Cooperative cracks in layered crystals

Abstract

The pattern development of multiple cracks in bilayer or multilayer 2D crystals encompasses rich yet largely unexplored physics. We study crack interactions across neighboring 2D layers using in situ scanning transmission electron microscopy and molecular dynamics simulations. In bilayer 2D crystals, parallel cracks attract while anti-parallel (‘En-Passant’) cracks repel, sharply contrasting with co-planar cracks. Beyond fracture toughening, interlayer slip alters crack driving forces by adding an antisymmetric shear component to the stress intensity factor. Supported by experimental observations and simulation results, we present a theoretical framework that integrates linear elastic fracture mechanics with the shear-lag model to guide the engineering of fracture patterns and improvement of material resistance to cracking.