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Researchers have long been studying the effects of the modification of friction material compositions on their tribological properties. Predictive models have also been developed, but they are of limited use in the design of new compositions. Therefore, this research aims to investigate the tribological behaviour of single ingredients in friction materials to develop a tribological dataset. This dataset could then be used as a foundation for a cellular automaton (CA) predictive model, intended to be a tool for designing friction materials. Tribological samples were almost entirely composed of four distinct friction material ingredients, and one sample composed of their mixture was successfully produced. Pin-on-disc (PoD) tribometer testing and scanning electron microscopy/energy-dispersive X-ray spectroscopy (SEM/EDXS) analysis were used for the tribological characterization. Each material showed distinct tribological properties and evolution of the contact surface features, and the synergistic effect of their mutual interaction was also demonstrated by their mixture. [ABSTRACT FROM AUTHOR]

Severe friction on wheel/rail contact interface in the process of a train emergency braking can cause significant thermal and mechanical phenomena. Obvious friction heat and serious material damage will appear on the contact surface. In this article, the variation law of temperature and surface damage during a wheel sliding contact process are investigated. To achieve the research objective, a three-dimensional (3D) thermo-mechanical coupling contact finite element model (FEM) is established, and the temperature-dependent material parameters are used. The FEM is adopted to analyze the temperature distribution law on the contact surface. At the same time, a sliding contact testing machine is used to study the damage of materials in the contact area during the sliding contact. The study results indicate, the highest temperature of wheel and rail material is respectively 1014 ℃ and 461.8 ℃ during sliding contact. High temperatures are located at the subsurface and surface areas of contact region. When the distance to contact surface exceeds 1.4 mm, the temperature changes slightly. The types of damage on wheel surface are grooves and material peeling, while the flaky spalling, corrosive pitting, adhesion and grooves appear on the rail surface. Meanwhile, many cracks can be found on the contact surface, which is a major factor leading to material damage. The research results of this article are of great significance for understanding the thermal and mechanical damage of wheel/rail materials. [ABSTRACT FROM AUTHOR]

This study aimed to reproduce and translate clinical presentations in an in vitro set-up and evaluate laboratory outcomes of mechanical properties (flexural strength, fatigue resistance, wear resistance) and link them to the clinical outcomes of the employed materials in the Radboud Tooth Wear Project (RTWP). Four dental resin composites were selected. 30 discs (Ø12.0 mm, 1.2 mm thick) were fabricated for each of Clearfil TM AP-X (AP), Filtek TM Supreme XTE (FS), Estenia TM C&B (ES), and Lava Ultimate (LU). Cyclic loading (200 N, 2 Hz frequency) was applied concentrically to 15 specimens per group with a spherical steatite indenter (r = 3.18 mm) in water in a contact-load-slide-liftoff motion (105 cycles). The wear scar was analysed using profilometry and the volume loss was digitally computed. Finally, all specimens were loaded (fatigued specimens with their worn surface loaded in tension) until fracture in a biaxial flexure apparatus. The differences in volume loss and flexural strength were determined using regression analysis. Compared to AP and FS, ES and LU showed a significantly lower volume loss (p < 0.05). Non-fatigued ES specimens had a similar flexural strength compared to nonfatigued AP, while non-fatigued FS and LU specimens had a lower flexural strength (p < 0.001; 95 %CI: −80.0 – 51.8). The fatigue test resulted in a significant decrease of the flexural strength of ES specimens, only (p < 0.001; 95 %CI: −96.1 – −54.6). These outcomes concur with the outcomes of clinical studies on the longevity of these composites in patients with tooth wear. Therefore, the employed laboratory test seems to have the potential to test materials in a clinically relevant way. [ABSTRACT FROM AUTHOR]

Abstract Severe friction on wheel/rail contact interface in the process of a train emergency braking can cause significant thermal and mechanical phenomena. Obvious friction heat and serious material damage will appear on the contact surface. In this article, the variation law of temperature and surface damage during a wheel sliding contact process are investigated. To achieve the research objective, a three-dimensional (3D) thermo-mechanical coupling contact finite element model (FEM) is established, and the temperature-dependent material parameters are used. The FEM is adopted to analyze the temperature distribution law on the contact surface. At the same time, a sliding contact testing machine is used to study the damage of materials in the contact area during the sliding contact. The study results indicate, the highest temperature of wheel and rail material is respectively 1014 ℃ and 461.8 ℃ during sliding contact. High temperatures are located at the subsurface and surface areas of contact region. When the distance to contact surface exceeds 1.4 mm, the temperature changes slightly. The types of damage on wheel surface are grooves and material peeling, while the flaky spalling, corrosive pitting, adhesion and grooves appear on the rail surface. Meanwhile, many cracks can be found on the contact surface, which is a major factor leading to material damage. The research results of this article are of great significance for understanding the thermal and mechanical damage of wheel/rail materials.

Present study delves into realm of coupled interfacial imperfections and their influence on propagation characteristics of shear horizontal (SH) waves in piezoelectric layered structures. The research scenario involves a piezoelectric layer sandwiched between exponentially graded piezoelectric superstrate and fiber-reinforced substratum, with specific boundary conditions at play. The upper boundary is treated as electrode, while the upper interface is considered both mechanically and electrically bonded. In contrast, the lower interface is configured with sliding contact conditions. Leveraging derived displacement components and applying pertinent boundary conditions, the dispersion equation is derived for both electrically open and short cases. To ascertain the validity and credibility of derived dispersion equation, results have been compared with established results from prior research and classical Love wave equation. Study further extends to numerical simulations and graphical demonstrations, which encompass a range of piezoelectric materials. Through comparative analysis, we uncover intriguing characteristics and analyse the significant influence of heterogeneity, electro-mechanical bonding parameters, and piezoelectric constants, along with dielectric properties, on the dispersion behaviour. This work not only advances the fundamental understanding of SH wave phenomena in composite structures but will also be useful in applications fields such as engineering geology, sensor technology, and geophysical exploration. [ABSTRACT FROM AUTHOR]

In this work, large-scale molecular dynamics (MD) computational simulations were performed in order to explore the sliding contact responses of rough surfaces with hexadecane lubricant and added nanoparticles. Simulation results revealed that the frictional state was dependent on the fluid, nanoparticle, and surface roughness. Three lubricating conditions were compared based on considerations of different amounts of fluid molecules. The lubricant was not able to separate the frictional contact surfaces if the quantity of lubricant molecules was insufficient. Particularly, there were no lubricating contributions when the amount of lubricant was too low, and the lubricant therefore only filled the pits in the surface roughness. Thus, the normal load was primarily supported by the contact between the two surfaces and nanoparticles, leading to significant surface morphology changes. In contrast, the frictional contact surfaces were able to be completely separated by the lubricant when there was a sufficient amount of fluid, and a very good lubricating effect could thus be achieved, resulting in a smaller friction force. In addition, the changes in surface morphology, contact area, and RMS are discussed in this paper, in order to reveal the dynamic frictional process. [ABSTRACT FROM AUTHOR]

To meet the requirement of wear-resistant packaging for transportation and allied industries, an indigenously synthesized alkali-treated jute filler-reinforced epoxy composite is put to tribological tests for determining its worth/applicability under external loading. On the basis of full factorial design of experiments (DoE) at multiple filler percentages, sliding distances (1000, 2000, and 3000 m), and loads (5, 10, and 15 N), wear tests are conducted with the help of a pin-on-disk multitribometer machine. The mechanical characterizations like hardness and tensile strength of the composites are also evaluated, and the results of experimented tensile strength are validated with the results of Digimat-FE tool. Among all the different jute filler wt.% (0%, 2.5%, 5%, 7.5%, 10% and 12.5%)-reinforced composite, 2.5 and 5 wt% filler-reinforced composites have produced better wear resistance properties and maximum tensile strength, respectively. On the other hand, agglomeration of fillers on the surface at higher jute filler wt% (= 12.5%) leads to a high amount of plastic deformation and debonding. The observations reported in the present study are supported by a single hidden layer artificial neural network (SHL-ANN) model with the error being as low as ± 2% when compared with linear regression model for different tribological properties. [ABSTRACT FROM AUTHOR]

The ongoing digitalization of processes and products in mechanical engineering is accompanied by an increasing demand for data. In order to provide this data, technical systems are being extended with sensory functions. To supply those sensory functions on rotating elements—such as shafts—with electrical energy, and to be able to transmit signals out of the system, sliding contacts can be used as a cost-effective and established solution. However, if electrical properties of machine elements are utilized for sensing purposes, such as condition monitoring of rolling element bearings by means of impedance measurement, sliding contacts are directly in the measurement path and can thus influence the measured impedance. The aim of this paper is to analyze the impedance of graphite and silver graphite carbon brushes under different rotational speeds, in different positions, and with different carrier frequencies. The material of the carbon brushes as well as the position have significant effects on the impedance behavior. Furthermore, carbon brushes show a significant running-in behavior. The results are discussed, and indications for use in impedance measurements are given. Silver graphite carbon brushes in axial positioning are particularly suitable for impedance measurements of sensory utilizable machine elements. Sufficient running-in time must be considered. [ABSTRACT FROM AUTHOR]

Aesthetic glass-ceramics are widely employed dental materials, both in bulk form and as veneers. As they are highly brittle, the durability of these materials is limited by fracture and wear processes originated from contacts with opposing dentition and/or third-body particles during mastication and bruxism. This work investigates the resistance to fracture of commercial dental glass-ceramics under sliding contact, simulated by means of scratch tests. It finds that materials with relatively larger crystals (feldspathic and leucite) require a lower stress to fracture upon sliding than lithium silicates containing smaller (but more elongated) crystals, due to their larger defects and lower toughness. Results are analyzed as a function of material microstructure within the framework of Weibull theory and fracture mechanics. Implications for materials selection and development in prosthetic dentistry are briefly discussed. [ABSTRACT FROM AUTHOR]

In this work, large-scale molecular dynamics (MD) computational simulations were performed in order to explore the sliding contact responses of rough surfaces with hexadecane lubricant and added nanoparticles. Simulation results revealed that the frictional state was dependent on the fluid, nanoparticle, and surface roughness. Three lubricating conditions were compared based on considerations of different amounts of fluid molecules. The lubricant was not able to separate the frictional contact surfaces if the quantity of lubricant molecules was insufficient. Particularly, there were no lubricating contributions when the amount of lubricant was too low, and the lubricant therefore only filled the pits in the surface roughness. Thus, the normal load was primarily supported by the contact between the two surfaces and nanoparticles, leading to significant surface morphology changes. In contrast, the frictional contact surfaces were able to be completely separated by the lubricant when there was a sufficient amount of fluid, and a very good lubricating effect could thus be achieved, resulting in a smaller friction force. In addition, the changes in surface morphology, contact area, and RMS are discussed in this paper, in order to reveal the dynamic frictional process.

Electrical traction systems come in different forms, depending on the railway and terrain. The collector shoe is a critical component that impacts the train's overall safety. The majority of collector shoes consist of several types of gray cast iron that are highly resistant to sliding wear. Wear is produced by friction and electrical current at temperatures over the melting point, which results in decreased sliding speeds. Applying an electric current to a sliding contact alters the process temperature of the wear without changing the sliding speed. The study is essential for industrial applications, especially in subway transit. This study aims to learn more about the wear characteristics of a composite aluminum–stainless steel conductor rail moving across a current collector. The authors employed a finite element analysis and a series of electric current testing. This research will produce some intriguing test findings. Based on a friction pair consisting of a composite conductor rail of aluminum and stainless steel and gray cast iron, a sliding friction contact model was built in the COMSOL finite element software. When the findings of the finite element analysis and the pin-on-plate test technique are compared, the maximum temperature variance is 10%, while the minimum temperature variation is 0.8%. Additionally, the results reveal that acclimation and rupture occur more rapidly when speed rises, and a steady temperature rise may be achieved more quickly. [ABSTRACT FROM AUTHOR]

The analysis of rail/wheel sliding friction heat is a very important research field. The numerical simulation is often adopted to calculate the friction heat, and experimental method is relatively few. In this paper, an experimental machine is designed to simulate the rail/wheel sliding contact. At the same time, a rail/wheel contact wear model and a friction heat transfer model are established. The characteristics of temperature on rail/wheel sliding contact are analyzed by experimental test and numerical calculation. The research results show that the temperature rise of wheel and rail is quick in the initial sliding contact stage, then gradually slows down. The temperature of wheel is higher than that of rail at the same depth from the contact surface. In the initial sliding stage, the wheel temperature rises faster than the rail temperature, which is related to the size of contact surface and the concentration degree of friction heat. Moreover, the results of this paper show that the temperature values of the rail/wheel obtained through experimental test and numerical calculation are in good agreement. The experimental and numerical calculation methods used in this article can be adopted to analyze the contact problems of other sliding friction pairs. [ABSTRACT FROM AUTHOR]

To assess potential antagonist wear and survival probability of silica-infiltrated zirconia compared to glass-graded, glazed, and polished zirconia. Table top restorations made of 3Y-TZP (3Y), 5Y-PSZ (5Y), and lithium disilicate (LD) were bonded onto epoxy resin preparations. Each zirconia was divided into five groups according to the surface treatment: polishing; glaze; polishing-glaze; glass infiltration; and silica infiltration. The LD restorations received a glaze layer. Specimens were subjected to sliding fatigue wear using a steatite antagonist (1.25 ×106 cycles, 200 N). The presence of cracks, fractures, and/or debonding was checked every one/third of the total number of cycles was completed. Roughness, microstructural, Scanning electron microscopy, wear and residual stress analyses were conducted. Kaplan–Meier, Mantel–Cox (log-rank) and ANOVA tests were performed for statistical analyses. The survival probability was different among the groups. Silica infiltration and polishing-glaze led to lower volume loss than glaze and glass-infiltration. Difference was observed for roughness among the zirconia and surface treatment, while lithium disilicate presented similar roughness compared to both glazed zirconia. Scanning electron microscopy revealed the removal of the surface treatment after sliding fatigue wear in all groups. Compressive stress was detected on 3Y surfaces, while tensile stress was observed on 5Y. 3Y and 5Y zirconia behaved similarly regarding antagonist wear, presenting higher antagonist wear than the glass ceramic. Silica-infiltrated and polished-glazed zirconia produced lower antagonist volume loss than glazed and glass-infiltrated zirconia. Silica-infiltrated 3Y and lithium disilicate restorations were the only groups to show survival probabilities lower than 85%. [ABSTRACT FROM AUTHOR]

In advanced railway systems, electricity is supplied to train through sliding contact of pantograph and power-transmission catenary, which causes continuous wear of transmission wire in pantograph-catenary system (PCS). It is of crucial to monitor wear to ensure the safety and smooth operations of electric trains in terms of precision and efficiency in services. This work has developed a novel inverse procedure that uses measurable mechanical quantities to predict and monitor contact wire wear regardless of whether pantograph passes. The inverse technique is based on rigorous mechanics principle and verified by numerical simulation. Three-dimensional (3D) finite element models (FEM) of PCS is first established to simulate both static mechanics behavior and dynamic contact process during sliding. A useful relationship between wear-level and displacement or contact force has been established through static studies. Intensive nonlinear dynamic contact analysis of PCS is then performed and found that the wear-level relates strongly to displacement variation of collector head, so as to devise an inverse procedure between those two when the train is running. In addition, simple formulae are derived by curve-fitting to estimate wire-level based on either static or dynamic measurements, for easy real-time applications of the results from our 3D FEM study. [ABSTRACT FROM AUTHOR]

The investigation delves into the propagation of Love-like waves within a stratified medium incorporating the impact of non-local elasticity and a sliding interface. The medium is characterized by an orthotropic viscoelastic layer with fractures and matrix porosity saturated with fluid positioned over an orthotropic viscoelastic half-space under initial stresses. The media is vertically heterogeneous with a binomial function of depth featuring a real positive exponent. Two distinct non-local parameters are considered for the layer and half-space, along with a sliding parameter accounting for interface sliding. The particle displacement components are expressed using modified Bessel functions of first and second kinds. A finite number of terms of the asymptotic representation of the modified Bessel functions and their derivatives have been used and compared with the exact solution. The dispersion equation is derived by neglecting fourth and subsequent powers of non-local parameters under suitable boundary conditions. Various cases are explored based on welded, partially, and fully sliding interfaces and compared with classical Love wave propagation. An interesting phenomenon has been found that under a fully sliding interface, the existence of Love-like wave vanishes, and the medium behaves as a separate layer and half-space with shear wave propagation. • For smooth contact, Love-like wave disappears, and shear wave propagate individually in layer and half-space. • Non-local parameter in the half-space accelerates wave decay with depth. • Various terms of the asymptotic representations of Bessel functions have been considered. [ABSTRACT FROM AUTHOR]

The ongoing digitalization of processes and products in mechanical engineering is accompanied by an increasing demand for data. In order to provide this data, technical systems are being extended with sensory functions. To supply those sensory functions on rotating elements—such as shafts—with electrical energy, and to be able to transmit signals out of the system, sliding contacts can be used as a cost-effective and established solution. However, if electrical properties of machine elements are utilized for sensing purposes, such as condition monitoring of rolling element bearings by means of impedance measurement, sliding contacts are directly in the measurement path and can thus influence the measured impedance. The aim of this paper is to analyze the impedance of graphite and silver graphite carbon brushes under different rotational speeds, in different positions, and with different carrier frequencies. The material of the carbon brushes as well as the position have significant effects on the impedance behavior. Furthermore, carbon brushes show a significant running-in behavior. The results are discussed, and indications for use in impedance measurements are given. Silver graphite carbon brushes in axial positioning are particularly suitable for impedance measurements of sensory utilizable machine elements. Sufficient running-in time must be considered.

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Subsurface damage of fused silica optics is one of the major factors restricting the performance of optical systems. The densification-affected deformation and fracture in fused silica under a sliding contact are investigated in this study, via three-dimensional finite element analysis (FEA). The finite element models of scratching with 70.3° conical and Berkovich indenters are established. A refined elliptical constitutive model is used to consider the influence of densification. The finite element models are experimentally verified by elastic recovery, and theoretically verified by hardness ratio. Results of densification and plastic deformation distributions indicate that the accuracy of existent sliding stress field models may be improved if the spherical/cylindrical yield region is replaced by an ellipsoid/cylindroid, and the embedding of the yield region is considered. The initiation sequence, and the locations and stages of radial, median, and lateral cracks are discussed by analyzing the predicted sliding stress fields. Median and radial cracks along the sliding direction tend to be the first cracks that emerge in the sliding and unloading stages, respectively. They coalesce to form a big median–radial crack that penetrates through the entire yield region. The fracture behavior of fused silica revealed in this study is essential in the low-damage machining of fused silica optics. [ABSTRACT FROM AUTHOR]

A two-dimensional temperature prediction model of the multi-conical friction pair during a single engagement period is established. Energy governing equations and non-static thermal contact conductance are coupled, and the transient surface temperatures are obtained by using the finite difference method. The transient temperature field and the effects of contact pressure and relative speed are studied. The positive interaction effect of these two factors on the temperature rise is observed. The maximum temperatures of the friction plate and clutch disc appear in different positions, where the former is closer to the outermost contact surface. With the combination of high thermal conductivity, the friction plate exhibits a more significant radial temperature gradient. And the accompanying thermal stress may induce deformation and ablation. In addition, the temperature decreases axially from the top of the cone. This work provides a prerequisite for studying the friction, wear and torque transmission performance of clutch, offering a reference for the further control and optimization design of novel clutch systems. [ABSTRACT FROM AUTHOR]

Dynamic substructuring methods are initially developed for time-invariant systems to evaluate the dynamic behavior of a complex structure by coupling the component substructures. Sometimes, the component substructures change their position over time, affecting the dynamics of the entire structure. This family of problems can be tackled using substructuring techniques by isolating the time dependency in the coupling conditions among the time-invariant substructures. Mechanical systems, composed of subsystems in relative motion with a sliding interface, can be analyzed using this approach. In previous work, the authors proposed a solution method in the time and frequency domain using this approach under the assumption that the relative sliding motion at the contact interfaces is a-priori known, at least approximately. This assumption implies that the perturbation generated by the friction-induced vibration is neglected. In subsequent work, a more realistic contact assumption was considered to account also for the local vibration of the contact point and the geometric nonlinearity due to the elastic deformation. In this paper, a simplification with respect to the realistic contact assumption is introduced, which neglects the angular variation of the direction normal to the contact interface. The simplified approach is advantageous because it is equally able to highlight the occurrence of friction-induced instabilities, and it reduces the computational burden. The results of the substructuring methods using different contact assumptions are compared with those of a reference numerical method to show how the choice of the contact algorithm allows for tackling a wide range of operating conditions, from simple position-dependent problems up to complex friction-induced vibration phenomena. [ABSTRACT FROM AUTHOR]

This study reports the propagation characteristics of torsional waves in a composite fibre-reinforced magnetoelastic layer lying over an inhomogeneous elastic half-space with sliding interface. Variation in material properties of the half-space is considered to possess exponential type inhomogeneity, whereas linearized Maxwell's perfectly conducting material is chosen for the superimposed layer. Generalized frequency equation is derived to characterize the torsional wave speed and its dependence on relevant parameters. Certain established models are stemmed as special cases of the present analysis for the two extrema of sliding contact parameter. Accordingly, the stemmed dispersion relations are found to be in agreement with the previously documented results. Torsional speed is numerically computed and represented pictorially using implicit surface plots for characterizing the effects of relevant parameters such as magneto-elastic coupling, sliding parameter, radial displacement, inhomogeneity, the direction of reinforcement and angle of the primary magnetic field. Findings of the present work may be utilized in signal testing, geophysical applications concerned with torsional wave based non-destructive evaluation. [ABSTRACT FROM AUTHOR]

Modern high-tech composite materials are widely used in various sectors of the economy, in particular, in railway transport. Among the areas of application of such innovative materials, the manufacturing of contact strips for pantographs of electric rolling stock should be mentioned. Innovation is primarily understood as the self-lubricating property of the working surface of the linings. The linings made of such materials differ from the traditional graphite (coal) ones by the increased content of metal additives, in particular copper, which limits the possibility of their use on electric rolling stock in the countries of the European Union. Regulatory restrictions on the content of copper (35% and 40%) are associated with possible damage to the contact wire, in the case of using overlays with a content of copper (metals) greater than these restrictions. On the railways of Ukraine (countries of the former USSR), there are also restrictions on the use of linings of different types according to the degree of wear of the contact wire, no more than 40 microns is allowed per 10 thousand passes of the locomotive pantograph along the contact wire. These standards are verified during operational and bench tests. The aim of the article is to present the types of tests and compare the obtained values with similar indicators in the case of using a traditional contact strip for pantographs of electric rolling stock. The results obtained confirm the possibility of using innovative linings on iron networks, since the wear of the contact wire during testing is much lower than that of the normative and knife than for traditional types of linings. In addition, during a set of tests, the fact of improving the quality of the working surface of the contact wire was established, which positively affects the extension of the service life of the contact wire. [ABSTRACT FROM AUTHOR]

The application of two-layer coatings is one of the most widely used ways to increase the performance capacity of heavily loaded frictional joints. Design of two-layer coatings for dry sliding friction surfaces and prediction of their efficiency involve the need to develop mathematical models of sliding contact allowing for wear and frictional heating. To achieve this goal, we consider a nonsteady quasi-static contact problem of uncoupled thermoelasticity of a rigid punch in the form of half-plane sliding with a constant velocity over the surface of a two-layer elastic coating bonded on its bottom face to a flat rigid substrate. During the sliding, the punch also penetrates into the two-layer coating in a direction normal to its surface. The punch friction against the coating surface is mathematically described by the Coulomb friction model. The heat flow generated by friction is directed into the coating depth. The frictional sliding contact gives rise to wear of the two-layer coating. The stated problem is solved using the Laplace integral transform. The basic characteristics of each layer, namely, displacements, temperature, and stresses, are presented in the form of the contour integrals of meromorphic functions. The analysis of the properties of the integrand poles in the complex plane of integration and determination of thermoelastic instability domains in the space of problem parameters are followed by evaluation of the contour integrals. The influence of the problem parameters on the sliding contact main characteristics, i.e., temperature, wear, and stresses, is studied. As an example, the wear of a two-layer coating with its upper layer made of titanium nitride and lower layer made of titanium (TiN/Ti) is considered. The numerical results show that by properly selecting the coating layer thicknesses, better wear resistance and lower contact temperature of the coating can be achieved. [ABSTRACT FROM AUTHOR]

Abstract Tailoring a material’s properties for low friction and little wear in a strategic fashion is a long-standing goal of materials tribology. Plastic deformation plays a major role when metals are employed in a sliding contact; therefore, the effects of stacking fault energy and mode of dislocation glide need to be elucidated. Here, we investigated how a decrease in the stacking fault energy affects friction, wear, and the ensuing sub-surface microstructure evolution. Brass samples with increasing zinc concentrations of 5, 15, and 36 wt% were tested in non-lubricated sphere-on-plate contacts with a reciprocating linear tribometer against Si3N4 spheres. Increasing the sliding distance from 0.5 (single trace) to 5,000 reciprocating cycles covered different stages in the lifetime of a sliding contact. Comparing the results among the three alloys revealed a profound effect of the zinc concentration on the tribological behavior. CuZn15 and CuZn36 showed similar friction and wear results, whereas CuZn5 had a roughly 60% higher friction coefficient (COF) than the other two alloys. CuZn15 and CuZn36 had a much smaller wear rate than CuZn5. Wavy dislocation motion in CuZn5 and CuZn15 allowed for dislocation self-organization into a horizontal line about 150 nm beneath the contact after a single trace of the sphere. This feature was absent in CuZn36 where owing to planar dislocation slip band-like features under a 45° angle to the surface were identified. These results hold the promise to help guide the future development of alloys tailored for specific tribological applications.

Depending on the mechanical and thermal energy introduced to a dry sliding interface, the near-surface regions of the mated bodies may undergo plastic deformation. In this work, we use large-scale molecular dynamics simulations to generate "differential computational orientation tomographs" (dCOT) and thus highlight changes to the microstructure near tribological FCC alloy surfaces, allowing us to detect subtle differences in lattice orientation and small distances in grain boundary migration. The analysis approach compares computationally generated orientation tomographs with their undeformed counterparts via a simple image analysis filter. We use our visualization method to discuss the acting microstructural mechanisms in a load- and time-resolved fashion, focusing on sliding conditions that lead to twinning, partial lattice rotation, and grain boundary-dominated processes. Extracting and laterally averaging the color saturation value of the generated tomographs allows us to produce quantitative time- and depth-resolved maps that give a good overview of the progress and severity of near-surface deformation. Corresponding maps of the lateral standard deviation in the color saturation show evidence of homogenization processes occurring in the tribologically loaded microstructure, frequently leading to the formation of a well-defined separation between deformed and undeformed regions. When integrated into a computational materials engineering framework, our approach could help optimize material design for tribological and other deformation problems.. [ABSTRACT FROM AUTHOR]

Objective: The objectives of this study were: first, to compare solute uptake driven by sliding to cyclic uniaxial compression. And secondly, to evaluate the role of the superficial region on passive diffusion to determine if mechanical action is merely overcoming the low permeability of the superficial region or exceeding equilibrium capacity of the tissue.Design: Tests were performed on osteochondral plugs under two types of conditions: cyclic loading (sliding vs axial compression) and unloaded passive diffusion (intact vs superficial zone removed). The articular surfaces were exposed to a fluorescent bath and uptake was quantified from the surface to the subchondral bone using fluorescent microscopy. Primary outcome measures were total mass transfer, mass transfer rate, and surface partition factor.Results: Mass transfer was 2.1-fold higher at 0.5 h for sliding compared to uniaxial compression (p = 0.004). This increased to 4.4-fold at 2 h (p = 0.002). Solute transport for both loading conditions at 2 h had reached or exceeded intact passive diffusion at 12 h. Total mass transport and mass transport per hour was higher in samples without the superficial region compared to intact samples at equilibrium. Rate of mass transfer was not declining for samples subject to sliding indicating solute uptake induced by sliding would exceed passive tissue capacity.Conclusions: These results are the first to quantify solute uptake between two components of joint articulation. The study demonstrates that sliding is a larger driver of solute transport compared to cyclic uniaxial compression. This has implications for cell nutrition, tissue engineering and biochemical signaling. [ABSTRACT FROM AUTHOR]

Real contact area is a challenging phenomenon in tribology, where despite established theoretical models, detailed experimental studies are still lacking. This work is focused on the evolution of the real contact area of multi-asperity steel contacts during sliding, by using sub-micron characterisation of entire multi-asperity contact area and simultaneous measurement of the friction force. Steel-sapphire contact was monitored by using an in-situ optical system in real time during 5 mm of unidirectional sliding in surface roughness range R a = 0.1–1.0 µm and normal loads up to the nominal contact pressure equal to steel yield strength (Y). The results showed that the initial real contact area caused by static loading increased during sliding. At low nominal contact pressure of 0.3 Y , the increase in real contact area was the largest: for R a = 0.1 µm it went from 9.5% of the nominal area under static conditions to 15.0% after sliding, a 56% relative increase, and for R a = 1.0 µm it went from 5.0% to 11.5% after sliding, a 106% increase. The increase in real contact area was smaller at higher nominal contact pressures of 0.6 Y and 1.0 Y. At 1.0 Y for R a = 0.1 µm the real contact area went from 18.0% to 21.8% after sliding and for R a = 1.0 µm it went from 9.4% to 12.9% after sliding. The coefficient of friction increased with roughness at the lowest nominal contact pressure 0.3 Y (for R a = 0.1 µm it was 0.24 and for R a = 1.0 µm it was 0.29) but became independent of roughness at higher contact pressures (on average 0.18). • In-situ measurement of real contact area evolution during 5 mm of sliding. • Whole multi-asperity steel contacts observed using optical method. • Real contact area increased due to sliding from the initial static conditions. • The largest increase from static to sliding conditions was at the lowest load. [ABSTRACT FROM AUTHOR]

The contact heat conduction problem between the rough sliding surfaces was studied through secondary development of finite element software ABAQUS.The thermal contact conductance was defined as a function of the sliding speed,the local contact pressure,material properties and the surface roughness, and the effeecs of three dimensionless parameters were also analyzed.The results reveal that reciprocating motion has a significant influence on contact heat conduction.When heat conduction between sliding surfaces reach a stable stape,the dimensionless mean heat flux per unit time increases with the rising dimensionless parameters η and ω the heat conduction decreases with the reduction of the contact pressure and the growth of the surface roughness.Besides,the variations of the dimensionless average temperature are consistent with those of the dimensionless average heat flux.

The existing level of application of hard coatings due to relatively high deposition temperatures is largely limited to the tool area. However, special interest deserves the possibility of applying contemporary PDV procedures for the conversion of constructional steels used for the manufacture of elements of the most varied tribomehanical sistems.Friction and wear behavior of different types of nodular cast irons in contact with carbon steel were studied. The lubricated sliding line contact was performed on the Pin and Disk tribometer. Value of wear were determined by PQ index. Pins were made of carbon steel without and with three types of coating (TiN, TiZrN, TiAIN) on the tool rake surface.

Competent design decisions for the optimum configuration of a coated contact require the prediction of the stress state developing in the coated body under contact load. Conventional methods of superposition of effects applied in the elasticity of homogenous bodies fail in case of multilayered materials as the response of the latters to point load has only been derived in the frequency domain. A technique for assessment of the elastic response of coated bodies to arbitrary loadings is advanced in this paper, by employing the convolution theorem in the calculation of the stresses and displacements resulting in a sliding contact process. The solution of the elastic frictional contact in full sliding is achieved iteratively, using a state-of-the-art method originally developed for the contact of rough homogenous bodies. Results presented in the literature for the sliding contact of coated bodied are replicated using the newly proposed algorithm. A parametric study is subsequently performed to assess the combined influence of the frictional coefficient, the coating thickness and the elastic modulus mismatch between the coating and the substrate, on the locations and intensity of the maximum von Mises equivalent stress.

Subsurface damage of fused silica optics is one of the major factors restricting the performance of optical systems. The densification-affected deformation and fracture in fused silica under a sliding contact are investigated in this study, via three-dimensional finite element analysis (FEA). The finite element models of scratching with 70.3° conical and Berkovich indenters are established. A refined elliptical constitutive model is used to consider the influence of densification. The finite element models are experimentally verified by elastic recovery, and theoretically verified by hardness ratio. Results of densification and plastic deformation distributions indicate that the accuracy of existent sliding stress field models may be improved if the spherical/cylindrical yield region is replaced by an ellipsoid/cylindroid, and the embedding of the yield region is considered. The initiation sequence, and the locations and stages of radial, median, and lateral cracks are discussed by analyzing the predicted sliding stress fields. Median and radial cracks along the sliding direction tend to be the first cracks that emerge in the sliding and unloading stages, respectively. They coalesce to form a big median–radial crack that penetrates through the entire yield region. The fracture behavior of fused silica revealed in this study is essential in the low-damage machining of fused silica optics.

The compression and shear of an elastic piecewise homogeneous strip with a semi-infinite crack at the interface are considered. The crack is completely closed, and its faces slide with friction. The analytical solution is obtained using the Wiener–Hopf method. The distributions of normal and tangential stresses on the crack line and its continuation are found, and the shear stress intensity factor is determined. It is shown that the crack faces lose contact in their middle when the ratio of shear and compressive intensities exceeds a certain critical value. [ABSTRACT FROM AUTHOR]

Dynamic substructuring methods are initially developed for time-invariant systems to evaluate the dynamic behavior of a complex structure by coupling the component substructures. Sometimes, the component substructures change their position over time, affecting the dynamics of the entire structure. This family of problems can be tackled using substructuring techniques by isolating the time dependency in the coupling conditions among the time-invariant substructures. Mechanical systems, composed of subsystems in relative motion with a sliding interface, can be analyzed using this approach. In previous work, the authors proposed a solution method in the time and frequency domain using this approach under the assumption that the relative sliding motion at the contact interfaces is a-priori known, at least approximately. This assumption implies that the perturbation generated by the friction-induced vibration is neglected. In subsequent work, a more realistic contact assumption was considered to account also for the local vibration of the contact point and the geometric nonlinearity due to the elastic deformation. In this paper, a simplification with respect to the realistic contact assumption is introduced, which neglects the angular variation of the direction normal to the contact interface. The simplified approach is advantageous because it is equally able to highlight the occurrence of friction-induced instabilities, and it reduces the computational burden. The results of the substructuring methods using different contact assumptions are compared with those of a reference numerical method to show how the choice of the contact algorithm allows for tackling a wide range of operating conditions, from simple position-dependent problems up to complex friction-induced vibration phenomena.

This paper presents an artificial intelligence (AI) method for the evolution prediction of surface scratching in sheet metals subjected to contact sliding. Ball-on-disk sliding was employed, and ball diameter, normal load, surface roughness, sliding cycles and the maximum scratching depth in the metal sheet were taken as the fuzzy variables to assess the contributions of individual variables to the surface damage. To improve the prediction accuracy, the quantum-behaved particle swarm optimisation (QPSO) algorithm was further developed and utilised to refine the fuzzy model by optimising the membership functions of the fuzzy variables. It was found that this AI technique, which integrates the fuzzy set theory with the improved QPSO algorithm, can accurately, reliably and efficiently predict the surface scratching evolution, which is otherwise impossible to be implemented. [ABSTRACT FROM AUTHOR]