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Robert Lewis Reuben - One of the best experts on this subject based on the ideXlab platform.

  • The effect of film thickness on initial Friction of elastic-plastically rough surface with a soft thin metallic film
    Journal of Tribology, 2002
    Co-Authors: Zhiqiang Liu, Anne Neville, Robert Lewis Reuben
    Abstract:

    The effect of a deposited soft thin metallic film on Friction properties of a hardened steel substrate has been investigated experimentally and theoretically. The dependency of the film thickness and contact load on the Static Friction Coefficient is presented. The experimental observations show that deformation of the film in contact was plastic, thereby confirming the assumption of the theoretical calculation. The effect of the film thickness on the contact area has been analyzed. A model for calculating the Static Friction Coefficient of contacting rough surfaces in the presence of a soft thin film has been used. Results from the numerical calculations have been compared with the present Static Friction measurements performed on a pin on plate reciprocating apparatus. The rise in Friction that occurs with increasing thickness for very thin films is discussed in detail. The calculated results, which predict the correct trend of the Friction behavior from the present experiment, cover an extremely large range of F/A n E from 10 -12 to 10 -2 , where three different dependencies of F/A n E on the Static Friction Coefficient can be identified. An investigation into the discrepancy between the calculated and experimental values for the Static Friction Coefficient μ suggests that an accurate prediction of the magnitude of μ depends to a great extent on the level of accuracy in measuring the value of the constant ξ, the effective hardness of the film.

  • Static Friction Modeling in the Presence of Soft Thin Metallic Films
    Journal of Tribology, 2001
    Co-Authors: Zhiqiang Liu, Anne Neville, Robert Lewis Reuben
    Abstract:

    A numerical model is presented for computing the Static Friction Coefficient of rough surfaces with a soft thin film. In the calculation, an improved model, based on that due to Derjaguin et al., is used in conjunction with an elastic-plastic contact model for contact with a soft coating. The effects of the film thickness and surface roughness on the Static Friction Coefficient and contact are investigated. The numerical results reflect published experimental observations and show the Static Friction Coefficient depends strongly on surface film thickness, external force and surface roughness. The Static Friction Coefficient (μ) increases with the surface film thickness when the plasticity index Ψ≥0.5 whilst μ increases with decreasing film thickness in the very thin film regime when (=0.25 and F/A n E< 10 4 . For real rough surfaces contact and Friction behavior is probably heavily influenced by the existence of such soft, thin surface films, which increase the contact area due to plastic deformation of the film and the contact stiffness of the surface in the case of thin film and light load.

Zhiqiang Liu - One of the best experts on this subject based on the ideXlab platform.

  • The effect of film thickness on initial Friction of elastic-plastically rough surface with a soft thin metallic film
    Journal of Tribology, 2002
    Co-Authors: Zhiqiang Liu, Anne Neville, Robert Lewis Reuben
    Abstract:

    The effect of a deposited soft thin metallic film on Friction properties of a hardened steel substrate has been investigated experimentally and theoretically. The dependency of the film thickness and contact load on the Static Friction Coefficient is presented. The experimental observations show that deformation of the film in contact was plastic, thereby confirming the assumption of the theoretical calculation. The effect of the film thickness on the contact area has been analyzed. A model for calculating the Static Friction Coefficient of contacting rough surfaces in the presence of a soft thin film has been used. Results from the numerical calculations have been compared with the present Static Friction measurements performed on a pin on plate reciprocating apparatus. The rise in Friction that occurs with increasing thickness for very thin films is discussed in detail. The calculated results, which predict the correct trend of the Friction behavior from the present experiment, cover an extremely large range of F/A n E from 10 -12 to 10 -2 , where three different dependencies of F/A n E on the Static Friction Coefficient can be identified. An investigation into the discrepancy between the calculated and experimental values for the Static Friction Coefficient μ suggests that an accurate prediction of the magnitude of μ depends to a great extent on the level of accuracy in measuring the value of the constant ξ, the effective hardness of the film.

  • Static Friction Modeling in the Presence of Soft Thin Metallic Films
    Journal of Tribology, 2001
    Co-Authors: Zhiqiang Liu, Anne Neville, Robert Lewis Reuben
    Abstract:

    A numerical model is presented for computing the Static Friction Coefficient of rough surfaces with a soft thin film. In the calculation, an improved model, based on that due to Derjaguin et al., is used in conjunction with an elastic-plastic contact model for contact with a soft coating. The effects of the film thickness and surface roughness on the Static Friction Coefficient and contact are investigated. The numerical results reflect published experimental observations and show the Static Friction Coefficient depends strongly on surface film thickness, external force and surface roughness. The Static Friction Coefficient (μ) increases with the surface film thickness when the plasticity index Ψ≥0.5 whilst μ increases with decreasing film thickness in the very thin film regime when (=0.25 and F/A n E< 10 4 . For real rough surfaces contact and Friction behavior is probably heavily influenced by the existence of such soft, thin surface films, which increase the contact area due to plastic deformation of the film and the contact stiffness of the surface in the case of thin film and light load.

Anne Neville - One of the best experts on this subject based on the ideXlab platform.

  • The effect of film thickness on initial Friction of elastic-plastically rough surface with a soft thin metallic film
    Journal of Tribology, 2002
    Co-Authors: Zhiqiang Liu, Anne Neville, Robert Lewis Reuben
    Abstract:

    The effect of a deposited soft thin metallic film on Friction properties of a hardened steel substrate has been investigated experimentally and theoretically. The dependency of the film thickness and contact load on the Static Friction Coefficient is presented. The experimental observations show that deformation of the film in contact was plastic, thereby confirming the assumption of the theoretical calculation. The effect of the film thickness on the contact area has been analyzed. A model for calculating the Static Friction Coefficient of contacting rough surfaces in the presence of a soft thin film has been used. Results from the numerical calculations have been compared with the present Static Friction measurements performed on a pin on plate reciprocating apparatus. The rise in Friction that occurs with increasing thickness for very thin films is discussed in detail. The calculated results, which predict the correct trend of the Friction behavior from the present experiment, cover an extremely large range of F/A n E from 10 -12 to 10 -2 , where three different dependencies of F/A n E on the Static Friction Coefficient can be identified. An investigation into the discrepancy between the calculated and experimental values for the Static Friction Coefficient μ suggests that an accurate prediction of the magnitude of μ depends to a great extent on the level of accuracy in measuring the value of the constant ξ, the effective hardness of the film.

  • Static Friction Modeling in the Presence of Soft Thin Metallic Films
    Journal of Tribology, 2001
    Co-Authors: Zhiqiang Liu, Anne Neville, Robert Lewis Reuben
    Abstract:

    A numerical model is presented for computing the Static Friction Coefficient of rough surfaces with a soft thin film. In the calculation, an improved model, based on that due to Derjaguin et al., is used in conjunction with an elastic-plastic contact model for contact with a soft coating. The effects of the film thickness and surface roughness on the Static Friction Coefficient and contact are investigated. The numerical results reflect published experimental observations and show the Static Friction Coefficient depends strongly on surface film thickness, external force and surface roughness. The Static Friction Coefficient (μ) increases with the surface film thickness when the plasticity index Ψ≥0.5 whilst μ increases with decreasing film thickness in the very thin film regime when (=0.25 and F/A n E< 10 4 . For real rough surfaces contact and Friction behavior is probably heavily influenced by the existence of such soft, thin surface films, which increase the contact area due to plastic deformation of the film and the contact stiffness of the surface in the case of thin film and light load.

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

  • model for the Static Friction Coefficient of spherical contact with a soft metal coating
    SN Applied Sciences, 2020
    Co-Authors: Haibo Zhang, Zhou Chen, Izhak Etsion
    Abstract:

    An elastic–plastic spherical contact with soft metallic coating under combined normal and tangential loading is studied by finite element analysis. Full-stick contact condition is assumed and sliding inception is related to vanishing tangential stiffness of the contact junction. Previously observed, both experimentally and theoretically, effects of increasing coating thickness on Static Friction Coefficient that were published in the literature are thoroughly explained here, to the authors’ best knowledge, for the first time. These effects include initial sharp drop of Friction as soon as a thinnest coating film is applied, followed by a transitional behavior from decrease to increase of Friction when the coating thickness is continuously increased. An intensive parametric study is performed and the effects of substrate and coating material properties on the Static Friction Coefficient are revealed and thoroughly explained. An empirical expression for the Static Friction Coefficient is derived along with the values for optimum coating thickness that provides the minimum Friction Coefficient.

  • Model for the Static Friction Coefficient in a full stick elastic-plastic coated spherical contact
    Friction, 2018
    Co-Authors: Zhou Chen, Izhak Etsion
    Abstract:

    Finite element analysis is used to investigate an elastic-plastic coated spherical contact in full stick contact condition under combined normal and tangential loading. Sliding inception is associated with a loss of tangential stiffness. The effect of coating thickness on the Static Friction Coefficient is intensively investigated for the case of hard coatings. For this case, with the increase in coating thickness, the Static Friction Coefficient first increases to its maximum value at a certain coating thickness, thereafter decreases, and eventually levels off. The effect of the normal load and material properties on this behavior is discussed. Finally, a model for the Static Friction Coefficient as a function of the coating thickness is provided for a wide range of material properties and normal loading.

  • Comment on Leonardo da Vinci's Friction Experiments: An Old Story Acknowledged and Repeated
    Tribology Letters, 2015
    Co-Authors: Izhak Etsion
    Abstract:

    It is very impressive to read the most recently published reproduction of Leonardo da Vinci’s Friction experiments [1]. In Table 1 of this paper, the authors reported measured average values of Static Friction Coefficient for various roughness levels of three types of wood surfaces. These values are between 0.25 and 0.29 for rough (Ra [ 3000 nm) surfaces, and they increase up to 0.72 for smooth (Ra = 200 nm) surfaces. Moreover, the lowest Friction Coefficient value of 0.25 is in agreement with da Vinci’s Friction experiments from 500 years ago. In these experiments, da Vinci also found that the Friction Coefficient is independent of the apparent contact area and the applied load. An interesting question is whether such effects of surface roughness on Friction Coefficient can be predicted by a theoretical model. A first hint in this direction was probably provided by Greenwood and Williamson [2] in 1966. In this seminal paper, a model (known as the GW model) for the elastic contact of rough surfaces is provided, showing that the real contact area is independent of the apparent contact area and is linearly proportional to the applied load. A plasticity index having the general form w = (E/H)(r/r), which was first introduced in the GW model, provides a measure of the plasticity level of the rough surface contact. In this index, E and H indicate modulus of elasticity and hardness, respectively, while r and r represent, respectively, standard deviation of asperity heights and average tip curvature of the asperities of the rough surface contact. The softer and rougher the rough surface is, the larger the plasticity index is. The first attempt to theoretically predict Static Friction of contacting rough surfaces was probably made by Chang et al. in 1988 [3]. In this model, it was shown that at low to moderate values of the plasticity index the Static Friction Coefficient l decreases with increasing applied load, but it becomes practically independent of the applied load as the plasticity index becomes large enough. Due to the oversimplifying assumptions made in this first crude model, the values of the Static Friction Coefficient were severely underestimated already at w = 2.5. The model of Ref. [3] has been gradually improved over the years by refining its original assumptions [4] and gaining further insight on how to handle a single spherical asperity under combined normal and tangential loading [5]. The Static Friction Coefficient model of Ref. [5] was further validated experimentally in Ref. [6]. Finally, based on the above improvements, Cohen et al. [7] presented a Static Friction model to cover plasticity index values up to w = 8, and more recently, Li et al. [8] extended this model up to w = 32. The results of Ref. [8] are shown in Fig. 1 in solid lines (in comparison with those from Ref. [7] in dashed line). An empirical relation of the Static Friction Coefficient l as a function of the dimensionless applied load and plasticity index that was offered in [8] is given by Eq. (1) in the form

  • A Model for Contact and Static Friction of Nominally Flat Rough Surfaces Under Full Stick Contact Condition model for elastic-plastic nominally flat contacting rough surfaces under combined
    2009
    Co-Authors: Denis Cohen, Y Kligerman, Izhak Etsion
    Abstract:

    normal and tangential loading with full stick contact condition is presented. The model incorporates an accurate finite element analysis for contact and sliding inception of a single elastic-plastic asperity in a statistical representation of surface roughness. It includes the effect of junction growth and treats the sliding inception as a failure mechanism, which is characterized by loss of tangential stiffness. A comparison between the present model and a previously published Friction model shows that the latter severely underestimates the maximum Friction force by up to three orders of magnitude. Strong effects of the normal load, nominal contact area, mechanical properties, and surface roughness on the Static Friction Coefficient are found, in breach of the classical laws of Friction. Empirical equations for the maximum Friction force, Static Friction Coefficient, real contact area due to the normal load alone and at sliding inception as functions of the normal load, material properties, and surface roughness are presented and compared with some limited available experimental results. DOI: 10.1115/1.2908925

  • Static Friction of Contacting Real Surfaces in the Presence of Sub-Boundary Lubrication
    Journal of Tribology, 1998
    Co-Authors: Andreas A Polycarpou, Izhak Etsion
    Abstract:

    A model for calculating the Static Friction Coefficient of contacting real (rough) surfaces in the presence of very thin liquid films (sub-boundary lubrication) is developed. The liquid has a very high affinity for the surfaces and its thickness is of the order of the surface roughness average. An extension of the Greenwood and Williamson (GW) asperity model and an improved Derjaguin, Muller and Toporov (DMT) adhesion model are utilized for calculating the contact and adhesion forces, respectively. The effects of the liquid film thickness and the surface topography on the Static Friction Coefficient are investigated. A critical film thickness is found above which the Friction Coefficient increases sharply. The critical thickness depends on the surface roughness and the external normal load. This phenomenon is more profound for very smooth surfaces and small normal loads, in agreement with published experimental work on magnetic hard disk interfaces.

K Komoriya - One of the best experts on this subject based on the ideXlab platform.

  • Static Friction Coefficient determination by force sensing and its application
    Intelligent Robots and Systems, 1994
    Co-Authors: R Bayrleithner, K Komoriya
    Abstract:

    One of the essential parts of dextrous manipulation with fingers is the use of sliding motion. Sliding manipulation techniques can fulfil tasks, such as a change of contact point between fingers and objects, a change in the location of objects without losing contact under unknown object-fingertip surface conditions or the determination of an optimal grasp force in order to avoid losing grasped objects. These techniques require a knowledge of the Friction Coefficients between the finger and the object. A method of slip detection and Static Friction Coefficient determination, requiring no additional sensors than the existing joint position and force sensors of a two fingered robot hand system, is proposed. This method is applicable to general use in multi-fingered robot hand systems. The authors describe the principle of slip detection using the stick-slip effect and the required control algorithm for grasp forces. The performance of the described method is demonstrated on a pick-up task application. Considerations due to experimental results are discussed. >

  • IROS - Static Friction Coefficient determination by force sensing and its application
    Proceedings of IEEE RSJ International Conference on Intelligent Robots and Systems (IROS'94), 1
    Co-Authors: R Bayrleithner, K Komoriya
    Abstract:

    One of the essential parts of dextrous manipulation with fingers is the use of sliding motion. Sliding manipulation techniques can fulfil tasks, such as a change of contact point between fingers and objects, a change in the location of objects without losing contact under unknown object-fingertip surface conditions or the determination of an optimal grasp force in order to avoid losing grasped objects. These techniques require a knowledge of the Friction Coefficients between the finger and the object. A method of slip detection and Static Friction Coefficient determination, requiring no additional sensors than the existing joint position and force sensors of a two fingered robot hand system, is proposed. This method is applicable to general use in multi-fingered robot hand systems. The authors describe the principle of slip detection using the stick-slip effect and the required control algorithm for grasp forces. The performance of the described method is demonstrated on a pick-up task application. Considerations due to experimental results are discussed. >