On the multiscale modeling of duplex stainless steel

Doctoral thesis, 2007

This thesis deals with the modeling and simulation of the influence of the material substructure on the macroscopic mechanical properties of duplex stainless steel (DSS). Two subscale levels and their interaction are considered: Grain structure (mesoscale) and crystallographic structure (microscale). Typical mesoscale parameters are the volume fraction, morphology and material properties of the two phases (ferrite and austenite). A multiscale modeling approach is adopted, whereby it is assumed that the macro- and mesoscales are separated such that it is possible to model the subscale effects within a representative volume element (RVE) and to obtain the macroscale response via volume averaging (computational homogenization). A new microscale material model based on crystal (visco)plasticity and damage has been developed as part of the thesis work. This model is used to study the evolution of damage within the grain structure of the RVE. The important issue of parameter identification of the material parameters in the crystal plasticity model is also considered. Specifically, the necessary macroscale experiments needed for obtaining a unique set of material parameter values is exploited. Finally, concurrent (FE$^2$) multiscale modeling simulations are performed. Different types of plane stress conditions in 2D simulations and the computation of the corresponding macroscale algorithmic tangent stiffness (ATS) tensor are discussed. The concurrent simulations are used for investigating the influence of cold--working on the macroscale mechanical properties for a thin metal sheet with strongly inhomogeneous deformation and stress states.