A study of cyclic behaviour of a nickel-based superalloy at elevated temperature using a viscoplastic-damage model

Cyclic response of a nickel-based superalloy, Alloy RR1000, has been studied at 650 °C using both experimental and numerical approaches. Experimental results from uniaxial strain-controlled tests showed both hardening and softening behaviour for the material. A viscoplastic-damage model has been developed to simulate the material behaviour, where a damage variable, based on plastic strain development, was introduced in the framework of viscoplasticity. A good agreement between the model simulations and the experimental results has been obtained for the full history of the cyclic response under simple cyclic and dwell loading conditions. The model was utilised to investigate the damage evolution near a crack tip for a single edge notch tension specimen (SENT), where the damage accumulation rate with respect to cycles was found to be linear once an inelastic strain threshold was reached. The damage development seems to be localised to the crack tip and becomes more significant at lower frequencies and longer dwell periods.