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Slow, isothermal crack propagation is widely suspected to be rate-controlled by thermally activated plastic deformation in the crack-tip region. Adiabatic conditions are generally established in the fracture-modified material at the tip of a crack during fast fracture. The temperature of this material is not the temperature of the specimen and is generally not measured during fast fracture. Thus, a complete thermodynamic description of adiabatic crack propagation data cannot be made. When the slow, isothermal crack propagation mechanisms are assumed to be operative during adiabatic crack propagation, then certain predictions can be made. For example: the changes in ς due to temperature and rate are always in the opposite sense; there is no minimum in ς versus crack velocity without a change in mechanism; the temperature rise in the crack-tip fracture-modified material is determined mainly by the activation enthalpy for crack propagation; the interpretation of fast fracture structural steel data from simple plastic models is suspect since these materials have dissimilar isothermal temperature dependencies.
fast fracture, adiabatic fracture, dynamic fracture, fracture thermodynamics
Professor, University of Rochester, Rochester, N.Y.