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In this study, the hole expansion tests are conducted for the first and third generation high-strength steels (dual-phase steel and quenching & partitioning steel) to investigate the edge fracture behavior. Two edge conditions based on separated manufacturing techniques (waterjet/wire cutting and punching) are prepared and then followed by hole expansion tests to characterize the edge fracture. On the modeling side, we illustrate the prediction of edge fracture by two different models, i) the istropic plasticity and fracture model and ii) the anisotropic plasticity and partially anisotropic fracture model. While Mises plasticity is used for isotropic yielding and hardening, the envoling non-associated Hill48 model [1] is employed to describe the plastic anisotropy and its evolution in terms of hardneing and r-values for both materials. The hybrid damage mechanics model is employed to describe the damage and fracture behaivor. Resulting from the formulation of the plasticity model, the damage/fracture model works either purely isotopic or partial anisotropic [2]. The parameters in the model are calibrated in an inverse way by comparing with the experimental results based on tensile tests of several designed geometries to trigger fracture under stress states from simple shear to plane-strain tension. Finite element model for hole blanking is built to simulate the sheared edge of the punched hole, while smooth edge condition is assumed for the machined hole, followed by the simulation on the hole expansion. The numerical results are compared between two materials, two edge conditions and two model formulations. It is concluded that the anistropy induced through thickness localization plays a dominating role on accurately prediction of the edge crack initiation and propagation.
1. Lian, J., et al., An evolving non-associated Hill48 plasticity model accounting for anisotropic hardening and r-value evolution and its application to forming limit prediction. International Journal of Solids and Structures, 2018. 151: p. 20-44.
2. Shen, F., S. Münstermann, and J. Lian, Investigation on the ductile fracture of high-strength pipeline steels using a partial anisotropic damage mechanics model. Engineering Fracture Mechanics, 2020. 227: p. 106900.