动接触应力分析

利用非Hertz滚动接触理论分析计算了磨耗型轮对、锥型轮对与钢轨之间滚动接触斑的作用力分布。再利用弹性力学中Bossinesq-Cerruti力/位移计算公式并借助Gauss数值积分方法,确定了两种型面轮轨滚动接触时体内的弹性位移、应变和应力的分布情况。数据结果为轮轨型面优化设计和轨底坡的设计提供了重要的参考依据。     

An extension of the Hertz theory for 2D coated components

The classic Hertz theory is not applicable when components in contact have coatings. An extension of the Hertz theory is presented in this paper for contact between coated cylinders. The concise form of the Hertz theory is adopted to express the maximum contact pressure and contact half-width in terms of applied load, equivalent radius, and an extended equivalent modulus. According to the form of an analytically known frequency response function, the extended equivalent modulus due to the presence of the coating is a function of Youngs moduli and Poissons ratios of the coating and the substrate, the coating thickness, and a parameter, which is obtained through substantial numerical simulation. This extension is easy to use and yields accurate predictions of the maximum contact pressure and contact half-width.     

An extension of the Hertz theory for three-dimensional coated bodies

This paper presents a work on extending the Hertz theory for circular and elliptical point contact problems involving coated bodies. The extended form of the Hertzian formulae are adopted to express maximum contact pressure, contact radius, and contact approach in terms of applied load, equivalent radius, and an extended equivalent modulus that properly considers the presence of a coating. The extended equivalent modulus is a function of Youngs moduli and Poissons ratios of the coating and the substrate, coating thickness, and a parameter, which is obtained through substantial numerical simulation. The extended Hertzian formulae are easy to use and give accurate predictions of contact characteristics.     

Surface stresses in coated steel surfaces—influence of a bond layer on surface fracture

Thin hard coatings in the thickness range of only a few micrometers deposited by physical vapour deposition (PVD) on components or tools can improve the friction and wear properties by several orders of magnitude. A 2 μm thick TiN (E=300 GPa) coating on a high-speed steel substrate with a bond layer at the interface between the coating and the substrate was modelled by micro-level three-dimensional finite-element method (3D FEM) in order to optimise a coated surface with regard to coating fracture. Both compliant low modulus (E=100 GPa) and stiff high modulus (E=500 GPa) bond layers at the coating/substrate interface of 200 and 500 nm thickness were investigated. First principal stresses were simulated for scratch test geometry in the load range of 7.5-15 N. Very high stress concentrations of above 5700 MPa tensile stresses were observed in the bond layer just behind the contact zone for the stiffer bond layer. The stiff bond layer generated 5 times higher tensile stress maxima compared to the compliant bond layer. There was approximately 3.5 times larger strain in the compliant bond layer compared to the stiff bond layer. The general coating design advice based on this exercise is that when a bond layer is used e.g. for coating/substrate adhesion improvement should the bond layer be less stiff than the coating not to generate high and critical tensile stresses. The thickness of the bond layer may vary and is not critical with respect to generated stresses in the surface.     

基体表面粗糙度对磁控溅射TiN涂层界面结合力的影响

利用球与平面的赫兹接触应力分布的经验修正公式∧［1］,对磁控溅处理前的基体表面粗糙度对沉积层和基体的界面结合力进行了研究,并和其他涂层界面结合力的测量方法方法进行了比较。结果表明：基体表面粗糙度对界面结合力有很大影响,表面粗糙度的改善有利于TiN层/基体的界面结合力的提高,同时改善了TiN层的摩擦学性能。     

齿轮接触安定分析

以Hertz理论为基础,建立齿轮的接触模型.针对齿轮接触表面层变曲率的特点,构造出局部坐标下残余应力应变场的分布状态,分析在此残余应力场分布状态下,齿轮接触的静力安定和机动安定的条件.采用应力应变释放的算法和不同啮合点局部坐标之间的转换法则,模拟齿轮在重复啮合过程中残余应力应变的累积过程,求解安定状态下残余应力的分布状况,确定齿轮接触的安定极限与摩擦因数和齿轮啮合位置之间的变化情况.     

Analysis of contact mechanics in ceramic-on-ceramic hip joint replacements

The contact mechanics in ceramic-on-ceramic hip implants has been analysed in this study using the finite element method. Only the ideal conditions where the contact occurs within the acetabular cup were considered. It has been shown that the contact pressure distribution and the contact area at the main articulating bearing surfaces depend largely on design parameters such as the radial clearance between the femoral head and the acetabular cup, as well as the thickness of the ceramic insert. For the ceramic-on-ceramic hip implants used in clinics today, with a minimum 5-mm-thick ceramic insert, it has been shown that the radius of the contact area between the femoral head and the acetabular cup is relatively small compared with that of the femoral head and the ceramic insert thickness. Consequently, Hertz contact theory can be used to estimate the contact parameters such as the maximum contact pressure and the contact area.     

Tribological analysis of fracture conditions in thin surface coatings by 3D FEM modelling and stress simulations

A tribological analysis of deformations and stresses generated and their influence on crack generation and surface fracture in a coated surface loaded by a sliding sphere in dry conditions is presented. A three-dimensional finite element method (3D FEM) model has been developed for calculating the first principal stress distribution in the scratch tester contact of a diamond spherical tip with 200 μm radius sliding with increasing load on a 2 μm thick titanium nitride coated steel surface. The model is comprehensive in that sense that it considers elastic, plastic and fracture behaviour of the surfaces. The hard coating will be stretched and accumulates high tensile stresses. At the same time, it is carrying part of the load and thus reducing the compressional stresses in the substrate under the sliding tip. The first crack is initiated at the top of the coating from bending and pulling actions and it grows down through the coating. The fracture toughness of the coating is calculated by identifying from a scratch test experiment the location of the first cracks and the crack density and using this as input data.     

A non-averaging method of determining the rheological properties of traction fluids

Traction machines have been frequently used to study the rheological responses of lubricants in elastohydrodynamic lubrication (EHL) contacts. Fundamental properties are inferred from EHL traction measurements based on the average pressures and temperatures in the contact. This average approach leads to uncertainty in the accuracy of the results due to the highly nonlinear resonse of the fluid such as viscosity to both pressure and temperature. A non-averaging method is developed in this paper to study the elastic and plastic properties of traction fluids operating in EHL contacts at small slide-to-roll ratios. A precision line-contact traction rig is used to measure the EHL traction at a given oil temperature and Hertz pressure. By choosing a sensible pressure-property expression, the parameters of the expression can be determined through the initial slope and peak traction coefficient of the traction measurements. The elastic shear modulus and the limiting shear stress of the lubricant corresponding to a single pressure can then be calculated for a range of pressures and temperatures of practical interest. Two high-traction fluids are studied, and their elastic moduli and limiting shear stresses presented.     

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.