Combined rate-independent plasticity and creep model for single crystal

Abstract

There is a need for accurate descriptions of the mechanical state of single crystal blades in gas turbine engines. These components are subject to such extreme temperatures and stresses that life prediction becomes highly inaccurate resulting in components that can only be shown to meet their requirements through experience. To help reduce this inadequacy in current design systems we have developed a thermo-viscoplastic constitutive model for single crystal materials. Our large strain formulation additively decomposes the inelastic strain rate into components along the octahedral and cubic slip planes. Each of these is further additively decomposed into a time dependent creep component and a time independent plastic component. We formulate robust and computationally efficient rate-independent crystal plasticity formulations and combined them with creep flow rules for Ni-based superalloys. The transient variation of each of the inelastic components includes a back stress for kinematic hardening and latent hardening parameters to account for the stress evolution with inelastic strain. Our combined creep and rate-independent formulations for the plastic strains were shown to be accurate when compared to stress–strain and texture evolution measurements. The complete formulation is able to accurately predict both monotonic and cyclic tests at different crystallographic orientations.