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PhD Thesis Proposal by
Hossein Salahshoor
(Advisor: Professor Julian. J. Rimoli)
“STRESS-INDUCED INSTABILITIES AND PHASE TRANSITIONS IN LATTICE-BASED SOLIDS: FROM MATERIALS TO METAMATERIALS”
March 8th, 11:00am-12:30pm
Montgomery Knight Rm 317
Abstract:
Stress-induced instabilities in lattices are a major category of material instabilities that often lead to significant changes in the material behavior. These instabilities can trigger various phenomenon across the scales including defect nucleation, shear bands, pattern formation, etc, where a common feature in most of them is the correspondence with a symmetry breaking. We study stress-induced instabilities in lattice-based solids, where the system is built up by a repetitive translation of a unit cell along its principal axes. The subject of our study is both the naturally existing crystalline materials and the architectured materials, so-called as metamaterials. Although we choose certain families of materials and metamaterials in our study, the approaches that we employ could be utilized to investigate instabilities of any system with translational symmetry.
In the case of crystalline materials, we focus on the stress-induced instabilities in single crystal metals. We study the onset of symmetry breaking in four distinct metals of both FCC and BCC structure, where we subject them to a combined shear-hydrostatic deformation and identify the point of symmetry breaking with the onset of instability. We perform both phonon and elastic stability analysis. We study the nature of the instability and show for the first time, to the best of our knowledge, that the short wavelength instabilities are abundant. Our results illustrate the potential pitfalls of relying on the widely used elastic stability analysis and disqualifies it as the method of choice.
In the case of metamaterials, we focus on the symmetry phase transitions in tensegrities. Tensegrities are an important class of metamaterials that have numerous applications in space structures. We study material symmetries of tensegrities by examining the eigenspaces of the effective elasticity tensor, obtained through a homogenization scheme. We demonstrate symmetry breaking and phase transitions, occurring solely due to pre-stressing the members of the lattice. We observe several phase transitions including cubic to tetragonal and tetragonal to orthotropic and vice-verses.
Committee:
Dr. Julian J. Rimoli, AE, Georgia Institute of Technology
Dr. Massimo Ruzzene, AE, Georgia Institute of Technology
Dr. George Kardomateas, AE, Georgia Institute of Technology
Dr. Arash Yavari, CEE, Georgia Institute of Technology
Dr. Dennis Kochmann, MPE, ETH Zürich
