Fracture patterns formed by tearing adhesive thin films from curved surfaces

It has been reported that tearing adhesive thin films from smooth developable surfaces can produce various fracture patterns, which can be either convergent or divergent. We experimentally show that the parallel one can be realized from a properly undulating surface. Then, we demonstrate that the formation of all the discovered patterns is governed by a unified rule, where the local geometry near the crack tip matters. Our theory can provide a master curve, universally capturing distinct crack behaviors in experiments. And diverse observed fracture patterns become predictable. Based on the unified perspective, we reveal that the stability of a parallel pattern is decided by the local concavity of the surface near the crack tips. In addition, this rule also applies to the tearing from nondevelopable surfaces, such as tearing the fruit skin from the pulp with a wide initial flap width. Finally, we suggest that such predictable tearing can be harnessed for controlled fragmentation of thin films and used for characterizing the mechanical properties of a film-substrate system where the substrate can own nonzero curvature.