On the stress state dependence of creep rupture

Abstract

The influence of the stress state on the creep rupture time is studied for polycrystalline metals at high temperatures. The study is based on a set of constitutive relations that account for the nucleation and growth of grain boundary cavities and for the effect of grain boundary sliding. Both diffusive growth and creep growth of cavities is incorporated and also the mechanism of creep constrained cavitation is described. The effect of multi-axial stress states on the lifetime is studied by computing isochronous rupture loci corresponding to a number of different combinations of material parameters. These rupture loci are compared with available experimental results for multi-axial stress states. Lifetime predictions for varying stresses or temperatures are also investigated, and compared with results of the linear cumulative damage rule and with experimental results. Finally, non-proportional loading is studied by analysing a tube subject to a constant tensile load and a torsional load which is reversed a number of times.