The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Miroslav Sedláček - One of the best experts on this subject based on the ideXlab platform.
-
Effectiveness and design of surface texturing for different lubrication regimes
Meccanica, 2012Co-Authors: Bojan Podgornik, L. M. Vilhena, Miroslav SedláčekAbstract:The aim of the present research work was to investigate the possibilities of designing surface texturing for different lubrication regimes and to evaluate its effectiveness, especially under starved, boundary and mixed lubrication regimes. This was achieved by combining an experimental tribological investigation with a surface-roughness analysis, a 2D FEM simulation and fluid dynamic modelling. The tribological investigation under unidirectional and reciprocating sliding was focused on the effect of the laser-texturing parameters—including the dimple depth and size, the dimple area density and the contact size—on the coefficient of friction under different lubrication regimes, achieved by varying the sliding speed, the normal load and the Lubricant Viscosity. The results of this investigation show that under starved lubrication conditions the textures resist sliding, resulting in increased friction, as was also indicated by the FEM simulation. Only when a very low dimple density was used could the oil-pocket effect be observed. In boundary lubrication the tribological behaviour of textured surfaces can be related to the surface-roughness parameters ( R _sk and R _ku), with smaller dimples and lower dimple densities leading to reduced levels of friction. The largest gain in terms of friction reduction was observed when approaching full-film lubrication, where fluid dynamic modelling was used to correlate the effect of the dimple depth, size and shape on friction.
-
effectiveness and design of surface texturing for different lubrication regimes
Meccanica, 2012Co-Authors: Bojan Podgornik, L. M. Vilhena, Miroslav SedláčekAbstract:The aim of the present research work was to investigate the possibilities of designing surface texturing for different lubrication regimes and to evaluate its effectiveness, especially under starved, boundary and mixed lubrication regimes. This was achieved by combining an experimental tribological investigation with a surface-roughness analysis, a 2D FEM simulation and fluid dynamic modelling. The tribological investigation under unidirectional and reciprocating sliding was focused on the effect of the laser-texturing parameters—including the dimple depth and size, the dimple area density and the contact size—on the coefficient of friction under different lubrication regimes, achieved by varying the sliding speed, the normal load and the Lubricant Viscosity.
Jason R Stokes - One of the best experts on this subject based on the ideXlab platform.
-
friction of lubricated hydrogels influence of load speed and Lubricant Viscosity
Biotribology, 2021Co-Authors: Lauren Geurds, Jason R StokesAbstract:Abstract Agarose hydrogels are used to study the tribological response of hydrogel materials. We demonstrate that the dynamic frictional behaviour of agarose hydrogels is influenced by their mechanical properties, Lubricant Viscosity and applied load. Within the linear viscoelastic regime of the hydrogels, we find the Stribeck-type framework proposed previously for elastomers and other viscoelastic materials describes their tribological behaviour and dependency on Lubricant Viscosity. However, this breaks down when sufficient stress in the contact is applied so that the hydrogel undergoes yielding (i.e. elastic-plastic deformation). As a result, we find that the friction- normal load relationship differs from the classic trend (F ~ W2/3) observed in elastomers above finite loads. Conventional interpretations of the friction associated with hydrogels should be revised with consideration for the non-linear deformation of the hydrogels. We suggest that theories on viscoelastic lubrication are generally applicable to hydrogels within their linear viscoelastic regime, and propose a conceptual model that considers the effects of bulk mechanical properties and measurement conditions including Lubricant Viscosity, measuring geometry, speed and load.
-
soft tribology lubrication in a compliant pdms pdms contact
Tribology International, 2007Co-Authors: J H H Bongaerts, Kelly Fourtouni, Jason R StokesAbstract:We investigate the influence of surface roughness and hydrophobicity on the lubrication of a soft contact, consisting of a poly(dimethylsiloxane) (PDMS) sphere and a flat PDMS disk. The full Stribeck curves, showing boundary, mixed and elastohydrodynamic (EHL) lubrication, are presented for varying surface roughness and hydrophobicity. It is found that neither surface roughness nor hydrophobicity influence the friction coefficient (p) within the EHL regime. However, increasing surface roughness decreases It in the boundary regime, while extending the limits of the boundary and mixed lubrication regimes to larger values of the product of velocity and Lubricant Viscosity (U eta). The transition from the mixed lubrication to EHL regime is found to take place at lower values of the film thickness parameter A for increasingly rough surfaces. We found Lambda = 0.7 in the case of a root mean square (r.m.s.) surface roughness of 3.6 mu m,suggesting that the effective surface roughness in a compliant compressed tribological contact is lower than that at ambient pressures. Rendering the PDMS surface hydrophilic promotes full-film lubrication and dramatically lowers It in the boundary regime by more than an order of magnitude. This influence of surface wetting is also displayed when examining a range of Lubricants using hydrophobic tribopairs, where the boundary mu decreases with decreasing Lubricant-substrate contact angle. Implications of these measurements are discussed in terms of the creation of model surfaces for biotribological applications. (C) 2007 Elsevier Ltd. All rights reserved.
-
soft tribology lubrication in a compliant pdms pdms contact
Tribology International, 2007Co-Authors: J H H Bongaerts, Kelly Fourtouni, Jason R StokesAbstract:We investigate the influence of surface roughness and hydrophobicity on the lubrication of a soft contact, consisting of a poly(dimethylsiloxane) (PDMS) sphere and a flat PDMS disk. The full Stribeck curves, showing boundary, mixed and elastohydrodynamic (EHL) lubrication, are presented for varying surface roughness and hydrophobicity. It is found that neither surface roughness nor hydrophobicity influence the friction coefficient (p) within the EHL regime. However, increasing surface roughness decreases It in the boundary regime, while extending the limits of the boundary and mixed lubrication regimes to larger values of the product of velocity and Lubricant Viscosity (U eta). The transition from the mixed lubrication to EHL regime is found to take place at lower values of the film thickness parameter A for increasingly rough surfaces. We found Lambda = 0.7 in the case of a root mean square (r.m.s.) surface roughness of 3.6 mu m,suggesting that the effective surface roughness in a compliant compressed tribological contact is lower than that at ambient pressures. Rendering the PDMS surface hydrophilic promotes full-film lubrication and dramatically lowers It in the boundary regime by more than an order of magnitude. This influence of surface wetting is also displayed when examining a range of Lubricants using hydrophobic tribopairs, where the boundary mu decreases with decreasing Lubricant-substrate contact angle. Implications of these measurements are discussed in terms of the creation of model surfaces for biotribological applications. (C) 2007 Elsevier Ltd. All rights reserved.
Bojan Podgornik - One of the best experts on this subject based on the ideXlab platform.
-
Effectiveness and design of surface texturing for different lubrication regimes
Meccanica, 2012Co-Authors: Bojan Podgornik, L. M. Vilhena, Miroslav SedláčekAbstract:The aim of the present research work was to investigate the possibilities of designing surface texturing for different lubrication regimes and to evaluate its effectiveness, especially under starved, boundary and mixed lubrication regimes. This was achieved by combining an experimental tribological investigation with a surface-roughness analysis, a 2D FEM simulation and fluid dynamic modelling. The tribological investigation under unidirectional and reciprocating sliding was focused on the effect of the laser-texturing parameters—including the dimple depth and size, the dimple area density and the contact size—on the coefficient of friction under different lubrication regimes, achieved by varying the sliding speed, the normal load and the Lubricant Viscosity. The results of this investigation show that under starved lubrication conditions the textures resist sliding, resulting in increased friction, as was also indicated by the FEM simulation. Only when a very low dimple density was used could the oil-pocket effect be observed. In boundary lubrication the tribological behaviour of textured surfaces can be related to the surface-roughness parameters ( R _sk and R _ku), with smaller dimples and lower dimple densities leading to reduced levels of friction. The largest gain in terms of friction reduction was observed when approaching full-film lubrication, where fluid dynamic modelling was used to correlate the effect of the dimple depth, size and shape on friction.
-
effectiveness and design of surface texturing for different lubrication regimes
Meccanica, 2012Co-Authors: Bojan Podgornik, L. M. Vilhena, Miroslav SedláčekAbstract:The aim of the present research work was to investigate the possibilities of designing surface texturing for different lubrication regimes and to evaluate its effectiveness, especially under starved, boundary and mixed lubrication regimes. This was achieved by combining an experimental tribological investigation with a surface-roughness analysis, a 2D FEM simulation and fluid dynamic modelling. The tribological investigation under unidirectional and reciprocating sliding was focused on the effect of the laser-texturing parameters—including the dimple depth and size, the dimple area density and the contact size—on the coefficient of friction under different lubrication regimes, achieved by varying the sliding speed, the normal load and the Lubricant Viscosity.
Zhibin Ye - One of the best experts on this subject based on the ideXlab platform.
-
Topology-Engineered Hyperbranched High-Molecular-Weight Polyethylenes as Lubricant Viscosity-Index Improvers of High Shear Stability
Industrial & Engineering Chemistry Research, 2007Co-Authors: Jianli Wang, Zhibin YeAbstract:Chain walking polymerization provides a novel strategy to synthesize highly branched high-molecular-weight polyethylenes with controllable chain topologies ranging from linear to hyperbranched dendritic structure. In this work, we report the performance of this novel series of polyethylenes as Lubricant Viscosity-index improvers. By examining a range of such model polymers possessing various tailor-designed chain topologies, we report the first systematic study on the unique effects of chain topology on the polymers' Viscosity thickening ability and shear stability. It is demonstrated that hyperbranched polyethylenes we prepared possess extremely high shear stability with almost zero shear degradation regardless of their high molecular weight. Our study shows that these hyperbranched polymers have great potential for formulating high-performance Lubricants with superior properties.
I F Machado - One of the best experts on this subject based on the ideXlab platform.
-
effect of laser surface texturing on friction behaviour in elastohydrodynamically lubricated point contacts under different sliding rolling conditions
Tribology International, 2020Co-Authors: G Boidi, I S Tertuliano, Francisco J Profito, W De Rossi, I F MachadoAbstract:Abstract The Laser Surface Texturing (LST) technique has been largely investigated to improve the tribological performance of lubricated contacts. The present contribution is aimed at scrutinizing the influence of three texture configurations fabricated by LST on the tribological performance of elastohydrodynamic (EHD) point contacts under different slide-to-roll ratios (SRR), entrainment velocities and inlet temperatures. Friction experiments were conducted through a series of ball-on-disk tests in the MTM-2 (Mini-Traction Machine) tribometer. Main results showed that the texture configurations promoted significant effects under boundary and mixed lubrication conditions, and also affected the full-film EHD regime at higher temperatures. Furthermore, the tribological performance of textured samples was strongly related to the texture depth. Shallower texture designs (∼0.5 μm) reduced friction compared to untextured material, whereas deeper features (>1 μm) generally led to detrimental results. In general, dimples configuration decreased the lift-off speed and promoted full-film EHD conditions for a larger range of speeds, whereas radial curved grooves yielded to friction reduction under mixed lubrication conditions, moving the transition from boundary to mixed regimes to lower speeds, especially for intermediate Lubricant Viscosity.
