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Fretting can lead to surface wear and/or crack nucleation depending on the sliding condition and contact geometry. To formalize this aspect, Ti-6Al-4V cylinder/plane and punch/plane contacts were investigated. The experimental crack nucleation domains in partial and gross slip conditions were established and simulated combining SWT cumulative damage analysis with FEM surface wear simulations. Good correlations were achieved if the experimental boundary conditions including system tangential accommodation and micro-rotations measured using DIC analysis, were considered. Fretting maps were simulated by predicting partial slip and gross slip displacement amplitudes above which cracks were respectively nucleated and removed by surface wear. Finally, it was shown that whatever the contact geometry, the gross slip cracking domain was inversely proportional to the surface wear rate.

Plint (IMechE 182 (1):300–306,1967) reported a reduced coefficient of friction with increasing roller sizes in EHL traction measurements. In this study, a similar scale effect has been observed when comparing measured traction curves at the same operating conditions between a ball-on-disc rig and a twin-disc machine of different geometrical sizes. This scale effect has been studied numerically for point contacts of different radii of curvature Rx based on thermal EHL simulations. Results show that the reduced friction for large Rx is caused by an increase in film thickness and the enhanced thermal effects. The mechanisms are: (1) heat is hard to conduct across a thicker EHL film due to bad thermal conductivity; (2) shear is mainly localized in the middle film.

Here we compare the wear performance of silica and polyurethane in a vacuum gripper. The problem is modeled numerically by evaluating the energy dissipated at the interface, and experimentally by examining surface damage in contact subjected to cyclic normal loading. In the numerical model, the energy dissipated during unloading is found to be negligible with respect to that of loading. Changing the contact geometry has a good effect in terms of frictional work reduction, but this is not as significant as the effect obtained by changing the material. Replacing silica with polyurethane reduces the frictional work by a factor of at least 20. The latter finding is qualitatively validated in experiments.

A transient three-dimensional thermal elastohydrodynamic calculation model is introduced to simulate the contact of tooth flanks of helical gear pairs with involute gearing. At any time, contact geometry is derived from the real involute curves of gears. In addition to the consideration of mass conserving cavitation and the non-Newtonian fluid behavior, models to capture conditions of mixed friction and microhydrodynamic effects are included. To consider the non-Newtonian fluid behavior, a shear thinning fluid model with limiting shear stress is applied. A selected helical gear pair is used as example to examine the influence DLC coated tooth flanks have on tribological behavior. It shows that friction and temperature behavior of the gearing can be significantly influenced with DLC coating.

In this investigation an approach to fretting fatigue life prediction is developed with consideration of damage-coupled elastic–plastic constitutive model and wear. Nonlinear kinematic hardening is employed in the analysis of elastic–plastic damage, and the total damage is divided into two parts, elastic damage and plastic damage, which are related to the cyclic stress and accumulated plastic strain, respectively. Wear is modeled by the energy wear law to simulate the evolution of contact geometry. A two dimensional plane strain finite element implementation is presented for fretting, including the case of partial slip and gross sliding. The progressive fatigue damage and wear is simulated and the results are compared with experimental data from the literature.

Stress distribution at the contact edge plays a dominant role in fretting fatigue strength. In the previous studies, based on the stress distribution at the contact edge, a generalized tangential stress range–compressive stress range (TSR–CSR) diagram has been proposed as a fretting fatigue fracture criterion. It has been also confirmed that the proposed diagram would be very useful to predict the fretting fatigue strength regardless of contact geometry, loading condition, material strength, environment, etc. for laboratory-type specimens. In the present study, fretting fatigue strengths of actual components, such as a dovetail joint and a bolted joint, have been predicted based on the generalized TSR–CSR diagram. To verify the effectiveness of the prediction based on the generalized TSR–CSR diagram, the fretting fatigue tests of dovetail joints and bolted joints were carried out. The fretting fatigue strengths of dovetail joints and bolted joints predicted based on the generalized TSR–CSR diagram were in good agreement with the experimental results.

The mixed-lubrication model of the planetary roller screw is proposed considering contact load, contact geometry of thread, surface roughness and transient effects. The influences of rotational speed of the screw, axial load and surface roughness on lubrication are discussed. Increasing rotational speed has a significant effect on the lubrication of contact areas. As the speed increases, the film thickness increases while the friction coefficient and contact-area ratio decrease, and the lubrication mode changes from mixed to full-film. As the load increases, the film-thickness ratio decreases while the friction coefficient and maximum subsurface von Mises stress increase. High-precision machining can improve lubrication by properly reducing the roughness of the machined surface, which would increase film thickness and decrease the contact-area ratio.

Fretting fatigue is a combination of two complex mechanical phenomena. Fretting appears between components that are subjected to small relative oscillatory motions. Once these connected components undergo cyclic fatigue load, fretting fatigue occurs. In general, fretting fatigue failure process can be divided into two main portions, namely crack initiation and crack propagation. Fretting fatigue crack initiation characteristics are very difficult to detect because damages such as micro-cracks are always hidden between two contact surfaces. In this paper Continuum Damage Mechanics (CDM) approach in conjunction with Finite Element Analyses (FEA) is used to find a predictor tool for fretting fatigue crack initiation lifetime. For this purpose an uncoupled damage evolution law is developed to model fretting fatigue crack initiation lifetime at various fretting condition such as contact geometry, axial stress, normal load and tangential load. The predicted results are validated with published experimental data from literature.

The scratch behavior of two amorphous polymers is investigated to understand how the materials characteristics affect the scratch resistance. A thermosetting resin and a thermoplastic polymer are studied using both an experimental set-up allowing in situ observations of the contact area during indentation and scratching with spherical tips, and a finite element modeling (FEM). The rheological properties of polymer surfaces are modeled assuming a linear elastic behavior and a plastic law with high strain hardening, described by G’Sell-Jonas equation. The local friction coefficient μ loc at the interface between the indenter and the material was modeled with a Coulomb's friction coefficient, for each computed ratio a / R , where a being the contact radius, and R the tip radius. A description of the plastic strain field, beneath the indenter during scratch is proposed as a function of the ration a / R set between 0.1 and 0.4 and the friction coefficient varying between 0 and 0.4. The results obtained by FEM are in good correlation with experimental observations and show that the plastic strain gradient beneath the indenter depends clearly on the ratio a / R , on the local friction coefficient and also the rheological parameters of tested material. An equivalent average plastic strain is calculated with FEM over a representative volume deformed plastically. The average plastic strain increases with the ratio a / R , as predicted by the empiric Tabor's rule, but also with the local friction coefficient, for a given ratio a / R , while the strain hardening ability tends to decrease plastic strain imposed during the contact. Clear correlations are demonstrated between the average plastic strain and geometrical parameters, classically used to describe the geometry of the contact area.

Contact evolution effects during fretting can be divided into two categories, namely, change of contact geometry due to wear and near-surface damage. In this paper a study on the effect of contact evolution on fretting crack nucleation in Ti–6Al–4V is carried out, based on a cylinder-on-flat contact fretting wear configuration. The fretted surfaces are carefully profiled so that the evolution of the contact geometry around fretting-induced cracks is identified. The evolution of the near-surface microstructure is identified by scanning electron microscopy. According to the experimental results, a predictive framework is presented to capture the competition and interaction between the contact evolution and crack initiation. The modelling of fretting wear is central to this approach, since it predicts not only the extent of wear damage, but also the concomitant change in fatigue pertinent stresses. The analysis of fretting wear tests, including partial slip and gross sliding conditions, without the substrate fatigue loading of fretting fatigue tests, provides an opportunity to investigate the crack initiation and thus validate predictions. A multi-axial fatigue damage parameter is employed within a cumulative fatigue-damage methodology to predict the wear-induced crack nucleation behaviour under different slip regimes.

The issue of thermal management of two components sliding against each other plays an important role in the proper functioning of the machine components. Jaeger, using his and Blok's hypotheses, presented the curves to compute the average and the maximum temperature rise in square and band shaped interfaces. It is often observed that designers refer to those curves even in scenarios when the contact geometry is different. In many cases, a more accurate temperature distribution is needed and using a constant heat partition to evaluate the temperature rise at the interface can lead to over-design or under-design of the components. In this study the authors apply a recently developed methodology of obtaining the temperature distribution at the interface of two sliding semi-infinite bodies by partitioning the heat between them in such a way that the temperature at every point in the interface is same for both the bodies. Elliptical contacts with a semi-ellipsoidal heat distribution are considered. In order to aid designers, curve fit equations are presented to calculate maximum temperature and average temperature rise in non-dimensional form over a wide range of Peclet numbers, thermal conductivity ratios and ellipticity ratios.

The present investigation focuses on the fretting wear kinetics of a Ti–6Al–4V/Ti–6Al–4V interface. The impact of contact size, contact geometry, variable gross slip sliding conditions and combined partial and gross slip sequences are studied. It is shown that for an adhesive wear tribosystem, the wear rate is better captured by coupling debris formation and debris ejection descriptions. Hence a “unified energy wear approach” is derived, providing a stable prediction of wear rates over a large spectrum of pressure, test duration and sliding amplitudes for constant and variable gross slip sliding conditions. By changing the contact size and geometry it is shown that the larger the contact dimension, the lower the energy wear rate. An extended energy wear concept, based on an asymptotic formulation is introduced, enabling macro, meso and micro contact configurations to be correlated. Combined partial slip/gross slip sequences are finally investigated to evaluate the stability of the energy wear formulation. The partial slip sequence is shown to promote fatigue degradation of the third body layer generated during the gross slip period. An incremental formulation integrating the contribution of partial slip fatigue damage of third body is derived.

Fretting fatigue behavior of unpeened and shot-peened Ti–6Al–4 V was investigated using a dual-actuator test setup which was capable of applying an independent pad displacement while maintaining a constant cyclic load on the specimen. The fretting regime was identified based on the shape of the hysteresis loop of tangential force versus relative slip range and the evolution of normalized tangential force. The fretting regime changed from stick to partial slip and then to gross slip with increasing relative slip range, and the transition from partial to gross slip occurred at a relative slip range of 50–60 μm regardless of the applied cyclic load, surface treatment, contact load and contact geometry. The fretting fatigue life initially decreased as the relative slip range increased and reached a minimum value, and then increased with increase of the relative slip range due to the transition in fretting regime from partial slip to gross slip. Shot-peened specimens had longer fatigue life than unpeened specimens at a given relative slip range, but the minimum fatigue life was found to be at the same value of relative slip range for both shot-peened and unpeened specimens. Tangential force was directly related to relative slip and this relationship was independent of other fretting variables.

The aim of this paper was to investigate the possibilities to use a model test to simulate the wear between cylinder bore and piston in a radial piston hydraulic motor. The tests were performed in a reciprocating test rig where the contact geometry is of the cylinder–plate type. The influence of different types of commercially available hydraulic fluids on wear protection and friction was studied. From the study, it was concluded that the use of water glycols can cause increased wear in hydraulic motors operating in low speed applications. It was also seen that the FZG test alone appears not to be enough as a hydraulic fluid wear test, at least not in the tribological conditions present in the performed wear test.

Friction is an important parameter that critically impacts the tribological performance of a head/disk interface. The head/disk interface with laser zone texture affords a model system for the study of dynamic friction by virtue of its precisely-controlled contact geometry. By using two types of head sliders, i.e. the conventional slider and the padded slider, and a matrix of hard disks with a wide range of laser zone texture parameters, head/disk contacts involving a small number as well as a large number of bumps are realized. A rich variety of dynamic friction behaviors are observed with respect to bump height and bump density variations. To shed new light on the nature of HDI dynamic friction, an analytical model that treats both the deformational and the adhesive friction components on equal footings is formulated. It is shown that, based on the model analysis, the friction is deformation-dominated for HDIs involving a small number of contacting bumps and adhesion-dominated for HDIs involving a large number of contacting bumps. In the former case the friction decreases with bump density, whereas in the latter the friction increases with bump density.

The multipass strip drawing tests of sheet metal car body parts in cylinder/sheet/cylinder contact geometry is particularly well adapted to the simulation of sheet/tool contact conditions during a stamping operation. Within this framework, a rough sheet rubs against a smooth tool. During the sliding contact, a modification in the average size of plateaus appears, the locations where the shear stress and normal pressures are transmitted. Owing to a profilometrical relocation technique between each tool passage, we use statistical parameters corresponding to the average width and length of the plateaus. The observed flattening of the plateaus and the quantity of free wear particles modifying the third body in the contact are particularly more important in the case of aluminum sheets than in those of mild steel sheets.

The response of wear rate and clinical failure load to contamination and material hardness has been determined for AISI 52100 steel. A ball-on-roller contact geometry was used, in which the stationary rollers had three grades of hardness: 42, 56, and 63 HRC. The test contaminant, aluminium oxide (Al2O3) powder in , 10–20, and 20–30 μm sizes, was injected into an SAE 10 base oil at 10, 100, and 200 mg/litre concentration levels. Machine load and sliding speed were varied in the range 15 to 210 kg and 0.26 to 1.05 m/s, respectively. A qualitative assessment of worn surfaces was also undertaken. For the largest contaminant size and concentration, the load-carrying capacity to failure was about half that for the uncontaminated condition of operation.

The tribological behaviour of engineering ceramic materials can be influenced by several tribosystem parameters. Friction and wear properties of different types of ceramics (silicon nitride, silicon carbide, alumina and zirconia) are evaluated for the case of oscillating sliding motion at room temperature. The influence of such parameters as: counterbody material; contact geometry; stroke; normal force; running time; frequency; and humidity of the sorrounding air are studied. For many situations the formation of reaction layers governs the tribological behaviour, leading to a two-phase behaviour of friction and wear. The transition from phase I (severe wear) to phase II (mild wear) depends on several parameters of the tribosystem and operational conditions.

A simulation model for the transient thermal elastohydrodynamic calculation of spiral bevel gears with octoidal toothing is presented. The three-dimensional contact geometry is derived directly from the precise geometrical definition of the tooth flank profiles. The tooth trace can be represented both as circular arc and as extended epicycloid. The simulation model is based on the numerical solution of the generalized Reynolds equation and includes models for mass conserving cavitation, non-Newtonian flow, mixed friction and microhydrodynamics. For the temperature calculation the energy equation for the fluid and the Fourier heat equation for the solid bodies are solved. Using the example of a spiral bevel gear pair with an extended epicycloid, the capability of the presented simulation model is shown.