Mechanical instabilities in soft solids

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.