LARGE-SCALE SIMULATIONS OF BRITTLE AND DUCTILE FAILURE IN FCC CRYSTALS

We are simulating the failure of three-dimensional notched fee solids under mode one tension using molecular dynamics, simple interatomic po tentials and system of tens of millions of atoms. We have discovered t hat crystal orientation with respect to the uniaxial loading is import ant; the solid fails by brittle cleavage for a notch with (1 1 0) face s and by ductile plasticity for a notch with (1 1 1) faces or(1 0 0) f aces. We argue that the competition between bond-breaking and interpla nar slippage is governed by the nonlinearity and anisotropy of the cry stal elasticity near materials failure. if the speed of the (1 1 0) br ittle crack velocity reaches approximately one-third of the Rayleigh s ound speed, a ''brittle-to-ductile'' transition occurs and is consiste nt with the onset of a dynamic instability of brittle fracture. Such a n instability was seen in our earlier two-dimensional fracture simulat ions of rare-gas films and appears to be a general feature of the dyna mic brittle fracture process. We close with a simulation showing the c onsequences of a brittle crack colliding with a void. Copyright (C) 19 98 Elsevier Science B.V.