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Author: Arzt, Eduard × Author: McMeeking, Robert M. × End date: 2019 × Start date: 2014 ×

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Now showing 1 - 3 of 3
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    Cohesive detachment of an elastic pillar from a dissimilar substrate
    (Amsterdam : Elsevier, 2017) Fleck, Norman A.; Khaderi, Syed Nizamuddin; McMeeking, Robert M.; Arzt, Eduard
    The adhesion of micron-scale surfaces due to intermolecular interactions is a subject of in- tense interest spanning electronics, biomechanics and the application of soft materials to engineering devices. The degree of adhesion is sensitive to the diameter of micro-pillars in addition to the degree of elastic mismatch between pillar and substrate. Adhesion- strength-controlled detachment of an elastic circular cylinder from a dissimilar substrate is predicted using a Dugdale-type of analysis, with a cohesive zone of uniform tensile strength emanating from the interface corner. Detachment initiates when the opening of the cohesive zone attains a critical value, giving way to crack formation. When the cohe- sive zone size at crack initiation is small compared to the pillar diameter, the initiation of detachment can be expressed in terms of a critical value H c of the corner stress inten- sity. The estimated pull-offforce is somewhat sensitive to the choice of stick/slip boundary condition used on the cohesive zone, especially when the substrate material is much stiffer than the pillar material. The analysis can be used to predict the sensitivity of detachment force to the size of pillar and to the degree of elastic mismatch between pillar and sub- strate.
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    Numerical study of adhesion enhancement by composite fibrils with soft tip layers
    (Amsterdam : Elsevier, 2016) Balijepalli, Ram Gopal; Fischer, Sarah C.L.; Hensel, René; McMeeking, Robert M.; Arzt, Eduard
    Bio-inspired fibrillar surfaces with reversible adhesion to stiff substrates have been thoroughly investigated over the last decade. In this paper we propose a novel composite fibril consisting of a soft tip layer and stiffer stalk with differently shaped interfaces (flat vs. curved) between them. A tensile stress is applied remotely on the free end of the fibril whose other end adheres to a rigid substrate. The stress distributions and the resulting adhesion of such structures were numerically investigated under plane strain (2D) and axisymmetric (3D) conditions. The stress intensities were evaluated for different combinations of layer thickness and Young’s moduli. The adhesion strength values were found to increase for thinner layers and larger modulus ratio; these trends are also reflected in selected experimental results. The results of this paper provide a new strategy for optimizing adhesion strength of fibrillar surfaces.
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    Fibrillar elastomeric micropatterns create tunable adhesion even to rough surfaces
    (Hoboken, NJ : Wiley, 2016) Barreau, Viktoriia; Hensel, René; Guimard, Nathalie K.; Ghatak, Animangsu; McMeeking, Robert M.; Arzt, Eduard
    Biologically inspired, fibrillar dry adhesives continue to attract much attention as they are instrumental for emerging applications and technologies. To date, the adhesion of micropatterned gecko-inspired surfaces has predominantly been tested on stiff, smooth substrates. However, all natural and almost all artificial surfaces have roughnesses on one or more different length scales. In the present approach, micropillar-patterned PDMS surfaces with superior adhesion to glass substrates with different roughnesses are designed and analyzed. The results reveal for the first time adhesive and nonadhesive states depending on the micropillar geometry relative to the surface roughness profile. The data obtained further demonstrate that, in the adhesive regime, fibrillar gecko-inspired adhesive structures can be used with advantage on rough surfaces; this finding may open up new applications in the fields of robotics, biomedicine, and space exploration.