Feature/gb diffusion

[sanathkeshav]

• @Class GBDiffusion
• @brief Material model for grain boundary diffusion in polycrystals
• This model implements diffusion in a polycrystalline material, differentiating between
• bulk crystal diffusion (isotropic) and grain boundary diffusion (transversely isotropic).
• The grain boundaries are characterized by their normal vectors and can have different
• diffusion properties parallel and perpendicular to the boundary plane.
• The model extends both ThermalModel and LinearModel<1> to provide a linear diffusion
• formulation that can be used in a thermal-like solver in FANS.
• @details The model:
• • Reads microstructure data containing grain boundaries from HDF5 files
• • Supports uniform or material-specific diffusivity values
• • Handles bulk regions with isotropic diffusion (D_bulk)
• • Handles grain boundaries with transversely isotropic diffusion (D_par, D_perp)
• • Provides visualization of grain boundary normals in post-processing
• Required material parameters in JSON format:
• • GB_unformity: Boolean flag for uniform GB properties
• • D_bulk: Bulk diffusion coefficient(s)
• • D_par: Diffusion coefficient parallel to grain boundaries
• • D_perp: Diffusion coefficient perpendicular to grain boundaries