Closely piling up of multiple adhesive fronts in adhesive friction due to re-attachment
As a fundamental force, friction exerts a profound influence on various aspects of our daily lives across multiple disciplines. To understand why adhesive friction is associated with the contact area, here we investigate the generic sliding of elastic solids adhered to a rigid surface by considering re-attachment/healing. We then reveal multiple adhesive fronts closely aligning along the interface with the number of these regions generally increasing with the contact area. These adhesive fronts exhibit rich dynamics and their accumulation along an interface can aid each other through re-attachment/healing in friction, apparently resulting in the increase in the calculated shear-off force with the contact area. Based on these findings, we propose a refined law of adhesive friction. Our analysis further suggests that accumulating adhesive fronts along the interface can trigger crack-like propagation of individual fronts at high velocities, which potentially bridges the gap between tribology and fracture mechanics. We also discuss the relevance of this work to earthquake mechanics, which might provide a unified framework that captures key aspects of fault behavior. We expect that this work can supply a fundamental understanding of healing-mediated interfacial phenomena in diverse systems spanning biology, geology, and engineering.