Failure Mode of Bubble Rafts under Tension
Seminar Room 1, Newton Institute
AbstractCo-author: Chin Chang Kuo (UC Irvine)
One of the interesting questions regarding the dynamics of foam is the characterization of their flow behavior. One often refers to distinct regimes in which the foam exhibits a primarily elastic response (solid-like) or it exhibits a primarily viscous response (fluid-like). In addition, one finds plastic flow regimes and various combinations of all three. Any attempt to provide a unified theoretical description of foam rheology must account for a wide-range of flow geometries and behavior. Most of the focus in flowing foam has been on closed geometries in which the system is driven either by a moving boundary or pressure gradient. We have recently completed a series of studies on the dynamics of foam in an open-flow situation in which the system is under tension. We use a quasi-two dimensional system of bubbles on the surface of water (bubble rafts). Two of the opposite sides of the system are free boundaries, and the other two sides are pulled apart at a constant rate. We f ocus on the failure mechanism by which the system separates in distinct sections of foam. We report on the different regimes that were observed, including fluid-like pinch-off and plastic-like fracture. We propose simple scaling arguments to account for the speed and aspect ratio dependence of the different failure modes.
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