| 1. |
- Andersson, Björn, 1989, et al.
(författare)
-
Homogenization based macroscopic model of phase transformations and cyclic plasticity in pearlitic steel
- 2022
-
Ingår i: Journal of Thermal Stresses. - : Informa UK Limited. - 0149-5739 .- 1521-074X. ; 45:6, s. 470-492
-
Tidskriftsartikel (refereegranskat)abstract
- In this contribution macroscopic modeling of phase transformations and mechanical behavior of low alloy steels are developed and investigated. Such modeling is of importance in simulations of transient thermo-mechanical processes which can cause phase transformations, examples from the railway industry include train braking induced frictional heating as well as rail grinding and welding operations. We adopt a modeling approach which includes phase transformation kinetics and individual constitutive models for the phases in combination with different homogenization methods. Algorithmic implementations of the isostrain, isostress and self-consistent homogenization methods are presented and demonstrated in finite element simulations of a laser heating experiment. Stress field results from the different homogenization methods are compared against each other and also against experimental data. The importance of including transformation induced plasticity in the modeling is highlighted, as well as the multi-phase stages of the heating and cooling.
|
|
| 2. |
- Esmaeili, Ali, 1983, et al.
(författare)
-
Modelling of cyclic plasticity and phase transformations during repeated local heating events in rail and wheel steels
- 2021
-
Ingår i: International Journal of Fatigue. - : Elsevier BV. - 0142-1123. ; 151
-
Tidskriftsartikel (refereegranskat)abstract
- Short term local friction heating events in railway operations might lead to phase transformations in pearlitic rail and wheel steels. A modelling framework for phase transformations combined with cyclic plasticity for the individual phases is presented. The phase transformation kinetics include e.g. austenitization due to heating, martensite formation due to rapid cooling and martensite tempering. The modelling framework has been calibrated against cyclic dilatometry test data and cyclic mechanical experiments. Simulations of a double heating event followed by rolling contact loadings show phase transformations and how cyclic residual stresses develop in the different phases.
|
|
| 3. |
- Esmaeili, Ali, 1983, et al.
(författare)
-
Modelling of temperature and strain rate dependent behaviour of pearlitic steel in block braked railway wheels
- 2021
-
Ingår i: Railway Engineering Science. - : Springer. - 2662-4745 .- 2662-4753. ; 29:4, s. 362-378
-
Tidskriftsartikel (refereegranskat)abstract
- Block braked railway wheels are subjected to thermal and rolling contact loading. The thermal loading results in high temperatures and thermal stresses which cause slow time dependent processes such as creep, relaxation and static recovery of the wheel material. At the same time, the rolling contact loading implies a very fast mechanical load application. This paper is focused on material modeling of pearlitic steel for a wide range of loading rates at elevated temperatures. The starting point is a viscoplasticity model including nonlinear isotropic and kinematic hardening. The Delobelle overstress function is employed to capture strain rate dependent response of the material. The model also includes static recovery of the hardening to capture slower viscous (diffusion dominated) behaviour of the material. Experiments for the pearlitic wheel steel ER7 in terms of cyclic strain-controlled uniaxial tests with hold-time, uniaxial ratchetting tests including rapid cycles and biaxial cyclic tests with tension/compression and torsion are used to calibrate the material model. These experiments were performed under isothermal conditions at different temperatures. In the ratchetting tests, higher loading rates are obtained and these have been used to calibrate the high strain rate response of the viscoplasticity model. The paper is concluded with a numerical example of a block braked wheel where the importance of accounting for the viscoplasticity in modelling is highlighted.
|
|
| 4. |
- Meyer, Knut Andreas, 1990, et al.
(författare)
-
Anisotropic yield surfaces after large shear deformations in pearlitic steel
- 2020
-
Ingår i: European Journal of Mechanics, A/Solids. - : Elsevier BV. - 0997-7538. ; 82
-
Tidskriftsartikel (refereegranskat)abstract
- Rolling contact fatigue often initiates in the highly deformed surface layer of railway rails. However, the behavior of pearlitic rail steels, subjected to such large shear strains, is not well known. Due to buckling, it is not possible to obtain the large shear deformation with tubular test bars. We have, therefore, developed a novel experimental methodology. Large shear strains (up to 1.13) were obtained by twisting cylindrical solid test bars under a compressive axial load. After that, these bars were re-machined into thin-walled tubular test bars. The remachined bars were then used to characterize the behavior of the deformed material. Changes in both the elastic and plastic responses are observed, quantified, and discussed. We evaluate the ability of different yield criteria to model the experimentally measured yield surfaces. Three anisotropic yield criteria are considered: Hill (1948), Barlat's yld2004-18p, and Karafillis and Boyce (1993). The accuracies of these criteria are evaluated and compared to the estimated experimental uncertainty. Furthermore, cross-validation is used to investigate the predictive abilities of the yield criteria. It turns out that the Hill yield criterion fits and predicts the experimental data very well. Finally, the evolution of yield surfaces is found to be strongly dependent on the amount of plastic deformation defining the yield limit.
|
|
| 5. |
- Talebi, Nasrin, 1992, et al.
(författare)
-
CRACK INITIATION CRITERIA FOR DEFORMED ANISOTROPIC R260 RAIL STEEL
- 2022
-
Ingår i: CM 2022 - 12th International Conference on Contact Mechanics and Wear of Rail/Wheel Systems, Conference Proceedings. ; , s. 857-864
-
Konferensbidrag (refereegranskat)abstract
- Rail material selection and maintenance planning require accurate material failure criteria. While many of these criteria consider low-cycle fatigue of virgin materials, rail failure is known to occur after severe plastic deformations. It is, therefore, relevant to consider the applicability of such criteria during large plastic deformations. In this study, we simulate previously performed high-shear tension-torsion experiments using finite strain theory to evaluate the local stresses and strains. Based on these results, failure criteria are calibrated and validated. The Jiang-Sehitoglu criterion accurately fits and predicts failure. However, the identified parameter values are different from literature values for similar materials.
|
|
| 6. |
- Talebi, Nasrin, 1992, et al.
(författare)
-
Evaluations and enhancements of fatigue crack initiation criteria for steels subjected to large shear deformations
- 2024
-
Ingår i: International Journal of Fatigue. - 0142-1123. ; 182
-
Tidskriftsartikel (refereegranskat)abstract
- While large accumulated plastic deformations occur in the rail surface layer where rolling contact fatigue cracks initiate, many available Low Cycle Fatigue (LCF) crack initiation criteria focus on small plastic strains. Accordingly, this paper evaluates available fatigue crack initiation criteria for highly shear-deformed R260 steels, reflecting the conditions in the surface layer of rails. Furthermore, modified crack initiation criteria are suggested. The evaluation is based on three different experiments: Large shear strain increments under varying axial loading (predeformation), strain-controlled LCF tests after some predeformation, and axial High Cycle Fatigue (HCF) experiments. For the predeformation, Finite Element (FE) simulations, with a large-strain plasticity model for cyclic and distortional hardening, provide predictions of the local stress and strain histories. A cross-validation procedure is used to assess the accuracy and reliability of both established and modified fatigue crack initiation criteria. The proposed modifications to one of the criteria show an improved fit to the experimental data. However, there is a tendency to overfitting, which can be improved by including more experimental data.
|
|
| 7. |
- Blinzler, Brina, 1987, et al.
(författare)
-
Integrated Computational Material Design for PMC Manufacturing with Trapped Rubber
- 2020
-
Ingår i: Materials. - : MDPI AG. - 1996-1944. ; 13:17
-
Tidskriftsartikel (refereegranskat)abstract
- As the use of continuous fiber polymer matrix composites expands into new fields, there is a growing need for more sustainable manufacturing processes. An integrated computational material design framework has been developed, which enables the design of tailored manufacturing systems for polymer matrix composite materials as a sustainable alternative to achieving high-quality components in high-rate production. Trapped rubber processing achieves high pressures during polymer matrix composite processing, utilizing the thermally induced volume change of a nearly incompressible material inside a closed cavity mold. In this interdisciplinary study, the structural analysis, material science and manufacturing engineering perspectives are all combined to determine the mold mechanics, and the manufacturing process in a cohesive and iterative design loop. This study performs the coupled thermo-mechanical analysis required to simulate the transients involved in composite manufacturing and the results are compared with a previously developed test method. The internal surface pressure and temperatures are computed, compared with the experimental results, and the resulting design process is simulated. Overall, this approach maintains high-quality consolidation during curing while allowing for the possibility for custom distributions of pressures and temperatures. This can lead to more sustainable manufacturing by reducing energy consumption and improving throughput.
|
|
| 8. |
- Dhar, S., et al.
(författare)
-
Multi-axial Fatigue of Head-Hardened Pearlitic and Austenitic Manganese Railway Steels: A Comparative Study
- 2020
-
Ingår i: Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science. - : Springer Science and Business Media LLC. - 1073-5623. ; 51:11, s. 5639-5652
-
Tidskriftsartikel (refereegranskat)abstract
- Switches and crossings (S&Cs) in rail networks suffer from damage and deformation due to severe loading of their complex geometric shapes. This article presents a comparative study of the cyclic deformation characteristics and fatigue behavior of two typical crossing materials, namely head-hardened pearlitic steel and Hadfield manganese steel, as well as the associated microstructural changes. Both uniaxial and biaxial loadings (proportional and non-proportional) are studied. The pearlitic steel endured more cycles to failure for a given strain amplitude compared to the manganese steel. The cyclic response of manganese steel shows significant hardening whereas softening was observed for the pearlitic steel except under biaxial non-proportional loading. The microstructures developed in the two types of steels after deformation are characterized by optical (OM) and transmission electron microscopy (TEM). TEM micrographs reveal that the deformed microstructure of the pearlitic steel consists of threading dislocations and dislocation tangles in the ferrite lamellae. The microstructures in the manganese steel after the different loadings are composed of dislocation cells with dislocation tangles inside, intersected by straight stacking fault lamellae. The observed microstructures are related to the results of the mechanical test, and the suitability of the steels for use in S&Cs is discussed.
|
|
| 9. |
- Dimitrios, Nikas, et al.
(författare)
-
Effect of annealing on microstructure in railway wheel steel
- 2022
-
Ingår i: 42Nd Riso International Symposium On Materials Science. - : Institute of Physics Publishing (IOPP). ; 1249
-
Konferensbidrag (refereegranskat)abstract
- Railway wheels are commonly made from medium carbon steels (similar to 0.55 wt.% C), heat treated to a near pearlitic microstructure with 5-10% pro-eutectoid ferrite. During the operation of freight trains, where block brakes are used, high thermal loads occur together with the high contact stresses, which combined can affect the mechanical properties of the material. In this study, the effects of annealing on local microstructure and mechanical properties in pearlitic railway wheel steel were investigated using electron microscopy and micro-hardness. It is found that after annealing at 650 degrees C, the room temperature hardness reduces about 25%, accompanied by significant spheroidization of cementite in the pearlitic colonies, though the size and the orientation gradients of the pearlitic colonies have not changed much. The relationship between the microstructural changes and the mechanical properties are discussed.
|
|
| 10. |
- Gren, Daniel, 1994, et al.
(författare)
-
Fatigue Crack Propagation on Uniaxial Loading of Biaxially Predeformed Pearlitic Rail Steel
- 2023
-
Ingår i: Metals. - 2075-4701. ; 13:10
-
Tidskriftsartikel (refereegranskat)abstract
- Rolling contact fatigue loading causes the surface material in the top of the rail to severely deform. The microstructure aligns along the shear direction and the mechanical behavior in terms of plastic flow becomes anisotropic. Cracks are initiated in the severely deformed surface region and propagates along the direction of microstructure flow lines. However, the effect of large shear deformation on fatigue crack growth is not yet well understood. In this study, uniaxial fatigue crack propagation of undeformed and biaxially predeformed pearlitic rail steel R260 has been investigated. The material was predeformed to different deformation states using combined axial compression and shear deformation, corresponding to material found at different depths in the severely deformed surface layer of rails. Fatigue crack propagation rate was dependent on the material state and influenced by both work hardening and microstructural anisotropy. It was found that predeformed material exhibited lower crack growth rates than undeformed material under this loading condition. The influence of predeformation on the crack growth direction was limited.
|
|
