Dislocation Nucleation in Shocked fcc Solids: Effects of Temperature and Preexisting Voids

Quantitative behaviors of shock-induced dislocation nucleation are investigated by means of molecular dynamics simulations on fcc Lennard-Jones solids: a model argon. In perfect crystals, it is found that the Hugoniot elastic limit (HEL) is a linearly decreasing function of temperature: from near-zero to melting temperatures. In a defective crystal with a void, dislocations are found to nucleate on the void surface. Also, HEL drastically decreases to 15% of the perfect crystal when the void radius is 3.4 nanometers. The decrease of HEL becomes larger as the void radius increases, but HEL becomes insensitive to temperature.

Figure 1

Temperature dependence of Hugoniot elastic limits of a perfect crystal (circles) and of a defective crystal containing a void of 1.71 nm radius (squares). The dashed line represents experimental data for the shear modulus [8]. The melting temperature is approximately 83 K.

Figure 2

Four partial dislocation loops nucleate on the void surface. Void radius is 2.4 nm and piston velocity is $70\mathrm{m}/\mathrm{s}$. Atoms of 12 nearest neighbors are not presented in order to see exclusively dislocations and void surface. Green, red, and blue atoms have 10, 11, and 13 nearest neighbors, respectively [15].

Figure 3

Thirteen picoseconds after Fig. 2. Partial dislocation loops are extended and Lomer-Cottrel sessile dislocation is formed.

Figure 4

Side view of Fig. 3. Two slip planes on the void surface are activated.

Figure 5

Log-log plot of HEL as a function of void radius. Solid and dashed lines are proportional to $r^{-0.5}$ and $r^{-1}$, respectively. Initial temperature is 6 K.