Controllable buckling & snapping
Shell structures are instability-prone. If we can understand and control these instabilities, we can use them to our advantage in engineering designs. Our work has focused on uncovering geometry- and mechanics-based guidelines for inducing instabilities in efficient and controllable ways.
Efficient snap-through in spherical caps
To drive snap-through in a bistable device or actuator, a non-mechanical stimulus (e.g. thermal, electrical, chemical…) is typically applied to the entire shell. This can mean high energy input and large amounts of active (i.e. stimulus-responsive) materials. Here, we show that you can make spherical caps snap with much less active material, without requiring a higher stimulus–as long as the active region lies on the shell boundary. This result is stimulus-agnostic, and can be mapped to many non-mechanical loads. We demonstrate with experiments using both swelling and magnetic stimuli.
- L. Stein-Montalvo, J.H. Lee, Y. Yang, M. Landesberg, H.S. Park, and D.P. Holmes. Efficient snap-through of spherical caps by applying a localized curvature stimulus. European Physical Journal E, 45, 3 (2022) doi: 10.1140/epje/s10189-021-00156-0
EPJE (2022)
Delayed buckling of viscoelastic spherical shells
Silicone elastomers are commonly used in engineering designs, e.g. as actuators in soft robotics. However, these materials are viscoelastic, so their response to loading depends on the load rate. At pressures below the elastic critical buckling load, shells made of these viscoelastic materials can still buckle, following a delay period. Here, we show that viscoelastic creep deformation acts like a geometric defect, slowly lowering the critical load to cause delayed buckling in seemingly stable elastomer shells under a constant load. This work can offer a pathway to introduce tunable, time-controlled actuation to existing mechanical actuators.
- L. Stein-Montalvo, D.P. Holmes, and G. Coupier. Delayed buckling of spherical shells due to viscoelastic knockdown of the critical load. Proc. R. Soc. A, 477 (2021) doi: 10.1098/rspa.2021.0253 (Write-up)