MS Thesis Defense: Guangchao Wan

Friday, June 28, 2019, 1:00–3:00pm

Rm. 201 (Rett's Room), MacLean ESC

“Bistability in Beams, Plates and Shells”

Abstract

Bistable structures have two stable shapes and each can have its own functionality. Examples are ubiquitous in natural and artificial systems such as the lobe of Venus flytrap and the toy popper. For application purpose, the introduction of bistability can greatly enrich the engineering design. For instance, the bistable structures can achieve shape transition without continuing energy input to maintain the new configuration, which can increase the energetic efficiency of the actuators. Therefore, it is requisite to develop a quantitative understanding of the bistability within the mechanical structures. In this thesis, we focus on three types of mechanical structures, i.e., beams, plates and shells, and investigate the relationship between the bistability and structure’s geometry. Firstly, we study the bistable behavior of an axially compressed beam with both ends clamped. A straight beam can buckle into two directions under compression and one buckled shape can become unstable if we change the distance between two ends and the rotation angles of two ends. Through a combination of the experiments, linearized Kirchhoff theory and finite element method (FEM), we identify that the clamped beam can go through three different bifurcation behaviors depending on the symmetry of the boundary conditions. In addition, we construct the stability diagram in terms of the boundary conditions, which can accurately provide the limit point upon bifurcation. Secondly, we study the bistability of a bilayer Chromium/Vanadium dioxide (Cr/VO2) nanomembrane. The Cr/VO2 nanomembrane can form a rolled shape or a “folded” shape driven from the misfit strain between layers and the clamped boundary condition. Based on the experiments and FEM, we explore the relationship between the bistability and the geometry of the nanomembrane, which can guide the assembly of the bistable nanomembrane into various, functional mesostructures. Thirdly, we concentrate on a bistable spherical shell that can stay as an “inverted” shape. By combining experiments, theory and FEM, we explore the effects from the geometric defects on the shell’s bistability and construct the stability diagram in terms of the shell’s geometry and defect’s size. The outcomes can help establish new guidance on the design space of a variety of bistable structures.

Thesis Committee

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