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- Dimitrios, Nikas, et al.
(author)
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Characterization of deformed pearlitic rail steel
- 2017
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In: IOP Conference Series. - : Institute of Physics Publishing (IOPP). ; 219:1, s. Art no:UNSP 012035-
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Conference paper (peer-reviewed)abstract
- Pearlitic steels are commonly used for railway rails because they combine good strength and wear properties. During service, the passage of trains results in a large accumulation of shear strains in the surface layer of the rail, leading to crack initiation. Knowledge of the material properties in this region is therefore important for fatigue life prediction. As the strain is limited to a thin surface layer, very large strain gradients can be found. This makes it very difficult to quantify changes in material behavior. In this study hardness measurements were performed close to the surface using the Knoop hardness test method. The orientation of the pearlitic lamellas was measured to give an overview of the deformed microstructure in the surface of the rail. Microstructural characterization of the material was done by optical microscopy and scanning electron microscopy to evaluate the changes in the microstructure due to the large deformation. A strong gradient can be observed in the top 50 μm of the rail, while deeper into the rail the microstructure of the base material is preserved.
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| 2. |
- Meyer, Knut Andreas, 1990, et al.
(author)
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A comparison of two frameworks for kinematic hardening in hyperelasto-plasticity
- 2017
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In: Proceedings of the 14th International Conference on Computational Plasticity - Fundamentals and Applications, COMPLAS 2017. - 9788494690969 ; , s. 342-350
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Conference paper (peer-reviewed)abstract
- In this work we compare two frameworks for thermodynamically consistent hyperelasto-plasticity with kinematic hardening. The first was formulated by Dettmer and Reese (2004), inspired by Lion (2000), and has been used to model sheet metal forming. The second, formulated by Wallin et al. (2003), has been used to model large shear strains and cyclic ratcheting behavior of pearlitic steel (Johansson et al. 2006). In this paper we show that these frameworks can result in equivalent models for certain choices of free energies. Furthermore, it is shown that the choices of free energy found in the literature only result in minor differences. These differences are discussed theoretically and investigated numerically.
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| 3. |
- Meyer, Knut Andreas, 1990
(author)
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Modeling and experimental characterization of pearlitic rail steels subjected to large biaxial strains
- 2017
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Licentiate thesis (other academic/artistic)abstract
- Large shear strains develop in the near-surface region under the running band of railway rails. Rolling Contact Fatigue (RCF) cracks often initiate in this region, causing major problems for the railway industry. However, characterization of the constitutive and fatigue behavior of this region is difficult due to the large gradient of properties. In the present thesis, the deformed microstructure in this region is characterized. An axial-torsion test rig is used to predeform cylindrical low-cycle fatigue specimens in order to obtain material properties similar to those of the near-surface region in rails. These specimens are more suitable for further mechanical testing, compared to those resulting from many of the other predeformation methods described in the literature. The obtained material is compared to field samples in terms of the material hardness and microstructure. The microstructure is evaluated with both optical microscopy and scanning electron microscopy. This comparison shows that the predeformed material state closely resembles what is found in some used rails at a depth between 50 and 100 μm.In order to describe the behavior of the material during the large shear deformations, a sound framework for finite strain metal plasticity is needed. Several options are available in the literature, but in this thesis two frameworks for hyperelasto-plasticity with kinematic hardening are investigated. It is shown that for appropriate choices of Helmholtz' free energy these frameworks are equivalent.Furthermore, several material models formulated within this framework are evaluated in terms of their abilities to predict the mechanical response during the predeformation. Particular emphasis is put on the role of the kinematic hardening laws and how these influence the response during the biaxial loading. It is found that by combining different models from the literature, the predeformation process can be modeled accurately.
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