^{1,2}, H. A. Wu

^{1}and S. N. Luo

^{2,a)}

### Abstract

Microstructure effects on shock response of Cu nanofoams are investigated with molecular dynamics simulations, including elastic-plastic deformation, Hugoniot states, void collapse, nanojetting, and vaporization. The microstructure features examined include pore shape, arrangement and size, as well as grain boundaries. The elastic-plastic transition, void collapse, and jetting including vaporization, are dependent on the microstructure, although to different extents. The void arrangement and aspect ratio play an important role. The effects of grain boundaries and void size are less pronounced. Considering the measurement scatter inherent for porous materials, the high pressure Hugoniot states are not sensitive to microstructure. Jetting during void collapse is due to tensorial velocity gradients (direction and amplitude), and a combined result of forward, divergent, and convergent flows with varying contributions; this mechanism and related processes are common for different microstructures. Free surface jetting involves necking and cavitation. Elliptical voids with large aspect ratios, and with their centers aligned linearly with the shock direction, are particularly efficient in inducing high speed jetting and vaporization.

This work was supported in part by National Science Foundation of China (11172289) and by the Fundamental Research Funds for the Central Universities of China.

I. INTRODUCTION

II. METHODOLOGY

III. RESULTS AND DISCUSSION

IV. SUMMARY

##### B82B1/00

## Figures

Unit configurations of columnar Cu nanofoams, created from a {100} single crystal or columnar nanocrystalline Cu, and projected along the z-axis (x: [100], y: [010], and z: [001]). The numbers denote configuration types 1–8. For types 7 and 8, color coding refers to a specific grain from which a columnar pore is created; neighboring grains are rotated by 30°. Grain boundaries are inherent in type 8 nanofoams.

Unit configurations of columnar Cu nanofoams, created from a {100} single crystal or columnar nanocrystalline Cu, and projected along the z-axis (x: [100], y: [010], and z: [001]). The numbers denote configuration types 1–8. For types 7 and 8, color coding refers to a specific grain from which a columnar pore is created; neighboring grains are rotated by 30°. Grain boundaries are inherent in type 8 nanofoams.

The profiles for type-2 nanofoam shock loaded at and 2 km s−1, showing a two-wave and a single-wave structure, respectively. The ux values for the former are multiplied by 2. Shock direction: left → right.

The profiles for type-2 nanofoam shock loaded at and 2 km s−1, showing a two-wave and a single-wave structure, respectively. The ux values for the former are multiplied by 2. Shock direction: left → right.

The stress ( ), shock velocity ( ), and particle velocity ( ) of the elastic precursor for different foam types. The values in (b) are multiplied by 10.

The stress ( ), shock velocity ( ), and particle velocity ( ) of the elastic precursor for different foam types. The values in (b) are multiplied by 10.

The Hugoniot states for different types of nanofoams shocked at and 2 km s−1. Experiment results, 23 full density Hugoniot, compacted Hugoniot, and a model fit 7 are also included for comparison.

Void collapse: snapshots of atomic configurations (projected onto the xy-plane) for . The numbers denote foam types. Grain boundary formation or deformation is seen for types 7 and 8. Color-coding is based on . Shock direction: left → right.

Void collapse: snapshots of atomic configurations (projected onto the xy-plane) for . The numbers denote foam types. Grain boundary formation or deformation is seen for types 7 and 8. Color-coding is based on . Shock direction: left → right.

Internal jetting: snapshots of atomic configurations (projected onto the xy-plane) for . The numbers denote foam types. Color-coding is based on . Shock direction: left → right.

Internal jetting: snapshots of atomic configurations (projected onto the xy-plane) for . The numbers denote foam types. Color-coding is based on . Shock direction: left → right.

Internal jetting: vector plots of the distribution of velocity projected onto the xy-plane for different types of foams shocked at . The snapshots are for t ∼ 90 ps. Numbers denote foam types. Shock direction: left → right.

Internal jetting: vector plots of the distribution of velocity projected onto the xy-plane for different types of foams shocked at . The snapshots are for t ∼ 90 ps. Numbers denote foam types. Shock direction: left → right.

Evolution of internal jetting and initiation of free surface jetting: vector plots of the distribution of velocity projected onto the xy-plane for the type-3 foam loaded at . Shock direction: left → right.

Evolution of internal jetting and initiation of free surface jetting: vector plots of the distribution of velocity projected onto the xy-plane for the type-3 foam loaded at . Shock direction: left → right.

Free surface jetting: snapshots of atomic configurations (projected onto the xy-plane) for . A quasi-steady state is achieved except for the case of type 4. The numbers denote foam types. Atoms are color-coded with ux in km s−1. Shock direction: left → right.

Free surface jetting: snapshots of atomic configurations (projected onto the xy-plane) for . A quasi-steady state is achieved except for the case of type 4. The numbers denote foam types. Atoms are color-coded with ux in km s−1. Shock direction: left → right.

Free surface jetting: vector plots of the distribution of velocity projected onto the xy-plane(a, b, d–f), and an atomic configuration (c) for , showing cavity nucleation in jet heads. The snapshots are for t = 105–114 ps. (c) is colored by potential energy, and corresponds to (d). Shock direction: left → right.

Free surface jetting: vector plots of the distribution of velocity projected onto the xy-plane(a, b, d–f), and an atomic configuration (c) for , showing cavity nucleation in jet heads. The snapshots are for t = 105–114 ps. (c) is colored by potential energy, and corresponds to (d). Shock direction: left → right.

Free surface vaporization: snapshots of atomic configurations (a; projected onto the xy-plane) and the corresponding 2D binning density profiles (b) for the type-4 foam loaded at . Color coding is based on ux in (a) and density in (b). Shock direction: left → right.

Free surface vaporization: snapshots of atomic configurations (a; projected onto the xy-plane) and the corresponding 2D binning density profiles (b) for the type-4 foam loaded at . Color coding is based on ux in (a) and density in (b). Shock direction: left → right.

Article metrics loading...

Full text loading...

Commenting has been disabled for this content