ATOMISTIC SIMULATION OF FRACTURE IN COAL AND FEAL

The behavior of mode I cracks in CoAl and FeAl is investigated using m olecular statics computer simulation methods with embedded atom (EAM) potentials developed by Vailhe and Farkas (not yet published). A doubl e ended crack of finite size embedded in a cylindrical simulation cell and fixed boundary conditions are prescribed along the periphery of t he cell, whereas periodic boundary conditions are imposed parallel to the crack front. The displacement field of the finite crack is represe nted by that of an equivalent pileup of opening dislocations distribut ed in a manner consistent with the anisotropy of the crystal and tract ion free conditions of the crack faces. The crack lies on the {110} pl ane and the crack front is located either along [100], [110] or [111] directions. Cleavage in found to occur in both materials for most crac k orientations. In one orientation, cleavage in FeAl is found to occur concurrently with dislocation emission. The crack tip response is rat ionalized in terms of the surface energy (gamma(s)) of the cleavage pl ane and the unstable stacking energies (gamma(us)) of the slip planes emanating from the crack front. (C) 1997 Elsevier Science Limited.