Effect of Interatomic Potential Choice on Fracture Modes of Graphene with Parallel Cracks

Abstract

Defect engineering via parallel cracks has been proposed as a route to tailor the fracture response of graphene. However, atomistic fracture predictions can be strongly sensitive to the interatomic potential. Here, we quantify the effect of potential choice by revisiting H-passivated graphene containing two parallel cracks separated by a gap $W_{\text{gap}}$ loaded in tension along the armchair (AC) and zigzag (ZZ) directions. Molecular dynamics simulations using the AIREBO potential under the same geometry and loading protocol previously studied with ReaxFF, are employed, so enabling a direct comparison. Stress-strain responses, Young's modulus, an effective mode-I stress intensity factor, and energy absorption are evaluated as functions of $W_{\text{gap}}$. Compared with ReaxFF, AIREBO predicts lower peak stresses and earlier catastrophic softening, leading to reduced post-peak deformation capacity and energy absorption. Ductility and energy absorption are shown to be highly potential-dependent, underscoring the need for careful potential selection in defect-engineered graphene fracture simulations.

Figures (4)

• Figure 1: Geometry of graphene with (a) a single crack of length 2$a_0$ and (b) parallel cracks, each of length 2$a_1$, where $2a_1\approx a_0$, separated by a gap $W_\text{gap}$. The local atomic structure around the cracks is shown in a magnified view, with carbon and hydrogen atoms colored cyan and blue, respectively.
• Figure 2: Results of armchair (AC) and zigzag (ZZ) structures. (a, b) Stress versus strain curves for armchair and zigzag, respectively, with varying $W_\text{gap}$, at a strain rate of $10^8$ s$^{-1}$. (c) Young's modulus versus $W_\text{gap}$ for both AC and ZZ structures. (d) Effective stress intensity factor versus $W_\text{gap}$, corresponding to the stress-strain curves shown in (a) and (b). (e) Energy absorption under the stress-strain curve. The vertical dashed lines at strain values are references for the next figures.
• Figure 3: Snapshots of fracture evolution at selected strain levels $\varepsilon$, with atoms colored by normalized von Mises stress $\sigma_\text{vm}$: (a) armchair configuration with $W_\text{gap}=1.719$ nm at $\varepsilon=0.005, 0.040, 0.045,$ and $0.050$; (b) zigzag configuration with $W_\text{gap}=1.701$ nm at $\varepsilon=0.005, 0.035, 0.040,$ and $0.045$.
• Figure 4: Lever-like structures formed in the region between the inner crack tips for (a) armchair and (b) zigzag configurations, except the largest-$W_\text{gap}$ case showing one crack propagation. Snapshots are shown for varying $W_\text{gap}$ at selected strain levels $\varepsilon$. The color contours denote the normalized von Mises stress, $\sigma_\text{vm}$, where $\sigma_\text{vm}$ is normalized by the maximum value in each corresponding case.