Doctoral Dissertations

Rui Yuan

Abstract

"Implementation of nanostructured metals and alloys for use in engineering applications requires a detailed knowledge of the underlying deformation mechanisms in these materials. It is well known that plastic deformation in metals and alloys is mainly mediated by dislocation activities. Nonetheless, TEM observations and atomistic simulations indicate that dislocation-mediated plasticity in nanostructured metals and alloys is significantly different from that in their coarse-grained counterparts. Therefore, this dissertation focuses on the exploration of the deformation mechanisms in nanostructured metals via crystal plasticity finite element modeling and simulation.

A statistical grain boundary dislocation source model accounting for dislocation nucleation and slip events was developed and incorporated into a 3D discrete crystal plasticity finite element model to study the mechanical behaviors of nanostructured metals including nanocrystalline, nanotwinned and heterogeneous lamellar structured metals. It was found that a Hall-Petch scaling of strength emerged from grain size limitation on dislocation source length, and that the Hall-Petch slope depended sensitively on texture and was proportional to the Taylor factor. Furthermore, it was shown that experimentally observed scaling between yield strength and twin thickness in columnar-grained nanotwinned Cu arose from statistical variability in dislocation source length, and that reducing twin thickness could increase plastic anisotropy as a result of the increase in mean stress to emit dislocations. In addition, it was revealed that a heterogeneous lamellar structure consisting of a nanocrystalline layer sandwiched between two coarse-grained lamellae could effectively homogenize plastic strain in the nanocrystalline layer, leading to suppressed strain heterogeneity and enhanced ductility"--Abstract, page iv.

Advisor(s)

Zhou, Caizhi

Committee Member(s)

Van Aken, David C.
O'Keefe, Matthew
Asle Zaeem, Mohsen
Du, Xiaoping

Department(s)

Materials Science and Engineering

Degree Name

Ph. D. in Materials Science and Engineering

Sponsor(s)

University of Missouri. Research Board
Missouri University of Science and Technology. Materials Research Center

Publisher

Missouri University of Science and Technology

Publication Date

Summer 2017

Journal article titles appearing in thesis/dissertation

  • Emergence of grain-size effects in nanocrystalline metals from statistical activation of discrete dislocation sources
  • Coupled crystal orientation-size effects on the strength of nano crystals
  • Statistical dislocation activation from grain boundaries and its role in the plastic anisotropy of nanotwinned copper
  • Homogenization of plastic deformation in heterogeneous lamella strcutures

Pagination

xiii, 146 pages

Note about bibliography

Includes bibliographic references.

Rights

© 2017 Rui Yuan, All rights reserved.

Document Type

Dissertation - Open Access

File Type

text

Language

English

Thesis Number

T 11194

Electronic OCLC #

1003043580

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