| 1. |
- Landström Voortman, Eric, 1993, et al.
(författare)
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Analysis and testing of tread braked railway wheel — Effects of hot spots on wheel performance
- 2024
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Ingår i: International Journal of Fatigue. - 0142-1123. ; 180
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Tidskriftsartikel (refereegranskat)abstract
- To investigate the impact of localised heating phenomena in the form of hot spots on wheel performance in general and on wheel residual stress state in particular, a combination of experimental testing and finite element simulations of tread braked wheels has been performed. Using a newly established full-scale railway brake test rig, a wheel is exposed to prolonged drag braking applications at constant power levels to induce high temperatures on the wheel tread. The distribution and evolution of the temperature is studied using a high-speed, high-resolution thermographic camera in addition to traditional sliding thermocouples. Measured temperature data are then used in combination with a thermomechanically calibrated material model to simulate the wheel behaviour. For this purpose, a 3D finite element model representing a sector of a railway wheel is used. The experimental results show that the temperatures measured utilising sliding thermocouples provide insufficient information since they cannot resolve the uneven tread temperatures given typical response times. Non-uniform heating is found to have a significant effect on tensile residual stresses in the rim. Especially the case with global uneven temperatures is found to generate potentially hazardous residual stresses. The results presents future challenges for the analysis and development of the brake-wheel-rail system.
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| 2. |
- Landström Voortman, Eric, 1993, et al.
(författare)
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Improved Finite Element Modelling of Tread Braked Wheel Performance Verified by Brake Rig Tests
- 2023
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The objective of the present study is to validate a finite element material model for railway wheel steel against brake rig test results. The material model for pearlitic ER7 wheel steel has been calibrated for thermomechanical loading based upon the regulatory requirements for brake rig tests using specimen test results. The material model has shown better adherence to thermomechanical results compared to previous material models, but ultimately full-scale validation is required. To verify and further develop the model, a combined experimental and numerical campaign was launched. Using a custom-built brake rig at Chalmers University, two different designs of European freight wheels are tested at power levels of 30 and 50 kW for durations of up to 45 min with maximum temperatures exceeding 600 °C. Wheel rim displacements are measured during experiments and residual stresses are measured before and after each test using an instrument employing the elastoacoustic effect. Temperatures are measured using thermocouples on the wheel web, sliding thermocouples on the tread and a high-speed thermographic camera. The experimental results are then compared to finite element simulations at the same brake power levels using the aforementioned material model. The results show possible correspondence between the experimental and finite element results, indicating that the numerical model may be accurate enough for preliminary predictions of braking damage, while also highlighting challenges of thermal model assumptions.
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| 3. |
- Landström Voortman, Eric, 1993, et al.
(författare)
-
Improved modelling of tread braked wheels using an advanced material model
- 2022
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Ingår i: FISITA Library. ; EB2022:RLB
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Konferensbidrag (refereegranskat)abstract
- The objective of the present study is to investigate and examine the capabilities of a novel material model, calibrated using anisothermal experimental data, when employed in detailed braking simulations corresponding to brake test rig conditions. To achieve this, an axisymmetric finite element model of a standard freight wheel exposed to tread braking is used to assess the performance of the material model. The finite element model accounts, in a simplified fashion, for residual stresses introduced by the rim hardening process at wheel manufacturing and also for variations in material properties based on typical hardness values on a wheel cross section. A range of braking situations are assessed to achieve different loads and temperatures, by mimicking downhill braking at constant speed for a prolonged time period. The results are compared between the new anisothermally calibrated model, two other similar material models previously developed for wheel simulations that are calibrated merely by isothermal data as well as a simpler model used in industry. Additionally, some comparisons are also made with the pertinent European standard on technical approval for forged wheels. The results show that the new calibrated material model predicts realistic material behaviour for a wide range of braking situations. Compared with previous models, conservative predictions are found with higher residual tensile stresses after braking and also larger residual displacements, as well as larger areas with plastic strains. The study also highlights the importance of knowing the spatial distribution of the residual stresses when comparing average residual stresses in the wheel rim. The new features of the material model contribute substantially to more accurate modelling of the processes occurring in the wheel during high temperature tread braking, although at the cost of prolonged duration of the numerical analyses.
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| 4. |
- Landström Voortman, Eric, 1993
(författare)
-
Thermomechanical behaviour of tread braked wheels
- 2022
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Tread brakes, also known as block brakes, are a type of friction brakes commonly used in the railway industry. They are a low-cost and low-maintenance solution compared to more complicated systems such as disc brakes or electrodynamic brakes. Modern composite brake blocks designed to lower noise emission, however, cause increased thermal loading of the wheel since these blocks attract and store lower amounts of the generated frictional heat compared to older cast iron blocks. Long-term drag braking may raise the temperature of the wheel rim by several hundred degrees. After cooling the resulting residual tensile stresses in the wheel rim may lead to a broken wheel. Also a permanent degradation of the pearlitic steel material is induced by the high temperatures. In the first part of the present work, a finite element material model is calibrated using isothermal and anisothermal experimental data from testing of railway wheel steel specimens, accounting for the macroscale material changes which occur during typical thermomechanical cycles at long-term braking. Results are presented with main focus on comparing finite element simulations to experimental measurements of the thermomechanical cycles. Material deterioration by spheroidisation of the pearlitic material is modelled using a time-temperature dependent law. In the second part, the material model is further evaluated using axisymmetric simulations of tread braked train wheels, and the wheel performance is evaluated according to current European standards. Results are presented that show a substantial increase in the magnitude of the modelled residual tensile stresses as compared to other widely-used material models. In the third part, experiments and measurements on tread braked wheels are conducted in a full-scale test rig. It is found that the temperature distribution in the axial and circumferential directions on the wheel tread exhibits substantial variations which can be of importance in the understanding of the full thermomechanical behaviour of a wheel. Numerical simulations show that there is an increase in residual tensile stress at locally hotter areas, a phenomenon which has a potential to compromise the safety of the system.
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| 5. |
- Landström Voortman, Eric, 1993, et al.
(författare)
-
Thermomechanical testing and modelling of railway wheel steel
- 2023
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Ingår i: International Journal of Fatigue. - : Elsevier BV. - 0142-1123. ; 168
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Tidskriftsartikel (refereegranskat)abstract
- Studies of thermal effects of tread braking on railway wheels show that the wheel temperatures may reach above 600 °C, at which the mechanical properties of the wheel steel are significantly impaired. Computational models that simulate the thermomechanical behaviour of the wheels are commonly based on results from laboratory tests which do not reflect actual in-service scenarios. Anisothermal testing and modelling are omitted due to the difficulties in designing relevant experiments and implementation of the results. In this paper, a preexisting numerical material model is extended in order to implement fully anisothermal behaviour. This is done by performing several thermomechanical experiments mimicking real-world service and worst-case scenarios ranging from room temperature up to 650 °C. The results from the laboratory testing are then used in combination with data from traditional isothermal tests to optimise the numerical material model by calibrating its material parameters. As part of this process it was found necessary to include a time- and temperature-dependent, non-recoverable (irreversible) mechanism for material softening and microstructural changes which occur above 400 °C. Finite element simulations with the material model using the new parameters and the softening law show markedly improved adherence to anisothermal and strain-controlled experimental results compared to the preexisting model(s). The results demonstrate that anisothermal testing is a requirement for models that are intended to simulate material behaviour for thermomechanical loads and thermally induced microstructural changes.
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