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Article Citation - Scopus: 2Temperature Effects in Deep Drawing of Advanced High Strengthsteels(MIM RESEARCH GROUP, 2021) Akcan, Kadir; Billur, Eren; Saraç, H. İbrahimAs advanced high strength steels (AHSS) find more use in automotive industry to meet crashworthiness and light weighting targets, concurrently. AHSS typically have higher strength, but lower formability; often limiting a part’s dimensions and geometric complexity. Several studies have clearly shown that, in sheet metal forming, significant portion of the work done to overcome friction and to plastically deform a sheet is converted into heat. In this study, a thermomechanical finite element model has been developed to calculate the temperature rise in forming DP800 (AHSS). The model was validated with experiments from literature. A multi-cycle model is developed to find out possible problems due to tool heating. The process and material are selected to speed up the heating. Under different realistic press conditions, failures are observed after 20 to 80 hits.Article Citation - WoS: 13Citation - Scopus: 17Effect of hydrogen on fracture locus of Fe-16Mn-0.6C-2.15Al TWIP steel(Pergamon-elsevier Science Ltd, 2020) Bal, Burak; Cetin, Baris; Bayram, Ferdi Caner; Billur, ErenEffect of hydrogen on the mechanical response and fracture locus of commercial TWIP steel was investigated comprehensively by tensile testing TWIP steel samples at room temperature and quasi-static regime. 5 different sample geometries were utilized to ensure different specific stress states and a digital image correlation (DIC) system was used during tensile tests. Electrochemical charging method was utilized for hydrogen charging and microstructural characterizations were carried out by scanning electron microscope. Stress triaxiality factors were calculated throughout the plastic deformation via finite element analysis (FEA) based simulations and average values were calculated at the most critical node. A specific Python script was developed to determine the equivalent fracture strain. Based on the experimental and numerical results, the relation between the equivalent fracture strain and stress triaxiality was determined and the effect of hydrogen on the corresponding fracture locus was quantified. The deterioration in the mechanical response due to hydrogen was observed regardless of the sample geometry and hydrogen changed the fracture mode from ductile to brittle. Moreover, hydrogen affected the fracture locus of TWIP steel by lowering the equivalent failure strains at given stress triaxiality levels. In this study, a modified Johnson-Cook failure mode was proposed and effect of hydrogen on damage constants were quantified. (C) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.Conference Object Predicting the Topology of the Bending Corner in Bending of Ultra High Strength Steels Through Finite Element Analysis(Tanger Ltd, 2019) Cetin, Baris; Billur, Eren; Baranoglu, Besim; Toptas, Ugur; Alic, Ozgur; Manufacturing Engineering; Automotive EngineeringIn bending of plates, unlike the case of sheet metal forming, a 3-D stress state is valid. Moreover, apart from the some very specific cases, the plane strain assumption is not appropriate either. Therefore; bending of thick ultra-high strength steel (UHSS) plates is a deformation process where 3-D stress and strain states exist in general. This study basically focuses on the prediction of the bending corner topology with non-linear finite element analysis method, since the laser-cut edges of the UHSS are particularly prone to edge cracking during bending operation. Within the scope of this study, an experimental set-up is designed which consists of bending tools and a servo mechanical press. The samples were bent by means of this set-up in an air-bending operation up to 90 degrees. This experimental work was followed by optical scanning measurements. And finally, the FEA results and the scanning data were compared in 3-D space. The results showed good correlation. As a future study, the 3-D strain field of the bending corner will be tried to be measured by a professional digital image correlation (DIC) system which could probably give more precise data when combined with the data from FEA.Article Citation - WoS: 2Citation - Scopus: 3Development of New Vehicle Safety Structures by Using Third Generation Steels(Sae int, 2022) Erzincanlioglu, Samet; Aydiner, Tamer; Aras, Firat; Celik, Hafize; Billur, Eren; Karabulut, Semih; Gumus, Iskender OnderResearch and development efforts in the automotive industry have been long focused on crashworthy, durable vehicles with the lowest mass possible as higher mass requires more energy and, thus, causes more CO2 emissions. One way of approaching these objectives is to reduce the total vehicle weight by using higher strength-to-weight ratio materials, such as Advanced High-Strength Steels (AHSS). Typically, as the steel gets stronger, its formability is reduced. The steel industry has been long developing (so-called) third-generation (Gen3) AHSS for the automotive industry. These grades offer higher formability compared to first-generation (Gent) and cost less compared to the second-generation (Gen2) AHSS. Transformation Induced Plasticity (TRIP)-aided Bainitic Ferrite (TBF) and Quenching and Partitioning (Q&P) steel families are considered to be the Gen3 AHSS. These grades can be cold-formed to more complex shapes, compared with the Geni Dual Phase (DP) and TRIP steels at equivalent strength levels. In this article, new single-piece A- and B-pillar reinforcements were designed using a Gen3 AHSS, TBF980. Spot-welding operations were eliminated due to part consolidation with the more formable steel. These parts will be the first structural automotive parts which were manufactured with cold-forming technology using TBF steels with a sstrength level close to 1 GPa or even more. Weight and cost reductions were realized by the new design while improving the crash performance.
