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Modeling and Programming Shape-Morphing Structured Media


McMahan, Connor Glenn (2022) Modeling and Programming Shape-Morphing Structured Media. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/rcw1-r139.


Shape-morphing and self-propelled locomotion are examples of mechanical behaviors that can be "programmed" in structured media by designing geometric features at micro- and mesostructural length scales. This programmability is possible because the small-scale geometry often imposes local kinematic modes that are strongly favored over other deformations. In turn, global behaviors are influenced by local kinematic preferences over the extent of the structured medium and by the kinematic compatibility (or incompatibility) between neighboring regions of the domain. This considerably expands the design space for effective mechanical properties, since objects made of the same bulk material but with different internal geometry will generally display very different behaviors. This motivates pursuing a mechanistic understanding of the connection between small-scale geometry and global kinematic behaviors. This thesis addresses challenges pertaining to the modeling and design of structured media that undergo large deformations.

The first part of the thesis focuses on the relation between micro- or mesoscale patterning and energetically favored modes of deformation. This is first discussed within the context of twisted bulk metallic glass ribbons whose edges display periodic undulations. The undulations cause twist concentrations in the narrower regions of the structural element, delaying the onset of material failure and permitting the design of structures whose deployment and compaction emerge from the ribbons' chirality. Following this discussion of a periodic system, we study sheets with non-uniform cut patterns that buckle out-of-plane. Motivated by computational challenges associated with the presence of geometric features at disparate length scales, we construct an effective continuum model for these non-periodic systems, allowing us to simulate their post-buckling behavior efficiently and with good accuracy.

The second part of the thesis discusses ways to leverage the connection between micro/mesoscale geometry and energetically favorable local kinematics to create "programmable matter" that undergo prescribed shape changes or self-propelled locomotion when exposed to an environmental stimulus. We first demonstrate the capabilities of an inverse design method that automates the design of structured plates that morph into target 3D geometries over time-dependent actuation paths. Finally, we present devices made of 3D-printed liquid crystal elastomer (LCE) hinges that change shape and self-propel when heated.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:shape-morphing structures; structured media; architected materials; soft robots; liquid crystal elastomers; shell theory; elastic stability
Degree Grantor:California Institute of Technology
Division:Engineering and Applied Science
Major Option:Mechanical Engineering
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Daraio, Chiara
Thesis Committee:
  • Bhattacharya, Kaushik (chair)
  • Pellegrino, Sergio
  • Ravichandran, Guruswami
  • Daraio, Chiara
Defense Date:17 August 2021
Record Number:CaltechTHESIS:09282021-231505066
Persistent URL:
Related URLs:
URLURL TypeDescription adapted for Chapter 2 adapted for Chapter 3 adapted for Chapter 4 adapted for Chapter 5 adapted for Chapter 6
McMahan, Connor Glenn0000-0001-5024-6138
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:14376
Deposited By: Connor McMahan
Deposited On:07 Oct 2021 18:27
Last Modified:08 Nov 2023 00:21

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