Creep simulation of asymmetric effects at large strains by stress mode decomposition

The paper presents a framework for creep modelling at large strains of materials exhibiting different behaviours in different loading scenarios, such as tension, compression and shear, respectively. To this end a flow rule is postulated within a thermodynamic consistent framework in a mixed variant formulation and decomposed into a sum of weighted stress mode related quantities. The different stress modes are chosen such that they are accessible to individual examination in the laboratory, where tension, compression and shear are typical examples. The characterisation of the stress modes is obtained in the octahedral plane of the deviatoric stress space in terms of the Lode angle, such that stress mode dependent scalar weighting functions can be constructed. Furthermore the numerical implementation into a finite element program of the constitutive equations is briefly described. In three finite element examples the proposed model is applied to investigate the asymmetric relaxation behaviour of a square plate with circular hole and also the evolution of creep damage in a short cantilever with hole and a gasturbine blade.