The Experts below are selected from a list of 240 Experts worldwide ranked by ideXlab platform

Izhak Etsion - One of the best experts on this subject based on the ideXlab platform.

  • Static Friction Behavior of Spherical Contact With Ultrathin Soft Coating
    Journal of Tribology, 2020
    Co-Authors: Haibo Zhang, Izhak Etsion
    Abstract:

    Abstract A surprising behavior of ultrathin Soft Coating is described in the relevant literature showing discontinuity (sharp drop) between the static friction coefficients before and after an ultrathin Soft Coating is applied on a harder substrate. Existing finite element (FE) models are unable to explain this unusual behavior since they suffer from convergence problem due to excessive distortion of elements in such ultrathin films. To address this problem, an FE model based on the coupled Eulerian–Lagrangian (CEL) method is presented. This method is able to capture the unexpected behavior of ultrathin Soft Coatings and hence, to provide a reliable scientific explanation to the experimental observation reported in the literature.

  • Strengthening Effect of Soft Thin Coatings
    Journal of Tribology, 2018
    Co-Authors: Roman Goltsberg, Shoam Levy, Yuri Kligerman, Izhak Etsion
    Abstract:

    A finite element analysis was used to study the onset of plasticity of a coated sphere compressed by a rigid flat. This was done for Soft Coatings on a harder substrate. Generally, the results agree very well with the findings in the literature for the opposite case of an indentation of a rigid sphere into a coated flat, with a Soft Coating. In this case, a weakening prevails over the entire range of Coating thicknesses, resulting in critical loads (at yield inception) lower than the critical load of the uncoated contact. However, a surprising strengthening effect was discovered, in this study, for very thin Coating thicknesses resulting in a higher resistance to plasticity, compared to an uncoated sphere. This phenomenon resembles a mirror image of the opposite weakening effect which was reported for very thin hard Coatings. These results may suggest that when very thin Coatings are to be applied in a spherical contact, a Softer, rather than harder, Coating should be considered in order to increase the contact's resistance to plasticity inception.

  • The evolution of fretting wear in a micro-spherical contact
    Wear, 2011
    Co-Authors: Yeoungchin Yoon, Izhak Etsion, Frank E Talke
    Abstract:

    Abstract The effect of surface roughness and materials combination on the evolution of fretting wear in a micro-spherical contact is investigated. The shape of the friction loop, the relative displacement amplitude, the maximum friction coefficient and the dissipated energy were determined as a function of the number of fretting cycles. Wear scars of the interface were analyzed at the completion of each test. It was found that the type of materials combination has a substantial effect on the results while surface roughness effects are small. One of the mating surfaces with a Soft Coating can provide high wear resistance.

Qingbing Dong - One of the best experts on this subject based on the ideXlab platform.

  • contact behaviors of a power law hardening elastic plastic asperity with Soft Coating flattened by a rigid flat
    International Journal of Mechanical Sciences, 2019
    Co-Authors: Bin Zhao, Hanzhang Xu, Xiqun Lu, Qingbing Dong
    Abstract:

    Abstract The contact between a rigid flat and a coated asperity is studied using the finite element method under frictionless and friction condition. The Soft Coating and hard substrate of the asperity are both considered as the power-law hardening elastic–plastic material, which is commonly used in main bearing of the marine engine. The effect of the material and geometrical properties of the Coating, including Young's modulus, yield strength, hardening exponent and original Coating thickness, on the contact behaviors is studied under the frictionless condition. The change of the contact area and Coating thickness in the loading process is explored, and the expressions of the Coating thickness which leads to the maximum weakening effect are obtained. The von Mises stress distribution at yield inception and the maximum stress in the loading process in the Coating are researched respectively. Also, the friction effect on the contact parameters was considered by integrating the empirical friction coefficient value into the contact model. This work would be helpful to find the optimal material and geometrical properties for the Soft Coating on the hard substrate which are power-law hardening elastic–plastic materials.

  • Contact behaviors of a power-law hardening elastic–plastic asperity with Soft Coating flattened by a rigid flat
    International Journal of Mechanical Sciences, 2019
    Co-Authors: Bin Zhao, Ma Xuan, Shi Xiujiang, Qingbing Dong
    Abstract:

    Abstract The contact between a rigid flat and a coated asperity is studied using the finite element method under frictionless and friction condition. The Soft Coating and hard substrate of the asperity are both considered as the power-law hardening elastic–plastic material, which is commonly used in main bearing of the marine engine. The effect of the material and geometrical properties of the Coating, including Young's modulus, yield strength, hardening exponent and original Coating thickness, on the contact behaviors is studied under the frictionless condition. The change of the contact area and Coating thickness in the loading process is explored, and the expressions of the Coating thickness which leads to the maximum weakening effect are obtained. The von Mises stress distribution at yield inception and the maximum stress in the loading process in the Coating are researched respectively. Also, the friction effect on the contact parameters was considered by integrating the empirical friction coefficient value into the contact model. This work would be helpful to find the optimal material and geometrical properties for the Soft Coating on the hard substrate which are power-law hardening elastic–plastic materials.

Joelle Frechette - One of the best experts on this subject based on the ideXlab platform.

  • Criterion for particle rebound during wet collisions on elastic Coatings
    Physical Review Fluids, 2019
    Co-Authors: Matthew R. Tan, Yumo Wang, Joelle Frechette
    Abstract:

    The bouncing of a rigid particle off a Soft Coating in a viscous fluid is analyzed. The Coating thickness moderates the degree to which elasticity affects the rebound criteria (and vice versa) in a fashion distinct from the effect of the elasticity or of the Stokes number.

  • Morphology of Soft and slippery contact via fluid drainage.
    arXiv: Soft Condensed Matter, 2018
    Co-Authors: Yumo Wang, Joelle Frechette
    Abstract:

    The dynamic of contact formation between Soft materials immersed in a fluid is accompanied by fluid drainage and elastic deformation. As a result, controlling the coupling between lubrication pressure and elasticity provides strategies to design materials with reversible and dynamic adhesion to wet or flooded surfaces. We characterize the elastic deformation of a Soft Coating with nanometer-scale roughness as it approaches and contacts a rigid surface in a fluid environment. The lubrication pressure during the approach causes elastic deformation and prevents contact formation. We observe deformation profiles that are drastically different from those observed for elastic half-space when the thickness of the Soft Coating is comparable to the hydrodynamic radius. In contrast, we show that surface roughness favors fluid drainage without altering the elastic deformation. As a result, the coupling between elasticity and slip (caused by surface roughness) can lead to trapped fluid pockets in the contact region.

  • Morphology of Soft and rough contact via fluid drainage.
    Soft matter, 2018
    Co-Authors: Yumo Wang, Joelle Frechette
    Abstract:

    The dynamic of contact formation between Soft materials immersed in a fluid is accompanied by fluid drainage and elastic deformation. As a result, controlling the coupling between lubrication pressure and elasticity provides strategies to design materials with reversible and dynamic adhesion to wet or flooded surfaces. We characterize the elastic deformation of a Soft Coating with nanometer-scale roughness as it approaches and contacts a rigid surface in a fluid environment. The lubrication pressure during the approach causes elastic deformation and prevents contact formation. We observe deformation profiles that are drastically different from those observed for elastic half-space when the thickness of the Soft Coating is comparable to the hydrodynamic radius. In contrast, we show that surface roughness favors fluid drainage without altering the elastic deformation. As a result, the coupling between elasticity and slip (caused by surface roughness) can lead to trapped fluid pockets in the contact region.

  • Elastic deformation of Soft Coatings due to lubrication forces.
    Soft matter, 2017
    Co-Authors: Yumo Wang, Matthew R. Tan, Joelle Frechette
    Abstract:

    Elastic deformation of rigid materials with Soft Coatings (stratified materials) due to lubrication forces can alter the interpretation of dynamic surface forces measurements and prevent contact formation between approaching surfaces. Understanding the role of elastic deformation on the process of fluid drainage is necessary, in particular for the case where one (or both) of the interacting materials consists of a rigid substrate with a Soft Coating. We combine lubrication theory and solid linear elasticity to describe the dynamic of fluid drainage past a compliant stratified boundary. The analysis presented covers the full range of Coating thicknesses, from an elastic foundation to a half-space for an incompressible Coating. We decouple the individual contributions of the Coating thickness and material properties on the elastic deformation, hydrodynamic forces, and fluid film thickness. We obtain a simple expression for the shift in contact position during force measurements that is valid for many experimental conditions. We compare directly the effect of stratification on the out-of-contact deformation to the well-known effect of stratification on indentation. We show that corrections developed for stratification in contact mechanics are not applicable to elastohydrodynamic deformation. Finally, we provide generalized contour maps that can be employed directly to estimate the elastic deformation present in most dynamic surface force measurements.

  • Elastic Deformation of Soft Coatings Due to Lubrication Forces
    2017
    Co-Authors: Yumo Wang, Matthew R. Tan, Joelle Frechette
    Abstract:

    Elastic deformation of rigid materials with Soft Coatings (stratified materials) due to lubrication forces can also alter the interpretation of dynamic surface forces measurements and prevent contact formation between approaching surfaces. Understanding the role of elastic deformation on the process of fluid drainage is necessary, and the case where one (or both) of the interacting materials consists of a rigid substrate with a Soft Coating is still limited. We combine lubrication theory and solid linear elasticity to describe the dynamic of fluid drainage past a compliant stratified boundary. The analysis presented covers the full range of Coating thicknesses, from an elastic foundation to a half-space for an incomressible Coating. We decouple the individual contributions of the Coating thickness and material properties on the elastic deformation, hydrodynamic forces, and fluid film thickness. We obtain a simple expression for the shift in contact position during force measurements that is valid for many experimental conditions. We compare directly the effect of stratification on the out-of-contact deformation to the well-known effect of stratification on indentation. We show that corrections developed for stratification in contact mechanics are not applicable to elastohydrodynamic deformation. Finally, we provide generalized contour maps that can be employed directly to estimate the elastic deformation present in most dynamic surface force measurements.

Frank E Talke - One of the best experts on this subject based on the ideXlab platform.

  • yield inception of a Soft Coating on a flat substrate indented by a rigid sphere
    Surface & Coatings Technology, 2014
    Co-Authors: Andrey Ovcharenko, Wenping Song, I Etsion, Frank E Talke
    Abstract:

    Abstract The yield inception of a deformable half space covered by a Soft Coating and indented by a rigid sphere is studied using the finite element method. A Soft Coating parameter, which controls the yield behavior of this problem, is defined. Dimensionless empirical expressions for the critical load, critical contact area and critical interference at yield inception are derived as functions of the dimensionless Soft Coating parameter. Three different locations of the yield inception of the coated system are observed. A comparison of yield inception behavior for an uncoated substrate and substrates with Soft and hard Coatings is made. A minimum value of dimensionless Coating thickness, which is required to protect the substrate from yielding, is proposed. It is shown that a Coating with low Young's modulus and high yield strength is most desirable for protecting the substrate against yielding.

  • The evolution of fretting wear in a micro-spherical contact
    Wear, 2011
    Co-Authors: Yeoungchin Yoon, Izhak Etsion, Frank E Talke
    Abstract:

    Abstract The effect of surface roughness and materials combination on the evolution of fretting wear in a micro-spherical contact is investigated. The shape of the friction loop, the relative displacement amplitude, the maximum friction coefficient and the dissipated energy were determined as a function of the number of fretting cycles. Wear scars of the interface were analyzed at the completion of each test. It was found that the type of materials combination has a substantial effect on the results while surface roughness effects are small. One of the mating surfaces with a Soft Coating can provide high wear resistance.

M Dominguez - One of the best experts on this subject based on the ideXlab platform.

  • A Diffusion Model for Sword in Sheath Failure Mode in Vapour Grown Carbon Fibers
    Advanced Performance Materials, 1997
    Co-Authors: A Madronero, M Verdu, Ludo Froyen, M Dominguez
    Abstract:

    A peculiar failure mode named “sword in sheath” was reported in previous studies on Vapour Grown Carbon Fibers (VGCFs). It consists in a gliding between the VGCFs catalytic hard core and pyrolitic Soft Coating. This is a very interesting failure mode, looking to the additional work of fracture that it supposes. After knowing that the main difference between the hard core and the Soften cortical carbon is the hydrogen content, some attempts of increase the hydrogen content in the cortical phase are made at the present work via annealing in a pure hydrogen atmosphere. A mathematical model is set up to describe the different phenomena that take place during the annealing. The hydrogen comes to the cortical carbon from the atmosphere and from the inner core. As a consequence of the very significant gradient of hydrogen concentration in the surrounding of the interface core—cortical phase, a shear mechanism is possible under tensile stress. For this reason sword in sheath takes place, mainly in not very thick fibers.

  • A diffusion model for sword in sheath failure mode in vapour grown carbon fibers
    Advanced Performance Materials, 1997
    Co-Authors: A Madronero, M Verdu, Ludo Froyen, M Dominguez
    Abstract:

    A peculiar failure mode named “sword in sheath” was reported in previous studies on Vapour Grown Carbon Fibers (VGCFs). It consists in a gliding between the VGCFs catalytic hard core and pyrolitic Soft Coating. This is a very interesting failure mode, looking to the additional work of fracture that it supposes.