Date of Award
Doctor of Philosophy (PhD)
Mechanical & Aerospace Engineering
The inherent hierarchical microstructural organization in natural materials is responsible for their excellent mechanical properties beyond that predicted by the simple rule-of-mixtures. Further exhibit synergy between strength and toughness, otherwise mutually exclusive in brittle materials. Conventional processing methods are unable to replicate hierarchical microstructures in engineering ceramics akin to that observed in natural materials. Ice-templating has emerged as a potential technique to fabricate bioinspired hierarchical materials. This process involves simultaneous unidirectional solidification and phase segregation of aqueous suspensions. Ice-templated porous ceramic materials have received significant attention for overcoming several limitations of conventional ceramic foams currently used in numerous engineering applications. The purpose of this dissertation is many-folds with a central theme of tunable compressive response, which has been revealed by investigating microstructure-mechanical property relationships in both ice-templated ceramics and infiltrated composites.
First, this dissertation developed a novel extrinsic methodology. The alternating current (AC) electric field was uniquely employed to tailor ice-templated microstructure and mechanical properties. This research revealed that local suspension concentration could be effectively manipulated by applying AC electric fields to aqueous ceramic suspensions, providing a novel approach to tune ice-templated microstructure and remarkably enhance compressive mechanical properties without compromising porosity.
Next, this dissertation investigated the loading orientation dependence of the compressive response of freeze cast ceramic-polymer composites, motivated by the structural gradient observed in natural materials. The results revealed a strong orientation dependence of compressive response and failure behavior (catastrophic vs. progressive). Furthermore, this dissertation investigated inelastic deformation mechanisms that evolve in these composites under compressive loading conditions and cause macroscopic failure. It was revealed that the deformation mechanisms were also strongly influenced by the loading orientation.
Finally, this dissertation investigated compressive response and damage evolution in ice-templated ceramics and composites under high-strain rate (dynamic) loading conditions. Ice-templated materials with higher porosity exhibited progressive crushing type damage evolution, irrespective of the strain rate regime. The results suggested greater structural stability in ice-templated ceramics at high-strain rates. This dissertation also investigated the influence of microstructure on the impact behavior of ice-templated sintered alumina materials and the relationship between dynamic compressive strength and impact response.
"Tunable Compressive Mechanical Behavior of Ice-Templated Materials"
(2021). Doctor of Philosophy (PhD), Dissertation, Mechanical & Aerospace Engineering, Old Dominion University, DOI: 10.25777/348v-0758