| 1. |
- Abbasi, Saeed, 1973-
(author)
-
Towards elimination of airborne particles from rail traffic
- 2013
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Doctoral thesis (other academic/artistic)abstract
- Since the investigation of wear particles from rail transport started in the late 1910s, the high mass concentrations of these particles have prompted concern among researchers interested in air quality. However, effective action has yet to be taken because relevant knowledge is still missing. This thesis provides knowledge of airborne wear particles originating from rail transport. Some aspects of their characteristic parameters, such as size, mass concentration, number concentration, and morphology, were investigated in the field and in laboratory tests. We also discuss means to mitigate non-exhaust emissions, as well as the advantages and disadvantages of various test set-ups in the seven appended journal papers:Paper A reviews recent studies of exhaust and non-exhaust emissions from rail vehicles. The results, measurements, adverse health effects, and proposed or applied solutions presented in this literature are summarized in this paper.Paper B summarizes the results of field tests we conducted. The effects of curve negotiation and braking under different real conditions were investigated in a field test in which on-board measurements were made. The elemental composition and morphology of the particles emitted and their potential sources were also investigated.Paper C describes how a pin-on-disc machine can be used to reproduce real operating conditions during mechanical train braking in a controlled laboratory setting. The results were validated by comparing the field test results with the results of laboratory studies.Paper D presents comprehensive results of laboratory studies of airborne particles from different braking materials. A new index is introduced in this paper, which can be used as a quantitative metric for assessing airborne wear particle emission rates.Paper E describes the effects of using various friction modifiers and lubricants on the characteristics of airborne particles from wheel–rail contact under lubricated and unlubricated conditions.Paper F reports work to simulate thermoelastic instability in the cast-iron braking material. We simulated the fluctuation of the flash temperature by considering the temperature dependency of the material properties and the transformation of the contact state due to thermomechanical phenomena and wear.Paper G reviews new full- and sub-scale measurements of non-exhaust emissions from ground transport. The advantages and disadvantages of on-board measurements, pin-on-disc tests, dynamometer tests, and test rig studies are discussed in this paper.
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| 2. |
- Alemani, Mattia
(author)
-
Particle emissions from car brakes : The influence of contact conditions on the pad-to-rotor interface
- 2017
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Doctoral thesis (other academic/artistic)abstract
- Due to their adverse health effects emissions have been regulated for over three decades. Brake wear particulate matter is the most important non-exhaust source, however current knowledge is mainly limited to observational studies. This thesis aims to investigate relations between the brake system contact conditions and the related emissions on a model scale; validate the results on a component level; and understand to what extent they are significant on a full-scale.Paper A investigates the influence of nominal contact pressure on a model scale. Results show that higher pressure corresponds to higher emissionsPaper B investigates the influence of the nominal contact pressure, for different friction materials, on a model scale. A temperature threshold, responsible for a relevant emission increase, is identified.Paper C investigates particle characteristics and wear mechanisms for different nominal contact pressures, on a model scale. Results show an enhanced tribo-layer at higher pressure levels.Paper D investigates the influence of brake system conditions on emissions, on a model scale. Results show that frictional power is the most important parameter. A transition temperature independent of the contact condition is identified.Paper E investigates similarities occurring on a component scale and a model scale in terms of emissions. Results show a promising correlation, and the possibility of using a pin-on-disc tribometer for R&D activities.Paper F investigates analogies occurring on a component scale and a model scale, in terms of friction performance, fictional surface and chemical composition. Results show similar phenomena occurring for the two test stands.Paper G analyses real brake system working conditions in a urban environment defining, by means of an inertia dyno bench, the related emissions. Results reveal emission factors compliant to EURO6 and EURO2 regulations, in terms of number and mass, respectively.
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| 3. |
- Ekström, Madeleine, 1984-
(author)
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Oxidation and corrosion fatigue aspects of cast exhaust manifolds
- 2015
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Doctoral thesis (other academic/artistic)abstract
- Emission regulations for heavy-duty diesel engines are becoming increasingly restrictive to limit the environmental impacts of exhaust gases and particles. Increasing the specific power output of diesel engines would improve fuel efficiency and greatly reduce emissions, but these changes could lead to increased exhaust gas temperature, increasing demands on the exhaust manifold material. This is currently the ferritic ductile cast iron alloy SiMo51, containing about 4 wt% Si and ~1 wt% Mo, which operates close to its fatigue and oxidation resistance limits at peak temperature (750C). To ensure high durability at higher temperatures, three different approaches to improving the life of exhaust manifolds were developed in this thesis.The first approach was to modify SiMo51 by adding different combinations of Cr and Ni to improve its high-temperature strength and oxidation resistance, or by applying a thermal barrier coating (TBC) to reduce the material temperature and thereby improve fatigue life. In the second approach, new materials for engine components, e.g. austenitic ductile iron and cast stainless steel, were investigated for their high-temperature fatigue and oxidation properties. In order to identify the most suitable alloys for this application, in the third the environmental effects of the corrosive diesel exhaust gas on the fatigue life of SiMo51 were investigated.The high-temperature oxidation resistance of SiMo51 at 700 and 800C in air was found to be improved by adding Cr, whereas Ni showed adverse effects. The effects of solid-solution hardening from Ni and precipitation hardening from Cr were low at 700C, with improvements only at lower temperatures. Applying a TBC system, providing thermal protection from a ceramic topcoat and oxidation protection from a metallic bond coat, resulted in only small reductions in material temperature, but according to finite element calculations still effectively improved the fatigue life of a turbo manifold. Possible alternative materials to SiMo51 identified were austenitic cast ductile iron Ni-resistant D5S and austenitic cast stainless steel HK30, which provided high durability of exhaust manifolds up to 800 and 900C, respectively. Corrosion fatigue testing of SiMo51 at 700C in diesel exhaust gas demonstrated that the corrosive gas reduced fatigue life by 30-50% compared with air and by 60-75% compared with an inert environment. The reduced fatigue life was associated with a mechanism whereby the crack tip oxidized, followed by crack growth. Thus another potential benefit of TBC systems is that the bond coat may reduce oxidation interactions and further improve fatigue life.These results can be used for selecting materials for exhaust applications. They also reveal many new research questions for future studies. Combining the different approaches of alloy modification, new material testing and improving the performance using coatings widened the scope of how component life in exhaust manifolds can be improved. Moreover, the findings on environmental interactions on SiMo51 fatigue provide a completely new understanding of these processes in ductile irons, important knowledge when designing components exposed to corrosive environments. The novel facility developed for high-temperature corrosion fatigue testing can be useful to other researchers working in this field.
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| 4. |
- Sosa, Mario, 1986-
(author)
-
Running-in of gears - surface and efficiency transformation
- 2017
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Doctoral thesis (other academic/artistic)abstract
- With ever shorter development times and market demands on overall system performance such as efficiency, reliability and low maintenance, accurate predictive tools are necessary and gear drives prove to be no exception. All these characteristics have an impact on a process which has remained a riddle: running-in. Even though no consensus on a definition of this phenomena is readily available, this thesis examines efficiency, surface roughness and simulation through the optics of running-in.Geared transmissions are known for their formidable efficiency and their extreme reliability. However, with an ever increasing power density, the ability to accurately predict mesh losses becomes of utmost importance. The accurate quantification of bearing losses as well as efficiency of ground and superfinished gears under dip lubrication are examined with respect to running-in. Results show a considerable influence on the calculation of gear mesh losses originating from which bearing loss model is chosen. Furthermore, when a larger running-in load is used on ground gears, an increase in efficiency can be observed during working operation, while for superfinished no significant changes are found. These efficiency/frictional changes are also shown to occur in the initial cycles of the running-in phase.From a surface transformation point of view running-in is shown to be a reduction of asperity tips in case hardened ground gears, while in superfinished gears no changes were seen. These gear surface changes were measured with a novel method with a surface profilometer in-situ before, after running-in and after efficiency testing. Results also show that such changes in ground gear roughness profile occur during the very initial cycles.In order to predict running-in, a simulation method was developed. Such method utilizes a 2D surface integral method to simulate contact between rough surfaces, but requires the use of surface hardness and an accurate lower cutoff wavelength. This cutoff wavelength proved to play a pivotal role in determining an accurate contact pressure at the proper level of granularity, hence a well defined real contact area. The predicted and measured run-in surfaces are compared and are found to be in accordance with each other.
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| 5. |
- Thibblin, Anders, 1980-
(author)
-
Thermal Barrier Coatings for Diesel Engines
- 2017
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Licentiate thesis (other academic/artistic)abstract
- Reducing the heat losses in heavy-duty diesel engines is of importance for improving engine efficiency and reducing CO2 emissions. Depositing thermal barrier coatings (TBCs) onto engine components has been demonstrated to have great potential to reduce heat loss from the combustion chamber as well as from exhaust components. The overall aim of this thesis is to evaluate the thermal cycling lifetime and thermal insulation properties of TBCs for the purpose of reducing heat losses and thermal fatigue in heavy-duty diesel engines.In the thermal cycling test inside exhaust manifolds, nanostructured yttria-stabilized zirconia (YSZ) performed best, followed by YSZ with conventional microstructure and then La2Zr2O7. Forsterite and mullite could not withstand the thermal cycling conditions and displayed large cracks or spallation. Two sol-gel composite coatings displayed promising thermal cycling performance results in a furnace test under similar conditions.Thermal cycling testing of YSZ coatings having different types of microstructure, in a furnace at temperatures up to 800°C, indicated that the type of microstructure exerted a great influence. For the atmospheric plasma sprayed coatings, a segmented microstructure resulted in the longest thermal cycling lifetime. An even longer lifetime was seen for a plasma spray–physical vapour deposition (PS-PVD) coating.In situ heat flux measurements inside the combustion chamber indicated that plasma-sprayed Gd2Zr2O7 was the TBC material providing the largest heat flux reduction. This is explained by a combination of low thermal conductivity and high reflectance. The plasma-sprayed YSZ and La2Zr2O7 coatings provided very small heat flux reductions. Long-term testing indicated a running-in behaviour of YSZ and Gd2Zr2O7, with a reduction in heat flux due to the growth of microcracks in YSZ and the growth of macrocracks in Gd2Zr2O7.
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| 6. |
- Zhu, Yi, 1984-
(author)
-
Adhesion in the wheel-rail contact
- 2013
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Doctoral thesis (other academic/artistic)abstract
- To attract more customers and compete with other modes of transportation, railway transport needs to ensure safety, punctuality, high comfort, and low cost; wheel–rail adhesion, i.e., the transmitted tangential force in the longitudinal direction during driving and braking, plays an important role in all these aspects. Adhesion needs to be kept at a certain level for railway operation and maintenance. However, wheel−rail contact is an open system contact. Different contaminants can present between the wheel and rail surfaces, forming a third-body layer that affects the adhesion. Prediction of wheel–rail adhesion is important for railway operations and research into vehicle dynamics; however, this prediction is difficult because of the presence of contaminants.This thesis deals with wheel–rail adhesion from a tribological perspective. The five appended papers discuss wheel–rail adhesion in terms of dry conditions, lubricated conditions, leaf contamination, iron oxides, and environmental conditions. The research methodologies used are numerical modelling, scaled laboratory experiments, and field tests. The research objective is to understand the mechanisms of the adhesion loss phenomenon. A numerical model was developed to predict wheel–rail adhesion based on real measured 3D surfaces. Computer simulation indicates that surface topography has a larger impact on lubricated than on dry contacts. Plastic deformation in asperities is found to be very important in the model. Ball-on-disc tests indicate that water can give an extremely low adhesion coefficient on smooth surfaces, possibly due to surface oxidation. Investigation of lubricated contacts at low speed indicates that oil reduces the adhesion coefficient by carrying a normal load, while adhesion loss due to water depends on the surface topography, water temperature, and surface oxidation. A field investigation indicates that leaves reduce the friction coefficient because of the chemical reaction between leaves and bulk materials. The thickness of the surface oxide layer was found to be an essential factor determining adhesion reduction. Pin-on-disc experiments found a transition in the friction coefficient with regard to the relative humidity, due to a trade-off between the water molecule film and the hematite on the surface.
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| 7. |
- Abbasi, Saeed
(author)
-
Characterisation of airborne particles from rail traffic
- 2011
-
Licentiate thesis (other academic/artistic)abstract
- Since the investigation of wear particles in rail transport started in late-1910s, the high mass concentration of these particles has raised worries among researchers concerned with air quality. However, effective action has yet to be taken because of lack of relevant knowledge. This thesis provides applicable information for the airborne wear particles in rail transport. Some aspects of their characteristics such as diameter size, mass concentration, number concentration, and morphology of particles were investigated in field tests and laboratory tests.The effects on particle characterisations from different operational conditions in the field tests, and applying different braking materials, conducting tests in different applied loads or sliding velocities in the laboratory tests were studied. The main advantage of conducting laboratory tests was to focus on studying particles from one source. The possibility of repetition, using high sensitive instruments and conducting tests at low costs are the other advantages of laboratory studies. Paper A describes how a pin-on-disc machine was used to reproduce similar real operational conditions during mechanical braking in a train. The results were validated by comparing the field tests results with the laboratory studies. The particles morphology and size distribution were also studied.Paper B presents a summary of field tests results. The effects of curve negotiating and applying braking in different real conditions were investigated with an on-board measurement.The element composition of the particles and their potential sources were also investigated outside of the particles morphologies.Paper C presents comprehensive results from laboratory studies on airborne particles from different braking materials. The differences in the particle characteristics in similar test conditions were attributable to different material compositions and dominant wear mechanisms. A new index was introduced in this paper and is suggested to be used as a qualitative factor with regard to the airborne wear particle emission rate.Paper D is a review of the recent studies of exhaust emission and non-exhaust emission from rail vehicles. A summary of results, measurements, adverse health effects, and proposed or applied solutions are reviewed in this paper.
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| 8. |
- Cabanettes, Frédéric, 1982-
(author)
-
Cam Roller Contact : Surfaces and Tribology
- 2010
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Doctoral thesis (other academic/artistic)abstract
- The automotive industry and the design of engines are strongly ruled by performance and legislation demands. In the valve train, mechanical components such as camshafts and rollers are defined by specifications including more and more constraints concerning their ability to face wear thus prolonging lifetime.The aim of the thesis is to develop tools facilitating the choice between different manufacturing processes for wear optimization purposes of cam and roller components for IC engine valve trains. Tools are both experimental and theoretical.For the experimental part, statistical and relocated studies of wear have been performed. It is shown that measuring the very same surface before and after experiments is preferable to understand wear mechanisms of cams and rollers. A set of analysis tools for describing changes between unworn and relocated worn surfaces is developed. As results, it is found that the predominant mechanism of wear for cams and rollers is a flattening of asperities: surfaces are pressed and plastic deformations occur.In parallel, simulations have been developed to explain theoretically the wear observed. Micro and macro simulations are developed to predict the ability of a given manufacturing process to resist wear. For the microscopic simulation, a rough contact model including elasto-plastic behavior of materials is used and shows good correlations with experiments. Concerning the macroscopic simulation, a model including form deviations due to manufacturing is developed and computes oil film thicknesses and deformations. The different parameters computed by both simulations are indicators of the wear performance of different surfaces. It is shown that such simulation can rank different manufacturing processes in terms of ability to face wear.
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| 9. |
- Gåård, Anders, 1977-
(author)
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Wear mechanisms in sheet metal forming : Effects of tool microstructure, adhesion and temperature
- 2008
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Doctoral thesis (other academic/artistic)abstract
- The general trend in the car body manufacturing industry is towards low-series production and reduction of press lubricants and car weight. The limited use of lubricants, in combination with the introduction of high and ultrahigh-strength sheet materials, continuously increases the demands on the forming tools. The major cause for tool failure during the forming process is transfer and accumulation of sheet material on the tool surfaces, generally referred to as galling. The adhered material creates unstable frictional conditions and scratching of the tool/sheet interface. To provide the means of forming new generations of sheet materials, development of new tool materialswith improved galling resistance is required, which may include tailored microstructures introducing specific carbides and nitrides, coatings and improved surface finish. In the present work, the galling wear mechanisms in real forming operations have been studied and emulated at a laboratory scale by developing a test equipment. The wear mechanisms, identified in the real forming process, were distinguished into a sequence of events. At the initial stage, local adhesive wear of the sheets led to transfer of sheet material to the tool surfaces. Successive forming operations resulted in growth of the transfer layer with initiation of scratching of the sheets. Finally, scratching changed into severe adhesive wear, associated withgross macroscopic damage. The wear process was successfully repeated in the laboratory test equipment in sliding between several tool materials, ranging from cast iron and conventional ingot cast tool steels, to advanced powder metallurgy tool steel, sliding against medium and high-strength steel sheets. By use of the test equipment, selected tool materials were ranked regarding galling resistance. The controlling mechanism for galling in sheet metal forming is adhesion. The initial sheet material transfer was found to occur, preferably, to the metallic matrix of the tool steels. Hence, the carbides in the particular steels appeared less prone to adhesion as compared to the metallic matrix. Therefore, an improved galling resistance was observed for a tool steel comprising a high amount of small homogeneously distributed carbides offering a low-strength interface to the transferred sheet material.Further, atomic force microscopy showed that nanoscale adhesion was influenced by temperature, with increasing adhesion as temperature increases. A similar dependence was observed at the macroscale where increasing surface temperature led to initiation of severe adhesive wear. The results were in good agreement to the nano scale observations and temperature-induced high adhesion was suggested as a possible mechanism.
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| 10. |
- Jon, Sundh, 1978-
(author)
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On wear transitions in the wheel-rail contact
- 2009
-
Doctoral thesis (other academic/artistic)abstract
- Wear transitions in the wheel–rail contact are of increasing interest since the general trend in railway traffic is toward increased velocities and axle loads. Curving increases the risk of flanging, causing the contact to change from an almost pure rolling wheel tread–rail head contact to more of a sliding wheel flange–rail gauge contact on the high rail in curves. Under wheel flange–rail gauge contact conditions, wear transitions to severe or catastrophic wear will occur if the contact is improperly lubricated. Such a transition is the most undesirable transition in the wheel–rail contact, as it represents a very expensive operating condition for railway companies. The contact conditions responsible for this transition are very severe as regards sliding velocity and contact pressure, and thus place high demands on both the lubricant and the wheel and rail materials. The focus of this thesis is on the transitions between different wear regimes in a wheel–rail contact. Wear is discussed both in traditional tribological terms and in terms of the categories used in the railway business, namely mild, severe and catastrophic wear. Most of the work was experimental and was performed at the Royal Institute of Technology (KTH), Department of Machine Design. The effects of contact pressure, sliding velocity, and type of lubricant have been investigated, producing results that resemble those of other studies presented in the literature. The absence of research relating to the wheel flange–rail gauge contact is addressed, and it is concluded that a lubricant film must be present on rails in curves to prevent severe or catastrophic wear. The formulation of this lubricant can further increase its wear- and seizure-preventing properties. To obtain a deeper understanding of wear transitions, methods such as airborne particle measurement and electron microscopy have been used. Paper A presents the test methodology used to detect seizure and discusses the wear-reducing influence of free carbon in highly loaded contacts. Paper B presents the testing of seizure-initiating conditions for a range of environmentally adapted lubricants applied to wheel and rail materials; a transient pin-on-disc test methodology was used for the testing. Paper C presents the use of pin-on-disc methodology to study the wear-reducing effects of a wide range of lubricants. The best performing lubricant was a mineral oil containing EP and AW additives. Paper D relates wear rates and transitions to airborne particles generated by an experimentally simulated wheel–rail contact. The airborne particles generated varied in size distribution and amount with wear rate and mechanism. Paper E relates additional analysis techniques, such as FIB sectioning, ESCA analysis, airborne particle measurements, and SEM imaging of airborne wear particles, to the contact temperature.
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| 11. |
- Larsson, Tara, 1993-
(author)
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The Effects of Oxygenated Fuels on DISI Engine Particle Emissions and Efficiency : Experimental investigation of the effects of oxygenated biofuels on particle emissions and engine performance
- 2021
-
Doctoral thesis (other academic/artistic)abstract
- The transport sector is one of the main sources of greenhouse gas emissions.Replacing fossil fuels with renewable fuels can help reduce the impact oftransportation on the climate. Liquid, oxygenated biofuels show great potentialas a replacement in spark-ignited engines, as they exhibit similarcombustion behavior to gasoline, and are compatible with existing infrastructure.This thesis aims to expand the knowledge on how oxygenated fuelsaffect emissions and performance in direct-injected spark-ignited (DISI) engines.Experiments on a gasoline optimised DISI engine at low and mid loadconditions, were conducted to establish how these fuels affect engine efficiency,combustion propagation, and emissions. A thorough investigationon how the particle emissions change with different fuels was also performed.The research evaluated five different oxygenated fuels in comparison to gasoline:ethanol, methanol, n-butanol, iso-butanol, and methyl tert-butyl ether.The oxygenated fuels all increased engine efficiency, even at low loads wherethe engine was not knock limited. The most significant increase in efficiencywas observed for methanol, with up to 12% improvement in indicated thermalefficiency compared to gasoline. At low loads all oxygenated fuels decreasedthe emissions of unburned hydrocarbons, carbon monixde and nitrogenoxides. The results at mid load conditions show that fuels with lowvolatility will increase these emissions. The findings also indicate that fuelvolatility will have a more significant impact on the particle emissions levelsthan fuel oxygen content. This effect is more pronounced at lower enginespeeds and higher engine loads.This thesis work reveals great potential to use liquid, oxygenated biofuelsin DISI engines to decrease transport-associated carbon dioxide emissions.Even without engine modifications, oxygenated fuels yield improved engineefficiency compared to gasoline. Optimized injection for fuels with decreasedvolatility is needed to reduce emissions at higher engine loads.
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| 12. |
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| 13. |
- Sjöberg, Sören, 1971-
(author)
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Influence of running-in on gear efficiency
- 2014
-
Doctoral thesis (other academic/artistic)abstract
- The general trend in gear industry is an increased focus on gear transmission efficiency. This thesis focuses on the understanding of how different gear manufacturing methods – particularly the contribution of the running-in process – affect the surface characteristics and friction response, with the purpose of increasing gearbox efficiency. The thesis consists of a summary and five appended papers.The research hypothesis in paper A and paper B was that the dry elastic contact area ratio is a descriptive parameter for the contact condition. Paper A deals with the influence of manufacturing method on the initial contact conditions. The emphasis in paper B is the changes that occur during running-in and correlating these changes to design requirements. Paper C examines the influence of manganese phosphate coating and lubricants, with respect to friction and the risk of scuffing at the initial contact. Paper D examines the effect of running-in load on the friction response for different surfaces. In paper E, the question of whether the load during running-in influences the gear mesh efficiency is further expounded.The main conclusions of this thesis are that the running-in influences the gear mesh efficiency; a high running-in load enhances the gear mesh efficiency. The difference in mesh efficiency is in the range of one tenth of a per cent. Thus, the influence of running-in cannot be neglected because it is in the same order of magnitude as reported for other gear efficiency enhancements. Furthermore, the dry elastic contact area ratio presents a descriptive measure of how surface topography influences the contact, at both a global (form deviation) and local (roughness) level. The surface topography caused by the manufacturing method has a significant influence on the contact area ratio. Shaving was found to have the highest contact area ratio, and would therefore be the best choice if deviations from case hardening could be minimised. It was also confirmed that surfaces coated with manganese phosphate raise the limiting load for scuffing failure up to 13 times compared to the uncoated ground equivalent.
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| 14. |
- Sosa, Mario, 1986-
(author)
-
Running-in of gears from a surfacetransformation and efficiency point of view
- 2015
-
Licentiate thesis (other academic/artistic)abstract
- Requirements today for machines have moved beyond functionality intoefficiency and reliability, gears are no exception. The presented work focuseson the analysis of the measurement, evolution and effect of running-in on geardrives from a surface roughness and efficiency point of view. With no consen-sus on a definition or observation of running-in of gear drives, measurementsof both efficiency and surface transformation during the predefined running-inis explored. A verified methodology on how to separate form, waviness androughness is presented. Two finishing methods, namely generation groundand superfinished, are analyzed in terms of efficiency and surface characteris-tics as manufactured, after running-in and after efficiency testing in order todetermine the effects of load level during running-in.Results show that separation of form can be achieved with a carefullychosen polynomial, while waviness is more subject to how the user definesa cut-off wavelength for the surface roughness. Ground gears show distinctsmoothening in terms of surface roughness at high running-in load, and nogeneral trend for low load. This behavior is also reflected in the efficiencysince higher loads gave overall lower efficiency after running-in when com-pared to lower loads. Superfinished gears in contrast show no running-in ef-fects in terms of efficiency. Additionally, ground gears exhibit general changein friction and surface roughness during the first cycles of running-in whenanalyzing high load. Overall gains in efficiency can be obtained from running-in; however, at most speeds improvements from polishing a surface, in thiscase superfinishing, proved to lead to higher efficiency.
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| 15. |
- Strömbergsson, Daniel
(author)
-
Improving detection and diagnosis of bearing failures in wind turbine drivetrains
- 2020
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Doctoral thesis (other academic/artistic)abstract
- Wind power has in the last 20 years grown into one of the main sources of renewable energy in the world, with both the amount and size of the turbines increasing substantially. One of the major challenges for the wind power industry is the premature failures of especially the drivetrain components. These failures cause a lot of turbine downtime, which increases the operation and maintenance costs of the turbines. Failures in the gearbox have been shown to lead to the highest downtime and the multitude of bearings within that subsystem is overrepresented in the total amount of component failures. Vibrationbased condition monitoring is considered the best method to find these types of defects early and avoid prolonged turbine downtime. Previous research has therefore been focused on the different aspects of condition monitoring; i.e. measurement technologies, signal analysis of vibration measurements to improve detection and diagnosis as well as the implementation of machine learning solutions. However, the majority of research work has yet to evaluate the performance of new developments using wind turbine field data, and still no fundamentally new developments have seen a large-scale implementation in the industry. Further, it is known that the positioning of the accelerometer, used to measure the vibrations, affects the ability to detect and diagnose defects. However, it is not known how to optimally position the accelerometers to monitor the individual drivetrain sub-systems. Also, previous research does not show how the influence of the measurement properties of the field data affect the ability to detect and diagnose component failures.Therefore, this thesis provides a comprehensive evaluation of how to improve the detection and diagnosis of bearing failures specifically in wind turbine drivetrains. In this thesis, a simulation model was developed to study how the accelerometer positioning affects the measurement quality. Vibration simulations of a similar sized bearing to ones found in the wind turbine drivetrain show an optimal accelerometer position as close to the primary loaded zone of the bearings as possible. The current placement of the accelerometers in the wind turbine drivetrain are often diametrically opposed to the loaded zone, and the performance of the vibration monitoring with respect to the commonly used signal analysis tools could thereby be increased. Further, wavelet-based signal analysis has been evaluated using historical wind turbine drivetrain field data. A new implementation of the wavelet packet transform to analyse enveloped vibration measurements in the frequency domain was developed, where the measurements were decomposed into packets matching the frequency resolution of the fast Fourier transform, and analysing the packet energy spectra. Finally, an anomaly detection solution utilizing an artificial neural network has been implemented to separate the condition indicator values, used for detection and diagnosis, from their inherent variance due to the dynamic turbine operation seen in the drivetrain rotational speed. The results in this thesis show the inadequacy of the commonly stored vibration measurements to the condition monitoring databases when used in post failure investigations and application of research developments on available field data. Measurements both taken over a long period of time and covering wide frequency range should be stored, instead of the either/or of today. Otherwise, the real-time monitoring of wind turbine drivetrain bearing failures cannot be replicated and monitoring improvements not fully evaluated. By implementing the wavelet packet transform, the detection and diagnosis performance was increased 250% compared to the fast Fourier transform, in an example of gearbox output shaft bearing failure. By implementing the anomaly detection by the artificial neural network, the performance increased further and was able to provide indications in a planet bearing failure case, which was not possible before. For turbine owners, these results provide both practical actions to take and provide an example of an easily implementable signal analysis tool to improve the detection and diagnosis of drivetrain bearing failures. The anomaly detection, which utilizes available historic data from healthy turbines and does not require any amount of labelled data for all considered types of bearing failures, also shows promise to detect failures in the drivetrain components which has been historically problematic. For the research community, the results mainly provides guidance into using historic field data when evaluating new developments. Also, they highlight potential pitfalls one can face using field data and what data properties to look for to successfully show the potential of your work.
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| 16. |
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| 17. |
- Zhu, Yi, 1984-
(author)
-
Adhesion in the wheel-rail contact under contaminated conditions
- 2011
-
Licentiate thesis (other academic/artistic)abstract
- Railway vehicles require a certain level of adhesion between wheel and rail to operate efficiently, reliably, and economically. Different levels of adhesion are needed depending on the vehicle running conditions. In the wheel tread–railhead contact, the dominant problem is low adhesion, as low adhesion on the railhead negatively affects railway operation: on one hand, the vehicle will lose traction resulting in delay when driving on low-adhesion tracks; on the other hand, low adhesion during deceleration will extend the braking distance, which is a safety issue. This thesis examines the influence of several contaminants, i.e., water, oil, and leaves, on the adhesion in the wheel tread–railhead contact. This study will improve our knowledge of the low-adhesion mechanism and of how various contaminants influence adhesion. The thesis consists of a summary overview of the topic and three appended papers (A–C). Papers A and B focus mainly on water and oil contamination examined using two methods, numerical simulation and lab testing. In paper A, real measured wheel and rail surfaces, low- and high-roughness surfaces, along with generated smooth surfaces are used as input to the numerical model for predicting the adhesion coefficient. Water-lubricated, oil-lubricated, and dry contacts are simulated in the model. In the research reported in paper B, scaled testing using a mini traction machine (MTM) was carried out to simulate the wheel–rail contact under lubricated conditions. Two types of disc surfaces of different roughnesses were run at different contact pressures and temperatures. A stylus machine and atomic force microscopy (AFM) were used to measure the surface topography. A study of leaf contamination on the railhead surface, based on field testing, is presented in paper C. Railhead surface samples were cut and the friction coefficient was measured on five occasions over the course of a year. Electron spectroscopy for chemical analysis (ESCA) and glow discharge optical emission spectrometry (GD-OES) were used to detect the chemical composition of the leaf-contamination layer on the railhead surface. The main conclusion of the thesis is that different contaminants reduce the adhesion coefficient in different ways. Oil reduces the adhesion coefficient by carrying the normal force due to its high viscosity. Water can reduce the adhesion coefficient to different degrees depending on the surface topography and water temperature. The mixture of an oxide layer and water contamination may have an essential impact. A leaf-formed blackish layer causes low adhesion by means of a chemical reaction between the leaves and bulk material. The thickness of the friction-reducing oxide layer predicts the friction coefficient and the extent of leaf contamination.
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| 18. |
- Östergren, Rickard, 1975-
(author)
-
Mathematical Learning Disability : Cognitive Conditions, Development and Predictions
- 2013
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Doctoral thesis (other academic/artistic)abstract
- The purpose of the present thesis was to test and contrast hypotheses about the cognitive conditions that support the development of mathematical learning disability (MLD). Following hypotheses were tested in the thesis: a) domain general deficit, the deficit is primarily located in the domain general systems such as the working memory, b) number sense deficit, the deficit is located in the innate approximate number system (ANS), c) numerosity coding deficit, the deficit is located to a exact number representation system, d) access deficit, the deficit is in the mapping between symbols and the innate number representational system (e.g., ANS), e) multiple deficit hypothesis states that MLD could be related to more than one deficit.Three studies examined the connection between cognitive abilities and arithmetic. Study one and three compared different groups of children with or without MLD (or risk of MLD). Study two investigated the connection between early number knowledge, verbal working memory and the development of arithmetic ability.The results favoring the multiple deficit hypothesis, more specifically the result indicate that number sense deficit together with working memory functions constitutes risk-factors to the development of MLD in children. A simple developmental model that is based on von Asters and Shalev´s (2007) model and the present results is suggested, in order to understand the development of MLD in children.
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| 19. |
- Bergseth, Ellen, 1979-
(author)
-
On tribological design in gear tooth contacts
- 2012
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Doctoral thesis (other academic/artistic)abstract
- The correct tribological design will have a considerable effect on a gear’s service life and efficiency. The purpose of this thesis is to clarify the impact of variation in the gear tooth flank tribological system on the gear contact load capacity – to increase the understanding of how surface topography and lubricant interact.In this thesis the variation in surface topography inherent in the manufacturing method has been shown, by experimental work and computer simulations, to be an important factor for the contact condition in the early life of gears. Surface analysis revealed that the formation and composition of surface boundary layers depends strongly on the chemical composition of the lubricant, but also on pre-existing surface boundary layers. Additionally, surface boundary layers play a major role in frictional behaviour, wear and in allowing the lubricant to react properly with the surfaces.Paper A presents the current ISO 6336 calculation of surface durability. A robust design approach was used to investigate the extent to which the current standard for calculation of surface durability allows for manufacturing variations and the choice of lubricant.Paper B investigates the extent to which a logarithmical profile modification can increase gear contact pressure robustness compared to traditional lead profiles for gears.Paper C compares different gear manufacturing methods and their as-manufactured (fresh unworn) surface topographies, using measured surface topographies as input to a contact simulation program.Paper D examines surface boundary layer formation and the corresponding wear in relation to different anti-wear additives in an environmentally adapted base oil.Papers E and F make use of specimens with surface topographies imitating two gear manufacturing methods (grinding and superfinishing) to be used in a twin-disc and barrel-on-disc machine respectively. The contacts are analysed by friction measurements and simulations combined with methods for surface analysis.
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| 20. |
- Bergstedt, Edwin, 1986-
(author)
-
A Comparative Investigation of Gear Performance BetweenWrought and Sintered Powder Metallurgical Steel : Utilizing In-situ Surface Profile Measurements to Investigate theInitiation and Evolution of Micropitting and Pitting Damage
- 2021
-
Doctoral thesis (other academic/artistic)abstract
- Vehicle electrification is a strong trend that introduces new challenges, such as increased input speed of the transmission and increased power density. Alsothe noise emittance of the gearbox is of increasing importance, as the sound of the gearbox is no longer masked by the internal combustion engine. Pressed and sintered powder metallurgical steel could be an interesting alternative towrought steel; the internal porosity has a dampening effect on the noise, and gears can be made in a fast and efficient process. However, current manufacturing of powder metallurgical steel has significant performance limitations. The Nanotechnology Enhanced Sintered Steel Processing project aims to reduce the gap in performance between conventional steel and powder metallurgical steel. One of the potential benefits is that with the inclusion of nano-powder the density can be increased. To validate the new material, its performance needs to be compared to the performance of current generation powder metallurgical materials and also to wrought steel. It is therefor crucial to be able to test and evaluate different materials and gears. This thesis has developed methods for testing, comparing, and evaluating the performance of gears. Powder metallurgical steel has been tested and compared to wrought steel; the efficiency as well as pitting life have been investigated in an FZG test rig. Also the effects of different surface finishing operations have been evaluated. The gear flanks were measured in-situ in the gearbox using a stylus instrument; an optimisation routine was created to fit the measurements to the theoretical involute profile. This enabled an in-depth analysis of surface wear and presented an opportunity to investigate micropitting initiation. It was found that the damage mechanisms of wrought steel and powder metallurgical steel are similar and related to the surface finishing method. However, the powder metallurgical steel was also susceptible to sub-surface cracks. Superfinished gears can be negatively influenced by the lack of tip relief as cracks initiate in the surface layer of the root, rapidly destroying the tooth.
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| 21. |
- Börjesson, Fredrik, 1965-
(author)
-
Approaches to Modularity in Product Architecture
- 2012
-
Licentiate thesis (other academic/artistic)abstract
- Modular product architecture is characterized by the existence of standardized interfaces between the physical building blocks. A module is a collection of technical solutions that perform a function, with interfaces selected for company-specific strategic reasons. Approaches to modularity are the structured methods by which modular product architectures are derived. The approaches include Modular Function Deployment (MFD), Design Structure Matrix (DSM), Function Structure Heuristics and many other, including hybrids. The thesis includes a survey of relevant theory and a discussion of four challenges in product architecture research, detailed in the appended papers. One common experience from project work is structured methods such as DSM or MFD often do not yield fully conclusive results. This is usually because the algorithms used to generate modules do not have enough relevant data. Thus, we ask whether it is possible to introduce new data to make the output more conclusive. A case study is used to answer this question. The analysis indicates that with additional properties to capture product geometry, and flow of matter, energy, or information, the output is more conclusive. If product development projects even have an architecture definition phase, very little time is spent actually selecting the most suitable tool. Several academic models are available, but they use incompatible criteria, and do not capture experience-based or subjective criteria we may wish to include. The research question is whether we can define selection criteria objectively using academic models and experience-based criteria. The author gathers criteria from three academic models, adds experience criteria, performs a pairwise comparison of all available criteria and applies a hierarchical cluster analysis, with subsequent interpretation. The resulting evaluation model is tested on five approaches to modularity. Several conclusions are discussed. One is that of the five approaches studied, MFD and DSM have the most complementary sets of strengths and weaknesses, and that hybrids between these two fundamental approaches would be particularly interesting. The majority of all product development tries to improve existing products. A common criticism against all structured approaches to modularity is they work best for existing products. Is this perhaps a misconception? We ask whether MFD and DSM can be used on novel product types at an early phase of product development. MFD and DSM are applied to the hybrid drive train of a Forwarder. The output of the selected approaches is compared and reconciled, indicating that conclusions about a suitable modular architecture can be derived, even when many technical solutions are unknown. Among several conclusions, one is the electronic inverter must support several operating modes that depend on high-level properties of the drive train itself (such as whether regeneration is used). A modular structure for the electronic inverter is proposed. Module generation in MFD is usually done with Hierarchical Cluster Analysis (HCA), where the results are presented in the form of a Dendrogram. Statistical software can generate a Dendrogram in a matter of seconds. For DSM, the situation is different. Most available algorithms require a fair amount of processing time. One popular algorithm, the Idicula-Gutierrez-Thebeau Algorithm (IGTA), requires a total time of a few hours for a problem of medium complexity (about 60 components). The research question is whether IGTA can be improved to execute faster, while maintaining or improving quality of output. Two algorithmic changes together reduce execution time required by a factor of seven to eight in the trials, and improve quality of output by about 15 percent.
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| 22. |
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| 23. |
- Hanson, Magnus, 1976-
(author)
-
On Adhesion and Galling in Metal Forming
- 2008
-
Doctoral thesis (other academic/artistic)abstract
- Metal forming is widely used in the industry to produce cans, tubes, car chassis, rods, wires etc. Forming certain materials such as stainless steel, aluminium and titanium, is often difficult, and problems associated with transfer of work material to the tool material are frequent. Transferred material may scratch and deform the following manufactured pieces, a phenomenon named galling. Lubricants can, to some degree, solve these problems. However, many forming oils are hazardous to the environment, and therefore it is highly desirable to replace them or get rid of them.This thesis investigates the nature of the galling phenomenon and tries to explain under which conditions such problems arise. Dry sliding tests have been performed in a dedicated load-scanner equipment. Difficult work materials have been tested against tool materials under various conditions and the samples have then been studied by advanced analytical techniques, such as ESCA and TEM, to study the detailed tribological mechanisms occurring in the contact between work and tool material.The general assumption is that material transfer only occurs when there is metal to metal contact. In this work it has been found that, for stainless steel, the oxide plays a very important role for the sticky behaviour of stainless steel, and that metal to metal contact is not a necessary condition for galling.Several PVD-coated tool materials have been tested and it was found that vanadium nitride coatings can be tuned regarding their chemical composition, to be more galling resistant than conventional coatings.The surface roughness of the tool material is very strongly coupled to the tools ability to resist galling. The smoother the tool surface, the less risk of material transfer and galling.Some work materials, like aluminium and titanium, transfer to even the smoothest tool materials. A proposed explanation for this is that their oxides are much harder than the bulk material and the tool material matrix. When deforming the work material, the oxide will fracture into small hard scales, which can indent the tool material. Indented hard scales will then contribute to material transfer of more work material to the tool.
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| 24. |
- Lius, Andreas, 1990-, et al.
(author)
-
Experimental and chemical-kinetic evaluation of a heavy-duty methanol PFI engine with direct water injection
- 2024
-
In: Fuel. - : Elsevier Ltd. - 0016-2361 .- 1873-7153. ; 359
-
Journal article (peer-reviewed)abstract
- Internal combustion engines are still widely used for propulsion in modern vehicles. Upcoming emission legislation imposes stricter limits on exhaust emissions. One method to achieve emission compliance is by using a three-way catalyst (TWC), which offers excellent emission reduction if the mixture is stoichiometric. However, stoichiometric mixtures in spark-ignited engines have the drawback of increased knock propensity. Knock can be mitigated by using water injection, which serves as both a diluent and utilizes latent heat to reduce the temperature, thereby reducing the reactivity of the unburned mixture. Methanol as a fuel has received more attention thanks to its high research octane number (RON) and its potential to contribute to decarbonization when produced as e- or bio-methanol. In the current study, Direct Water Injection (DWI) was evaluated on a Heavy-Duty (HD) single-cylinder research engine fueled by methanol. This work aims to fill a research gap on methanol-fueled engines with water injection. A direct injection system of water was chosen as it offers the freedom to inject during the closed cycle. Furthermore, a chemical kinetic study on the oxidation of stoichiometric methanol–water mixtures was conducted based on findings in the literature suggesting that, under certain conditions, water mixed with alcohol (in this case, ethanol) can reduce the ignition delay. The experimental results demonstrate that DWI effectively suppresses knock and reduced Nitrogen Oxides (NOx), albeit with deteriorated combustion efficiency. The chemical kinetic study suggested that at lower to intermediate temperatures, water acts as an efficient third-body collider, which lowers the ignition delay. However, this effect is not significant for the typical timescales encountered in HD engines.
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| 25. |
- Perricone, Guido, 1973-
(author)
-
Laboratory measurements of airborne emissions from car brakes for clean air
- 2020
-
Doctoral thesis (other academic/artistic)abstract
- Brake systems are used to safely stop vehicles. The brake pads are pressed against the brake disc, transforming the kinetic energy of the vehicle into heat to be dissipated. In this process a tribological contact causing wear takes place at the interface of the pads and disc: particles are generated, a fraction of which is airborne and therefore creates an aerosol. To meet demands on air quality and sustainable transport, significant challenges are to find means to measure particles, and provide solutions able to decrease such source of emissions.Paper A proposes a test cycle executed in an inertia brake dynamometer during which a measurement of the airborne particles is carried out: the sampling point is close to the source of emissions. The experimental results are then analysed to determine how many particles are generated per test section.Paper B presents a redesign of an inertial disc brake dynamometer with the aim to have clean air while measuring particles, and isokinetic sampling. A comparison in terms of number and size distributions of the brake emissions with and without control of the cleanness of the intake air is studied.Paper C is the ranking, from the non-exhaust brake emissions point of view, of five different current brake pair materials using the novel redesigned inertia disc brake dynamometer. Particles are both counted, collect on filters and weighed.Paper D investigates the evolution of the friction performance in terms of friction coefficient and emissions, over five repetitions of the same test procedure – so considering the running-in effect. The friction performance is discussed as a consequence of the dominating wear mechanisms.Paper E conducts a study on real driving data that are transformed into a brake dynamometer testing procedure by an energy–temperature approach. The consequent emissions study allows the calculation of brake emission factors.Paper F presents a comparison of the brake particle emissions measurement when volatile and semi-volatile organic compounds (if any), as for exhaust emissions, are thermal treated before being measured.Paper G illustrates a holistic approach, developed within the REBRAKE EU-financed project, for reducing airborne emissions for car brakes by 50% integrating different perspectives: the tribological testing of the friction pair at different scale levels, the analysis of the relevant wear products and correlated wear mechanisms, the development of specific contact mechanics simulation approaches, and the optimisation of the friction pair materials.
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| 26. |
- Sjöberg, Sören, 1971-
(author)
-
On the running-in of gears
- 2010
-
Licentiate thesis (other academic/artistic)abstract
- The general trend in gear industry, today, is an increased focus on gear transmission efficiency. Gear transmission efficiency losses arise from loaded and unloaded gear contacts, seals, lubricant and bearings. One way of minimising the losses is to lower the lubricant viscosity. This will reduce the speed dependent losses. However, the load dependent losses might increase. To avoid this, the ratio between lubricant film thickness and surface roughness must be maintained, which can be fulfilled by producing smoother gear surfaces. As a starting point for this realisation process, the present manufacturing processes, the design tools and the characteristics of the gear flank interface must be further investigated and developed. This must be achieved with an emphasis on economic production.This thesis focuses on our understanding of how different gear manufacturing methods —particularly the contribution of the running-in process—affect the surface characteristics, with the view of increasing gearbox efficiency. The thesis consists of a summary and three appended papers.Paper A and paper B discuss the relationship between design parameters and real gear wheel surfaces manufactured with different manufacturing methods. The research hypothesis was that the contact area ratio is a descriptive parameter for the contact condition. Paper A deals with the influence of manufacturing method on the initial contact conditions and also serves as a validation of the simulation program used. The emphasis in Paper B is the changes that occur during running-in, and to correlate these changes to design requirements. Paper C approaches the influences of manganese phosphate-coating and lubricants with respect to friction and the risk of scuffing at the initial contact.The main conclusions of this thesis are that the contact area ratio presents a descriptive measure of how surface topography influences the contact, seen at both a global (form deviation) and local (roughness) level. The surface topography caused by the manufacturing method has a significant influence on the contact area ratio. This is an important result, since neither national standards nor commercially available gear evaluation programs handle surface topography on the local scale. Shaving was found to have the highest contact area ratio, and should therefore be the best choice if deviations from case hardening could be minimised. It is also confirmed that gear-like surfaces coated with manganese phosphate have a low coefficient of friction, and raise the limiting load for scuffing failure enormously compared to the ground equivalent.
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| 27. |
- Tornehed, Petter
(author)
-
Particulate Emissions Associated with Diesel Engine Oil Consumption
- 2010
-
Doctoral thesis (other academic/artistic)abstract
- Particulate emissions from diesel engines have been a key issue for diesel engine developers in recent decades. Their work has succeeded in reducing the exhaust particles from the combustion of fuel, which has led to increasing interest in the contribution of particulates from lubrication oil. When discussing oil-related particulate emissions, hydrocarbon particles are customarily referred to. This thesis uses a broader definition, in which oil-related particulate emissions are modelled not only by the hydrocarbons, but also include the ash, carbons, and sulphate oil particulate emissions. The model developed in the project uses input data as oil consumption and oil ash content combined with tuning parameters, such as the oil ash transfer rate (ash emissions divided by oil consumption and oil ash content). Controlled engine tests have been performed to verify assumptions and fill knowledge gaps. The model can be applied to a variety of diesel engines, although the tuning factors might have to be reset. For example, introducing diesel particulate filters would dramatically reduce the oil ash emissions, since oil ash would accumulate in the filter. Oil consumption has played a central role in the present research. The modelling results indicate that special attention should be paid to oil consumption under running conditions with a low in-cylinder temperature, since the oil survival rate is high there. Under low-load and motoring conditions, hydrocarbons proved to be the main contributor to oil-related particulate emissions. At high engine load, oil ash emissions were the largest contributor to oil-related particulate emissions.
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| 28. |
- Tu, Minghui, 1992-
(author)
-
Measuring and Modelling PM Levels on Underground Platforms
- 2021
-
Doctoral thesis (other academic/artistic)abstract
- Urban railways have become an essential part of the transportation network of cities due to their convenience and high capacity. To make full use of urban space, many urban railway platforms are built underground. However, according to local surveys and studies, the concentration of airborne particles on underground platforms is significantly higher than that of particle concentrations aboveground. These platform particulates are often rich in heavy metal elements such as iron, copper and manganese, which may adversely affect the health of commuters riding urban railways. Therefore, the primary purpose of this research is to explore various factors that affect the airborne particle concentrations on urban underground railway platforms and then provide some suggestions for improving the air quality of the urban railway commuting environment.The papers appended are all based on the analysis of field measurements on the Stockholm urban railway platforms in Sweden between 2016 and2020 (Paper A to E). According to different research purposes, diverse statistical models have been established. By exploring the model parameter factors, it is possible to quantify the airborne particle concentrations on underground platforms. The thesis started with the qualitative trend between train movement and platform particle concentration and found that train operation and braking are closely related to the increase in platform particle concentration (Paper A). Then, by comparing linear and non-linear train frequency and particle concentration relationship models, the critical direction for studying the train frequency factor using the linear model was determined (Paper B). After that, the train frequency factor was deconstructed into two approaches. Namely, train brake effect factor, train accumulative effect factor (Paper C) and equivalent train frequency factor, train-type factor (Paper D and E). Finally,non-train-related elements were added to the train-related model as an extension (Paper E). A preliminary quantitative study of non-train-related factors was conducted.Based on the above research results, this thesis proposes three possible methods to improve the air quality of underground platforms. These consist of: replacing train types that emit higher particles with those that emit lower ones; deploying the intelligent control ventilation system; and adding night cleaning in the underground system.
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| 29. |
- Wahlström, Jens
(author)
-
A study of airborne wear particles from automotive disc brakes
- 2011
-
Doctoral thesis (other academic/artistic)abstract
- During braking, both the disc and pads in disc brakes are worn. Since disc brakes are not sealed,some of the wear particles generated can become airborne. Several studies have found anassociation between adverse health effects and the concentration of particles in the atmosphere,so it is of interest to improve our knowledge of the airborne wear particles generated by discbrakes. This thesis deals with experimental and computational methods focusing on airborne wearparticles from disc brakes. The eight appended papers discuss the possibility to both measure andnumerically determine the concentration and size distribution of airborne wear particles thatoriginate from the pad-to-disc contact. The objective is to increase the scientific knowledge ofairborne wear particles generated from disc brakes. Papers A, B and C describe tests of disc brake materials conducted in a modified pin-on-discmachine. The results show that the test set-up can be used to measure and rank disc brakematerials with respect to the concentration of airborne particles generated. Ultrafine (nanosized),fine and coarse airborne wear particles that contain metals such as iron, copper and tin werefound. Papers D and E describe a novel disc brake assembly test stand and tests of disc brake materialsconducted in it. The results show that the test set-up can be used to measure the concentrationand size distribution of airborne wear particles generated from disc brake materials. The resultsalso indicate an ability to rank different pad/disc combinations with respect to the concentrationof airborne wear particles. Furthermore, the results suggest that this test stand can be used tostudy rust layer removal from the disc and that airborne particles are generated even at low brakepressures, such as used to remove dirt from the disc. Paper F compares measurements made in passenger car field tests with measurements made in adisc brake assembly test stand and in a pin-on-disc machine. A promising correlation between thethree different test methods is found. Paper G presents and discusses a simulation methodology that numerically determines theconcentration and size distribution of airborne wear particles generated from the pad-to-disccontact in disc brakes by using general-purpose finite element software. Paper H discusses a cellular automaton model that describes the microscopic contact situationbetween the pad and disc in disc brakes. This model is used to numerically determine the amountof wear that leaves the contact. The results correlate qualitatively with experimental observationsfound in the literature.
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| 30. |
- Wahlström, Jens, 1979-
(author)
-
Towards a simulation methodology for prediction of airborne wear particles from disc brakes
- 2009
-
Licentiate thesis (other academic/artistic)abstract
- During braking, both the rotor and the pads in disc brakes are worn. Since disc brakes are not sealed, some of the wear particles generated can become airborne. Several studies have found an association between adverse health effects and the concentration of particles in the atmosphere, so it is of interest to improve our knowledge of the airborne wear particles generated by disc brakes. However, in field tests it is difficult to distinguish these particles from others in the surrounding environment, so it may be preferable to use laboratory test stands and/or simulation models to study the amount of airborne wear particles generated. This thesis deals with a simulation methodology for prediction of airborne wear particles from disc brakes and three experimental methods for testing disc brake materials with focus on airborne wear particles. The four appended papers discuss the possibility to both measure and predict the number and size distribution of airborne wear particles that originate from the pad to rotor contact. The objective is to develop a simulation methodology that predicts the number and size distribution of airborne wear particles from disc brakes. Paper A describes how a modified pin-on-disc machine was used to study airborne wear particles originating from different disc brake materials. The results indicate that the test setup can be used to measure and rank the number concentration and size distribution of the airborne wear particles generated. Paper B describes a disc brake assembly test stand for measurements of airborne wear particles from disc brakes. The results indicate that the test setup can be used to measure the number concentration and size distribution of airborne wear particles generated from disc brake materials. The results also indicate a promising ability to rank different pad/rotor material combinations with respect to the number concentration of airborne wear particles. Paper C compares measurements made in passenger car field tests with measurements made in a disc brake assembly test stand and in a pin-on-disc machine. A promising correlation between the three different test methods is found. Paper D presents a simulation methodology for predicting the number and size distribution of airborne wear particles using finite element analysis (FEA). The simulated number distribution is compared with experimental measurements at component level. The result indicates that the proposed methodology may be used to predict the number concentration and size distribution of airborne particles generated in the pad-to-rotor contact.
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| 31. |
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| 32. |
- Xinmin, Li
(author)
-
Efficiency and wear properties of spur gears made of powder metallurgy materials
- 2016
-
Doctoral thesis (other academic/artistic)abstract
- Powder metallurgy (PM) is usually used in manufacturing parts with complex geometries, such as gears and structural parts. The main attractions of PM are the high rate of material utilization, environmental friendliness of production, economic advantages (especially for complex geometries), and possibility of obtaining lighter components. To find a wide range of applications and compete with regular steel gears, PM gear transmissions should have good transmission efficiency and wear properties. Furthermore, they should have low contact noise and adequate surface fatigue properties. Because of the porosity structure of PM gears both on gear flanks and in the body, the friction and wear properties of PM gear flank contacts differ somewhat from those of regular steel gears. This doctoral thesis examines the efficiency and wear properties of PM gears. Paper A compares the wear, friction, and damage mechanism properties of two sintered gear materials with those of a standard gear material. Paper B deals with the gear mesh torque loss mechanism of PM and regular steel gears by combining both pin-on-disc frictional and FZG efficiency tests. Paper C comparatively examines the efficiency of PM and regular steel gears by conducting FZG gear efficiency tests. Paper D focuses on the wear and friction properties of PM and regular steel gear materials treated using the triboconditioning process. Paper E studies the friction and wear properties attributable to different pore sizes in PM gear materials. The results indicate that regular steel meshed with PM gear material and PM meshed with PM gear material are good candidate combinations for gear transmissions. This is because the porosities of PM material can lower the friction coefficient while the wear rate can be the same as or even better than that of regular steel contacts. The triboconditioning process enhances the wear resistance and reduces the friction coefficient of the PM gear material. The friction and wear coefficients of PM meshed with PM gear material display increasing trends with increasing pore size. The friction and wear coefficients of regular steel meshed with PM gear material display decreasing trends with increasing pore size.
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