Analysis of the coupled effect of plastic damage and creep damage in nimonic 80A at finite deformation

Abstract

The coupled effect and the anisotropic feature of plastic damage and creep damage in Nimonic 80A are analysed with special emphasis on the finite deformation and the material spin of the damaged material. In view of that both the plastic and the creep damage are governed by the formation of grain boundary cavities, it is first assumed that the states of plastic damage and creep damage are represented in terms of symmetric second-rank damage tensors Ω P and Ω C , the sum of these tensors Ω = Ω P + Ω C represents the damage state of the material. The evolution equations of these variables are 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, is formulated by taking account of the acceleration due to material damage as well as the material softening caused by the formation of the dislocation network at particle interfaces. Finally, 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 is analysed. The numerical results are compared with the corresponding experimental results to discuss the validity of the proposed theory. Though considerable rotation of principal damage direction was observed in the process of torsional creep, its effect on the creep damage process was found to be rather small.