13th International Conference on the Technology of Plasticity (ICTP 2021): Constitutive Behavior I
Program Organizers: Glenn Daehn, Ohio State University; Libby Culley, The Ohio State University; Anupam Vivek, Ohio State University; Jian Cao, Northwestern University; Brad Kinsey, University of New Hampshire; Erman Tekkaya, TU Dortmund; Yoshinori Yoshida, Gifu University
Monday 9:15 AM
July 26, 2021
Room: Virtual: Room B
Location: Virtual
Session Chair: Hoon Huh, KAIST; Anupam Vivek, The Ohio State University
Analysis of the Thermomechanical Flow Behavior of Carburized Sheet Metal in Hot Stamping: Alexander Horn1; Marion Merklein1; 1Friedrich-Alexander Universität Erlangen-Nürnberg
The reduction of fuel consumption due to restrictions regarding CO2 emissions is one of the major driving forces for lightweight design in the automotive industry. In this context, hot stamping of ultra-high strength steels has developed to a state of the art process for manufacturing safety-relevant components. With regard to passenger safety and weight reduction, further potential lies in the functional optimization of the parts. Prior local carburization followed by hot stamping is a new process variant for tailored properties, which overcomes the limitations of established processes. Due to the varying carbon content after carburization, the sheets have graded mechanical properties. Within this contribution, the influence of temperature, time and carburization parameters on the flow behavior will be investigated. For this purpose, tensile tests at elevated temperatures will be carried out in a physical simulator of type Gleeble and the flow curves will be modeled with a suitable hardening law.
Dynamic Recrystallization Behaviors of 5083 Aluminum Alloys with Different Initial Microstructures under Hot Compression: Sheng Ding1; Jun Yanagimoto1; 1The University of Tokyo
To study the dynamic softening behaviors of 5083 aluminum alloys under hot compression, hot compression tests of 5083 aluminum alloys with extruded and homogenized initial microstructures were conducted at strain rate ranging from 0.1 to 10/s and deformation temperatures ranging from 350 to 450°C. The obtained flow curves under a homogenized initial microstructure were lower than those under an extruded initial microstructure, suggesting that different initial microstructures lead to different microstructure evolution processes. Electron backscatter diffraction (EBSD) was used to observe the microstructure evolution process. The characteristics of continuous dynamic recrystallization, particle-stimulated recrystallization and conventional dynamic recrystallization were confirmed. The experiments deformed at the same temperature and strain rate but with different strains showed the transition from continuous to conventional recrystallization. The recrystallization mechanism of 5083 aluminum alloys with different initial microstructures is thus finally illustrated.
Simulation of Cold Forging Processes Using a Mixed Isotropic-Kinematik Hardening Model: Lander Galdos1; Julen Agirre1; Nagore Otegi1; Joseba Mendiguren1; Eneka Saenz de Argandoña1; 1Mondragon Unibertsitatea
Cold forging is a manufacturing process where a bar stock is inserted into a die and squeezed with a second closed die. It is one of the most widely used chipless forming processes, often requiring no machining or additional operations to get tight tolerances. Because materials to be formed are increasingly harder and the geometrical complexity is greater, the finite element simulation is becoming an essential tool for process design. This study proposes the use of the Chaboche hardening model for the cold forging simulation of a 42CrMoS4Al material industrial automotive ball pin. The material model has been fitted with experimental data obtained from cyclic torsion tests at different reversal plastic strains as well as monotonic torsion tests at different strain rates. Comparison between the classical isotropic hardening and the new mixed hardening model are presented for the different forging steps.
Influence of the Quenching Rate and Natural Ageing Duration on the Formability and Mechanical Properties of EN AW-7075: Bernd-Arno Behrens1; Sven Hübner1; Hendrik Vogt1; Oleksandr Golovko2; Sabine Behrens2; Florian Nürnberger2; 1Institute of Forming Technology and Machines, Leibniz University Hannover; 2Institute of Materials Science, Leibniz University Hannover
In recent years, 7xxx-aluminum alloys have been the subject of numerous investigations in the field of warm and hot forming and suited heat treatments to fully utilize its potential for applications in automotive bodies. Alternatively, forming blanks of these alloys at room temperature in the W temper state is favorable since conventional tools can be used. However, this condition is unstable. As the ageing duration after quenching increases, the formability decreases due to natural ageing. Hence, the objective of the investigations was to determine the formability of EN AW-7075 as a function of the ageing time. Furthermore, since the quenching rate after solution heat treatment influences the resulting mechanical properties, an adapted process route to manufacture components with tailored properties was explored. For this purpose, samples were partially quenched and then artificially aged. To determine the influence of the quenching rate, hardness tests and microstructure analysis were carried out.
Evaluationg of Press Forming Technique for Bent Automotive Body Parts Using In-plane Shear Deformation: Yusuke Fujii1; Masaki Urabe1; Yuji Yamasaki1; Yoshikiyo Tamai1; 1JFE steel
Press forming of automotive frame parts which bent in the height direction with high strength steel sheet suffers from fracture and wrinkle caused by bending deformation.We has succeeded in developing new cold press forming technique with a process of two steps: first step for inducing in-plane shear deformation and second step for shaping into the bent part. The shear deformation in the first step was obtained by draw forming in unconventional press direction and had effect of suppressing the bending deformation. Relationship between the bent angle of the part and the shear deformation was clarified by experiments of small simplified model. When induced in-plane shear deformation increased, the part which had higher bent angle could be formed. The efficacy of the developed technique was confirmed by experimental trials using a real-size model of a front side member rear with 1180 MPa grade ultra-high strength steel sheet.
Calibration and Verification of Stress-strain Curve in High Strain Region of Mild Steel Sheet: Hideo Tsutamori1; Hiroaki Oonishi1; Takeshi Nishiwaki1; 1Daido University
Stress-strain curve in high strain region is one of the most important models that must be taken into consideration for high-precision sheet forming simulation. In this study, using mild steel sheets, tensile tests were conducted with a necked shape specimen at the center in order to generate non-uniform elongation. Using image analysis, strain-load relationships were obtained using multiple gauge lengths, and stress-strain relationships were obtained by inverse analysis using FE simulation. With sufficiently small gauge length it is possible to obtain stress-strain relationships in high strain region. The advantage of this method is that it can be implemented with a uniaxial tensile test machine only as experimental apparatus. For validation, original hole expansion test model is proposed, that is not affected by friction. The thickness strain distribution along the hole with large plastic strain is compared with experimental and numerical results to indicate validity of this method.
Towards an Efficient Industrial Implementation of W-temper Forming for 7xxx Series Al Alloys: Ricardo Tran1; Lukas Kertsch2; Sebastian Marx1; Shreyas Hebbar2; Verena Psyk1; Alexander Butz2; 1Fraunhofer Institute for Machine Tools and Forming Technology IWU; 2Fraunhofer Institute for Mechanics of Materials IWM
Manufacturing technologies for parts made from ultra-high strength 7xxx series aluminum sheet material have been a focus of research in recent years. A promising approach is W-temper forming, where sheet material is cold formed after a heat treatment. Conventional heat treatment routes are very time consuming and inefficient. In this study a new more efficient and industry-orientated transfer tool concept has been developed. Heating and cooling of the sheets takes place in separate contact tempering stages, which allow superior heating and cooling rates in comparison to conventional methods. To analyze the influences of temperature rates and deformation on microstructure and mechanical behavior, thermo-mechanical experiments in a Gleeble simulator were carried out. The results prove the great potential of the transfer tool concept with an inline heat treatment for series production. The process dependent mechanical properties determine a suitable process window for the industrial application of the W-temper forming of the analyzed alloys.