INSTABILITY DYNAMICS IN 3-DIMENSIONAL FRACTURE - AN ATOMISTIC SIMULATION

We are simulating the dynamical failure of three-dimensional notched s olids under tension at the atomistic level using classical molecular d ynamics and system sizes from 10 to more than 100 millions atoms. We f ind 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'' transitio n where plasticity becomes dominant through the prolific emission of l oop dislocations and the arrest of the crack motion. The atomic roughe ning is consistent with the onset of the brittle fracture instability suggested by experiment and seen in our earlier two-dimensional fractu re simulations of rare-gas films, lending support to the notion that t his instability is a general feature of the rapid brittle fracture pro cess. (C) 1997 Elsevier Science Ltd.