We studied pattern formation in granular media in two distinct states: in the dry and non-cohesive (powder) state, on the one hand, and in the wet and cohesive (paste) state, on the other. In the first case, we have shown that gas injection in a thin layer of powder within a Hele Shaw cell leads to fractal patterns remarkably similar to viscous fingering patterns obtained with complex fluids. In the second case, we have shown that the tensile cohesive viscoplastic fracture of a layer of paste leads to self-affine rough surfaces with a Hurst exponent close to 0.88, very close to the value obtained for fragile fracture by other authors.18 Our observations reinforce the universality of two fractal growth processes and add a new element to the ambivalent nature of the granular state of matter.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.