DYNAMICS AND INSTABILITIES OF PLANAR TENSILE CRACKS IN HETEROGENEOUS MEDIA

The dynamics of tensile crack fronts restricted to advance in a plane are studied. In an ideal linear elastic medium, a propagating mode alo ng the crack front with a velocity slightly less than the Rayleigh wav e velocity, is found to exist. But the dependence of the effective fra cture toughness Gamma(v)) on the crack velocity is shown to destabiliz e the crack front if d Gamma/dv < 0. Short wavelength radiation due to weak random heterogeneities tends to lead to this instability at low velocities. The implications of these results for the crack dynamics a re discussed.