Theory of viscoelastic adhesion and friction

We present a novel theory of the adhesive contact of linear viscoelastic materials sliding at constant velocity against rough substrates. Despite the non-conservative behaviour of the system, the closure equation, needed to calculate the unknown size of the contact area, can be rigorously formulated in the form of a local energy balance. The results highlight three main peculiar features of the contact, which are strictly ascribable to the interplay of adhesion and viscoelasticity. First, a velocity dependent pull-off force is predicted, whose maximum value occurs at intermediate sliding velocity. Second, the energy release rates G1 and G2 at the contact trailing and leading edges respectively, present a non-monotonic dependence on the indenter sliding velocity. Third, the velocity dependence of the hysteretic friction mu is significantly altered and presents a friction peak much more pronounced compared to the adhesiveless viscoelastic case. Theoretical predictions are in very good agreement with existing experimental data.(c) 2022 Elsevier Ltd. All rights reserved.