Julien Chopin (Science et Ingéniérie de la Matière Molle, ESPCI, Paris). Morphology and dynamics of crack fronts in model heterogeneous materials.

Due to progress in micro fabrication, microstructure of materials can be tailored to achieve unprecedented macroscopic properties (auxetic behavior, superhydrophobicity and omniphobicity, strong and reversible adhesion). Regarding the mechanical properties of heterogeneous materials, it is still unclear how large-scale mechanical properties are linked to characteristics of the microstructure such as the size and distribution of heterogeneities.

 In this talk, I will present experimental investigations on the spatiotemporal dynamics of a crack front propagating at the interface between a rigid substrate and an elastomer. We found that the equation of motion is intrinsically nonlinear when the interface is homogeneous. I will then discuss the micro-instabilities induced by isolated heterogeneities. Our findings show that cracks follow an overdamped dynamics with a characteristic velocity that emerges from the relationship between the fracture energy and the crack growth velocity. We found that dissipation mechanisms taking place within the process zone control the depinning dynamics. Finally, I will briefly discuss the statistical properties of cracks propagating in a fully disordered interface.