| 1. |
- Ahlström, Johan, 1969, et al.
(författare)
-
Temperature-dependent evolution of the cyclic yield stress of railway wheel steels
- 2016
-
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)
-
Temperature-dependent evolution of the cyclic yield stress of railway wheel steels
- 2015
-
Ingår i: Proceedings of the 10th International Conference on Contact Mechanics and Wear of Rail/Wheel Systems (CM2015).
-
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)
-
An efficient approach to the analysis of rail surface irregularities accounting for dynamic train–track interaction and inelastic deformations
- 2015
-
Ingår i: Vehicle System Dynamics. - : Informa UK Limited. - 1744-5159 .- 0042-3114. ; 53:11, s. 1667-1685
-
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)
-
Evaluation of stress intensity factors under multiaxial and compressive conditions using low order displacement or stress field fitting
- 2018
-
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)
-
Integrated analysis of dynamic vehicle-track interaction and plasticity induced damage in the presence of squat defects
- 2015
-
Ingår i: Proceedings of the 10th International International Conference on Contact Mechanics and Wear of Rail/Wheel Systems, Colorado Springs, USA, August-September 2015.
-
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)
-
Integrated analysis of dynamic vehicle–track interaction and plasticity induced damage in the presence of squat defects
- 2016
-
Ingår i: Wear. - : Elsevier BV. - 0043-1648. ; 366-367:SI, s. 139-145
-
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)
-
Numerical assessment of the loading of rolling contact fatigue cracks close to rail surface irregularities
- 2020
-
Ingår i: Fatigue and Fracture of Engineering Materials and Structures. - : Wiley. - 8756-758X .- 1460-2695. ; 43:5, s. 947-954
-
Tidskriftsartikel (refereegranskat)abstract
- Rolling contact fatigue damage of railway rails in the form of squats, characterised by local depressions and cracks located at the rail surface, has been linked to the occurrence of local rail surface irregularities. This study concerns rolling contact fatigue cracks in the vicinity of fairly smooth surface irregularities, here denoted dimples. The influence of factors such as dimple geometry, cluster effects, and crack size is evaluated. To this end, dynamic vehicle–track simulations featuring realistic wheel and rail profiles are employed to characterise the dynamic impact during a wheel passage. The contact load in the vicinity of the dimples is then mapped onto a 3D finite element model of a rail section containing a crack in the rail head. The crack loading is finally quantified by multimodal stress intensity factors. The analyses establish that also shallow dimples might have a significant impact on the crack loading. This effect is increased for larger or multiple irregularities but decreases as the crack grows.
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| 8. |
- Andersson, Robin, 1986, et al.
(författare)
-
Numerical investigation of crack initiation in rails and wheels affected by martensite spots
- 2018
-
Ingår i: International Journal of Fatigue. - : Elsevier BV. - 0142-1123. ; 114, s. 238-251
-
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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| 9. |
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| 10. |
- Andersson, Robin, 1986, et al.
(författare)
-
The influence of rail surface irregularities on contact forces and local stresses
- 2015
-
Ingår i: Vehicle System Dynamics. - : Informa UK Limited. - 1744-5159 .- 0042-3114. ; 53:1, s. 68-87
-
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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| 11. |
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| 12. |
- Caprioli, Sara, 1978, et al.
(författare)
-
THERMO-MECHANICAL CRACKING OF RAILWAY WHEEL
- 2011
-
Ingår i: Proceedings for Svenska mekanikdagar 2011. ; , s. 1-
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Thermo-mechanical wheel tread damages are common in railway wheels. While the damagemagnitude is limited this is a rather benign phenomenon. However under harsher operationalconditions (winter conditions, poorly tuned damping/suspension, poorly matched wheel–railcontact profiles etc) the extent of the problem may increase dramatically and lead to epidemicsof wheel damages. Since this calls for wheel re-profiling, the result may be extensiveoperational disturbances.The presentation deals with thermo-mechanical damage. In practice one of the failuremodes, thermal cracking or rolling contact fatigue, usually dominates. However, it is mostlikely that the combined thermal and rolling contact loading will have an influence in increasingthe resulting damage as compared to both phenomena acting separately.In the literature there are a multitude of studies on both thermal and rolling contactloading. analyses of the combined load case are however scarce. One major reason for this isthat a combined loading makes a simplification to 2D very cumbersome (not to say futile).Here, a numerical study of the impact of simultaneous thermal and mechanical loading on arailway wheel tread as imposed by braking and rolling contact is presented. 3D finite element(FE) simulations of the thermo-mechanical problem featuring a material model which accountsfor thermal expansion and plastic deformations are carried out. Both pure rolling and tractiverolling are considered. The results indicate a significant influence of the thermal loading onthe resulting stress/strain response also in cases of relatively moderate temperature increases.In particular, a combination of thermal loading and high traction rolling is found to be verydetrimental.The resulting damage of the wheel tread is manifested by the formation of small surfacecracks. In cases of high thermal loading, these cracks will evolve to deep radial cracks thatcan, in a worst-case scenario, cause catastrophic wheel failures. Since this is a potential safetyproblem it is important to understand the driving mechanisms behind these cracks.To this end, a numerical study of thermal cracking of a wheel subjected to high thermalloading was carried out. The analysis features a computationally efficient approach where2D FE stress analysis owing to thermal loading during braking and subsequent cooling iscombined with an analytical evaluation of resulting stress intensity factors of a radially orientedsurface crack in the wheel tread. The analysis identifies critical sizes for when existingsurface cracks are prone to propagate under thermal loading and resulting crack lengths afterpropagation. The results imply that fully functional brake systems are not likely to inducethermal crack propagation under normal stop braking, but that with pre-existing defects asevere drag braking due to malfunctioning brakes may cause very deep cracking. Further theanalysis concludes the thermal cracking to be a (more or less) static phenomenon related tothe most severe brake cycle. In other words: later brake cycles of similar or lower severitywill not cause any significant propagation of existing cracks. To further validate the analysisof the semi-analytical analysis, preliminary 3D FE-simulations have been performed.
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| 13. |
- Deuce, Roger, et al.
(författare)
-
Mechanical deterioration of wheels and rails under winter conditions – mechanisms and consequences
- 2019
-
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
-
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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| 14. |
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| 15. |
- Ekberg, Anders, 1967, et al.
(författare)
-
Alarm limits for wheel–rail impact loads – part 2: analysis of crack growth and fracture
- 2009
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- The crack growth and subsequent fracture of rails is governed by the imposed rolling contact load from operational vehicles. This study focuses on the growth of longer cracks. In contrast to shorter cracks that are mainly driven by the influence of the contact stress field in combination with the effect of trapped liquid, these cracks are mainly driven by the global bending of the rail. In addition there is, for all-welded rails, a major influence of the rail temperature.The aim of the study is to find a scientific basis for regulations regarding allowed wheel de- fects. These defects generate wheel–rail impact loads that in severe cases may promote fracture from pre-existing cracks in the rail. Present wheel removal criteria relate wheel defect alarm limits to the size (length) of a wheel flat. This is not an optimal situation since it may be both difficult and dangerous to locate and measure the length of a wheel flat. Further, a given size of a wheel flat will result in different impact loads if present on different types of vehicles due to differences in train speed, axle load, etc, and on different tracks with differences in track proper- ties. In this study, the focus is instead on the wheel–rail impact load magnitude and its influence on the risk of rail breaks.
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| 16. |
- Ekberg, Anders, 1967, et al.
(författare)
-
Allowable wheel loads, crack sizes and inspection intervals to prevent rail breaks
- 2015
-
Ingår i: Proceedings of the 11th International Heavy Haul Association Conference (IHHA 2015).
-
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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| 17. |
- Ekberg, Anders, 1967, et al.
(författare)
-
An engineering model for rolling contact fatigue
- 2002
-
Ingår i: Fatigue and Fracture of Engineering Materials and Structures. - 8756-758X .- 1460-2695. ; 25, s. 899-909
-
Tidskriftsartikel (refereegranskat)
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| 18. |
|
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| 19. |
- Ekberg, Anders, 1967, et al.
(författare)
-
Asset management – A brief introduction with focus on the ISO 55000 standard and mechanical deterioration of railway related assets
- 2021
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- The brief introduction focuses on railway related physical assets subjected to significant mechanical deterioration – that is wear and tear. This typically relates to track and railway vehicles that need to be regularly maintained. It discusses management of such assets in the light of the ISO 55000 series of standards. It sets out with an introduction to the ISO 55000 series. This overview is narrowed down to show how knowledge and predictive abilities regarding mechanical deterioration fits into asset management. It is followed by an overview of different modes of mechanical deterioration and failures, and how these can be assessed in risk analyses. A standardised and mandated way of performing risk analyses is the common safety method for risk analyses, which is described in chapter sec:Common-safety-method. The overview is then concluded with some brief comments on railway applications.
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| 20. |
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| 21. |
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| 22. |
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| 23. |
- Ekberg, Anders, 1967, et al.
(författare)
-
Identifying the root causes of damage on the wheels of heavy haul locomotives and its mitigation
- 2014
-
Ingår i: Proceedings of the Institution of Mechanical Engineers, Part F: Journal of Rail and Rapid Transit. - : SAGE Publications. - 0954-4097 .- 2041-3017. ; 228:6, s. 663-672
-
Tidskriftsartikel (refereegranskat)abstract
- The paper illustrates how damage patterns in the form of rolling contact fatigue (RCF) on wheels, can be employed to identify and improve underlying operational conditions. The focus is on RCF of locomotive wheels operating on the Iron Ore Line in northern Sweden and Norway. Seasonal changes and damage patterns are charted. Potential root causes for observed damage patterns are identified and investigated. Mitigating actions are proposed and the efficiency of implemented actions is quantified.
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| 24. |
- Ekberg, Anders, 1967, et al.
(författare)
-
Identifying the root causes of damage on the wheels of heavy haul wheel damage phenomena
- 2013
-
Ingår i: Proceedings of the 10th International Heavy Haul Conference (IHHA 2013), February 4–6, New Dehli, India. ; , s. 520-526
-
Konferensbidrag (refereegranskat)abstract
- The paper illustrates how damage patterns, in particular in the form of rolling contact fatigue (RCF), can be employed to identify underlying operational conditions. In particular the focus is on RCF of wheel occurring at the Iron Ore line in north Sweden and Norway. The paper charts seasonal changes and damage patterns, and potential root causes are identified and investigated. Finally mitigating actions are proposed.
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| 25. |
- Ekberg, Anders, 1967, et al.
(författare)
-
INNOTRACK Deliverable 4.2.1 -- Simplified relation for the influence of rail/joint degradation on operational loads and subsequent deterioration
- 2007
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- In this tentative report we present a summary of the work carried out during approximately the first nine months of the INNOTRACK project regarding the influence of rail/joint degradation on operational loads and subsequent deterioration. The focus is here on the vertical train–track interaction and related deterioration.The work within this field can be divided in two categories. The first concerns the collection of input and validation data. In this category the current deliverable includes measurements of in-field axle loads, in-field monitoring of squats and compilation of material data.The second category is the actual numerical simulation and resulting quantifications of increased operational loads and deteriorations. Here the deliverable includes a state-of-the-art study of the effect of material characteristics on material deterioration and the practical implications. Further, the deliverable contains reports of parametric studies of the influence of rail corrugation, the growth of larger rail cracks, the influence of the design of insulated joints and the influence of rail squats.
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| 26. |
- Ekberg, Anders, 1967, et al.
(författare)
-
Integrating rolling contact fatigue analysis with simulation of dynamic train–track interaction
- 2003
-
Ingår i: Proceedings of the 3rd International Conference ‘XXI Century Rolling Stock (ideas, requirements, projects)’, St Petersburg, Russia, July 3–5, 2003. ; , s. 11 pp-
-
Konferensbidrag (refereegranskat)
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| 27. |
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| 28. |
- Ekberg, Anders, 1967, et al.
(författare)
-
PRESOL – pre-processor för solkurveanalys
- 2007
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Presol är ett skript som genererar indata-filer för finita element-analys av inverkan av termisk last på spårstrukturer och prediktering av uppkomst av solkurvor med hjälp av Abaqus. Målsättningen med skriptet är att det skall underlätta genereringen så mycket som möjligt samtidigt som det är flexibelt.Denna manual beskriver den del av skriptet som användaren behöver modifiera. Dokumentation av de funktioner som utför själva genereringen av indata-filen sker med hjälp av kommentarer i dessa.Manualen är upplagd så att den del av skript-koden som en användare kommer i kontakt med gås igenom och kommenteras.
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| 29. |
- Ekberg, Anders, 1967, et al.
(författare)
-
RAIL AND WHEEL HEALTH MANAGEMENT
- 2022
-
Ingår i: CM 2022 - 12th International Conference on Contact Mechanics and Wear of Rail/Wheel Systems, Conference Proceedings. ; , s. 179-188
-
Konferensbidrag (refereegranskat)abstract
- Rail and wheel health management is investigated with focus on deterioration phenomena in the wheel/rail contact interface – plastic deformation, wear, and rolling contact fatigue (RCF). How operational conditions affect deterioration, and how they can be included in track health predictions is discussed together with a more in-depth description of deterioration mechanisms. Here means of measuring, quantifying, and predicting deterioration is in focus. This provides the basis for the outline of a rail and wheel health management framework. As discussed in the paper, the proposed framework is well in line with the requirements in the ISO 55000 standard for asset management.
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| 30. |
- Ekberg, Anders, 1967, et al.
(författare)
-
Rail and wheel health management
- 2023
-
Ingår i: Wear. - 0043-1648. ; 526-527
-
Tidskriftsartikel (refereegranskat)abstract
- Rail and wheel health management is investigated with focus on deterioration phenomena in the wheel/rail contact interface – plastic deformation, wear, and rolling contact fatigue (RCF). How operational conditions affect deterioration, and how they can be included in wheel/rail health predictions is linked to a more in-depth description of deterioration mechanisms. Here means of measuring, quantifying, and predicting deterioration is in focus. This discussion provides the basis for the outline of a rail and wheel health management framework. As discussed in the paper, the proposed framework is well in line with the requirements in the ISO 55000 standard for asset management.
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| 31. |
- Ekberg, Anders, 1967, et al.
(författare)
-
Realtidsanalys av utmattningspåkänning från uppmätta spårkrafter
- 2007
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Abstract Denna rapport sammanfattar arbetet med utmattningsprediktering inom CHARMEC-projektet SP11 -- Vertikala krafter på höghastighetståg. Detaljerade redovisningar på engelska ges i de två rapporterna [1, 2]. Kortfattat är de viktigaste resultaten av denna projektdel att ett kriterium som kan användas för att kvantifiera rullkontaktutmattningspåkänningen vid fältmätningar av hjul--räl-krafter har utvecklats. Dessutom har inverkan av enstaka höga kontaktkrafter analyserats. Varningsnivåer för kontaktkrafter med avseende på olika former av utmattning har getts.
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| 32. |
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| 33. |
- Ekberg, Anders, 1967, et al.
(författare)
-
Risk of fatigue of train car chassis due to pressure waves between meeting trains
- 2020
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- The report investigates consequences of modified track spacing on pressure waves induced by meeting high-speed trains. The aim is to investigate consequences in terms of an increased risk of fatigue of car body components and which potential counter-effects may have. The study is intended as a first investigation that should be valid under fairly generic conditions. Simplified analyses are employed due to the generic conditions considered. Under more specified conditions, refined analyses can be employed to improve the analysis and improve quantification of the various mitigating actions.
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| 34. |
- Ekberg, Anders, 1967, et al.
(författare)
-
Stress gradient effects in surface initiated rolling contact fatigue of rails and wheels
- 2016
-
Ingår i: Wear. - : Elsevier BV. - 0043-1648. ; 366-367, s. 188-193
-
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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| 35. |
- 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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| 36. |
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| 37. |
- Ekberg, Anders, 1967, et al.
(författare)
-
Surface fatigue initiated transverse defects and broken rails -- an International Review
- 2014
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- The current report briefly compares some operational experience of cracked and broken rails from China, Russia, South Africa, Sweden, UK and USA. Four key questions are addressed:1. Is the critical crack length, i.e. the length of a surface initiated crack that causes a rail break (reasonably) constant in an international perspective?2. Is it (reasonably) constant over a line?3. Can the depth when a rolling contact fatigue crack deviates to a transverse propagation be estimated?4. Is it (reasonably) constant in an international perspective?The answers can briefly be summarized as1. No. Deviations in crack sizes from roughly 10% up to roughly 80% of the railhead area at fracture have been found.2. Not generally, but for some lines this seems to be the case if fractures at the same season are considered (i.e. climate effects are excluded).3. There are indications that this depth is in the order of 5 mm with a fair amount of scatter. However it is very difficult to identify from a photo whether an area of the fracture surface actually corresponds to inclined fatigue crack propagation.4. With a reservation in the considerable scatter, there seems to be some consistency also in an international perspective.Details on how these conclusions were reached are given in the report.
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| 38. |
- Ekberg, Anders, 1967, et al.
(författare)
-
The influence of vertical load transients on wheel and rail deterioration
- 2007
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- The influence of high magnitude transient loads on deterioration of wheels and rails is studied. Initially the frequency of occurence of transient loads needed to influence rolling contact fatigue crack growth in wheels is established. The focus is then turned to the influence of fatigue crack initiation and growth in rails. Alert limits are proposed and discussed along with the need for further studies.
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| 39. |
- Ekberg, Anders, 1967, et al.
(författare)
-
Wheel/rail rolling contact fatigue - probe, predict, prevent
- 2012
-
Ingår i: Proceedings of the 9th International Conference on Contact Mechanics and Wear of Rail/Wheel Systems (CM2012). ; , s. 29-41
-
Konferensbidrag (refereegranskat)abstract
- With the aim of putting prediction and prevention of rolling contact fatigue of wheels and rails in context, the paper sets out with a description of the phenomena. This is followed by a discussion on predictive models with emphasis on influencing factors needed to be accounted for and how these can be incorporated in a predictive model. This forms the basis for a discussion on preventive measures. Finally a brief outlook of expected future trends is given.
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| 40. |
- Ekberg, Anders, 1967, et al.
(författare)
-
Wheel/rail rolling contact fatigue – Probe, predict, prevent
- 2014
-
Ingår i: Wear. - : Elsevier BV. - 0043-1648. ; 314:1-2, s. 2-12
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Tidskriftsartikel (refereegranskat)abstract
- With the aim of putting prediction and prevention of rolling contact fatigue of wheels and rails in context, the paper sets out with a description of the phenomena. This is followed by a discussion on predictive models with emphasis on influencing factors needed to be accounted for and how these can be incorporated in a predictive model of surface and subsurface initiated rolling contact fatigue (RCF). The focus is on predictive models fast enough to be integrated with multibody dynamic simulations of train–track interaction. In particular an attempt is made to highlight how current predictive models of surface initiated RCF can be extended to incorporate all affecting phenomena. The discussion on influencing factors then forms the basis for a discussion on suitable and efficient measures to maintain RCF under control. Finally the paper provides a brief summary on similarities and differences between wheel and rail damage, and an outlook of expected future trends in terms of expected damage patterns and possibilities to meet these.
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| 41. |
- Franklin, Francis, et al.
(författare)
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INNOTRACK Deliverable 4.2.5 -- Improved model for the influence of vehicle conditions (wheel flats, speed, axle load) on the loading and subsequent deterioration of rails
- 2009
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- The aim of this deliverable is an improved model for the influence of vehicle conditions on the loading and subsequent deterioration of rails. In particular, this report focuses on:1.Wear data from SUROS twin-disc tests with CORUS 260 and premium grade pearlitic rail steels (CORUS 400, VA 350 and VA 400), and metallurgical analysis (micro-hardness and shear strain measurement) of section disc samples.2.The effect of wheel hardness on rail wear rate, and vice versa: findings from the academic literature, and observations from InnoTrack SP4 SUROS twin-disc tests.3. Development, calibration and validation of Newcastle University’s wear and crack initiation model (dynarat, a.k.a. the ‘brick’ model):a. development of material models for each of the tested rail steels; b. calibration of the wear model against the results of the CORUS 260 dry tests; and c. validation of the wear model against the results for the premium grade steels.4.Wear modelling (using the calibrated wear model) of wheel-rail contact on top of the rail head, focussing on the effects of load and traction; develop a method for quickly estimating wear.5.The effect of out-of-round (OOR) wheels on wear and crack initiation.Wear-Hardness CorrelationFour pearlitic rail steels were tested against VAS R7 wheel steel. Three twin-disc tests were performed for each rail steel: 5000 cycles dry; 5000 cycles dry followed by 5000 cycles wet (i.e., water-lubricated); and 15000 cycles dry.In general, the harder the rail disc material becomes at the surface, the harder the wheel disc material becomes at the surface. Rail disc wear decreases when rail steel hardness increases. In wet tests, wheel disc wear rate drops as rail disc hardness increases. In the system as a whole (i.e., considering both wheel and rail discs), using harder CORUS 400 and VA 400 rail steels lowers the total wear rate.From a review of the academic literature, there is no conclusive finding that harder rails wear wheels more, or vice versa. In general, harder materials wear less, but material hardness is not the only determining factor of wear performance; microstructure and strain-hardening behaviour are critical factors, and rolling contact fatigue performance is equally important. However, as a fairly general rule:→To reduce system wear, harder steel grades should be used for both wheel and rail.Wear Model Development, Calibration and ValidationThe mixed (dry-wet) SUROS tests caused severe rolling contact fatigue, affecting hardness readings and wear rates, but the dry tests have provided an excellent resource for wear model development and calibration.Test specimens have been sectioned and analysed. Microhardness measurements have suggested a possible softening effect at very small strains, and a new strain-hardening equation is used to fit to the strain-hardness data for each of the four steels. Wear model calibration has led to a number of core developments to the model itself.The wear rate predictions for the premium grade rail steels match measured values (approximately) for the 5000 cycles dry tests, but over-predict the wear rate for the 15000 cycles dry tests by a factor of 2-3. (The dry-wet test predictions do not match, but are not expected to, since the ratcheting wear model does not account for major surface deterioration caused by significant surface cracking.)→ Following major development, the wear model has been calibrated successfully for CORUS 260 rail steel under dry contact conditions.→The wear model has been partly validated for the premium grades. Additional test work and metallurgical analysis should lead to improved material hardening models.Effect of Vehicle Characteristics: Rail Wear PredictionsThe wear model, calibrated for CORUS 260 and dry contact, was used to study the effect on rail wear of vehicle characteristics through their effect on the wheel-rail contact. The patch was assumed to be elliptical and the pressure distribution to be Hertzian; in addition, the contact was assumed to be on the top the rail, suitable for straight track, not curves, and the traction to be longitudinal only.Traction coefficient has a significant effect on the wear rate. For distributed traction systems the traction coefficient may often be about 0.1, i.e., an average wear rate of about 0.75nm/cycle. For locomotives the traction coefficient may be 0.3 or even higher, i.e., an average wear rate of 1.5nm/cycle or more.→There was a very clear linear trend of wear rate against peak contact pressure (for the range of pressures studied).→ Wear equations, giving wear rate for a given pressure and traction coefficient, have been extrapolated which can be used for quick estimation of rail wear.Out-of-Round WheelsThe effect of pressure variation (with wavelengths above about 20mm) on rail wear rate was studied by considering each wheel pass as an independent event. Wear simulations were thus performed by varying the normal load with each passing wheel, and the predictions compared with the constant average-load case. No significant difference was observed.→Out-of-round pressure variations do not affect rail wear significantly.The effect of periodic variation of wheel-rail contact patch pressure on propagation of semi-circular cracks up to 12mm radius (i.e., penetrating to a depth of about 6mm at 30°angle to the surface) was studied using the ‘2.5D’ Green’s-function-based model. The following conclusions were reached:→ For pressure variations with a wavelength less than about 2mm, the maximum pressure should be used to calculate crack growth rate.→For pressure variations with a wavelength greater than about 20mm, there is no advantage to modelling pressure variation within a single load pass, and that modelling successive wheel passes with different static pressures would be sufficient.→ Out-of-round wheels with roughness features between these two wavelengths would accelerate crack propagation, but would require more detailed modelling.Rail crack growth and rail breaksFor an analysis of long crack growth and rail breaks numerical simulations validated and calibrated towards full-scale field tests featuring flatted wheels have been employed. The main conclusions from the simulations were the detrimental influence of rail temperature and low ballast stiffness (where hanging sleeper(s) is an extreme case.The influences of the most important parameters have been quantified. The results are presented in Annexes 4, 5 and 6 and summarized in Section 6.2. The main conclusions and operational recommendations are:→Critical crack sizes (i.e., crack sizes for which fracture is likely) for rail head and foot cracks depend significantly on the temperature (or rather the temperature below the stress free temperature). For cold conditions, critical crack sizes of roughly 1 and 3 cm are found for rail foot and rail head cracks respectively.→ Crack growth rates are significantly increased close to fracture. Consequently, operationally allowed crack sizes need to be much smaller. Exactly how much smaller depends on the accuracy of inspections (i.e., how small cracks can with certainty be detected) and inspection intervals. To guide in this decision, crack growths evaluated for different operational conditions and presented in Annex 6 can be employed.→A decrease in the assured largest crack size after an inspection (i.e., the size of a crack that with full certainty can be found at an inspection) will have a major influence on the needed length of the inspection intervals.→Low ballast stiffness will normally lead to higher rail bending moments. To avoid this influence the ballast stiffness per half sleeper should be kept above some 30 MN/m. Hanging sleepers will remove the beneficial effect of high ballast stiffness and should be avoided. In particular this seems to be the case for high-speed operations (200 km/h in the current study).→It is recommended to combine the mitigation of a hanging sleeper with an inspection for rail head and rail foot cracks.→The temperature will have a very significant effect on both crack growth rates and risk of final fracture. To this end it is recommended that the magnitude of allowed wheel–rail impact forces be related to the temperature. Further, inspection intervals need to be significantly reduced during cold periods. Guidance in defining alarm limits and inspection intervals can be obtained from the results presented in Annex 6.→Due to the significant increase in crack growth rates in cold climate, it is recommended that there is an inspection before a cold period to minimize the occurrence of larger cracks that may propagate to fracture.→The wheel–rail impact force will have an effect on the risk of fracture. To establish alarm limits is a balance between allowed forces and allowed crack sizes. Due to this, a higher alarm limit can be allowed if shorter crack sizes are assured (e.g., by more frequent inspections).→It is wise to introduce multiple alarm levels for several reasons:o A wheel that induces a high impact load is likely to cause damage on the vehicle (in the wheel, in the roller bearing, etc.). This may lead to increased costs and operational disturbances.o Also, wheels that induce impact loads below an alarm limit corresponding to rail breaks may cause smaller, arrested cracks to start growing. In particular, this is likely to be an issue for rail head cracks where a higher load may cause a crack to deviate transversally, which eventually may lead to a rail break.o The introduction of low-level alarms is likely to give the maintenance organisation improved possibilities of planning and optimising maintenance procedures. If only a one-level alarm exists there is an obvious risk that a vehicle that just passes the limit may fail in a subsequent control where operational conditions are slightly different. This will, obviously, result in unnecessary costs and operational disturbances.o For the same reason a
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| 42. |
- Fröhling, Robert, et al.
(författare)
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Developing hollow wear limits based on field experience and numerical simulations
- 2006
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Ingår i: Proceedings 7th International Conference on Contact Mechanics and Wear of Rail/Wheel Systems. ; , s. 9 pp-
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Konferensbidrag (refereegranskat)abstract
- The current paper deals with the influence of hollow wheels on the risk for surface initiated rolling contact fatigue. To this end, the problem is introduced and field experiences are outlined. The problem is then analyzed more in detail through numerical simulations of bogie curving. Quasi-static simulations featuring several hollowed profiles are carried out to give a first rough estimation of the severity. Simulations of the dynamic curving behaviour are carried out for a selected case to provide a more detailed image of the detrimental nature of wear hollowing. These are complimented by a FE-simulation for a detailed study of the contact configuration. Finally, the results are discussed and conclusions are drawn. In particular it is shown how high rolling contact fatigue impact is associated with high lateral forces and a narrow contact patch. It is also seen to be likely that quasi-static simulations underestimate fatigue impact and that the current practice of characterizing hollow wear by the wear depth is flawed.
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| 43. |
- Fröhling, Robert, et al.
(författare)
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The detrimental effects of hollow wear – field experiences and numerical simulations
- 2008
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Ingår i: Wear. - : Elsevier BV. - 0043-1648. ; 265:9-10, s. 1283-1291
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Tidskriftsartikel (refereegranskat)abstract
- The current paper deals with the influence of hollow wheels on the risk for surface initiated rolling contact fatigue. To this end, the problem is introduced and field experiences are outlined. The problem is then analyzed more in detail through numerical simulations of bogie curving. Quasi-static simulations featuring several hollowed profiles are carried out to give a first rough estimation of the severity. Simulations of the dynamic curving behaviour are carried out for a selected case to provide a more detailed image of the detrimental nature of wear hollowing. These are complemented by a FE-simulation for a detailed study of the contact configuration. Finally, the results are discussed and conclusions are drawn. In particular it is shown how high rolling contact fatigue impact is associated with high lateral forces and a narrow contact patch. It is also seen to be likely that quasi-static simulations underestimate fatigue impact and that the current practice of characterizing hollow wear by the wear depth is flawed.
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| 44. |
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| 45. |
- Johnson, Erland, 1962, et al.
(författare)
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Lateral spårstabilitet -- slutrapport
- 2007
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Det gemensamma CHARMEC/SP-projektet Lateral spårstabilitet startade 2003 och avslutades under våren 2007. Det övergripande målet för projektet var att motverka uppkomsten av solkurvor. Detta skulle åstadkommas genom att öka möjligheten att besvara de två fundamentala frågorna när det gäller uppkomsten av solkurvor: Vilken kompressiv axialkraft verkar i rälen och vilket sidomotstånd har spåret? Detta övergripande mål bröts ned i tre delprojekt: · Utveckling av bättre metoder för mätning av spänningsfri temperatur · Numerisk simulering av ballastens sidomotstånd · Utveckling av en numerisk modell för prediktering av uppkomst av solkur- vor. Detta är en kortfattad sammanställning av vad som utförts och vilka resul- tat som uppnåtts. Detaljerad information finns i de hänvisade rapporterna.
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| 46. |
- Kabo, Elena, 1972
(författare)
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A numerical study of the lateral ballast resistance in railway tracks
- 2006
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Ingår i: Proceedings of the Institution of Mechanical Engineers, Part F: Journal of Rail and Rapid Transit. - 0954-4097 .- 2041-3017. ; 220:4, s. 425-433
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Tidskriftsartikel (refereegranskat)abstract
- Three-dimensional elastoplastic finite-element (FE) simulations of ballast deformation in a track with focus on lateral resistance have been conducted. Ballast geometry, vertical and lateral loading, and friction between ballast and sleeper are being varied in a parametric study. Sleeper displacements are studied under different conditions in order to find out which lateral resistance the ballast will provide and how this resistance depends on the various parameters. In addition to extending the state of the art, the knowledge gained in the study will be essential in the design of a structural element to represent the ballast in a model of the full track that is to be used for analysing lateral track stability.
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| 47. |
- Kabo, Elena, 1972, et al.
(författare)
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A simplified index for evaluating subsurface initiated rolling contact fatigue from field measurements
- 2011
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Ingår i: Wear. - : Elsevier BV. - 0043-1648 .- 1873-2577. ; 271:1-2, s. 120-124
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Tidskriftsartikel (refereegranskat)abstract
- A previous simplification of the Dang Van equivalent stress measure for assessment of subsurface initiated rolling contact fatigue (RCF) related to wheel-rail contact is modified. The new criterion is intended for real-time assessment of subsurface RCF from measured wheel-rail contact forces. The only needed parameters in the new expression for the equivalent stress are the vertical force and the wheel and rail radii. Comparisons between the new and the original criterion are carried out and show good agreement for the studied cases of tangent track operations. By employing principles of vehicle dynamics the criterion is further extended to the case of operations in curves. Reasonable consistency was found for curve radii down to approximately 2000 m.
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| 48. |
- Kabo, Elena, 1972, et al.
(författare)
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Analysis of static fractures of rails due to wheel flats
- 2009
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- The analysis focuses on larger cracks in rails that have deviated to a transverse propagation. In the railhead this corresponds to crack sizes larger than about a centimetre. For rail foot cracks, the restriction is that linear elastic fracture mechanics should be valid in the study of crack growth. This corresponds to crack sizes larger than some millimetres. For the cracks studied it is presumed that rail bending drives crack growth.
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| 49. |
- Kabo, Elena, 1972, et al.
(författare)
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Assessing risks of subsurface initiated rolling contact fatigue from field measurements
- 2009
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Ingår i: Proceedings of the 8th International Conference on Contact Mechanics and Wear of Rail/Wheel Systems. ; 1, s. 355-361
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Konferensbidrag (refereegranskat)abstract
- A previous simplification of the Dang Van equivalent stress measure for cases of wheel–rail contact is modified. The new criterion is suited for real-time rolling contact fatigue assessment of measured wheel–rail contact forces. The only parameters in the new expression for the equivalent stress are the vertical force and the wheel and rail radii.Comparisons between the new and the original criterion are carried out and show good agreement for the studied cases of tangent track operation. By employing principles of vehicle dynamics the criterion is further extended to the case of operations in curves. Finally the influence of transient loads on the growth of RCF cracks in wheels was investigated. It was demonstrated that transients need to be spaced closer than roughly 10 meters to give any substantial increase in crack growth rates.
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| 50. |
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