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Creep resistance and strain-rate sensitivity of nanocrystalline materials

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Title
Creep resistance and strain-rate sensitivity of nanocrystalline materials
Name (ID = NAME001); (type = personal)
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Barai
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Pallab
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Pallab Barai
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author
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Weng
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George
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Advisory Committee
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George J Weng
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chair
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Baruh
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Haim
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Advisory Committee
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Haim Baruh
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Bottega
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William
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Advisory Committee
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William J Bottega
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Rutgers University
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degree grantor
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Graduate School - New Brunswick
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Text
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theses
OriginInfo
DateCreated (qualifier = exact)
2008
DateOther (qualifier = exact); (type = degree)
2008-05
Language
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English
PhysicalDescription
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electronic
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application/pdf
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text/xml
Extent
xii, 99 pages
Abstract
A micromechanics-based continuum model is developed to determine the creep resistance and strain-rate sensitivity of the nanocrystalline materials. The solid is idealized as a two (or three) phase composite, where the grains were treated as spherical inclusions, the grain boundary as the matrix and the pores/voids as the third phase (if present in the solid) of the composite. The strain of an individual phase is taken to be the sum of elastic and creep/viscoplastic components. Within the elastic context the homogenization scheme is developed based on the Eshelby-Mori-Tanaka approach. The Laplace transform was used to convert the linear elastic homogenization
method to a linear viscoelastic one, and then to convert the viscoelastic response to viscoplastic one, during which the Maxwell viscosity of the viscoelastic phases is replaced by the secant viscosity of the viscoplastic phases. A nonlinear-rate dependent constitutive equation is assumed for both the grain interior and grain boundary to calculate the secant viscosity of the individual phase at a given stage of deformation. The drag stress of the grain interior is assumed to follow the Hall-Petch effect, but that of the grain boundary phase is taken to be size-independent. By using the field-fluctuation method, the effective stress (or effective strain rate) of the constitutive phase is derived in terms of the applied stress (or applied strain rate). The change in porosity under different loading conditions is also incorporated within the model.
The validity of the model was verified by comparing the predicted stress-strain results with the experimental data of Sanders et al. [42], Wang et al. [43] and Wang et al. [44] for the creep response, and Khan et al. [48] and Khan and Zhang [49] for the constant strain-rate loading. The model is capable of capturing both hardening and softening of material as grain size decreases from coarse grain to the nanometer range. The latter characteristic is also known as the inverse Hall-Petch effect and this occurs in both creep and constant strain-rate response. As a result, the critical grain size at which the solid has maximum strength can be estimated using this method. With the presence of porosity, the developed model is also able to capture the nonlinearity in the stress-strain plot under hydrostatic loading.
Note (type = degree)
M.S.
Note (type = bibliography)
Includes bibliographical references (p. 94-98).
Subject (ID = SUBJ1); (authority = RUETD)
Topic
Mechanical and Aerospace Engineering
Subject (ID = SUBJ2); (authority = ETD-LCSH)
Topic
Materials--Creep
Subject (ID = SUBJ3); (authority = ETD-LCSH)
Topic
Nanocrystals
Subject (ID = SUBJ4); (authority = ETD-LCSH)
Topic
Nanostructured materials
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Title
Graduate School - New Brunswick Electronic Theses and Dissertations
Identifier (type = local)
rucore19991600001
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http://hdl.rutgers.edu/1782.2/rucore10001600001.ETD.17274
Identifier
ETD_895
Location
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NjNbRU
Identifier (type = doi)
doi:10.7282/T35B02TP
Genre (authority = ExL-Esploro)
ETD graduate
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Open
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Name
PALLAB BARAI
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Copyright holder
Affiliation
Rutgers University. Graduate School - New Brunswick
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Non-exclusive ETD license
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I hereby grant to the Rutgers University Libraries and to my school the non-exclusive right to archive, reproduce and distribute my thesis or dissertation, in whole or in part, and/or my abstract, in whole or in part, in and from an electronic format, subject to the release date subsequently stipulated in this submittal form and approved by my school. I represent and stipulate that the thesis or dissertation and its abstract are my original work, that they do not infringe or violate any rights of others, and that I make these grants as the sole owner of the rights to my thesis or dissertation and its abstract. I represent that I have obtained written permissions, when necessary, from the owner(s) of each third party copyrighted matter to be included in my thesis or dissertation and will supply copies of such upon request by my school. I acknowledge that RU ETD and my school will not distribute my thesis or dissertation or its abstract if, in their reasonable judgment, they believe all such rights have not been secured. I acknowledge that I retain ownership rights to the copyright of my work. I also retain the right to use all or part of this thesis or dissertation in future works, such as articles or books.
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