No abstract

No abstract

No abstract

No abstract

This study presents incremental finite element computations of creep-fatigue crack growth in Alloy 718 at 650 C in air. Alloy 718 is representative of creepbrittle materials, in which viscoplastic deformation is restricted near the tip of a growing crack. The computations predict crack growth using a unique combination of an irreversible cohesive zone formulation and a strain gradient viscoplastic material model based on the Kocks-Mecking formulation. Cohesive zone damage parameters are estimated using sustained loading and constantamplitude cyclic loading experiments. Computations of crack extension under three different waveforms containing overloads all predict post-overload retardation. The amount of retardation depends strongly on the overload ratio, consistent with experiments in the literature using similar waveforms. Analysis of the crack-tip fields demonstrates retardation is associated with unloading in the highly deformed material near the advancing crack tip. Dynamic recovery and geometrically necessary dislocations are shown to significantly influence post-overload crack extension.