‘Sideways’ and stable crack propagation in a silicone elastomer

This talk will describe a peculiar form of fracture that we have found in a highly stretchable silicone elastomer. Namely, under certain conditions a crack will deviate from its ‘standard’ trajectory and instead propagate perpendicular to that trajectory. The crack arrests stably, allowing the material ahead of the crack front to continue to sustain load, and thereby enabling enormous stretchabilities. We call this phenomenon ‘sideways’ cracking. To explain this behavior, we first perform finite element simulations that demonstrate a propensity for sideways cracking, even in isotropic elastomers. Next, we provide a hypothesis on the origin of sideways cracking that invokes microstructural anisotropy. To substantiate this hypothesis, we transversely pre-stretch samples to various extents prior to fracture testing, as to determine the influence of microstructural arrangement (chain alignment) on fracture energy. We conclude by describing how a number of loading conditions, such as sample geometry and strain rate affect this phenomenon. Overall, this talk aims to provide fundamental mechanical insight into basic phenomena associated with fracture of elastomers.