Lubricants

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3 pages, 156 KiB

Open AccessEditorial

Adhesion, Friction and Lubrication of Viscoelastic Materials

by Giuseppe Carbone and Francesco Bottiglione

Lubricants 2021, 9(3), 23; https://doi.org/10.3390/lubricants9030023 - 25 Feb 2021

Cited by 1 | Viewed by 2430

Abstract

The mechanical behavior of viscoelastic materials is a key factor of many physical phenomena occurring at the interface of contacting bodies [...] Full article

(This article belongs to the Special Issue Adhesion, Friction and Lubrication of Viscoelastic Materials)

Research

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12 pages, 6968 KiB

Open AccessArticle

SPH Modelling of Hydrodynamic Lubrication along Rough Surfaces

by Marco Paggi, Andrea Amicarelli and Pietro Lenarda

Lubricants 2019, 7(12), 103; https://doi.org/10.3390/lubricants7120103 - 21 Nov 2019

Cited by 8 | Viewed by 4547

Abstract

Rough and textured surfaces are of paramount importance for lubrication, both in nature and in technology. While surface roughness relevantly influences both friction and wear, artificial surface texturing improves the performance of slider bearings as an energy efficiency action. The simulation of hydrodynamic [...] Read more.

Rough and textured surfaces are of paramount importance for lubrication, both in nature and in technology. While surface roughness relevantly influences both friction and wear, artificial surface texturing improves the performance of slider bearings as an energy efficiency action. The simulation of hydrodynamic lubrication by taking into account complex surfaces as boundaries requires the use of computational fluid dynamics (CFD) software able to predict the pressure and the velocity profile through the thickness of the fluid and at any point within the 3D domain. In the present study, a CFD–smoothed particle hydrodynamics (SPH) code is applied to simulate hydrodynamic lubrication for a linear slider bearing in the presence of a 3D rough surface, showing the capabilities of CFD–SPH in modelling such complex interaction phenomena. Numerical assessments involve the load capacity, the 3D fields of the velocity vector, and the pressure 3D field (both within the fluid domain and at the fluid–plate interface). Full article

(This article belongs to the Special Issue Adhesion, Friction and Lubrication of Viscoelastic Materials)

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12 pages, 2678 KiB

Open AccessArticle

A Discussion on Present Theories of Rubber Friction, with Particular Reference to Different Possible Choices of Arbitrary Roughness Cutoff Parameters

by Andrea Genovese, Flavio Farroni, Antonio Papangelo and Michele Ciavarella

Lubricants 2019, 7(10), 85; https://doi.org/10.3390/lubricants7100085 - 26 Sep 2019

Cited by 25 | Viewed by 4458

Abstract

Since the early study by Grosch in 1963 it has been known that rubber friction shows generally two maxima with respect to speed—the first one attributed to adhesion, and another at higher velocities attributed to viscoelastic losses. The theory of Klüppel and Heinrich [...] Read more.

Since the early study by Grosch in 1963 it has been known that rubber friction shows generally two maxima with respect to speed—the first one attributed to adhesion, and another at higher velocities attributed to viscoelastic losses. The theory of Klüppel and Heinrich and that of Persson suggests that viscoelastic losses crucially depend on the “multiscale” aspect of roughness and in particular on truncation at fine scales. In this study, we comment a little on both theories, giving some examples using Persson’s theory on the uncertainties involved in the truncation of the roughness spectrum. It is shown how different choices of Persson’s model parameters, for example the high-frequency cutoff, equally fit experimental data on viscoelastic friction, hence it is unclear how to rigorously separate the adhesive and the viscoelastic contributions from experiments. Full article

(This article belongs to the Special Issue Adhesion, Friction and Lubrication of Viscoelastic Materials)

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24 pages, 32021 KiB

Open AccessArticle

Fretting Behavior of Thermoplastic Polyurethanes

by Chao Wang, Andreas Hausberger, Michael Berer, Gerald Pinter, Florian Grün and Thomas Schwarz

Lubricants 2019, 7(9), 73; https://doi.org/10.3390/lubricants7090073 - 23 Aug 2019

Cited by 7 | Viewed by 3807

Abstract

Fretting tests were conducted with five different thermoplastic polyurethanes against a steel ball. Their fretting behaviors were investigated under various test parameters, such as normal load and displacement amplitude. In order to test the sliding performances, tribological tests were conducted using a ring-on-disc [...] Read more.

Fretting tests were conducted with five different thermoplastic polyurethanes against a steel ball. Their fretting behaviors were investigated under various test parameters, such as normal load and displacement amplitude. In order to test the sliding performances, tribological tests were conducted using a ring-on-disc setup. The results show that their fretting behaviors can be related to the dynamic mechanical properties, which were characterized by dynamic mechanical analysis (DMA). The three fretting regimes were identified by means of hysteresis and wear scar analysis. In addition, investigations were carried out until the transition regimes occurred. Different wear processes were revealed for each of the three regimes. Differences were identified using dissipated energy. The profiles of wear scars and the counterparts were analyzed using a microscope. The coefficient of friction was calculated separately for the partial slip and gross slip regimes. In the mixed fretting regime, the coefficient of friction is almost at the same level among the five materials. In the partial slip regime, however, it can be distinguished. Temperature measurements were conducted on the counterparts during the tests. Overall, the material that showed the best tribological properties also performed the best in the fretting tests. Full article

(This article belongs to the Special Issue Adhesion, Friction and Lubrication of Viscoelastic Materials)

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12 pages, 1178 KiB

Open AccessArticle

The Indentation Rolling Resistance in Belt Conveyors: A Model for the Viscoelastic Friction

by Nicola Menga, Francesco Bottiglione and Giuseppe Carbone

Lubricants 2019, 7(7), 58; https://doi.org/10.3390/lubricants7070058 - 5 Jul 2019

Cited by 6 | Viewed by 5122

Abstract

In this paper, we study the steady-state rolling contact of a linear viscoelastic layer of finite thickness and a rigid indenter made of a periodic array of equally spaced rigid cylinders. The viscoelastic contact model is derived by means of Green’s function approach, [...] Read more.

In this paper, we study the steady-state rolling contact of a linear viscoelastic layer of finite thickness and a rigid indenter made of a periodic array of equally spaced rigid cylinders. The viscoelastic contact model is derived by means of Green’s function approach, which allows solving the contact problem with the sliding velocity as a control parameter. The contact problem is solved by means of an accurate numerical procedure developed for general two-dimensional contact geometries. The effect of geometrical quantities (layer thickness, cylinders radii, and cylinders spacing), material properties (viscoelastic moduli, relaxation time) and operative conditions (load, velocity) are all investigated. Physical quantities typical of contact problems (contact areas, deformed profiles, etc.) are calculated and discussed. Special emphasis is dedicated to the viscoelastic friction force coefficient and to the energy dissipated per unit time. The discussion is focused on the role played by the deformation localized at the contact spots and the one in the bulk of the thin layer, due to layer bending. The model is proposed as an accurate solution for engineering applications such as belt conveyors, in which the energy dissipated on the rolling contact of idle rollers can, in some cases, be by far the most important contribution to their energy consumption. Full article

(This article belongs to the Special Issue Adhesion, Friction and Lubrication of Viscoelastic Materials)

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21 pages, 1868 KiB

Open AccessArticle

Modeling the Contact Mechanics of Hydrogels

by Martin H. Müser, Han Li and Roland Bennewitz

Lubricants 2019, 7(4), 35; https://doi.org/10.3390/lubricants7040035 - 11 Apr 2019

Cited by 5 | Viewed by 5115

Abstract

A computationally lean model for the coarse-grained description of contact mechanics of hydrogels is proposed and characterized. It consists of a simple bead-spring model for the interaction within a chain, potentials describing the interaction between monomers and mold or confining walls, and a [...] Read more.

A computationally lean model for the coarse-grained description of contact mechanics of hydrogels is proposed and characterized. It consists of a simple bead-spring model for the interaction within a chain, potentials describing the interaction between monomers and mold or confining walls, and a coarse-grained potential reflecting the solvent-mediated effective repulsion between non-bonded monomers. Moreover, crosslinking only takes place after the polymers have equilibrated in their mold. As such, the model is able to reflect the density, solvent quality, and the mold hydrophobicity that existed during the crosslinking of the polymers. Finally, such produced hydrogels are exposed to sinusoidal indenters. The simulations reveal a wavevector-dependent effective modulus

E^{*} (q)

with the following properties: (i) stiffening under mechanical pressure, and a sensitivity of

E^{*} (q)

on (ii) the degree of crosslinking at large wavelengths, (iii) the solvent quality, and (iv) the hydrophobicity of the mold in which the polymers were crosslinked. Finally, the simulations provide evidence that the elastic heterogeneity inherent to hydrogels can suffice to pin a compressed hydrogel to a microscopically frictionless wall that is undulated at a mesoscopic length scale. Although the model and simulations of this feasibility study are only two-dimensional, its generalization to three dimensions can be achieved in a straightforward fashion. Full article

(This article belongs to the Special Issue Adhesion, Friction and Lubrication of Viscoelastic Materials)

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14 pages, 631 KiB

Open AccessArticle

Linear and Nonlinear Viscoelastic Modulus of Rubber

by T. V. Tolpekina, W. Pyckhout-Hintzen and B.N.J. Persson

Lubricants 2019, 7(3), 22; https://doi.org/10.3390/lubricants7030022 - 8 Mar 2019

Cited by 16 | Viewed by 6714

Abstract

We study the linear and nonlinear viscoelastic properties of two tire tread compounds. We discuss the difference in nonlinear response between the oscillatory tensile and shear modes. We also analyze strain relaxation (creep) data for the same systems. We discuss what type of [...] Read more.

We study the linear and nonlinear viscoelastic properties of two tire tread compounds. We discuss the difference in nonlinear response between the oscillatory tensile and shear modes. We also analyze strain relaxation (creep) data for the same systems. We discuss what type of measurements are most suitable for obtaining the viscoelastic modulus used in rubber friction calculations. Full article

(This article belongs to the Special Issue Adhesion, Friction and Lubrication of Viscoelastic Materials)

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11 pages, 2982 KiB

Open AccessArticle

Modeling Sliding Friction of a Multiscale Wavy Surface over a Viscoelastic Foundation Taking into Account Adhesion

by Yulia Makhovskaya

Lubricants 2019, 7(2), 13; https://doi.org/10.3390/lubricants7020013 - 29 Jan 2019

Cited by 8 | Viewed by 4425

Abstract

A model for calculating the hysteretic friction force for a multilevel wavy surface sliding in dry conditions over the surface of a viscoelastic foundation is suggested, taking into account adhesion force acting in the direction normal to the contact surface. At each scale [...] Read more.

A model for calculating the hysteretic friction force for a multilevel wavy surface sliding in dry conditions over the surface of a viscoelastic foundation is suggested, taking into account adhesion force acting in the direction normal to the contact surface. At each scale level, the contact problem for a 3D periodic wavy indenter is solved by using the strip method to reduce the problem to 2D formulation in a strip. Different regimes of contact and adhesion interaction are possible in each strip, including partial and saturated contact. The friction force is calculated as a sum of two terms. The first term is due to hysteretic losses occurring when asperities of this scale level cyclically deform the viscoelastic foundation during sliding. The second term is the law of friction determined from the solution of the contact problem at the inferior scale level. For the case of a two-level wavy surface, the contribution of both levels into the total friction force is calculated and analyzed depending on the sliding velocity and specific energy of adhesion of the contacting surfaces. Full article

(This article belongs to the Special Issue Adhesion, Friction and Lubrication of Viscoelastic Materials)

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Review

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25 pages, 2080 KiB

Open AccessReview

Adhesion and Friction for Three Tire Tread Compounds

by T. V. Tolpekina and B. N. J. Persson

Lubricants 2019, 7(3), 20; https://doi.org/10.3390/lubricants7030020 - 26 Feb 2019

Cited by 36 | Viewed by 8473

Abstract

We study the adhesion and friction for three tire tread rubber compounds. The adhesion study is for a smooth silica glass ball in contact with smooth sheets of the rubber in dry condition and in water. The friction studies are for rubber sliding [...] Read more.

We study the adhesion and friction for three tire tread rubber compounds. The adhesion study is for a smooth silica glass ball in contact with smooth sheets of the rubber in dry condition and in water. The friction studies are for rubber sliding on smooth glass, concrete, and asphalt road surfaces. We have performed the Leonardo da Vinci-type friction experiments and experiments using a linear friction tester. On the asphalt road, we also performed vehicle breaking distance measurements. The linear and non-linear viscoelastic properties of the rubber compounds were measured in shear and tension modes using two different Dynamic Mechanical Analysis (DMA) instruments. The surface topography of all surfaces was determined using stylus measurements and scanned-in silicon rubber replicas. The experimental data were analyzed using the Persson contact mechanics and rubber friction theory. Full article

(This article belongs to the Special Issue Adhesion, Friction and Lubrication of Viscoelastic Materials)

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Other

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18 pages, 17897 KiB

Open AccessTechnical Note

Friction of Tungsten-Based Coatings of Steel under Sliding Contact

by Matthew David Marko

Lubricants 2019, 7(2), 14; https://doi.org/10.3390/lubricants7020014 - 31 Jan 2019

Cited by 3 | Viewed by 9853

Abstract

An investigation was made to determine the effects of tungsten surface coating on the coefficient of friction of sliding contact between lubricated steel surfaces. The four-ball test was modified, using a tungsten carbide ball bearing in the spindle to cause sliding contact onto [...] Read more.

An investigation was made to determine the effects of tungsten surface coating on the coefficient of friction of sliding contact between lubricated steel surfaces. The four-ball test was modified, using a tungsten carbide ball bearing in the spindle to cause sliding contact onto three hard steel ball bearings coated with tungsten disulfide lamellar dry lubricant coating, with a coating of grease lubrication applied to the ball bearings. The coatings, loads, speed, and grease level were varied to best understand the impact of different conditions on the friction coefficient. Full article

(This article belongs to the Special Issue Adhesion, Friction and Lubrication of Viscoelastic Materials)

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