Attractive and repulsive cracks in a heterogeneous material
  We study experimentally the paths of an assembly of cracks growing in interaction in a heterogeneous two-dimensional elastic brittle material submitted to uniaxial stress. For a given initial crack assembly geometry, we observe two types of crack path. The first one corresponds to a repulsion followed by an attraction on one end of the crack and a tip to tip attraction on the other end. The second one corresponds to a pure attraction. Only one of the crack path type is observed in a given sample. Thus, selection between the two types appears as a statistical collective process. 
Pierre-Philippe Cortet (Phys-ENS), Guillaume Huillard (Phys-ENS),   Lo\"ic Vanel (Phys-ENS), Sergio Ciliberto (Phys-ENS)