Self-healing properties of flaws in nanoscale materials: Effects of soft and hard molecular dynamics simulations and boundaries studied using a continuum mechanical model

Soft and hard boundary effects on the flaw in self-healing capabilities of the nanoscale copper clusters and biomaterials have been studied using molecular dynamics simulations as well as the theoretical analyses. When the copper nanocluster size decreases to a compatible magnitude to its flaw, different boundary conditions change the flaw self-healing capability and lead to different dislocation generation and atom rearrangement after the copper nanocluster is healed. The theoretical predictions for the copper nanocluster are in good agreement with the molecular dynamics simulations. Further theoretical investigations demonstrate that the mineral layer in biomaterials possess a high flaw self-healing capability because of the nanometer scale and natural soft boundaries caused by the stacking protein and aragonite layered structures.

Figure 1

(Color online) MD snapshots of a copper nanocluster with a cleavage created by removing two row atoms at $300\mathrm{K}$ under free and rigid boundary conditions for (a) $L∕h=2.67$, $L∕L_C=4$ and (b) $L∕h=5.71$, $L∕L_C=4$. The cross sections in the height directions include 30 and 14 rows of copper atoms for (a) and (b), respectively. The green atoms shown in the right figures are fixed in the three directions.

Figure 2

(Color online) MD snapshots of 2400 atom copper nanocluster with a cleavage created by removing three row atoms at $300\mathrm{K}$ under a free boundary condition, $L∕h=2.67$ and $L∕L_C=4$.

Figure 3

(Color online) Total potential energy distribution of (a) the 7100-atom cluster under free boundary conditions, (b) the 7100-atom cluster under rigid boundary conditions, and (c) the 3100-atom cluster under free boundary conditions after $100\mathrm{ps}$ relaxations at $300\mathrm{K}$. Blue, red, yellow, green, and cyan colors indicate the potential energy from higher to lower. Boundary atoms possess the highest potential energy, which is emphasized by the blue color. The arrows denote the dislocations.

Figure 4

The geometry of a cross section of a flaw, the material is divided into two parts along the flaw.

Figure 5

(Color online) Theoretical predictions and MD simulations for the critical conditions of the flaw self-healing in Cu nanoclusters under the free and rigid boundary conditions. The error bars of MD simulations are obtained by increasing one atom layer height for the cleavagelike flaw.

Figure 6

(Color online) The critical conditions for the flaw healing inside the mineral layer under different boundary conditions, ${\overline{E}}_1∕{\overline{E}}_2=1$, $t_2∕t_1=1$, $\overline{K}∕Ek=0.01$, and $\overline{K}∕Ek=10$.

Figure 7

(Color online) The critical conditions for the flaw healing inside the interface of mineral and protein layers under different boundary conditions. (a) ${\overline{E}}_1∕{\overline{E}}_2=0.01$, $t_2∕t_1=40$ and (b) ${\overline{E}}_1∕{\overline{E}}_2=0.1$, $t_2∕t_1=40$.