Abstract
Adhesion and, its interplay with friction, is central in several engineering applications involving soft contacts. Recently, there has been an incredible push towards a better understanding on how the apparent contact area evolves when a shear load is applied to an adhesive soft contact, both experimentally and theoretically. Although soft materials are well-known to exhibit rate-dependent properties, there is still a lack of understanding in how the loading rate could affect the contact area shrinking. Indeed, most of the experiments involving a sphere-flat contact have been conducted at a fixed loading rate, and, so far, analytical models have assumed a constant work of adhesion, independent on the peeling velocity. Here, by using linear elastic fracture mechanics, an analytical model is derived for the contact of a rigid sphere on a soft adhesive substrate, which is aimed at elucidating the effect that a rate-dependent work of adhesion has on the contact area shrinking. The model results show that contact area reduction is very sensitive to the loading rate, with slower loading rates promoting a stronger shrinking, which seems in agreement with Literature results. Furthermore it is shown that rate effects enhance the apparent interfacial toughness, i.e. more energy is needed to drive the system from full stick up to gross sliding.
Highlights
Adhesion is a flourishing area of tribology, which is central in both science and technology [1]
We will focus on the effects that a ratedependent work of adhesion has on the reduction of contact area under increasing tangential load
(Inset) Work of adhesion was a function of the peeling velocityvp for n = 0.2 and n = 0.8 dashed curve restricted to the case of small normal loads, as to avoid nonlinear effects due to large deformations, in the following, unless differently stated, we will set P = 0
Summary
Adhesion is a flourishing area of tribology, which is central in both science and technology [1]. Nature has developed several high efficient systems capable to control interfacial adhesion, as common experience proves when geckos, lizards and, in general, insects climb vertical walls or run on ceilings. Exploiting van der Walls forces in an efficient manner, is a primary scientific and technological task, when it interferes with friction, as this has a tremendous impact on cutting edge technologies under development, such as soft robots [2], developing an artificial sense of touch [3], human–robot interactions [4], pressure-sensitive adhesives [5,6,7], grippers [8]. Savkoor and Briggs [12] further developed the work of
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