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Tensile elastic instabilities

The prototypical elastic instability is the Euler buckling of a slender column under compression. This instability arrises a geometric reason: buckling allows the column to return to its original contour length, and hence to save elastic energy. Soft solids, are capable of undergoing large deformations, and so are subject to a much richer geometric effects, and can undergo a correspondingly rich set of elastic instabilities, including aneurism instabilities, folding and wrinkling instabilities, and solid cavitation. These instabilities cause simple shapes to spontaneously turn into complex shapes, and have been harnessed by biology to sculpt organs during development - for example my own work has shown the brain folds via a compressive buckling instability. There is clearly an opportunity for human engineers to use these instabilities to make devices that switch shape during use. In this project we will examine the instability of the surface of a soft solid when subject to an E or B field - the solid analogue of the famous ferrofluid Rosensweig instability. The motivating idea is that a flat surface will, at sufficient field strength, become unstable and form a rough topography (spikes), allowing the manipulation of surface properties such as friction, adhesion and wettability.