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Interpreting the softening of nanomaterials through gradient plasticity

Published online by Cambridge University Press:  10 June 2011

Xu Zhang  and
Katerina E. Aifantis
Xu Zhang
Affiliation:
School of Civil Engineering and Mechanics, Huazhong University of Science and Technology, Wuhan 430074, China; and Laboratory of Mechanics and Materials, Aristotle University of Thessaloniki, Thessaloniki 54124, Greece
Katerina E. Aifantis*
Affiliation:
Laboratory of Mechanics and Materials, Aristotle University of Thessaloniki, Thessaloniki 54124, Greece; and Physics Department, Michigan Technological University, Houghton, Michigan 49931
*
a)Address all correspondence to this author. e-mail: k.aifantis@mom.gen.auth.gr
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Abstract

Experimental and simulation studies have shown that decreasing the grain size below a critical value results in softening rather than hardening in both the yield stress and flow stress of nanomaterials. In this work, a gradient plasticity framework is presented that can capture this softening behavior by treating grain boundaries as a separate phase with a finite thickness. The theoretical expression obtained for the yield stress as a function of the grain size can capture numerous experimental data that exhibit this “normal” to “abnormal” Hall–Petch transition, and an analytical equation is obtained that can predict the grain size at which this transition occurs. Furthermore, analytical expressions are obtained for the flow stress in nanomaterials, and they are in precise agreement with atomistic simulations on nanocrystalline Cu, which predict that below a critical grain size the flow stress decreases proportional to it.

Keywords

NanoscaleNanostructure
Type
Articles
Information
Journal of Materials Research , Volume 26 , Issue 11 , 14 June 2011 , pp. 1399 - 1405
Copyright
Copyright © Materials Research Society 2011

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