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- 2019
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Tidskriftsartikel (refereegranskat)
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| 2. |
- Esmaeili, Ali, 1983, et al.
(författare)
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A methodology to predict thermomechanical cracking of railway wheel treads: From experiments to numerical predictions
- 2017
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Ingår i: International Journal of Fatigue. - : Elsevier BV. - 0142-1123. ; 105, s. 71-85
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Tidskriftsartikel (refereegranskat)abstract
- In the present study, thermomechanical cracking of railway wheel treads is studied by full-scale brake rig tests and finite element simulations. The main goal of the paper is to perform thermomechanical rolling contact fatigue life predictions. The wheel tread material is subjected to simultaneous mechanical and thermal loads due to rolling contact and stop braking, respectively. Full-scale tests featuring three series of repeated stop braking cases have been performed in a brake rig featuring a tread braked wheel that is in rolling contact with a so-called rail-wheel. The brake rig test conditions have been simulated numerically using the finite element method where the effect of “hot bands” on the tread is accounted for as indicated by the experimental findings. Stresses induced by temperature from braking as well as tractive rolling contact loading on the tread are considered. The mechanical response of the wheel material ER7 is obtained from a plastic Chaboche material model calibrated against data from cyclic experiments at room temperature and up to 625 °C. Finally, a strategy for prediction of fatigue life with respect to ratchetting failure is discussed.
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| 3. |
- Singh Walia, Mandeep, 1987
(författare)
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Mechanical braking systems for trains: A study of temperatures, fatigue and wear by experiments and simulations
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Increased demand for shorter travel times, higher axle loads, increased volumes and increased punctuality of railway traffic calls for a better design and management of the railway subsystems. The present thesis deals with aspects of mechanical friction brakes, in the form of tread brakes and disc brakes. These are critical for reliable, safe and economical operation of trains. The thesis establishes models and simulation tools for frictional braking systems that may operate in parallel with an electrodynamic braking system. A main focus is the influence of thermal loading on rolling contact fatigue from tread brakes at stop braking. A simulation methodology for thermomechanical cracking of railway wheel treads due to rolling contact and repeated stop braking by tread brakes, is established based on full-scale brake rig experiments. Building on the same approach, plastic deformation of the tread is also investigated. The results indicate that tread damage increases drastically for frictional temperatures above some 450 ºC. Another focus is temperatures and wear of tread brakes and disc brakes under operational loading. In two field test campaigns, detailed instrumentation and continuous measurements of relevant temperatures and braking parameters are combined with intermittent measurement of wear of friction brake components. Wear of brake blocks and wheel treads is quantified. It is found that the tread wear introduced by the block contact dominates for trailing wheelsets, whereas for powered wheelsets wear from tractive forces in the wheel–rail contact can be of equal importance. In a study on disc brakes, temperatures and wear performance are compared for two friction pairs: one new segmented disc with sintered pads and a traditional disc with an undivided friction ring combined with organic pads. It is found that the discs have similar braking temperatures, but that the wear of disc and pads is substantially lower for the segmented disc. A numerical investigation of thermomechanical fatigue damage of the two disc types indicates that the segmented disc also has a substantially longer fatigue life.
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| 4. |
- Singh Walia, Mandeep, 1987, et al.
(författare)
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Temperatures and wear at railway tread braking: Field experiments and simulations
- 2019
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Ingår i: Wear. - : Elsevier BV. - 0043-1648. ; 440-441
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Tidskriftsartikel (refereegranskat)abstract
- Field tests were carried out for a commuter train in revenue service equipped with cast iron and organic composite brake blocks. Temperatures for wheel tread, wheel web and brake blocks and wear of wheel treads and brake blocks were recorded. The measured temperatures are used for calibrating a thermal model for assessment of wheel and block temperatures. The wear of cast iron and organic composite brake blocks is estimated using simulated temperatures and temperature-dependent wear models based on pin-on-disc experiments. It is found that a wear rate adaption factor, tentatively motivated by the presence of thermoelastic instabilities at full-scale braking that cannot be found at small-scale testing, is required for producing a simulated wear that is in agreement with results from field tests. Wheel tread wear is assessed as change in flange height for both powered and trailing wheels and for the studied train it is found that the levels of annual total wear of these types of wheels are similar in magnitude. Modelling of the tread wear originating from block–wheel contact and wheel−rail contact, combined with a comparison with measured wear magnitudes, makes it possible to quantify the wear from these two tread contacts. It is found for the powered wheels that wear induced by the wheel-rail contact and the block-wheel contact have equal importance, whereas for the trailer wheels the wear emanating from the block-wheel contact is dominating.
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| 5. |
- Walia, Mandeep Singh, 1987, et al.
(författare)
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Temperatures and wear at railway tread braking: Field experiments and simulation
- 2018
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Ingår i: Proceedings of the 11th International Conference on Contact Mechanics and Wear of Rail/wheel Systems, CM 2018. - 9789461869630 ; , s. 1029-1036
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Konferensbidrag (refereegranskat)abstract
- Field tests were carried out for a commuter train in revenue service equipped with cast iron and organic composite brake blocks. Temperatures for wheel tread, wheel web and brake blocks and wear of wheel treads and brake blocks were recorded. The measured temperatures are used for calibrating a thermal model for assessment of wheel and block temperatures. In addition, the results from thermal and wear simulations are presented. Comparisons are made between measured and simulated temperatures and wear. The wear of the cast iron brake blocks estimated using simulated temperatures and a temperature-dependent wear model calibrated from pin-on-disc experiments is in agreement with measured wear results from field tests.
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| 6. |
- Walia, Mandeep Singh, 1987, et al.
(författare)
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Thermal impact on rolling contact fatigue and capacity of railway wheels
- 2016
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Ingår i: Proceedings Eurobrake 2016 (Milan). ; , s. 10-
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Konferensbidrag (refereegranskat)abstract
- Tread braked railway wheels are subjected to complex loading due to combined rolling contact stresses and thermally induced stresses. The main objective of the present study is to find the limits for tread braking with respect to temperature impact on rolling contact fatigue (RCF) of the wheel tread. A wheel with an S-shaped web is studied for some different stop braking loads. Using 3D FE simulations, the effects of simultaneous thermal loading from braking and mechanical loading, with traversing wheel-rail rolling contact, are studied. In order to account for the elevated temperatures, the simulations utilise a temperature-dependent elastoplastic material model. The mechanical loads account for frictional rolling contact stress distributions induced by braking, using a novel method that is based on elastoplastic contact simulations. Partial slip is considered and interfacial shear stresses are introduced in the wheel-rail contact area. Evolution of damage in the vicinity of the wheel tread is studied for various brake loading cases. In order to assess limits for the tread braking, the calculated damage is compared to previously developed critical damage levels which were based on full-scale brake rig testing. Results are presented for a parametric study with thermomechanical loading based on different load cases. The influence from operational parameters such as axle loads, initial speeds, decelerations and block material is studied. The results show that the temperature has a strong influence on the rolling contact fatigue of the wheel treads and, hence, also on the thermal capacity of the wheels. The study gives preliminary limits for revenue traffic, described as combinations of tread temperatures and wheel-rail rolling contact loading, which should be respected to avoid thermal cracking of the wheel treads.
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| 7. |
- Walia, Mandeep Singh, 1987, et al.
(författare)
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Thermomechanical capacity of wheel treads at stop braking: A parametric study
- 2018
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Ingår i: International Journal of Fatigue. - : Elsevier BV. - 0142-1123. ; 113, s. 407-415
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Tidskriftsartikel (refereegranskat)abstract
- During tread braking, the treads of railway wheels are subjected to a complex loading due to combined rolling contact and thermally induced stresses. In revenue traffic the running mode of the train varies and the operational parameters will influence the life of the wheels. To prevent excessive damage, it is therefore important to understand at which operational conditions wheel damage becomes unacceptable. The current study aims to find limits for tread braking with respect to the influence of thermal stresses on rolling contact fatigue (RCF) of the wheel tread when subjected to repeated stop braking. A parametric study, using 3D FE simulations and involving operational parameters such as axle load, maximum vehicle speed, deceleration, brake block material and initial wheel temperature, is carried out for a new wheel with an S-shaped web. Additional analyses investigate impact from wheel geometry by studying a wheel with a straight web and a wheel with a thin (worn) rim. The effects of simultaneous thermal loading from wheel–block frictional contact during braking and mechanical loading, due to the traversing wheel–rail rolling contact, are studied in an uncoupled thermomechanical analysis. In the wheel–rail contact simulations, frictional rolling contact stress distributions induced by braking are accounted for. Interfacial shear stresses and partial slip are also included in the model. A temperature-dependent elastoplastic model is utilised to characterise changes in material behaviour during braking. In the vicinity of the wheel tread, damage evolutions for the studied brake load cases are evaluated. The results show that high tread temperatures, in particular temperatures above 450 °C, have a strong detrimental influence on the RCF formation and, hence, also on the thermomechanical capacity of the wheel. On the other hand, it is found that for braking temperatures between 300 °C and 375 °C, the fatigue resistance is increased due to strain hardening effects. In addition, the parametric study points towards actual braking load cases that can give such temperatures in terms of initial speeds, axle loads, etcetera. Specifically, the study shows that the train axle load, that controls the normal wheel–rail contact force, has a substantial impact on the life of the wheel treads. Wheels having straight webs and S-shaped wheel web exhibit the same fatigue life of their treads, whereas a reduction in wheel rim thickness promotes ratchetting due to increased flexural stresses from the mechanical wheel–rail contact loading.
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| 8. |
- Walia, Mandeep Singh, 1987
(författare)
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Towards enhanced mechanical braking systems for trains. Thermomechanical capacity of wheel treads at stop braking
- 2017
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Modern trains are equipped with different braking systems, between which the braking effort can be distributed. Among these, tread braking is still the most common system for friction braking. Tread brake systems are cheap and robust. However, extensive usage of tread brakes demands knowledge of operational limits to ensure safety and decrease life cycle costs (LCC) of the running gear.In the present work, a state-of-the-art literature survey has been compiled which covers topics related to establishing operational limits such as: brake control and blended braking, braking temperatures, brake block materials, wear and rolling contact fatigue of wheels due to tread braking, and capacity of tread brakes and brake discs.A methodology to simulate full-scale brake rig tests, including wheel-rail contact, has been further developed. It includes an axisymmetric thermal analysis, a 3D mechanical wheel-rail contact analysis, and a 3D thermomechanical analysis of the braked wheel. The behaviour of ER7 grade railway wheel material is mimicked by use of a plasticity model calibrated against results from cyclic experiments on test specimens. The results from the simulations in terms of predicted fatigue lives show good agreement with full-scale test rig results for three combinations of initial velocity and brake block material.The developed methodology is employed in parametric studies. These consist of braking load cases characterised by operational parameters such as axle load, maximum vehicle speed, deceleration, block material, and initial wheel temperature. Damage evolution in the wheel tread is studied. A strong infuence of high temperatures on rolling contact fatigue formation in the wheel tread was observed. In particular, braking temperatures over 450 °C can result in a very short life up to crack initiation. However, for braking temperatures in the range of 300 - 350 °C, wheel tread material is more resistant to fatigue due to strain hardening.
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| 9. |
- Walia, Mandeep Singh, 1987, et al.
(författare)
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Wear and plastic deformation of the wheel tread at block braking : Results from brake rig experiments and simulations
- 2019
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- In the present work, results from a series of full-scale tread braking experiments that include a wheel–railwheel rolling contact, are compared to the results from FE simulations with focus on tread plasticity and wear. Brake rig tests have been performed to reveal tread plasticity and tread wear in the form of sequences of constant temperature rolling at 200 °C, 250 °C, and 300 °C, all for a wheel–railwheel contact load of 60 kN. The evolution of the tread profile is measured during the experiments and is compared to estimations from the FE simulations and wear calculations. Finally, calculated tread wear introduced by braking and specific influence from rolling contact plasticity on the tread profile evolution are estimated and compared to the measured wear.
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