Force-induced breakdown of flexible polymerized membrane

TL;DR

This study uses molecular dynamics simulations to analyze how a 2D elastic membrane, similar to graphene, breaks under tension, revealing size-dependent failure times, crack formation mechanisms, and the influence of force and temperature.

Contribution

It provides new quantitative insights into the fracture dynamics of 2D elastic membranes under tension, including size scaling laws and the relation to Griffith's theory.

Findings

Bond rupture occurs mainly at the sheet periphery.

Failure time decreases with membrane size as a power law.

Crack spreading velocity increases rapidly with external tension.

Abstract

We consider the fracture of a free-standing two-dimensional (2D) elastic-brittle network to be used as protective coating subject to constant tensile stress applied on its rim. Using a Molecular Dynamics simulation with Langevin thermostat, we investigate the scission and recombination of bonds, and the formation of cracks in the 2D graphene-like hexagonal sheet for different pulling force $f$ and temperature $T$. We find that bond rupture occurs almost always at the sheet periphery and the First Mean Breakage Time $<\tau>$ of bonds decays with membrane size as $<\tau> \propto N^{-\beta}$ where $\beta \approx 0.50\pm 0.03$ and $N$ denotes the number of atoms in the membrane. The probability distribution of bond scission times $t$ is given by a Poisson function $W(t) \propto t^{1/3} \exp (-t / <\tau>)$. The mean failure time $<\tau_r>$ that takes to rip-off the sheet declines with growing size $N$ as a power law $<\tau_r> \propto N^{-\phi(f)}$. We also find $<\tau_r> \propto \exp(\Delta U_0/k_BT)$ where the nucleation barrier for crack formation $\Delta U_0 \propto f^{-2}$, in agreement with Griffith's theory. $<\tau_r>$ displays an Arrhenian dependence of $<\tau_r>$ on temperature $T$. Our results indicate a rapid increase in crack spreading velocity with growing external tension $f$.