COVID-19 Information

PhD Thesis Defense: Guangchao Wan

Friday, December 4, 2020, 1:30pm

Videoconference

For info on how to attend this videoconference, please email guangchao.wan.TH@dartmouth.edu

“Geometry-driven Multistable Structures and Their Applications”

Abstract

Multistable structures that feature more than one stable shape are ubiquitous in biological and engineered systems. Examples include the lobes of the Venus flytrap and slap bracelets. They can realize the shape transitions in response to certain external stimuli and maintain the new, stable configurations without continuous energy input, so can be employed as deployable structures with high energy-efficiency. During the shape transition (snap-through), the stored elastic energy will be converted to kinetic energy and speed up the process, thus enabling a variety of applications in actuators and soft robotics. Moreover, such a snap-through behavior, as well as the nonlinear cross-well dynamics, of multistable structures have been exploited to design energy harvesters that have high power output and a broad spectrum of effective excitation frequencies.

The focus of this thesis is on the mechanistic understanding of the multistable structures, including their static and dynamic behaviors, and their applications, for example, in energy harvesting when integrated with piezoelectric materials. In the first section, we study the bistability of a defected shell through experiments, theory, and simulations. Quantitative relationship between the defect’s size and the shell’s bistability is identified, and good agreement is found between theory, simulations, and experiments. In the second section, the bistability of a triple-layer plate is investigated through the combination of experiments, theory, and simulations. We demonstrate that the plate’s bistability originates from its asymmetric geometry and show its reconfigurability. In the third section, we study the snap-through of a bistable shell driven by the inelastic deformation. Based on the theoretical analysis and finite element simulations, we calculate the variation of the shell’s shape versus time and identify the critical slowing down effect during the snap-through process. In the fourth section, we use strain-engineering to create multistable structures and integrate them with piezoelectric materials to fabricate energy harvesters can be used to convert biomechanical energy to electrical energy to charge implant medical devices. Experiments and theoretical analysis demonstrate that the fabricated bistable energy harvester has high power output and can stay effective over a wide range of excitation frequency.

Collectively, this thesis quantitatively identifies the static and dynamic behaviors of several geometry-driven multistable structures and further discusses the advantages of exploiting multistable structures in energy harvesting. The results can greatly enrich the current design space of multistable structures across multiple length scales and facilitate the relevant applications including reconfigurable structures, actuators, soft robotics and nonlinear energy harvesters.  

Thesis Committee

For more information, contact Daryl Laware at daryl.a.laware@dartmouth.edu.