| 1. |
- Pieringer, Astrid, 1979, et al.
(författare)
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Investigation of railway curve squeal using a combination of frequency- and time-domain models
- 2016
-
Ingår i: Proceedings of the 12h International Workshop on Railway Noise (IWRN12), Terrigal, Australia, September 12-16. ; , s. 444 - 451
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Konferensbidrag (refereegranskat)abstract
- Railway curve squeal arises from self-excited vibrations during curving. In this paper, a frequency- and a timedomainapproach for curve squeal are compared. In particular, the capability of the frequency-domain model topredict the onset of squeal and the squeal frequencies is studied. In the frequency-domain model, linear stabilityis investigated through complex eigenvalue analysis. The time-domain model is based on a Green's functionsapproach and uses a convolution procedure to obtain the system response. To ensure comparability, the samesubmodels are implemented in both squeal models. The structural flexibility of a rotating wheel is modelled byadopting Eulerian coordinates. To account for the moving wheel‒rail contact load, the so-called moving elementmethod is used to model the track. The local friction characteristics in the contact zone is modelled inaccordance with Coulomb's law with a constant friction coefficient. The frictional instability arises due togeometrical coupling. In the time-domain model, Kalker's non-linear, non-steady state rolling contact modelincluding the algorithms NORM and TANG for normal and tangential contact, respectively, is solved in eachtime step. In the frequency-domain model, the normal wheel/rail contact is modelled by a linearization of theforce-displacement relation obtained with NORM around the quasi-static state and full-slip conditions areconsidered in tangential direction. Conditions similar to those of a curve on the Stockholm metro exposed tosevere curve squeal are studied with both squeal models. The influence of the wheel-rail friction coefficient andthe direction of the resulting creep force on the occurrence of squeal is investigated for vanishing train speed. Results from both models are similar in terms of the instability range in the parameter space and the predictedsqueal frequencies.
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| 2. |
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| 3. |
- Lundberg, Oskar, 1980-
(författare)
-
On the influence of surface roughness on rolling contact forces
- 2016
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Road vehicle tyres, railway wheels and ball bearings all generate rolling contact forces which are transferred within a finite area of contact between the rolling element and the substrate. Either it is visible or not for the human eye, a certain degree of roughness is always present on the contacting surfaces and it influences the generation of both vertical and lateral contactforces. The purpose of this investigation is to enhance the understanding and modelling of the influence from small-scale surface roughness on the generation of rolling contact forces. To this end, a computationally efficient method to include roughness-induced contact nonlinearities in the dynamic modelling of rolling contacts is proposed. The method is implemented in a time domain model for vertical wheel–track interaction to model rolling-induced rail vibrations, showing good agreement with measurements. Furthermore, a test rig is developed and used for the investigation of tyre–road rolling contact forces. Detailed studies are performed on the influence of substrate roughness on the resulting contact forces for a tyre tread block which is rolling at different operating conditions. The choice of substrate as well as the rolling velocity and the slip ratio is observed to have significant influence on the resulting friction coefficient. For high slip ratios, stick–slip oscillations appear, exhibiting frequency content which is largely dependent on the choice of substrate. The outcomes of this study can potentially be used to improve future tyre–road contacts with respect to wear, traction and noise generation.
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| 4. |
- Torstensson, Peter, 1981, et al.
(författare)
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Hybrid model for prediction of impact noise generated at railway crossings
- 2016
-
Ingår i: Proceedings of the 12h International Workshop on Railway Noise (IWRN12), Terrigal, Australia, September 12-16 (2016). ; , s. 539 - 545
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Konferensbidrag (refereegranskat)abstract
- A hybrid model for the prediction of impact noise at railway crossings is presented. The hybrid model combines the simulation of vertical wheel‒rail contact force in the time domain and the prediction of sound pressure level using a linear frequency-domain model. The time-domain model uses moving Green’s functions for the vehicle and track models (accounting for wheel flexibility and a discretely supported rail with space-variant beam properties) and a non-Hertzian wheel‒rail contact model. The time-domain and frequency-domain models are coupled based on the concept of an equivalent roughness spectrum. The model is demonstrated by investigating the influence of axle load, vehicle speed and wheel profile on generated impact noise levels. A negligible influence on impact noise is observed for axle loads in the interval 15 – 25 tonnes. On the other hand, increasing vehicle speed from 80 km/h to 150 km/h, or comparing a nominal S1002 wheel profile with a severely hollow worn profile, result in substantially higher levels of impact noise; for the given wheel and track conditions the differences are in the order of 10 dB(A).
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| 5. |
- Winroth, Julia, 1981, et al.
(författare)
-
Contact stiffness considerations when simulating tyre/road noise
- 2017
-
Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 1095-8568 .- 0022-460X. ; 409, s. 274-286
-
Tidskriftsartikel (refereegranskat)abstract
- Tyre/road simulation tools that can capture tyre vibrations, rolling resistance and noise generation are useful for understanding the complex processes that are involved and thereby promoting further development and optimisation. The most detailed tyre/road contact models use a spatial discretisation of the contact and assume an interfacial stiffness to account for the small-scale roughness within the elements. This interfacial stiffness has been found to have a significant impact on the simulated noise emissions but no thorough investigations of this sensitivity have been conducted. Three mechanisms are thought to be involved: The horn effect, the modal composition of the vibrational field of the tyre and the contact forces exciting the tyre vibrations. This study used a numerical tyre/road noise simulation tool based on physical relations to investigate these aspects. The model includes a detailed time-domain contact model with linear or non-linear contact springs that accounts for the effect of local tread deformation on smaller length scales. Results confirm that an increase in contact spring stiffness causes a significant increase of the simulated tyre/road noise. This is primarily caused by a corresponding increase in the contact forces, resulting in larger vibrational amplitudes. The horn effect and the modal composition are relatively unaffected and have minor effects on the radiated noise. A more detailed non-linear contact spring formulation with lower stiffness at small indentations results in a reduced high-frequency content in the contact forces and the simulated noise.
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| 6. |
- Gomez-Gallegos, A. A., 1983-, et al.
(författare)
-
A comparative study assessing the wear behaviour of different ceramic die materials during superplastic forming
- 2017
-
Ingår i: Materialwissenschaft und Werkstofftechnik. - : Wiley-VCH Verlagsgesellschaft. - 0933-5137 .- 1521-4052. ; 48:10, s. 983-992
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Tidskriftsartikel (refereegranskat)abstract
- Superplastic forming is an advanced manufacturing process where metallic sheets are heated to their superplastic region to be then blow formed within a die set. The process allows for the forming of complex parts but it is typically restricted to low volume production and high value pieces. Despite their brittle nature, ceramic dies are a developing technology for superplastic forming as they offer lower production costs and shorter lead times than conventional metallic dies, thus reducing process costs. This work presents a method to assess ceramic die wear by means of a novel test rig developed a at the Advance Forming Research Centre of the University of Strathclyde, Scotland, UK where the superplastic forming die-part interaction can be replicated at laboratory scale. Controllable normal load tests at standard superplastic forming conditions on three different reinforced ceramic materials are carried out with a view to understanding their wear mechanisms and to ultimately identify methods to improve their wear resistance.
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| 7. |
- Silva-Magalhães, Ana, et al.
(författare)
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In-situ temperature measurement in friction stir welding of thick section aluminium alloys
- 2019
-
Ingår i: Journal of Manufacturing processes. - : Elsevier. - 1526-6125 .- 2212-4616. ; 39, s. 12-17
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Tidskriftsartikel (refereegranskat)abstract
- Friction stir welding (FSW) is a reliable joining technology with a wide industrial uptake. However, several fundamentals of the process such as the temperature inside the stirred zone of the weld and its influence on mechanical properties, are not yet fully understood. This paper shows a method for accurate temperature measurements in multiple locations around the tool, to identify the location of the peak temperature, the temperature variations between the advancing and the retreating side of the tool and its relation to the tool geometry. Both standardised thermocouples in the FSW tool and the novel “tool-workpiece thermocouple” method were used to record temperatures.Bead-on-plate welds in 20 mm thickness AA6082-T6 were produced while the temperatures were measured in three locations on the FSW tool: at the shoulder outer diameter, at the transition from shoulder to probe and at the probe tip. It was found that the hottest point in the stirred zone was 607 °C and was located at the transition between the shoulder and probe, on the retreating-trailing side of the tool. The lowest temperature was found at the probe tip on the retreating-leading side of the tool.The results offer a better understanding of the temperature distribution around a FSW tool. The method presented can be applied to verification of thermal simulation models, tool design optimization, quality assurance and temperature feedback control.
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| 8. |
- Casanueva, Carlos, 1981-, et al.
(författare)
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Comparison of wear prediction models for different contact conditions
- 2016
-
Ingår i: Proceedings of the 24th Symposium of the International Association for Vehicle System Dynamics (IAVSD 2015), Graz, Austria, 17-21 August 2015. - : CRC Press. - 9781138028852 - 9781498777025 ; , s. 871-878
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Konferensbidrag (refereegranskat)abstract
- Simulation of wheel and rail wear allows to predict long term profile evolution and thus, study the consequences of wheel damage in the dynamic behaviour of the vehicle, or study future maintenance requirements. Several models have been developed which try to solve the wear issue by relating the energy dissipated in the wheel-rail contact to the worn out material, from which two can be highlighted (Tg/A and Archard) which have significant differences on contact level. Even though, the prediction of long term wheel profile evolution has been validated with these two models, which means that for regular applications they seem to have an equivalent behaviour. In this work similarities and differences between the long term wear prediction methodologies are analysed, discussing their actual limitations. Then, these differences are exploited in specific operational cases to compare their wear prediction performance.
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| 9. |
- Gåård, Anders, 1977-, et al.
(författare)
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Nano-scale friction of multi-phase powder metallurgy tool steels
- 2015
-
Ingår i: Advanced Materials Research. - : Trans Tech Publications. - 1022-6680 .- 1662-8985. ; 1119, s. 70-74
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Tidskriftsartikel (refereegranskat)abstract
- Friction is a fundamental phenomenon in tribology involving complex mechanisms between thecontacting surfaces. Measurements of friction are often made using devices with substantially largercontact area than dimensions corresponding to microstructural features of the materials. Hence, for multi-phase materials,influence of particular microstructural constituents is not resolved. In the present work, a tribometerwith a contact area in the nano-scale range was used to map friction for different types of tool steelswith different chemical- and phase composition. Owing to the small tip radius, frictionalcharacteristics of primary carbides and the steel matrix were measured and compared. Dependingon chemical composition, a difference was observed where the coefficient of friction wasapproximately twice higher for the steel possessing highest coefficient of friction, including bothcarbides and the steel matrix.
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| 10. |
- Larsson, Joakim, 1989-, et al.
(författare)
-
The effect of bearing length on the surface quality of drawn wire
- 2019
-
Konferensbidrag (refereegranskat)abstract
- In wire drawing, the geometry of drawing dies influences the performance of the wire process. This study investigates the effect of bearing lengths on the surface quality of the drawn wire. Wire drawing tests were done using an industrial wiredrawing machine utilizing drawing dies with different bearing lengths. The influence of bearing length on surface quality is discussed.
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| 11. |
- Almeida, Diogo, 1991-, et al.
(författare)
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Dexterous manipulation with compliant grasps and external contacts
- 2017
-
Ingår i: IEEE International Conference on Intelligent Robots and Systems. - : IEEE. - 2153-0858 .- 2153-0866. ; 2017-September, s. 1913-1920
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Konferensbidrag (refereegranskat)abstract
- We propose a method that allows for dexterous manipulation of an object by exploiting contact with an external surface. The technique requires a compliant grasp, enabling the motion of the object in the robot hand while allowing for significant contact forces to be present on the external surface. We show that under this type of grasp it is possible to estimate and control the pose of the object with respect to the surface, leveraging the trade-off between force control and manipulative dexterity. The method is independent of the object geometry, relying only on the assumptions of type of grasp and the existence of a contact with a known surface. Furthermore, by adapting the estimated grasp compliance, the method can handle unmodelled effects. The approach is demonstrated and evaluated with experiments on object pose regulation and pivoting against a rigid surface, where a mechanical spring provides the required compliance.
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| 12. |
- Tofique, Muhammad Waqas, 1986-, et al.
(författare)
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Development of the distributed dislocation dipole technique for the analysis of closure of complex fractures involving kinks and branches
- 2018
-
Ingår i: European journal of mechanics. A, Solids. - : Elsevier. - 0997-7538 .- 1873-7285. ; 69, s. 168-178
-
Tidskriftsartikel (refereegranskat)abstract
- This paper presents the development of the distributed dislocation dipole technique (DDDT) for the analysis of straight, kinked and branched cracks where parts of the cracks may close during loading. The method has been developed for plane problems. Crack cases in which closure occurs are analyzed by reformulating the Buecicner's principle, taking into account the contact stresses at the contacting portions of the crack surfaces. Stress intensity factors corresponding to opening and the in-plane sliding mode of deformation at the crack tips are computed. Several test cases involving straight, kinked and/or branched cracks where parts of the cracks undergoes crack surface closure when subjected to the outer loading are analyzed. The results obtained from the DDDT are compared to those obtained from a Finite Element Method (FEM) analysis of the same crack cases. This comparison shows that the computation of stress intensity factors for the cases involving crack surface closure are less accurate than those for fully open crack cases. However, for the cases under consideration, the stress intensity factors were still computed with a maximum difference of approximately 2 per cent compared to the FEM calculations if Jacobi polynomial expansions of at least the twelfth order were used to represent the crack surface opening and sliding displacements. In most cases under consideration, sixth order Jacobi polynomial expansions were sufficient to obtain results within that margin of deviation.
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| 13. |
- Radovan, Drazumeric, et al.
(författare)
-
Truing of diamond wheels - Geometry, kinematics and removal mechanisms
- 2018
-
Ingår i: CIRP Annals - Manufacturing Technology. - : Elsevier BV. - 1726-0604 .- 0007-8506. ; 67:1, s. 345-348
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Tidskriftsartikel (refereegranskat)abstract
- An investigation is made into traverse truing of diamond grinding wheels using various truing grit types, grit sizes and truing parameters. Geometry and kinematics of the truing contact are modeled. Specific energies are found to depend on truing-grit size but not on truing parameters, indicating little to no size effect. Removal mechanisms are analyzed via SEM examination of diamond- and truing-wheel swarf. A fundamental relationship is established relating the truing compliance number to the truing efficiency, which encompasses truing parameters and truing- and diamond-grit sizes. Recommendations are made for optimum conditions to minimize force-constrained truing time.
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| 14. |
- Söderberg, Rikard, 1963, et al.
(författare)
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An information and simulation framework for increased quality in welded components
- 2018
-
Ingår i: CIRP Annals - Manufacturing Technology. - : Elsevier BV. - 1726-0604 .- 0007-8506. ; 67:1, s. 165-168
-
Tidskriftsartikel (refereegranskat)abstract
- The recent trend toward using simulation models with real-time data as digital twins is rapidly increasing in industry. In this paper, a digital framework supporting real-time geometrical quality control of welded components, is presented. The concept is based on a structured process model for all operations included in typical welding, strategies for selective assembly, automatic adjustment of fixtures and optimization of weld sequence. The concept utilizes recently developed algorithms for fast welding simulation and in-line scanning to be used in the optimization loop of an automated welding station—a digital twin for a welding cell.
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| 15. |
- Kahlin, Magnus
(författare)
-
Fatigue Performance of Additive Manufactured Ti6Al4V in Aerospace Applications
- 2017
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Additive Manufacturing (AM) for metals includes is a group of production methodst hat use a layer-by-layer approach to directly manufacture final parts. In recent years, the production rate and material quality of additive manufactured materials have improved rapidly which has gained increased interest from the industry to use AM not only for prototyping, but for serial production. AM offers a greater design freedom, compared to conventional production methods, which allows for parts with new innovative design. This is very attractive to the aerospace industry, in which parts could be designed to have reduced weight and improved performance contributing to reduced fuel consumption, increased payload and extended flight range. There are, however, challenges yet to solve before the potential of AM could be fully utilized in aerospace applications. One of the major challenges is how to deal with the poor fatigue behaviour of AM material with rough as-built surface.The aim of this thesis is to increase the knowledge of how AM can be used for high performance industrial parts by investigating the fatigue behaviour of the titanium alloy Ti6Al4V produced with different AM processes. Foremost, the intention is to improve the understanding of how rough as-built AM surfaces in combination with AM built geometrical notches affects the fatigue properties.This was done by performing constant amplitude fatigue testing to compare different combinations of AM material produced by Electron Beam Melting(EBM) and Laser Sintering (LS) with machined or rough as-built surfaces with or without geometrical notches and Hot Isostatic Pressing (HIP) treatment. Furthermore, the material response can be different between constant amplitude and variable amplitude fatigue loading due to effects of overloads and local plastic deformations. The results from constant amplitude testing were used to predict the fatigue life for variable amplitude loading by cumulative damage approach and these predictions were then verified by experimental variable amplitude testing.The constant amplitude fatigue strength of material with rough as-built surfaces was found to be 65-75 % lower, compared to conventional wrought bar, in which HIP treatments had neglectable influence on the fatigue strength. Furthermore, the fatigue life predictions with cumulative damage calculations showed good agreement with the experimental results which indicates that a cumulative damage approach can be used, at least for a tensile dominated load sequences, to predict the fatigue behaviour of additive manufactured Ti6Al4V.
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| 16. |
- Homayoun, Mohammad-Reza, et al.
(författare)
-
Effect of Hygrothermal Ageing on Tribological Behaviour of PTFE-Based Composites
- 2018
-
Ingår i: Lubricants. - : MDPI. - 2075-4442. ; 6:4
-
Tidskriftsartikel (refereegranskat)abstract
- The present study investigates the influence of hygrothermal ageing on the tribological behaviour of polytetrafluoroethylene (PTFE) polymer composites. Three PTFE composites along with unfilled PTFE were tested in sliding contact against Inconel 625 (a Ni-based alloy) plates in both dry and water-lubricated conditions, utilising a unidirectional pin-on-disc tribometer. The tribo-tests were performed at a constant sliding speed of 0.13 m/s with a normal load of 84N providing an apparent contact pressure of 5 MPa. Hygrothermal conditioning was carried out at two different temperatures, and the water absorption evolution and kinetic parameters were estimated. Various characterisation methods were used to identify the wear mechanisms and influence of hygrothermal ageing on the degradation of the filler/matrix. The different tribological behaviour for different PTFE composites was observed within the ageing timeframe. The wear resistance of the fibre-filled samples was reduced compared to the non-aged ones over the ageing timeframe. However, the friction and wear resistance of the bronze-filled PTFE were enhanced by hygrothermal ageing.
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| 17. |
- Rodiouchkina, Maria, 1987-, et al.
(författare)
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Material Characterization and Influence of Sliding Speed and Pressure on Friction and Wear Behavior of Self-Lubricating Bearing Materials for Hydropower Applications
- 2018
-
Ingår i: Lubricants. - Basel : MDPI. - 2075-4442. ; 6:2
-
Tidskriftsartikel (refereegranskat)abstract
- Nowadays, hydropower plants are forced to have more frequent power control and the self-lubricated bearings used in the applications are one of the most critical components affected by the continuously changing operating conditions. In this study, microstructure and composition of two commercially available bearing materials (Orkot TXM Marine and Thordon ThorPlas) used in hydropower turbines were studied. In addition, the influence of sliding speed and applied pressure on the friction and wear behavior of the materials was investigated systematically for dry sliding conditions. The bearing materials were characterized using X-ray microtomography, Nuclear Magnetic Resonance (NMR) spectroscopy and Inductively Coupled Plasma–Sector Field Mass Spectrometry (ICP-SFMS) techniques. Friction and wear tests were carried out with a polymer pin sliding against a stainless steel (SS2333) plate with a linear reciprocating motion. Test conditions were: room temperature, 9–28 MPa pressure and 10–40 mm/s sliding speed ranges. Surface analysis of the polymer pins and the wear tracks were performed by optical profilometry, Scanning Electron Microscope (SEM) and Energy Dispersive Spectroscopy (EDS) techniques. Test results show that, for both materials, the coefficient of friction (COF) is decreasing at higher pressures. Surface analysis reveals higher concentrations of solid lubricants in the transfer layers formed at higher pressures, explaining the decrease in COF. Furthermore, the specific wear rate coefficients are increasing at higher sliding speeds, especially at lower pressures. Results of this study demonstrate that, under dry sliding conditions, changes in sliding speed and pressure have a significant influence on the tribological behavior of these bearing materials.
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| 18. |
- Andersson, Robin, 1986, et al.
(författare)
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Integrated analysis of dynamic vehicle-track interaction and plasticity induced damage in the presence of squat defects
- 2015
-
Ingår i: Proceedings of the 10th International International Conference on Contact Mechanics and Wear of Rail/Wheel Systems, Colorado Springs, USA, August-September 2015.
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Konferensbidrag (refereegranskat)abstract
- Despite significant efforts, the mechanisms behind the formation of squats – a form of rolling contact fatigue damage – are not fully understood. This study employs numerical simulations to investigate the propensity of squat initiation in the vicinity of small, isolated rail surface irregularities. Time domain dynamic vehicle–track interaction analysis is used to obtain wheel–rail contact stress distributions, which are mapped onto a continuum finite element model that accounts for plastic deformation of the rail material. The evaluated stress and strain fields are quantified using two RCF impact measures: accumulated effective strain and the Jiang-Sehitoglu multiaxial low cycle fatigue parameter. It is shown that the RCF impact increases with increasing size of the surface irregularity and that clustering of irregularities might strongly promote RCF. The friction coefficient is identified as a very influential parameter. Further, the effect of variations in friction along the rail is evaluated. It is shown that a short rail section of low friction results in fairly high RCF impact.
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| 19. |
- Andersson, Robin, 1986, et al.
(författare)
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Integrated analysis of dynamic vehicle–track interaction and plasticity induced damage in the presence of squat defects
- 2016
-
Ingår i: Wear. - : Elsevier BV. - 0043-1648. ; 366-367:SI, s. 139-145
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Tidskriftsartikel (refereegranskat)abstract
- Despite significant efforts, the mechanisms behind the formation of squats – a form of rolling contact fatigue (RCF) damage – are not fully understood. This study employs numerical simulations to investigate the propensity of squat initiation in the vicinity of small, isolated rail surface irregularities. Time-domain dynamic vehicle–track interaction analysis is used to obtain wheel–rail contact stress distributions, which are mapped onto a continuum finite element model that accounts for plastic deformation of the rail material. The evaluated stress and strain fields are quantified using two RCF impact measures: accumulated effective strain and the Jiang–Sehitoglu multiaxial low cycle fatigue parameter. It is shown that the RCF impact increases with increasing size of the surface irregularity and that clustering of irregularities might strongly promote RCF. The friction coefficient is identified as a very influential parameter and also the effect of variations in friction along the rail is evaluated.
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| 20. |
- Bolzon, Micheal, 1990, et al.
(författare)
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Effects of Wheel Configuration on the Flow Field and the Drag Coefficient of a Passenger Vehicle
- 2019
-
Ingår i: International Journal of Automotive Technology. - : Springer Science and Business Media LLC. - 1976-3832 .- 1229-9138. ; 20:4, s. 763-777
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Tidskriftsartikel (refereegranskat)abstract
- The effects of wheel rotation, rim coverage area, fan spokes, spoke sharpness, and tread pattern on the flow field and drag coefficient of a passenger vehicle were investigated. Force measurements and wake surveys were taken on a 1/5th scale passenger vehicle at a Reynolds number of 2.0 × 106. The wake surveys were conducted at three planes. Vorticity, total pressure coefficient, and local drag coefficient plots are presented. Wheel rotation reduced the drag coefficient of all of the wheel configurations tested, which generally agrees with literature. Wheel rotation reduced the front wheel’s jetting vortex’s drag while increasing the drag from the center of the front wheel to the upper rim track. Reducing the rim coverage area increased the drag coefficient. This increase was attributed to an increased jetting vortex drag and a change in flow separation around the front wheel. The fan spoke rim performed the worst, regardless of rotation. Rounding the spoke edges reduced the drag coefficient of a rotating wheel. The tread pattern slightly reduced the shoulder vortex vorticity and slightly increased the separation around the front wheel.
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| 21. |
- Carlberger, Andreas, 1992, et al.
(författare)
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An iterative methodology for the prediction of dynamic vehicle–track interaction and long-term periodic rail wear
- 2018
-
Ingår i: Proceedings of the Institution of Mechanical Engineers, Part F: Journal of Rail and Rapid Transit. - : SAGE Publications. - 0954-4097 .- 2041-3017. ; 232:6, s. 1718-1730
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Tidskriftsartikel (refereegranskat)abstract
- In this study, a versatile numerical method for the prediction of long-term growth of rail roughness is presented and its functionality is demonstrated for the development of rail corrugation on small radius curves. The procedure includes two sub-modules: (1) a time-domain model for the simulation of dynamic vehicle–track interaction in a wide range of frequencies by using a commercial software for multibody dynamics and (2) a post-calculation of sliding wear based on the Archard’s model in combination with a non-Hertzian and transient wheel–rail contact model. The structural flexibility of the wheelset is accounted for by using the finite element method. The rail wear generated by a large number of passing trains is assessed by recurrently updating the rail surface based on the wear depth calculated in each post- processing step. The current work sets out from a previous study in which a model for the prediction of long-term growth of rail roughness on small radius curves was developed in a general-purpose programming language. By transfer- ring the model into a commercial software, the aim is to develop an engineering tool that is more applicable for different operational conditions, such as various vehicle and track designs and track alignments. The proposed method is verified by comparing the simulation results against those obtained with the pre-existing software. Conditions similar to a 120 m radius curve on the Stockholm metro exposed to corrugation growth on the low rail are considered. The corrugation is found to be generated by the leading wheelsets. The prevailing wavelength-fixing mechanisms are identified and discussed.
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| 22. |
- Duvefelt, Kenneth, et al.
(författare)
-
Model for contact between finger and sinusoidal plane to evaluate adhesion and deformation component of friction
- 2016
-
Ingår i: Tribology International. - : Elsevier. - 0301-679X .- 1879-2464. ; 96, s. 389-394
-
Tidskriftsartikel (refereegranskat)abstract
- One of the main parameters affecting finger friction, friction-induced vibrations in the finger, and consequently tactility is surface topography. Recently Skedung et al. performed finger friction measurements on fine controlled surfaces. These surfaces were sinusoidal with wavelengths from 0.27 to 8.8 mu m and amplitudes from 0.007 to 6 mu m. Building on those tests an analytical model for the contact was developed to explain the differences in friction coefficient. The contact was modelled as trapezoids in a circular pattern pressed against a sinusoidal plane. Results showed that the calculated contact area and therefore friction coefficient corresponded well with the measurements. This model can be used to see how the different surface parameters influence friction.
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| 23. |
- Fröhling, Robert, et al.
(författare)
-
Preface: Special issue on heavy haul
- 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. 595-595
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
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| 24. |
- Kumar, Mayank, 1991-, et al.
(författare)
-
Influence of cutting fluid on reliability of threaded fastener joints
- 2019
-
Ingår i: SAE technical paper series. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International. - 0148-7191. ; :December
-
Tidskriftsartikel (refereegranskat)abstract
- This study reports on the effect of cutting fluids on friction behavior of the threaded fasteners. Underhead and thread friction are measured during tightening process of the hex-head threaded fasteners coated with different zinc-based coatings: electroplated zinc, zinc flake, and electroplated zinc nickel, commonly used in the automotive industry. The tests and data analysis are conducted considering ISO 16047 as a baseline. Test conditions are set close to the actual production conditions found in the motor vehicle industry. Water-based and ester-based cutting fluids are selected to unveil their impact on the reliability of the threaded fastener joints. It is shown that a change in the underhead interface conditions from dry to lubricated drastically reduces friction for the electroplated zinc and zinc nickel coatings.
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| 25. |
- Joshi, Abhishek, 1985
(författare)
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Electrical Characterisations of Bearings
- 2019
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Mechanical bearings are an integral part of industry, and are used in various places in order to reduce friction between two interacting surfaces and are used to transmit power and loads. Mechanical bearings are one of the most extensively used components within the wind industry, but on the other hand they are also one of the most dominantly failing failed components. In order to increase the feasibility of wind energy, and to make the wind power more sustainable, a reduction in operation and maintenance cost of wind energy is important. The failures in bearings in the wind energy sector and other industries increased after the introduction of switched power electronic switches (Insulated Gate Bipolar Transistors, or IGBT) within the power converters. The reasons of early failures have been linked to the presence of a common mode voltage at the neutral of the converter and its coupling on the shaft, where the bearings are located. The system is also vulnerable to different types of bearing currents, which are discussed in this report. A small voltage in range of 10's of volts could lead to large electric-field stress of 30 to 40 V/µm in a bearing depending on nominal film thickness at the operating point. The build-up of large electric field stresses in the bearing leads to ohmic electrical conduction through the bearing. Presently, the mitigation techniques mainly discharge the voltage across the bearing by providing a low resistance path for the flowing current using different methods, such as carbon brushes, or shaft rings, but damages due to bearing current activity and early failures still exist. Another way to mitigate bearing currents is to use filters in the electrical connections, to obstruct or to reduce the amplitude of the bearing currents, but they fail to completely eliminate them. The use of insulating coating on surfaces of the bearing and ceramic rolling elements helps to provide a high resistive path for the current in case of DC voltage, but act capacitively and let the current pass through the bearing when high frequency circulating type bearing currents flow in the system. Nevertheless, to device a successful mitigation technique, it is important to fully understand the electrical breakdown and discharge activity within the bearing’s insulation (i.e., the lubricating film) along with electrical properties of the bearing during running conditions. In our research, we have focused on understanding the electrical properties of the mechanical bearing at different operating conditions and elaborating it through an electrical circuit model. The components of this electrical circuit model are found out experimentally through different laboratory tests. The mechanical bearing is sometimes found to behave as an insulator of electricity and is hence characterizecharacterised by an impedance during the ‘Insulating state’ of the bearing in the model. The impedance in this insulating state is further categorized as a parallel combination of a resistor and a capacitor (parallel RC branch), which corresponds to the ‘real’ and ‘imaginary’ part of the measured bearing impedance. Furthermore, when the bearing enters in into a partial breakdown state, the voltage across the bearing is ‘discharged’, resulting in flow of current through the bearing until the voltage across the bearing again recovers. The Electrical electrical characterization characterisation of bearing lubricants has been performed in order to find out the relevant electrical properties, such as relative permittivity, electrical conductivity and electric breakdown strength at rather short gaps. The electrical behaviorbehaviour of the mechanical bearing at different operating conditions such as rotational speed, mechanical load along with magnitude, frequency and shape of applied voltage has been found out experimentally in order to understand and elucidate the electrical properties of a mechanical bearing in operation.
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| 26. |
- Hossein Nia, Saeed, et al.
(författare)
-
Fast Wear Calculation for Wheel Profile Optimization
- 2015
-
Ingår i: 10th International Conference on Contact Mechanics and Wear of Rail/Wheel Systems, Colorado Springs, August 30 - September 3, 2015. - : 10th Contact Mechanics Conference.
-
Konferensbidrag (refereegranskat)
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| 27. |
- Schnabel, Stephan, et al.
(författare)
-
Elastic Waves of a Single Elasto-Hydrodynamically Lubricated Contact
- 2017
-
Ingår i: Tribology letters. - : Springer. - 1023-8883 .- 1573-2711. ; 65:1
-
Tidskriftsartikel (refereegranskat)abstract
- Elastic waves are widely used for condition monitoring of rolling element bearings through vibration or acoustic emission measurements . While vibration signals are understood to a high degree due to many scientific investigations as well as a long history of usage in the field, acoustic emission signals of rolling element bearings are poorly understood. Therefore, this investigation presents simulation studies and measurements of a single elasto-hydrodynamically lubricated (EHL) contact. In this investigation the EHL contact is a ball bouncing on a lubricated plate. The simulation based on Green’s function and the measurements based on a accelerometer to some extent agree. A shift of zero frequencies towards higher frequencies when compared to Hertzian reference measurements was determined for an infinite plate setup. Taking boundary restrictions into account, elastic waves of a Hertzian contact and an EHL contact only differ by a damping of higher resonances which is most likely caused by the EHL film.
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| 28. |
- Albinsson, Anton, 1989, et al.
(författare)
-
Validation of vehicle-based tyre testing methods
- 2019
-
Ingår i: Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering. - : SAGE Publications. - 2041-2991 .- 0954-4070. ; 233:1, s. 18-27
-
Tidskriftsartikel (refereegranskat)abstract
- The development process for passenger cars is both time- and resource-consuming. Full vehicle testing is an extensive part of the development process that consumes large amount of resources, especially within the field of vehicle dynamics and active safety. By replacing physical testing with complete vehicle simulations, both the development time and cost can potentially be reduced. This requires accurate simulation models that represent the real vehicle. One major chal- lenge with full vehicle simulation models is the representation of tyres in terms of force and moment generation. The force and moment generation of the tyres is affected by both operating conditions and road surface. Vehicle-based tyre testing offers a fast and efficient way to rescale force and moment tyre models to different road surfaces, in this study the Pacejka 2002 model. The resulting tyre model is sensitive to both the operating conditions during testing and the road surface used. This study investigates the influence of the slip angle sweep rate and road surface on the lateral tyre force characteristics of the fitted tyre model. Tyre models fitted to different manoeuvres are compared and the influence on the full vehicle behaviour is investigated in IPG Carmaker. The results show that by using the wrong road surface, the resulting tyre model can end up outside the tolerances specified by the ISO standard for vehicle simulation model verifi- cation in steady-state cornering. The use of Pacejka 2002 models parameterized in a steady-state manoeuvre to simulate the vehicle behaviour in sine-with-dwell manoeuvres is also discussed.
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| 29. |
- Bergseth, Ellen, 1979-, et al.
(författare)
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A Wear Detection Parameter for the Wheel–Rail Contact Based on Emitted Noise
- 2019
-
Ingår i: Tribology Transactions. - : Informa UK Limited. - 1040-2004 .- 1547-397X. ; 62:3, s. 496-503
-
Tidskriftsartikel (refereegranskat)abstract
- This article describes how a wheel–rail wear detection parameter based on noise was developed by running a rapid transit train instrumented with microphones in a depot with a small curve radius. This full-scale test made use of previous knowledge gained from lab-scale tests. The lab- and full-scale tests showed that noise could be used as an indicator of wear transition, when normal wear turns into severe or catastrophic wear. This transition was accompanied by a significant increase in sound pressure and a broader sound pressure amplitude spectrum; that is, a narrow initial amplitude distribution in the normal wear regime and a broader distribution in the severe wear regime. The measured noise from the inner/low and outer/high rails was analyzed in conjunction with the wear from the outer wheel and comparisons were made between cleaned (exposed to severe wear) and lubricated (no wear) rail. Based on those analyses, a wear detection parameter criterion was developed for this specific train. This wear parameter has been implemented in a real-time condition monitoring system so that warnings of the risk for severe wear could be sent to the maintenance department. Validation of the wear parameter and challenges linked to open system conditions are discussed in this article.
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| 30. |
- Dugic, Izudin, 1962-, et al.
(författare)
-
Non-metallic inclusion and their effect on fatigue strength for case-hardened carbon steel in gears
- 2018
-
Ingår i: TMS 2018 147th Annual Meeting & Exhibition Supplemental Proceedings. TMS 2018. - Cham : Springer. - 9783319725253 ; , s. 123-133
-
Konferensbidrag (refereegranskat)abstract
- Steel is a very essential structural material and its production worldwide has shown significant increase over the last years. In steels there always exist a large number of inclusions which can have a degrading effect on the fatigue properties. This study is focused on the link between the characteristics of non-metallic inclusions and how they affect fatigue strength of the standardized case-hardened carbon steel 20MnCr5 and a version of this steel with a more favorable inclusion distribution, a so-called Clean steel. For the evaluation of the mechanical properties the test result from rotary bending tests are compared and an improvement by 37.5% in fatigue strength can be noted between the different steels. The new performed ultrasonic tests illustrate the difference in the size of defects in materials with different manufacturing processes and degree of reduction. By studying international and European standards for non-destructive testing and investigation of alloy compounds, the current material specification can be adjusted. © The Minerals, Metals & Materials Society 2018.
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| 31. |
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| 32. |
- Minovski, Blago, 1986, et al.
(författare)
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A numerical investigation of thermal engine encapsulation concept for a passenger vehicle and its effect on fuel consumption
- 2019
-
Ingår i: Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering. - : SAGE Publications. - 2041-2991 .- 0954-4070. ; 233:3, s. 557-571
-
Tidskriftsartikel (refereegranskat)abstract
- Increasingly tough regulations for emission levels and a growing demand for an environmentally clean motor industry impose high requirements in modern automotive development. During recent decades, carmakers have been utilizing various strategies to minimize energy losses in the powertrain to meet legislative and market demands. A great part of research efforts has been focused on improving engine performance during cold starts characterized by increased friction losses. Thermal engine encapsulation is an effective design choice to reduce engine friction in applications with frequent cold starts. In the present work, a coupled 1-D–3-D system-level approach is used to investigate the effects of a novel engine-mounted encapsulation concept featuring air shutters on fuel consumption in a Volvo S80 passenger vehicle. Simulations are performed for sequences of the Worldwide harmonized light vehicles test cycle (WLTC) drive cycle, which include different time intervals of engine inactivity when the car is parked in air of an quiescent ambient temperature. The results show that engine encapsulation with high area coverage (97%) can retain engine oil temperature above 19°C for up to 16 h after engine shutdown at an ambient temperature of 5°C, leading to 2.5% fuel saving during engine warm-up when cold starts occur between 2 and 8 h after key-off. Encapsulations with a lower area coverage (90%) have proven to be less effective, with fuel saving of 1.25% as the temperatures of the oil and engine structures decrease more quickly after key-off compared to the fully enclosed encapsulation.
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| 33. |
- Nyberg, Erik, 1986-, et al.
(författare)
-
Formation of Boundary Film from Ionic Liquids Enhanced by Additives
- 2017
-
Ingår i: Applied Sciences. - Basel : MDPI. - 2076-3417. ; 7:5
-
Tidskriftsartikel (refereegranskat)abstract
- Room temperature ionic liquids (RTILs) have several properties that make them interesting candidates as base fluids for extreme conditions. However, a lack of compatibility with tribo-improving additives combined with an often overly aggressive nature is limiting their use as base fluids. To overcome these drawbacks, hydrocarbon-imitating RTIL base fluids have recently been developed. In this study, the effects of several common additives in the novel RTIL (P-SiSO) were examined by laboratory tribotesting. A reciprocating steel-steel ball-on-flat setup in an air atmosphere was used, where the lubricant performance was evaluated over a range of loads and temperatures. Surface analyses after testing were carried out using optical profilometry, scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDS). Neat P-SiSO displayed high performance in the tribotests. At an elevated load and temperature, a shift in lubrication mode was observed with an accompanying increase in friction and wear. Surface analysis revealed a boundary film rich in Si and O in the primary lubrication mode, while P was detected after a shift to the secondary lubrication mode. An amine additive was effective in reducing wear and friction under harsh conditions. The amine was determined to increase formation of the protective Si–O film, presumably by enhancing the anion activity.
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| 34. |
- Shahzamanian Sichani, Matin, 1986-
(författare)
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On Efficient Modelling of Wheel-Rail Contact in Vehicle Dynamics Simulation
- 2016
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The wheel-rail contact is at the core of all research related to vehicletrackinteraction. This tiny interface governs the dynamic performanceof rail vehicles through the forces it transmits and, like any high stressconcentration zone, it is subjected to serious damage phenomena. Thus,a clear understanding of the rolling contact between wheel and rail is keyto realistic vehicle dynamics simulation and damage analysis.In a multi-body dynamics simulation, the demanding contact problemshould be evaluated at about every millisecond for several wheel-rail pairs.Hence, a rigorous treatment of the contact is highly time-consuming.Simplifying assumptions are therefore made to accelerate the simulationprocess. This gives rise to a trade-o between the accuracy and computationaleciency of the contact model in use.Conventionally, Hertz+FASTSIM is used for calculation of the contactforces thanks to its low computational cost. However, the elliptic patchand pressure distribution obtained by Hertz' theory is often not realisticin wheel-rail contact. Moreover, the use of parabolic traction bound inFASTSIM causes considerable error in the tangential stress estimation.This combination leads to inaccurate damage predictions.Fast non-elliptic contact models are proposed by others to tacklethis issue while avoiding the tedious numerical procedures. The studiesconducted in the present work show that the accuracy of these models iscase-dependent.To improve the accuracy of non-elliptic patch and pressure estimation,a new method is proposed. The method is implemented in an algorithmnamed ANALYN. Comparisons show improvements in patch and, particularly,pressure estimations using ANALYN.In addition, an alternative to the widely-used FASTSIM is developed, named FaStrip. Unlike FASTSIM, it employs an elliptic traction boundand is able to estimate the non-linear characteristic of tangential stressdistribution. Comparisons show more accurate estimation of tangentialstress and slip velocity distribution as well as creep forces with FaStrip.Ultimately, an ecient non-elliptic wheel-rail contact model consistingof ANALYN and FaStrip is proposed. The reasonable computationalcost of the model enables it to be used on-line in dynamics simulationand its accuracy can improve the damage predictions.
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| 35. |
- Mallipeddi, Dinesh, 1987, et al.
(författare)
-
Effect of Running-In (Load and Speed) on Surface Characteristics of Honed Gears
- 2019
-
Ingår i: Tribology Transactions. - : Informa UK Limited. - 1040-2004 .- 1547-397X. ; 62:3, s. 412-418
-
Tidskriftsartikel (refereegranskat)abstract
- The initial running-in cycles alter the surface integrity characteristics and influence gear performance. This article shows how the surface characteristics of honed spur gears evolved due to the combined effect of running-in load (0.9 or 1.7 GPa) and speed (0.5 or 8.3 m/s) in Forschungsstelle fur Zahnräder und Getriebebau tests. Running-in affected the surface layers to a depth of 5 µm. High running-in load promoted plastic deformation of asperities, created microstructural changes associated with surface cracks, and relaxed residual stresses. It also enhanced the amount of phosphorous from extreme pressure (EP) additives at the surface. The surface contact fatigue failure—that is, micropitting—was promoted by running-in speed rather than load.
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| 36. |
- Mallipeddi, Dinesh, 1987, et al.
(författare)
-
The effect of manufacturing method and running-in load on the surface integrity of efficiency tested ground, honed and superfinished gears
- 2019
-
Ingår i: Tribology International. - : Elsevier BV. - 0301-679X .- 1879-2464. ; 131, s. 277-287
-
Tidskriftsartikel (refereegranskat)abstract
- This study compares gear surface characteristics generated by grinding, honing and superfinishing of case-hardened steel, including the evolution during efficiency testing with two different prior running-in loads (0.9 GPa and 1.7 GPa). The most influential factor was surface roughness. Micro-pitting was associated with surface asperities and hence only seen in ground and honed gears, while being absent for super-finished gears. The micro-pitting was enhanced by running-in load, but only for rough surfaces. Deformation-induced localized microstructure impact was associated with cracks. Residual stresses reached similar levels after efficiency testing. Phosphorous content in the gear surface was connected to surface roughness and running-in load.
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| 37. |
- Yeginbayeva, Irma, 1986, et al.
(författare)
-
Review and Historical Overview of Experimental Facilities Used in Hull Coating Hydrodynamic Tests
- 2019
-
Ingår i: Proceedings of the Institution of Mechanical Engineers Part M: Journal of Engineering for the Maritime Environment. - : SAGE Publications. - 2041-3084 .- 1475-0902. ; 233:4, s. 1240-1259
-
Forskningsöversikt (refereegranskat)abstract
- The prediction of hydrodynamic performance of hull coatings with different surface conditions is a challenging task. Moreover, with the emergence of new prototype coatings that are relatively smooth in terms of roughness characteristics, the accurate estimation of their drag is particularly important, as this will enable a good grading of drag reducing benefits of coatings. In the context of coating studies, the experimental methods are considered as the backbone and results obtained from experimental facilities with the required performance will enable accurate scaling of test results to full-scale ship results. Although numerical simulations like Computational Fluid Dynamics (CFD) has acquired the level of accuracy good enough to replace some of the systematic model testing used for ship design optimisation, it is still not evident if the simulations will be able to replicate the physical reality such as coating type, its roughness and biofilms accurate enough to enable predictions of the power requirements for ships. Therefore, this paper gives insight into various coating hydrodynamic testing facilities and methods that are capable of measuring drag characteristics of coatings. The work highlights the details of each method, identifies the concepts and parameters needed to describe, implement and analyse hydrodynamic coating drag measurements. The paper also summarises the merits and demerits of each type of facility based on reports and studies reported in open literature. Finally, the authors propose a recommendation that can be incorporated into the design of the new hydrodynamic facility.
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| 38. |
- Yu, Rixin, et al.
(författare)
-
Statistics conditioned to isoscalar surfaces in highly turbulent premixed reacting systems
- 2019
-
Ingår i: Computers and Fluids. - : Elsevier BV. - 0045-7930. ; 187, s. 69-82
-
Tidskriftsartikel (refereegranskat)abstract
- The paper aims at clarifying some issues associated with evaluation of surface-averaged quantities in Direct Numerical Simulation (DNS) of a turbulent reacting flow. For a quantity ϕ(t, x) averaged over an isosurface c(t,x)=c^ of a reaction progress variable c, there exist at least two different definitions of surface averages; an area-weighted surface average 〈ϕ〉 s | c^,t and an unweighted surface average 〈ϕ〉 v | c^,t . These two fine-grained averages can also be extended to coarse-grained surface averages 〈ϕ〉 S | c^,ϵ,t and 〈ϕ〉 V | c^,ϵ,t over an interval of c^≤c(t,x)≤c^+ϵ. In a highly turbulent medium, the difference 〈ϕ〉 s −〈ϕ〉 v between the area-weighted and unweighted surface averages can be significant for most quantities ϕ of basic interest. The sign of this difference depends on the sign of the correlation between ϕ and |∇c|, can be opposite for different ϕ or even for different isosurfaces of the same scalar field ϕ. For a quantity ϕ that can become singular in the zero-gradient points |∇c|(t,x)=0, its unweighted or area-weighted surface averages can still be bounded. The difference between area-weighted and unweighted surface averages of 1/|∇c| or |∇c| is relevant to explaining the well-known, but still challenging controversy between available data on the influence of turbulence on the local flame thickness.
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| 39. |
- Hoier, Philipp, 1988, et al.
(författare)
-
Flank wear characteristics of WC-Co tools when turning Alloy 718 with high-pressure coolant supply
- 2017
-
Ingår i: Journal of Manufacturing Processes. - Dearbord, Mich. : Society of Manufacturing Engineers, North American Manufacturing Research Institution. - 1526-6125 .- 2212-4616. ; 30:Supplement C, s. 116-123
-
Tidskriftsartikel (refereegranskat)abstract
- In the present study, the tool wear mechanisms of uncoated cemented tungsten carbide (WC-Co) tools during machining Alloy 718 with high-pressure coolant supply are investigated. Worn flank faces are analyzed by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX). With increasing spiral cutting length, larger areas on the tool surface are subjected to erosion of Co-binder by the coolant jet impact. Moreover, the amount and morphology of workpiece-precipitates adhered on worn flank surfaces are influenced significantly by the extent of flank wear land (due to increasing spiral cutting length). The reasons for the obtained results are addressed with respect to the underlying mechanisms. Possible implications for the tool wear behavior are discussed.
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| 40. |
- Esmaeili, Ali, 1983, et al.
(författare)
-
Thermomechanical cracking of railway wheel treads: a combined experimental and numerical approach
- 2015
-
Ingår i: Proceedings of the 10th International Conference on Contact Mechanics and Wear of Rail/Wheel Systems (CM2015). ; , s. 8-
-
Konferensbidrag (refereegranskat)abstract
- In the present study, thermal cracking of railway wheel treads is studied by full-scale brake rig tests and finite element simulations. The focus is on thermomechanical rolling contact fatigue (RCF) 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 at the Railway Technical Research Institute (RTRI) in Japan in a brake rig featuring a tread braked wheel that is in rolling contact with a railwheel. The brake rig test conditions have been simulated numerically using the finite element method. To this end, the effect of “hot bands” on the tread is accounted for as indicated by the experimental findings. Thermomechanical stresses induced by braking as well as Hertzian contact loading on the tread including tractive loads based on a partial slip assumption are considered. The mechanical response of the wheel material ER7 is obtained from a viscoplastic Chaboche material model calibrated against data from cyclic experiments with hold-time from room temperatures up to 650 °C. Finally, a strategy for prediction of fatigue life with respect to ratcheting failure is discussed.
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| 41. |
- Li, Xin, 1985, et al.
(författare)
-
Simulation of wheel–rail impact load and sleeper–ballast contact pressure in railway crossings using a Green's function approach
- 2019
-
Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 1095-8568 .- 0022-460X. ; 463
-
Tidskriftsartikel (refereegranskat)abstract
- A method for the simulation of dynamic vehicle–track interaction and evaluation of measures to improve the design of railway crossings is presented. To accurately represent the high-frequency dynamics and non-linear contact conditions of the vehicle–track system, the vertical interaction between a wheelset and the crossing is simulated in the time domain using a Green's function approach based on extensive finite element models of track and wheelset in combination with an implementation of Kalker's variational method to solve the non-Hertzian, and potentially multiple, wheel–rail contact. Both wheels of the wheelset in simultaneous contact with the crossing rail and the outer rail are considered. Rigid and flexible wheelset models are compared. The sampled contact geometry of the crossing, including the discrete irregularity between the wing rail and the crossing nose, is used to determine a three-dimensional surface geometry between each pair of adjacent rail cross-sections. A parameter study is performed to investigate the influence of crossing design on the maximum vertical wheel–rail contact force and the contact pressure generated at the sleeper–ballast interface. It is concluded that a design with a combination of increased sleeper width, softer rail pads and implementation of under sleeper pads (USP) will reduce the track stiffness gradients in the crossing panel and mitigate the risk of differential track settlement by lowering the sleeper–ballast contact pressure.
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| 42. |
- Skrypnyk, Rostyslav, 1991, et al.
(författare)
-
Metamodel for elasto-plastic wheel–rail contact with application to damage in a railway crossing
- 2018
-
Ingår i: The Dynamics of Vehicles on Roads and Tracks. ; 2, s. 705-710
-
Konferensbidrag (refereegranskat)abstract
- A cross-disciplinary and iterative simulation methodology, integrating several numerical tools, for predicting the long-term damage in rail profiles of a railway crossing is described. To reduce computational effort, two simplifications are introduced: (i) To accurately represent traffic conditions in the field, a load collective accounting for statistical distributions of worn wheel profile, vehicle speed and wheel–rail friction coefficient is generated by Latin hypercube sampling and used as input in multibody simulations (MBS) of vehicle–track dynamic interaction. (ii) Based on the output from the MBS simulations, a tuned Hertzian-based metamodel for wheel–rail normal contact accounting for elasto-plastic material behaviour is applied to calculate the contact stress and contact patch size at discretized positions along and across the crossing rail. The metamodel allows for a vast reduction of simulation time compared to the original finite element model as it is given in analytical form.
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| 43. |
- Skrypnyk, Rostyslav, 1991, et al.
(författare)
-
Prediction of plastic deformation and wear in railway crossings – Comparing the performance of two rail steel grades
- 2019
-
Ingår i: Wear. - : Elsevier BV. - 0043-1648. ; 428-429, s. 302-314
-
Tidskriftsartikel (refereegranskat)abstract
- Railway crossings are subjected to a severe load environment leading to damage and degradation of rail profiles. The damage is the result of the high magnitudes of contact pressure and slip generated in the wheel–rail contacts during each wheel transition between wing rail and crossing nose. In this paper, numerical predictions of the long-term accumulation of plastic deformation and wear are presented and compared for two rail grades used in crossings. The comparison is performed using a framework that includes simulations of dynamic vehicle–track interaction, wheel–rail contact and rail damage. A load sequence generated by means of Latin hypercube sampling, taking into account variations in worn wheel profile, vehicle speed and wheel–rail friction coefficient, is considered. A Hertzian-based metamodel for wheel–rail normal contact accounting for inelastic material response is used for the simulation of wheel–rail contact. The methodology is demonstrated by calculating the plastic deformation for one cross-section of the crossing nose using an Ohno-Wang cyclic plasticity model, while wear is predicted by means of the Archard model for sliding wear. For the studied conditions and after the simulation of 41400 load cycles, representing an accumulated traffic load of 0.8 MGT, it is concluded that the fine-pearlitic rail grade R350HT experiences half of the ratchetting strain compared to the austenitic hot-rolled manganese steel Mn13. Based on a wear model calibrated for Mn13, the maximum wear of the studied cross-section is about 2% of the maximum plastic deformation.
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| 44. |
- Skrypnyk, Rostyslav, 1991, et al.
(författare)
-
Simulation of damage in railway crossings - a comparison of rail steel grades R350HT and rolled Mn13
- 2018
-
Ingår i: Proceedings of the 11th International Conference on Contact Mechanics and Wear of Rail/wheel Systems (CM2018). - 2590-0609. - 9789461869630 ; , s. 902-907
-
Konferensbidrag (refereegranskat)abstract
- The application of a multidisciplinary methodology for the prediction of rail damage in railway crossings is demonstrated. Two rail steel grades are compared: R350HT and rolled Mn13. Based on a load sequence designed by Latin hypercube sampling considering the variation in traffic conditions, the results include the calculated plastic deformation and wear after a load collective corresponding to 0.8 MGT of traffic. The methodology has been introduced in earlier work but is here improved in terms of computational efficiency. Wheel-rail normal contact is solved using a Hertzian-based metamodel accounting for the inelastic material response. It is shown that the rolled Mn13 crossing experiences more ratchetting strain than the R350HT counterpart.
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| 45. |
- Skrypnyk, Rostyslav, 1991
(författare)
-
Towards simulation-based optimisation of materials in railway crossings
- 2018
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Railway crossings are subjected to an intense load environment caused by the rail discontinuities needed to accommodate the passage of wheel flanges in intersecting traffic directions. This gives rise to high costs associated with repair and maintenance. For given traffic conditions, several approaches can be undertaken to mitigate the material degradation and hence reduce the life cycle cost. In the present thesis, the option of selecting a more suitable crossing material is explored. To obtain a guideline for material selection, the in-track performance of different materials during the life of a crossing needs to be predicted. In this work, an existing simulation methodology is extended to improve robustness and computational efficiency. The methodology is able to account for the dynamic vehicle-track interaction, resolve the elasto-plastic wheel-rail contact, and account for the main damage mechanisms related to the running surface of a crossing. In this thesis, the methodology is updated with a metamodel for plastic wheel-rail normal contact that is introduced to meet the computational challenge of a large number of finite element simulations. The metamodel is inspired by the contact theory of Hertz, and for a given material it computes the size of the contact patch and the maximum contact pressure as a function of the normal force and the local curvatures of the bodies in contact. The model is calibrated based on finite element simulations with an elasto-plastic material model. It is shown that the metamodel can yield accurate results while accounting for the inelastic material behaviour. Furthermore, the simulation methodology is employed to compare the performance of two rail steel grades that are used in crossings: the fine-pearlitic steel R350HT and the austenitic rolled manganese steel Mn13. A representative load sequence generated by means of Latin hypercube sampling, taking into account variations in worn wheel profile, vehicle speed and wheel-rail friction coefficient, is considered. After 0.8 MGT of traffic, it is predicted that the use of rolled Mn13 will result in approximately two times larger ratchetting strain as compared to the R350HT.
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| 46. |
- Torstensson, Peter, 1981, et al.
(författare)
-
Rail corrugation growth on curves - measurements, modelling and mitigation
- 2015
-
Ingår i: Notes on Numerical Fluid Mechanics and Multidisciplinary Design. - Berlin, Heidelberg : Springer Berlin Heidelberg. - 1612-2909 .- 1860-0824. ; 126, s. 659-666
-
Tidskriftsartikel (refereegranskat)abstract
- The development of rail corrugation (so called rutting corrugation) on a 120 m radius curve on the metro of Stockholm Public Transport was studied by field measurements, laboratory measurements and numerical simulations. The corrugation develops exclusively on the (inner) low rail with wavelengths of about 5 cm and 8 cm. A time-domain model for prediction of long-term roughness growth on small radius curves is developed and validated against measured data. The wavelength-fixing mechanisms of the corrugation are bending eigenmodes of the leading wheelsets. The application of a friction modifier effectively mitigates the problem.
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| 47. |
- Walia, Mandeep Singh, 1987, et al.
(författare)
-
Temperatures and wear at railway tread braking: Field experiments and simulation
- 2018
-
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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| 48. |
- Joshi, Abhishek, 1985
(författare)
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Electrical characterization of mechanical bearings
- 2015
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Mechanical bearings are an integral part of industry, and are used in various places to reduce friction between two interacting surfaces and are used to transmit power and loads. Mechanical bearings are one of the most extensively used components within the wind industry, but on the other hand they are also one the most dominantly failed components. To increase the feasibility of wind energy, and to make the wind power more sustainable, a reduction in operation and maintenance cost of wind energy is important. The failures in bearings in wind energy sector and other industries increased after introduction of switched power electronic switches (Insulated Gate Bipolar Transistors or IGBT) within the power converters. The reasons of early failures have been linked to presence of common mode voltage at the neutral of the converter and its coupling on the shaft, where the bearings are located. The system is also vulnerable to different types of bearing currents, which are discussed in this report.Presently, the mitigation techniques mainly discharge the voltage across the bearing by providing a low resistance path for the flowing current using different methods, such as carbon brushes, shaft rings, but damages due to bearing current activity and early failures still exist. Another way to mitigate bearing currents is to use filters in the electrical connections, to obstruct or to reduce the amplitude of the bearing currents, but they fail to completely eliminate them. The use of insulating coating on surfaces of the bearing and ceramic rolling elements helps to provide high resistive path for current in case of DC voltage, but act capacitively and let the current pass through the bearing when high frequency circulating type bearing currents flow in the system. Nevertheless, to device a successful mitigation technique, it is important to fully understand the electrical breakdown and discharge activity within the bearing’s insulation (i.e., the lubricating film) along with electrical properties of bearing during running conditions.In our research, we have focused on understanding the electrical properties of the mechanical bearing at different operating conditions and elaborating it through an electrical circuit model. The components of this electrical circuit model are found out experimentally through different laboratory tests. The mechanical bearing is sometimes found to behave as an insulator of electricity and is hence characterized by an impedance during the ‘Insulating state’ of the bearing in the model. The impedance in this insulating state is further categorized as a parallel combination of resistor and a capacitor (parallel RC branch), which corresponds to the ‘real’ and ‘imaginary’ part of the measured bearing impedance. Furthermore, when the bearing enters in a partial breakdown state, the voltage across the bearing is ‘discharged’ resulting in flow of current through the bearing until the voltage across the bearing again recovers. Electrical characterization of bearing lubricants has been performed to find out the relevant electrical properties such as relative permittivity, electrical conductivity and electric breakdown strength at rather short gaps. The electrical behavior of the mechanical bearing at different operating conditions such as rotational speed, mechanical load along with magnitude, frequency and shape of applied voltage has been found out experimentally in order to understand and elucidate the electrical properties of a mechanical bearing in operation.
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| 49. |
- Aranke, Omkar, 1994-, et al.
(författare)
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Coatings for automotive gray cast iron brake discs : A review
- 2019
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Ingår i: Coatings. - : MDPI AG. - 2079-6412. ; 9:9
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Tidskriftsartikel (refereegranskat)abstract
- Gray cast iron (GCI) is a popular automotive brake disc material by virtue of its high melting point as well as excellent heat storage and damping capability. GCI is also attractive because of its good castability and machinability, combined with its cost-effectiveness. Although several lightweight alloys have been explored as alternatives in an attempt to achieve weight reduction, their widespread use has been limited by low melting point and high inherent costs. Therefore, GCI is still the preferred material for brake discs due to its robust performance. However, poor corrosion resistance and excessive wear of brake disc material during service continue to be areas of concern, with the latter leading to brake emissions in the form of dust and particulate matter that have adverse effects on human health. With the exhaust emission norms becoming increasingly stringent, it is important to address the problem of brake disc wear without compromising the braking performance of the material. Surface treatment of GCI brake discs in the form of a suitable coating represents a promising solution to this problem. This paper reviews the different coating technologies and materials that have been traditionally used and examines the prospects of some emergent thermal spray technologies, along with the industrial implications of adopting them for brake disc applications. © 2019 by the authors.
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| 50. |
- Izquierdo, Milagros, 1963-, et al.
(författare)
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Isometric Point-Circle Configurations on Surfaces from Uniform Maps
- 2016
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Ingår i: Springer Proceedings in Mathematics and Statistics. - Cham : Springer-Verlag New York. - 2194-1009. ; 159, s. 201-212, s. 201-212
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Tidskriftsartikel (refereegranskat)abstract
- We embed neighborhood geometries of graphs on surfaces as point-circle configurations. We give examples coming from regular maps on surfaces with a maximum number of automorphisms for their genus, and survey geometric realization of pentagonal geometries coming from Moore graphs. An infinite family of point-circle v4'>v4v4 configurations on p-gonal surfaces with two p-gonal morphisms is given. The image of these configurations on the sphere under the two p-gonal morphisms is also described.
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