Morphology of adhesive creases

When a soft elastic material is compressed beyond a certain critical strain, the free surface turns unstable and forms a crease. This corresponds to a sharp fold of the surface onto itself, leading to intricate morphologies as observed for growing tissues and swelling gels. Self-adhesion within the folded region is known to affect nucleation and hysteresis, but a detailed description has remained elusive. Here we resolve the geometry and mechanics of adhesive creases, combining numerical simulations, analysis and experimental results — with specific attention to the singular edge of the self-contact. It turns out that adhesive creases exhibit a universal shape that arises from a balance of elastic and surface energies. From this we derive a scaling theory for the intricate bifurcation scenario, explaining the hysteretic nucleation of adhesive creases.