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Mechanical Investigations: Experimental Fracture Techniques and Frozen Small-Molecule Organics

Citation

Edwards, Bryce Walker (2021) Mechanical Investigations: Experimental Fracture Techniques and Frozen Small-Molecule Organics. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/8f8y-5h58. https://resolver.caltech.edu/CaltechTHESIS:06012021-150444627

Abstract

Fracture of architected lattices: Three-dimensional diamond, kagome, and octet lattices were prepared for validation of a standard compact tension fracture experiment at two different length scales. Solid polymer lattices were written via two-photon lithography at the microscale, and solid polymer lattices are printed via digital light processing at the macroscale. Several of the macrolattices were pyrolyzed into carbon lattices to yield a brittle material for testing. The scaling laws of fracture toughness with relative density are explored, and this offers one of the first experimental studies of a fully 3D kagome lattice.

Mechanical properties of solid benzene: We explore the mechanical properties and deformation of 10 um-sized cuboid-shaped solid benzene crystals made by freezing directly onto a liquid-nitrogen-cooled sample stage and compressed quasi-statically to 10% strain at 125 K with an in-situ nanomechanical instrument inside a Scanning Electron Microscope (SEM). Cryo-Transmission Electron Microscopy (cryo-TEM) and diffraction of frozen benzene confirms the orthorhombic crystal structure of benzene. Compressive contact pressure-strain response generated from load-displacement data suggests the deformation mechanism to occur via densification, with a loading modulus of 9 GPa, slightly larger than that of other small molecules composed of aromatic rings, such as naphthalene and biphenyl. Molecular dynamics (MD) simulations of experimentally equivalent compressions of 10-30 nm benzene samples of the same crystal structure and geometry along the principal lattice directions at 10-30 K suggest densification could, initially, occur by local amorphization of the compressed region. The discovered deformation mechanism, stiffness, and strength of benzene at 125 K can inform our understanding of geological processes on cold planetary bodies. For example, the surface of Saturn’s moon Titan is teeming with solid organics at an ambient temperature of 95 K; this work will have significant impact on designing in-situ sampling tools for future missions to Titan and to substantiate speculative surface compositions.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:Materials Science; Fracture; Lattice
Degree Grantor:California Institute of Technology
Division:Engineering and Applied Science
Major Option:Materials Science
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Greer, Julia R.
Thesis Committee:
  • Faber, Katherine T. (chair)
  • Johnson, William Lewis
  • Ravichandran, Guruswami
  • Greer, Julia R.
Defense Date:17 December 2020
Record Number:CaltechTHESIS:06012021-150444627
Persistent URL:https://resolver.caltech.edu/CaltechTHESIS:06012021-150444627
DOI:10.7907/8f8y-5h58
ORCID:
AuthorORCID
Edwards, Bryce Walker0000-0002-2393-5488
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:14219
Collection:CaltechTHESIS
Deposited By: Bryce Edwards
Deposited On:02 Jun 2021 23:31
Last Modified:09 Jun 2021 19:20

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