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 potentials and system of tens of millions of atoms. We have discovered that crystal orientation with respect to the uniaxial loading is important; the solid fails by brittle cleavage for a notch with (1 1 0) faces and by ductile plasticity for a notch with (1 1 1) faces or(1 0 0) faces. We argue that the competition between bond-breaking and interplanar slippage is governed by the nonlinearity and anisotropy of the crystal elasticity near materials failure. if the speed of the (1 1 0) brittle crack velocity reaches approximately one-third of the Rayleigh sound speed, a "brittle-to-ductile" transition occurs and is consistent with the onset of a dynamic instability of brittle fracture. Such an instability was seen in our earlier two-dimensional fracture simulations of rare-gas films and appears to be a general feature of the dynamic brittle fracture process. We close with a simulation showing the consequences of a brittle crack colliding with a void. Copyright (C) 1998 Elsevier Science B.V.