Simulating sliding wear with finite element method

Wear of components is often a critical factor influencing the product service life. Wear prediction is therefore an important part of engineering. The wear simulation approach with commercial finite element (FE) software ANSYS is presented in this paper. A modelling and simulation procedure is proposed and used with the linear wear law and the Euler integration scheme. Good care, however, must be taken to assure model validity and numerical solution convergence. A spherical pin-on-disc unlubricated steel contact was analysed both experimentally and with FEM, and the Lim and Ashby wear map was used to identify the wear mechanism. It was shown that the FEA wear simulation results of a given geometry and loading can be treated on the basis of wear coefficient−sliding distance change equivalence. The finite element software ANSYS is well suited for the solving of contact problems as well as the wear simulation. The actual scatter of the wear coefficient being within the limits of ±40–60% led to considerable deviation of wear simulation results. These results must therefore be evaluated on a relative scale to compare different design options.     

Contact and wear of paper-based friction materials for oil-immersed clutches—wear model for composite materials

Paper-based friction materials are widely used for oil-immersed clutches in automatic transmissions for passenger cars. It is known that repetition of engagements of the clutches causes wear of the friction materials leading to running-in with an increase in contact area. Observation of the contact of a typical paper-based friction material has been made by contact microscopy using the reflection of polarized light. The results have shown that contact is made at the top of its particulate and fibrous constituents, and comparison with the results of laser microscopy has revealed that the contact area observed by the contact microscopy is the contour contact area. An analysis has been made to describe this behavior by employing a mechanical model in which spherical and columnar asperities are supported by an elastic halfspace and wear under the loads they support. Analytical results describe the observed change in the contour contact area and demonstrate applicability of the model to wear of composite materials.     

高温线接触条件下表面抗磨损性能的试验研究

模拟内燃机汽缸－活塞环工况,采用ＳＲＶ摩擦磨损试验机进行高温线接触条件下,抗磨损性能的试验。试验表明：经激光微精处理的试件,在参数合理的情况下可使其抗磨损性能大幅度提高。这为发动机汽缸处理的实际应用提供了参考。     

Mechanisms of sliding wear of metals and alloys at elevated temperatures

Sliding wear at elevated temperature is an important material removal mechanism in large number of engineering applications such as metal forming operation, gas turbine engines, etc. The material loss during sliding at elevated temperature is governed by the antagonistic effect of wear process and oxidation. The objective of the present work is to give an outline of the current status and future trends of wear at elevated temperature of selected metallic materials. Starting with a brief overview of present level of understanding of the elevated temperature wear of various metals and alloys, the initial parts of the paper describes various important development in recent years on elevated temperature sliding wear. The salient features which have helped us to gain in depth scientific knowledge of elevated temperature wear are discussed in the light of recent developments. The overview is further substantiated by detailed study and observation in recent times in particular, the work done at the Vienna University of Technology (Institute of Microtechnique and Precision Engineering) and at the Austrian Center of Competence for Tribology. Specific examples from the recent literatures are described to exemplify the mechanisms of formation of various types of layers during high-temperature wear. Some thoughts on the future directions for research are also outlined.     

A Study of Wear Chemistry and Contact Temperature Using a Microsample Four-Ball Wear Test

This study demonstrates that insight into the tribological reactions taking place in mixed and boundary lubrication can be provided by combining microsample four-ball wear tests with chemical analysis using gel permeation chromatography (GPC) as the principal analytical tool. At the end of the microsample four-ball wear test the lubricant turns into a grease-like mixture preventing the liquid lubricant from recirculating into the wear track and thus causing failure. Analyses of the various lubricant samples after their failure in the microsample test all show a relatively small amount of insoluble deposits and a large quantity of unreacted fresh lubricant. Virtually no intermediate reaction products were found. Combining this information with lubricant stability and the fact that a large quantity of lubricant flowed through the sliding junction while only a small portion was oxidized suggests that two very different thermal environments exist in the concentrated contact. The insoluble deposits are typical of thermal oxidative reactions that require temperatures of400°C or above. The unreacted lubricant found at failure indicates that this portion of the lubricant sample was maintained at temperatures of 150°C or below. The formation of grease-like mixture with as little as four percent reacted material indicates the remaining liquid lubricant and its insoluble reaction deposits were well mixed throughout the test. These findings suggest that the hot zones causing severe lubricant degradation are in the immediate vicinity of the asperity-asperity contacts while the low temperature zone - the valleys between asperities which are in the majority - are much cooler.     

Contact mechanics and the wear of metals

It is commonly observed that metallic wear debris takes the form of thin platelets, leading to the term ‘delamination wear’. Modelling this phenomenon has proved a stiff challenge in Contact Mechanics since the fractures which give rise to wear particles lie parallel, or nearly so, to the surface; i.e. on planes of maximum compressive stress. Sectioning the surface layer beneath a wear track has revealed it to have acquired severe plastic strains, which suggests that the cracks are ductile fractures, driven by plastic strain rather than elastic stress intensity. The paper reviews recent research into the progressive plastic deformation of surfaces in repeated sliding: the process known as ‘ratchetting’. Included is an analysis of ‘running-in’ of rough surfaces by repeated sliding and a discussion of the criterion of rupture under cyclic plastic strain.     

A predictive modeling scheme for wear in tribometers

Study of wear in complex micro-mechanical components is often accomplished experimentally using a pin-on-disc and twin-disc tribometer. The present paper proposes an approach that involves a computationally efficient incremental implementation of Archard's wear model on the global scale for modeling sliding and slipping wear in such experiments. It will be shown that this fast simplistic numerical tool can be used to identify the wear coefficient from pin-on-disc experimental data and also predict the wear depths within a limited range of parameter variation. Furthermore, it will also be used to study the effect of introducing friction coefficient into the wear model and also to model water lubricated experiments. A similar tool is presented to model wear due to a defined slip in a twin-disc tribometer. The resulting wear depths from this tool is verified using experimental data and two different finite element based numerical tools namely, the Wear-Processor, which is a FE post-processor, and a user-defined subroutine UMESHMOTION in the commercial FE package ABAQUS. It will be shown that the latter two tools have the potential for use in predicting wear and the effective life span of any general tribosystem using the identified wear coefficient from relevant tribometry data.     

Correlated wear measurements using gold implantation, backscattering, nuclear activation analysis and profilometry

High and ultra-mild wear of Al-Si alloys under lubrication is measured (a) by comparison of initial and retained gold concentration in surfaces, (b) by tracking gold in the effluent lubricant or (c) alloy specific elements, and (d) by stylus profilometry. Wear >1 μm is best captured by method (d). However, (d) fails when both tribologically induced films have formed and wear is below 100 nm. Method (c) is efficient in a broad range of wear if element concentrations can be determined precisely. Methods (a) and (b) satisfy this requirement but they are only efficient for ultra-mild wear.     

Enhancement effect of nanoparticles on the sliding wear of short fiber-reinforced polymer composites: A critical discussion of wear mechanisms

Short fiber-reinforced polymers (SFRPs) form an important class of tribo-materials owing to their high specific strength, good load-carrying capacity and rapid, low-cost processibility. Nevertheless, further developments are still under way to tailor their properties for more extreme loading conditions and to explore new fields of application for these materials. Recently, nano-sized inorganic particles have come under consideration. It was found that the addition of a small percentage of rigid nanoparticles to SFRPs may significantly improve their wear resistance, especially under high pv (the product of p (pressure) and v (velocity)) conditions. However, the detailed mechanisms of such improvement have not been fully understood yet.The objective of this study is to achieve an in-depth understanding of the role of the nanoparticles in modifying the sliding wear behavior of SFRPs. In particular, the effects of nanoparticles on contact mechanics and wear behavior of the transfer film were investigated. It was found that the additional nanoparticles do not directly contribute to the formation of a high performance transfer film. However, the presence of nanoparticles in the contact region can effectively reduce the adhesion between the transfer film and the polymeric specimen, resulting in a lower coefficient of friction. In particular, the rolling behavior of nanoparticles can significantly enhance the tribological performance of SFRPs especially under extreme sliding conditions.     

Three-body impact wear study on conventional and new P/M + HIPed wear resistant materials

A new hammer-mill type impact wear testing facility was built for impact wear testing and characterization. Tests with the hammer-mill impact wear device were carried out on conventional wear resistant materials such as Mn-steels of different compositions, white cast iron, and on new P/M+HIPed wear resistant materials. To verify the validity in using this laboratory wear testing apparatus, wear behavior and worn surfaces obtained on conventional and new Mn-steels generated from this device were compared with wear phenomena and worn surfaces developed in industrial applications, i.e. from certain types of rock crushers. The strain hardening effect in different Mn-steel grades was studied first. Second, the wear resistance of materials with different properties was studied using two different grades of abrasive. With silica sand (high hardness, low compressive strength), conventional Mn-steel and white cast iron perform in a manner comparable with the P/M+HIPed materials. With volcanite sand (low hardness, very high compressive strength), the P/M+HIPed wear resistant materials appear to have the best wear resistance.     

齿轮跑合的磨损机制研究

通过齿轮副跑合的模拟试验,得出齿轮副在跑合过程中磨损形式的转化规律。     

Effect of arc discharge on the wear rate and wear mode transition of a copper-impregnated metallized carbon contact strip sliding against a copper disk

Wear of the contact strip on the pantograph of electric railway vehicles is governed mainly by arc discharge occurring simultaneously with break of contact between the strip and trolley wire. As a step to clarify the wear mechanism of metallized carbon contact strips under the occurrence of contact break arc discharge, a detailed sliding wear test of 30 min duration was carried out for the combination of a copper-impregnated carbon strip and a copper disk at a sliding speed of 100 km/h. The worn surfaces of the strip and disk were observed every 5 min. The voltage drop and electric current were measured throughout the test, and the occurrence and energy of the arc discharge were evaluated for each revolution of the disk. The wear process is considered in terms of the wear mode transition, and the effect of arc discharge on the mode transition and wear rate of the strip is discussed.     

The influence of surface deformation on mechanical wear

The evidence for the plastic strain of wearing surfaces and its influence upon them is briefly described. Two distinct analytical approximations are available for calculating these effects: an elasto-plastic approximation, and a rigid-plastic approximation. These lead to two different damage rules and two different methods of idealizing asperity shape. Experiments and finite element analysis help to delineate the range of application of each of these models, and their associated damage rules, but it is clear that further theoretical developments are needed if wear is to be reliably predicted for most engineering contacts.     

Thermal wear and electrical sliding wear behaviors of the polyimide modified polymer-matrix pantograph contact strip

In the present study, the polyimide resin (PI)/cashew-modified resin (YM) polymer-matrix pantograph contact strip (PMPCS) was prepared by using hot repressing, hydro-solidification and dipping treatment processes. The thermal properties of cured resins were studied by thermogravimetry analyzer and differential scanning calorimetry. The thermal wear and electrical sliding wear behaviors of PMPCS against copper were evaluated by a ring block wear tester at elevated temperature under dry sliding conditions and a wear tester which simulated the train motion under laboratory conditions, respectively. Worn surfaces and wear debris of PMPCS were analyzed by scanning electron microscopy and energy dispersive spectrometer, and the wear mechanism was discussed. It has been found that the thermal stability of the PI/YM is superior to that of the YM under the same testing conditions. The results also showed that PI/YM-PMPCS had superior wear resistance than that of YM-PMPCS at elevated temperature and with electrical current. At elevated temperature, the wear mechanism of tribological pair evolved from adhesive wear to oxidative wear with mild delamination wear. Arc erosion wear, oxidative wear, and adhesive wear were the dominant mechanisms of tribological pair during the electrical wearing process.     

Dynamic modelling of wear evolution in rolling bearings

Condition monitoring tools aim to monitor the deterioration process i.e. wear evolution of defects. The wear evolution is quite complex process due to the involvement of several wear and stress concentration mechanisms. Therefore, the purpose of this paper is to provide a dynamic model of wear evolution that considers the topographical and tribological changes over the lifetime. The model suggests the use of multiple force diagrams to simulate the dynamic impact and utilises several models of contact mechanics to estimate the transition points between the wear evolution stages. The simulated results of the developed evolution model are in principal agreement with the experimental results.     

轨道结构参数对轮轨滚动接触应力影响

利用三维弹性体非Hertz滚动接触理论及数值程序CONTACT,并借助于弹性力学中的Bossinesq-Cerruti力1位移公式和Gauss数值积分方法,分析JM3型踏面轮对沿曲线轨道滚动接触时轨底坡、轨距和曲线半径等轨道参数对轮轨滚动接触斑最大切应力、等效应力、正压力和磨耗数的影响.数值结果表明,当内外轨底坡为1/20时,轮轨接触斑的应力、磨耗数及正压力分布达到最小值,其中最大切应力与等效应力可分别降低40.15%、39.37%;现行使用1/40轨底坡情况下轮轨接触斑正压力较大,建议对磨耗型车轮踏面进行优化设计.适当增加轨距能达到降低轮轨最大切应力、等效应力和正压力的效果.曲线工况下接触斑正压力值显著增加,曲线半径能改变轮轨接触斑粘滑区的分布且减小曲线半径值会增加接触斑的总滑动量,从而导致轮轨磨耗数的显著增加.     

Transition of elevated-temperature wear mechanisms and the oxidative delamination wear in hot-working die steels

Dry sliding wear tests of H13 and H21 steels were performed at 400 °C. The wear mechanisms and their transitions were studied, and an oxidative delamination wear was suggested. A mild oxidative wear prevailed with oxide fatigue delamination under less than 3.54 MPa. Under 3.54-5.31 MPa, the oxidative wear prevailed with oxide fatigue delamination and the oxidative delamination wear. As the pressure surpassed 5.31 MPa, a severe wear prevailed with the oxidative delamination wear and the plastic extrusion. The oxidative delamination wear meant that the delamination occurred inside the matrix underneath tribo-oxides with long-ditch delamination and belt-like wear debris.     

The characterization of wear transitions in sliding wear process contaminated with silica and iron powder

When a machine is in operation, two moving surfaces interact to generate a large amount of wear particles. The wear debris generated inside the machine or contaminants from outside plays important roles in both two-body and three-body wear. For all mining and port machinery, their lubricants are very likely to be polluted by contaminants such as silica and other metallic debris such as iron and nickel. In order to seek a deeper understanding of the effects of different contaminants on wear process, this project investigated sliding wear processes when silica powder and iron powder exist in lubricants.Four sliding wear tests were conducted on a pin-on-disc tester with and without the contaminants. Visual inspection, ferrography analysis, particle quantity analysis using a particle analyzer, and numerical surface analysis using confocal laser scanning microscopy (CLSM) were conducted to study the wear particles and wear surfaces. Supported by the data generated from the comprehensive analyses on the wear particles and wear surfaces, the investigation of the effects of the added contaminants to the wear processes and wear mechanisms have been carried out and presented in this paper.     

Third body effects on friction and wear during fretting of steel contacts

Fretting wear proceeds through particle detachment from the contacting surfaces which, while trapped in the contact zone, can affect the frictional and wear response. Ball-on-flat fretting experiments were carried out between steel specimens under gross slip regime. A transition in the coefficient of friction was linked to a critical contact pressure. The microstructure and chemical composition of the third body evolve with the applied pressure. The evolution of the friction coefficient is strongly dependent on the third body properties. The wear is controlled by the applied load and thus the real contact area within the wear track.     

Determination of temperature and wear during braking

A model of the braking process has been proposed. We have obtained the contact temperature, the value of wear and the sliding speed for general experimental dependencies of the coefficient of friction and that of wear on the temperature. The problem has been reduced to a system of nonlinear integral equations of the Volterra type by means of the Laplace integral transform with respect to time. In case when the coefficient of friction is constant and for a linear dependence of the wear coefficient on the temperature we succeeded in obtaining the solution of the system of the integral equations in a closed form. In this way we have obtained simple engineering formulae for the computation of the contact temperature and wear. The results of the computations are presented in diagrams.