Atomistic Representation of Anomalies in the Failure Behaviour of Nanocrystalline Silicene

TL;DR

This study uses molecular dynamics to explore how grain size and cracks influence the failure behavior of nanocrystalline silicene, revealing unique fracture mechanisms and the limitations of continuum theories in predicting its fracture toughness.

Contribution

First atomistic simulation study comparing failure mechanisms of nanocrystalline silicene with continuum theories, highlighting anomalous crack behavior and grain size effects.

Findings

Transition from inverse pseudo Hall Petch to pseudo Hall Petch at 17.32 nm grain size

Identification of crack sensitive and insensitive failure modes

Discrepancy between Griffith's theory and MD in fracture toughness prediction

Abstract

Silicene, a 2D analogue of graphene, has spurred a tremendous research interest in the scientific community for its unique properties essential for next generation electronic devices. In this work, for the first time, we present a molecular dynamics (MD) investigation to determine the fracture strength and toughness of nanocrystalline silicene (nc silicene) sheet of varied grain size and pre existing crack length at room temperature. Our results suggest that the transition from an inverse pseudo Hall Petch to a pseudo Hall Petch behavior in nc silicene occurs at a critical grain size of 17.32 nm. This phenomenon is also prevalent in nanocrystalline graphene. However, nc silicene with pre existing cracks exhibits anomalous crack propagation and fracture toughness behaviour. We have observed two distinct types of failure mechanisms (crack sensitive and insensitive failure) and devised the mechanophysical conditions under which they occur. Fracture toughness calculated from both Griffiths theory and MD simulations indicate that the former overpredicts the fracture toughness of nc silicene. The most striking outcome, however, is that despite the presence of a pre existing crack, the crack sensitivity of nc silicene is found to be dependent on the grain size and their orientations. This study is the first direct comparison of atomistic simulations to the continuum theories to predict the anomalous behaviour in deformation and failure mechanisms of nc silicene.