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Quasi-static rheology of foams. Part 1. Oscillating strain
Published online by Cambridge University Press: 31 August 2007
Abstract
A quasi-static simulation is used to study the mechanical response of a disordered bidimensional aqueous foam submitted to an oscillating shear strain. The application of shear progressively extends the elastic domain, i.e. the strain range within which no plastic process occurs. It is associated with the development of an irreversible normal stress difference, and a decrease in the shear modulus, which are both signatures of the appearance of anisotropy in the film network. Beyond this mechanical measurement, the evolutionof the structural properties of the foam is investigated. We focus in particular on the energy E0 defined as the minimum line-length energy under zero shear stress. For strainamplitude less than ~0.5, this quantity is found to decay with the number of applied cycles as a result of the curing of topological defects. However, for higher strain amplitude, plastic events appear to increase the structural disorder and tend to gather near the shearing walls. This process is a precursor of the shear-banding transition observed in fully developed flows, which will be studied in the companion paper. Movies are available with the online version of the paper.
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Kabla and Debregeas supplementary movie
Movie 1. A simulated two-dimensional polydisperse foam is subjected to a quasi-static oscillating imposed shear strain of maximum amplitude 0.3, by incrementally moving the lower rigid boundary. The rapid local neighbour-switching events among the bubbles, called T1 events, can be localized by the colour flashes.
Kabla and Debregeas supplementary movie
Movie 1. A simulated two-dimensional polydisperse foam is subjected to a quasi-static oscillating imposed shear strain of maximum amplitude 0.3, by incrementally moving the lower rigid boundary. The rapid local neighbour-switching events among the bubbles, called T1 events, can be localized by the colour flashes.
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