Chaotic dynamics in an atomistic model of environmentally assisted fracture

A simple atomistic model of a crack tip is used to demonstrate the existence of chaotic motion of crack-tip atoms. The model, which has been developed in detail elsewhere in the literature, consists of a linear chain of four atoms. Nearest neighbors interact via Morse-function potentials, with environment-induced lattice decohesion simulated by reducing the strength of the inner bond. Dynamic calculations are carried out by allowing the two inner atoms to move freely, starting from rest in a given initial configuration, with the two end atoms being held rigidly in place, Under certain conditions, associated with large departures from minimum potential energy, the motion of the inner atoms is shown to be chaotic in a manner that is consistent with the Kosloff-Rice description of chaotic dynamics in a classical Hamiltonian system. Possible implications of the results relative to the fracture of actual materials are discussed.