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    ANALYSIS OF THE FRACTURE BEHAVIOUR OF DUAL-PHASE STEELS USING THE GISSMO AND JOHNSON-COOK MODELS
    (Univ Zagreb Fac Mechanical Engineering & Naval Architecture, 2023) Topilla, Labinot; Toros, Serkan
    This research explores an extended method of fracture mechanics to determine the parameters of the Johnson Cook and GISSMO models. The primary objective of the optimization process and iterative finite element method (FEM) was to identify optimised modelling parameters suitable for specimens with different shapes to predict the failure behaviour of dual-phase steels (DP), specifically DP600 and DP800 steels. Numerous experimental tests were conducted on these DP steels, which mainly consist of ferrite and martensite phases. The specimens underwent deformation at three different tensile velocities. To determine the flow curves, a Simplified Johnson-Cook model (MAT_SJC_098) was employed, while the Johnson-Cook model (MAT_JC_015) was used to identify failure, and a combined JC-GISSMO model was used to determine damage. The numerical simulation results were then compared with the experimental results. In conclusion, all modelling methods used in this research yielded the desired results.
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    Stress-strain distribution and failure mechanisms in dual-phase steels investigated with microstructure-based modeling
    (Latin Amer J Solids Structures, 2022) Topilla, Labinot; Toros, Serkan
    In this study, the microstructural-based finite element modeling of dual-phase steels was investigated to visualize the crack initiation and its propagation through the phases that exist in the material. The parameters of various failure models, including Gurson, Gurson-Johnson-Cook, and Johnson-Cook (JC), were calibrated for different microstructure levels of DP600, DP800, and DP1000 steels. The onset of cracking, nucleation, void growth, and coalescence was determined using the models. As a result of the optimization studies, there is not much difference between the flow curves of the materials and the tensile values calculated from the tensile tests for DP600 and DP800, while it is slightly higher for DP1000. However, considering the fracture, martensite phases were found to be the main determinant of this situation. Cracks that start in the martensite phases then propagate through the ferrite phase and eventually cause the material to break. According to the results of the simulations, the difference between the experiments and the simulation results of the Gurson is 3.33%, the Gurson-JC is 1.82%, and the JC model is 2.39%.