Fretting-induced friction and wear in large flat-on-flat contact with quenched and tempered steel

Fretting may cause severe surface damage and lead to unexpected fatigue failure. Our test apparatus was designed based on reciprocating, large, annular flat-on-flat contact without any edge effects in the direction of the fretting movement. Fretting wear tests were run with quenched and tempered steel with different normal pressures and sliding amplitudes under gross sliding conditions. The development of the friction coefficient and total wear mass depended mostly on the accumulated sliding distance. Initially, friction and wear were highly adhesive but gradually changed to abrasive due to third body accumulation in the interface.     

Development of a friction energy capacity approach to predict the surface coating endurance under complex oscillating sliding conditions

In the case of surface coatings application it is crucial to establish when the substrate is reached to prevent catastrophic consequences. In this study, a model based on local dissipated energy is developed and related to the friction process. Indeed, the friction dissipated energy is a unique parameter that takes into account the major loading variables which are the pressure, sliding distance and the friction coefficient. To illustrate the approach a sphere/plane (Alumina/TiC) contact is studied under gross slip fretting regime. Considering the contact area extension, the wear depth evolution can be predicted from the cumulated dissipated energy density. Nevertheless, some difference is observed between the predicted and detected surface coating endurance. This has been explained by a coating spalling phenomenon observed below a critical residual coating thickness. Introducing an effective wear coating parameter, the coating endurance is better quantified and finally an effective energy density threshold, associated to a friction energy capacity approach, is introduced to rationalize the coating endurance prediction. The surface treatment lifetime is then simply deduced from an energy ratio between this specific energy capacity and a mean energy density dissipated per fretting cycle. The stability of this approach has been validated under constant and variable sliding conditions and illustrated through an Energy Density–Coating Endurance chart.     

Different aspects of the role of wear debris in fretting wear

Two different aspects of the role of oxide wear debris in fretting wear are studied by allowing them to escape from the interface during sliding. This is accomplished by laser surface texturing that forms regular micro-pores topography on the friction surfaces which enables this escape. It is found that the role of oxide wear debris depends on the dominant fretting wear mechanism. Their presence in the interface protects the friction surfaces when the dominant wear mechanism is adhesive and harms the friction surfaces when this mechanism is abrasive. The escape of oxide wear debris into the micro-pores results in up to 84% reduction in the electrical contact resistance of the textured fretting surfaces.     

Multiscale computation of fretting wear at the blade/disk interface

Dovetail joints between fan blades and the disk of turbine engines are subjected to fretting. The objective of this research is to realize wear prediction by computational methods. The goal is obviously the estimation of wear kinetics, but also to obtain worn surfaces, and permit the manufacturer to realize complementary design analyses with worn surfaces. A wear law developed for titanium alloy and based on the friction dissipated energy is used. A computational method based on a three scale analysis is presented. The originality consists of coupling a semi-analytical (SA) contact solver with the FE method for the structural behavior, allowing a fine discretization of the contact zone. Contact computations are fast enough to realize cyclic wear computations. Results for the blade/disk system are exhibited.     

Characterization of fretting wear behavior of Cu–Al coating on Ti–6Al–4V substrate

Fretting wear and fretting fatigue are two commonly observed material damages when two contacting bodies with a clamping load are under the oscillatory motion. In this study, fretting wear damage of Cu–Al coating on titanium alloy, Ti–6Al–4V substrate was investigated using the dissipated energy approach. Fretting tests were conducted with either no fatigue load or the maximum fatigue load of 300 MPa and stress ratio of 0.1 on the substrate (specimen). In order to investigate the effect of contact load and contact size, different pad sizes and contact loads were used in the tests. Accumulated dissipated energy versus wear volume data showed a linear relationship regardless of fatigue loading condition on specimen with the smaller pad size. However, two separate linear relationships were observed based on the fatigue loading condition with the larger pad size, such that a relatively more dissipated energy was required for a certain amount of wear with fatigue load on the specimen. The linear relationship between the accumulated dissipated energy and wear volume for both pad sizes extended from partial to gross slip regimes and was not affected by the applied contact load. Further, fretting tests with and without fatigue load resulted in different shapes of fretting loops when the larger pad size was used.     

On evaluation of wear resistance of tooth enamel and dental materials

A survey of the literature shows that in many studies on the wear resistance of tooth enamel or dental materials a large scatter of experimental data has been obtained when wear tests were performed at a fixed load. Despite the steady loading, wear conditions vary during sliding, since tooth enamel as well as dental materials have inhomogeneous structure. This leads to changes in contact interactions between sliding surfaces, and as a result, we get changes in the friction and wear behaviour of tested materials. This is why at the same loading the wear can be different. In this study, more reliable approach to evaluation of the wear resistance of human enamel and dental materials is proposed. The procedure is based on the correlation between the volumetric wear and the friction energy dissipated during sliding. The model can be useful to compare the wear resistance of different dental materials tested in different ambient conditions.     

Dissipated energy and fretting damage in CoCrAlY-MoS2 coatings

This paper describes fretting wear behaviour of low friction CoCrAlY-MoS₂ coatings on titanium alloy substrates in terms of dissipated energy and friction coefficient. Experimental characterisation was achieved by measuring the friction coefficient vs fretting cycles, or slid distance. Test results were analysed using exponential evolution functions for fretting damage. Dissipated energy was derived, and predicted and measured values compared. Quantitative evaluation of the fretting damage was performed by measuring substrate area emerged. Results show that the friction coefficient evolution rate of CoCrAlY-MoS₂ coating correlates well with the damaged area fraction and the accumulated dissipated energy.     

Expressing wear rate in sliding contacts based on dissipated energy

The wear of materials in sliding contacts is considered as resulting from an energy dissipation due to friction between the contacting first bodies. Up to now, no standard procedure in tribology is available to relate that dissipated energy with wear losses for different sliding wear tests and conditions. In this paper, a procedure is proposed to correlate the volumetric wear loss of one first body with the dissipated energy for unidirectional and bidirectional ball-on-flat tests. The model can be useful to predict the service lifetime of components from a limited number of laboratory tests. The validity and limitation of the wear loss versus dissipated energy model is illustrated for hard coatings like TiN and (Ti, Al)N, and multilayered (Ti, Al)N/TiN coatings. The effect of the applied normal load and the relative humidity (RH) of the ambient air on the wear rate for these different coatings are shown as well. A mild oxidational wear model is used to describe the material loss on these coatings in sliding contacts.     

Evaluation of fretting wear based on the frictional work and cyclic saturation concepts

It is time consuming or even impossible to simulate the whole process of fretting wear, since it always involves millions of cyclic loadings. This paper focuses on the modeling and evaluation method of fretting wear for the typical bridge type fretting test with a flat pad. The frictional work on the contact interface is chosen as the parameter to evaluate the fretting wear. To verify the fretting wear model, the predicted wear profile is compared with that obtained by the experimental results. Fretting wear always includes plastic deformations due to the edge stress singularity. The effect of cumulative plastic deformation is also taken into account in the wear model. The role of the coefficient of friction at the contact interface on the fretting wear has also been discussed.     

Fretting corrosion of materials for orthopaedic implants: a study of a metal/polymer contact in an artificial physiological medium

The fretting corrosion behaviour of a 316L SS flat against a PMMA counterface has been investigated in an artificial physiological medium. A specific device has been used to visualize the in situ degradation at the contact interface. Simultaneous analysis of the coefficient of friction and free corrosion potential has shown four distinct stages during fretting experiments. An energy-oriented approach to the fretting process was conducted in tandem with measurement of wear. This method has shown a linear progression in the wear volume of the samples as a function of the interfacial energy dissipated during fretting. The presence of chlorides contributes to a considerable acceleration of the degradation of the stainless steel surface. This process was explained by a mechanism related to crevice corrosion activated by friction.     

Study on transition between fretting and reciprocating sliding wear

An experimental investigation was conducted to find the associated changes in characteristics of wear before and after the transition between fretting and reciprocating sliding wear. A set of experiments were carried out using a AISI 52100 steel ball rubbing against a plate specimen made from the same steel under dry condition. Wear coefficient, wear volume, coefficient of friction, profile of the scars and wear debris were analyzed. The results displayed that there were significant differences in wear coefficient, wear volume, profile of the wear scars and wear debris before and after the transition. Wear coefficient and wear volume at a constant sliding distance were found to be the most appropriate for identifying the transition amplitude between fretting and reciprocating sliding wear.     

Fretting Wear Behavior of Cu–Al Coating on Ti-6Al-4V Substrate under Dry and Wet (Lubricated) Contact Condition

The fretting wear behavior of Cu–Al coating was investigated with and without fatigue load under the dry and wet (lubricated) contact conditions. The Cu–Al coating was plasma deposited on titanium alloy, Ti-6Al-4V. Fretting regime was determined from the shape of fretting hysteresis loop. Fretting regime changed from partial slip to total (gross) slip at ∼15 μm of the applied relative displacement, and this transition point was independent of fatigue loading and contact surface (lubricated versus dry) conditions. Wet contact condition reduced frictional force during cycling, as evidenced by the lower-tangential force. Wear analysis using the accumulated dissipated energy approach did not show any effect of contact surface condition. In other words, the relationship between the accumulated dissipated energy and wear volume showed a linear relationship, and it was independent of loading and contact surface conditions, as well as of the fretting regime. Further, the relationship between the wear depth and accumulated dissipated energy did not show any effect of loading and contact surface conditions, as well as of the fretting regime up to instant when the maximum wear depth was equal to the coating thickness. The views expressed in this article are those of the authors and do not reflect the official policy or position of the United State Air Force, Department of Defense, or the U.S. Government.     

Friction and wear properties of bronze–graphite composite under water lubrication

Bronze–graphite composite was prepared using powder metallurgy. The friction and wear behaviors of the resulting composites in dry- and water-lubricated sliding against a stainless steel were comparatively investigated on an MM-200 friction and wear tester in a ring-on-block contact configuration. The wear mechanisms of the bronze–graphite composite were discussed based on examination of the worn surface morphologies of both the composite block and the stainless steel ring by means of scanning electron microscopy equipped with an energy dispersion spectrometry and on determination of some typical elements on the worn surfaces by means of X-ray photoelectron spectroscopy. It was found that the friction coefficient was higher under water lubrication than that under dry sliding and it showed margined change with increasing load under the both sliding conditions. A considerably decreased wear rate of the bronze–graphite composite was registered under water-lubricated sliding than under dry sliding, though it rose significantly at a relatively higher load. This was attributed to the hindered transfer of the composite onto the counterpart steel surface under water-lubricated sliding and the cooling effect of the water as a lubricant, while its stronger transfer onto the steel surface accounted for its higher wear rate under dry sliding. Thus, the bronze–graphite composite with much better wear-resistance under water-lubricated sliding than under dry sliding against the stainless steel could be a potential candidate as the tribo-material in aqueous environment.     

Analysis of energy dissipation in fretting corrosion experiments with materials used as hip prosthesis

This paper analyses energy dissipation of fretting corrosion in total hip prosthesis. Fretting corrosion is arisen between metallic prosthesis and bone and/or bone cement, leading to aseptic loosening. In this study, fretting corrosion tests are conducted in Ringer's solution. Stainless steel (316L) and poly (methyl methacrylate) are used for total hip prosthesis. Various potentials are applied in fretting corrosion tests and then dissipated energy is determined with number of cycles. Results show that dissipated energy is rapidly accumulated during the initial running-in period and accumulation of dissipated energy change can be expressed with a power-law form. After the initial running-in period, dissipated energy is linearly accumulated with respect to number of cycles. It is identified that a parameter in the power-law relation can describe the influence of applied potentials in fretting corrosion. In addition, the parameter shows relation to wear volume measured in stainless steel.     

Effect of shot peening on the fretting wear of Ti–6Al–4V

In this paper, we report on the fretting wear behaviour of polished and shot peened Ti–6Al–4V specimens. For fretting experiments, due to micro-displacements at the interface between two contacting surfaces, two types of damage can be observed: crack initiation and debris formation. Shot peening, which is already well known for improving fatigue resistance of titanium alloys, is shown to have a beneficial effect on the crack initiation and propagation under fretting wear loading, as cracks observed on specimens after cylinder-on-flat fretting tests are shorter in shot peened specimens than in polished ones. It is also demonstrated that shot peening decreases the friction coefficient only at the beginning of the test, as long as the asperities induced by shot peening are not worn-off. The effects of displacement amplitude, normal force and test duration on the wear volume have been investigated: in all cases, shot peening has no significant impact on the wear process. The same amount of debris are formed and ejected for both polished and shot peened specimens. Moreover, it is found that, for both types of specimens, the linear relation, developed for steels and hard coatings, between wear volume and cumulated dissipated energy is not valid in the present case as different wear volumes are measured for the same cumulated dissipated energy, depending on the experimental conditions (normal force, displacement amplitude). Using the test duration as the variable parameter, energy wear coefficients are calculated for different experimental conditions.     

Neural network prediction of brake friction materials wear

Wear of brake friction materials depends on many factors such as temperature, applied load, sliding velocity, properties of mating materials, and durability of the transfer layer. Prediction of friction materials wear versus their formulation and manufacturing conditions in synergy with brakes operating conditions can be considered as a crucial issue for further friction materials development. In this paper, the artificial neural network abilities have been used for predicting wear of the friction materials versus influence of all relevant factors. The neural model of friction materials wear has been developed taking into account: (i) complete formulation of the friction material (18 ingredients), (ii) the most important manufacturing conditions of the friction material (5 parameters), (iii) applied load and sliding velocity of the friction material both represented by work done by brake application, and (iv) brake interface temperature.     

Origins of the wear resistance of AlSi cylinder bore surfaces studies by surface analytical tools

This paper investigates the origin of the wear resistance of hypereutectic AlSi cylinder bore surfaces using atomic force microscopy, auger electron spectroscopy and focused ion beam analysis. Our findings suggest that the piston ring is not sliding on top of the raised silicon primary crystals, as often assumed. Instead, a new surface material is formed during running-in, which is sintered by wear particles as a result of the energy dissipated during sliding. The process can be understood as a friction induced particle strengthening of the aluminium matrix which raises the shear strength of the original material. Eventually this surface provides the wear resistance of the cylinder bore.     

Palliatives in fretting: A dynamical approach

Fretting damages are connected to numerous aspects like friction, wear, contact mechanics, fatigue and material sciences. Its quantification also requests to consider the loading history as well as the sliding condition. Based on a “fretting sliding” approach, and considering fretting wear test conditions, various palliative solutions have been investigated. Shot peening treatment, introducing compressive residual stresses, appears pertinent against crack propagation but ineffective against crack nucleation due to the activation of surface relaxation phenomena. Hard thin coatings present stable residual stresses independently of the sliding conditions. However, they only delay the crack nucleation process, when the coating is worn through, cracking phenomena are activated. To quantify the coating endurance against wear, an energy density approach has been developed. The stability of this approach has been confirmed regarding the contact size effect and illustrated through the analysis of synergic interaction between soft thick coating and solid lubricant.