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Experimental Verification of the Strain-Gradient Plasticity Model for Indentation

Published online by Cambridge University Press:  03 March 2011

Linmao Qian ,
Hui Yang ,
Minhao Zhu  and
Zhongrong Zhou
Linmao Qian
Affiliation:
Tribology Research Institute, National Traction Power Laboratory, Southwest Jiaotong University, Chengdu 610031, People’s Republic of China
Hui Yang
Affiliation:
Tribology Research Institute, National Traction Power Laboratory, Southwest Jiaotong University, Chengdu 610031, People’s Republic of China
Minhao Zhu
Affiliation:
Tribology Research Institute, National Traction Power Laboratory, Southwest Jiaotong University, Chengdu 610031, People’s Republic of China
Zhongrong Zhou
Affiliation:
Tribology Research Institute, National Traction Power Laboratory, Southwest Jiaotong University, Chengdu 610031, People’s Republic of China
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Abstract

The indentation size effect of pure iron samples with various pre-plastic tensile strains has been experimentally investigated and analyzed. With the increase in the strain, the indentation size effect of iron samples becomes weak, accompanied by the multiplication of the statistically stored dislocations. All of the hardness (H) versus indentation depth (h) curves fit the strain-gradient plasticity model for indentation of Nix and Gao well. Two fitting parameters, the hardness in the limit of infinite depth (H0) and the characteristic length (h*), were obtained for each curve. The hardness (H0) of iron samples can also be estimated as the microhardness (H) at a very large depth, h ≅ 10h*. Both the fitted H0 and the measured H0′ increase linearly with the tensile yield stress σy of iron samples, indicating a dependence of H0 on the statistically stored dislocation density through σy. Furthermore, 1/√h* shows a linear increase with the tensile yield stress σy, which also agrees qualitatively with the general prediction of the Nix and Gao theory. Therefore, our experiments and analysis demonstrate that the strain-gradient plasticity model for indentation of Nix and Gao can interpret the indentation size effect with satisfied precision.

Keywords

HardnessNanoindentationStress/strain relationship
Type
Articles
Information
Journal of Materials Research , Volume 20 , Issue 11 , November 2005 , pp. 3150 - 3156
Copyright
Copyright © Materials Research Society 2005

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