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Internal length scale and grain boundary yield strength in gradient models of polycrystal plasticity: How do they relate to the dislocation microstructure?

Published online by Cambridge University Press:  12 September 2014

Xu Zhang ,
Katerina E. Aifantis ,
Jochen Senger ,
Daniel Weygand  and
Michael Zaiser
Xu Zhang
Affiliation:
School of Mechanics and Engineering, Southwest Jiaotong University, Chengdu 610031, China; Lab of Mechanics and Materials, Aristotle University of Thessaloniki, Thessaloniki 54124, Greece; and University of Erlangen, Institute for Materials Simulation WW8, Fürth 90762, Germany
Katerina E. Aifantis
Affiliation:
Lab of Mechanics and Materials, Aristotle University of Thessaloniki, Thessaloniki 54124, Greece; and Department of Civil Engineering-Engineering Mechanics, University of Arizona, Tucson, AZ 85721, USA
Jochen Senger
Affiliation:
Institute for Applied Materials IAM, Karlsruhe Institute of Technology, Karlsruhe 76131, Germany
Daniel Weygand
Affiliation:
Institute for Applied Materials IAM, Karlsruhe Institute of Technology, Karlsruhe 76131, Germany
Michael Zaiser*
Affiliation:
University of Erlangen, Department of Materials Science and Engineering, Institute for Materials Simulation WW8, Fürth 90762, Germany
*
a)Address all correspondence to this author. e-mail: michael.zaiser@ww.uni-erlangen.de
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Abstract

Gradient plasticity provides an effective theoretical framework to interpret heterogeneous and irreversible deformation processes on micron and submicron scales. By incorporating internal length scales into a plasticity framework, gradient plasticity gives access to size effects, strain heterogeneities at interfaces, and characteristic lengths of strain localization. To relate the magnitude of the internal length scale to parameters of the dislocation microstructure of the material, 3D discrete dislocation dynamics (DDD) simulations were performed for tricrystals of different dislocation source lengths (100, 200, and 300 nm). Comparing the strain profiles deduced from DDD with gradient plasticity predictions demonstrated that the internal length scale depends on the flow-stress-controlling mechanism. Different dislocation mechanisms produce different internal lengths. Furthermore, by comparing a gradient plasticity framework with interfacial yielding to the simulations it was found that, even though in the DDD simulations grain boundaries (GBs) were physically impenetrable to dislocations, on the continuum scale the assumption of plastically deformable GBs produces a better match of the DDD data than the assumption of rigid GBs. The associated effective GB strength again depends on the dislocation microstructure in the grain interior.

Type
Invited Feature Paper
Information
Journal of Materials Research , Volume 29 , Issue 18 , 28 September 2014 , pp. 2116 - 2128
Copyright
Copyright © Materials Research Society 2014 

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