大变温工况下电接触件的力学特性与接触性能分析

为提高电钻杆用冠簧式接触件在大变温钻井工况下的电接触性能,对接触件展开了力学特性和电接触性能研究。基于静力学和热力耦合有限元分析方法,通过分析簧片挠度与接触压力、插入力与插针插入深度的关系,研究了大变温工况下不同装配间隙接触件的插入力、接触压力、接触面积变化规律。研究结果表明：接触压力随挠度增大而增大,增幅逐渐减小,插入力随插入深度先增大后减小最后趋于稳定;温升导致接触件接触压力、接触面积减小,降低了电接触性能,当装配间隙为0.07 mm≤δ≤0.2 mm时对电接触性能的影响程度较小;综合考虑150 ℃下的接触压力、接触面积和最大等效塑性应变,冠簧式接触件最优装配间隙为0.07 mm。该研究结果可为电钻杆用冠簧式接触件的结构设计及优化提供参考。     

二维多粗糙峰涂层表面的弹塑性接触力学分析

应用有限元方法对二维多粗糙峰涂层表面的弹塑性接触力学行为进行了分析。对不同涂层材料弹性模量、不同屈服极限、不同涂层厚度及不同表面形貌的粗糙表面与刚性平面的弹塑性接触问题进行了模拟,分析了这几种因素对接触压力、接触面积、表面轮廓变形及应力场分布的影响。     

热源影响下的涂层板滑动接触问题研究

基于离散卷积快速傅里叶变换(DC-FFT),推导了三维热弹性涂层压头-涂层板接触问题的频率响应函数的半解析解,应用数值模拟方法验证了半解析解的正确性,进而探讨涂层压头及涂层板的接触应力与涂层厚度h之间的关系.结果表明:三维热弹性域下涂层厚度与表面接触压力表现为负增长趋势,随着涂层厚度增加,表面接触压力呈现先快后慢的下降...     

粗糙表面热弹塑性接触问题的无网格法

建立可考虑屈服应力温度相关的粗糙表面热弹塑性接触无网格法数值计算模型.研究摩擦力和不同热输入情况下圆柱体与弹塑性平面的接触力学特性,探讨摩擦热效应对表面温升、接触压力和接触面积的影响.结果表明在考虑剪切摩擦力作用后,弹塑性接触压力分布不再关于接触区域中轴线对称而出现了"塌陷"现象.通过无网格法解与有限元法解比较发现不恰当的有限元网格划分会造成接触压力的数值震荡,而无网格法可避免这一现象的发生.发现忽略温度相关效应将高估最大接触压力而低估相应外载荷下产生的接触面积.     

接管纵向弯矩作用下补强圈与壳体间的接触行为

在应用薄壳理论对压力容器开孔补强结构进行分析时 ,常常假设补强圈与壳体间没有接触 ,对于该假设的合理性并没有相应的依据。本文采用ANSYS软件提供的非线性有限元技术模拟了纵向弯矩作用下补强圈与圆柱壳体间的接触行为 ,分析了接触行为对整个结构最大应力的影响 ,考察了接触变形和接触压力的变化 ,同时还分析了补强圈与壳体之间的间隙变化及不同d/Di 值对接触压力的影响     

航发叶片砂碟磨削接触特性及材料去除机理

航空发动机叶片型面曲率复杂变化、薄壁结构加工刚性弱，使其精密磨削接触状态多变、磨具轨迹规划困难，引起加工表面质量一致性差。为实现叶片磨削工艺优化，基于叶片磨削工艺特点分析，开展叶片砂碟磨削工艺接触特性及材料去除机理研究，利用降维法建立砂碟磨削材料去除率理论模型，通过砂碟磨削接触特性以及材料去除过程仿真研究，揭示了砂碟磨削不同工艺参数对叶片法向接触压力分布、等效法向接触压力、接触面积、接触轮变形及材料去除深度的影响规律，结合砂碟磨削工艺试验，对仿真结果进行验证。研究结果表明，砂碟磨削接触倾角与法向接触压力、接触面积呈负相关，与接触轮最大变形量呈正相关，接触倾角从10°增大到30°，本质使磨具更加锋利，材料去除深度峰值增大约59.78%，有效磨削区域显著降低；随着磨削深度从0.1 mm增大至0.3 mm，法向接触压力、接触面积及接触轮最大变形量均增大，有效磨削区域显著增大，材料去除深度峰值增大1.57倍，达到0.188mm；接触倾角与磨削深度是影响砂碟磨削材料去除的主要因素，对获得高质量表面并实现磨削工艺控制具有重要的作用。     

考虑粗糙度效应的微孔化机械密封摩擦副接触特性分析

针对机械密封装置在启停阶段或某些特定工况下出现高温以及摩擦磨损严重等问题，探究考虑粗糙度效应的微孔化机械密封端面接触压力及温升的变化规律，以揭示机械密封端面的真实接触状态。基于分形理论建立机械密封静环粗糙表面和动环微孔接触模型，采用数值计算方法，研究微孔对机械密封端面接触压力和温升的影响，以及表面粗糙度对机械密封端面接触面积、接触压力、温升的影响。结果表明：微凸体经过微孔时，微凸体嵌入微孔边缘使得接触压力峰值增大，导致切削发生；摩擦过程中，压力最高点位置因为微凸体的弹塑性变形而不固定，改善了微凸体的受力情况；微孔降低了密封端面的接触面积，从而使得微凸体的接触减少、压力极值点减少，降低了密封端面摩擦副的温度，改善了密封端面的磨损状况；表面粗糙度越小，接触面积越大，接触压力、端面温度更加均匀，表面粗糙度越大，端面磨损风险更加严重。     

半导体放电加工中接触电阻的影响因素研究

从理论上分析了产生接触电阻的原因,建立了切割回路中的导电原理模型。分析了如进电方式、进电材料、接触压力等因素对接触电阻的影响。实验结果表明:选择进电材料时,进电材料的功函数与所要加工的半导体的功函数尽量接近;选择接触形式,两个材料接触时要形成面接触,同时在允许的范围内尽量增大接触压力来减小接触间隙,这样会得到更小的接触电阻。     

材料属性温度相关热弹塑性接触问题研究

应用有限元方法建立了可考虑屈服应力温度相关效应的粗糙表面热弹塑性接触模型.研究了摩擦力和不同热输入情况下圆柱体与弹塑性平面的接触力学特性.求解了考虑屈服应力温度相关效应的粗糙表面热弹塑性接触问题,探讨了摩擦热效应对表面温升、接触压力、平均间隙及接触体应力分布的影响.提出了考虑热膨胀系数温度相关效应的热弹塑性接触模型.通过刚性圆柱体与半无限大平面的热弹塑性接触研究了热膨胀系数温度相关效应对接触体应力分布的影响.     

材料属性温度相关热弹塑性接触问题研究

应用有限元方法建立了可考虑屈服应力温度相关效应的粗糙表面热弹塑性接触模型。研究了摩擦力和不同热输入情况下圆柱体与弹塑性平面的接触力学特性。求解了考虑屈服应力温度相关效应的粗糙表面热弹塑性接触问题,探讨了摩擦热效应对表面温升、接触压力、平均间隙及接触体应力分布的影响。提出了考虑热膨胀系数温度相关效应的热弹塑性接触模型。通过刚性圆柱体与半无限大平面的热弹塑性接触研究了热膨胀系数温度相关效应对接触体应力分布的影响。
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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。     

A Theoretical Analysis of Mixed Lubrication by Macro Micro Approach: Part I—Results in a Gear Surface Contact

Mixed lubrication is a key to bring the performance analysis to the failure analysis in most tribological components. A macro-micro approach to mixed lubrication has been developed in the present model. The relation between the average contact pressure and the average gap for a typical rough contact patch is first determined numerically in micro scale. Using this relation, the average gap, average oil-film pressure, and average contact pressure in a mixed-lubricated elastohydrodynamic contact can be solved simultaneously in macro scale by treating the contact to be smooth. The total pressure is assumed a superposition of average asperity contact pressure and lubricant pressure. The new approach is simple, efficient and robust, and covers entire range of the load ratio, from unity (dry contact) to zero (full-film EHL). In addition, it can be used for a wide range of operating conditions and on a much larger contact area with a much less computing time than deterministic simulation of mixed lubrication. Implementation of the Fast Fourier Transform (FFT) allows for a rapid calculation of the elastic deformation and asperity con/act pressure. As a demonstration to this new approach, a parametric study of dimensionless speed, load and contact shape on the load ratio and gap ratio was conducted for a gear rough surface of the load ratio, from unity (dry contact) to zero (full-film EHL). In addition, it can be used for a wide range of operating conditions and on a much larger contact area with a much less computing time than deterministic simulation of mixed lubrication. Impletmentation of the Fast Fourier Transform (FFT) allows for a rapid calculation of the elastic deformation and asperity contact pressure. As a demonstration to this new approach, a parametric study of dimensionless speed, load and contact shape on the load ratio and gap ratio was conducted for a gear rough surface     

ANALYSIS ON THERMAL ELASTO-PLASTIC ASPERITY CONTACTS OF LAYERED MEDIA

A thermal elasto-plastic asperity contact model is investigated, which takes into account the steady-state heat transfer and the asperity distortion due to thermal elasto-plastic deformations. A hard coating and a soft coating are applied to study the correlations between contact area and contact pressure, average gap and contact pressure, coating thickness and contours of the contact stress distribution, etc. The effects of material properties, coating thickness, frictional coefficient, and the heat input combinations on the stress distribution are investigated and discussed. The frictional heat input increases the maximum value of yon Mises stress. Finally, the appropriate thickness of the hard coating is also discussed. To protect the substrate, one can choose hard coating and the thickness of that is suggested that can be hc=70 Rm.     

Surface topography and properties of frictional contacts

The influence of surface topography on contacting solids is considered. The rough surface model is suggested and is used for the calculation of some tribological contact characteristics. A rough surface is modelled by a set of asperities of regular shape (wedge, cone, cylindrical, spherical segment), of differing height. A simple height distribution function and asperity shape function are used. These functions may be integrated analytically in further calculations.The surface model is used for calculation of one of the main contact parameters - real contact pressure (or real contact area) and other principal contact parameters, such as deformation, number of contact spots, average spot area, average distance between contact spots and intercontact gap.It is shown how the above parameters may be used for the calculation of such operational contact characteristics as friction coefficient, wear rate and electrical and thermal resistance.     

On the Relation of Load to Average Gap in the Contact Between Surfaces with Longitudinal Roughness

A computer simulation model for the contact between longitudinally-oriented rough surfaces has been formulated. This model closely duplicates the actual surf ace contact deformation behavior by taking into account the elastic interactions between the asperities. There were no assumptions made about the shapes, or any deformation behavior of the asperities, except for their obeying the laws of elasticity. The plastic deformations on the high asperity peaks were taken into account by setting a ceiling on their contact pressures at the material hardness value. The simulations used real surface profiles which were digitized from unworn circumferentially ground steel surfaces. Each pair of these profiles was mathematically combined to form an equivalent rough profile pressing against an infinitely rigid flat and having the appropriately adjusted elastic modulus. A total of 28 different pairs of profiles were used in the simulations. Each contacting pair was subjected to 30 different load levels and the local contact pressures and deformations were calculated. The contact simulations yielded some important mathematical relationships between parameters, such as the real area of contact, average gap, and average asperity load through statistical curve fitting. Two analytical functions were generated to relate the average load to average gap and the real area of contact to load.     

Elasto-Plastic Contact of Rough Surfaces

An isothermal elasto-plastic asperity contact model is developed and presented in this paper, which deals with micro plastic flows of materials and the influence of the elasto-plastic deformation of materials on the behavior of contacting surfaces. The model is solved with the incremental form of a simplex-type algorithm. The von Mises yield criterion is used to determine the onset of the plastic deformation. The effectiveness and validity of the model are studied through analyzing a Hertzian contact problem. Substrate stresses are calculated and differences are observed. Furthermore, the contact pressure, real area of contact, and average gap of real rough surfaces under the elastic, elastic-perfectly-plastic, and the elasto-plastic contact conditions are numerically investigated and the results are compared.     

Normal contact between rough surfaces by the Discrete Element Method

This paper presents the study of nonadhesive, frictionless contact between elastic solids realized by the Discrete Element Method. This numerical method dedicated to multi-contact problems is applied to the field of tribology by studying the normal contact between a rigid rough surface and an elastic body modeled by spheres. A specific interparticle stiffnesses derived from homogenization techniques is implemented. From numerical tests carried out on spheres packings, we observe that the desired main macroscopic elastic constants are correctly modeled. Concerning the study of normal contact between rough surfaces, the obtained results are in accordance to existing theoretical models and numerical results from the literature, thereby demonstrating the potential of the Discrete Element Method to study the normal contact between contacting elastic bodies with rough surfaces. In particular, we recover the linear dependence of the real contact area with the normal load. In addition, we show that decreasing the surface roughness increases the average contact pressure.     

A finite surface element model for plane-strain elastic contact

A deterministic numerical model for plane-strain elastic frictionless contact between topographically anisotropic surfaces is derived, verified and demonstrated. The interface is divided into long rectangular surface elements sharing deflection nodes on the x axis bisecting the interface. The contact pressure distribution is piecewise linear from node to node. Given a digitized microtopographical profile z(x) of each surface, the model uses a partitioned Gauss-Seidel method to compute iteratively the pressure or gap at each node and hence the normal load and contact area fraction. The pressure moment is set to zero by allowing one body to rotate about the y axis. The elastic load limit of the interface is determined by monitoring the computed subsurface stresses. A uniform average pressure distribution can be achieved by bowing the input profiles to a particular convex geometry, thus enabling the model to simulate the deformation mechanics of a small region within a larger interface. The model is efficient and accurate for multiple-contact interfaces between randomly rough surfaces represented by profiles a few thousand nodes long.     

Analysis and Convenient Formulas for Elasto-Plastic Contacts of Nominally Flat Surfaces: Average Gap,Contact Area Ratio,and Plastically Deformed Volume

Interaction of nominally flat engineering surfaces that leads to a large contact area exists in many mechanical systems. Considering periodic similarity of surface geometry, a numerical three-dimensional elasto-plastic contact model can be used to simulate the contact behaviors of two nominally flat surfaces with the assistance of the continuous convolution and Fourier transform (CC-FT) algorithm. This model utilizes the analytical frequency response functions (FRF) of elastic/plastic responses of materials and provides contact performance results, including the average surface gap, the contact area ratio, and the volume of plastically deformed material, which may be defined as performance variables. Following the digital filtration technology, rough surfaces can be numerically generated with specified autocorrelation length and the first four orders of statistical moments. A group of contact simulations are conducted with various working conditions. The effects of topographic and material properties on the contact behaviors are discussed. With a multi-variables regression method, empirical formulas are developed for the performance variables as functions of surface statistical characteristics, material properties, a hardening parameter, and the applied load in terms of pressure.