A new model of dynamic spherical cavity expansion with constant velocity in a brttle material has been developed on the basis of the hypothesis of an ultimate fracture front velocity proposed by Nikolayevskii. With the use of this model, the Alekseevskii-Tate model is modified for long-rod penetration into brittle materials. The ultimate fracture front velocities relative to the material moving before this front are considered as a physical characteristic specific to every material and fracture mode. Therefore, fracture front velocities (as well as crack propagation velocities) relative to unperturbed material depend on the cavity expansion velocity and can exceed the Rayleigh wave velocity. Unlike the models based on the hypothesis of an ultimate fracture stress, this proposed model explains the possibly of short term "dynamic overloads" of the material: tensile in elastic precursor and shearing in the cracked material zone.
展开▼
