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Geometry and mechanics of liquid crystal elastomers

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Liquid crystal elastomers (LCEs) are rubbery soft solids that contain the orientational order of a liquid crystal. They exhibit an aligned-isotropic phase transition, which is associated with a very large spontaneous contraction along the alignment (~50%), making LCEs promising artificial muscles. In this talk, I will give an introduction to LCEs, and discuss three recent mechanics problems arising from our work on them. One key idea is a flat LCE sheet can be fabricated with a pattern of molecular alignment, which turns into a pattern of contraction upon stimulation, morphing the sheet into a (Gauss) curved surface – i.e. LCEs can be used to form programmable shape-shifting devices. The material is the machine. A concentric circle pattern will morph the sheet into a conical shell, and such samples are surprisingly strong actuator capable of lifting 1000x their own weight. This leads to my first mechanics problem: how much load can such a conical shell bear without buckling. I will discuss that LCE cone buckling is actually accelerated by boundary layer deformations, which leading to a new buckling formula with a t2.5 scaling with thickness, as compared to t2 for classic Koiter like results. Secondly, I will discuss how to design patterns of contraction to create surfaces with curved folds, which are analogues of the curved folds found in origami, except with a geometrically intrinsic character, and hence much greater strength. Finally, I will discuss the “soft-elasticity” of LCEs—- a phenomenon in which the alignment rotates in response to strain, leading to large deformations at almost zero stress. I will demonstrate how such soft-modes lead to interesting microstructures in the material and, and generate a new surface instability that forms large amplitude cross-hatch topography.

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Meeting ID: 837 2933 8532

This talk is part of the Engineering Department Structures Research Seminars series.

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