This study evaluates the tribological properties of DIN 1.2740 hot tool steel against Super Cr13 martensitic stainless steel at 700 °C. The results show that the coefficient of friction (COF) ranged from 0.15 to 0.63, indicating moderate frictional interaction. The wear rate of DIN 1.2740 was observed to be low, suggesting good resistance to wear at high temperatures. The complex surface oxide layer that formed on the pin's top surface, significantly reducing the COF and acting as a solid lubricant at elevated temperatures. The oxide layer was also fragile and unable to withstand the high sliding velocities and high loads. The steel exhibited a high surface roughness when subjected to increasing normal loads and increasing sliding velocities.

The present study uses a pin-on-disc tribometer to evaluate friction, wear, and airborne particle emissions for a rail-wheel contact. Test pins from UIC60 900A rail carbon steels were in contact with three types of test discs surfaces: R7 wheel carbon steel, laser cladding overlayed martensitic stainless steel, and laser cladding overlayed Ni-based-8% MnS self-lubricating alloy. Test results show about halving of the coefficient of friction, 0.42 to 0.22, and one ten-power lower specific pin and disc wear of discs with self-lubricating overlay compared to standard railway carbon steel contacts. Using stainless-steel overlayed discs also resulted in one ten-power lower specific disc wear, but pin wear is unchanged. Particle emission for the tests with discs with self-lubricating overlay is constant at almost 200 particles/cm3 while running in the distance is needed for the other tests. Almost all generated airborne wear particles were in the sub-100 nm range. The use of laser-cladded (LC) overlay reduced the number of airborne wear particles in the sub-100 nm range by more than a factor of 10.

Wave energy is a huge power source that can make a significant contribution to the production of renewable energy in the future. It can generate as much as 10% of the world´s present energy consumption [1]. However, Wave Energy Converters (WECs) is a relatively new field, which requires new technology development, and testing before efficient WECs can give any significant contribution to the energy production. The main difficulties lie in the harsh marine environment and the fact that wave power is delivered with high forces and low speeds. The high forces necessitates strong and durable mechanical structures and the slow speed makes efficient energy conversion challenging. Further, there is a very large variation in wave height over time, and during storms, the largest waves can be 10-25 times higher than the average wave height at the site. The maximum forces and motions can thereby be tremendous if not handled properly, and makes the development of efficient Wave Energy Converters (WEC) challenging. The dimensioning forces strongly depend on the wave power concept, the WEC implementation and the actual Power Take-Off (PTO) system. Of the many different types of WECs being researched and developed, this paper focuses on the development of a winch based point absorber wave energy converters (WBPA-WECs). This paper presents the development of a solution for a flexible chain where an elastomeric bearing is used as a means to achieve the relative motion between the links in a chain. With this solution no sliding is present and the motion is achieved as a deformation in the elastomeric bearing. A design process is formulated for determining a suitable configuration of layers of steel shims and elastomers. A test rig for bearing tests has been developed and results from these experimental tests in combination with material tests and FE analysis are presented in the paper. These are presented in the context of illustrating the proposed design process for designing these type of laminated elastomer bearings. The different steps in this design process have been illustrated for the defined test bearing and we can conclude that our findings indicate that the proposed process can be an important support method for further development of this approach with elastomer bearings.

Reducing the environmental impact of machinery relies on all machinery components operating more efficiently. Rolling element bearings are an indispensable part of all modern machinery, enabling and facilitating machine operation. Greases, an often overlooked machine component, are an essential part of rolling bearings and have the greatest scope for improving the bearing efficiency. Thus, studying the mechanisms of friction generation and energy loss originating from the grease and all of its components in a grease-lubricated bearing is fundamental for further improving their efficiency.  This is a challenging task since only fully formulated commercial greases are often available, making it difficult to study in isolation the contribution of each individual component to the friction process. The complexity of studying grease lubrication increases further due to the intricacy of measuring friction within the bearing. Robust methodologies and standards for measuring grease efficiency within a rolling element bearing are scarce and must be developed.

This doctoral thesis investigated the effect of different grease components, such as different grease thickeners and a non-halogenated ionic liquid grease additive, on the frictional performance of rolling bearings operating under conditions typical of those encountered in electric motors. This required that a new and robust experimental set-up was designed with the purpose of continuously measuring friction torques from a rolling element for prolonged periods.  An evaluation of the role of each of the grease components in the process of friction generation thus became possible. First, the effect of the running-in procedure on the grease ageing was studied. Imposing an increasing speed profile appeared to induce a mild ageing on the greases. In the second and third studies, the effect of different thickeners on the lubrication performance during the bleeding phase was studied under steady-state conditions. Compared to lithium-complex grease, polypropylene grease reduced the energy consumption of the grease-lubricated bearing. A modified polypropylene grease, with recycled polypropylene in the thickener, was also tested. The experiments with the recycled polypropylene grease finished successfully with no traces of bearing damage and friction torque values lying between the lithium complex and polypropylene greases. This represented a milestone in the development of greases with recycled materials. In a fourth study, the effects of three different grease thickeners (lithium complex, polyurea (diurea) and polypropylene) were evaluated on lubrication performance and energy-saving potential during prolonged conditions of transient and variable speeds, typical for electric motors of battery electric vehicles. From the analysis of the resulting friction torques, it was concluded that the thickener influences the friction torque through the process of dynamic bleeding and that friction torques under both steady-state and transient speed conditions were predominantly controlled by rolling friction.  In the fifth study,  the addition of a non-halogenated ionic liquid to a LiX grease resulted in a drastic 45% reduction of energy dissipation. The feasibility and potential of using this novel grease under e-motor conditions were discussed. Finally, the overall environmental footprint (kg CO2-eq) of a grease-lubricated bearing system was estimated (production of grease and bearing together with energy consumption over a typical service life). Reducing friction torques and their corresponding energy losses through a better design of individual grease formulations appears to ensure that the greatest impact on CO2-eq released can be obtained.

The churning phase of a grease-lubricated rolling bearing significantly impacts the ageing of the grease, affecting both bearing performance and service life. The knowledge about the influence of the running-in procedure on grease ageing is limited. In this paper, we studied grease ageing in a ball-bearing running-in process with two additive-free greases made with the same base oil but different thickeners: lithium-complex and polyurea. Rheological characterization of the used greases was performed after two different 48-hour running-in speed profiles. Both procedures employed a step-wise running-in process, either increasing or decreasing speed, while maintaining the same total duration and using the same speeds. The results reveal that grease ageing in the bulk and near the raceway varies significantly depending on the speed profile used and the level of ageing induced by the speed profiles is thickener-dependent. The PU grease exhibits more severe ageing when subjected to a running-in profile with sudden high speeds (decreasing speed profile). Conversely, the LiX grease is more susceptible to ageing during a running-in profile with increasing speeds. The implications of the applicability of these speed profiles in industrial and research applications are also discussed. 

Due to their advanced tribological and electric properties, ionic liquids (ILs) are seen as potential lubricant additives in emerging green technologies. To verify their potential in complex machinery, an evaluation of tribological performance at the component and machine level is necessary. This work presents the effect of using a non-halogenated ionic liquid as a grease additive in bearings operating under driving cycle conditions. These harsh conditions are designed to be analogous to what a grease-bearing system must endure in an electric vehicle motor. One-month experiments, equivalent to 23,000 km of vehicle operation, were used to evaluate grease additive performance. Our results reveal that the addition of the ionic liquid resulted in a high-impact improvement, reducing bearing friction losses by up to 45%. Grease rheology and surface wetting measurements indicate that the sharp drop in friction torque is related to a complex balance of factors that results in a limited amount of highly effective lubricant products at the contact inlets (optimum degree of starvation).

Performance of Lithium Complex (LiX), Polyurea (PU), and Polypropylene (PP) greases in SKF6208 bearings subjected to driving cycle conditions for 28 days (equivalent to 23,000 km of electric vehicle operation) was studied by continuously measuring bearing friction torque and temperature. The energy dissipation was correlated to the differences in oil bleeding and rheology for the three greases. Evolution of the friction torque, friction torque hysteresis, and changes in grease rheology were dominated by the oil release property. The latter was determined by the thickener system and its particular response to the conditions imposed by the driving cycle. A quantitative estimate of the carbon footprint from using these greases to lubricate bearings under driving cycle conditions is also presented.

In our previous publication, we showed that grease thickened with polypropylene could be a potential contributor to electric motor efficiency by reducing the bearing energy consumption by 22% in comparison to the most common type of grease: lithium grease.  

This work studies the feasibility of using polypropylene grease, with recycled polymer material as part of its thickener, in rolling element bearings operating under conditions typical of an electric motor. The frictional performance of a bearing lubricated with the recycled polymer grease was evaluated in deep groove ball bearings operating for 385-hour experiments under a wide range of speeds (up to 10,000 rpm). Friction torque results were complemented with rheological tests of the greases before and after the tests. The recycled polypropylene grease denoted significant rheological changes after the bearing tests. Such rheological changes were reflected in the higher energy dissipation in comparison to a reference polypropylene grease. However, the grease with recycled polypropylene led to a lower energy dissipation than a reference lithium complex grease. This represents a milestone in the development of greases with recycled materials in the grease thickener and shows the potential of using this grease in a real application. 

According to the European Council, 75% of the greenhouse emissions are caused by energy production and use. In order to decarbonize the energy sector, more research is focused towards the renewable energy sources. Among the many available resources, wave energy is one of the key resources to consider. As part of the research, KTH is developing a winch based point absorber wave energy converter. The winch consists of a chain link with elastomer bearings wound around a drum. The winding and unwinding motion of chain converts wave motion into electricity. A typical winch based wave energy converter undergoes around 80 million cycles in its lifetime. This calls for a durable system design requiring minimal service and maintenance. With an elastomer bearing, the winding and unwinding of the chain over the drum is realized as deformation of the elastomer thereby eliminating sliding. While the use of elastomer enables an efficient design, it also makes it more challenging due to its highly non-linear and viscoelastic behavior. A constitutive model is necessary to determine material characteristics of an elastomer for different loading conditions. In this work, a systematic design process is outlined and an attempt is made to determine a suitable hyperelastic material model for the elastomer. The study is focused on two materials - silicone and polyurethane. The test samples are compressed and followed by shear in deformation. For material model determination, the test data is curve fit and later verified using finite element method. The material is assumed incompressible.

With a rapid shift in our society to e-mobility, novel grease formulations for machine efficiency, reliability, and availability are even more important than ever. Greases are expected to provide low friction and noise while extending the machine service life. Whether the grease should be electrically conductive or not remains a subject of debate. The chapter discusses grease architecture and how to tune it in view of the latest and upcoming specification requirements. Selection strategies for base oils, thickeners, and additives are discussed. Integrating these components in the final formulation is a delicate process of balancing required properties that can be contradictory. Grease testing methods are addressed reflecting the need for complementary characterization of grease energy efficiency, conductivity, and protection against fretting. The arguments are made in connection to the representative transmission components.

The paper shows how grease thickener polarity affects performance of the typical powertrain components: gears and rolling element bearings. Greases based on a non-polar polypropylene thickener reduce friction losses (more than 20%) in high-speed deep groove ball bearings and provide a longer service life (more than 2 times) in highly loaded bevel gears, compared to the greases based on polar lithium thickeners. The electrification and sustainability trends have led to additional requirements to be addresses during grease design process: tunable electric conductivity and reduced environment footprint. The grease design challenges caused by the novel requirements and potential solutions are discussed.

A series of 19 ionic liquids (ILs) based on phosphonium and imidazolium cations of varying alkyl-chain lengths with the orthoborate anions bis(oxalato)borate [BOB]−, bis(mandelato)borate, [BMB]− and bis(salicylato)borate, [BScB]−, are synthesized and studied using small-angle neutron scattering (SANS). All measured systems display nanostructuring, with 1-methyl-3-n-alkyl imidazolium-orthoborates forming clearly bicontinuous L3 spongelike phases when the alkyl chains are longer than C6 (hexyl). L3 phases are fitted using the Teubner and Strey model, and diffusely-nanostructured systems are primarily fitted using the Ornstein-Zernicke correlation length model. Strongly-nanostructured systems have a strong dependence on the cation, with molecular architecture variation explored to determine the driving forces for self-assembly. The ability to form well-defined complex phases is effectively extinguished in several ways: methylation of the most acidic imidazolium ring proton, replacing the imidazolium 3-methyl group with a longer hydrocarbon chain, substitution of [BOB]− by [BMB]−, or exchanging the imidazolium for phosphonium systems, irrespective of phosphonium architecture. The results suggest there is only a small window of opportunity, in terms of molecular amphiphilicity and cation:anion volume matching, for the formation of stable extensive bicontinuous domains in pure bulk orthoborate-based ILs. Particularly important for self-assembly processes appear to be the ability to form H-bonding networks, which offer additional versatility in imidazolium systems.

Commercial (protiated) samples of the "green" and biodegradable bioester 2-ethylhexyl laurate (2-EHL) were mixed with D-2-EHL synthesized by hydrothermal deuteration, with the mixtures demonstrating bulk structuring in small-angle neutron scattering measurements. Analysis in a polymer scattering framework yielded a radius of gyration (R (g)) of 6.5 angstrom and a Kuhn length (alternatively described as the persistence length or average segment length) of 11.2 angstrom. Samples of 2-EHL dispersed in acetonitrile formed self-assembled structures exceeding the molecular dimensions of the 2-EHL, with a mean aggregation number (N-agg) of 3.5 +/- 0.2 molecules across the tested concentrations. We therefore present structural evidence that this ester can function as a nonionic (co)-surfactant. The available surfactant-like conformations appear to enable performance beyond the low calculated hydrophilic-lipophilic balance value of 2.9. Overall, our data offer an explanation for 2-EHL's interfacial adsorption properties via self-assembly, resulting in strong emolliency and lubricity for this sustainable ester-based bio-oil.

Modern gearing applications, in particular electrification, impose new challenges in many different fields of engineering and research. In specific, new demands are imposed on gears, including higher rotational speed, lower noise acceptance, and increased efficiency, as well as increased resistance against pitting and scuffing. To meet these demands, a better understanding of gear contacts is needed. The Eurostars project Effigears proposes a novel multi-perspective methodology for assessment of gear efficiency and contact analysis. The methodology consists of using a novel surface treatment method, Triboconditioning (R), implemented in a streamfinishing process, surface measurements using a scattered light method, experimental testing using the standardized FZG test rig, and contact simulations using a novel thermal elasto-hydrodynamic lubrication tool. It is found, in preliminary tests, that enhanced gear performance may be enhanced due to Triboconditioning (R) surface treat-ment. Findings also include better understanding of how surface characteristics and lubricants affect scuffing and pitting, and the effect of load distribution on gearset behavior.

Non-exhaust sources, such as brakes, tyres, roads, and clutches, emit a large portion of airborne particles in road transportation, from ultrafine to coarse sizes. While airborne wear particle emissions from brakes and road-tyre contacts have been studied extensively, emissions from clutches have been overlooked. A preliminary study using a novel test rig has indicated that dry clutches also emit airborne wear particles. This paper presents a multi-method for the assessment of ultrafine particles from dry clutches regarding the number concentration, size distribution and chemical composition. The results show that ultrafine particles are emitted both during run-in and at the steady state, featuring a bi-modal size distribution. Elementary analysis shows that the particles consist of several elements, predominately iron, silicon, and sulfur. It can be concluded from this study that ultrafine particles are always generated when the clutch is operated. Clutches in automobiles are shown to produce ultrafine particles, consisting of several metallic elements, which become airborne.

Polyamide 66 (PA66) is one of the commonly used polymer gear materials. This paper focuses on the tribological properties of glass fiber reinforced PA66 composites in self-mated contact using a pin-on-disc tribometer. The effects of glass fiber content, PV (the product of the contact pressure and sliding speed), and lubrication on the tribological properties of the specimens are also investigated. The results show that the glass fiber reinforced PA66 exhibit higher coefficients of friction and specific wear rates than PA66 under dry sliding conditions. This is probably due to the peeled glass fibers during the sliding process acting as abrasive particles which have an aggressive effect on the surface. Under grease lubricated conditions, PA66 + 33% GF has the lowest coefficient of friction and specific wear rate due to its higher strength. Under dry sliding conditions, all specimens show the highest friction coefficient and specific wear rate at 30 MPa<middle dot>m/s with the change of PV value. Under grease lubricated conditions, all specimens show the highest friction coefficient and specific wear rate at 4 MPa<middle dot>m/s with the change of PV value. The addition of grease improves friction and wear of PA66 composites under most of the experimental conditions. However, the specific wear rates of PA66 and PA66 + 13% GF under grease lubrication are higher than those under dry sliding conditions at low PV values. This may be due to the fact that greases can reduce the surface mechanical strength of PA66 and PA66 + 13% GF.

Polyoxymethylene (POM) is now widely used as a gear material due to its excellent mechanical properties. There have been several studies on the tribology of POM; however, most of them focused solely on the material itself without integrating practical applications. This study investigates the tribological properties of POM-POM combinations in conjunction with the application of POM gears. Using a pin-on-disk machine, we simulate the sliding part of gear meshing. The influences of contact pressures (40 and 50 MPa), sliding speed (0.1 and 0.5 m/s), and lubrication on the tribological performance of POM pin sliding against POM disk were studied. The results showed that grease can reduce adhesion between sliding surfaces and effectively improve the tribological performance of the POM-POM combination. The friction coefficient decreases with increasing contact pressure, which is consistent with the existing models of the frictional behavior of polymer-polymer systems. The wear coefficient exhibits contrasting relationships with increasing contact pressure at high and low velocities. Because the wear mechanism changes from predominantly abrasion at low velocity to adhesion-peeling off at high velocity. Both the friction and wear coefficients decrease with increasing sliding velocity. The specific mechanisms of the influence of different lubrication conditions, pressures, velocities, and PV values on friction and wear are described and discussed throughout this article.

Tooth surface material loss caused by gear wear alters the surface morphology of gears, which impacts their vibration, noise, and remaining lifespan. Although gear wear modeling and prediction have been extensively studied, this paper proposes a novel approach based on the theorem of degradation entropy generation (DEG). A point-by-point calculation method is introduced to determine the degradation coefficient for each measurement point on the tooth profile, accounting for varying working conditions along the tooth profile during the actual meshing process of the gear pair. First, the FZG gear's bearing capacity is tested. Next, a surface roughness profilometer is employed to in-situ measure the tooth profile after each load stage. The profile deviation curve and the amount of profile wear following each load stage are obtained by processing the measured profile morphology data. Then, the pitting safety factor for each point on the tooth surface is calculated according to the ISO 6336–22:2018 standard and used to correct the degradation coefficient for that point. Finally, the entropy generation of the system during each load stage of the FZG gear is calculated. The degradation coefficient suggested in the DEG theorem is employed to link gear wear with system entropy generation, realizing gear wear modeling and prediction. The results demonstrate that the gear wear calculation method based on the DEG theorem can accurately predict the evolution of tooth profile surface morphology during the experimental process. This research provides a unified calculation method for surface morphology evolution caused by gear wear during service.

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.

Methanol as a fuel is gaining popularity due to its favorable properties and potential for sustainable production as bio- or electro-methanol. By operating according to the Spark-Ignited (SI) principle with a Three-Way Catalyst (TWC), low emissions can be achieved. The main phenomena limiting the efficiency of the SI engine when operating with stoichiometric mixtures are knock and, occasionally, pre-ignition. One method to suppress both knock and pre-ignition is water injection. This study explores the possibility of suppressing knock in-cycle using direct water injection for cycles with an elevated risk of knocking. The prediction was based on the observation that, at knock-limited operation, only cycles with the most advanced combustion phasing knock. Furthermore, at knock-limited loads, combustion predominantly consisted of a single combustion mode: deflagration. The results demonstrated partial knock suppression and allowed for a combustion phasing advancement of 1.5°at loads of 10 and 15 bar gross indicated mean effective pressure. The earliest practical point during the combustion cycle to confidently determine if knock will occur was when about 10%–20% of the fuel had been consumed. However, theoretically, in a best-case scenario, this could be as early as when 5% of the fuel was consumed. An experiment simulating pre-ignition also demonstrated the ability to detect such cycles and partially suppress the ensuing knock. A major limitation of the method is that the window between detecting a cycle with a high likelihood of knock and knock onset was less than 7°at 1000 rpm.

The investigation in this article focuses on the rolling resistance torque and thermal inlet shear factor in tapered roller bearings (TRBs) through systematic experiments using a modular test setup. TRBs typically operate under Elastohydrodynamic Lubrication (EHL) conditions. At sufficiently high speeds, the majority of rolling friction is due to a significant shift of the pressure centre in the EHL contact. While at lower speeds, sliding friction in the roller-rib contact becomes dominant, which operates under mixed lubrication conditions. Limited literature exists on the impact of inlet shear heating on effective lubricant temperature ((Formula presented.)) and rolling friction in TRBs. To fill this gap, experimental measurements of the total frictional torque under axial loading at different speeds and oil temperatures are performed. With existing models for different friction contributions described in the literature, the rolling resistance due to EHL has been determined for various operating conditions. The effects of dimension-less speed (U), material (G), and load (W) parameters have also been investigated. Under fully flooded conditions, it was observed that the influence of material (G) and load (W) parameters on rolling friction is minor, while the impact of velocity (U) is significant. In the context of rolling resistance, the heating due to shear of the lubricant in the inlet zone plays a significant role. For higher rotational velocities, the estimated rotational torque reduction resulting from inlet shear heating was found to be approximately 6–8%.

Road, rail, air, and sea transport generate a major fraction of outdoor ultrafine particles. However, there is no common methodology for comparable sub 100 nm particle emissions measurement. This paper presents the nPETS (grant agreement No 954377) concept to understand and mitigate the effects of emerging non-regulated nanoparticle emissions. This paper presents the concept and selected results. For example, nucleation and condensation mechanisms occur more frequently in the urban background site, leading to new particle formation, while mostly fresh emissions are measured in the traffic site.

The use of studded tires can cause significant wear of road surfaces then also affect the air quality in urban areas. The studs of today's studded tires are manufactured from hard metal containing cobalt. In this study, we investigated using alternative cobalt-free hard metal studs to reduce particulate emissions in the future. The tire-to-road interface is subjected to both impact wear and sliding abrasive wear. The alternative hard metal studs were evaluated in parallel with standard studs using two different laboratory test rigs specially designed for wear and particulate emission testing. Stone materials commonly used in the road tarmacadam were utilized as counter material. The results showed that the cobalt-free studs generated lower particle concentrations and less road wear.

Pendlares luftkvalitet kan variera, beroende på om man reser med tex. tunnelbana, buss, båt, eller om man som alternativ cyklar eller promenerar. Denna rapport presenterar luftkvalitetsmätningar för pendlare i Stockholm. PM10, PM2.5 och sot (BC) har mätts i passagerarutrymmen i tunnelbanevagnar, bussar och båtar, samt vid cykling och vid promenader. Dessa mätresultat jämfördes med halterna som uppmättes när man väntade på hållplatser, och också med den urbana bakgrundsnivån i Stockholm.

Mätresultaten från denna studie visar att pendlare som reser med båt eller buss har en luftkvalitet (timmedelvärde) som understiger WHO:s rekommenderade dygnsmedelvärden för PM2.5- och PM10-halter. Vid resa i tunnelbanevagn, så överskreds WHO:s medelvärden när tågen trafikerade spårtunnlar. För äldre otäta tunnelbanevagnar uppmättes de högsta PM2.5 och PM10-halterna i denna studie. Även de uppmätta sot-halterna var de högsta vid resa i de äldre otäta tunnelbanevagnarna. Vid promenad och cykling uppmättes PM2.5-, PM10- och sot-halter som var i paritet de som uppmättes för bussresenärer. Resultaten visade också på små skillnader i luftkvalitet på var i passagerarutrymmena man placerade sig vid resan.

Road traffic is an important source of urban air pollutants. Due to increasingly strict controls of exhaust emissions from road traffic, their contribution to the total emissions has strongly decreased over time in high-income countries. In contrast, non-exhaust emissions from road vehicles are not yet legislated and now make up the major proportion of road traffic emissions in many countries. Brake wear, which occurs due to friction between brake linings and their rotating counterpart, is one of the main non-exhaust sources contributing to particle emissions. Since the focus of brake wear emission has largely been on particulate pollutants, little is currently known about gaseous emissions such as volatile organic compounds from braking and their fate in the atmosphere. This study investigates the oxidative ageing of gaseous brake wear emissions generated with a pin-on-disc tribometer, using an oxidation flow reactor. The results demonstrate, for the first time, that the photooxidation of gaseous brake wear emissions can lead to formation of secondary particulate matter, which could amplify the environmental impact of brake wear emissions.

As rail projects become increasingly complex, a Systems Engineering approach - widely used in various technical disciplines - can be effectively applied. This scoping review evaluates the application and current state of the art for Systems Engineering (SE) in complex rail projects and focuses on Technical Management and Technical Processes as per ISO 15288 standards. The review highlights the rationale and challenges of SE in managing the processes in ISO 15288 within rail infrastructure. Findings reveal a lack of consensus on SE practices and terminology, emphasizing the need for standardized approaches. Further research is needed to align research and industry practices with ISO standards for improved implementation.

TiB2+TiB coatings were formed on Ti-6Al-4V through a molten-salt diffusional process at temperatures of 850 degrees C and 900 degrees C for 16 h. The thickness of the TiB layer increased by about two times at the higher process temperature, while the thickness of the TiB2 layer remained constant. Tribocorrosion rate of Ti-6Al-4V and the coated samples was evaluated in a reciprocating sliding under a normal load of 15 N in a phosphate buffer saline (PBS) solution for 3600-36000 cycles against an alumina ball. The results showed that the tribocorrosion rate of the borided samples decreased up to 56 times compared with Ti-6Al-4V after 36000 cycles. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) studies showed the presence of oxide-rich patches on the wear surface of Ti-6Al-4V with a thickness of up to 1 mu m. TEM and atomic force microscopy (AFM) images also revealed the presence of a tribofilm with a thickness of up to 200 nm on the surface of the boride coating. In addition, X-ray photoelectron spectroscopy (XPS) analysis confirmed the tribofilm formed on the wear surface of coated samples contained B2O3/H3BO3 compound, resulting in a more stable fluctuation in coefficient of friction and open circuit potential during sliding. The SEM images of the alumina wear surface showed cracks and titanium transfer layers in contact with the borided layers and Ti-6Al-4V, respectively.

The present study has developed new insights into the wear transition mode of cermets and provides a better understanding of the role of abrasive characteristics in three-body abrasive wear. Two sintered and fully densified cermets, NbC–Ni (NbC–12Ni–10Mo2C) and WC-Co (WC-9.5Co) with similar micro-hardness (HV30 ≈ 13.5 GPa) were selected in this study. The abrasion response of cermets against different abrasive characteristics namely size (67–245 μm), hardness (silica, alumina and SiC), and shape (round and angular) was experimentally investigated according to the ASTM G65 standard. The test results showed that the specific wear rate (SWR) of the cermets increased significantly with increasing abrasive size and hardness. The size effect shows that the dominant wear micro-mechanisms shift from binder removal (rolling) to mixed binder-carbide extrusion (sliding) as the abrasives particle size changes from smaller (67 μm) to larger (245 μm). The hardness ratio between the abrasives and cermets (Ha/Hs) highlights that silica and alumina abrasives provide mild wear (Ha/Hs < 1.5), while SiC abrasives cause severe wear (Ha/Hs > 1.5). Both cermets exhibited similar SWR during mild wear, but NbC–Ni showed 7 times higher SWR than WC-Co during severe wear. The abrasives shape effect does not show a significant difference on the wear rate of the cermets.

Knowledge of wear and associated damage mechanism that is prevalent during abrasive wear conditions using NbC-based cermets is lacking. In the current investigation, the abrasive wear response and associated damage mechanisms of cermets due to characteristics effect of grit particles such as size and hardness have been explored. The present study evaluates the abrasive wear response of NbC-12Ni-10Mo2C (NbC-Ni) cermet during two-body abrasive wear, which was experimentally simulated by a pin abrasion tester following the ASTM G132 standard. The WC-Co cemented carbide (WC-15.6Co) with similar hardness was used as a reference material in this study for a comprehensive comparison of materials. The investigated test parameters included different applied loads (4–16 N) and abrasive particle sizes (22–200 μm) for a 30 m sliding distance at 0.15 m/s sliding velocity. Silicon carbide (SiC) and aluminium oxide (Al2O3) were used as abrasive counter bodies. Test results clearly show the particle size effect and the critical abrasive particle size (CPS) for the cermet lies between 82 μm and 125 μm for both abrasives (SiC, Al2O3). It is noticed that the wear rate shows three different trends as the particle size increases, initial increase then a steady state during critical particle size and becomes unpredictable. This effect reflects the transition of wear micro-mechanisms dominated from binder removal (below CPS) to fracture and fragmentations (beyond CPS). The wear mode transition map from plastic grooving to fracture-dominated failure (fragmentation and granular cracks) was created by correlating factors such as the severity of contact and specific wear rate with microscopic observations. The wear produced by SiC abrasives was about an order of magnitude higher (≈18×) than with Al2O3 abrasives. In addition, the material comparison highlight that the abrasive wear rate of NbC-Ni cermet was about 37–86% (SiC) to 66–83% (Al2O3) higher than for the WC-Co cemented carbide, despite both cermets having similar micro-hardness. In addition, the present study illustrates that the abrasion of cermets is not only related to mechanical properties such as hardness and fracture toughness but is inherently related to composite chemical properties such as wettability and interfacial strength. This work provides new insight into the wear response of NbC-Ni cermets and WC-Co cemented carbides regarding different abrasive counterfaces, abrasive particle sizes and transition of abrasive wear mechanisms.

Four nonhalogenated ionic liquids (ILs) based on the same phosphonium cation are investigated in terms of the anion suitability for enhancing the lubricity of a biodegradable oil. For all test conditions, typical for industrial machine components, the lubrication is shown to be governed by nonsacrificial films formed by the physisorption of ionic species on the tribo-surfaces. The anionic structure appears to have an important role in the formation of friction modifying films. The orthoborate ILs exhibit the formation of robust ionic boundary films, resulting in reduced friction and better wear protection. On the contrary, the surface adsorption of phosphinate and phosphate ILs appears to antagonistically disrupt the intrinsic lubrication properties of the biodegradable oil, resulting in high friction and wear. Through additional investigations, it is postulated that the higher dissociation of orthoborate ILs in the biodegradable oil allows the formation of hierarchical and electrostatically overscreened layer structures with long-range order, whereas the ILs with phosphate and phosphinate anions exhibit low dissociation in biodegradable oil, possibly due to the ion pairs being surrounded by a hydrocarbon halo, which presumably results in weak adsorption to form a mixed interfacial layer with no long-range order.

Ionic liquids (ILs) have emerged as viable solutions for developing new-age lubricants, both as neat lubricants and lubricant additives. Enabled by the presence of discrete ions, ILs have the possibility to render electrically conductive lubricants, which is a feasible strategy for developing lubricant systems compatible with modern e-drive conditions. However, this requires the characterization of the electrical properties of lubricants, which is a bottleneck for developing electrically conductive greases, given their complex architecture. This work introduces an electrochemical impedance spectroscopy measurement methodology to evaluate grease samples’ electrical properties. Compared to the commonly used conductivity meters, this method, through its multi-frequency alternating current (AC) impedance approach, can effectively distinguish the individual contributions of the bulk and the sample-electrode interface to the measured electrical response. Impedance spectra of grease samples are obtained using an electrochemical cell with parallel plate electrodes, mounted on a temperature-controlled cell stand and coupled with a potentiostat. The grease's bulk conductivity is extracted by fitting the impedance data to relevant equivalent electrical circuits. The bulk conductivity of lithium complex grease doped with ILs is evaluated and compared to greases with conventional conductivity additives (copper powder and conductive carbon black). The analysis of temperature-dependent conductivity reveals the rather different conductivity mechanisms for different additives. For greases doped with ILs, a comparison against the electrical conductivity of neat ILs reveals that, in addition to the ion dissociation, the interaction of the ions with the different grease components (base oil, thickener) is crucial in defining the grease conductivity.

One way to reduce energy consumption and waste - a necessity to achieve the UN-mandated limitation of average global temperature in-creases - is to select suitable lubricants so that energy-losses through friction and wear are minimised. In this context, non-halogenated ionicliquids (ILs) are promising candidates to achieve this aim due to their intrinsic ionic properties, low vapour pressure and high thermal stability. These are properties desirable for lubricants. Non-halogenated ILs area relatively new type of chemical compounds in tribology. Therefore, systematic studies are required in order to elaborate understanding oftheir functional properties and to increase their readiness level for use innew and emerging technologies such as battery electric vehicles.

This doctoral thesis focuses on the lubrication performance of ILs consisting of phosphonium or imidazolium cations and orthoborate anions. Tribological tests were performed with two different tribological configurations (continuous sliding ball-on-three plates tests and reciprocatingsliding ball-on-disc tests) under different tribological contact conditions(temperature, from 80◦ C to 140 ◦ C; sliding distances of 200 m, 2000 mand 4300 m). In addition, dynamic viscosity, density and ionic conductivity of these ILs were determined for comparative purposes e.g. with commonly used lubricants.

The elemental composition and the structure of the anionic and cationic constituents of the ILs determine their lubrication behaviour and their physical properties. The latter are mainly affected by the alkyl chain length of cations and other structural features, such as the presence of aromatic rings in anions. However, the lubricating performance of ILs depends on their elemental composition, their propensity to surface self-assembly and the effects of the breakdown products of these ILs induced by the thermo-mechanical conditions of the tribo-contact. Imidazolium-based ILs outperform phosphonium based ILs in terms of friction-reduction, but the opposite is observed for wear-prevention. This behaviour is attributable to the breakdown products of the imidazolium ILs caused by lubrication tests. Furthermore, contaminants/impurities present in the ILs (such as trace remnants of the precursor moleculesused in the synthesis of ILs) can affect lubrication, either through improved physical properties or through an accelerated breakdown of the ILs under tribo-contact conditions. This is demonstrated with a phosphonium bis(oxalato)-borate IL and the traces of its transition anionic complex (TAC). It is revealed, that there is a delicate balance to be struck between decomposition of the ILs/TAC and the beneficial effects of the decomposition products on friction and wear. This thesis also shows that the non-halogenated phosphonium IL, added to polar and non-polar biodegradable oils, can work as an anti-wear additive by forming boundary films. This effect was only minor in the case of the polar biodegradable oil due to the competition between the ions of the IL and the polar base oil molecules for surface area.

In conclusion, this work contributes significantly to the characterisation of non-halogenated ILs as novel lubricants. It does so by expanding the understanding of the influence of structural and elemental variationson their lubricating performance and physical properties. Furthermore, lubrication mechanisms for phosphonium and imidazolium ILs are suggested. As a consequence, non-halogenated ILs appear to be excellent candidates for more energy-efficient lubrication.

The ability to stop a gear fatigue test before catastrophic failure has many advantages. However, today, a wide-ly accepted approach is not available. This case study applies a vibration-based condition monitoring methodologyto detect early gear failures. The gear studied takes part in an all-wheel-drive drivetrain system. Vibration signalsfrom four run-to-failure fatigue tests at two constant torque-speed combinations were used as input to time-synchronous averaging and autoregression model generation. The applied methodology shows promising resultsfor early failure detection, and the process is feasible for implementation in an automated environment. Real timeanalysis is also possible since the autoregression model generates a healthy state TSA signal during the early tes-ting stages. However, the time to failure detection varies with operating conditions, with low sensitivity at high-speed and low-torque conditions.

In order to improve the performance of speed prediction in the state of free driving at urban intersections, a new method for speed prediction that considers the interaction characteristics of the host vehicle with other traffic participants is proposed. First, a vehicle target classification method is proposed to distinguish the driving direction of other vehicles relative to the host vehicle, and the target detection algorithm YOLOv5 is used to identify potential traffic conflicts and vulnerable traffic participants. Then, the identified traffic participant and historical speed are combined to establish a speed prediction model based on long short-term memory network. The effectiveness of traffic participant information in improving speed prediction performance is verified in three different driving scenarios, i.e. left turn, right turn and straight. The results show that compared with the baseline model that only takes historical speed as input, the speed prediction model considering traffic participants shows better performance. It solves the problem of the gradual decline in the accuracy of the prediction model in a prediction domain, and shows stronger adaptability to the complex traffic environment of urban intersections.

Over recent decades, the adverse impacts of airborne particles on human health have received wide attention. Elevated PM concentrations on underground platforms might pose a significant public health issue within underground metro systems. This study explores the impact of introducing a new type of train on the concentration of airborne particles on an underground metro platform through statistical modelling, analyses interactions between various factors, and estimates air quality on underground platforms after introducing a new type of train. Based on the data from a long-term field measurement, a linear mixed model, the multi-factor interaction model, which is an expansion of a previous multi-factor model, explored the impacts of train operations, passenger flow, urban background PM levels, ventilation, nighttime maintenance work, and their interactions on hourly PM10, PM2.5, and PM1 values on the platform. The model results show a positive correlation between those factors and platform PM10, PM2.5 and PM1 values, with significant interactions among these factors. The new model has a higher estimate quality than the previous model. Based on the combination of the model and measurement results, the levels of underground PM decreased significantly after replacing the old type of trains with new ones.

Polyamide 11 (PA11) and copolyester (TPC-E) were compounded through melt extrusion with low levels (below 10%) of expanded graphite (EG), aiming at the manufacturing of a thermally and electrically conductive composite resistant to friction and with acceptable mechanical properties. Thermal characterisation showed that the EG presence had no influence on the onset degradation temperature or melting temperature. While the specific density of the produced composite materials increased linearly with increasing levels of EG, the tensile modulus and flexural modulus showed a significant increase already at the introduction of 1 wt% EG. However, the elongation at break decreased significantly for higher loadings, which is typical for composite materials. We observed the increase in the dielectric and thermal conductivity, and the dissipated power displayed a much larger increase where high frequencies (e.g., 10 GHz) were taken into account. The tribological results showed significant changes at 4 wt% for the PA11 composite and 6 wt% for the TPC-E composite. Morphological analysis of the wear surfaces indicated that the main wear mechanism changed from abrasive wear to adhesive wear, which contributes to the enhanced wear resistance of the developed materials. Overall, we manufactured new composite materials with enhanced dielectric properties and superior wear resistance while maintaining good processability, specifically upon using 4–6 wt% of EG.

PA66 is a commonly used material for plastic gears due to its excellent high-temperature resistance, high strength, self-lubrication, and friction resistance. In this study, the effect of different humidity levels on the tribological properties of PA66 materials in self-mated contacts are investigated using a pin-on-disk test rig. The results show that the friction coefficient and wear rate of the PA66-PA66 sliding combination increase drastically after humidity treatment mainly due to the surface plasticization caused by water absorption and the decrease of cohesive strength and glass transition temperature. Moreover, the limiting PV value of PA66 materials decreased significantly after moisture absorption, and when the actual PV value exceeds this reduced material limit, the degree of friction and wear increases drastically. The wear mechanism of the PA66-PA66 sliding combination is mainly adhesive wear without humidity treatment. The wear mechanism is adhesive wear combined with abrasive wear after humidity treatment (50%, 70%, 90%, immersion in water) and abrasive wear is most significant at 50% humidity. Abrasive wear decreases with the increase of the moisture content, while adhesive wear increases.

For human-driven trucks transiting to highly automated ones, we need to make the post-diagnosis decision-making more automated and intelligent, which is critical for vehicle reliability and transport efficiency. For this purpose, we learn from industry practitioners to depict the current post-diagnosis decision-making process in the truck industry and identify the gaps between the current practice and a desired future in a highly automated context. We also design an intelligent post-diagnosis decision support system using advanced technologies to bridge critical gaps. Based on a real-world freight delivery scenario and a risk-based decision-making approach, a concrete instance of the decision support system design is presented as a case study, including the design of graphical user interfaces. This work is mainly for adapting the post-diagnosis decision-making of trucks to a highly automated context and substantially increasing the performance and quality of the decision-making process.

As wave and tidal energy generators advance towards full-scale deployment and commercialization, addressing challenges in the marine environment regarding the lubrication of the components integrating the Power- Take-Off (PTO) system become crucial. Environmental acceptable lubricants that can be biodegraded such as watersoluble polymers are being considered as an alternative to control friction and wear in ocean energy generators. However, compared to synthetic lubricants or mineral oil, they have shown limitations in preventing corrosion, wear, and excessive friction, which can result in premature failure of moving parts. This study explores the potential of different water-soluble polymers as environmentallyfriendly lubricants that meet stringent regulations and provide effective protection against wear and corrosion in offshore conditions. The analysis focuses on the polymers ability to form an elastohydrodynamic film, mitigate surface degradation, prevent corrosion, as well as their rheological properties at different concentrations. The findings reveal that large polymers such as PAG when added in low concentrations in the water can form a separating film under high contact pressure in the low-speed region, while viscosity has shown to have less impact on the ability of the polymer to form a full film. Increasing polymer concentration in the aqueous solution negatively affects the corrosion resistance of steel components at the expense of improving the film-build up. These results offer valuable insights for designing lubrication solutions to protect offshore energy devices.