Adaptive finite element simulation of wear evolution in radial sliding bearings

This article employs an adaptive wear modeling method to study the wear progress in radial sliding bearings contacting with a rotary shaft. Mixed Lagrangian–Eulerian formulation has been used to simulate the contact condition between the bearing and the shaft, and the local wear evolution is modeled using the Archard equation. In the developed wear processor algorithm, not only remeshing is performed on the contact elements, but also is executed for their proximity elements. In this way the wear simulation becomes independent of the size of the contact elements. Validation was done for a laminated polymeric composite bearing. The composite has been modeled as a linear orthotropic material. The wear coefficients were obtained from flat-on-flat experiments and were applied as pressure and velocity dependent parameters in the wear processor. Finally, the effect of the clearance on the wear of the radial bearings has been studied numerically. The simulations also demonstrate how the contact pressure evolves during the wear process, and how the clearance influences this evolution.     

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.     

Prediction of fretting wear using boundary element method

The simulation method of the fretting wear prediction using boundary element method is developed. The contact pressure and the contact width which is the first step to predict fretting wear are obtained from contact analysis of a semi-infinite solid based on the use of influence functions and patch solutions. The geometrical updating is based on nodal wear depths computed using Archard’s equation for sliding wear. The prediction of fretting wear for two cases of contact problems is performed; one is two-dimensional cylinder on flat contact which is for the comparison with a previous model by finite element method; the other is three-dimensional spherical contact. It is observed that for two-dimensional cylindrical contact the boundary element method developed in this study reduced the calculation time by 1/48 compared to FE method. We also showed the use of developed simulation technique is efficient to predict the fretting wear for three-dimensional spherical contact.     

A system for wear prediction in lubricated sliding contacts

A system of analysis is developed to predict the rate of wear in sliding contacts. The essence of the approach is the proposal that the rate of wear can be predicted only in probabilistic terms. Therefore, the estimation of the probability of wear, which can be regarded as synonymous with the probability of surface asperity contacts, precedes the calculation of the wear rate. Further, recognising the fact that wear takes place within the actual area of contact, it is argued that this area consists of plastic and elastic contacts between asperities which, in turn, have different shear strengths and contribute differently to the wear process. In the case of lubricated contact, a frictional film defect represents the influence of a lubricant on the wear process. Moreover, as in this type of contact the load is supported by both lubricating film and contacting asperities, a special procedure is provided to estimate the load supported by the asperities, because it is only that part of the load which contributes to the wear. The catastrophic form of wear in lubricated contacts, that is termed ‘scuffing’, is also considered, and the probability of scuffing, under a given set of operating conditions, is estimated. The predictive system has been tested and its predictions are compared with available experimental results.     

A practical method for finite element ring rolling simulation using the ALE flow formulation

Finite element ring rolling simulation by conventional Lagrangian codes carries an excessive computational cost. The main reason for this is the large number of incremental stages typically required to complete a full simulation. The nature of ring rolling however means that the amount of deformation taking place in a given increment is relatively small compared with typical metal forming processes. This paper describes measures that make the analysis of ring rolling a practicable proposition. The resulting model is based on a threefold approach, comprising the finite element flow formulation, an arbitrary Lagrangian Eulerian update strategy, and a novel iterative solution scheme called the successive preconditioned conjugate gradient method. The approach exploits the slowly evolving nature of the problem with the effect of reducing the time penalty for each deformation increment. In addition, a number of issues specific to ring rolling have been addressed including the problem of how the mandrel interface is dealt with for arbitrarily shaped rollers. The importance of addressing this particular issue is also illustrated. The method is validated by comparison with earlier experimental work and previously developed models for both pure radial, and radial–axial ring rolling.     

A direct formulation and numerical implementation of the boundary element method for two-dimensional problems of elasto-plasticity

A new direct formulation of the boundary element method based on the initial stress approach has been developed which is more generally applicable than existing formulations. A complete scheme of numerical calculations is presented and it has been demonstrated that the method can be used for routine analysis of engineering plasticity problems.     

Finite element simulation and experimental validation of fretting wear

A finite element-based method is presented for simulating both the fretting wear and the evolution of fretting variables with number of wear cycles in a cylinder-on-flat fretting configuration for application to aeroengine transmission components. The method is based on a modified version of Archard’s equation and is implemented within a commercial finite element code. Fretting tests are employed to determine the coefficient of friction (COF) and the wear coefficient applicable to the contact configuration and loading conditions. The wear simulation technique is incremental in nature and the total simulation time has been minimised via mesh and increment size optimisation. The predicted wear profiles have been compared with profilometer measurements of fretting test scars.     

A reciprocating wear test for evaluating boundary lubrication

A reciprocating wear tester was used to investigated the nature of antiwear boundary lubrication films formed by several ZDDP additives in mineral oil. Under the test conditions examined in this work, antiwear films are relatively thick (approximately 0.1 μm), and so can be readily detected by optical microscopy. Film formation occurs after only a few centimetres of sliding on smooth hard surfaces, whereupon wear essentialy ceases. On rough surfaces, film formation does not take place until the surfaces have run-in, whereupon wear again ceases. Antiwear films did not form on steel pins softer than Rc 25, which wore by an oxidative mechanism. The extent of run-in or rough surfaces before film formation can be used as a measure of the effectiveness of an antiwear additive. Antiwear films are resistant to wear, so once formed they can provide sustained wear protection in base oil. However, antiwear films can be removed by wear in the presence of hydroperoxides, or by running against a new rough countersurface.     

Low-stiffness spring element constraint boundary condition method for machining deformation simulation

Journal of Mechanical Science and Technology - The 3-2-1 constraint principle has been widely applied as the boundary conditions for the finite element method (FEM) to simulate machining...     

A relation between wear volume and sliding time for composite materials

Friction and wear experiments on two graphite fiber-aluminum matrix composites and two commercially pure metals (aluminum and copper) were conducted on a brake-type friction machine. The counterface material was graphitic cast iron. The composite samples were tested with the graphite fibers perpendicular to the counterface; the load varied from 5 to 100 N. The initial sliding velocity varied from 2.0 to 11.4 m s^?1. The wear resistance of the HM-Al 1100 graphite fiber-aluminum matrix composite was found to be more than one order of magnitude better than that of the unreinforced matrix material. With aluminum and copper, the wear volume per braking cycle is proportional to the product of load and sliding distance in accord with both the adhesion and delamination theories of wear. For the two composite materials studied, the wear volume per braking cycle is proportional to the product of load and sliding time which cannot be explained by either of the two wear models. Thus the wear mechanism of composites might be fundamentally different from that of pure metals.     

High-temperature sliding wear of metals

Temperature can have a considerable effect on the extent of wear damage to metallic components. During reciprocating sliding, under conditions where frictional heating has little impact on surface temperatures, there is generally a transition from severe wear to mild wear after a time of sliding that decreases with increase in ambient temperature. This is due to the generation and retention of oxide and partially-oxidized metal debris particles on the contacting load-bearing surfaces; these are compacted and agglomerated by the sliding action, giving protective layers on such surfaces. At low temperatures, from 20 to 200°C, the layers generally consist of loosely-compacted particles; at higher temperatures, there is an increase in the rates of generation and retention of particles while compaction, sintering and oxidation of the particles in the layers are facilitated, leading to development of hard, very protective oxide ‘glaze’ surfaces. This paper reviews some of the main findings of extensive research programmes into the development of such wear-protective layers, including a model that accounts closely for the observed effects of temperature on wear rates during like-on-like sliding.     

Residual stresses and sliding wear

The residual stresses that develop during the wear of AISI-SAE 1018 and 4340 steels have been examined. The entire three-dimensional stress tensor was obtained. A normal stress perpendicular to the surface, predicted by theory, has been found, but its magnitude is too small to affect the wear rate. There are also significant shear stresses. The wear process rapidly alters any initial stress distribution produced by heat treatment or peening to such a degree that the wear rate is not affected by these stresses, unless they are initially larger than those that can be produced by the wear parameters.     

Silicon segregation in sliding wear

Friction experiments were conducted on a couple consisting of an Fe-Ni pin sliding against a tool steel disk. The Fe-Ni pin contained a small amount of silicon (0.18%). In a mild vacuum environment (0.1 mmHg at 10% relative humidity) at loads below a critical value (13.0 N, at a sliding speed of 0.22 m s^?1), silicon segregation to the pin surface took place, resulting in the formation of a glassy film. Under these experimental conditions the friction coefficient and wear values were very low (0.28 and 5 × 10^?3mm³km^?1 respectively). At loads higher than the critical value (in the same mild vacuum environment) as well as under atmospheric conditions, no silicon segregation could be detected. The corresponding values of the friction coefficient and the wear rate were much higher (0.54 and about 0.4 mm³ km^?1 respectively). It is suggested that the beneficial glassy layer can build up only when the rate of diffusion of silicon to the surface is higher than the rate of material removal (wear).     

Multilayer composite ceramicmetal-DLC coatings for sliding wear applications

The design of anti-friction coatings able to perform well in different wear conditions without lubricants requires a combination of adequate hardness and toughness, good adhesion, a low friction coefficient and a low wear rate. Recently introduced metaldiamond like carbon (DLC) coatings produced by magnetron sputtering of metals from targets, which are to a controlled extent covered with carbon from the chamber atmosphere, can be a step towards the achievement of such a combination. These coatings consist of an amorphous a:CH matrix with the possible incorporation of metal (Ta, W, Nb, Ti), metal carbide and/or graphite grains. Previous studies of Ti_x%-DLC coatings showed their good protective properties against abrasive, impact and single scratch wear, as well as a requirement for supporting interlayers to successfully apply such coatings to low-cost steels. In the present work an example of the selection of metal-ceramic Ti-TiN-TiCN supporting interlayers is given based on studies of their morphology, structure and mechanical properties. This resulted in the development of Ti-TiN-TiCN-[TiC-(Ti_x%-DLC)] multilayer composite coatings. Several coatings were prepared with the same supporting interlayer and a variation in the preparation of the Ti_x%-DLC layer. Ball-on-disc experiments were carried out to investigate these coatings in conditions of sliding wear against steel and cemented tungsten carbide balls. CrN, TiN and TiCN coatings were also deposited and tested in the same conditions to provide a reference. Low friction coefficients (below 0.2 at an air humidity of 50% RH) in combination with low normalized wear rates were found for multilayer coatings with upper Ti_20%-DLC and Ti_35%-DLC layers.     

A three-dimensional finite element method for plate bending

A three-dimensional finite element method is proposed for plate bending. The displacement function is assumed to have a particular form with respect to the thickness variable.The assumed displacement function is substituted into the three-dimensional potential energy functional and a two-dimensional variational problem emerges.The two-dimensional problem is treated by the finite element method and it is seen that for conforming solutions the only requirement is continuity of the basis functions.The method includes transverse shear and thickness effects and may be used for both thin and moderately thick shells.To illustrate the method and to compare it with other results, the problems of a square plate under point and distributed loads and with simply supported and clamped boundary are treated numerically.     

Friction and wear behavior of three-dimensional braided carbon fiber/epoxy composites under dry sliding conditions

Sliding friction and wear characteristics of three-dimensional (3-D) braided carbon fabric reinforced epoxy resin (C_3D/EP) composites were investigated. Tests were performed on a MM200 tester under normal loads of 50, 150, and 250 N and velocities of 0.42 and 0.84 m/s. A quenched medium carbon steel with a hardness of HRC 52 was used as the counterpart material. The specific wear rate and the coefficient of friction were examined as a function of testing conditions (load, velocity, and sliding distance) and material parameters (fiber volume fraction and fiber–matrix bonding). The results showed that the coefficient of friction and the specific wear rate changed considerably during the running-in period and reached stable values at the steady wear stage. Fiber volume fraction and testing conditions (load and velocity) affected the wear more significantly than the friction. It was also found that fiber–matrix bonding had an impact on the friction and wear of the 3-D composites. Furthermore, the specific wear rate decreased with the increase in the product of load and velocity. Worn surfaces and debris were observed by scanning electron microscope (SEM) and wear mechanisms were discussed in this study.     

Frictional contact analysis under tangential loading using a local axes boundary element formulation

This paper presents a quadratic boundary element (BE) formulation for contact problems under normal and tangential loading using a local axes system to couple the contact variables. A brief review of the BE formulation is presented with emphasis on the coupling of contact variables to satisfy equilibrium and compatibility conditions. Four contact examples are shown to demonstrate the accuracy of the alternative BE formulation.     

A formulation for rigid-plastic finite element method considering work-hardening effect

An incremental formulation incorporating the effect of shape change is derived for the non-steady large deformation problem of rate-independent rigid-plastic solids. The deformation during a step is studied using the convective coordinate system. Introducing basic assumptions for the deformation path and considering the equilibrium at the deformed state a variational formulation is derived to determine the deformation during a step. The corresponding finite element equations are found in order to analyze the sheet metal deformation for which the effect of shape change is significant. Based on the derived equations, the FEM program is developed to analyze the hydrostatic bulging process for circular and rectangular diaphragms. The computational results are then compared with the existing solution as well as the available experimental results.     

Some aspects of the friction and wear of electrical sliding contacts under conditions of boundary lubrication

The friction characteristics of lubricated electrical sliding contacts are considered. Data are presented concerning the effects of the current, the lubricant properties, the velocity and the load on the friction and wear behaviour of the contacts. In light-current electrical contacts the effectiveness of the lubricant does not depend on its conductivity but on its ability to prevent the formation of a non-conductive film by lubricating action. Under semifluid lubricating conditions the heavy current acts by discharge through the lubricant film, and the lubricant conductivity generally determines the friction and wear characteristics of the contact. Colloidal metal particles produce additional conductivity in the clearance between the contacting surfaces, prevent electrical erosion and, in some cases, form plastic films which decrease the coefficient of friction and the wear rate of the contact.     

Dry sliding wear of diamond materials

In pin-on-disc tests, diamond composites, consisting of diamonds imbedded in a silicon matrix, were run against themselves in air at a sliding speed of 125 cm s^?1 and for loads up to 3.6 kgf. In addition, a few experiments involving sintered diamond compacts rubbing against a rotating metal ring in a ring-and-block configuration were conducted. For the diamond composite wear tests, wear was found to be proportional to load and sliding distance for P ? 3.0 kgf. For both the diamond composite and the diamond compact, the wear rates were very low and similar to those previously observed for single-crystal diamonds rubbed by diamond and metal.