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dc.contributor.advisorKulkarni, Yashashree
dc.creatorJiao, Shuyin
dc.date.accessioned2017-08-07T20:58:18Z
dc.date.available2017-08-07T20:58:18Z
dc.date.createdAugust 2015
dc.date.issued2015-08
dc.date.submittedAugust 2015
dc.identifier.citationPortions of this document appear in: Bezares, Jiddu, Shuyin Jiao, Yue Liu, Daniel Bufford, Lei Lu, Xinghang Zhang, Yashashree Kulkarni, and Robert J. Asaro. "Indentation of nanotwinned fcc metals: Implications for nanotwin stability." Acta Materialia 60, no. 11 (2012): 4623-4635. https://doi.org/10.1016/j.actamat.2012.03.020
dc.identifier.urihttp://hdl.handle.net/10657/1973
dc.description.abstractResearch over the past decade has provided compelling evidence that nanotwinned structures may be optimal motifs for the design of high-strength high-ductility materials. This dissertation presents our atomistic study of the deformation mechanisms governing the radiation tolerance, high temperature creep, and fracture response of nanotwinned face-centered cubic (fcc) metals. We employ molecular dynamics (MD) to elucidate the synergistic role of grain boundaries (GBs) and coherent twin boundaries (CTBs) in the radiation tolerance of nanotwinned Cu. While GBs are known to be excellent sinks for point defects, CTBs do not absorb point defects. A beneficial corollary is that the structural integrity of CTBs remains intact as radiation-induced defects pass through them and get absorbed into GBs. Thus, our tension simulations reveal that nanotwinned metals continue to exhibit high strength even after being subjected to radiation damage. We also perform atomistic simulations of cyclic nanoindentation to complement experimental studies of cyclic nano- and micro-indentation, along with indentation creep, on nanotwinned Cu and Ag. Taken together, the studies provide evidence that nanotwinned fcc structures are more stable than their nanocrystalline counterparts. Inspired by the excellent mechanical stability of nanotwinned metals during indentation creep, we investigate high temperature creep in polycrystalline nanotwinned Cu using MD. The simulations reveal that the nanotwinned metals exhibit greater creep resistance with decreasing twin boundary (TB) spacing at all applied stresses. Nanotwinned metals with very high density of TBs exhibit a new creep deformation mechanism at high stresses governed by TB migration. This is in contrast to nanocrystalline and nanotwinned metals with larger twin spacing, which exhibit a more conventional transition from GB diffusion and sliding to dislocation nucleation. Finally, our investigation of the crack propagation along CTBs in a range of fcc metals with various crack and sample geometries indicates that the alternating brittle-ductile behavior of CTBs observed perviously is sensitive to the material, and crack length. In summary, our results furnish insights into the role of TBs in governing the remarkable mechanical stability, creep resistance and radiation tolerance of nanotwinned metals, making them strong candidates for future structural materials for extreme environments.
dc.format.mimetypeapplication/pdf
dc.language.isoeng
dc.rightsThe author of this work is the copyright owner. UH Libraries and the Texas Digital Library have their permission to store and provide access to this work. UH Libraries has secured permission to reproduce any and all previously published materials contained in the work. Further transmission, reproduction, or presentation of this work is prohibited except with permission of the author(s).
dc.subjectTwin boundaries
dc.subjectRadiation
dc.subjectCreep
dc.subjectNanotwinned metals
dc.subjectMolecular dynamics
dc.subjectGrain stability
dc.subjectFracture
dc.titleMolecular Dynamics Study of Radiation and Creep Response of Nanotwinned FCC Metals
dc.date.updated2017-08-07T20:58:18Z
dc.type.genreThesis
thesis.degree.nameDoctor of Philosophy
thesis.degree.levelDoctoral
thesis.degree.disciplineMechanical Engineering
thesis.degree.grantorUniversity of Houston
thesis.degree.departmentMechanical Engineering, Department of
dc.contributor.committeeMemberSharma, Pradeep
dc.contributor.committeeMemberLi, Mo
dc.contributor.committeeMemberWhite, Kenneth W.
dc.contributor.committeeMemberAgrawal, Ashutosh
dc.creator.orcid0000-0002-2777-8125
dc.type.dcmitext
dc.format.digitalOriginborn digital
dc.description.departmentMechanical Engineering, Department of
thesis.degree.collegeCullen College of Engineering


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