Nucleation and glide of dislocations in a monodisperse two-dimensional foam under uniaxial deformation

Abstract

Experimental observations of the deformation of a monodisperse two-dimensional (2D) monolayer foam in tension/compression are reported. The foam samples are bound by two parallel walls at a variable separation, w. At critical values of w, dislocations (5/7 pairs) nucleate at the periphery of the foam which then glide along directions at 60° to the walls. The dislocations may suffer reflection at the walls, with a change in Burgers vector. As a result of the glide process, the number of close-packed rows of cells parallel to the walls changes by one and a neck develops. Rearrangements of the bubbles to more stable configurations are also observed, following dislocation glide. A detailed analysis of the topology of nucleation, glide and reflection of dislocation is undertaken.

The stress—strain relation is derived and used to calculate the yield stress of the honeycomb foam from the experimentally measured strains at which topological transitions occur. The yield stress is considerably lowered by the nucleation of dislocations and is affected by the liquid fraction in the foam.