Journal
INTERNATIONAL JOURNAL OF PLASTICITY
Volume 29, Issue -, Pages 155-172Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.ijplas.2011.08.007
Keywords
Strengthening and mechanisms; Crystal plasticity; Finite elements; Nickel; Size effects
Funding
- Belgian State - Belgian Science Policy [P6/24]
- FRS-FNRS
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The miniaturization of metallic samples has been proved to deeply affect their mechanical properties leading to a softening or a hardening effect depending on the order of the dimension reduction. The objective of this work is to provide new numerical results which explain the softening mechanisms on the mechanical behavior for nickel polycrystals which have been experimentally characterized by the authors in a previous published paper (Keller et al., 2011). Based on a strain gradient crystalline plasticity model identified for nickel, simulations of tensile tests were performed for samples with different thicknesses and grain sizes. The simulations correctly reproduce the softening effect linked to a decrease in the thickness and in the number of grains across the thickness. The analysis of the plasticity mechanisms shows that the softening is due to surface effects which are discussed in terms of grain orientations, dislocation mean free path and long-range back-stress. The model also predicts a hardening mechanism for further dimension reduction if the samples have only grain boundaries perpendicular to the tensile direction. In this case, the modification of the mechanical behavior is due to strain gradients formation. (C) 2011 Elsevier Ltd. All rights reserved.
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