Granular Shape Memory Ceramics
| dc.contributor.author | Rauch, Hunter | en |
| dc.contributor.committeechair | Yu, Hang | en |
| dc.contributor.committeemember | Viehland, Dwight D. | en |
| dc.contributor.committeemember | Lu, Peizhen | en |
| dc.contributor.committeemember | Mirzaeifar, Reza | en |
| dc.contributor.department | Materials Science and Engineering | en |
| dc.date.accessioned | 2022-10-28T06:00:13Z | en |
| dc.date.available | 2022-10-28T06:00:13Z | en |
| dc.date.issued | 2021-05-05 | en |
| dc.description.abstract | Shape memory ceramics (SMCs) are burgeoning functional materials based on zirconia with a reversible, stress-inducible martensitic phase transformation. Compared to metallic shape memory alloys, SMCs have broader operating temperatures, higher critical stresses, and larger mechanical hysteresis loops. These advantages make SMCs attractive for high-output actuation and sensing in extreme environments or energy dissipation applications; however, the key phase transformation generates large stresses and strains that accumulate at grain boundaries and result in fracture of monolithic SMCs. This means that material forms with decreased mechanical constraint are necessary. Transformation without fracture has been previously demonstrated with SMC micropillars and individual microparticles, but these material forms lack useful applications. By utilizing easily scalable granular packings of discrete free particles, the transformation can be triggered in bulk without fracture in much the same way. The granular packing material form introduces significant complexity as the internal stress distributions responsible for the phase transformation are highly heterogeneous on the macro-, meso-, and micro-scales. Moreover, the unconstrained phase transformation behaves differently than the constrained transformation, which is more studied in zirconia. The interactions of these various factors are explored from a fundamental perspective in this work, notably including (1) a unique 'continuous mode' of both forward and reverse transformation in granular packings, (2) the dependence of transformation behavior on macro-, meso-, and microstructure, and (3) the evolution of the granular packings' structure and energy dissipation capacity over 10,000 loading cycles. Diverse experimental techniques are employed, ranging from mechanical testing and calorimetry to in situ neutron diffraction, to support theory based on the martensitic phase transformation in zirconia, the shape memory and superelastic effects, and granular material physics. | en |
| dc.description.abstractgeneral | Shape memory materials are capable of remembering their original shape even when they are deformed, and can return to that shape when they are heated. This unique property stems from a phenomenon called martensitic phase transformation which bridges the gap between microscopic structural changes and macroscopic shape changes as a response to specific environmental changes. Most of the common shape memory materials are metallic, like nitinol (NiTi), which has uses in orthodontic wires and cardiological stents, but there are also ceramic materials that can display the shape memory effect. These shape memory ceramics are based on zirconia (ZrO2), and are distinct from metallic shape memory materials because of their brittle behavior and high temperature stability owing to their chemical structure. The work presented in this thesis concerns the behavior of shape memory ceramics in granular form (i.e., loose powders) over a range of external conditions. Diverse experimental techniques are employed to investigate differences between granular and non-granular shape memory ceramics. This work shows how the unique structure of a granular material, which is dominated by highly uneven force distributions and microscopic effects, interacts with the martensitic phase transformation in shape memory ceramics to produce a 'continuous' mode of transformation that differs from non-granular shape memory materials. This continuous mode is itself dependent on the granular material's macro-, meso-, and micro-structure, and on the shape memory material's composition and history. In the future, shape memory ceramics might leverage the insights gained from this work for applications including energy dissipation or on-demand shape changes (i.e., actuation). | en |
| dc.description.degree | Doctor of Philosophy | en |
| dc.format.medium | ETD | en |
| dc.identifier.other | vt_gsexam:30067 | en |
| dc.identifier.uri | http://hdl.handle.net/10919/112305 | en |
| dc.publisher | Virginia Tech | en |
| dc.rights | In Copyright | en |
| dc.rights.uri | http://rightsstatements.org/vocab/InC/1.0/ | en |
| dc.subject | shape memory ceramics | en |
| dc.subject | granular materials | en |
| dc.subject | phase transformation | en |
| dc.subject | in situ neutron diffraction | en |
| dc.title | Granular Shape Memory Ceramics | en |
| dc.type | Dissertation | en |
| thesis.degree.discipline | Materials Science and Engineering | en |
| thesis.degree.grantor | Virginia Polytechnic Institute and State University | en |
| thesis.degree.level | doctoral | en |
| thesis.degree.name | Doctor of Philosophy | en |