Mechanical instabilities in soft solids

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Soft solid materials, such as gels, rubbers, skin and muscle, are characterized by their ability to undergo large elastic strains. These large deformations introduce geometric non-linearities into their behaviour, which underpin a wide range of novel elastic instabilities in which, at high load, the material spontaneously adopts a more complicated shape. These instabilities include well known classics such as ballooning and buckling, and also recently uncovered instabilities such as surface creasing and elastic fingering. Shape forming elastic instabilities have normally been thought of as failure modes, but we now understand they have been exploited by evolution to sculpt developing organs, and have great potential for exploitation by engineers to underpin shape-shifting devices and small scale shape fabrication. The aim of this project is to use theoretical and computational tools to enhance our understanding of large strain elastic instabilities. The project will start with a learning phase, focused on deriving a soliton-like theory of ballooning and mapping the peristalsis-ballooning transition in inflated cavities. The main body of the project will then focus on elastic instabilities that are triggered by the large thermal/optical strains found in liquid crystal elastomers (LCEs). In particular, the project will study the folding/wrinkling instabilities that occur when a stiff LCE layer is adhered to a soft substrate then caused to expand relative to the substrate. A unique feature of LCEs is that the expansion strain can be spatially patterned by imprinting a desired nematic director pattern at fabrication, offering control over the wrinkle patterns that will emerge. This project will study the relationship between wrinkle pattern and encoded director pattern, culminating in the creation of surfaces on which designer topography arises via buckling on heating or illumination. This project fits squarely in three EPSRC areas: Biophysics and soft matter physics, continuum mechanics, and polymer materials.