Micromechanical modeling of failure in dual phase steels through cohesive zone and crystal plasticity modeling frameworks

Date

2023-9-7

Author

Aydıner, İlbilge Umay

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Dual-phase (DP) steels are characterized by their great formability and interesting material properties, which primarily originate from their unique composition, combining the ductile ferrite phase with the hard and brittle martensite phase. In order to analyze their plastic and failure behavior, a thorough investigation of their microstructure is essential, employing a rigorous micromechanics-based approach. At the microscale, DP steels exhibit various failure mechanisms that need to be addressed through proper plasticity and failure models. These include interface decohesion between ferrite-martensite (F/M) and ferrite-ferrite (F/F) phases, as well as martensite cracking. A crystal plasticity and cohesive zone modeling based failure framework for three dimensional Representative Volume Element (RVE) calculations is followed to reflect the influence of microstructure evolution to macroscopic response. The rate-dependent crystal plasticity framework is used for the ductile ferrite phase while isotropic J2 plasticity model is employed for the brittle martensite phase. Cohesive zone elements are introduced at the interfaces between ferrite-martensite and ferrite-ferrite phases to analyze intergranular cracking. Additionally, intragranular failure within the martensite phase is addressed using an uncoupled damage model. Initially, an extensive parameter identification study was conducted to calibrate the aforementioned failure models. Then, various 3D polycrystalline RVEs having different microstructural characteristics are analyzed and discussed in detail to evaluate the capacity of these models in predicting the response in comparison to observations in the literature. The spatial distribution of the martensite phase and the triaxial stress state experienced by the material has been identified as critical factors influencing the failure mechanism in dual-phase steels.

Subject Keywords

Dual-phase steel, Crystal plasticity, Cohesive zone model, Ductile failure, FEM

URI

https://hdl.handle.net/11511/105502

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Graduate School of Natural and Applied Sciences, Thesis