Adhesive contact of viscoelastic spheres: A hand-waving introduction

We give an overview of the general features of the linear viscoelastic adhesive contact model. The two main features are (1) a delay between the contraction of the contact radius and the onset of the indenter retraction, and (2) the enhancement of the adherence force. We emphasize the role played by stress relaxation within the contact zone in these phenomena and give simple forms of the viscoelastic adhesive contact equations to account for it. Two characteristic timescales are identified, respectively associated with the crack tip and the contact zone. Their asymmetric roles in the growing and receding contact phases is evidenced. Energy release rates for both phases are calculated together with their irreversible components.