Snapping Shells: Coupling Geometry, Dynamics, and Materials to Harvest Energy through Instability

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When a structure snaps to an alternate shape -- like the inversion of an umbrella on a windy day -- its structural and material integrity are often permanently lost. Many soft structures, however, are able to reverse the change between two shapes. This presents a fascinating opportunity to design dynamic and adaptable engineering structures. The rapid leaf closure of the Venus flytrap is an example of how snapping provides functionality in nature. This award supports fundamental research on the mechanics of instabilities in structures. In particular, it considers structures made of advanced and active materials which are capable of converting deformation into energy. Its results will help engineers design systems that use instabilities as a feature rather than a fault, thereby enabling structures that easily and predictably change shape over a short timescale, converting and storing energy in the process. Such structures have applications in U.S. industries with needs for autonomous power sources. Since snapping structures have been employed with great amusement in the `jumping disc' and `popper' toys that jump with an audible pop, this research will help increase public interest in science. Many soft, slender structures are able to rapidly change between two stable configurations by a snap-through elastic instability. This research will establish the mechanical and geometric criteria for shell bistability. It will determine the effect of shell geometry on the speed of snap-through, the post-snap vibrations, and the rate of asymmetric-to-symmetric shell dissipation. The effect of material properties will be examined to understand the self-actuated snap-back of shells, structures that are temporarily bistable. The research team will prepare shells out of an electrically active material. This will allow the research team to conduct novel measurements of the in-plane strain in shells during instability. These measurements will contribute important experimental insight to the theory of shell structures. Finally, the dielectric elastomeric shells will also offer a natural means for harvesting energy during the snap-through deformation. The research team will further develop BLINK, the innovative program that introduces students to the fast-moving science that our eyes often miss. The program will culminate with students using the mechanics of toy poppers as a way to study Newton's laws of motion. The implementation of this program, and subsequent creation of relevant online video content, will provide opportunities for students and the general public to realize the importance of mechanics research in answering current technological challenges.