Instability dynamics in three-dimensional fracture: An atomistic simulation

We are simulating the dynamical failure of three-dimensional notched solids under tension at the atomistic level using classical molecular dynamics and system sizes from 10 to more than 100 millions atoms. We find that a rare-gas solid (e.g. xenon) may begin cleaving brittley at failure. When the crack velocity approaches one third of the Rayleigh sound speed, the crack tip begins to roughen on the atomic scale. This is immediately followed by a ''dynamic brittle-to-ductile'' transition where plasticity becomes dominant through the prolific emission of loop dislocations and the arrest of the crack motion. The atomic roughening is consistent with the onset of the brittle fracture instability suggested by experiment and seen in our earlier two-dimensional fracture simulations of rare-gas films, lending support to the notion that this instability is a general feature of the rapid brittle fracture process. (C) 1997 Elsevier Science Ltd.