Phase Field Fracture Modelling of Crack Initiation and Propagation in Dual-Phase Microstructures B. Tatli∗, C. Erdogan, T. Yalçinkaya Department of Aerospace Engineering, Middle East Technical University, Ankara 06800, Türkiye ∗ btatli@metu.edu.tr Keywords: dual-phase steel, crystal plasticity, phase field modeling, ductile fracture. Due to their unique composition, dual-phase (DP) steels, which blend the ductile ferrite phase with the hard and brittle martensite phase, exhibit exceptional formability and intriguing material characteristics. However, the mismatched deformation characteristics of the two phases within DP steels leads to intricate failure mechanisms at the micro-scale, such as martensite cracking and interface decohesion between the ferrite-martensite (F/M) and ferrite- ferrite (F/F) phases [1, 2]. To gain insight into the plasticity and failure characteristics of DP steels, it is essential to conduct a thorough analysis of its microstructure through the utilization of a micromechanicsbased methodology. This has been addressed before using crystal plasticity and cohesive zone modelling approaches in [3]. Nonetheless, such studies require the implementation of cohesive zone elements in predetermined crack initiation zones. In this work, phase field fracture methodology is coupled with crystal plasticity framework to simulate the initiation and propagation of cracks in DP steels. This numerical framework is capable of simulating the initiation of cracks as well as the intra/inter granular propagation in crystal plasticity finite element (CPFE) simulations without any further damage modelling. The isotropic J2 plasticity model is employed for the brittle martensite phase, while the ductile ferrite phase utilizes a rate-dependent crystal plasticity framework. All the computations are performed with ABAQUS integrating both material and phase field fracture models through user material subroutines. To identify the necessary parameters for each phase, a parameter identification study is carried out. Three-dimensional representative volume elements (RVEs) with various crystallographic orientation sets and morphologies are simulated in order to assess the model’s performance with respect to experimental evidence. Further, obtained results are compared with the findings in [3] as well. References [1] Tang, A., Liu, H., Chen, R., Liu, G., Lai, Q., Zhong, Y., Wang, L., Wang, J., Lu, Q., and Shen, Y. (2021). Mesoscopic origin of damage nucleation in dual-phase steels. Int. J. Plast., 137, 102920. [2] Qin, S., Lu, Y., Sinnott, S. B., and Beese, A. M. (2020). Influence of phase and interface properties on the stress state dependent fracture initiation behavior in DP steels through computational modeling. Mater. Sci. Eng. A, 776, 138981. [3] Aydiner, I.U., Tatli, B. and Yalçinkaya, T. (2023). Micromechanical modeling of failure in dual phase steels. Material Research Proceedings, 28, 1443-1452. 76
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