Foam rheology
Foams, like many soft materials, behave as a solid when pushed gently and flow when pushed harder. With Georges Debrégeas, during a PhD at the Collège de France, we used a simulation of a two-dimensional dry foam, tested against experiments on foams confined between two plates, to follow what happens when a single bubble rearrangement releases stress in its surroundings. After a short transient, the flow localises in a narrow shear band (Kabla and Debrégeas, Physical Review Letters 2003). A detailed study followed the response to small deformations, with the build-up of anisotropy in the network of films, and the transition to shear banding at larger strains (Kabla and Debrégeas; Kabla, Scheibert and Debrégeas, Journal of Fluid Mechanics 2007). These models of plastic events and their spatial correlations remain a reference for later work on the flow of disordered materials, including living tissues.