Role of Occlusion in Non-Coulombic Slip of the Finger Pad

Dzidek, Brygida; Adams, M.J.; Zhang, Zhibing; Johnson, S. A.; Bochereau, Séréna; Hayward, Vincent

doi:10.1007/978-3-662-44193-0_15

Cited by 16 publications

(28 citation statements)

References 17 publications

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“…As mentioned earlier, increased hydration results in increased adhesion friction according to equation (1). A similar hypothesis has been postulated by Dzidek et al In experiments with a human finger sliding in a reciprocating manner against smooth glass and polypropylene, the authors found that the coefficient of friction increased by up to an order of magnitude within an occlusion time of 20 s but that this effect was less for higher roughness of the skin-contacting material [51].…”

Section: Effect Of Sliding Timesupporting

confidence: 71%

Comparison of the Friction Behavior of Occluded Human Skin and Synthetic Skin in Dry and Moist Conditions

Franklin

Baranowska

Hendriks

et al. 2016

Tribology Transactions

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The goal of this work was to assess the suitability of a commercial synthetic skin to simulate occluded human skin friction behaviour in dry and moist skin conditions and under different applied surface pressures, with the view to using this material as a tribological test-bed for healthcare and personal care devices that are in direct contact with the skin during use. A flat rotating ring friction measurement device, in which one part of the skin surface is continuously covered (i.e. occluded), was used to compare the friction behaviour of human skin and the synthetic skin in controlled nominally dry and nominally moist skin conditions. Three loading levels were tested, simulating light, medium and high skin pressures typical of many lifestyleand personal health-related applications. The results showed that the friction behaviour of the synthetic skin tested here was notably different to that of human skin in vivo in terms of the effects of skin hydration, sliding time and applied surface pressure. It is concluded that, for use as a tribological test-bed, the tested synthetic skin model does not provide an acceptable alternative to in vivo tests using human skin.

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Section: Effect Of Sliding Timesupporting

confidence: 71%

Comparison of the Friction Behavior of Occluded Human Skin and Synthetic Skin in Dry and Moist Conditions

Franklin

Baranowska

Hendriks

et al. 2016

Tribology Transactions

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“…Interestingly, λ 2 is 7.1 ± 0.2 s, which is considerably shorter than the value of 18 ± 5 s for λ 1 , which is the characteristic time for the increase in friction of the same finger on glass [15]. This result implies that the growth rate of junct is significantly greater than that of real .…”

Section: Discussionmentioning

confidence: 78%

“…For sphere-on-flat (point) or cylinder-on-flat (line) Hertzian junctions, real is proportional to 2/3 or 1/2 , respectively, so that the frictional force is modelled by = where = 2/3 or 1/2 provided that the dependence of τ on the contact pressure is small; is termed the frictional load index [14]. For contacts of the finger pad, which generally are strongly time-dependent, we observed in the case of an occlusive contact that ~1 initially and that it decreased with sliding time to reach a value of ~2/3 [15]. Similarly to (1), the temporal dynamics could be described empirically by a first-order kinetics relationship,…”

Section: Introductionmentioning

confidence: 91%

Frictional dynamics of finger pads are governed by four length-scales and two time-scales

Dzidek

Bochereau

Johnson

et al. 2016

2016 IEEE Haptics Symposium (HAPTICS)

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Abstract-The evolution of the contact area of a finger pad against a surface is critical during tactile interaction, whether for gripping or discriminating surfaces. The contact area made by a finger pad is commonly considered at two distinct length scales corresponding to the gross area, gross , and to the smaller ridge area, ridge , that excludes the interstitial spaces between the ridges. Here, these quantities were obtained from highresolution imaging of contacts during loading and stress relaxation. While gross rapidly reaches an ultimate value, the contact made by the ridges is initially formed from unconnected junctions with a total contact area, junct , which continues to increase for several seconds during the holding period. Thus, the contact area grows in a two-step process where the number of junctions made by the ridges first increases, followed by a growth of their size and connectivity. Immediately after contact the stratum corneum is in a glassy state and the individual junctions form a multiple asperity contact. At longer contact times, the asperities soften owing to the occlusion of moisture excreted from the sweat pores in the ridges. Thus, the real area of contact, real , which drives the creation of friction, grows with time at a relatively slow rate. It is concluded that multiasperity dynamic contact models should be preferred compared with static models in order to describe the physics of finger pad contact mechanics and friction.

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“…We also previously reported that, with increasing contact time, the friction of a finger pad gradually changes from Coulombic to a nonlinear dependence on a normal load in a manner that is typical of elastomers, when the asperities are sufficiently compliant to flatten under the applied load (29). This phenomenon is a direct result of a glassy-rubbery transition of the stratum corneum caused by the moisture-driven plasticization.…”

Section: Discussionmentioning

confidence: 82%

“…We observed previously that the value of the coefficient of friction, µ, for a finger pad sliding on a smooth glass surface also increased with the contact time, because the increase in Atrue is greater than the decrease in τ (20). The value of µ can increase by up to an order of magnitude for small normal loads, and its evolution at a constant normal load can be described by a first-order kinetics relationship with a characteristic time of up to 20 s (29). Thus, it is probable that φ(t) generally exhibits a similar behavior, but a technique able to reliably measure Atrue for rough surfaces has yet to developed.…”

Section: Discussionmentioning

confidence: 94%

Why pens have rubbery grips

Dzidek

Bochereau

Johnson

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

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The process by which human fingers gives rise to stable contacts with smooth, hard objects is surprisingly slow. Using highresolution imaging, we found that, when pressed against glass, the actual contact made by finger pad ridges evolved over time following a first-order kinetics relationship. This evolution was the result of a two-stage coalescence process of microscopic junctions made between the keratin of the stratum corneum of the skin and the glass surface. This process was driven by the secretion of moisture from the sweat glands, since increased hydration in stratum corneum causes it to become softer. Saturation was typically reached within 20 s of loading the contact, regardless of the initial moisture state of the finger and of the normal force applied. Hence, the gross contact area, frequently used as a benchmark quantity in grip and perceptual studies, is a poor reflection of the actual contact mechanics that take place between human fingers and smooth, impermeable surfaces. In contrast, the formation of a steady-state contact area is almost instantaneous if the counter surface is soft relative to keratin in a dry state. It is for this reason that elastomers are commonly used to coat grip surfaces.finger friction | true contact area kinetics | biotribology | fingerprints

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Role of Occlusion in Non-Coulombic Slip of the Finger Pad

Cited by 16 publications

References 17 publications

Comparison of the Friction Behavior of Occluded Human Skin and Synthetic Skin in Dry and Moist Conditions

Comparison of the Friction Behavior of Occluded Human Skin and Synthetic Skin in Dry and Moist Conditions

Frictional dynamics of finger pads are governed by four length-scales and two time-scales

Why pens have rubbery grips

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