| 1. |
- Ahlström, Johan, 1969, et al.
(författare)
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Temperature-dependent evolution of the cyclic yield stress of railway wheel steels
- 2016
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Ingår i: Wear. - : Elsevier BV. - 0043-1648. ; 366:SI, s. 378-382
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Tidskriftsartikel (refereegranskat)abstract
- The evolution of the cyclic yield stress for a railway wheel steel (UIC ER7T) during cyclic plastic straining has been characterized at different temperatures from -60 to 600 °C. Different constant strain amplitude levels were examined and for temperatures above 200 °C, hold periods were included to study stress relaxation during constant compressive strain. The results are of use in predicting material deformation and damage. This is demonstrated by the application to improve a criterion for surface initiated rolling contact fatigue damage.
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| 2. |
- Ahlström, Johan, 1969, et al.
(författare)
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Temperature-dependent evolution of the cyclic yield stress of railway wheel steels
- 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
- The evolution of the cyclic yield stress for a railway wheel steel (UIC ER7T) during cyclic plastic straining has been characterized at different temperatures from -60 – 600°C. Two strain amplitude levels were examined and for temperatures above 200°C, hold periods were included to study stress relaxation during constant compressive strain. The results are of use in predicting material deformation and damage. This is demonstrated by the application to improve a criterion for surface initiated rolling contact fatigue damage.
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| 3. |
- Andersson, Robin, 1986, et al.
(författare)
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An efficient approach to the analysis of rail surface irregularities accounting for dynamic train–track interaction and inelastic deformations
- 2015
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Ingår i: Vehicle System Dynamics. - : Informa UK Limited. - 1744-5159 .- 0042-3114. ; 53:11, s. 1667-1685
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Tidskriftsartikel (refereegranskat)abstract
- A two-dimensional computational model for assessment of rolling contact fatigue induced by discrete rail surface irregularities, especially in the context of so-called squats, is presented. Dynamic excitation in a wide frequency range is considered in computationally efficient time-domain simulations of high-frequency dynamic vehicle-track interaction accounting for transient non-Hertzian wheel–rail contact. Results from dynamic simulations are mapped onto a finite element model to resolve the cyclic, elastoplastic stress response in the rail. Ratcheting under multiple wheel passages is quantified. In addition, low cycle fatigue impact is quantified using the Jiang–Sehitoglu fatigue parameter. The functionality of the model is demonstrated by numerical examples.
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| 4. |
- Andersson, Robin, 1986, et al.
(författare)
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Evaluation of stress intensity factors under multiaxial and compressive conditions using low order displacement or stress field fitting
- 2018
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Ingår i: Engineering Fracture Mechanics. - : Elsevier BV. - 0013-7944. ; 189, s. 204-220
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Tidskriftsartikel (refereegranskat)abstract
- A methodology for evaluation of stress intensity factors from the asymptotic displacement (or stress) fields at a crack front is proposed. The methodology strives to be of practical use in conjunction with commercial FE-codes, also when approaches such as XFEM are employed. To this end, the matching of the fields is carried out through a minimalistic, low order, ansatz of the displacement and stress fields. As demonstrated, the proposed methodology can deal with multiaxial loading of curved crack fronts in three-dimensional bodies. The methodology shows good accuracy also for compressive loading when crack face friction can be neglected.
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| 5. |
- Andersson, Robin, 1986, et al.
(författare)
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Integrated analysis of dynamic vehicle-track interaction and plasticity induced damage in the presence of squat defects
- 2015
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Ingår i: Proceedings of the 10th International International Conference on Contact Mechanics and Wear of Rail/Wheel Systems, Colorado Springs, USA, August-September 2015.
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Konferensbidrag (refereegranskat)abstract
- Despite significant efforts, the mechanisms behind the formation of squats – a form of rolling contact fatigue damage – are not fully understood. This study employs numerical simulations to investigate the propensity of squat initiation in the vicinity of small, isolated rail surface irregularities. Time domain dynamic vehicle–track interaction analysis is used to obtain wheel–rail contact stress distributions, which are mapped onto a continuum finite element model that accounts for plastic deformation of the rail material. The evaluated stress and strain fields are quantified using two RCF impact measures: accumulated effective strain and the Jiang-Sehitoglu multiaxial low cycle fatigue parameter. It is shown that the RCF impact increases with increasing size of the surface irregularity and that clustering of irregularities might strongly promote RCF. The friction coefficient is identified as a very influential parameter. Further, the effect of variations in friction along the rail is evaluated. It is shown that a short rail section of low friction results in fairly high RCF impact.
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| 6. |
- Andersson, Robin, 1986, et al.
(författare)
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Integrated analysis of dynamic vehicle–track interaction and plasticity induced damage in the presence of squat defects
- 2016
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Ingår i: Wear. - : Elsevier BV. - 0043-1648. ; 366-367:SI, s. 139-145
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Tidskriftsartikel (refereegranskat)abstract
- Despite significant efforts, the mechanisms behind the formation of squats – a form of rolling contact fatigue (RCF) damage – are not fully understood. This study employs numerical simulations to investigate the propensity of squat initiation in the vicinity of small, isolated rail surface irregularities. Time-domain dynamic vehicle–track interaction analysis is used to obtain wheel–rail contact stress distributions, which are mapped onto a continuum finite element model that accounts for plastic deformation of the rail material. The evaluated stress and strain fields are quantified using two RCF impact measures: accumulated effective strain and the Jiang–Sehitoglu multiaxial low cycle fatigue parameter. It is shown that the RCF impact increases with increasing size of the surface irregularity and that clustering of irregularities might strongly promote RCF. The friction coefficient is identified as a very influential parameter and also the effect of variations in friction along the rail is evaluated.
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| 7. |
- Andersson, Robin, 1986, et al.
(författare)
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Numerical investigation of crack initiation in rails and wheels affected by martensite spots
- 2018
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Ingår i: International Journal of Fatigue. - : Elsevier BV. - 0142-1123. ; 114, s. 238-251
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Tidskriftsartikel (refereegranskat)abstract
- White etching layers (WELs) in the form of thermally induced martensite spots are often associated to so-called stud defects on rail surfaces and so-called rolling contact fatigue clusters on wheel treads. These defects might promote further material deterioration of rails and wheels and it is thus of importance to deepen the knowledge regarding their initiation mechanisms. The aim of this study is to gain insight into the problem by making qualitative assessments of different operational scenarios, involving various axle loads and amount of friction. To this end, this paper considers crack initiation, quantified through the Jiang–Sehitoglu low cycle fatigue criterion, in the vicinity of pre-existing WELs (in the form of martensite spots) subjected to varying contact load conditions. Three-dimensional finite element analyses are conducted to model phase transformations as well as the resulting residual stresses. It is seen that the contact pressure magnitude and WEL thickness affect the results only moderately, while the traction coefficient has a significant detrimental influence. It is furthermore seen that occasional wheel passages that are off-set in the lateral direction with respect to the WEL spot’s centre might be responsible for crack initiation on the gauge corner side of the rail surface.
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| 8. |
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| 9. |
- Andersson, Robin, 1986, et al.
(författare)
-
The influence of rail surface irregularities on contact forces and local stresses
- 2015
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Ingår i: Vehicle System Dynamics. - : Informa UK Limited. - 1744-5159 .- 0042-3114. ; 53:1, s. 68-87
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Tidskriftsartikel (refereegranskat)abstract
- The effect of initial rail surface irregularities on promoting further surface degradation is investi-gated. The study concerns rolling contact fatigue formation, in particular in the form of the so-calledsquats. The impact of surface irregularities in the form of dimples is quantified by peak magnitudesof dynamic contact stresses and contact forces. To this end simulations of two-dimensional (laterextended to three-dimensional) vertical dynamic vehicle–track interaction are employed. The mostinfluencing parameters are identified. It is shown that even very shallow dimples might have a largeimpact on local contact stresses. Peak magnitudes of contact forces and stresses due to the influenceof rail dimples are shown to exceed those due to rail corrugation.
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| 10. |
- Deuce, Roger, et al.
(författare)
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Mechanical deterioration of wheels and rails under winter conditions – mechanisms and consequences
- 2019
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Ingår i: Proceedings of the Institution of Mechanical Engineers, Part F: Journal of Rail and Rapid Transit. - : SAGE Publications. - 0954-4097 .- 2041-3017. ; 233:6, s. 640-648
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Tidskriftsartikel (refereegranskat)abstract
- This study focuses on identifying and understanding the core phenomena behind winter-related issues with regard to railways. State-of-the-art knowledge regarding the mechanical deterioration of wheels and rails is employed to obtain a first estimation of the influence of the different phenomena and to find out under which circumstances they are influential. The interaction between these different phenomena is discussed, as this additional level of complexity is necessary to develop a complete understanding.
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| 11. |
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| 12. |
- Ekberg, Anders, 1967, et al.
(författare)
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Allowable wheel loads, crack sizes and inspection intervals to prevent rail breaks
- 2015
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Ingår i: Proceedings of the 11th International Heavy Haul Association Conference (IHHA 2015).
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Konferensbidrag (refereegranskat)abstract
- Cost-efficient and reliable heavy haul operation requires a minimum of operational disturbances. To this end, the current study focuses on wheel load management with the aim to establish wheel load monitoring and mitigation actions (in terms of limits on allowable wheel defects) that minimize traffic disruptions.As a first step, the relation between wheel impact load magnitudes (resulting from the out-of-round wheels) and critical rail crack sizes that would result in rail breaks is established. Variations in parameters such as track stiffness, rail temperature, impact load characteristics and hanging sleepers etc. are investigated and a “bad case scenario” that implies severe, but realistic operational conditions is established. In this manner allowable wheel impact load magnitudes can be linked to pertinent critical crack sizes that must be identified during inspections. An interesting finding is that thermal stresses have such a major effect that a seasonal variation in allowable wheel load limit seems justified.Predicted critical crack sizes (presuming allowed wheel load magnitudes) are then contrasted to critical crack sizes at operational rail breaks. A large scatter in operational critical crack sizes is found and reasons for this fact are discussed. Finally operational aspects of implementing the suggested limit values are discussed.
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| 13. |
- Ekberg, Anders, 1967, et al.
(författare)
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Stress gradient effects in surface initiated rolling contact fatigue of rails and wheels
- 2016
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Ingår i: Wear. - : Elsevier BV. - 0043-1648. ; 366-367, s. 188-193
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Tidskriftsartikel (refereegranskat)abstract
- The paper investigates gradient effects, which relate to how highly stressed regions should be dealt with in fatigue design analyses. In particular stress gradients in rolling contact are investigated with a focus on differences in response between full and partial slip conditions. To this end the multiaxial state of stress beneath a wheel–rail contact featuring full or partial slip is quantified using a multiaxial equivalent stress criterion. A comparative study shows that the significant differences in peak interfacial shear stress magnitudes between full and partial slip conditions are significantly reduced when translated to equivalent stress magnitudes. An innovative procedure to quantify the gradient effects by comparing the multiaxial contact stress field to uniaxial conditions is developed and employed. For the studied cases stress gradients beneath the frictional contact were found to be similar to stress gradients outside a uniaxially loaded large plate featuring a small hole with a radius in the order of 0.5–0.7 mm. The study concludes that the use of local magnitudes of interfacial shear stress in the analysis of surface initiated rolling contact fatigue under partial slip conditions is conservative. The analysis framework established in the current study can be used to estimate the level of conservativeness.
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| 14. |
- Ekberg, Anders, 1967, et al.
(författare)
-
Stress gradient effects in surface initiated rolling contact fatigue of rails and wheels
- 2015
-
Ingår i: Proceedings of the 10th International Conference on Contact Mechanics and Wear of Rail/Wheel Systems (CM2015).
-
Konferensbidrag (refereegranskat)abstract
- The paper investigates gradient effects, which relates to how highly stressed regions should be dealt with in fatigue design analyses. In particular stress gradients in rolling contact are investigated with a focus on differences in response between full or partial slip conditions. To this end the multiaxial state of stress beneath a wheel–rail contact featuring full or partial slip is quantified using a mulitaxial equivalent stress criterion. A comparative study shows that the significant differences in peak interfacial shear stress magnitudes between full and partial slip conditions are significantly reduced when translated to equivalent stress magnitudes. In addition, stress gradients beneath a frictional contact are compared to stress gradients outside a uniaxially loaded small hole in a plate and was found to correspond to hole radii in the order of 0.5– 0.7 millimetres for the cases studied. The study concludes that the use of local magnitudes of interfacial shear stress in the analysis of surface initiated rolling contact fatigue is conservative. The analysis framework established in the current study can be used to estimate the level of conservativeness.
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| 15. |
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| 16. |
- Kabo, Elena, 1972, et al.
(författare)
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Rolling contact fatigue assessment of repair rail welds
- 2018
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Ingår i: Proceedings of the 11th International Conference on Contact Mechanics and Wear of Rail/wheel Systems (CM2018). - 2590-0609. - 9789461869630 ; , s. 450-456
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Konferensbidrag (refereegranskat)abstract
- A repair welding procedure is numerically simulated. To validate the numerical model, analyses of the temperature evolution are compared to full-scale test results. Further simulations are then carried out to evaluate the residual stress formation during welding and how the residual stress field is influenced by subsequent wheel passages. The influence of residual stresses from welding and the subsequent residual stress redistribution during operations on the risk of rolling contact fatigue (RCF) is discussed and analyzed. It is found that high tensile stresses are formed during welding, however these shake down substantially during subsequent operations. The influence on RCF is found to be moderate on the surface and somewhat more severe in a layer at the bottom of the repair weld. In addition to residual stresses, there is also a risk that welding introduces material defects and alters material properties. The influence of such phenomena on RCF are discussed.
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| 17. |
- Kabo, Elena, 1972, et al.
(författare)
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Rolling contact fatigue assessment of repair rail welds
- 2019
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Ingår i: Wear. - : Elsevier BV. - 0043-1648. ; 436-437
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Tidskriftsartikel (refereegranskat)abstract
- A repair welding procedure is numerically simulated. To validate the numerical model, analyses of the temperature evolution in a repaired rail are compared to existing full-scale test results. Thermomechanical simulations are carried out to evaluate the residual stress formation during welding and how the residual stress field is influenced by subsequent wheel passages during operations. The risk of rolling contact fatigue (RCF) is analysed and results discussed. It is found that tensile stress magnitudes resulting from welding decrease substantially during rolling contact loading. The influence of the residual stresses on RCF is found to be minor on the surface and somewhat more severe in a layer at the bottom of the repair weld. In addition to residual stresses, there is also a risk that welding introduces material defects and alters material properties. The influence of these factors on the risk of RCF is discussed.
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| 18. |
- Karttunen, Kalle, 1976, et al.
(författare)
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Estimation of gauge corner and flange root degradation from rail, wheel and track geometries
- 2016
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Ingår i: Wear. - : Elsevier BV. - 0043-1648. ; 366-367, s. 294-302
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Tidskriftsartikel (refereegranskat)abstract
- A methodology to predict gauge corner and flange root degradation in terms of rolling contact fatigue (RCF) and wear from measured rail, wheel and track geometries by so-called meta-models is presented. The methodology sets out from a parametrisation of the gauge corner and the flange root geometries. Then statistics of measured rail and wheel profiles are employed in a experimental design methodology to create scenarios, which are employed in multibody simulations from where degradation indices are evaluated. Finally, classification and regression analysis is used to derive decision boundaries and meta-models. These predict whether contact will occur at the gauge corner and (when this is the case) quantify RCF and wear impacts. The derived meta-models are used to rank measured profiles based on how detrimental they are. Robustness is assessed through comparisons between two vehicle types. The ability to rank measured profiles without the need for computationally expensive simulations (including the need for additional presumptions that such simulations require) makes the study valuable e.g. for maintenance planning.
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| 19. |
- Karttunen, Kalle, 1976, et al.
(författare)
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Gauge corner and flange root degradation estimation from rail, wheel and track geometry
- 2015
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Ingår i: Proceedings of the 10th International Conference on Contact Mechanics and Wear of Rail/Wheel Systems (CM2015). ; , s. 9-
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Konferensbidrag (refereegranskat)abstract
- A methodology to predict gauge corner and flange root degradation in terms of rolling contact fatigue (RCF) and wear from measured rail, wheel and track geometries by so-called meta-models is presented. The methodology sets out from a parameterisation of the gauge corner and the flange root profiles. Statistics of measured rail and wheel profiles are then used to create scenarios, which are employed in multibody dynamics simulations with degradation quantified by RCF and wear indices. Finally regression analysis is employed to derive meta-models to predict whether contact will occur at the gauge corner and (when this is the case) quantify RCF and wear impact. Derived meta-models are used to rank measured profiles based on how detrimental they are. Robustness is assessed through comparisons for two different vehicles. The ability to rank measured profiles without computationally expensive simulations (including needs for additional presumptions that such simulations require) makes the study valuable e.g. for maintenance planning.
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| 20. |
- Maglio, Michele, 1993, et al.
(författare)
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Digitalisation of condition monitoring data as input for fatigue evaluation of wheelsets
- 2019
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Ingår i: Proceedings of the XIX International Wheelset Congress.
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Konferensbidrag (refereegranskat)abstract
- A field test in which a train was run at different speeds over an impact load detector is described. One of the wheelsets in the train had severe wheel tread damage. The results are presented and the relation between the speed of the train and the magnitude of the impact loads registered for the two wheels is discussed. The defects on the wheel tread have been studied and scanned by means of 3D laser and their characteristics are described. An in-house software for the simulation of dynamic wheel–rail interaction has been improved by including the possibility to account for the cross-coupling of the two wheels within the same wheelset. The contact algorithm and a possible implementation of discrete defects in the in-house software are discussed. The in-house software gives, among other possible outputs, the maximum dynamic loads occurring at both wheels of the wheelset. To show an example of the utility of such information, fatigue analyses for the axle are performed for the different running conditions used during the field tests. The impact loads measured on the day of the tests are given as input to the fatigue analyses.
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| 21. |
- Maglio, Michele, 1993, et al.
(författare)
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Thermo-mechanical analyses of discrete defect repair process for rails
- 2018
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Discrete defects in a rail head may form due to aggressive wheel–rail contact in terms of thermal and/or mechanical loads, or due to indentations from foreign objects trapped in the contact. If large, such defects need to be repaired or the rail section removed. These are costly operations that cause operational disturbances. Discrete defect repair (DDR) procedures that include repair welding provide a cost-efficient alternative to rail replacements. Investigations of such repair methods have been conducted in the frame of the European project In2Rail and reported in Deliverable report D3.1, see Kallander (2017). The present work has been focused on investigating a novel DDR procedure through numerical simulations. The new technique employs significantly lower preheat temperature (80 °C in contrast to widely used 350 °C) and equipment that can be carried to the working place. However, the low preheating temperature introduces high temperature differences between the molten filler material and the surrounding rail steel. This may lead to the formation of defects and has to be assessed. The quality of the weld is highly influenced by the thermal field induced by the repair welding process. This topic was investigated in detail by thermal analyses in Maglio (2017). The study showed the possibility of numerical simulations and investigated in detail requirements and sensitivities of numerical models. In particular, it quantified the sensitivity related to both simulation parameters and to experimental measurements. The thermal analysis has been extended to a thermomechanical analysis that is able to investigate the residual state of stress after repair welding. Such analyses can be used to compare repair welding methods and also investigate the sensitivity to different operational parameters.
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| 22. |
- Paulsson, Björn, 1946-, et al.
(författare)
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Upgrading of infrastructure in order to meet new operation and market demands
- 2017
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Rapport (refereegranskat)abstract
- The European objective of a modal shift of freight transports to railways will require extensive upgrading of existing railway lines since very few dedicated freight railways are currently being built and existing lines were built for traffic demands at the time of construction. A transition to increased and enhanced railway freight operations can therefore be costly and complicated. To minimize negative effects, a guideline for upgrading was developed within the Capacity4Rail project. This handbook presents the major findings. In particular it outlines different upgrading possibilities and their implications, and details structured approaches to upgrading analyses. It discusses possibilities for upgrading of substructures, bridges, tunnels, and the track structure. In these areas, an overview of challenges and possibilities is presented together with examples of experience from operational upgrading. It concludes that freight line upgrading using a more streamlined approach as outlined in the guideline is a necessity if EU objectives on modal shifts in transportation are to be met. Further, it demonstrates why a political drive is necessary to increase efforts to upgrade freight lines.
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