Abstract

While there is a good understanding of the overall behavior of heterogeneous materials concerning properties that are characterized by a variational principle, much remains unknown concerning those properties that are characterized by evolutionary processes. This talk will discuss the simple process of peeling an adhesive tape from a rigid substrate as a case study to demonstrate the complexities that can arise in this situation. Specifically, we show that that one can dramatically enhance the overall adhesive strength by patterning the elastic modulus of the tape, and induce asymmetry where the force needed to peel the membrane depends not only on the direction but also the sense of the peel. Remarkably, these modifications in peeling strength come from variations in the energy associated with bending of the tape near the peeling front which is negligible compared to the overall energy in the system. This illustrates that in evolutionary processes, perturbations with apparently negligible energy can have an anomalously large macroscopic effect. The talk will conclude with broader lessons for other phenomena including fracture, dislocations, phase boundaries and wetting fronts.

This is based on joint work with S. Xia, L. Ponson and G. Ravichandran