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Modelling of Damage Development and Strain Ratchetting Using a Viscoplastic Constitutive Formulation

Simulation of both damage development and strain ratchetting in uniaxial loading conditions has been presented for a nickel-based superalloy at 650°C using the unified Chaboche viscoplastic model. A third kinematic hardening component was employed to simulate strain ratchetting; and a damage variable, based on plastic strain development, was also incorporated to simulate the damage evolution behaviour. Good agreement between the model predictions and the experimental results was obtained for both damage evolution and strain ratchetting. The model was then utilised to investigate the cyclic deformation behaviour near a crack tip for a single edge notch tension (SENT) specimen. Finite element analyses showed that strain ratchetting is seems to be a characteristic of the fatigue crack tip, which has been used as a criterion to predict the crack growth rates.