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Advances in Materials Science and Engineering
Volume 2017, Article ID 5418769, 9 pages
Research Article

Stochastic Effect of Grain Elongation on Nanocrystalline Materials Strain and Strain Rate Produced by Accumulative Roll-Bonding and Equal Channel Angular Pressing

1Department of Mechanical Engineering, Faculty of Engineering and Technology, Vaal University of Technology, Private Bag X021, Vanderbijlpark 1900, South Africa
2Department of Industrial Engineering and Operations Management, Faculty of Engineering and Technology, Vaal University of Technology, Private Bag X021, Vanderbijlpark 1900, South Africa

Correspondence should be addressed to P. Baonhe Sob; moc.liamtekcor@bos_ehnoab

Received 20 February 2017; Accepted 3 May 2017; Published 12 June 2017

Academic Editor: Paulo M. S. T. De Castro

Copyright © 2017 P. Baonhe Sob et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


Severe plastic deformation techniques are acknowledged to produce elongated grains during fabrication of nanostructured materials. Previous models relating grain size to mechanical properties considered only equivalent radius, thus ignoring other approaches of measuring grain sizes such as semiminor axis, semimajor axis, and major axis radii that determine true grain shape. In this paper, stochastic models of nanomaterials mechanical properties that include the ignored parameters have been proposed. The proposed models are tested with data from nanocrystalline aluminum samples. The following facts were experimentally observed and also revealed by the models. Grain elongates to a maximum value and then decreases with further grain refinement due to grain breakages. Materials yield stress increases with elongation to a maximum and then decreases continuously. The varying approaches of measuring grain radius reveal a common trend of Hall-Petch and Reverse Hall-Petch Relationship but with different critical grain sizes. Materials with high curvature grains have more enhanced yield stress. Reducing strain rates leads to materials with more enhanced yield stress, with critical strain rates values beyond which further reductions do not lead to yield stress enhancement. It can be concluded that, by considering different approaches of measuring grain sizes, reasons for different yield stress for nanomaterials that were observed but could not be explained have been dealt with.