Foam in a two-dimensional Couette shear: a local measurement of bubble deformation

We re-analyse experiments on a foam sheared in a two-dimensional Couette geometry [Debregeas et al., Phys. Rev. Lett. 87, 178305 (2001)]. We characterise the bubble deformation by a texture tensor. Our measurements are local in time: they show two regimes, one transient and one stationary. They provide both the average and fluctuations of the anisotropy. Measurements are also local in space: they show that both the deformation and the elastic contribution to the stress field do not localise, varying smoothly across the shear gap. We can thus describe the foam as a continuous medium with elastic properties.