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AM Cottenden – One of the best experts on this subject based on the ideXlab platform.

  • a study of friction mechanisms between a surrogate skin lorica soft and nonwoven fabrics
    Journal of The Mechanical Behavior of Biomedical Materials, 2013
    Co-Authors: David J Cottenden, AM Cottenden

    Abstract:

    Hygiene products such as incontinence pads bring nonwoven fabrics into contact with users’ skin, which can cause damage in various ways, including the nonwoven abrading the skin by friction. The aim of the work described here was to develop and use methods for understanding the origin of friction between nonwoven fabrics and skin by relating measured normal and friction forces to the nature and area of the contact (fibre footprint) between them. The method development work reported here used a skin surrogate (Lorica Soft) in place of skin for reproducibility. The work was primarily experimental in nature, and involved two separate approaches. In the first, a microscope with a shallow depth of field was used to determine the length of nonwoven fibre in contact with a facing surface as a function of pressure, from which the contact area could be inferred; and, in the second, friction between chosen nonwoven fabrics and Lorica Soft was measured at a variety of anatomically relevant pressures (0.25-32.1kPa) and speeds (0.05-5mms(-1)). Both techniques were extensively validated, and showed reproducibility of about 5% in length and force, respectively. Straightforward inspection of the data for Lorica Soft against the nonwovens showed that AmontonsLaw (with respect to load) was obeyed to high precision (R(2)>0.999 in all cases), though there was the suggestion of sub-linearity at low loads. More detailed consideration of the friction traces suggested that two different friction mechanisms are important, and comparison with the contact data suggests tentatively that they may correspond to adhesion between two different populations of contacts, one “rough” and one “smooth”. This additional insight is a good illustration of how these techniques may prove valuable in studying other, similar interfaces. In particular, they could be used to investigate interfaces between nonwovens and skin, which was the primary motivation for developing them.

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  • A study of friction mechanisms between a surrogate skin (lorica soft) and nonwoven fabrics
    Journal of the Mechanical Behavior of Biomedical Materials, 2013
    Co-Authors: AM Cottenden

    Abstract:

    Hygiene products such as incontinence pads bring nonwoven fabrics into contact with users’ skin, which can cause damage in various ways, including the nonwoven abrading the skin by friction. The aim of the work described here was to develop and use methods for understanding the origin of friction between nonwoven fabrics and skin by relating measured normal and friction forces to the nature and area of the contact (fibre footprint) between them. The method development work reported here used a skin surrogate (Lorica Soft) in place of skin for reproducibility. The work was primarily experimental in nature, and involved two separate approaches. In the first, a microscope with a shallow depth of field was used to determine the length of nonwoven fibre in contact with a facing surface as a function of pressure, from which the contact area could be inferred; and, in the second, friction between chosen nonwoven fabrics and Lorica Soft was measured at a variety of anatomically relevant pressures (0.25-32.1kPa) and speeds (0.05-5mms). Both techniques were extensively validated, and showed reproducibility of about 5% in length and force, respectively. Straightforward inspection of the data for Lorica Soft against the nonwovens showed that AmontonsLaw (with respect to load) was obeyed to high precision ( > 0.999 in all cases), though there was the suggestion of sub-linearity at low loads. More detailed consideration of the friction traces suggested that two different friction mechanisms are important, and comparison with the contact data suggests tentatively that they may correspond to adhesion between two different populations of contacts, one “rough” and one “smooth”. This additional insight is a good illustration of how these techniques may prove valuable in studying other, similar interfaces. In particular, they could be used to investigate interfaces between nonwovens and skin, which was the primary motivation for developing them. © 2013 Elsevier Ltd.

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  • An analytical model of the motion of a conformable sheet over a general convex surface in the presence of frictional coupling
    Q J MECH APPL MATH, 2009
    Co-Authors: AM Cottenden

    Abstract:

    Friction is important across a wide range of applications. In particular, in health care, friction is thought to be the cause of some pressure ulcers in largely immobile patients, and abrasion due to friction contributes to the deterioration of skin health in incontinence pad users, especially in the presence of liquid. Some of these frictional forces are due to stress in materials wrapped around curved anatomical surfaces, which are often complicated shapes. The little work to date that has considered friction arising by this mechanism has assumed very simplified geometries (prisms, or even cylinders), which have enabled coefficients of friction to be extracted from laboratory tests on arms, but which are certainly not applicable to, for example, the diaper region. This work describes the development of a much more general mathematical model for friction between a draped, stressed sheet and the substrate, relating geometry, material mechanical properties and stress for essentially any convex surface. A general, wide, class of frictional interfaces is described (which includes those which obey AmontonsLaw), and the model is presented in differential form for a generic member of this class. Finally, an analytical solution is developed for convex, instantaneously rigid substrates isomorphic to the plane draped with a low-density sheet exhibiting no Poisson contraction, a fair approximation to some anatomical situations. The solution is explicitly calculated for a general prism and a general cone, producing expressions consistent with previous published models and with limited new experimental data.

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Georges Debrégeas – One of the best experts on this subject based on the ideXlab platform.

  • Probing the micromechanics of a multi-contact interface at the onset of frictional sliding
    European Physical Journal E: Soft matter and biological physics, 2013
    Co-Authors: Alexis Prevost, Julien Scheibert, Georges Debrégeas

    Abstract:

    Digital Image Correlation is used to study the micromechanics of a multi-contact interface formed between a rough elastomer and a smooth glass surface. The in-plane elastomer deformation is monitored during the incipient sliding regime, \textit{i.e.} the transition between static and sliding contact. As the shear load is increased, an annular slip region, in coexistence with a central stick region, is found to progressively invade the contact. From the interfacial displacement field, the tangential stress field can be further computed using a numerical inversion procedure. These local mechanical measurements are found to be correctly captured by Cattaneo and Mindlin (CM)’s model. However, close comparison reveals significant discrepancies in both the displacements and stress fields that reflect the oversimplifying hypothesis underlying CM’s scenario. In particular, our optical measurements allow us to exhibit an elasto-plastic like friction constitutive equation that differs from the rigid-plastic behavior assumed in CM’s model. This local constitutive Law, which involves a roughness-related length scale, is consistent with the model of Bureau \textit{et al.} [Proc. R. Soc. London A \textbf{459}, 2787 (2003)] derived for homogeneously loaded macroscopic multi-contact interfaces, thus extending its validity to mesoscopic scales.measurements allow for the first quantitative test of Cattaneo and Mindlin (CM) classical model of the incipient sliding of a smooth interface. Small deviations are observed and interpreted as a result of the finite compliance of the rough interface, a behavior which contrasts with AmontonsLaw of friction assumed to be valid locally in CM’s model. We illustrate how these measurements actually provide a method for probing the rheology of the rough interface, which we find to be of the elasto-plastic type.

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  • mems based contact stress field measurements at a rough elastomeric layer local test of Amontons friction Law in static and steady sliding regimes
    14th International Conference on Experimental Mechanics (ICEM14), 2010
    Co-Authors: Julien Scheibert, Alexis Prevost, Joel Frelat, Eytan Katzav, Adda M Bedia, Georges Debrégeas

    Abstract:

    We present the results of recent friction experiments in which a MEMS-based sensing device is used to measure both the normal and tangential stress fields at the base of a rough elastomer film in frictional contact with smooth, rigid, glass indentors. We con- sider successively multicontacts under (i) static normal loading by a spherical indentor and (ii) frictional steady sliding conditions against a cylindrical indentor, for an increas- ing normal load. In both cases, the measured fields are compared to elastic calculations assuming (i) a smooth interface and (ii) Amontons‘ friction Law. In the static case, signifi- cant deviations are observed which decrease with increasing load and which vanish when a lubricant is used. In the steady sliding case, AmontonsLaw reproduces rather satisfacto- rily the experiments provided that the normal/tangential coupling at the contact interface is taken into account. We discuss the origin of the difference between the Amontons fields and the measured ones, in particular the effect of the finite normal and tangential compli- ances of the multicontact interface.

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  • mems based contact stress field measurements at a rough elastomeric layer local test of Amontons friction Law in static and steady sliding regimes
    14th International Conference on Experimental Mechanics (ICEM14), 2010
    Co-Authors: Julien Scheibert, Alexis Prevost, Joel Frelat, Eytan Katzav, Adda M Bedia, Georges Debrégeas

    Abstract:

    We present the results of recent friction experiments in which a MEMS-based sensing device is used to measure both the normal and tangential stress fields at the base of a rough elastomer film in frictional contact with smooth, rigid, glass indentors. We con- sider successively multicontacts under (i) static normal loading by a spherical indentor and (ii) frictional steady sliding conditions against a cylindrical indentor, for an increas- ing normal load. In both cases, the measured fields are compared to elastic calculations assuming (i) a smooth interface and (ii) Amontons‘ friction Law. In the static case, signifi- cant deviations are observed which decrease with increasing load and which vanish when a lubricant is used. In the steady sliding case, AmontonsLaw reproduces rather satisfacto- rily the experiments provided that the normal/tangential coupling at the contact interface is taken into account. We discuss the origin of the difference between the Amontons fields and the measured ones, in particular the effect of the finite normal and tangential compli- ances of the multicontact interface.

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Artur Vaganian – One of the best experts on this subject based on the ideXlab platform.

  • On generalized Coulomb–AmontonsLaw in the context of rigid body dynamics
    Nonlinear Dynamics, 2020
    Co-Authors: Artur Vaganian

    Abstract:

    A generalization of Coulomb–AmontonsLaw of dry friction recently proposed by V. V. Kozlov is considered in the context of rigid body dynamics. Universal requirements for dry friction tensor formulated by V. V. Kozlov are complemented by a condition taking into account the contact nature of dry friction, and applied to several models. For the famous Painlevé problem, a generalized Coulomb–Amontons’ force without singularities, yet such that the dissipation takes place only at the point of contact, is found. By the example of the motion of a rigid ball on a plane with a single point of contact, it is shown that these principles are consistent with the well-known equations, studied by G.-G. Coriolis. Further, a ball simultaneously touching two perpendicular planes at two points of contact is considered. The corresponding equations of motion are derived and analyzed. An exact particular solution that describes a technique used in practice in billiards is obtained. It is shown that unlike the single contact case, the Lagrange multipliers can depend on friction coefficients. With this in mind, a generalization of the conditions on the tensor of dry friction for the case of an arbitrary number of contacts is proposed.

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  • On generalized Coulomb-AmontonsLaw in the context of rigid body dynamics
    Nonlinear Dynamics, 2019
    Co-Authors: Artur Vaganian

    Abstract:

    A generalization of Coulomb–AmontonsLaw of dry friction recently proposed by V. V. Kozlov is considered in the context of rigid body dynamics. Universal requirements for dry friction tensor formulated by V. V. Kozlov are complemented by a condition taking into account the contact nature of dry friction, and applied to several models. For the famous Painleve problem, a generalized Coulomb–Amontons’ force without singularities, yet such that the dissipation takes place only at the point of contact, is found. By the example of the motion of a rigid ball on a plane with a single point of contact, it is shown that these principles are consistent with the well-known equations, studied by G.-G. Coriolis. Further, a ball simultaneously touching two perpendicular planes at two points of contact is considered. The corresponding equations of motion are derived and analyzed. An exact particular solution that describes a technique used in practice in billiards is obtained. It is shown that unlike the single contact case, the Lagrange multipliers can depend on friction coefficients. With this in mind, a generalization of the conditions on the tensor of dry friction for the case of an arbitrary number of contacts is proposed.

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