On the multiscale modeling of duplex stainless steel

This thesis deals with the modeling and simulation of\nthe influence of the material substructure on the macroscopic\nmechanical properties of duplex stainless steel (DSS). Two\nsubscale levels and their interaction are considered: Grain\nstructure (mesoscale) and crystallographic structure (microscale).\nTypical mesoscale parameters are the volume fraction, morphology\nand material properties of the two phases (ferrite and austenite).\nA multiscale modeling approach is adopted, whereby it is assumed\nthat the macro- and mesoscales are separated such that it is\npossible to model the subscale effects within a representative\nvolume element (RVE) and to obtain the macroscale response via\nvolume averaging (computational homogenization). A new microscale\nmaterial model based on crystal (visco)plasticity and damage has\nbeen developed as part of the thesis work. This model is used to\nstudy the evolution of damage within the grain structure of the\nRVE. The important issue of parameter identification of the\nmaterial parameters in the crystal plasticity model is also\nconsidered. Specifically, the necessary macroscale experiments\nneeded for obtaining a unique set of material parameter values is\nexploited. Finally, concurrent (FE$^2$) multiscale modeling\nsimulations are performed. Different types of plane stress\nconditions in 2D simulations and the computation of the\ncorresponding macroscale algorithmic tangent stiffness (ATS)\ntensor are discussed. The concurrent simulations are used for\ninvestigating the influence of cold--working on the macroscale\nmechanical properties for a thin metal sheet with strongly\ninhomogeneous deformation and stress states.