Thermomechanical analysis of elastoplastic medium in sliding contact with fractal surface

The effects of mechanical and thermal surface loadings on deformation of elastic–plastic semi-infinite medium were analyzed simultaneously by using the finite element method. Rigid rough surface of a magnetic head and smooth surface of an elastic–plastic hard disk were chosen to perform a comprehensive thermo-elastic–plastic contact analysis at the head–disk interface (HDI). A two-dimensional finite element model of a rigid rough surface characterized by fractal geometry sliding over an elastic–plastic medium was then developed. The evolution of deformation in the semi-infinite medium due to thermomechanical surface loading is interpreted in terms of temperature, von Mises equivalent stress, and equivalent plastic strain. In addition to this, the effects of friction coefficient, sliding, and interference distance on deformation behavior were also analyzed. It is shown that frictional heating increases not only the contact area but also the contact pressure and stresses.     

热力耦合下微接触点塑性应变沿深度变化分析

在考虑粗糙实体弹塑性变形、热力耦合、微凸体间相互作用和摩擦热流耦合等影响下,运用有限元法数值模拟具有三维分形特性的粗糙面与刚性平面间滑动摩擦过程,分析了粗糙实体接触凸点塑性变形随深度变化情况。发现：在速度的突变和闪点温度形成时,摩擦接触表层等效塑性应变增大明显;在这一摩擦表层,过不同接触点的纵向剖面塑性应变沿深度分布不同：有的是接触表面塑性变形最大,有的是在接触微凸体表面下某一深度塑性变形最严重,而接触凸点表面的塑性应变稍小些。这与相关文献用SEM研究干摩擦后金属摩擦表层变形照片后发现的结果一致。滑动摩擦过程中,金属粗糙摩擦接触表层塑性变形的不断累积,将会导致材料表层中的夹杂或微观缺陷周围萌生微孔和裂纹源。     

Thermomechanical analysis of ultra-high molecular weight polyethylene-metal hip prostheses

In order to predict the frictional heating and the contact stresses between the polyethylene cup and the metallic ball-head forming the articulation of a hip prosthesis a three-dimensional finite element model was developed and calculated. The non-linear model includes a fully coupled thermomechanical formulation of the mechanical properties of the ultra-high-molecular-weight polyethylene, and a large-sliding Coulomb frictional contact between the two components. The model predicts the temperature of the polyethylene with an accuracy that was tested by comparing the model predictions with the temperature measurements. The temperature measurements were taken by thermocouples placed on the cup surface, the head surface and the inside of the thermostatic bath, during a complete test within a hip joint wear simulator. The model was found to be very accurate, predicting the measured temperatures with an accuracy better than 2 per cent. The temperature peak (51 degrees C) was predicted at the contact surface. The model results indicate that frictional heat is mostly dissipated through the metallic ball-head. The full coupling between the thermal and the mechanical conditions used in this study appears to be necessary if accurate predictions of the polyethylene deformation are required.     

Study of plastic shear deformation in surface layer at friction. Simulation results. Part II. Effect of friction parameters

Deformation and temperature in the surface layer of plastic material and thickness of the plasticized layer are calculated using the one-dimensional macroscopic friction model developed in the first part of the paper [1]. We have studied the effect of sliding velocity, contact spot area, hardening ability, and thermal conductivity of material on the frictional heating and plastic deformation of the surface layer during a single touch between the contact spot and counterbody. Repeated contacts of the specimen and counterbody are simulated and the accumulation of plastic shear is considered for different contact spot sizes.     

Microwear mechanism of head carbon film during head disk interface sliding contact

Thermomechanical sliding contact of head disk interface (HDI) causes critical wear on the carbon film of a head slider. An improved contact model accounting for both asperity and substrate deformation is applied to analyze the HDI contact behavior, while theories of frictional heat generation and heat transfer are used to investigate the change in HDI temperature. Based on actual HDI design and operation parameters, parametric study of thermomechanical HDI contact has been performed. It was found that severe wear of head carbon film would be significantly attributed to thermal degradation of carbon material during its sliding contact.     

磨粒微观滑动接触过程热效应的有限元分析

利用ANSYS有限元软件分析了磨粒与被磨损材料表面滑动接触过程中,在摩擦热和力场的耦合作用下,接触区表现出的局部温度变化、应力变化等特性。结果表明,在磨粒滑移过程中,磨粒相当于接受固定热源作用,接触区温度逐渐上升,温度存在起伏波动现象,瞬现温升最高点在磨粒接触区两侧,反映出接触状态的不连续性,接触区状态的非稳定性;被磨材料表面的各点在进入接触前、经历接触时、脱离接触时,接触区温度存在先升高再下降的变化过程,同时,接触区的应力、剪应力、接触压力也发生变化。磨粒滑动过程的热效应问题研究将有助于揭示接触过程中材料表面损伤机制。     

Comparative analysis based on adiabatic shear instability for scuffing failure between unidirectional and reciprocating sliding motion

The principal goal of the experiments described here is to study the sliding motion effects on the scuffing life on the basis of adiabatic shear plastic instability. Experimentally we observed that the load capacity of the surface decreased and micro-scuffing initiated frequently under the reciprocating sliding motion as compared to under the unidirectional sliding motion. According to the adiabatic shear instability model, the scuffing initiation occurs when the rate of thermal softening exceeds that of work hardening due to plastic deformation. In order to ascertain the thermal softening in sliding surfaces, the contact temperatures were calculated. We found that the higher friction coefficient under the reciprocating sliding motion caused the higher contact temperature than that under the unidirectional motion. Therefore, the rate of thermal softening could exceed that of work hardening easily under the reciprocating sliding motion owing to frictional heating. We speculated that the scuffing initiation could roughen the sliding surfaces rapidly under the reciprocating sliding motion and confirmed that our assumption demonstrated above, was consistent with the experimental observation. In conclusion, there is a synergy effect in relation to scuffing failure because the frictional heating, surface roughening, and scuffing initiation function together to enhance each other, and consequently, the load capacity of surfaces could decrease under reciprocating sliding.     

火箭橇滑块摩擦热的结构耦合场分析

利用ANSYS软件建立火箭橇试验中滑块与轨道的滑动摩擦热-结构耦合场模型,研究特定载荷和运行工况下滑块的温度场和应力场。结果表明:滑块材料的热参数和滑块轨道间的摩擦因数对接触面温度有很大影响,接触面温度随摩擦因数增大而增大;分析指定路径上的应力分布可知,摩擦热影响区和热应力集中区域约为从接触面开始至向上6 mm范围内,滑块在运行中的破坏发生在该区域。     

Thermo-mechanical analysis of the magnetic head–disk interface with a fractal surface description

Rigid rough surface of a magnetic head and smooth surface of a hard disk are chosen to perform a comprehensive thermo-mechanical contact analysis at the magnetic head–disk interface, which is characterized by using the fractal geometry. The effects of mechanical and thermal surface loadings on deformation of the semi-infinite medium in normal and sliding contacts are analyzed simultaneously by developing a 2D finite element model. It is shown that frictional heating increases not only the contact area but also the contact pressure and stresses. The maximum temperature occurs at the tip of the asperities of the semi-infinite medium.     

Numerical analysis of rolling-sliding contact with the frictional heat in rail

Thermal damage caused by frictional heat of rolling-sliding contact is one of the most important failure forms of wheel and rail. Many studies of wheel-rail frictional heating have been devoted to the temperature field, but few literatures focus on wheel-rail thermal stress caused by frictional heating. However, the wheel-rail creepage is one of important influencing factors of the thermal stress In this paper, a thermo-mechanical coupling model of wheel-rail rolling-sliding contact is developed using thermo-elasto-plastic finite element method. The effect of the wheel-rail elastic creepage on the distribution of heat flux is investigated using the numerical model in which the temperature-dependent material properties are taken into consideration. The moving wheel-rail contact force and the frictional heating are used to simulate the wheel rolling on the rail. The effect of the creepage on the temperature rise, thermal strain, residual stress and residual strain under wheel-rail sliding-rolling contact are investigated. The investigation results show that the thermally affected zone exists mainly in a very thin layer of material near the rail contact surface during the rolling-sliding contact. Both the temperature and thermal strain of rail increase with increasing creepage. The residual stresses induced by the frictional heat in the surface layer of rail appear to be tensile. When the creepage is large, the frictional heat has a significant influence on the residual stresses and residual strains of rail. This paper develops a thermo-meehanical coupling model of wheel-rail rolling-sliding contact, and the obtained results can help to understand the mechanism of wheel/rail frictional thermal fatigue.     

A 3-D finite element method for non-isothermal sheet-forming processes

In sheet forming of ductile materials, the forming limit and strain distribution are governed by plastic instability and fracture following strain localization. A number of phenomena influence the localization process, including the best-known plastic properties of strain hardening, strain-rate sensitivity and yield-surface shape. The temperature gradient caused by deformation heating, heat transfer, and friction between sheet and tools also controls strain localization. In this paper, a numerical method for analyzing the non-isothermal, rigid-viscoplastic deformation of sheets is presented. The method consists of two parts: a rigid-viscoplastic finite element model (FEM) to solve the plastic deformation, and transient heat transfer FEM to evaluate the temperature change throughout the specimen during the deformation process. Bishop's step-wise decoupled method is adopted to handle coupling between mechanical deformation and the temperature change. Using this method, the effect of temperature distribution on strain patterns was investigated. As illustrative 3-D examples, hemispherical punch-stretching and square punch-stretching operations have been analyzed, including deformation heating, frictional heating, heat transfer to tooling and air, and internal heat conduction in the workpiece. The role of temperature gradients is revealed by examination of the simulation results.     

圆柱面和圆锥面摩擦传动的摩擦特性及热性能分析

本对圆柱面和圆锥面的摩擦特性及热性能进行分析，利用摩擦学原理及传热学理论，分析了摩擦材料的损坏原因，并提出了合理解决对策以及两种摩擦副的特点，得出摩擦轮是由于滑动并产生较大热量而导致烧损的主要结论。     

RESEARCH ON DESIGN METHOD OF A MULTIPLE DISC WET BRAKE IN LUBRICATED ENVIRONMENT

The rmomechnical phenomena occurring between friction pairs greatly change the distributions oflining pressure and friction surface temperature of a multiple disc wet brake. It has become one of the maincauses of brake failure. In order to understand these thermomechanical phenomena, several design and mate-rial factors tha have great influence on thermomechanical phenomena, such as heat transfer coefficient, fric-tion factor, sliding velocity initial lining pressure and so on, are analyzed. An isothermal design method isproposed for designing a multiple disc wet brake.     

Deformational contact and friction on viscoelastic substrates

The deformation of a rigid slider of arbitrary shape sliding smoothly over the surface of a general linear viscoelastic layer is studied. A solution of the two-dimensional problem is presented in order to calculate rigorously the contact area, deformational friction and frictional heating. For a rigid cylinder moving on a standard linear viscoelastic substrate the distinctive effects of varying the size and shape on the contact area are calculated exactly as a special case of our general solution. The results, given in terms of the slider speed and the hysteresis properties of a viscoelastic solid, agree well with the excellent qualitative prediction of Moore's theory. More importantly, the calculation concludes that all the sudden changes in the size and shape of contact, the deformational friction and heat generation correspond to the maximum loss tangent of the viscoelastic material.     

Improvement of wear resistance of quenched structural steel by nanostructuring frictional treatment

The paper deals with the study of the structure, deformation hardening, and wear resistance under abrasive and sliding friction of quenched structural steel 50 (0.51% of C), which is subjected to frictional treatment by a hard alloy indenter. The resistance of a steel surface layer hardened by frictional treatment to mechanical effects is estimated using the kinetic indentation method. It is shown that frictional treatment yields a considerable increase in the wear resistance of quenched medium-carbon steel tested in pairs with flint and corundum, as well as under the conditions of adhesive wear and boundary friction, due to the hampering of the processes of microcutting, seizure, and plastic deformation. This is favored by the higher resistance of the nanostructured layer to residual deformation during contact loading.     

Effect of thermal deformation on machine tool slide guide motion

This paper describes the effects on machine slide-guide contact conditions caused by thermal deformation. Since a slide guide has a large friction surface, the motion is greatly influenced by thermal distortion caused by heat generation in the ball nut and the bearing support, during machining processes. This study investigated the typical behavior of the friction coefficient in response to both the external load and the linear speed. This then led to investigating the thermal effects on the slide motion. The thermal deformation of the slide table was measured with respect to the running time and the linear motion and the frictional power were monitored and compared directly with the thermal distortion.     

大偏心下滑动轴承热弹流润滑状态及特性*

滑动轴承在大偏心条件下工作时，热效应及弹性变形使得油膜润滑状态发生变化，进而影响摩擦特性。为此建立耦合轴瓦弹性变形、轴颈轴瓦粗糙峰接触、油膜温度分布及黏温-黏压关系的滑动轴承混合润滑模型，采用有限差分法求解得到不同工况下油膜压力场、温度场分布，分析热效应及弹性变形对润滑状态转变及轴承各特性参数的影响；搭建实验台测量试件内表面温度分布，测试结果验证了计算模型的正确性。结果表明：大偏心时热效应和弹性变形使得油膜润滑状态出现转化；粗糙峰的接触使摩擦热增加，且在最小油膜处形成温度峰值；热效应和轴瓦弹性变形使得接触压力峰值集中在轴承两端，承载能力和摩擦力均有所下降。     

An integrated approach to evaluating the tribo-contact for coated cutting inserts

The orthogonal machining process when end turning medium carbon and austenitic stainless steels with cemented WC-Co tools coated with single-layer (TiC), two-layer (TiC/TiN), and three-layer (TiC/Al₂O₃/TiN) hard thin films was investigated. Extensive experimental investigations including the thermal, mechanical and tribological responses of the tribo-contact between the coating–substrate system and the chip, under different cutting conditions, were carried out. The study sheds light on the cutting forces, the interface temperatures and the tribo-contact conditions, including the friction energy dissipated at the tool–chip interface, the frictional heat flux conducting into either the chip or the insert, the mean coefficient of sliding friction and the contact loads exerted on the tool rake face. Finally, it was demonstrated how the intrinsic coating properties control the heat flux flowing into both components of such a closed tribo-system and the mechanical stresses on the contact area.     

Heat checking in the contact zone of a bearing seal (a two-dimensional model of a single moving asperity)

When two bodies are in sliding contact under heavy loads, local high temperature may occur as a result of excessive frictional heating near the contacting surfaces. Because of a combination of thermal heating and the mechanical load, the material may crack in the neighborhood of the contact zone. This phenomenon is called heat checking. It commonly occurs in mechanical seals and brakes. In recent years there has been increased emphasis on finding a solution. In this paper a simple model is proposed to determine those parameters which can be optimized to control the heat checking of the materials.Because of the size difference between the contact area and the seal, the mathematical model is represented by a half-space subjected to a fast-moving load which is distributed over a small area. The load comes from a combination of an arbitrarily distributed heat source and mechanical loads of pressure and friction. The general solutions are expressed in the form of integral equations with determined Green's functions. Numerical results for fracture criteria are then obtained using a computer program.For the current problem, a nominal pressure of 365 MPa (53000 Ibf in^?2) and a corresponding friction of 183 MPa (26500 Ibf in^?2) are used. The induced heat source is 1.5 × 10⁷ in Ibf in^?2 s^?1 (1.70 × 10⁶Jm^?2s^?1). Such a load results in fracture where the crack is first initiated immediately beneath the surface at the trailing edge of the moving load.     

Thermal and thermomechanical phenomena in sliding contact

The paper deals with the development of heat problems in friction, beginning from the works of H. Blok to the present day. Blok put forward the concept of flash temperature, which has become a fundamental one in frictional heating. The main models of frictional heating, developed by Blok, Jaeger, Archard, and Kuhlmann-Wilsdorf, are analyzed. The influence of different factors on flash temperature and its distribution over the friction surface is discussed. The effect of frictional heating on the mechanisms of material wear is considered.