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Research Papers

Surface Stress Effects on the Yield Strength in Nanotwinned Polycrystal Face-Centered-Cubic Metallic Nanowires

[+] Author and Article Information
Linli Zhu

Department of Engineering Mechanics,
School of Aeronautics and Astronautics,
Zhejiang University,
Hangzhou 310027, Zhejiang Province, China
Department of Mechanical and
Biomedical Engineering,
City University of Hong Kong,
Kowloon, Hong Kong, China
e-mail: llzhu@zju.edu.cn

Xiang Guo

School of Mechanical Engineering,
Tianjin University,
Tianjin 300072, China

Jian Lu

Department of Mechanical and
Biomedical Engineering,
City University of Hong Kong,
Kowloon, Hong Kong, China
e-mail: jianlu@cityu.edu.hk

1Corresponding authors.

Contributed by the Applied Mechanics Division of ASME for publication in the JOURNAL OF APPLIED MECHANICS. Manuscript received May 22, 2014; final manuscript received July 10, 2014; accepted manuscript posted July 18, 2014; published online August 5, 2014. Editor: Yonggang Huang.

J. Appl. Mech 81(10), 101002 (Aug 05, 2014) (6 pages) Paper No: JAM-14-1224; doi: 10.1115/1.4028039 History: Received May 22, 2014; Revised July 10, 2014; Accepted July 18, 2014

The influence of surface stress on the yield strength of nanotwinned polycrystal face-centered-cubic (FCC) metallic nanowire is theoretically investigated. The contribution of surface boundaries on the strengthening/softening is analyzed in the framework of continuum mechanics theory by accounting for the surface energy effects. The other strengthening mechanisms originated from the inner boundaries are described by the Taylor model for the nanotwinned polycrystalline metals. The theoretical results demonstrate that the yield strength of nanotwinned polycrystal wires is dependent on the twin spacing, grain size and the geometrical size of the wire. The surface stress effects on the strength perform more and more significantly with decreasing the wire diameter, especially for the diameter smaller than 20 nm. In addition, the dependence of surface stress on the strength is also relevant to the size of microstructures as well as the magnitude and direction of surface stress. These results may be useful in evaluating the size-dependent mechanical performance of nanostructured materials.

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Figures

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Fig. 2

The tensile and compressive yield strength of nanotwinned polycrystal copper nanowires varied with the diameter of nanowires with different twin spacings. The twin spacings are 2 nm, 5 nm, and 10 nm, respectively, and the grain size is 20 nm. The surface stress is adopted as 1.396 N/m. The cubic symbol is the data from MD simulation [27].

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Fig. 6

The yield strength as a function of the surface stress with different twin spacings. The grains size and wire diameter are both 20 nm, and the twin spacings are 2 nm and 10 nm.

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Fig. 1

Schematics of a nanotwinned polycrystal nanowire under uniaxial external load

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Fig. 3

The grain size dependence of the tensile and compressive yield strength in nanotwinned polycrystal copper nanowires. The twin spacings are 2 nm, 5 nm, and 10 nm, respectively, and the diameter of the wire is 30 nm. The surface stress is adopted as 1.396 N/m.

Grahic Jump Location
Fig. 4

The twin spacing dependence of the tensile and compressive yield strength in nanotwinned polycrystal copper nanowires. The grains size and wire diameter are 40 nm and 20 nm, respectively. The surface stress is adopted as 1.396 N/m.

Grahic Jump Location
Fig. 5

The yield strength as a function of wire diameter in nanotwinned polycrystal copper nanowires with different surface stresses. The grains size is 20 nm, and the twin spacings are 2 nm and 10 nm. The surface stress is adopted as 0 N/m, − 5 N/m, and 5 N/m.

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