QUASI-STATIC CRACK-PROPAGATION IN HETEROGENEOUS MEDIA

The dynamics of a single crack moving through a heterogeneous medium i s studied in the quasistatic approximation, which may be directly appl icable to cracks grown under fatigue. In a model scalar system and for mode III (tearing) loading, the crack surface is found to be self-aff ine with a roughness exponent of zeta = 1/2. Mode I (tensile) loading, however, leads to a crack surface that is only logarithmically rough, quite unlike those seen in most experiments. Residual stresses are fo und, potentially, to lead to increased crack surface roughness. But el astic wave propagation effects may be needed to explain the very rough crack surfaces observed experimentally.