Abstract
A thermodynamic analysis relating changes in fracture toughness to thermal length changes and the enthalpy of the tetragonal-to-monoclinic phase transformation in partially stabilized zirconia (PSZ) was proposed previously. The Clausius-Clapeyron equation is used to relate volume and shear phase changes to the crack-tip deformation zone. Shear transformations, which have a unique role in fracture toughening of PSZ, shield the crack tip from the applied stress intensity factor for a crack that is held stationary. Crack-tip shields from volume and normalized strain transformations are computed to be zero for stationary cracks and this deformation zone is much smaller than the shear transformation zone. Shear transformations in bulk specimens are deduced by measuring length changes vs temperature on samples that were previously subjected to a uniaxial compressive stress, i. e. , with a shear component, during a thermal cycle.