Abstract
The coupled and the anisotropic features of plastic damage and creep damage in Nimonic 80A were analysed with a special emphasis on the finite deformation and the material spin of the damaged material. In view of the fact that both the plastic and the creep damage are governed by the formation of grain boundary cavities, it was first assumed that the states of plastic damage and creep damage were represented in terms of symmetric second rank damage tensors Ωp and Ωc; the sum of these tensors Ω=Ωp+Ωc represents the damage state of the material. The evolution equations of these variables were established on the basis of the experimental observations on the nucleation and growth of microscopic cavities. The creep constitutive equation of the material, on the other hand, was formulated by taking account of an acceleration of creep rate due to material damage as well as of the material softening caused by the formation of a dislocation network at particle interfaces.
Finally, the creep damage process at finite deformation of Nimonic 80A at 750°C subjected to prior plastic damage brought about by the plastic prestrain at room temperature was analysed. The numerical results were compared with the corresponding experimental results to discuss the validity of the proposed theory. Though a considerable rotation of the principal damage direction was observed in the process of torsional creep, its effect on the creep damage process was found to be rather small.
