基于ANSYS的轮轨摩擦滑动接触应力分析

以Hertz接触理论为依据,利用ANSYS建立2D有限元计算模型,模拟原地打滑、完全制动等轮轨滑动摩擦接触行为。分析了轮轨静接触和滑动接触时接触应力分布情况,研究了接触状态、轴重、滑动速度、载荷类型和钢轨轨顶圆半径对接触应力的影响。结合Hertz接触理论计算结果、剥离损伤理论和自激振动理论进行了轮轨损伤分析。     

A mixed model to predict friction forces in lubricated contact with non-newtonian fluids

A mixed model to predict friction forces in thermohydrodynamic lubricated contacts with non-Newtonian fluids is proposed, with an integral formulation and a finite element method resolution. The mixed model is used here for the first time in lubrication. It takes into account the implicit rheological laws. The shear stress field appears in this formulation as a nodal unknown and eases the use of rheological laws with yield criteria.     

Finite element methods for contact problems with friction

The numerical treatment of contact problems involves the formulation of the geometry, the statement of interface laws, the variational formulation and the development of algorithms. In this paper an overview with regard to the numerical simulation of frictional problems is presented when general constitutive equations are formulated in the contact interface. To be most general we will apply a geometrical model and its discretization for contact which is valid for large deformations. Furthermore the algorithms to integrate the interface laws will be discussed for the tangential stress components. Special emphasis is laid on the development of algorithms which allow an efficient treatment of frictional contact problems.     

A multi-scale model for friction in cold rolling of aluminium alloy

A simple and robust friction model is proposed for cold metal rolling in the mixed lubrication regime, based on physical phenomena across two length scales. At the primary roughness scale, the evolution of asperity contact area is associated with the asperity flattening process and hydrodynamic entrainment between the roll and strip surfaces. The friction coefficient on the asperity contacts is related to a theoretical oil film thickness and secondary-scale roll surface roughness. The boundary friction coefficient at the “true” asperity contacts is associated with tribo-chemical reactions between fresh metal, metal oxide, boundary additives, the tool and any transfer layer on the tool. The asperity friction model is verified by strip drawing simulations under thin film lubrication conditions with a polished tool, taking the fitting parameter of the boundary lubrication friction factor on the true contact areas equal to 0.1. Predicted values of average friction coefficient, using a boundary friction factor in the range 0.07–0.1, are in good agreement with measurements from laboratory and industrial rolling mill trials.     

超声滚压工艺对TC4钛合金表面残余应力的影响

钛合金关节轴承是航空发动机的重要部件之一,但由于其润滑条件较差,极易产生磨损从而导致失效事故。采用超声滚压工艺对钛合金试件表面进行强化试验,以有效增强试件表面耐磨性能和抗疲劳特性,并着重研究静压力、滚压次数和主轴转速等超声滚压强化工艺参数对钛合金表面残余压应力与剪切应力的影响规律。试验结果与理论分析结果表明,残余压应力随着静压力、滚压次数和主轴转速的提高而增大,剪切应力随着静压力、滚压次数和主轴转速的提高而总体减小;滚压后试件表面可获得-2 000～-500 MPa的残余压应力和-600～-300 MPa的剪切应力。超声滚压技术可以有效提高钛合金材料表面的残余压应力,并有效降低表面的剪切应力。     

Experimental measuring procedure for the friction torque in rolling bearings

The reduction of the power loss generated in mechanical transmissions and the use of low friction biodegradable lubricants has been attracting considerable attention in recent times. Therefore, it is necessary to develop methods to test and evaluate the performance of such lubricants and compare them with conventional ones. In this sense, a Four‐Ball Machine was modified allowing the test of rolling bearings. A 51107 thrust ball bearing was used to test two different greases and the corresponding base oils. Friction torque and operating temperatures were continuously monitored to quantify the power loss and the heat evacuation for each lubricant tested. Copyright © 2010 John Wiley & Sons, Ltd.     

Modelling lubricated friction for dynamic contact systems

Multi-valued friction is often observed in lubricated contact systems operating under unsteady sliding conditions. In the past, this behaviour has been modelled using a measured time delay between changes in sliding velocity and resulting changes in friction. More recent work has revealed that fluctuations in normal separation are the principal cause of this deviation from steady friction behaviour. This paper demonstrates that tangential contact dynamics can result in apparent deviations from steady friction that can resemble true deviations found from fluctuations in normal separation. Two different dynamic models are considered. One model accommodates the tangential rider dynamics of a friction test apparatus. The other model considers the possibility of tangential dynamics associated with asperity contacts.     

Force characteristics of dry friction when contact oscillates

A comparative evaluation of the applicability of elastoplastic and rigid-plastic force characteristics of dry friction to calculating contact-oscillating systems is discussed. It is shown that elastoplastic characteristics of the hysteretic type are applicable at amplitudes of oscillations less than or comparable with the ultimate predisplacement. The features are considered of the dynamic links in the sliding friction contact that may lead to the known least dependence of the force of friction. It is noted that application of rigid-plastic friction characteristics to calculation of low-amplitude quasi-elastic contact oscillations leads to contradiction with the experimental data.     

Selection of a contact geometry model when simulating thermal friction processes

In this paper an analysis of the uniformity of temperature distribution on the surface of a semi-infinite friction body, mutual heat interference of discrete contact areas, and the accuracy of the concentrated model of thermal and mechanical contact of rubbing solids in response to the degree of contact discreteness is conducted. The conducted research yields a criterion of selection for the contact geometry model. A classification of heat friction problems that allows the selection of an appropriate model of contact geometry for simulation of heat friction processes is proposed.     

Evolution of and preconditions for generation of corrugations on a plane surface in rolling contact

A hard roller under normal load is driven by the flat surface of a soft disc. Corrugations are generated on the disc when certain surface morphological, load, speed and mechanical property-oriented conditions are met. The evolutionary process of corrugation generation and the preconditions necessary for it are investigated morphologically and mechanically for four disc materials: mild steel, brass, PTFE and PMMA.     

The influence of contact geometry on friction and wear characteristics

This paper describes some results of evaluating the influence of contact geometry on tribological characteristics. Friction characteristics obtained for a distributed contact (pin‐on‐disc and block‐on‐ring), a linear concentrated contact (pin and vee‐block and block‐on‐ring) and a point concentrated contact (ball‐on‐disc and three cylinder‐cone) are presented. The wear scars were analysed using scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS). The results show different values of friction and wear coefficients for the different types of contact geometry. The paper also assesses the effect of non‐test characteristics, e. g., vibration.     

A theoretical study on the application of asymmetric rolling for the estimation of friction

In this work, a method for the estimation of friction coefficient is proposed based on the asymmetric rolling operation. Asymmetry is produced by operating the lower and upper rolls at different speeds. A slab method based computer code is developed for estimating the curvature of the rolled sheet under asymmetric rolling conditions. Strain-hardening behavior of the material has been incorporated and Wanheim and Bay's friction model is employed. The developed code is used for solving the inverse problem of estimating the coefficient of friction by measuring the curvature of the rolled sheet under known operating conditions. The simulations show a good potential of the method.     

An analysis of three-dimensional elasto-plastic sinusoidal contact

Researchers have developed many models to simulate the elasto-plastic contact of spheres. However, there does not appear to exist a closed-form analytical model for elasto-plastic three-dimensional sinusoidal contact. This work uses a finite element model (FEM) to characterize elasto-plastic sinusoidal contact. Although at initial contact the sphere and sinusoidal case are very similar and can both be described by the classic elastic Hertz contact case, once the contact is pressed past a certain range of deformation the two cases are very different. The model produces equations which can be used to approximately relate the area of contact to the contact pressure for elasto-plastic sinusoidal contact. The equations are fit to the FEM results and existing elastic solutions of sinusoidal contact. An empirical expression for the average pressure which causes complete contact between elasto-plastic sinusoidal contacts is also provided.     

Development of plastic zones and residual stress in elasto-plastic contact problems with stress singularities in elastic range

Stress singularities appear in such elastic contact problems as a plane indenter compressing a semi-infinite body, or the axisymmetric case of a turbine disc shrunk onto a shaft. The stress is infinite at the edge of the corner of the indenter and the disc as well as in neighbouring areas of the semi-infinite body and the shaft.In this paper the complex investigation of the distributions of plastic zones, deformations, pressure and residual stress has been presented for plane indenters of different shapes being in elasto-plastic contact with semi-infinite bodies. Different strain-hardening characteristics of the material, different yield criteria and states of stress/strain have been considered.The aim of the investigation is to find an answer to the question, what happens to the stress singularity, which appears in the elastic solution? The considered problem is of interest from the cognitive point of view and is of real importance in engineering practice.     

An enriched finite element algorithm for numerical computation of contact friction problems

In this paper, the extended finite element method (XFEM) is employed to model the presence of discontinuities caused by frictional contact. The method is used in modeling strong discontinuity within a standard finite element framework. In extended finite element method (XFEM) technique, the special functions are included in standard FEM to simulate discontinuity without considering the boundary conditions in meshing the domain. In this study, the classical finite element approximation is enriched by applying additional terms to simulate the frictional behavior of contact between two bodies. These terms, which are included for enrichment of nodal displacements, depend on the contact condition between two surfaces. The partition of unity method is applied to discretize the contact area with triangular sub-elements whose Gauss points are used for integration of the domain of elements. Finally, numerical examples are presented to demonstrate the applicability of the XFEM in modeling of frictional contact behavior.     

Experimental evaluation of friction between contacting discs for the simulation of gear contact

Instant gear contact can be simulated with contacting discs, which provides steady operating conditions and eliminates most of the dynamics and manufacturing tolerances involved in real gears, resulting in an accurately controlled contact condition. A high-pressure twin-disc test device was developed, where loading and rolling velocity can be varied continuously. It is equipped with disc bulk temperature, mean contact resistance and friction moment measurements. The test discs were grinded transversal to the disc rolling direction with proper crowning corresponding to the real gear flank properties. The test device was applied by studying the friction behaviour against the slide-to-roll ratio at different contact pressures, rolling velocities and surface roughness. The measurements were performed using mineral base oil in the range of operation conditions often used in industrial gears. In general, the measured friction coefficient behaviour correlates with earlier published results and is logical with measured bulk temperature and mean contact resistance. The limiting shear stress of the lubricant has an essential role in friction behaviour. Copyright © 2006 John Wiley & Sons, Ltd.     

三辊滚压非线性接触应力分析

以三辊滚压为基本模型,通过对模型的建立及相应边界条件的施加,来确定三辊滚压过程中产生的压下量及接触区域宽度等相关参数。利用ANSYS分析软件中状态非线性分析功能,求解三辊滚压非线性接触状态的Hertz接触宽度(b1、b2)、竖向位移(l)、应力分布等参数。分析出使镁铝合金材料从外及里四分之一厚度范围内,发生塑性变形所需压下力值。     

Stress drop and contact stiffness measured from stick-slip experiments on PMMA-PMMA friction

We present results from an extensive stick-slip study on PMMA-PMMA dry friction, where we studied the influence of a wide range of normal stresses, loading velocities and roughnesses of the sliding surfaces. In this paper we focus (a) on the analysis of a residual coefficient of friction, i.e., shear stress measured at the end of the slip phase divided by the corresponding normal stress, and (b) on the contact stiffness measured by plotting the relative displacement between sample against the shear stress during the stick phase. It is shown that the residual coefficient of friction (i) decreases as normal stress increases, (ii) shows a slight increase when the roughness of the sliding surfaces increases and (iii) does not vary according to the loading velocity. The contact stiffness proved independent of loading conditions and of the roughness of the sliding surfaces. These results are interpreted in terms of asperity interlocking. This revised version was published online in July 2006 with corrections to the Cover Date.     

搅拌摩擦焊和钨极氩弧焊焊接接头的残余应力

利用X射线衍射法测量了铝合金搅拌摩擦焊和钨极氩弧焊(TIG)焊接接头表面的残余应力分布.结果表明:两种接头在焊缝区及其周围的残余应力存在着明显的变化,在平行于焊缝方向,应力呈"W"型的分布,焊缝外残余应力值迅速下降;钨极氩弧焊焊接接头残余应力的最大值位于热影响区;在热影响区,搅拌摩擦焊接接头残余应力平均值比TIG焊接接头的约低15%～25%.     

Elastoplastic finite element analyses of an upsetting-sliding test for the determination of friction at medium and high contact pressure

The upsetting-sliding test is a friction test employed for the determination of the tangential stress-contact pressure relationship at a specimen-tool or target part-contactor contact surface. It is used in addition to the analysis of forming sequences or mechanical design. The specimen, or target part, used in the test is the same that the one involved in the studied forming sequence so that the physical and chemical characteristics of the contact involved by the test and sequence are the same. In the test, the contact pressure is exerted by an inclined front surface indenter which takes the place of the tool or the contactor. Then, the indenter is moved in contact with the generator line surface of the specimen or the target part. The computation of the tangential stress, contact pressure and effective plastic strain firstly with respect to the penetration, sizing length and front face angle and, secondly, with respect to the frictional variations are performed with a three-dimensional finite element model. An initial guide for the determination of the indenter length and front angle and indenter penetration in the specimen is proposed in order to define the most realistic tangential stress-contact pressure curves.