A radial piston hydraulic motor has several components involving sliding or rolling interfaces which may encounter tribological problems. Seizure is one of them and it results in complete stoppage of motion between the relatively moving components and has serious consequences in terms of the operation of a hydraulic motor. Extreme running conditions, like low viscosity and high pressure and speed can cause the rupture of lubricating films and this may lead to the seizure of hydraulic motors. The occurrence of seizure often leads to undesirable damage to the motor components and unscheduled maintenance and can prove to be highly expensive. The work reported in this thesis has focused on investigating the mechanisms of seizure and developing suitable tribo test methods for simulating the sliding interfaces of the hydraulic motor. Extensive motor tests have been performed at low viscosity, high pressure and high speed. The results of this work enabled in describing the seizure progression, namely break down of lubricant film, particle entrapment and thermal expansion. Further, tests have been carried out in a rotary tribometer by using a thrust washer conformal test configuration. In this, the influence of area ratio has been studied and this configuration appears to simulate the piston-cylinder contact effectively during boundary lubricated conditions.

Elasto-hydrodynamic lubricated (EHL) contacts can be found in various machine elements or systems, like rolling element bearings, cam followers or gear transmissions. The service life of these elements and systems are depending to some extent on the performance of EHL contacts. Today most tribological contacts are lubricated with the same type of lubricant throughout the entire service life. However operating conditions can change over the components service life and the contacts will therefore require different lubricant properties. In order to expend the service life of the component, the lubrication of the tribological contacts has to be optimized based on the current operating conditions. A future vision is to develop machine elements which can adopt to the actual operating condition, so called triboactive systems. A first step of necessary research in order to develop such systems is presented in this work.In order to enable operation dependent lubrication the mechanism of monitoring techniques and their interaction with different operating conditions have to be investigated. In this work the effect of surface topography, slide to roll ratio and additives on the running-in and the monitoring by contact impedance were studied. Characteristic dependences between the surface parameter Rq and the contact capacitance and between the surface parameter Rz and the contact resistance were found. Further tests with iron oxide (FE3O4) contaminated bearings, monitored by vibration and acoustic emission were carried out. Premature failure due to iron oxide contamination is the most common problem for rolling element bearings operating in mining environment. Thereby the effect of iron oxide contamination on the vibration and acoustic emission monitoring for two different types of greases were investigated. It was found that a simple RMS analysis of the vibration and acoustic emission signals enables the detection of improvements of contaminated contacts by lubrication. Both vibration and acoustic emission from the investigated bearings were reduced by adding extreme pressure additives (EP) to the contaminated contacts.Monitoring of the lubrication condition is necessary to generate information about the current performance of the tribological contact. However, in order to improve the performance of tribological contacts by changes of the lubricant or additives, the effect of such additives on the lubrication condition and the performance of the tribological contact need to be studied more in detail. The presented running-in tests in this work showed that EP additives are only favourable in the very first stage of running-in. The advantage of EP additives for running-in increases with increased surface roughness and increased slide to roll ratio.Another advantage of EP additives was observed during the tests with iron oxide contaminants. The use of EP additives reduced the acoustic emissions of the tribological contact by 70% and reduced the increase of surface roughness of the raceways by as much as 60%. Furthermore the tests indicate a lower wear rate for contaminated EHL contacts lubricated with greases containing EP additives in comparison to plain grease without EP additives, in case of iron oxide contaminated EHL contacts.

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The effect of greenhouse gas emissions contributing to the global warming is today becoming an increasingly important problem worldwide and has led to increased efforts being made on improving tribological performance of interacting surfaces in mechanical systems. Due to increasingly stringent CO2regulations, a reduced fuel consumption has become a key area of interest for the automotive industry where low cost, low emission solutions are continuously developed and where low friction alternatives to machine elements currently in use are evaluated. Crankshaft roller bearings have been shown to reduce the mechanical friction in internal combustion engines compared to the plain (sliding) bearings used today, further leading to a reduced fuel consumption and thereby reduced CO2emissions. However, the transition from plain (sliding) bearings into crankshaft roller bearings means new challenges with e.g. increased noise, vibration and harshness (NVH) levels and reduced durability of the bearings. Therefore, in order to optimise the crankshaft roller bearings that operate under the highly transient conditions in the engine, an increased understanding of the tribological system is required. Research related to elastohydrodynamic lubrication (EHL) has led to the possibility to improve friction performance and durability of machine elements where lubricated non-conformal contact geometries interact. Traditionally, simplifications of the contacting geometries and the assumption of steady-state conditions have often been applied to the EHL analysis. The purpose of this work has thus been to develop a simulation model based on previous work done in the field and further utilise the model to simulate the contact on a detailed level, incorporating transient effects and the influence of oil behaviour using state-of-the-art modelling. The influence of the piezoviscous response and the compressibility-pressure behaviour of the lubricant on the sub-surface stress field were studied, showing that stiff lubricants may lead to increased stress concentrations in the vicinity of the surface, which may further influence the durability of the bearing. It was also seen that highly transient loading conditions applied to the contact initiate oscillations in the lubricated system, affecting pressure, film thickness and sub-surface stresses over time. These findings further elucidate the importance of including non-steady behaviour while analysing highly transient lubricating conditions of EHL contacts. By considering and optimising the aforementioned effects during design of crankshaft roller bearings, an improved NVH performance and an increased durability of the crankshaft roller bearing may be achieved.

Wave energy and wave energy converters is a fast rapidly developing field of research and energy harvesting. In recent years, more and more designs have seen operational success, and more and more are in development. Wave energy converters face a challenge not properly explored until recently, high loaded, oscillating motion in a highly hostile environment. Which poses a multitude of challenges ranging from contact fatigue to corrosion wear. However, this field is still in early development, seeing little to no research published about it. This work intends to inform about the challenges these wave energy designs pose in tribology and more specifically to bearings, through a literature study and review. The review establishes a rating for different bearing designs based on how applicable a certain bearing selection would be based on available research. Reaching the conclusion that whilst currently inappropriate to employ, seawater lubricated bearings could reach commercial viability in the future for wave energy devices. Additionally, with the help of excellent sealing solutions and well conducted lubrication regimes, both sliding bearings and rolling element bearings have their advantages and disadvantages and can make use of a multitude of different materials. / Vågkraft och vågkraftsgeneratorer är ett område som växer snabbt i intresse för både forskning och produktutveckling. På senare år har fler och fler vågkraftsgeneratorer och designer för dessa sett framgång i prototyptester och flera är på fortsatt utveckling. Vågkraftsgeneratorer står inför flera utmaningar, med de sammansatta faktorerna av en väldigt korrosiv miljö, höga krafter och oscillerande rörelse. Vilket stället flera krav på designers på allt ifrån korrosionsskydd till materialkunskap krig utmattning av maskinkomponenter. Dessvärre finns ytterst lite noga dokumenterad forskning kring området då det är en väldigt ung bransch. Denna rapport söker att utforska och informera kring de utmaningar som kan ställas på vågkraftsgeneratorer inom specifikt tribologi och specifikt för lager och lagerval. Arbetet fokuserar på en litteraturstudie över de möjliga utmaningarna området skapar. Grundat på relevant forskning inom liknande områden betygsattes ett urval av lagerval för vågkraftsgeneratorer. Där slutsatserna pekar på att då det möjligtvis är olämpligt i nuvarande läge att nytta saltvatten som smörjningsmedel, i framtiden kan detta bli en kommersiell verklighet. Där både glidlager och rullningslager har sina fördelar och nackdelar inom applikationen, med noga valda materialkombinationer, smörjningsmedel och tätningar.

The journal bearing is a critical machine element typically used to support rotating motion in high speed machinery. Through the generation of a hydrodynamic pressure in its thin lubricant film,which is usually in the order of 10-100μmthick depending on the diameter of the journal itself, the bearing is able to withstand large loads, both statically and dynamically, while having a very low rate of wear. It is of course essential that these components provide for a safe operation with as little wear and frictional losses as possible and it is therefore of great interest to develop simulation models of constantly increasing accuracy. Typical relevant quantities when designing a bearing are the load carrying capacity, metal/oil temperature, minimum film thickness, stiffness, damping and power loss. Classical lubrication theory builds upon the Navier-Stokes equations which, with the thin film approximation, can be reduced to a single equation which governs the hydrodynamic pressure build up in the lubricant. Since the problem now has been reduced to solving a single non linear partial differential equation in 2 dimensions, a significant advantage in terms of simulation time compared to the full set of Navier-Stokes equations can be enjoyed with an, in most cases, insignificant error of approximation. However, with time, as the need for bearings capable of operating at higher loads,speeds and with new designs involving more complex geometries, such as, for example, textured surfaces, the applicability of classic thin film theory should not be taken for granted, especially not when there is an increasing amount of turbulence involved. The purpose of the work contained in this thesis is to develop and asses the performance of a state of the art 3D TEHD model using the commercial finite element multi physics software COMSOL Multiphysics. Of special interest is the assessment of the Menter Shear Stress Transport (SST) turbulence model, which is a widely used, standard, 2-equation RANS eddy viscosity model, in predicting characteristic values for a bearing operating in the transition range between laminar and turbulent flow. A comparative study is carried out where the present model is benchmarked against experimental data on a large 4 pad tilting pad journal bearing. The present model is also compared to one of the classic models based on thin film theory. The present model is also used to study the influence of the geometry that constitutes the leading edge groove in a tilting pad journal bearing on the turbulence levels. Finally the possibility of using a shear thinning lubricant for reducing the bearing power loss is investigated. The calculations were all performed using the resources of the super computer cluster at HPC2N at Ume ̊a University. The results clearly show the inadequacy of the SST turbulence model when performing calculations on a bearing operating in the transition range between laminar and turbulent flow. Moreover, the model predicts slightly higher average values of turbulence in a leading edge grooved bearing compared to a conventional one, yet a higher maximum value in the latter.

Axial piston machines are operating at high pressure and varying speeds, which requires high reliability of the components. The machine components are separated by a fluid film, but sometimes this film gets penetrated by the surface asperities causing the machine to operate with metal-to-metal contact. In order to improve the design and predict the operating conditions might numerical tools be used. The goal with this thesis was to describe how the tribological contacts in Parkers machines can be modelled, considering oil and surface roughness. The so called Luleå Mixed Lubrication Model have therefore been investigated and it has been described how the model can be used in Parkers machines. The model uses a two-scale method to include the influence of real surface topographies of the components, it gives information about how the surface roughness affect the lubrication conditions. Different options of softwares have been investigated and compared to get an understanding of what possibilities and shortcomings they might have when it comes to this kind of simulations. Results show that all interesting contacts can't be treated the same, therefore must each contact be investigated separetly even though the Luleå Mixed Lubrication Model is used in all cases.

High strength aluminum alloys have for a long time been a popular material utilized in the automotive and aerospace sector due to coveted mechanical properties in terms of weight, strength, fatigue, and corrosion. However, tribological mechanisms such as tribo-film formation and material transfer during the metal cutting manufacturing process of aluminum impose significant reduction of machining and tool-life performance. Additionally, environmental aspects associated with metal cutting manufacturing has got more interest and pushed cutting tool development in new directions to meet increased customer demands. One possible way of achieving this, is the implementation and utilization of diamond based cutting tools which has been shown to perform well in machining of high strength aluminum. However, in depth knowledge regarding the tribological properties of diamond based cutting tools is currently lacking. Thus, the aim of this master thesis has been to investigate the refined tribological characteristics and properties of WC-Co cemented carbide cutting tools coated with synthetically grown CVD diamond. Tribological testing methods, such as frictional scratch/sliding, pin-turning, contact-zone temperature measuring, and longitudinal turning have been conducted to acquire extensive amount of research material in the form of test samples and data information. Furthermore, pin-turning tests were performed using a newly developed Tribojan pin-turning equipment and the performance of this was evaluated as a subgoal task. Specimen sample analysis have primarily been performed through LOM and SEM/EDS microscopy techniques. The results acquired from testing, microscopy analysis and data set evaluation have showed promising results in terms of frictional characteristic and material transfer properties regarding CVD diamond coated surfaces. The average CoF of CVD diamond sliding against an Alumec 89 aluminum alloy surface were somewhat lower as compared with similar sliding of a conventional uncoated WC-Co cemented carbide material. Furthermore, the frictional behavior and characteristic of CVD diamond appears to be more consistent and regular over longer sliding distances. The contact interaction between the CVD diamond coated surface and Alumec 89 appears to have a more abrasive nature due to the rough surface structure and material properties of the coating. The corresponding tribo-pair contact interaction with WC-Co cemented carbide shows more adhesive tendencies. Additionally, the contact-zone temperature development during pin-turning is shown to be somewhat lower during CVD diamond/Alumec 89 surface interactions. Regarding material transfer properties, CVD diamond are shown to perform well when interacting with high-strength aluminum. The amount of material adherence is significantly reduced on CVD diamond coated surfaces. During longitudinal turning using CVD diamond coated cutting tools, no significant wear was observed. On the other hand, evidence of both adhesive and abrasive wear was observed during turning using conventional uncoated WC-Co cemented carbide tools. Finally, tribological mechanisms acting during Tribojan pin-turning tests was shown to be relatively comparable with an actual machining operation, which indicate that the testing method perform well as compliment to standard frictional sliding and machining testing. / Höghållfasta aluminiumlegeringar har länge varit ett populärt material inom bil- och flygindustrin på grund av deras eftertraktade mekaniska egenskaper när det gäller vikt, styrka, utmattning och korrosion. Däremot medför tribologiska fenomen, så som tribofilmbildning och materialöverföring under metallskärande tillverkningsprocesser för aluminium, en betydande minskning av prestanda hos utrustning och skärverktygens livslängd. Dessutom har miljöaspekterna i samband med metallskärande tillverkning fått ökat intresse och därmed drivit utvecklingen av skärverktyg i nya riktningar för att uppfylla kundernas ökade krav. Ett möjligt sätt att uppnå detta är att införa och använda diamantbelagda skärverktyg, vilka har visat sig fungera bra vid bearbetning av höghållfast aluminium. Dock saknas det för närvarande djupgående kunskaper om de tribologiska egenskaperna hos dessa diamantbaserade skärverktyg. Syftet med detta examensarbete har därför varit att undersöka de förfinade tribologiska egenskaperna hos WC-Co skärverktyg av hårdmetall belagda med syntetiskt odlad CVD-diamant. Tribologiska testmetoder, så som friktionsskrapning/glidning, pinnsvarvning, temperaturmätning i kontaktzonen samt longitudinell svarvning, har genomförts för att samla in analysmaterial i form av prover och datainformation. Dessutom utfördes pinnsvarvningstesterna med hjälp av en nyutvecklad så kallad Tribojan-utrustning, vars prestanda har utvärderats som ett delmål i projektet. Analyser av provexemplar har huvudsakligen utförts med hjälp av mikroskopitekniker så som LOM och SEM/EDS. Resultaten från provning, mikroskopianalys och utvärdering av data har visat lovande resultat när det gäller friktions och materialöverföringsegenskaper för CVD-diamantbelagda ytor. Den genomsnittliga CoF för CVD-diamant som glider mot en yta av aluminiumlegeringen Alumec 89 var något lägre jämfört med motsvarande glidning av konventionellt WC-Co hårdmetallmaterial. Dessutom verkar friktionsbeteendet hos CVD-diamant vara mer konsekvent och regelbunden över längre glidsträckor. Kontaktinteraktionen mellan ytor av CVD-diamant och Alumec 89 verkar också ha en mer abrasiv karaktär på grund av diamantbeläggningens grova ytstruktur och materialegenskaper. Motsvarande kontaktinteraktion mellan Alumec 89 och obelagd WC-Co hårdmetall visar däremot mer adhesiva tendenser. Dessutom tenderar temperaturutvecklingen i kontaktzonen under pinnsvarvning vara något lägre vid ytinteraktioner mellan CVD-diamant och Alumec 89. När det gäller materialöverföringsegenskaperna visar sig CVD-diamant fungera bra vid interaktion med höghållfast aluminium. Materialets vidhäftning minskar betydligt på diamantbelagda ytor. Vid kontinuerlig longitudinell svarvning med diamantbelagda skärverktyg observerades inget betydande slitage. Å andra sidan hittades tecken på både adhesivt och abrasivt slitage under svarvning med konventionella obelagda WC-Co hårdmetallverktyg. Slutligen visade det sig att de tribologiska mekanismerna som verkade under Tribojan-pinnsvarvning vara relativt jämförbara med faktisk bearbetning, vilket tyder på att testmetoden fungerar bra som komplement till friktions och svarvtester.

There are two main goals of this thesis. Firstly, to improve and develop an existing hot weartester at Karlstad University so that it may test more samples of different sizes. Secondly, totest previously impossible samples and investigate their tribological properties and measurethe coefficient of friction with high reproducibility. The development work on the tribometer wasdone by a prestudy including; Investigating the hot wear tester, idea generation in CAD andcollecting information from the creator and prior users of it. After a few rounds of conceptgeneration and discussion with the supervisor and workshop staff, a new sample holder withdifferent sample adapters was created. Five tests of four different materials were conductedand their friction was measured. The new sample holder was able to solve the mainconcerns with the old design and showed great promise in producing reproducible results,better than any previous versions. The friction of the different TiAlN samples, at roomtemperature, seemed to indicate that there is a certain amount of Al% that maximizes frictionand that there is no simple linear relationship between Al% and coefficient of friction. Finallyit can be concluded that the initial goals of the thesis have been met, and that a newscientific instrument has been created to aid in the further understanding of tribology. / Det finns två huvudsakliga mål med detta examensarbete. För det första, att förbättra ochutveckla en existerande varmnötare på Karlstad Universitet så att den kan testa fler proverav olika storlekar. För det andra, att testa tidigare omöjliga prov och undersöka derastribologiska egenskaper och mäta friktionskoefficienten med hög reproducerbarhet.Utvecklingsarbetet av tribometern skedde via en förstudie som innehöll följande:Undersökning av varmnötaren, idégenerering i CAD och samling av information frånvarmnötarens skapare, samt tidigare användare. Efter några iterationer avkonceptgenerering och diskussioner med handledare och verkstadspersonal så skapadesen ny provhållare med flera olika adaptrar. Fem tester med fyra olika material utfördes ochderas friktion mättes. Den nya provhållaren löste de huvudsakliga problemen med dengamla designen och påvisade goda förhoppningar angående att producera tester med högreproducerbarhet. Markant bättre än tidigare versioner. Friktionsmätningarna från de olikaTiAlN-proverna, vid rumstemperatur, indikerade att det finns en viss mängd Al% sommaximerar friktionen och att det inte finns något linjärt samband mellan Al% ochfriktionskoefficient. Slutligen kan det konstateras att de initiala målen för examensarbetet harblivit uppnådda, och att ett nytt vetenskapligt instrument har blivit skapat för att hjälpa utökaförståelse inom tribologi.

Ultra high molecular weight polyethylene (UHMWPE) is a polymer commonly used in various applications, particularly in hip joint replacements. Despite its good performance, it is susceptible to oxidation degradation, which can be mitigated with the addition of vitamin E, and to excessive wear against metal countersurfaces, which can potentially be improved with the addition of nanoparticles. In this work, sixteen newly developed UHMWPE nanocomposites with different nanofillers (multi-walled carbon nanotubes, graphene oxide and nanodiamonds), blended with and without vitamin E, and both irradiation crosslinked and non-crosslinked were studied. Thermomechanical characterisation (dynamic mechanical analysis and thermogravimetric analysis) and tribological pin-on-disc testing showed that both nanofillers and the addition of vitamin E ensured improved the performance of the nanocomposites compared to the virgin UHMWPE. Vitamin E improved the oxidative and thermal stability of UHMWPE, decreased the wear and increased the coefficient of friction. The nanoparticle reinforcements contributed to improved thermal stability to some degree and decreased the wear. Crosslinking was also shown to result in improved thermomechanical performance, although it appears that the addition of vitamin E inhibits the crosslinking process.