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Item type:Publication, Access status: with files , Static friction coefficient depends on geometryClassical theories state that the friction coefficient is independent of geometry, depending only on the real contact area determined by roughness. However, experimental evidence shows significant differences between static and dynamic friction coefficients. Recent models introduce an energetic theory for friction, analogous to the Griffith theory for fracture, resulting in a constant dynamic friction coefficient at heavy loads but a larger static coefficient at low loads. We show that, for power-law punches, the ratio of static to dynamic friction coefficients at low normal loads is higher for flatter profiles and, in principle, grows unbounded at zero load. This may explain the observed variability in friction ratios. The model’s predictions align well with recent experimental results.Publicationtype: Journal Article16 11 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , A linear cohesive model of zero degree peeling of a viscoelastic tape from a substratePeeling in viscoelastic materials has been studied experimentally for many years mostly at 90 or 180 degrees angle, and typically the classical Rivlin energy balance equation is used to obtain a velocity-dependent work of fracture. The latter has been shown to be the product of an angular term and a velocity-dependent term, but there is no simple model to explain this behaviour: attempts have been made to generalize the Kendall elastic equation to viscoelasticity, but they lead to no velocity dependence (and infinite load) with frictional dissipation at zero angles, and in general at large angles. In the present model, we consider the original Kendall’s “sticking conditions,” for which a linear cohesive model is formulated for the viscoelastic tape as being on an elastic foundation, and peeling velocity is found to be proportional to the cubic power of the force for Maxwell material, or standard material with a large ratio between instantaneous and relaxed moduli. An explicit closed-form solution to this problem is first derived in this work. Experimental results on zero peel angle are scarce, and may be affected by the finite length of adhered and unadhered parts: hence, a complete picture of peeling behaviour at zero angles is elusive.Publicationtype: Journal Article26