Lattice orientation effect on the nanovoid growth in copper under shock loading

Wenjun Zhu, Zhengfei Song, Xiaoliang Deng, Hongliang He, and Xiaoyin Cheng

Phys. Rev. B 75, 024104 – Published 8 January 2007

Abstract

Molecular-dynamics (MD) simulations have revealed that under shock loading a nanovoid in copper grows to be of ellipsoidal shape and different loading directions ([100] and $[1 \bar{1} 1]$ ) change the orientation of its major axis. This anisotropic growth is caused by preferential shear dislocation loop emission from the equator of the void under [100] loading and preferential shear dislocation loop emission deviating away from the equator under $[1 \bar{1} 1]$ loading. A two-dimensional stress model has been proposed to explain the anisotropic plasticity. It is found that the loading direction changes the distribution of the resolved shear stress along the slip plane around the void and induces different dislocation emission mechanisms.

Received 10 March 2006

DOI:https://doi.org/10.1103/PhysRevB.75.024104

Authors & Affiliations

Wenjun Zhu^1,2,*, Zhengfei Song¹, Xiaoliang Deng^1,2, Hongliang He¹, and Xiaoyin Cheng³

¹Laboratory for Shock Wave and Detonation Physics Research, Institute of Fluid Physics, Mianyang 621900, People’s Republic of China
²Department of Physics, Sichuan University, Chengdu 610065, People’s Republic of China
³Nanotechnology Center, ITC, The Hong Kong Polytechnic University, Kowloon, Hong Kong

^*Electronic mail: wjzhu@caep.ac.cn

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Vol. 75, Iss. 2 — 1 January 2007

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Images

Figure 1
Snapshots from MD simulations, showing associated plasticity of void growth under different loading direction and shock strength. The initial void diameter is $1.5 nm$ . Only atoms with hexagonal close-packed (HCP) structure (light gray) and amorphous structure (dark gray) are shown. The times for the snapshots are $8 ps$ after the simulations start. (a) $17.5 GPa$ shock strength and the [100] loading direction. (b) $20 GPa$ shock strength and the [100] loading direction. For (a) and (b), shear dislocation loops preferentially emit from equator region. (c) $20 GPa$ shock strength and the $[1 \bar{1} 1]$ loading direction. (d) $23.5 GPa$ shock strength and the $[1 \bar{1} 1]$ loading direction. For (c) and (d), the tetrahedron configurations formed by shear dislocation loops are predominantly emitted.Reuse & Permissions
Figure 2
The evolution of the axes of the void. The solid line represents the evolution of the axis paralleling to the loading direction and the dash-dotted line is for the axis perpendicular to the loading direction. The initial length of both axes is $15 Å$ . (a) $17.5 GPa$ shock strength and the [100] loading direction. (b) $20 GPa$ shock strength and the $[1 \bar{1} 1]$ loading direction.Reuse & Permissions
Figure 3
A three-dimensional illustration of the mechanisms of the void growth for the $[1 \bar{1} 1]$ loading direction. (a) When the shock strength is below $22 GPa$ , the sectors of surface enclosed by each three shear dislocation loops forming three sides of a tetrahedron configuration are pulled out as the loops expand outward. (b) When the shock strength exceeds $22 GPa$ , besides the tetrahedron configuration there are more shear dislocation loops emitting from the equator region (only one shear dislocation loop cross the equator is illustrated).Reuse & Permissions
Figure 4
A two dimensional representation of a stress-free hole in infinite medium under uniform biaxial far-field tension. $T_{x}$ and $T_{y}$ are biaxial far field tension. Under uniaxial strain condition, $T_{x} > T_{y}$ . Only one of the slip family planes is shown. When the [100] and [011] coincide with $x$ and $y$ axes, respectively, the condition corresponds to the [100] loading condition. When $[1 \bar{1} 1]$ and [211] coincide with $x$ and $y$ axes, respectively, the condition corresponds to the $[1 \bar{1} 1]$ loading condition. The slip plane has an angle of $α$ with loading direction. $R$ is the radius of the cylinder void.Reuse & Permissions
Figure 5
The distribution of the resolved shear stress along the slip plane on the surface of cylinder void in infinite medium under biaxial far field tension. $T_{x}$ and $T_{y}$ are the far field tensions along and perpendicular to the loading direction, respectively. The biaxial loading ratio is $k = T_{y} ∕ T_{x}$ . The solid line represents the condition that the slip plane has an angle of 35.2° with respect to the loading direction and $k$ is 0.71. The dash-dotted line represents the condition that the slip plane has an angle of 19.5° with respect to the loading direction and $k$ is 0.47.Reuse & Permissions

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