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TY - THES AU - Habibi, Niloufar TI - Scale-bridging investigation into edge cracking of multiphase steels PB - Rheinisch-Westfälische Technische Hochschule Aachen VL - Dissertation CY - Aachen M1 - RWTH-2024-07145 SP - 1 Online-Ressource : Illustrationen PY - 2024 N1 - Veröffentlicht auf dem Publikationsserver der RWTH Aachen University N1 - Dissertation, Rheinisch-Westfälische Technische Hochschule Aachen, 2024 AB - Edge cracking is one of the main challenges in widespread applications of dual-phase (DP) steel sheets. It does not only restrict the formability at component edges during forming processes but also cannot be anticipated by the conventional forming limits, which makes the design of a successful forming process possible only by trial and error approaches. To overcome this issue, a thorough understanding of this phenomenon is required. Therefore, a scale-bridging investigation was conducted in the present dissertation to study the potential reasons for edge cracking, such as materials properties, edge quality, and edge forming processes. However, all these reasons could be summed up as damage evolution in the material throughout the applied complicated deformation condition. For the macro-scale study, a phenomenological uncoupled damage criterion along with a kinematic hardening model was developed to describe the plasticity and fracture behavior of the examined steels. To cover a wide range of stress states, various experiments were designed, which underwent mostly proportional loading. For the meso-scale, Tresca fracture model, maximum shear stress, was applied to predict the damage initiation in the generated representative volume elements (RVEs). These RVEs were constructed according to the actual microstructural features, like grain size, phase fraction, and texture, as well as mechanical properties of individual phases, which were derived using nano-indentation and an inversely calibrated crystal plasticity model. The results of both scales showed that when microstructural and mechanical properties of the ferrite and martensite phases are more similar in a DP steel, the deformation is distributed more homogenously throughout the material, which leads the local formability to increase, damage initiation to be retarded, and consequently edge cracking sensitivity to decrease. Moreover, it was revealed that the data of available experimental methods for edge cracking evaluation cannot be directly used in complex edge forming processes. The hole expansion test (HET) applies distinct stress states at different locations on the specimen, which could cause crack initiation was even far from the edges. Edge-fracture-tensile testing (EFTT) method could be successful for the comparison of edge crack resistance between different materials, however it considers only one stress state at the edge. While finite element modeling of edge manufacturing and the subsequent edge deforming process along with a proper plasticity-damage model was reported as a promising method for investigation of edge cracking in different materials and deformation processes. LB - PUB:(DE-HGF)11 DO - DOI:10.18154/RWTH-2024-07145 UR - https://publications.rwth-aachen.de/record/990110 ER -