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Peeling 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. [ABSTRACT FROM AUTHOR]

We develop an extension of the Maugis-Dugdale solution for viscoelastic spheres. We show that we can define two characteristic Tabor parameters, a larger one μ R corresponding to relaxed modulus E R and a smaller one μ I for instantaneous modulus E I of the material. Only if both are very large (corresponding to the JKR regime, μ R > μ I > 5) the pull-off load increase due to viscoelastic effect is possibly very large at large pulling speeds, as given by existing solutions and approximately equal to the ratio E I / E R , and otherwise the amplification at very high speeds is much reduced and we give a very simple upper bound of the pull-off load as a function of the relaxed Tabor parameter, independently on the exact form of the viscoelastic linear modulus. An example detailed calculation is given for standard material and constant velocity of load reduction. A dependence on preload is found. [ABSTRACT FROM AUTHOR]

• Cohesive model of Schapery and Persson-Brener energy model are similar as scaling laws. • The main effect of cohesive law shape is a shift in reference velocity. • Persson-Brener model cutoff radius can be chosen to fit approximately the cohesive model results. Crack propagation in viscoelastic materials cannot be understood with the use of classical fracture mechanics, which predicts no dependence on the speed of propagation, unless cohesive models like Barenblatt or Dugdale are introduced, as done by Knauss & Schapery first in the 1970s. However, there is another approach, suggested qualitatively by de Gennes in 1996, and quantitatively by Persson and Brener in 2005, which attempts an energy (power) balance by considering viscoelastic dissipation in the bulk of the material. Here, we revisit the main results of the two theories and show that they lead to approximately the same scaling laws not just for the standard material, but also for power law materials (which have a continuous spectrum of relaxation times). Recent findings by Schapery have concluded that the shape of the cohesive law results essentially in a shift in velocity which depends both on cohesive law shape and viscoelastic properties. Therefore, the Persson-Brener cutoff radius in the integral of dissipation can be chosen to fit approximately the cohesive model results to match the shift of the reference velocity. [ABSTRACT FROM AUTHOR]

Since the early study by Grosch in 1963 it has been known that rubber friction shows generally two maxima with respect to speed—the first one attributed to adhesion, and another at higher velocities attributed to viscoelastic losses. The theory of Klüppel and Heinrich and that of Persson suggests that viscoelastic losses crucially depend on the "multiscale" aspect of roughness and in particular on truncation at fine scales. In this study, we comment a little on both theories, giving some examples using Persson's theory on the uncertainties involved in the truncation of the roughness spectrum. It is shown how different choices of Persson's model parameters, for example the high-frequency cutoff, equally fit experimental data on viscoelastic friction, hence it is unclear how to rigorously separate the adhesive and the viscoelastic contributions from experiments. [ABSTRACT FROM AUTHOR]

The problem of the detachment of a flat indenter from a plane adhesive viscoelastic strip of thickness " b " is studied. For any given retraction speed, three different detachment regimes are found: (i) for very small " b " the detachment stress is constant and equal to the theoretical strength of the interface, (ii) for intermediate values of " b " the detachment stress decays approximately as b − 1 / 2 , (iii) for thick layers a constant detachment stress is obtained corresponding to case the punch is detaching from a halfplane. By using the boundary element method a comprehensive numerical study is performed which assumes a linear viscoelastic material with a single relaxation time and a Lennard-Jones force-separation law. Pull-off stress is found to consistently and monotonically increase with unloading rate, but to be almost insensitive to the history of the contact. Due to viscoelasticity, unloading at high enough retraction velocity may allow punches of macroscopic size to reach the theoretical strength of the interface. Finally, a corrective term in Greenwood or Persson theories considering finite size effects is proposed with good agreement between theoretical and numerical results. [Display omitted] • Ultra-strong adhesion is reached unloading from very thin soft viscoelastic layers. • Macroscopic flat punches may reach the theoretical interfacial adhesive strength. • Viscoelastic crack propagation theories are extended to finite size systems. [ABSTRACT FROM AUTHOR]