Shear induced normal stress differences in aqueous foams

TL;DR

This paper demonstrates the existence of a Poynting-like effect in aqueous foams, showing that shear deformation induces normal stress differences influenced by elastic, viscous, and plastic stresses, supported by experimental and modeling evidence.

Contribution

First experimental evidence of Poynting-like normal stress differences in aqueous foams, extending elastic solid theory to complex foam rheology.

Findings

Shear induces normal stress differences in foams.

Viscous and plastic stresses significantly affect the effect.

A constitutive model explains the observed behavior.

Abstract

A finite simple shear deformation of an elastic solid induces unequal normal stresses. This nonlinear phenomenon, known as the Poynting effect, is governed by a universal relation between shear strain and first normal stresses difference, valid for non-dissipative elastic materials. We provide the first experimental evidence that an analog of the Poynting effect exists in aqueous foams where besides the elastic stress, there are significant viscous or plastic stresses. These results are interpreted in the framework of a constitutive model, derived from a physical description of foam rheology.