| 1. |
- Ekberg, Anders, 1967, et al.
(författare)
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Alarm limits for wheel–rail impact loads – part 2: analysis of crack growth and fracture
- 2009
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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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| 2. |
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| 3. |
- Ekberg, Anders, 1967, et al.
(författare)
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INNOTRACK Deliverable 4.2.1 -- Simplified relation for the influence of rail/joint degradation on operational loads and subsequent deterioration
- 2007
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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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| 4. |
- Ekberg, Anders, 1967, et al.
(författare)
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PRESOL – pre-processor för solkurveanalys
- 2007
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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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| 5. |
- Ekberg, Anders, 1967, et al.
(författare)
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Realtidsanalys av utmattningspåkänning från uppmätta spårkrafter
- 2007
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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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| 6. |
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| 7. |
- Ekberg, Anders, 1967, et al.
(författare)
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The influence of vertical load transients on wheel and rail deterioration
- 2007
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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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| 8. |
- Franklin, Francis, et al.
(författare)
-
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
-
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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| 9. |
- 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-
-
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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| 10. |
- 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
-
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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| 11. |
- 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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| 12. |
- Kabo, Elena, 1972
(författare)
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A numerical study of the lateral ballast resistance in railway tracks
- 2006
-
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
-
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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| 13. |
- Kabo, Elena, 1972, et al.
(författare)
-
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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| 14. |
- Kabo, Elena, 1972, et al.
(författare)
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Assessing risks of subsurface initiated rolling contact fatigue from field measurements
- 2009
-
Ingår i: Proceedings of the 8th International Conference on Contact Mechanics and Wear of Rail/Wheel Systems. ; 1, s. 355-361
-
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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| 15. |
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| 16. |
- Kabo, Elena, 1972, et al.
(författare)
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Index for real-time prediction of sub-surface initiated rolling contact fatigue in railway wheels
- 2007
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- 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.Abstract Comparisons between the new and the original criterion are carried out and show good agreement for the studied cases.
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| 17. |
- Kabo, Elena, 1972
(författare)
-
INNOTRACK Deliverable D4.3.5, Simulation of material deformation and RCF
- 2009
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Testing of rail steels has a long tradition in the railway industry both in the form of full-scale and scaled tests. However test results from different test stands have largely been self-standing, which have made quantitative comparison between different test rigs and towards operational scenarios difficult.The main purpose of this deliverable is to investigate the possibility of bridging this gap by numerical simulation aimed at predicting rolling contact fatigue (RCF) initiation. Two modelling approaches are employed: Methods that aim at relating the evaluated contact stress distribution directly to the RCF initiation life are denoted “engineering approaches”. In contrast “finite element (FE) based approaches” evaluate the (elasto-plastic) material response owing to the acting contact stresses and relates the fatigue life to the resulting stresses/strains in the material.To obtain reliable RCF life predictions is found to currently be on the brink of what is possible. The report takes the approaches outlined above as far as possible and reports intermediate results, complications etc.In the report prediction based on engineering approaches sets out from previously derived contact stress distributions [5]. These are complemented by simulations of dynamic wheel–rail interaction in order to evaluate possible additional longitudinal tractive stresses due to the rolling on the wheel on the rail. For the case studied, these were found to be comparable to the lateral tractive stresses. It should here be noted that an evaluation of wheel–rail dynamics based on Hertzian contact theory is not sufficient for high-resolution evaluation of the contact stress distribution for the case studied. Further such an analysis is extremely sensitive to the geometry of the contacting surfaces. Supported by these simulations it was presumed that the contact conditions corresponded to full slip for all the three test rigs simulated. Based on this a shakedown map based fatigue index was evaluated and a plot of the fatigue index versus the fatigue life in a log-log diagram was shown to give a reasonable match to a straight line, which would indicate a Wöhler-like fatigue life relationship. If this relationship holds for further scrutinization it would be a major step forward for fatigue life prediction and comparisons between test rigs and towards operational scenarios. However the current analysis contains major uncertainties most notably in estimated wheel–rail friction. The FE based approaches sets out by calibrating an elasto-plastic material model of the rail steel towards experimental stress–strain data. FE-models of the two full-scale test rigs are then developed and load cycles featuring the loaded wheel rolling over an representative rail section are carried out. The stress–strain response in highly loaded material points on the rail surface are then evaluated and quantified. Methods to predict resulting fatigue life are then described both based on the presumption that the dominating fatigue mechanism is low-cycle-fatigue (in the sense that fatigue life is governed by the strain range) or ratcheting (in the sense that fatigue life is governed by accumulated plastic strain).The simulations highlighted the fact that the studied combination of very local high deformations, large displacements, high contact pressures and interfacial shear stresses, conformal contact and need for sophisticated constitutive models is currently extremely cumbersome to simulate. Reliable results for one test rig for two load conditions have been obtained after tedious work of tuning analysis parameters. These results show a high sensitivity also for rather low variations in applied lateral load magnitudes. Further the results show that plastic deformations in the FE-simulations introduce a level of “smoothing”, which levels out very high stress concentrations. On the other hand this also makes a priori identifications of critical material points difficult. The results finally show that the use of non-linear hardening seems crucial and that the proposed methods of fatigue assessment seem credible. In addition simulations of the second rig stumbled upon a bug in the commercial code, which resulted in an erroneous evaluation of the contact stresses. Although this rendered these results useless it highlighted the sensitivity and complexity of the problem at hand. Measures are currently taken to find a work-around for the identified bug.In summary, the current report is in our opinion a major step forward in comparing different bench tests to each other and to operational conditions by numerical simulation. Based on the results this should indeed be feasible although very complicated. However the main benefit of the report lies perhaps in the identification of the limitations of today’s top-notch approaches and simulation toolboxes.Finally a word of caution is needed: As the simulations here and in [5] clearly show, the problem at hand is inherently sensitive. Consequently the accuracy of predictions (be it numerical, empirical, experimentally-based etc) will always be limited.
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| 18. |
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| 19. |
- Kabo, Elena, 1972, et al.
(författare)
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Numerisk prediktering av uppkomst av solkurvor – modellering, analys, inledande parameterstudie, samt indatagenerering
- 2007
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Rapporten beskriver en numerisk modell utvecklad inom det gemensamma CHARMEC/SP-projektet SP7 -- Lateral spårstabilitet för att analysera risken för uppkomst av solkurvor. Rapporten diskuterar hur beräkningsresultat framtagna med modellen kan analyseras, tolkas och översättas till kriterier för att bedöma när solkurvor uppkommer. För att demonstrera modellens förmåga har en inledande parameterstudie genomförts. Resultat från denna presenteras.
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| 20. |
- Kabo, Elena, 1972, et al.
(författare)
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Prediction of dynamic train-track interaction and subsequent material deterioration in the presence of insulated rail joints
- 2006
-
Ingår i: Vehicle System Dynamics. - 1744-5159 .- 0042-3114. ; 44:S1, s. 718 - 729
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Tidskriftsartikel (refereegranskat)abstract
- Numerical analysis of high-frequency dynamic train-track interaction is combined with the analysis of material deterioration in terms of rolling contact fatigue (RCF) and plastic deformations to analyze the influence of insulated rail joints. These joints form local rail irregularities and lead to a local change of dynamic track stiffness. Dynamic responses at wheel passes are evaluated. Further, related plastic deformations at the joint and increased RCF impact along a stretch of the track adjacent to the joint are predicted.
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| 21. |
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| 22. |
- Lansler, Eka, 1974, et al.
(författare)
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Subsurface crack face displacements in railway wheels
- 2005
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Ingår i: Wear. - : Elsevier BV. - 0043-1648. ; 258:7-8, s. 1038-1047
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Tidskriftsartikel (refereegranskat)abstract
- In a railway wheel subsurface cracks may form at macroscopic defects under the wheel tread, propagate and, if not managed, cause catastrophic wheel failures. The deformation of such subsurface cracks under rolling contact conditions is the main issue of the current paper. Parametric studies are carried out with a two-dimensional elasto-plastic finite element (FE) model of a part of a wheel containing a subsurface crack. The purpose of the simulation is to study crack face displacements under varying conditions. The influence of crack length, crack location (depth), crack face friction, as well as wheel/rail contact load magnitude and contact geometry is investigated. The numerical results show that mode I deformations are negligible. Further, load magnitudes and contact geometry play crucial roles for the relative tangential crack face displacements. The current study of deformation of subsurface cracks under rolling contact conditions will form the basis for future studies on crack growth prediction.
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| 23. |
- Lansler, Eka, 1974, et al.
(författare)
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The influence of plastic deformations on growth of subsurface rolling contact fatigue cracks in railway wheels
- 2006
-
Ingår i: Proceedings of the Institution of Mechanical Engineers, Part F: Journal of Rail and Rapid Transit. - 0954-4097 .- 2041-3017. ; 220:4, s. 461-473
-
Tidskriftsartikel (refereegranskat)abstract
- A subsurface rolling contact fatigue crack in a railway wheel is studied. Stress and strain fields are evaluated by elasto-plastic finite-element simulations. The robustness and validity of the numerical model are investigated. A suitable measure to characterize crack propagation is then sought. Numerical results show that the effect of crack tip plasticity is small for cases studied, indicating that linear elastic fracture mechanics approaches are applicable. Further, the magnitudes of the stress intensity factor in mode I, KI, are negative implying crack closure. Motivated by these findings, the stress intensity factor range in mode II, ΔKII, is employed as a measure of crack propagation. Finally, studies are carried out to quantify the effects of altered contact load conditions and crack face friction.
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| 24. |
- Li, Zili, et al.
(författare)
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INNOTRACK Deliverable 4.2.4 -- Improved model for loading and subsequent deterioration due to squats and corrugation
- 2009
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- In this research a hybrid multibody-finite element model was developed and applied to the analyses of the initiation and growth of squats, and to the identification of the most influential parameters of squatting. The growth process of squats was postulated based on numerical simulation, and was subsequently validated by field monitoring. Further a critical size for small rail top geometrical defects to grow into squats has been derived and validated. This critical size may be directly applied to visual inspection and classification of squats so that false reporting of squats can be avoided. The critical size can be applied as a minimum action rule for preventive or early corrective maintenance actions, such as rail grinding. The model may also have the capability to relate the severity of some track short defects quantitatively to some measurement of the dynamic wheel-rail interaction at the defects so that automatic detection of the defects at their early stage is possible. Finally corrective and preventive measures against squats are discussed.
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| 25. |
- Nielsen, Jens, 1963, et al.
(författare)
-
Alarm limits for wheel–rail impact loads – part 1: rail bending moments generated by wheel flats
- 2009
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Wheel tread defects, such as wheel flats, generate wheel–rail impact loads that in severe cases may promote fracture from pre-existing cracks in the rail. The present Swedish wheel removal criterion relates the alarm limit 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 properties. In this study, the influence of wheel–rail impact load magnitude on resulting rail bending moment is studied using a numerical model for simulation of dynamic vehicle–track interaction. Three different types of traffic are investigated: heavy haul at 60 km/h (axle load 30 tonnes), freight at 100 km/h (25 tonnes) and passenger at 200 km/h (21 tonnes). Positive bending moments generating tensional stresses in the rail foot and negative bending moments leading to tensional stresses in the rail head are calculated. The model is calibrated with respect to field measurements. An idealised time history of the impact load due to a wheel flat is suggested, and worst-case scenarios are sought for in parametric studies. It is shown that magnitudes of rail bending moments are significantly influenced by sleeper support stiffness and in particular if adjacent sleepers are not well supported (hung sleepers).
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| 26. |
- Nielsen, Jens, 1963, et al.
(författare)
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Larmgräns för hjulskadedetektorer – En utredning av risk för rälbrott på Malmbanan
- 2007
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- En larmgräns för maximal tillåten vertikal kontaktkraft mellan hjul och räl i samband med hjulskador skall bestämmas av Banverket. Syftet med denna studie är att via fältförsök och numeriska simuleringar redovisa ett underlag för detta beslut. Risk för brott orsakad av intiell spricka i rälhuvud respektive i rälfot analyseras. Inverkan av omgivningstemperatur beaktas. I denna studie förutsätts sprickorna vara rent transversella. Två typer av sprickor studeras, dels en spricka i rälhuvudet som initierats som en head-check och dels en kantspricka i rälsfoten. Tillväxt av stora sprickor och rälbrott styrs förutom av temperaturspänningar av böjmomentet i rälen. Detta orsakas dels av kvasistatiska bidrag från hjulpassager, men också av dynamiska tillskott från stötlaster som genereras av orunda hjul. Momentbidragen är beroende av inte bara den dynamiska lastmagnituden utan även av exempelvis tågets hastighet, lastens frekvensinnehåll, spårets egenskaper, axellast och axelavstånd. Strategin i denna studie är därför att söka ett värsta lastfall med avseende på indata för lastens tidshistoria och på position inom sliperfacket där hjulskadan slår i rälen. Målsättningen är att finna en approximativ korrelation mellan maximal kontaktkraft och resulterande max/min värden på rälens böjmoment utan hänsyn till böjmomentets frekvensinnehåll. Malmbanan med axellast 30 ton och hastighet 60 km/h har valts som trafikfall. Från beräknade böjmoment och temperaturlaster kan spänningsintensitetsfaktorer för sprickor i rälhuvud och rälfot bestämmas för olika spricklängder. Från de resultat som redovisas i rapporten kan tillåtna vertikallaster sedan bestämmas utgående från bestämda spricklängder och rältemperaturer.
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| 27. |
- Sandström, Johan, 1978, et al.
(författare)
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Isolerskarvar – jämförelse mellan 4 mm och 8 mm skarvöppning
- 2007
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- En inledande analys av hur skarvöppningens bredd påverkar spänning, töjning och utmattningslivslängd i omgivande rälmaterial redovisas. Analyserna visar att en större skarvöppning leder till högre påkänning i form av högre plastiska töjningar.
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| 28. |
- Ullrich, Detlev, et al.
(författare)
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INNOTRACK Deliverable D4.3.7, Innovative laboratory tests for rail steels – Final report
- 2009
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- This paper presents a first thorough investigation of different laboratory tests for rail materials combined with numerical simulations and metallographic investigations. A specific methodology for the latter is given in the Appendix. Laboratory tests for new rail materials are desirable supplements to field tests in order to save time and money. Thus, less valuable products can be early withdrawn from expensive field tests. Within this work package, test conditions for laboratory tests of rail materials have been defined and compared to field conditions. Existing test equipment and evaluation methods of the WP partners have been exploited for the laboratory tests in order to find out the applicability to the pre-defined field conditions.The tests were performed at the SUROS twin disk test machine, at the VAS linear full-scale test rig and at DB full-scale roller rigs. The results were compared among other with respect to metallography and material deterioration.Subsequent numerical calculations showed that the full-scale tests more or less deviate systematically from the expected contact conditions due to bending of wheel and rail. In addition, predictions regarding RCF have been carried out and compared to test results.It is shown that twin disk tests as well as tests on a full-scale linear test rig are suitable for practical use. The tests on full-scale roller rigs failed due to the need for specific rail samples, which ultimately destroyed the fixtures during the tests. An evaluation of the different tests including a rough estimate of effort is given.
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| 29. |
- Ullrich, Detlev, et al.
(författare)
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INNOTRACK Deliverable D4.3.8, Innovative laboratory tests for rail steels
- 2009
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- There is a need for laboratory tests of rail material by railway opera-tors as well as by manufactures. The tests should represent oper-ational conditions for the rail material. They should allow withdraw-ing less valuable products from far more expensive field tests.This guideline is based on the experience from the WP4.3 partners with respect to laboratory tests for rail steels. As the operational demands on rail material may differ from site to site (with respect to the curvature etc.), a suitable preparation of the laboratory tests is necessary. It should start with a definition of the conditions to be tested, e.g. with a testing matrix. According to present knowledge, related tests can be done at twin disk test rigs or at specialized full-scale linear test rigs. Full-scale roller rigs are not recommended because the fixing of the samples is difficult and the preparation of the rail material requires a huge effort. After testing the wear, RCF and deformation should be evaluated in accordance with a consistent evaluation scheme. Metallographic in-vestigations could be applied especially with respect to quantifying material deterioration.The compliance with the pre-defined requirements should be moni-tored throughout the test since contact conditions may vary due to profile wear and specific test rig deviations. If such deviations occur, the test conditions should be re-evaluated through numerical simula-tions. Thus, the effect on the test results may be estimated.The results of testing on twin disk tests as well as those on a linear test rig can provide results suitable for practical use. An evaluation of the different tests including a rough estimate of effort is given.
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| 30. |
- Vernersson, Tore V, 1968, et al.
(författare)
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Wheel tread damage – a numerical study of railway wheel tread plasticity under thermomechanical loading
- 2009
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Ingår i: Proceedings of the 9th International Heavy Haul Conference. ; 1, s. 465-472
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Konferensbidrag (refereegranskat)abstract
- A numerical study is presented where the impact of simultaneous thermal and mechanical loading on a railway wheel tread as imposed by braking and rolling contact is reported. A comparison is made of 2D and 3D finite element simulations of the thermomechanical problem featuring a material model that accounts for thermal expansion and plastic deformations. It is found that 2D simulations give unrealistic predictions of plastic deformations. The 3D simulations demonstrate a significant influence of the thermal loading on the induced tensile stresses also in cases of rather moderate temperature increases.
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