套片式翅片管机械胀接接触热阻分析与模拟优化

本文采用有限元模拟方法,得到了套片式翅片管换热器机械胀接的翅片与基管间的胀后节点接触应力分布。提出模拟的总体接触应力并不是节点接触应力算术平均的观点和总体接触应力的计算式。通过对套片式换热器试件进行传热性能实验,获取了翅片与基管之间的接触热阻数值,由模拟计算的总体接触应力与实验接触热阻数值,计算两者的关联式。采用有限元模拟方法预测各种胀接量下的总体接触应力及最优的胀接尺寸,利用弹塑性理论计算对比模拟计算进行验证。结果发现,材料弹塑性理论计算结果与模拟计算结果的相对偏差为7. 3%,偏差较小,证明两者均具有效性。     

销轴连接结构的接触应力分析

销轴连接结构是工程中最为常用的一种传力结构,对其进行细致的接触应力分析,研究各参数对接触应力大小和分布的影响,对此类传力结构的设计与应用显得尤为重要。该文以佛山东平大桥为例,在验证有限元模型接触参数设置的基础上,计算东平大桥在竖转脱架状态下销轴连接结构的接触应力,计算结果与实测结果相比,基本反应了接触应力的大小和分布,证明了有限元模型的可靠性。在此基础上,研究了提升力大小、材料本构关系等参数对销轴连接结构接触应力大小和分布的影响,得到以下结果:材料本构关系和提升力大小的选取是影响销轴连接结构接触应力大小和分布的关键因素;接触区域的摩擦因数对计算结果几乎无影响。     

斗轮堆取料机车轮踏面的接触强度计算

通过理论计算与实际案例相结合的方法,对斗轮堆取料机车轮踏面与轨道接触应力进行了计算,进一步明确了载荷、车轮踏面的硬度、车轮的直径和转速,轨面的形状等参数与接触应力的关系,为以后的设计提供了理论依据。     

印刷机偏心滚子轴承接触应力与变形仿真分析

目的对偏心轴承接触应力与滚子静、动态变形进行研究,得到接触应力与变形和结构与工况因素的关系。方法在Hertz线接触与弹流润滑理论下,建立滚子接触应力模型及静、动态滚子间接触变形的关系模型,利用有限元软件Ansys仿真计算。建立静、动(润滑与转速)态下滚子变形之间的关系公式,分析印刷机偏心双列圆柱滚子轴承的接触应力与变形及相互关系。结果滚子与内外套圈的接触应力均随径向载荷的增大而增大,滚子与内套圈的接触应力大于滚子与外套圈的接触应力;滚子的总接触变形量与径向载荷呈正比关系,滚子的内外接触应力与滚子的总接触变形量也呈正比关系;滚子的边缘出现应力集中,须用设计凸度的方法降低,从而更好地提高偏心轴承的整体性能。结论根据接触应力与变形的关系,可为偏心轴承的设计与优化提供理论依据。     

螺旋齿轮面接触应力理论计算

应用赫兹理论和齿轮啮合理论给出螺旋齿轮齿面接触应力的计算方法和相关公式,算例的计算结果表明螺旋齿轮齿面接触应力明显大于相近参数的圆柱斜齿轮,这是此类齿轮用于主传动时普遍出现齿面磨损的一个重要原因,因此在设计确定齿轮参数量必须校核接触应力。     

润扬大桥悬索桥北锚碇基础接触应力仿真分析

针对润扬大桥悬索桥北锚碇基础的浇筑施工、运行过程，基于大型有限元分析软件Marc进行二次开发，建立了锚碇基础和土体共同作用的三维有限元仿真计算模型。考虑锚碇基础浇筑过程中地下水位改变引起基底水压力的变化对锚碇基础接触应力分布的影响，对锚碇体浇筑到运行的全过程进行了仿真数值计算，揭示了岩层地基上悬索桥重力式嵌岩锚碇基础接触应力在施工到运行过程中的变化规律。工程实例数值计算结果表明，在不同施工浇筑阶段，尽管锚碇基础不同部位的接触应力呈现出不同的变化特征，北锚碇基础在施工到运行全过程中基础接触应力总体满足设计要求。     

大型非均质轧辊辊间接触应力分布规律的研究

针对轧辊表面剥落失效现象,采用非线性有限元方法,考虑轧辊表面淬硬层与其心部金属材料组织性能差别,对四辊轧机工作辊与支撑辊间接触应力问题进行模拟。并将模拟结果与传统强度校核方法进行了对比分析,结果表明非均质条件下的辊间接触应力和支撑辊辊内剪应力峰值及其作用深度均大于传统Hertz公式的计算结果,对于深入分析轧辊的失效行为具有重要意义。     

圆筒混合机滚圈与托辊强度计算

大型混料设备滚圈与托辊间接触应力很大,校核钢制托辊与滚圈的接触应力是大型混合机设计成功与否的重要因素之一。本文就接触应力进行详细计算,验证设计参数是合理的。     

边缘效应对凹坑织构接触应力的影响

边缘效应是引起织构表面应力集中现象的主要因素之一,织构的摩擦学性能与受载时织构边缘的最大应力密切相关。本文通过有限元分析了凹坑织构在初始和稳定摩擦阶段的静态接触应力分布,研究了在不同摩擦状态下边缘效应对织构表面接触应力的影响。为降低织构的边缘效应因素,同时计算了具有圆弧过渡边缘织构表面的应力分布。计算结果表明,织构最大接触应力趋势与摩擦系数的变化呈正相关,边缘圆弧过渡可显著降低织构的最大应力。     

球面销试样的摩擦学应用研究

采用球面销磨削设备制备的球面销试样,测试了不同尺寸的UHMWP材料的球面销与钢盘配副的摩擦性能,从接触面积与接触应力计算入手,讨论了接触应力的分布规律,探讨了UHMWPE球面销与钢盘配副时的摩擦系数与球体半径及载荷的变化关系.研究结果对弹塑性材料的接触和摩擦磨损机理研究具有借鉴意义.     

微动疲劳裂纹萌生位置及形成方式研究

着重研究了微动桥足不同几何形状——方足(r=0mm)及带不同半径r(0.3mm、0.6mm、0.9mm)对微动区接触应力的影响,用不同的r值模拟微动桥足在微动疲劳中的磨损状况。采用ANSYS有限元分析软件详细计算了接触表面的应力分布和磨损区、粘着区、滑动区及张开区的大小,进而讨论裂纹的萌生位置,并建立了不同的r大小即磨损状况与裂纹萌生位置的关系。同时针对方足微动桥/平面试件的接触几何,计算了不同名义接触压力分布形式对接触面上应力分布的影响。此外,还对方足微动桥/平面试件接触几何进行了三维有限元分析,证明了萌生裂纹通常是以多源方式同时出现。计算结果与实验结果吻合很好。     

Crack initiation from micro surface holes in bearings under rolling contact fatigue

Investigations concerning surface crack growth are necessary for understanding the mechanism of rolling contact fatigue (RCF) of bearings because the surface defects cause flaking failures. In the present work, micro holes were artificially made prior to the RCF tests and the initiation of the surface cracks from the micro holes was observed in order to find the key factors for understanding their features. Crack initiation directions were compared to the stress intensity factors calculated by a simple method based on the theory. The extent to which ‘contact pressure (wedge effect)’ and ‘contact stresses’ are applicable for understanding the correlations between the crack initiation directions and stress intensity factors is discussed. The crack initiation directions are strongly correlated to the stress intensity factors caused by the contact stresses alone. We concluded that the crack growth and initiation are dominated by stress intensity factors caused by contact stresses rather than the wedge effect.     

Surface crack growth of silicon nitride bearings under rolling contact fatigue

Surface crack growth of silicone nitride ceramic bearings under rolling contact fatigue has been investigated from the viewpoints of contact stresses (ring crack model) and fluid pressure (wedge effect model). The mechanisms of these two models have been investigated independently; however, it was impossible to separate the effects of contact stresses and fluid pressure on surface crack growth. In this paper the effects of contact stresses (ring crack model) on surface crack growth are investigated. In the ring crack model the crack growth is caused by contact stresses around the circumference of the contact circle. The growth of surface cracks located inside and outside the contact track was observed in order to obtain data from which we could reexamine the ring crack model. The outside cracks under rolling contact fatigue were propagated by contact stresses alone and also the inside cracks grew as slowly as the outside cracks. We concluded that the cracks are propagated by the single effect of contact stresses. Preliminary observations of surface crack growth showed that the cracks were unaffected by wear and residual stresses.     

Cyclic plastic behavior of dovetail under fretting load

The high gradient stresses near the edge of contact zone in dovetail assemblies will result in the appearance of a small plastic zone, which makes it difficult to calculate the contact stresses accurately. These calculated stresses are the premise to evaluate the strength of dovetail assemblies, but the majority of previous research on the solution of contact stresses have been usually carried out under linear elastic conditions. Thus this study focuses on characterizing the plasticity occurred in the dovetail assemblies under cyclic loading. A viscoplastic constitutive model of the titanium alloy TC4 is established based on the Chaboche theory. Furthermore, the calculation of contact stresses is carried out by use of the finite element method (FEM) with the constitutive model. The distribution feature of the contact stresses along the contact surface and the depth direction is obtained. The results show that the cyclic stress characteristics i.e. stress gradient, cyclic peak stress, and stress ratio, are not the same at different locations, namely different nodes of the FE model along the contact surface and the depth direction. These differences would make it more difficult to select suitable parameters for life prediction and to identify the most important effect factor. It is meaningful that the results of the study could provide some useful data and an idea for obtaining suitable parameters in fretting fatigue life prediction. The life prediction method with the effect of stress gradient considered may become an efficient approach to predict the fretting fatigue life of dovetail assemblies.     

Stress Hypotheses and material stresses in Hertzian contacts

Using idealised assumptions, the stress condition in the semi infinite body of the Hertzian contact region can be calculated for various geometries as a function of the surface pressure (normal force), the friction (tangential force at the surface) and the residual stresses in the material. Equivalent stresses can be formed from the coordinate stresses using various stress hypotheses (distortion energy hypothesis, shear stress hypothesis and alternating shear stress hypothesis). The effects of friction, residual stresses and contact geometry on the location and magnitude of the equivalent stresses appearing in the material have been investigated, the stress hypotheses being evaluated in terms of the extent to which they take account of these effects in an appropriate form. These investigations show clearly that the distortion energy hypothesis is the best representation of the extent of material stress in the case of dynamically loaded rolling elements. The shear stress hypothesis can be considered as a good approximation whereas the alternating shear stress hypothesis is only capable of providing useful conclusions to a limited extent.     

Werkstoffanstrengung im Hertzschen Kontakt – Einfluß von Reibung und Eigenspannungen

Stress Fields in Concentrated Contacts – Influence of Normal Load, Tangential Load and Internal Stresses The stresses in the half space of a Hertzian Contact (coordinate stresses and equivalent stresses) are shown in dependence of geometry and Hertzian contact stress. The equivalent stresses were calculated with the Huber, von Mises, Henky criterion. The superposition of combined normal and tangential load with residual stresses in the material was calculated for point and line contact. The course of the maximum of the equivalent stress in dependence of the residual stresses with the parameter friction coefficient is shown.     

高分子材料的粘弹性摩擦接触力学研究

采用非线性有限元方法研究了高分子材料的粘弹性摩擦接触问题,采用初应变法将粘弹性材料的蠕变应变转化为等价的虚拟节点力,并结合线性粘弹性理论对蠕变应变进行迭代修正,从而获得了粘弹性材料满足摩擦接触条件的解答。文中考虑了接触问题的边界非线性和粘弹性材料的材料非线性。并考虑了接触过程中温度,模量等级时间的增加而改变。     

The effect of mechanical loading on the contact resistance of coated aluminium

Measurements of contact resistance, related to resistance spot welding, were made using pre-treated (coated) and abraded aluminium alloy strip. With conventional domed electrodes, the contact resistance was much larger at the sheet-to-sheet (faying) contact than at the electrode-sheet contact. The effect is believed to be associated with the role of sliding in breaking down contact resistance of sheet with an insulating surface film. When the coating was removed the difference between faying surface and electrode-sheet contact was much smaller. Macroscopic shear stresses are developed by electrode-sheet contact whereas no shear stresses are present at the faying surface. The hypothesis is supported by experiments made with asymmetrical electrode pairs which give rise to varying shear stresses in faying surface contact. Some implications for the control of spot welding of different aluminium surfaces are discussed.     

Shakedown limit of rail surfaces including material hardening and thermal stresses

Sliding friction between railway wheels and rails results in elevated contact temperatures and gives rise to severe thermal stresses at the wheel and rail surfaces. The thermal stresses have to be superimposed on the mechanical contact stresses. Due to the distribution of stresses, the rail surface is generally subjected to higher stresses than the wheel surface. The elastic limit is reduced and yield begins at lower mechanical loads. During the first cycles of plastic deformation, the material hardens and residual stresses build up. The residual stresses provide the structure to shake down to pure elastic behaviour in subsequent load cycles up to a shakedown limit. The kind of hardening observed for rail steel has a considerable influence on the shakedown limit. The shakedown limit is dropped to lower mechanical loads due to the thermal stresses in the rail surface as well. This might cause structural changes in the rail material and rail damage.     

Calculations of the coefficient of friction under elastic contact conditions

Expressions for the friction coefficient were derived for the case of elastic contact between rough materials. The computation was based on the assumption that the friction force in the case under consideration is due to hysteresis losses during the deformation of a thin surface layer of one friction pair component by protuberances on the counterpart surface and due to molecular interaction at the solid/solid interface in the contact zones. The minimum value of the friction coefficient was calculated, and it was shown that it depends on the degree of surface roughness, physicomechanical properties of friction pair materials and the magnitude of tangential stresses ₀ at the solid/solid interface.