Deformation Mechanisms at Grain Boundaries in Polycrystal Plasticity
Al-Fadhalah, Khaled Jabr
This item is only available for download by members of the University of Illinois community. Students, faculty, and staff at the U of I may log in with your NetID and password to view the item. If you are trying to access an Illinois-restricted dissertation or thesis, you can request a copy through your library's Inter-Library Loan office or purchase a copy directly from ProQuest.
Permalink
https://hdl.handle.net/2142/83806
Description
Title
Deformation Mechanisms at Grain Boundaries in Polycrystal Plasticity
Author(s)
Al-Fadhalah, Khaled Jabr
Issue Date
2004
Doctoral Committee Chair(s)
Beaudoin, Armand J.
Department of Study
Mechanical Engineering
Discipline
Mechanical Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Materials Science
Language
eng
Abstract
Strengthening by grain boundaries is commonly attributed to the dislocation pile-up at the boundary describing the effect of grain size, i.e. the Hall-Petch relation. In this work, the importance of the boundary structure is emphasized, along with grain size, in predicting the flow stress using alternative deformation mechanisms. The effect of boundary structure on the plastic deformation of metals is modeled by computing the aggregate response of composite grains in the visco-plastic self-consistent scheme. Assuming a planar boundary, the composite grain model accounts for the interaction between neighboring grains by satisfying the compatibility and equilibrium constraints across the boundary. For silver with 2 mum grains, in-situ Transmission Electron Microscopy studies suggest that annealing twin boundaries are sources for lattice dislocations. These sources contribute to an extended yield point, modeled using a formulation for slip system hardening that accounts for the evolution of mobile and forest dislocation densities---depicting boundary-dislocation and dislocation-dislocation interactions, respectively. In addition, the composite grain model is applied to predict the unique rolling texture of Cu/Nb nanostructured multilayers occurs due to the confined layer slip of single Orowan loops. The model regards each grain as a composite composed of Cu and Nb crystals. A hardening effect is introduced to account for the interaction between glide and interface dislocations. This unconventional hardening promotes symmetry of slip activity and consequently slows evolution of the rolling texture for Cu/Nb nanolayers.
Use this login method if you
don't
have an
@illinois.edu
email address.
(Oops, I do have one)
IDEALS migrated to a new platform on June 23, 2022. If you created
your account prior to this date, you will have to reset your password
using the forgot-password link below.
