Buckling of sheared and compressed microfibrils

Nadermann, Nichole; Kumar, Ajeet; Goyal, Sachin; Hui, Chung‐Yuen

doi:10.1098/rsif.2010.0147

Cited by 12 publications

(11 citation statements)

References 27 publications

(45 reference statements)

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“…Specifically, after a normal preload F N 0 is applied to bring the surfaces into contact, the normal displacement is fixed during shear. As pointed out in our recent work, fibres in the array can buckle during shear if the normal load is fixed during shear (Nadermann et al 2010). In general, buckling will cause the fibres to detach and will lower the static friction (Shen et al 2009).…”

Section: Introductionmentioning

confidence: 76%

Numerical study of shearing of a microfibre during friction testing of a microfibre array

Kumar

Hui

2010

Proc. R. Soc. A.

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Friction testing of microfibre arrays is typically conducted under displacement boundary conditions. For example, after the application of a compressive preload, the translation stage is fixed in the vertical direction while a shear displacement is applied by translating the stage laterally. A nonlinear rod model is used to compute the normal and shear forces acting on a typical microfibre during such a test. The normal load acting on a typical fibre is found to switch from compression to tension as the shear displacement increases. The critical shear force to detach a fibre is found to depend linearly on the compressive preload. The fibre is also found to become more stable as it is sheared, hence it never buckles. On the other hand, instead of fixing the vertical displacement, when a fibre is subjected to constant normal load, it becomes unstable upon shearing. We show that the buckling load (the applied normal load to make a fibre unstable) of a microfibril is reduced by the application of a shear displacement.

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Section: Introductionmentioning

confidence: 76%

Numerical study of shearing of a microfibre during friction testing of a microfibre array

Kumar

Hui

2010

Proc. R. Soc. A.

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“…This study is not presented here, but when the bristles are implanted more vertically, buckling becomes very clear (Fig. 13) [60].…”

Section: Discussionmentioning

confidence: 95%

Indentation of hairy surfaces: Role of friction and entanglement

Camillieri

Bueno

2015

Tribology International

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“…Treating a single fibre as an elastica, [54] showed that fibres maintain side contact at zero normal load if the work of adhesion between the fibre and the surface exceeds the elastic energy stored in the deformed fibre. While vertical fibres must have a high aspect ratio to fulfil this criterion [55] , angled fibres require less energy to be sufficiently deformed to make side contact [54] , [56] , [57] . When strong shear forces act on the acanthae, the resulting moment may exceed the level required to bend the acanthae into side contact, so that they maintain surface contact even for zero or negative loads (adhesion).…”

Section: Discussionmentioning

confidence: 99%

Functionally Different Pads on the Same Foot Allow Control of Attachment: Stick Insects Have Load-Sensitive “Heel” Pads for Friction and Shear-Sensitive “Toe” Pads for Adhesion

2013

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Stick insects (Carausius morosus) have two distinct types of attachment pad per leg, tarsal “heel” pads (euplantulae) and a pre-tarsal “toe” pad (arolium). Here we show that these two pad types are specialised for fundamentally different functions. When standing upright, stick insects rested on their proximal euplantulae, while arolia were the only pads in surface contact when hanging upside down. Single-pad force measurements showed that the adhesion of euplantulae was extremely small, but friction forces strongly increased with normal load and coefficients of friction were 1. The pre-tarsal arolium, in contrast, generated adhesion that strongly increased with pulling forces, allowing adhesion to be activated and deactivated by shear forces, which can be produced actively, or passively as a result of the insects' sprawled posture. The shear-sensitivity of the arolium was present even when corrected for contact area, and was independent of normal preloads covering nearly an order of magnitude. Attachment of both heel and toe pads is thus activated partly by the forces that arise passively in the situations in which they are used by the insects, ensuring safe attachment. Our results suggest that stick insect euplantulae are specialised “friction pads” that produce traction when pressed against the substrate, while arolia are “true” adhesive pads that stick to the substrate when activated by pulling forces.

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Buckling of sheared and compressed microfibrils

Cited by 12 publications

References 27 publications

Numerical study of shearing of a microfibre during friction testing of a microfibre array

Numerical study of shearing of a microfibre during friction testing of a microfibre array

Indentation of hairy surfaces: Role of friction and entanglement

Functionally Different Pads on the Same Foot Allow Control of Attachment: Stick Insects Have Load-Sensitive “Heel” Pads for Friction and Shear-Sensitive “Toe” Pads for Adhesion

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