Modelling Concept Based upon Axially Symmetrical Models
The present chapter presents identification strategies of yield stress investigation of steels based on tensile and compression tests at very high temperatures as well as in the semi-solid state. The methodologies of stress-strain curves investigation com
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Modelling Concept Based upon Axially Symmetrical Models
The present chapter presents identification strategies of yield stress investigation of steels based on tensile and compression tests at very high temperatures as well as in the semi-solid state. The methodologies of stress-strain curves investigation combine the possibility of direct simulation using the Gleeble 3800 thermo-mechanical simulator with the developed dedicated DEFFEM system with implemented axial-symmetrical solutions. The constitutive parameters identified by these procedures have been successfully applied in additional three-dimensional tests (see Chap. 9). Due to very high sensitivity of the material rheology to temperature changes, the testing procedure requires as uniformly distributed temperature as possible. As part of the research aimed at the development of the foundation of the methodology for determining the mentioned stress-strain relationships, comprehensive tests were performed covering the influence of the applied grips on the temperature distribution along the heating zone and in the sample cross-section, as well as macro- and microstructural tests, and comprehensive tomographic tests. The findings of the conducted tests allowed the obtained computer simulation results to be verified. The computer simulations were performed using the modelling concept based upon axially symmetrical models.
8.1
Direct Simulation Using the Gleeble Thermo-Mechanical Simulator
Deformation processes of steels in the semi-solid state and their resistance heating close to the solidus line are effectively supported by the use of physical simulations [1]. Resistance heating is the first stage of the testing procedure. Steel grade C45 was selected as the test material. Cylindrical specimens with a diameter of 10 mm and a length of 125 mm were tested with the Gleeble 3800 thermo-mechanical simulator. The specimen was heated by resistance heating, with an automatically controlled © Springer International Publishing Switzerland 2017 M. Hojny, Modeling Steel Deformation in the Semi-Solid State, Advanced Structured Materials 47, DOI 10.1007/978-3-319-40863-7_8
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8 Modelling Concept Based upon Axially Symmetrical Models
Fig. 8.1 Samples with thermocouples locations used for the experiments: TC1, TC2, TC3 and TC4 thermocouples
alternating current being introduced into the specimen through cooper grips. At the first stage, the specimen was rapidly heated up to 1350 °C at a heating rate of 20 ° C/s. At the second stage, the specimen was slowly heated up to 1430 °C at a heating rate of 1 °C/s and held at this temperature for 30 s. Finally, the specimen was cooled down to the nominal test temperature (Tnom ) at a cooling rate of 10 °C/s and held at this temperature for either one minute or 10 s depending on the kind of test. Material testing of semi-solid steel should be carried out under isothermal conditions (as isothermal as possible) due to the very high sensitivity of the steel rheology to temperature changes. This is why the temperature distribution in
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