Tristan Baumberger (Institut des Nanosciences de Paris). Fracture physics of soft solids: slow crack front instabilities.

Hydrogels, made of polymer networks entrapping a large fraction of solvent, are highly deformable (poro-)elastic solids which can be made extremely tough. Consequently, these systems exhibit a mesoscopic length scale, much larger than the size of the process zone, below which linear elasticity must fail. I will address some specificities of Non Linear Elastic Fracture Mechanics from the point of view and with the tools of the experimental physicist. I will  focus on crack front instabilities such as spontaneous symmetry-breaking, mixed mode step formation.  I will  show how the highly accessible, elastically blunted crack tip, enables straightforward local modification of the process zone, leading to pinning,  speeding up of even blasting the crack tip, just by pouring a drop of water containing suitable solutes ( ions, nanoparticles, …) into the crack opening.