Sliding Interface Research Articles

Comparison of user interfaces for measuring the matrix sentence test on a smartphone

Objective Smartphone-based self-testing could facilitate large-scale data collection and remote diagnostics. For this purpose, the matrix sentence test (MST) is an ideal candidate due to its repeatability and accuracy. In clinical practice, the MST requires professional audiological equipment and supervision, which is infeasible for smartphone-based self-testing. Therefore, it is crucial to investigate the feasibility of self-administering the MST on smartphones, including the development of an appropriate user interface for the small screen size. Design We compared the traditional closed matrix user interface (10 × 5 matrix) to three alternative, newly-developed interfaces (slide, type, wheel) regarding SRT consistency, user preference, and completion time. Study sample We included 15 younger normal hearing and 14 older hearing-impaired participants in our study. Results The slide interface is most suitable for mobile implementation, providing consistent and fast SRTs and enabling all participants to perform the tasks effectively. While the traditional matrix interface works well for most participants, some participants experienced difficulties due to its small size on the screen. Conclusions We propose the newly-introduced slide interface as a plausible alternative for smartphone screens. This might be more attractive for elderly patients that may exhibit more challenges with dexterity and vision than our test subjects employed here.

Synergistic Effect of Microconvex Texture and Particle Medium on the Tribological Property of the Rubber Sliding Interface.

In this study, we examined how surface topography and particle medium interact to affect the tribological performance of rubber sliding interfaces, uncovering the mechanisms of particle lubrication under various conditions. We found that microtextured surfaces, created using a mold transfer method, modestly reduced the friction coefficient of rubber under both dry and lubricated states, primarily by altering the real contact area. Additionally, the presence of different microconvex textures on the surface topography significantly influenced rubber's tribological properties. Our three-dimensional morphological analysis revealed that microtextured rubber surfaces with higher Sa, Sku, and Sal and lower Str values consistently showed lower friction coefficients during sliding. The friction mechanism was attributed to the combined effects of the material properties, surface topography, and contact area. With the addition of a particle medium, the dry friction coefficient of the rubber interface decreased but exhibited an initial increase, followed by a decrease with increasing particle diameter. When particles were mixed with a water-based cutting fluid, the concentration, diameter, and wettability of the particles significantly impacted the tribological properties due to the synergistic effects of surface topography and particle lubrication. This work enhances our understanding of tribological control for viscoelastic materials through surface design, providing a theoretical basis for the tribological optimization of rubber surfaces.

Analysis of Torsional Vibration in a Fractured Poroelastic Half-Space Coated with Metal Foam and Sliding Interfaces

Metal foams are highly useful in industries because of their lightweight, energy and vibration absorption properties. This study investigated the propagation of torsional waves in an elastic layer over a fluid-saturated fractured poroelastic half-space with a metal foam coated layer. It is assumed that the interfaces are in sliding contact with two different sliding parameters. The coated layer is closed-cell aluminium foam. We use the separation variable technique and the Bessel function to solve the equation of motion in different layers. The displacement components are written in terms of the second kind Whittaker functions. Using an asymptotic formulation of the Whittaker function and appropriate boundary conditions, the dispersion equation is derived in terms of the determinant. The control of the vibration due to the metal foam-coated layer is one of the important goals of this study. Also, numerical and graphical analyses have been done with the help of Mathematica software to see the effect of different parameters on torsional wave propagation. It is found that the presence of coated metal foam layer decreases the phase velocity of the torsional wave propagation. The work may be helpful in the seismology, automobile, and aerospace industries.

Electrically suppressed hysteresis at nanoscale sliding interface

Contact adhesion hysteresis is widely observed between two quasi-static interfaces of micro-nano devices. Representatively, the hysteresis behavior has been found at the nanoscale sliding interface, which poses a significant obstacle to enhancing the tribological properties of the interfaces. In this paper, the hysteresis suppression mechanism by employing interfacial potential is investigated with a hard disk drive. Applying an external voltage to the head-disk interface results in the suppression of sliding contact hysteresis, which is also theoretically studied using a lumped parameter model. The motion state map indicates that inhibition of transformation from freedom flying state to bouncing state leads to the suppression of contact hysteresis. Subsequent wear experiments confirm that applying an external voltage is an effective method to enhance wear durability due to the reduction of hysteresis.

Modeling of multi-phase, multi-fluid flows with applications to marine hydrokinetic turbines

In this paper, a numerical formulation for modeling turbulent multi-phase, multi-fluid flows over real-life marine devices is presented. The flow field is governed by the Navier–Stokes equations with an Arbitrary-Lagrangian–Eulerian (ALE) description of the continuum for handling independent domain movements. The multi-phase phenomenon is modeled for an iso-thermal homogeneous mixture of water vapor and liquid phases using a transport equation for the vapor volume fraction. The multi-fluid phenomenon is modeled using the level-set method where a geometric function, namely, the signed distance function (SDF) describes the level-set field. Turbulence modeling is handled in the context of the variational multiscale (VMS) method resulting in an ALE-VMS formulation for multi-phase, multi-fluid flows over moving hydrodynamic objects. Several augmentations to the formulation are discussed in this paper including the sliding interface (SI) operator and its role in enforcing the compatibility of solution fields between in-contact computational subdomains during the different steps of the solution. This formulation is validated against experimental data for a real-life horizontal-axis marine turbine under different flow conditions including single-phase flows, multi-phase flows and multi-fluid flows. The performance of the turbine as well as the expected flow behaviors are compared to the experimental data with success. An additional case is simulated for a multi-phase, multi-fluid flow condition showing the capabilities and robustness of the presented numerical formulation.

Gel-mediated chemo-mechanical control of calcium carbonate crystal formation

The production of synthetic crystals with controlled shapes and properties is an enticing prospect, yet, the production of such materials is an ongoing challenge. Here, we present a strategy for chemo-mechanically directing the growth of crystals with non-equilibrium structures using a custom-designed double-diffusion cell. We combine chemical additives (e.g., Mg2+ ions) and mechanical confinement (e.g., hydrogel networks) to modulate the growth of calcium carbonate crystals. Specifically, the combination of Mg2+ ions with a strong agarose gel results in calcitic structures, at the gel-glass slide interface, with distinct fried egg-like morphologies and radial or Maltese-cross extinction patterns. In contrast, precipitation with only Mg2+ or agarose results in aragonite spherulites or squished calcite rhombohedra, respectively. Raman spectroscopy and energy dispersive spectroscopy of the “fried eggs” reveals that they are composed of Mg-calcite, which becomes less disordered over time, and the “egg whites” make this transition before the “yolks”. We propose that the “fried eggs” form due to a spherulitic growth process molded by the crystallization-induced delamination of the gel away from the glass slide at the gel-glass interface. In support of the importance of the gel-glass interface, the “fried eggs” do not form when the glass slide is treated with a hydrophobic silane, suppressing heterogeneous nucleation and weakening the interfacial adhesion between the gel and glass, making it easier for the gel to delaminate, thus reducing the confinement effect. As such, this work highlights the important chemo-mechanical role that gel environments can play in crystal formation.

Consideration of Rotational Motion in the Proper Generalized Decomposition by a Sliding Interface Technique

The simulation of rotating electrical machines, particularly in the development process, involves many parameters, such as the current excitation, permanent magnet materials, and the relative rotor position. To reduce the computational effort related to a large number of degrees of freedom (DOFs), the proper generalized decomposition (PGD) can be employed. Although the mentioned reduction technique is able to efficiently cope with parameter variations, it is limited to conformal meshes. However, the consideration of moving parts in the model for the simulation of rotating electrical machines is a necessity to characterize the machine’s behavior. For this purpose, the sliding interface technique, based on Lagrange multipliers (LMs) can be utilized. In this contribution, the sliding interface technique, which imposes no restrictions on the finite element discretization of the interface between stator and rotor, is combined with the PGD to lift the restriction of the latter to conformal meshes while keeping the symmetry and positive definiteness of the system without the creation of additional elements. This approach enables the parametric simulation of rotating electrical machines by the PGD.

Superlow Friction of a-C:H Coatings in Vacuum: Passivation Regimes and Structural Characterization of the Sliding Interfaces

A combination of atomistic simulations and vacuum tribometry allows atomic-scale insights into the chemical structure of superlubricious hydrogenated diamond-like carbon (a-C:H) interfaces in vacuum. Quantum molecular dynamics shearing simulations provide a structure-property map of the friction regimes that characterize the dry sliding of a-C:H. Shear stresses and structural properties at the sliding interfaces are crucially determined by the hydrogen content CH in the shear zone of the a-C:H coating. Extremely small CH (below 3 at.%) cause cold welding, mechanical mixing and high friction. At intermediate CH (ranging approximately from 3 to 20 at.%), cold welding in combination with mechanical mixing remains the dominant sliding mode, but some a-C:H samples undergo aromatization, resulting in a superlubricious sliding interface. A further increase in CH (above 20 at.%) prevents cold welding completely and changes the superlubricity mechanism from aromatic to hydrogen passivation. The hydrogen-passivated surfaces are composed of short hydrocarbon chains hinting at a tribo-induced oligomerization reaction. In the absence of cold welding, friction strongly correlates with nanoscale roughness, measured by the overlap of colliding protrusions at the sliding interface. Finally, the atomistic friction map is related to reciprocating friction experiments in ultrahigh vacuum. Accompanying X-ray photoelectron and Auger electron spectroscopy (XPS, XAES) analyses elucidate structural changes during vacuum sliding of a hydrogen-rich a-C:H with 36 at.% hydrogen. Initially, the a-C:H is covered by a nanometer-thick hydrogen-depleted surface layer. After a short running-in phase that results in hydrogen accumulation, superlubricity is established. XPS and XAES indicate a non-aromatic 1–2-nm-thick surface layer with polyethylene-like composition in agreement with our simulations.

In situ Friction-Induced Copper Nanoparticles at the Sliding Interface Between Steel Tribo-Pairs and their Tribological Properties

This work investigates in situ friction-generated copper nanoparticles at the sliding in the precursor solution of copper formate tetrahydrate and octylamine, which induced by frictional heat, it can effectively mitigate wear while slightly reducing friction coefficient. The frictional heat between tribo-pairs accelerated the decomposition of the precursor into in situ generated copper nanoparticles, as indicated by black stripe regions on the worn surface. This study opened a new strategy to achieve low friction and wear through the thermal decomposition of the liquid lubricants during sliding.

Probing Tribological Behaviors of Cr-DLC in Corrosion Solution by Tailoring Sliding Interface

Friction pairs are regarded significantly as one unified system to avert excessive energy and material loss caused by friction in harsh environment taking into account of its complicated physical and chemical process in the friction interface. Here, we carried out the experiment of Cr-doped diamond-like carbon (Cr-DLC) sliding against different counterparts in hydrochloric acid (HCl) in order to find a better solution for the tribocorrosion failure of Cr-DLC in harsh environment. The results indicated that the material of counterparts and interfacial tribochemical products had significant impact on the friction behavior of Cr-DLC. The friction coefficients of Cr-DLC sliding against different counterparts were highly dependent with the associated Hertzian contact radius calculated by the Hertzian contact theory, while the wear rates were related to the interfacial tribochemical products in HCl. Moreover, the hardness ratio and the elastic energy density of friction pair were introduced to analysis the wear behavior of Cr-DLC film sliding against mated materials. All of the results indicated that the Cr-DLC film sliding against tetrahedral amorphous carbon (ta-C) showed the most outstanding tribological performance. Understanding the fundamental mechanism of Cr-DLC film sliding against different counterpart materials would expand the practical application of Cr-DLC thin film in corrosive environment.

Scanning Probing of the Tribovoltaic Effect at the Sliding Interface of Two Semiconductors.

Contact electrification (CE or triboelectrification) is a common phenomenon, which can occur for almost all types of materials. In previous studies, the CE between insulators and metals has been widely discussed, while CE involving semiconductors is only recently. Here, a tribo-current is generated by sliding an N-type diamond coated tip on a P-type or N-type Si wafers. The density of surface states of the Si wafer is changed by introducing different densities of doping. It is found that the tribo-current between two sliding semiconductors increases with increasing density of surface states of the semiconductor and the sliding load. The results suggest that the tribo-current is induced by the tribovoltaic effect, in which the electron-hole pairs at the sliding interface are excited by the energy release during friction, which may be due to the transition of electrons between the surface states during contact, or bond formation across the sliding interface. The electron-hole pairs at the sliding interface are subsequently separated by the built-in electric field at the PN or NN heterojunctions, which results in a tribo-current, in analogy to that which occurs in the photovoltaic effect.

In Situ Friction-Induced Graphene Originating from Methanol at the Sliding Interface between the WC Self-Mated Tribo-Pair and Its Tribological Performance.

Alcohols are reported to have superlubricity at low loads during sliding; however, their lubricity under high loads has rarely been reported. Meanwhile, the lubrication mechanism of alcohols under high loads is still not well understood. Here, we first report the lubricity of methanol under 98 N and 1450 rpm and demonstrate the formation of graphene and fullerene-like nanostructures induced by tribochemical reactions. Results show that the lubrication mechanism was mainly attributed to the friction-induced graphene under boundary lubrication condition. Besides that, the wear rate of a YG8 hard alloy ball mainly occurred at the run-in processes, and the friction-induced graphene effectively inhibited further wear after the run-in processes. The formation mechanism of graphene was well investigated, and the flash temperature rise and catalyst (WC, WO2, and WO3) were the major causes for the formation of graphene.

Effect of Wear on the Evolution of Contact Pressure at a Bimaterial Sliding Interface

The eigenfunction method pioneered by Galin (J Appl Math Mech 40: 981–986, 1976) is extended to provide a general solution to the transient evolution of contact pressure and wear of two sliding elastic half-planes, under the assumption that there is full contact and that the Archard–Reye wear law applies. The governing equations are first developed for sinusoidal profiles with exponential growth rates. The contact condition and the wear law lead to a characteristic equation for the growth rate and more general solutions are developed by superposition. The case of general initial profiles can then be written down as a Fourier integral. Decay rates increase with wavenumber, so fine-scale features are worn away early in the process. Qualitative features of the problem are governed by two dimensionless wear coefficients, which for many material combinations are small compared with unity. If one of the bodies does not wear and is non-plane, the system evolves to a non-trivial steady state in which the wearing body acquires a profile which migrates over its surface.

A Comparative Study on Effectiveness of Using Horasan Mortar as a Pure Friction Sliding Interface Material

In this study, the possibility to use Horasan mortar as a sliding interface material for pure friction aseismic isolation system is investigated. Both experimental and numerical studies are conducted to examine the effectiveness of using this material in structural isolation systems of buildings with no overturning moment, as it has shown some attractive experiences in time based on the existing related literature. Responses of four storey lightweight building are numerically investigated by finite element modelling in MATLAB; whereas the University Consortium on Instructional Shake Table (UCIST) is used to study the responses of the same building during experimental works. Comparison of both studies is shown to be in a good agreement in terms of resulting structural response accelerations, velocity and displacements. Approximately 28 - 31 % reduction of base floor acceleration is achieved; and the maximum sliding velocity and displacement are found to lie between 0.33-0.45 m/sec and 0.0353-0.0559 m respectively; which fall within the recommended standards’ limits. As a result, these findings demonstrate the effectiveness of using Horasan mortar as friction interface material which has additionally gained experience in more than ten centuries.

A Comparative Study on Effectiveness of Using Horasan Mortar as a Pure Friction Sliding Interface Material

In this study, the possibility to use Horasan mortar as a sliding interface material for pure friction aseismic isolation system is investigated. Both experimental and numerical studies are conducted to examine the effectiveness of using this material in structural isolation systems of buildings with no overturning moment, as it has shown some attractive experiences in time based on the existing related literature. Responses of four storey lightweight building are numerically investigated by finite element modelling in MATLAB; whereas the University Consortium on Instructional Shake Table (UCIST) is used to study the responses of the same building during experimental works. Comparison of both studies is shown to be in a good agreement in terms of resulting structural response accelerations, velocity and displacements. Approximately 28 - 31 % reduction of base floor acceleration is achieved; and the maximum sliding velocity and displacement are found to lie between 0.33-0.45 m/sec and 0.0353-0.0559 m respectively; which fall within the recommended standards’ limits. As a result, these findings demonstrate the effectiveness of using Horasan mortar as friction interface material which has additionally gained experience in more than ten centuries.

The Impact of the Deformation Phenomenon on the Process of Lubricating and Improving the Efficiency Between the Slipper and Swashplate in Axial Piston Machines

The process of lubricating a sliding interface between the Slipper and the swashplate in axial piston machines is a major solution for the improvement of its efficiency and performance. This lubrication process is largely influenced by the phenomenon of the thermoelastic and hydrodynamic deformation of the solid-liquid structure on this interface. This paper is mainly based on the study of the causes and processes of deformation, as well as the conditions of improvement of this deformation by the lubrication on the interface slipper/swashplate. For this, a mathematical model detailing the model deformation elastic and hydrodynamic on the slide interface Slipper/swashplate is made. The major parameters in the deformation such as the loads and the oil size are simulated. The energy equation is solved to understand the effect of the temperature on the oil behavior. The Reynold equation is solved to simulate the hydrodynamic pressure between the Slipper and the swashplate. A test rig is specially built to measure the torques and loads, the pressure, the oil height, and the temperature between the Slipper and the swashplate for different input conditions. The comparison between the simulation results and the experimental ones proves the coherence and the precision of the results of this research. Finally, some propositions to improve the performance of the axial piston machines for the lubrication mechanism on the Slipper/swashplate interface are given.

A Sliding Interface Approach with Application to Twin-Screw Extruders

A Sliding Interface Approach with Application to Twin-Screw Extruders

Supercritical focusing coherent anti-Stokes Raman scattering microscopy for high-resolution vibrational imaging.

We report the development of, to the best of our knowledge, a novel supercritical focusing coherent anti-Stokes Raman scattering (SCF-CARS) microscopy for high-resolution vibrational imaging. Two optimized phase patterns with a combination of concentric rings with an alternative 0 and π phase are generated by using a spatial light modulator and applied to the pump beam for minimizing its focal spot size. One of the phase patterns is for both the lateral and axial resolution enhancement, and the other can further improve the lateral resolution, but it sacrifices the axial resolution to some extent. We demonstrate this high-resolution SCF-CARS microscopy technique by imaging the polymethyl methacrylate (PMMA) nano-cylinder on a microscope slide and glass-air interface, as well as biomedical samples, for example, tooth.

Thixotropic Mechanics in Soft Hydrated Sliding Interfaces

Soft hydrated permeable surfaces exhibit unique lubrication behaviors, including recently discovered frictional hysteresis. This duration-dependent frictional effect can be analogous to the thixotropic fluid response under shear-driven Couette flow. We illustrate torque-speed hysteresis loops using tribo-rheometry measurements between an aluminum annulus and polyacrylamide surface. Frictional torque response was measured under stepwise sliding speed increments at five different step durations. The torque-sliding speed curves exhibit hysteresis loops and the shape of the hysteresis loops depends on step durations. Longer duration shows greater hysteresis with higher average friction. Torque curves at highest speeds converge to one line with a power law exponent of α = 0.7. Based on the experimental data, a hydrogel lubrication model was developed using a thixotropic fluid model, where viscosity change is described as a competition between structural buildup and breakdown. Simulation using the model correlates well with the experimental results, indicating the existence of effective structural change on the hydrogel surface.

Contrasting Roles of Water at Sliding Interfaces between Silicon-Based Materials: First-Principles Molecular Dynamics Sliding Simulations

It is known that the wear of silicon-based materials is due to the tribochemical reaction with water at the sliding interface, but the detailed mechanisms remain under debate. In this study, we used a first-principles molecular dynamics method to investigate the tribochemical wear mechanism. When a small amount of water was present at the sliding interface, the formation of interfacial bridge bonds connecting the two surfaces was observed. These bonds transmitted shear force to the surfaces that induced strain therein. The strained surface Si–O bonds subsequently reacted with water (Si–O–Si + H2O → Si–OH + Si–OH), that is, the hydrolysis reaction occurred. Because the hydrolysis reaction resulted in dissociation of the surface Si–O bonds, water promoted tribochemical wear. However, when a large amount of water was present, it separated the two surfaces. The water thereby suppressed the formation of interfacial bridge bonds and in turn the hydrolysis of Si–O bonds and thus tribochemical wear. Our results i...