Developing a physics-based model within a crystal plasticity finite element framework to analyze texture evolution and deformation heterogeneity in dual-phase steel materials

Official URL: https://risc01.sabanciuniv.edu/record=b3403576

In the first phase of the research a crystal plasticity model based on dislocation density was developed to understand the complex mechanical behavior of body-centered cubic (BCC) materials. The model incorporated non-Schmid effects using three-term projection operators. To evaluate the model, numerical results obtained under various crystal orientations, temperatures, and strain rates were compared with the corresponding experimental results reported in the literature. The capacity of the model to capture tension-compression asymmetry as one of the distinctive features of the BCC structure was also examined. Simulations were implemented at different scales. According to the results the model could accurately simulate the experimentally observed stress-strain curves and explain the tension-compression asymmetry in the flow stresses of α-iron. In the second phase of the study, the scheme from the first phase was enhanced to feature dual phase properties. For this purpose, an isotropic (J2) plasticity subroutine was developed to represent martensite phase effects in the numerical model. It was subsequently combined with the density-based crystal plasticity finite element model (CPFEM), to simulate martensite and ferrite phases collective response in a dual phase steel 600 (DP600). Data on the phase area fraction, crystallographic grain orientation, and microstructural texture of a sample of the DP alloy were obtained experimentally using the electron backscattered diffraction (EBSD) method and were applied to create a single-layer representative volume element (RVE) of the material. Furthermore, the scheme is applied with synthetic models to demonstrate the evolution of simulation outputs, including dislocation density, suppression of deformation, load partitioning, and interruption of stress flow. The effect of martensite geometrical deployment with focus on banding issue on the strain localization and eventually overall hardening behavior of the dual phase steel is investigated. To evaluate the model's reliability in capturing the actual strain response, an experimental study conducted on a similar material from the literature is used. The resultant strain distribution and localization of our model are compared and analyzed against the reported experiment. Our results showed that the martensite phase plays an important role in the stress and strain distribution in the alloy by reducing plastic deformation. The misorientation evolution of the ferrite grains in a DP structure is extracted by post processing the result files, revealing the restrictive influence of the neighboring martensite regions on the ferrite phase and its impact on plasticity. The results indicate that the presence of the martensite phase leads to considerable heterogeneity in the stress distribution, an increase in misorientation polarization, and strain hardening. Ultimately, the hybrid simulation scheme that is developed in this study provides a clear insight into the effective microstructural factors in the plastic deformation behavior of DP steels, specifically the retexturing response and the effect of the martensite phase on ferrite plasticity under various loading conditions.