Crystal plasticity modeling of ductile fracture locus in advanced high-strength steels

• Crystal plasticity modeling of ductile fracture locus in DP steel is proposed. • Correlation between macro-scale FEA and meso-scale CPFEM is well established. • Ductile fracture locus is accurately predicted and its application precisely captures the ductile fracture initiation in metal forming process. • Damage initiation is highly sensitive to the criterion used, highlighting its importance in accurate modeling of material degradation. This study proposes a crystal plasticity modeling framework to predict the macroscopic ductile fracture locus of dual-phase (DP) advanced high-strength steel (AHSS) sheet under various plastic deformation modes. A meso-scale crystal plasticity finite element method (CPFEM) is introduced and correlated with macro-scale finite element analysis (FEA). Unlike phenomenological FEA approaches, the proposed method directly incorporates microstructural features and their interactions via CPFEM to evaluate the ductile fracture locus. The experiments of microstructural measurement, uniaxial tensile, fracture and Nakajima tests are conducted to develop and validate the proposed framework. Results show that CPFEM-predicted fracture strains agree with experiments. The ductile fracture locus under various deformation modes is accurately predicted using experimental data from only a single deformation mode for calibrating the proposed approach, indicating the model’s predictive capability. For predicting ductile fracture initiation, various promising damage criteria are suggested based on the evolutions of damaged elements and plastic strain in the constituent phases. It elucidates that the ductile fracture initiation is very sensitive to the chosen criterion, highlighting the importance of selecting an appropriate failure criterion in accurate modeling of material degradation. Moreover, the calibrated ductile fracture locus is successfully applied for metal forming simulations to precisely capture the experimental results of displacement at the onset of fracture and the location of fracture in Nakajima tests, further demonstrating the reliability and robustness of the proposed approach. These findings indicate that the proposed framework in this work offers significant potential for predicting ductile fracture in AHSS.