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Wear in rolling contact is a complex phenomenon because it is multi-scale and multi-physical by nature and involves many strongly correlated parameters. It makes the numerical calculation of wear very challenging. In order to simulate wear, a better understanding of the influencing parameters involved in the wear calculation is of importance. This work presents a new numerical calculation of railway wheel wear based on Archard's equation combined with a spatial statistic approach called the Universal Kriging technique. The influence of factors, such as the contact mechanics model and the wear coefficient were studied through numerical experiments. The outcomes provide a new insight into the roles of the contact modelling and of the uncertainties of the wear coefficient in the numerical calculation of wear under various contact conditions. By considering the uncertainties of the wear coefficient, the approach provides a min.-max. range for wear estimation instead of a single deterministic value; furthermore, it can provide a detailed wear distribution over the contact patch for damage analysis. In combination with an accurate model of wheel-rail contact, this new wear model offers a more realistic wear prediction compared to the methods presently used for wheel wear estimation in railway vehicles.

The aim of the research is to determine the metallographical and mechanical properties (residual stresses, hardness, phases and texture) of carburized surfaces using finite element method and study the failure of surface during relative motion, and the possibilities of the test methods, which can give us information about the behaviour of these surfaces. This work focuses on contact fatigue tests and properties. Nowadays it can be established that application of finite element method is a reliable way to simulate carburization. It is possible to determine exact approximation for the hardness and carbon content values near the surface after carburization and quenching, but take into account that the simulation of tempering is still an issue, if the material contains retained austenit, the hardness values of the test will be higher near the surface, because of the retained austenit-bainit transformation, so the simulations had to be validated by carburized cylindrical (disc-like) specimens, made of low alloy case hardening steel (16MnCr5). These specimens were tested with glow discharge optical emission spectroscopy, to measure the chemical composition of the surface layer. It is important to know what kind of residual stresses can be observed in the surface after carburization, therefore it was extensively studied during the simulation. Furthermore the values of the hardness in the surface of the specimens have been determined. Having compared the simulation and experiments, good agreement has been found between the results, so the finite element method was validated successfully. For high cycle rolling fatigue test rollers were manufactured. Two disc fatigue tests were carried out on five rollers. Four tests were stopped due to trigger sign by surface damage, while one of those was stopped due to break of the shaft after one millions of rotation. Microstructural investigations have been started on the rollers.

Space Industry commonly uses molybdenum disulphide (MoS2) as a solid lubricant film on gears in a variety of mechanisms. These mechanisms are often exposed to humid air during fabrication, integration into higher-level assemblies, and storage. It is generally accepted that operating MoS2 films in humid environments has a detrimental effect on the film's lifetime compared to operation in vacuum. However, the effect of exposure of such films to humid air with subsequent operation in vacuum is not well understood. In this study, a sputtered MoS2 dry film lubricant coating was applied to steel gears, which were then tested in a vacuum environment. Half of the spur gears coated with MoS2 were exposed to approximately 58 percent relative humidity for up to 77 days before testing. The other half set of gears were not exposed to humid air before testing. All gears were tested in a vacuum gear test rig. Gear tooth forces and the radial displacement of the gears were recorded during testing. These data together with photos, videos, Scanning Electron Microscope (SEM) inspections of worn gears, and Energy-Dispersive X-ray (EDX) spectra were analysed. For purposes of this study, the coating durability was defined as the time until the start of the coating degradation as was evident from increase of friction. Assessment of the results obtained from all experiments indicate that gears exposed to humid air prior to operation in vacuum showed nearly 36 percent reduction in coating durability, on average. SEM and EDX analyses of wear debris indicate mainly MoS2 was present with minor traces of other elements. The worn surfaces of gears show significant content of MoS2 still remaining in the gear teeth's contact area.

The following study presents an in situ sensor system which can measure the temperature change of rolling contacts for heavy duty during fluid as well as mixed friction. This thin-film sensor was optimized with regard to its size, spatial resolution, and wear resistance. Extensive tests were carried out with a two-disk test rig and the data of the temperature change were presented. The results show the complex processes within a rolling contact and the strongly interaction of pressure, friction, and temperature development within the contact zone. Due to the detailed sensor and disk characterization, the data are suitable for comparing calculation methods.

In recent years, graphene-based lubrication was in the focus of nano- and microtribological studies. While the sliding properties of graphene based dry lubrication were previously investigated on the nano- and micro-scale, few studies can be found in the literature for the application of graphene as an additive to oil and grease in rolling contacts. In order to apply graphene platelets as dry lubricants and as grease additives in machine elements, tests were carried out on a rolling bearing test rig under typical load conditions. For these investigations, multilayer graphene platelets of varied staple thickness were functionalized on angular contact ball bearing surfaces as a dry lubricant, which forms a thin film. In addition, bearings were lubricated with grease containing graphene platelets. In this case, a small ratio of graphene was dispersed with grease. The graphene platelets were divided into three groups of different thickness: 2 nm, 6&ndash, 8 nm, and 11&ndash, 15 nm. Additionally, the tests were compared to graphite nanoparticles (spheres with a size of 3&ndash, 4 nm) as dry lubricant and graphite-containing grease. The experimental studies were carried out under oscillating motion. The respective load in the tribological contact was 1.5 GPa. During the tests, the pivoting angle was measured by utilizing a rotary encoder. In addition, the friction torque was recorded under a frequency of 0.2 Hz. As the balls&rsquo, velocity at the reversal point is zero, the lubrication conditions are critical. The dry lubricated bearings were compared to grease lubricated bearings. Additionally, the frictional properties of the respective greases were investigated by applying a sliding tribometer. In this case, a ball rotates against three contact planes, which causes a tribological contact under a contact pressure of 1 GPa. It was shown that applying graphene as a dry lubricant and as a grease additive under rolling contact conditions reduces friction significantly.

5th CIRP Conference on Surface Integrity, Virtuell, CSI 2020, online, 1 Jun 2020 - 5 Jun 2020; Procedia CIRP 87, 474-479 (2020). doi:10.1016/j.procir.2020.02.111 special issue: "Part of special issue: 5th CIRP Conference on Surface Integrity (CSI 2020) / Edited by Pedro J. Arrazola, Aitor Madariaga", Published by Elsevier, Amsterdam [u.a.]

We focus this study on the dynamics of a Rubber-Layer Roller Bearing (RLRB) for vibrational base isolation. By exploiting viscoelastic friction arising from rigid cylinders rolling on concave rigid plates padded with rubber layers, the device is able to provide a nonlinear damping behavior. Specifically, we consider the case of a two degrees of freedom system, in which an inertial mass is base-isolated from ground motion by mean of RLRB. We firstly investigate the system dynamic response under sinusoidal ground motion, then we focus on a real earthquake excitation. In both cases, the system equipped with nonlinear RLRB device presents smaller inertial load and displacement compared to the case of a system exploiting linear damping. Further, we show that an optimization can be performed on the physical parameters of the device (i.e. the viscoelastic material relaxation time and the cylinders spacing) in order to further enhance the system dynamic behavior.

A load-sharing-based mixed lubrication model, applicable to cam–roller contacts, is developed. Roller slippage is taken into account by means of a roller friction model. Roughness effects in the dry asperity contact component of the mixed lubrication model are taken into account by measuring the real surface topography. The proportion of normal and tangential load due to asperity interaction is obtained from a dry contact stick–slip solver. Lubrication conditions in a cam–roller follower unit, as part of the fuel injection equipment in a heavy-duty diesel engine, are analyzed. Main findings are that stick–slip transitions (or variable asperity contact friction coefficient) are of crucial importance in regions of the cam where the acting contact forces are very high. The contact forces are directly related to the sliding velocity/roller slippage at the cam–roller contact and thus also to the static friction mechanism of asperity interactions. Assuming a constant asperity contact friction coefficient (or assuming that gross sliding has already occurred) in highly loaded regions may lead to large overestimation in the minimal required cam–roller contact friction coefficient in order to keep the roller rolling. The importance of including stick–slip transitions into the mixed lubrication model for the cam–roller contact is amplified with decreasing cam rotational velocity.

Bearing steel under severe loading condition undergoes substantial subsurface microstructural alterations known as Dark etching regions and white etching bands. White etching bands (WEBs) develop after hundreds of millions of stress cycles in bearing components and have been reported for several decades but the formation mechanism of white bands is not fully elucidated. Current research presents a systematic rolling contact fatigue (RCF) testing in a rotary tribometer under accelerated conditions, where rolling cycles are simulated in a 4-ball test configuration. The post RCF investigations have been carried out to understand the formation mechanism of WEBs in a ball-on-ball point contact load. WEBs have been characterised with the help of nanoindentation and Energy-dispersive X-ray spectroscopy analysis. The quantitative analysis of WEBs growth with subsurface stress field has revealed that the unique orientations of white bands are governed by the plane of maximum relative normal stress along the contact track. Moreover, the accelerated growth and reversal of WEBs sequence at elevated temperature have revealed that the WEBs formation is dependent on temperature/load combination. The observed growth of lenticular carbides in current research is also compared with dislocation gliding model and the role of carbon diffusion within WEBs is highlighted.

A significant fraction of operational cost in oil sands mining is directly or indirectly related to undercarriage component wear. One of the strategies to minimize the cost is to repair/rebuild the worn components. Recent advancement of welding technology offers an economical way to achieve this goal. Depending on the involved wear mechanisms, the selection of appropriate overlay material can considerably extend the service life of worn undercarriage components. Due to their excellent wear resistance, tungsten carbide based overlays is a unique choice for this purpose. In this study, three WC-based overlays with different carbide types were selected for evaluation. Wear resistance was assessed via low-stress abrasion (ASTM G65 ) and rolling contact abrasion (RCA). RCA tests were conducted with two slip ratios, where 0.3% slip ratio simulates pure rolling/high-stress contact fatigue, and a 3.0% slip combines fatigue and abrasion as observed in undercarriage components. Based on the wear test results, it was found that, despite their good low-stress abrasion resistance, WC-based overlays display high rolling contact abrasion damage and is not suitable for the restoration of undercarriage components. SEM observation on wear scars correlates the wear performance with carbide type and corresponding mechanisms.

In metalworking, rolling is a metal-forming process in which slab is passed through one or more pairs of the rolling dies to reduce the thickness and to make the thickness uniform. Modeling of rolling die contact with the slab primarily needs to describe the Tribology of contact phenomena. The central concern of numerical modeling is used in this work to indicate a set of equations, derived from the contact principle, that transfer the physical event into the mathematical equations. Continuum rolling contact phenomena is considered to explain how a contact region is formed between rolling die and slab and how the tangential force is distributed over the contact area with coefficient of friction. At the end, elasticity stress behavior of rolling die contact with the slab for a number of cyclic loads is modeled. The model includes new proposed constitutive equations for discontinuity of the velocity&ndash, pressure distribution in rolling contact from the entry side to exit side of the neutral point. To verify the model, finite element simulation and experimental data from the literature are considered. The results show good agreement with finite element simulation and experimental data.

The aim of this paper is to develop a full Finite Element (FE) computational method for the dynamics of unstable frictional rolling contact systems in order to calculate reference solutions in many applications, especially curve squeal for railway transportation but also roller bearing or metal cutting. The proposed method is characterized by the use of a fine FE discretization of the contact surface in a Eulerian frame, nonlinear frictional contact laws and model reduction techniques. An application to the frictional rolling contact between two annular cylinders is presented in both quasi-static and dynamic cases with mode coupling instabilities. The validation of the approach in quasi-static conditions is carried out by comparison with CONTACT software. Stability and transient results show that the technique is able to simulate friction-induced vibrations at high frequencies. Reduced models are tested and show a good agreement with the full model.

Although both wear and fatigue are inevitably associated with the wheel/rail contact, they are normally studied as different phenomena and both are commonly considered excluding. Wear of railway wheels and rails is usually studied by relating wear rate to the T γ or T γ / A parameters or by plotting the so called “wear maps”, where different rolling parameters are related to the wear rate. On the other hand, fatigue in wheel/rail contact is mainly studied from the surface and subsurface stress or deformation fields and from the crack growth rate. However, one of the main causes of wear in rolling contact is the loss of material due to delamination processes that have their origin in the presence of surface fatigue cracks. So, if wear and fatigue are related, it should be possible to study both of them using the same method. In this paper, the fatigue index, based on the shakedown theory and used to predict the surface initiated fatigue of railway wheels, is proposed as a means to study the wear rate in rolling contact. The fatigue index is directly related to the apparition and growth of fatigue cracks at the surface and, thus, directly related to the peeling and spalling processes that constitute the severe and catastrophic wear mechanisms. The data collected from a series of twin-disc tests show that the wear rate correlates with the fatigue index following an exponential evolution independently of the normal load. Furthermore, a fatigue index around 0 marks the onset of severe wear.

Commonly used four-ball testing configuration when used to investigate rolling contact behavior of polyetheretherketone (PEEK) produced some unexpected peculiarities, namely direct contact between ceramic balls. Direct contact between lower three balls is normally not expected to take place when elastic materials (ferrous or ceramics) are tested. However, due to the viscoelastic nature of PEEK surface damage of the ceramic balls were observed leading to the production of wear debris which in turn facilitated premature failure of PEEK components of the assembly. It is postulated that caution is required when using the four-ball testing configuration to assess rolling contact performance of viscoelastic materials, such as engineering polymers. The research reported in this paper was supported by funding from Gdansk University of Technology, Gdansk, Poland(Grant DS-2012).

[EN] The existence of a wheel rail friction coefficient that depends on the slip velocity has been associated in the literature with important railway problems like the curving squeal and certain corrugation problems in rails. Rolling contact models that take into account this effect were carried out through the so-called Exact Theories adopting an exact elastic model of the solids in contact, and Simplified Theories which assume simplified elastic models such as Winkler. The former ones, based on Kalker s Variational Theory, give rise to numerical problems; the latter ones need to adopt hypotheses that significantly deviate from actual conditions, leading to unrealistic solutions of the contact problem. In this paper, a methodology based on Kalker s Variational Theory is presented, in which a local slip velocity-dependent friction law is considered. A formulation to get steady-state conditions of rolling contact by means of regularisation of the Coulomb s law is proposed. The model allows establishing relationships in order to estimate the global properties (creepage velocities vs. total longitudinal forces) through local properties (local slip velocity vs. coefficient of friction) or vice versa. The proposed model shows a good agreement with experimental tests while solving the numerical problems previously mentioned., The authors acknowledge the financial contribution of the Spanish Ministry of Economy and Competitiveness through the Project TRA2013-45596-C2-1-R.

This paper proposes a novel experimental test apparatus that permits direct measurements of tyre/asperity normal contact forces under rolling conditions without interfacial layer. A reduced-sized pneumatic tyre is set rolling on the exterior surface of a cylindrical test rig simulating a smooth road surface except a single asperity of simple geometric shape connected to an embedded force transducer. Distinct asperity geometries lead to similar shapes of force signal but different magnitudes whose relationships with the indentation have exponents close to those in classical analytical solutions. By analyzing the time signals of the contact force and their frequency contents for different rolling speeds, the quasi-static nature of the contact, commonly assumed in numerical models, is verified.

In this study, the tractive rolling contact problem between a rigid cylinder and a graded coating is investigated. The main objective of this study is to investigate the effect of the stiffness ratio, the coefficient of friction and the coating thickness on the surface contact tractions, the surface in-plane stress, the stick zone length and the creep ratio parameter that may have a bearing on the fatigue life of the component. Assuming that the shear modulus varies exponentially through the thickness of the coating, the governing integral equations associated with the rolling contact problem are constructed. Furthermore, it is supposed that the contact patch is controlled by a central stick zone accompanied by two slip zones. The conventional Goodman approximation is employed in order to decouple the governing singular integral equations. Finally, the numerical solution of the integral equations is obtained by applying the Gauss-Chebyshev integration method. (c) 2011 Elsevier Ltd. All rights reserved.

In this paper, starting from results of Part I (Afferrante et al. [1] ), we develop a procedure to evaluate the frequency dependent receptances of the energy dissipation at the contact interface, which is the quantity of interest in corrugation studies as the most known wear laws assume the local wear proportional to the frictional dissipation. These results are applied to the calculation of the growth rate of corrugation in railway tracks with an initial sinusoidal undulation. In particular, the wheel inertia and the transient contact mechanics effects are considered using a continuum description of the rail (hence neglecting pinned–pinned resonance due to the beam bending between two successive supports) by the simplest model (the Euler beam) which we can use to describe the normal receptance of the rail. The presence of a finite partial slip zone in the contact area can significantly modify the results, partially explaining the scatter of the experimental data collected in the literature. In particular, we found that partial slip affects the predicted apparent wavelength of highest growth of corrugation, and with respect to the full stick conditions, higher tractive ratio increases significantly the growth factors and non-linearity, showing an unexpected absolute maximum of growth at intermediate velocities, and the “resonance-free” regime becomes increasingly not a constant “frequency”, spanning a range of frequency between 700 and 1500 Hz even for a given system and set of loads. Only a full investigation involving all other resonances in the system may clarify further the correspondence with experimental values, since the corrugation “enigma” may be due to a combination of effects.

Diamond-like carbon (DLC) is being advanced as an excellent surface modification technology for a growing number of applications because of its low friction coefficient and excellent wear resistance. Due to the excellent characteristics of certain mechanical elements, such as a bearing, high levels of functionality are expected. Unfortunately, it is difficult to take full advantage of such high functionality because of insufficient endurance under high-pressure operating conditions. In order to make use of DLC as a bearing surface coating, the mechanism of DLC delamination under high-pressure conditions needs to be clarified. This paper discusses the mechanism of delamination of the intermediate layer of a DLC coating on a bearing in a test rig and by numerical simulation using FEM analysis. Test results revealed that the smaller the Young's modulus value of the intermediate layer (a factor affecting durability) of the DLC coating, the greater the resistance to delamination.

Thin wall ductile iron castings are being used in the industry as a way to improve the strength to weight ratio of machine parts. The high cooling rate, suffered by thin wall parts during the solidification process, promotes several microstructural changes, such as, carbide precipitation and a noticeable nodule count increment. The present work, studies the effect that the increase in nodule count has on the rolling contact fatigue resistance of ductile iron with different matrix microstructures. Ductile cast iron test samples, with nodule counts ranging between 150 and 1400 nod/mm2 were obtained. The samples were then heat treated in order to obtain three sets of different ADI grades and also a quenched and tempered set. The rolling contact fatigue properties were evaluated by using a flat washer type test rig. Different relations of the contact area versus the nodule size were obtained by using three different counterparts. The results show that an increase in the nodule count promotes a noticeable increase in the rolling contact fatigue life, being more important for the quenched and tempered samples. The relation between contact area surface and nodule size was the main variable influencing the rolling contact fatigue life. Fil: Dommarco, Ricardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; Argentina Fil: Jaureguiberry, A. J.. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; Argentina Fil: Sikora, Jorge Antonio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; Argentina

In this paper, the fully coupled rolling contact problem of a graded coating/substrate system under the action of a rigid cylinder is investigated. Using the singular integral equation approach, the governing equations of the rolling contact problem are constructed for all possible stick/slip regimes. Applying the Gauss-Chebyshev numerical integration method, the governing equations are converted to systems of algebraic equations. A new numerical algorithm is proposed to solve these systems of equations. Both the coupled and the uncoupled solutions to the problem are found through an implemented iterative procedure. In Part I of this paper, the analytical formulation of the rolling contact problem and the discretization of the governing equations are introduced for all assumed stick/slip regimes. A detailed discussion of the proposed numerical algorithm, the iteration procedure and the numerical results, obtained using the analytical formulation, are given in Part II. (C) 2013 Elsevier Ltd. All rights reserved., Y. Alinia would like to thank the Scientific and Technological Research Council of Turkey (TUBITAK) for the financial support during his visit to TOBB University of Economics and Technology as a research fellow for a year. M.A. Guler greatly acknowledges the support by Fulbright Visiting Scholar Program.

In this paper, a three-dimensional finite element model of rigid hemisphere repeatedly rolling over a rough flat surface under constant normal load is discussed. The aim of this research is to study the von Mises residual stress and plastic strain distribution and to determine the steady-state phase of the repeated rolling contacts. The results show that the change of residual stress distribution takes place in the first-two rolling cycles and there is no significant change for the residual stress from the second to third rolling cycle, i.e. the surface is run-in after a few cycles. The increase of the contact load affects the area of the von Mises residual stress at the surface and subsurface and also the number of the deforming asperities. The residual stress distribution is getting wider as the normal force increases. The plastic strain is captured after the third cycle of rolling. Small area of plastic strain is found for the rough surface for the low forces applied which indicates the surface deformed mainly elastically. The rough surface is predicted to be plastically deformed for the highest force applied.

The main aim of this work was a study of the microstructure transformations with the residual stress formation that is induced by rolling contact friction and adhesive wore in the wheel–rail system. Several small railsurface samples, we term them as the ‘chips’, and a piece of wheel sample were chosen for the analyses of the surface changes on the wheel–rail surface. A multitude of different experiments were carried out in order to analyse the microstructure changes at the surface and the near-surface region of the material samples and, thus, to contribute to the understanding of the complex wheel–rail rolling contact phenomena – and its degradation mechanisms. The formation of nano-structured martensite and carbides on the rail and wheel surface causes the extremely high microhardness valuees and the strong corrosion resistance of the so called White Etching Layers (WEL). First Published Online: 26 Jun 2012

A deep comprehension of the damage mechanisms involved in contact fatigue is basic to optimize materials and heat treatments for specific applications. In this work, rolling disc-on-disc contact fatigue tests have been performed on three different materials: a hardened and tempered UNI EN 42CrMo4, a nitrided UNI EN 42CrMo4 steel, and a carburized UNI EN 18NiCrMo5 steel. The test method adopted was optimized to better realize such conditions able to develop micropitting on different materials. The main aim of this test campaign was to investigate and compare damage on surface, in terms of initiating and propagating mechanisms. Extensive microfractographic analyses were performed on the damaged samples by the use of a scanning electronic microscope (SEM). For hardened and tempered steel, failure mode was micropitting, started from surface, but evolved into pitting because of crack path extending more deeply beneath the surface. Pits always originated on top surface and propagated as like a common fatigue cr...

International audience; Hadfield steel is well known for its high work hardening capacity and wear resistance. The alloy X120Mn12 is specifically used in railroad castings such as frogs and crossings in west European countries such as France. The influence of various contact parameters on the mechanical behaviour of this alloy was investigated by rolling contact tests. The results are described and discussed using micro-hardness measurements, optical and scanning electronic microscopy and EBSD analyses.

The present study investigates the behaviour of polymeric rollers employed in a cam mechanism of an industrial machine, consisting of two concentrically fitted rings made of polyurethane and short fibre-reinforced PEEK. A cyclic mechanical characterisation of the materials was at first carried out by strain controlled fatigue tests. The safe range of working conditions of the rollers in terms of rotating speed and contact load was then investigated by rolling contact tests carried out on roller prototypes with a dedicated test rig. These tests allowed obtaining important information about the different damage mechanisms occurring in the component: above a critical working temperature, rollers failure resulted from rings unfitting due to excessive deformations, while fatigue crack nucleation in the outer ring at the interface with the inner one was observed below this threshold, at high contact load levels. No contact fatigue damage appeared. FEM models of the roller were also developed, based on cyclic material data, in order to analyse the cyclic stress and strain field and to predict the fatigue life, finding a satisfactory agreement with the experimental rolling contact tests results.

International audience; We present a classical rolling contact apparatus where two discs roll and slide under a constant normal loading. Experimental results concerning bearing steel used in ambient air or under severe temperature conditions (liquid nitrogen) are presented. A simplified model proposed by Kalker (Fastsim) is used to identify the dynamic friction coefficient between these discs and to study the apparatus parameters' influence on dissipated energy. Wear evolution is simulated using classical Archard's law and compared to measured profiles. Influence of ambient conditions is highlighted by comparing friction and wear coefficients.

International audience; Wear phenomena involve a large number of physical and mechanical parameters which are not always well known or controlled during relative movement between two bodies. Numerous industrial applications necessitate an evaluation of technological component life time and wear modelling often fails to give accurate estimation. We use the classical Archard's wear model where wear is related to dissipated power. It appears that great dispersion can occur in the estimation of dissipated power related to a lack of knowledge of certain parameters. We present here a probabilistic approach of the contact problem resolution. We consider the specific contact problem in the case of steady state rolling. A wear apparatus has been used to test different materials and we use the simplified model Fastsim to evaluate slip and tangential traction in the contact zone. For each parameter of the simulation, we construct a probabilistic density function with the only information available. A Monte-Carlo method is implemented and the resolution of numerous cases allows the dissipated energy to be evaluated as a mean value and a confidence region for 95% viability.

Design of engineering components is concerned with their strength and durability characteristics. While design for strength is influenced by the bulk material characteristics, the design for durability is dependant on the surface characteristics. Majority of the component failures are surface originated. Surface engineering could play a vital role in minimizing such failures. Thermal sprayed coatings, one of the versatile surface coating techniques, can be applied to components of machinery surfaces to avoid such failures. The present paper presents a methodology for contact stress evaluation of surface coated elements, adopting a layered structure approach, and thereby analytically predict their spalling life. Further data on cycles to single pit formation, and spalling of spray fused coatings obtained from experimental testing are presented for assessing the applicability of life prediction models to layered structures such as sprayed coatings. Experimental investigations were conducted on spray fused coatings using a twin disk RCF test setup. The surface and subsurface contact stress distribution have been obtained analytically by Smith–Liu equations along with first order model perturbation method (FOMP), to account for the variation of elastic modulus constants of the layered structure. Applying Lundberg-Palmgren and Tallian life prediction models, the spalling life of these coatings has been predicted analytically and compared with experimental life values. [S0742-4787(00)02502-9]