Anomalous ductile-brittle fracture behaviour in fcc crystals

The fracture behaviour of fee crystals has been investigated by numerically simulating the dynamical failure of a three-dimensional notched crystal using molecular dynamics, simple interatomic potentials for a rare-gas solid and system sizes of about ten million atoms. We find that the solid fails by brittle cleavage for cracking on a {110} face growing in a [110] direction and by ductile plasticity for cracking on a {111} face growing in a [110] direction. Comparison of equilibrium surface energies on the crack face and Schmid factors on the primary slip systems indicates that the classical theories of fracture give predictions in contradiction with the simulation results. A hyperelasticity model is proposed to explain this discrepancy. This anomalous fracture behaviour of fee crystals has a profound implication on general modelling of dynamic failure of solids.