Mechanical and Civil Engineering Seminar
Haolu (Jane) Zhang, Mechanical Engineering Graduate Student
PhD Thesis Defense
Abstract:
Microstructure-governed damage resistance in materials enables a variety of functional applications, such as durable biomedical implants and robust product packaging. As industrial applications continue to shrink in size, it became increasingly apparent that when a material's external structural size and internal microstructural size become comparable, its mechanical behavior starts to deviate from that of bulk, such is the smaller-is-stronger size-effect in metals. This elucidation necessitates the characterization of materials at lengthscales relevant to their internal microstructure to guarantee accuracy in the design of real-world applications.
Our work aims at deciphering the microstructure-mechanics relationship for materials at lengthscales bridging the gap between the atomic level and macroscale, with shape memory ceramics, scorpion shells, and jellyfish biogel as sample systems. We use electron and x-ray diffraction to characterize microstructures such as twinning, defects, and fiber organization, while revealing strength, toughness, and other deformation mechanisms through in-situ nanomechanical experiments. We show improved shape recovery in an otherwise brittle ceramic by tuning its phase compatibility at the nanoscale and reveal unprecedented smaller-is-stronger size-dependence for its twinning-induced plasticity. We then unveil competing fiber orientations in Scorpion shells that follow fiber-mechanics principles and demonstrate combined poroelasticity/viscoelasticity constitutive relation in Jellyfish that explains their self-healing behavior. The correlation between microstructure and mechanical behavior unveil unique damage mitigation and energy dissipation techniques in both brittle ceramics and natural biomaterials at each order of lengthscale, paving the road to designing macroscopic materials with hierarchical mechanical behavior and improved plasticity.
Please attend this Defense virtually:
https://caltech.zoom.us/j/82823044981?pwd=ZWUwa2VqSnFtTnlOMDJ3NXFCYjZ4Zz09
Meeting ID: 828 2304 4981
Passcode: 064028