Computational modeling of crystal plasticity and intergranular decohesion coupled to stress-assisted oxidation in high-temperature polycrystalline alloys

Research Project, 2019 – 2023

The proposed project concerns the modeling and simulation of plasticity, damage and fracture in high-temperature polycrystalline alloys, such as Ni-based alloys used in gas turbine components. Gradient-enhanced crystal viscoplasticity in the large strain kinematics setting is adopted for the intragrain material behavior. To include cross-coupling of the critical (yield) Schmid stresses and of the SSD hardening stresses represents an extension of the state-of-the art. The gradient-effects, in terms of the influence of misfit of crystallographical orientations on mutual sides of a grain boundary, are incorporated. Another topic is the formulation of decohesion and crack development along grain boundaries. The cohesive zone model takes into account the influence of intergranular oxides, which develop rapidly in front of the "open" crack tip. Since the rate of diffusion of oxygen depends on the magnitude of traction, it appears that oxidation and fracture evolution are intertwined phenomena that must also be solved as truly coupled processes. The ultimate goal is to carry out simulations in order to predict how the life of a component is influenced by external loading, hold time and the material microstructure. Most importantly, the modelling features will be supported by and validated against experiments via inverse analyses of cyclically loaded micro-cantilever beams made of Allvac 718 Plus. These experiments will be carried out at the Dept. of Physics, Chalmers.