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

TL;DR

This study analyzes bubble deformation in a 2D foam under shear using local measurements, revealing non-localized deformation and elastic behavior, and distinguishing transient and steady regimes.

Contribution

It introduces a local measurement method using a texture tensor to characterize bubble deformation and demonstrates foam's elastic properties as a continuous medium.

Findings

Deformation and stress do not localize, vary smoothly across the shear gap.

Two regimes identified: transient and stationary.

Foam behaves as a continuous elastic medium.

Abstract

We re-analyse experiments on a foam sheared in a two-dimensional Couette geometry [Debregeas <i>et al.</i>, Phys. Rev. Lett. <b>87</b>, 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.