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%.
The objective of this research was to analyse the stress and strain behaviours of the triaxiality specimens (specimens of different shaping) of dual-phase steels, respectively DP600 and DP800, whose microstructures mainly comprise ferrite and martensite phases. These steels find wide application in the automotive industry, which is constantly searching for better quality materials in the aim of increasing vehicle safety, protecting the environment, and reducing fuel consumption. In this case, for all tested specimens the experimental uniaxial tensile tests were performed at three different strain rates, 0.0083 s −1 , 0.042 s −1 , and 0.16 s −1 , to determine mechanical properties such as stress, strain, yield strength, and ultimate tensile strength of mentioned steels. In addition, uniaxial tensile tests with characteristics similar to those experimental were carried out through the finite element modelling method using the Mat_Picewise_Linear_Plasticity_024 model, to determine the mentioned mechanical properties, but also to determine the failure parameters or plastic strain up to failure, of all triaxiality modelled specimens. The obtained results were validated by comparing the experimental results with numerical simulation results. The comparative scale of accuracy between both steels was made at the fracture strain, and the average accuracy of both steels for the standard (s) specimens was < 1 %, for the (20a) specimens 1.50 %, for the (4a) specimens 4 %, and for (a) specimens 3.50 %. Finally, it was concluded that the proposed material model and calibrated failure data fitted very well.
The microstructure of Dual Phases steel is known to be mostly composed of the ferrite phase, which offers ductility, and the martensite phase, which provides strength. However, the shapes, orientations and directions of the grains of these two phases are different and vary depending on the degree of observation. Therefore, the objective of this research was to compare the stress and strain distribution at different strain rates of standard specimens of DP steels, namely DP600 and DP800 steels. Besides, in this study, the finite element modeling method is used through optimization to determine the GTN fracture failure, constitutive and nucleation parameters of the mentioned steels based on their rolling directions and strain rates. The experimental and numerical simulation results are also compared, and are in good agreement.
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