Modeling of localization and necking in dual phase steels through polycrystalline plasticity

Çakmak, Serhat Onur.
In this thesis, the effect of ferrite crystallographic orientation distribution and other microstructural parameters such as martensite morphology, martensite volume fraction, and ferrite grain size on the plastic deformation, localization, and the necking behavior of dual-phase steels are investigated. Two different type of finite element models, i.e. full size micron-scale polycrystalline samples and polycrystalline Representative Volume Element (RVEs) are built through Voronoi tessellation. Local crystal plasticity and J2 plasticity with isotropic hardening frameworks are used to model ferrite and martensite phases, respectively. This work demonstrated that the martensite morphology and the ferrite orientation distribution affect highly the formation of the shear bands and the necking location in the samples. In addition, they significantly affect stress-strain partitioning, location of the plastic localization, tensile strength and hot spots for void formation in the RVEs.