EFFECT OF BOUNDARY-CONDITIONS IN MODE-I FRACTURE IN BRITTLE MATERIALS

We present results on the effect of geometrical boundary conditions on the stress distribution at the tip of cracks in mode I fracture. We h ave made molecular dynamics simulations on a 2-D triangular lattice of point masses connected by brittle Hookean springs. We study the confi guration of the stress field in rectangular shape lattices of differen t aspect ratios and with initial notches of varying lengths subjected to constant strain. We show that the stress of the most stretched spri ng at the tip of the notch presents a saturation as a function of notc h length. The detailed form of this saturation depends on the aspect r atio of the lattice. Simulation on the dynamics of propagating cracks suggest that the selection of the tip velocity is strongly dependent o n the initial notch length. The saturation of the stress intensity fac tor provides an appealing explanation for some of the experimental obs ervations by Boudet et al. (1995) and Marder et al. (1995).