| 1. |
- Cao, Yu, 1969, et al.
(författare)
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Temperature and strain rate effects on the mechanical behavior of dual phase steel
- 2015
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Ingår i: Materials Science & Engineering A: Structural Materials: Properties, Microstructure and Processing. - : Elsevier BV. - 0921-5093. ; 636, s. 124-132
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Tidskriftsartikel (refereegranskat)abstract
- The effect of temperature and strain rate on the mechanical behavior of a commercial dual phase steel (DP 800) has been investigated experimentally by uniaxial tensile tests in this study, covering temperatures (−60 °C to 100 °C) and strain rates (1×10–4 to 1×10+2 s−1) encompassing conditions experienced in automotive crash situations. Yield and ultimate tensile strength, ductility, temperature effects and strain rate sensitivity have been determined and discussed. It was found that the Voce equation [σ=σs−(σs−σ0)exp(−εθ0/σs))] can be satisfactorily applied to describe the tensile flow curves by means of a modified Kocks–Mecking model. In this model the parameter θ0 is fixed, whereas both σ0 and σs consist of athermal and thermal stress components. The athermal component is only weakly dependent on temperature through the elastic shear modulus μ. The thermal stress component is governed by temperature and strain rate. Statistical analysis based on the experimental data has allowed all parameters in the Voce equation to be quantified.
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| 2. |
- Cao, Yu, 1969, et al.
(författare)
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The influence of temperatures and strain rates on the mechanical behavior of dual phase steel in different conditions
- 2015
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Ingår i: Journal of Materials Research and Technology. - : Elsevier BV. - 2238-7854. ; 4:1, s. 68-74
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Tidskriftsartikel (refereegranskat)abstract
- This study deals with the mechanical behavior of DP steel. A commercial dual phase steel (DP 800) was strained to 3.5% followed by annealing at 180 degrees C for 30 min to simulate the pressing of the plates and the paint bake cycle involved in the manufacturing process of automobile body structures. The effect of temperarure and strain rate on the machanical behavior of this material was investigated by uniaxial tensile tests, covering applicable temperatures (-60 degree C to +100 degree C) and strain rates (1x10exp-4 s-1 to 1x10exp+2 s-1) experienced in automotive crash situations. Yield and ultimate tensile strength, ductility, temperature effects and strain rate sensitivity as well as strain rate hardening rate have been determined and discussed.
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| 3. |
- Esmaeili, Ali, 1983, et al.
(författare)
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A methodology to predict thermomechanical cracking of railway wheel treads: From experiments to numerical predictions
- 2017
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Ingår i: International Journal of Fatigue. - : Elsevier BV. - 0142-1123. ; 105, s. 71-85
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Tidskriftsartikel (refereegranskat)abstract
- In the present study, thermomechanical cracking of railway wheel treads is studied by full-scale brake rig tests and finite element simulations. The main goal of the paper is to perform thermomechanical rolling contact fatigue life predictions. The wheel tread material is subjected to simultaneous mechanical and thermal loads due to rolling contact and stop braking, respectively. Full-scale tests featuring three series of repeated stop braking cases have been performed in a brake rig featuring a tread braked wheel that is in rolling contact with a so-called rail-wheel. The brake rig test conditions have been simulated numerically using the finite element method where the effect of “hot bands” on the tread is accounted for as indicated by the experimental findings. Stresses induced by temperature from braking as well as tractive rolling contact loading on the tread are considered. The mechanical response of the wheel material ER7 is obtained from a plastic Chaboche material model calibrated against data from cyclic experiments at room temperature and up to 625 °C. Finally, a strategy for prediction of fatigue life with respect to ratchetting failure is discussed.
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| 4. |
- Esmaeili, Ali, 1983, et al.
(författare)
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Modelling of cyclic plasticity and phase transformations during repeated local heating events in rail and wheel steels
- 2018
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Ingår i: Proceedings - 11th International Conference on Contact Mechanics and Wear of Rail/Wheel Systems. - 9789461869630 ; , s. 245-252
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Konferensbidrag (refereegranskat)abstract
- Short term local friction heating in railway operation might occur when a railway wheelset skids along the rail. The consequent temperature elevation is significant and in the pearlitic rail and wheel steels results in phase transformations. The temperature dependent differences in thermal expansion, density and mechanical properties of the phases result in residual stresses which can cause thermal damage in rail and wheel steels. This study is an improvement of Finite Element (FE) modelling incorporating phase transformation kinetics law describing transformation and evolution of volume fraction of phases. The FE modelling has included coupled thermal and mechanical analysis to compute residual stresses near the wheel-rail contact.
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| 5. |
- Esmaeili, Ali, 1983, et al.
(författare)
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Thermomechanical cracking of railway wheel treads: a combined experimental and numerical approach
- 2015
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Ingår i: Proceedings of the 10th International Conference on Contact Mechanics and Wear of Rail/Wheel Systems (CM2015). ; , s. 8-
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Konferensbidrag (refereegranskat)abstract
- In the present study, thermal cracking of railway wheel treads is studied by full-scale brake rig tests and finite element simulations. The focus is on thermomechanical rolling contact fatigue (RCF) life predictions. The wheel tread material is subjected to simultaneous mechanical and thermal loads due to rolling contact and stop braking, respectively. Full-scale tests featuring three series of repeated stop braking cases have been performed at the Railway Technical Research Institute (RTRI) in Japan in a brake rig featuring a tread braked wheel that is in rolling contact with a railwheel. The brake rig test conditions have been simulated numerically using the finite element method. To this end, the effect of “hot bands” on the tread is accounted for as indicated by the experimental findings. Thermomechanical stresses induced by braking as well as Hertzian contact loading on the tread including tractive loads based on a partial slip assumption are considered. The mechanical response of the wheel material ER7 is obtained from a viscoplastic Chaboche material model calibrated against data from cyclic experiments with hold-time from room temperatures up to 650 °C. Finally, a strategy for prediction of fatigue life with respect to ratcheting failure is discussed.
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| 6. |
- Meyer, Knut Andreas, 1990, et al.
(författare)
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Characterization of yield surface evolution due to large plastic shear strains in pearlitic rail steel
- 2018
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Ingår i: Proceedings - 11th International Conference on Contact Mechanics and Wear of Rail/Wheel Systems. - 2590-0609. - 9789461869630 ; 2018, s. 745-752
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Konferensbidrag (refereegranskat)abstract
- In order to analyze the material state in the rail surface layer during service, R260 rail steel has been subjected to large shear strains. The evolution of the yield surface at different amounts of predeformation, corresponding to different depths in the railhead, has been characterized. As expected, it is found that the size of the yield surface and the degree of anisotropy increase with the amount of predeformation. However, the major changes occur already after the first of six predeformation cycles, indicating that the yield surface is anisotropic several millimeters into the railhead.
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| 7. |
- Meyer, Knut Andreas, 1990, et al.
(författare)
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Material model calibration against axial-torsion-pressure experiments accounting for the non-uniform stress distribution
- 2019
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Ingår i: Finite Elements in Analysis and Design. - : Elsevier BV. - 0168-874X. ; 163, s. 1-13
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Tidskriftsartikel (refereegranskat)abstract
- The need to calibrate material models towards complex multiaxial stress states has received much attention in the last decades. Such stress states are often obtained by axial, torsion and pressure experiments on tubular test bars. These experiments are typically simulated by considering the behavior in a single material point, using the thin-walled assumption of uniform stresses and strains. In this paper, a new simulation methodology that does not rely on the thin-walled assumption has been developed. The accuracy improvements are compared with experimental uncertainties for tubular test bars. Compared to using ABAQUS for equivalent simulations, a speed increase of 100–200 times was found. This simulation methodology has been implemented in an open source software material calibration software called matmodfit. The calibration of material parameters is first demonstrated for cyclic ratcheting axial-torsion experiments using thin-walled test bars. Thereafter, calibration of material parameters from experiments on solid test bars subjected to very large shear deformation under axial compression is performed. This demonstrates a key advantage with the proposed method: Thick-walled or even solid test bars can be modeled without loss of simulation accuracy at a low computational cost.
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| 8. |
- Meyer, Knut Andreas, 1990, et al.
(författare)
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MODELING EVOLUTION OF ANISOTROPY IN PEARLITIC STEEL DURING COLD WORKING
- 2015
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Ingår i: Proceedings of the NSCM28. ; , s. 111-114
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Simulated evolution of anisotropy by reorientation of cementite lamellae in pearlitic steel is compared to experimental data. The modeling of reorientationand the homogenization of the yield function are discussed
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| 9. |
- Meyer, Knut Andreas, 1990, et al.
(författare)
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Modeling of kinematic hardening at large biaxial deformations in pearlitic rail steel
- 2018
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Ingår i: International Journal of Solids and Structures. - : Elsevier BV. - 0020-7683. ; 130, s. 122-132
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Tidskriftsartikel (refereegranskat)abstract
- Using an Axial-Torsion testing machine, pearlitic R260 steel specimens are twisted until fracture under different axial loads. A well established framework for finite elastoplasticity with kinematic hardening is used to model the deformation of the specimens. In particular, we evaluate the ability of different kinematic hardening laws to predict the observed biaxial load versus displacement response. It is found that the combination of Armstrong-Frederick dynamic recovery and Burlet-Cailletaud radial evanescence saturation is efficient even for the large strains achieved in this study. The results are less conclusive on the appropriateness of replacing the Armstrong-Frederick with an Ohno-Wang type of kinematic hardening law.
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| 10. |
- Ahlström, Johan, 1969
(författare)
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Crack initiation caused by repeated local heating events – Modelling of possible mechanisms
- 2015
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Ingår i: Proceedings of the 10th International Conference on Contact Mechanics and Wear of Rail/Wheel Systems (CM2015)..
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Konferensbidrag (refereegranskat)abstract
- Thermally initiated damage mechanisms by short-term local surface heating of a rail or wheel have been examined. A Finite Element (FE) model incorporating phase transformation from near pearlitic steel to austenite, and then to martensite was built to examine developing strength and residual stress fields. The FE model also incorporates thermal contraction on tempering of the martensite by following heat pulses. The material is modeled as isotropic, but with properties varying with phase, temperature and tempering state. Different thermal sequences that could cause crack initiation are examined.
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