Creep of Nimonic 80A in torsion and tension

Abstract

With the object of observing the influence of stress system, the creep of Nimonic 80A has been studied in torsion and tension over the range of effective stress σ from 100 to 500 MPa and at the temperature 750°C. For a given σ, tertiary creep and fracture occur sooner in tension than in torsion, while nucleation of cavities is faster. The cavities evidently accelerate creep strain and, since creep strain produces cavities, the behaviour as regards both strain and cavitation is autocatalytic. The results are expressed and explained in terms of (σ₁/σ), where σ₁ is the maximum principal stress, and a predictive law for fracture life is derived from constitutive relations connecting strain, cavity volume, and stress.