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Mobile Miner 40V is a machine used for rock excavation and developed by Epiroc. This machine is equipped with a large cutter wheel to perform the excavation. After a test run, some surfaces associated with bearings within the cutter wheel were found to be damaged due to scuffing - severe sliding wear. There is a static load applied to the surfaces due to gravity. However, the reason for this damaged issue was believed that there is a large dynamic load applied to the surfaces during the excavation. This dynamic load was not found in a previous FE model used to verify safety issues. Therefore, a new FE model that is more in line with reality, and a failure analysis were required. Additionally, a feasibility study for a cutter wheel with a larger dimension was also needed since a larger cutter wheel is desirable. Firstly, wear mechanisms were reviewed, and some theories were chosen to analyze the damaged issue. Since it was unknown whether the surfaces were well-lubricated or not, both cases were investigated. The Archard wear equation was used to analyze the poor-lubricated situation, while the lubrication number and the Reynolds equation were used to analyze the well-lubricated case. Secondly, contact mechanisms between the surfaces were also investigated. The investigation of the contact mechanisms involved several theories, such as the Hertzian contact theory and the impact load factor. Besides these theoretical analyses, a numerical analysis was performed. Lastly, a new FE model was established in Ansys. Both the cutter wheel which was subjected to scuffing(existing cutter wheel), and the cutter wheel with a larger dimension(larger cutter wheel) were analyzed by the use of the new FE model. The maximum and minimum wear rates obtained by the Archard wear equation are approximately 1.9・10-2mm3/m and 4.8・10-3mm3/m, which are considered as a completely unacceptable level in engineering applications. The maximum and minimum critical loads obtained by the Reynold equation are approximately 1.8kN and 24.8kN, which both are larger than the static load applied to the surfaces. The maximum and minimum critical mean contact pressures obtained by the lubrication number are approximately 65MPa and 240MPa, which both are larger than the mean contact pressure generated by the static load. No evidence shows that there is a large dynamic load applied to the surfaces during the excavation. The largest possible contact pressure on the bearings in the existing cutter wheel is very close to the limit of severely damaged. The largest possible contact pressure on the bearings in the larger cutter wheel is believed to exceed the limit of severely damaged. The previous assumption that the surfaces were damaged due to a large dynamic load was wrong. The obtained results support that the surfaces were only subjected to a static load and were damaged due to inadequate lubrication. The existing cutter wheel is operated safely with the current load cases. However, the forward thrust force is suggested to decrease when the cutting angle is large. There is a high risk if the larger cutter wheel is operated with the current load cases.

Over the last decade, the application of ultra-high strength steel as safety components and structural reinforcements in automobile applications has increased due to their favourable high-strength-to-weight ratio. The complex shaped components are widely produced using hot stamping. However, this process encounters problems such as galling and increased wear of the tools due to harsh operating conditions associated to the elevated temperatures. Moreover, quenching is a critical step that affects the hot formed components. Slow cooling rates results in inhomogeneous mechanical properties and increased cycle time. Therefore, fast and homogeneous quenching of the formed components in combination with reduction of wear rates during hot forming are important targets to ensure the quality and efficiency of the process. The use of additive manufacturing (AM) technologies opens up potential solutions for novel tooling concepts. The manufacturing of complex shape cooling channels and integration of high-performance alloys at the surface could benefit the tribological performance in the forming operation. However, the research into high temperature tribological behaviour of AM materials in hot forming applications is very limited. The aim of this work is to study the tribological performance of additively manufactured materials. Two steels were used – a maraging steel and modified H13 tool steel. The hot work tool steel H13 is commonly applied for dies in metal forming processes. In this thesis it was used to study additive manufacturing as the processing route instead of conventional casting. The choice of a maraging steel is motivated by a possible application of high-performance alloys as a top layer on dies. The materials were post-machined and studied in milled, ground and shot-blasted conditions. The different post-machining operations were applied to study the effect of surface finish on the tribological behaviour and also to evaluate different methods of post-machining an AM surface. As fabricated dies are usually manufactured with milled surface. During its use, the dies undergo refurbishment after certain number of cycles and the surface condition is changed to a ground surface. These surface finishes are commonly tested for hot forming applications. The shot blasted operation was chosen as alternative surface finish. The process allows to prepare large sized tools easily and the surface has beneficial compressive stresses. The tribological behaviour of AM steels was studied using a hot strip drawing tribometer during sliding against a conventional Al-Si coated 22MnB5 steel. The workpiece temperature during the tests was 600 and 700°C. The results of the tribological performance of AM materials were compared to conventionally cast tool steel QRO90.The results have shown that the friction behaviour of both maraging and H13 steels at 600°C was stable and similar whereas at 700°C the COF was more unstable and resulted in an earlier failure of the tests due to increased material transfer of Al-Si coating from the workpiece surface.The main wear mechanisms for AM materials were galling and abrasion at both temperatures. Abrasion is more severe for the AM steels in comparison to cast tool steel QRO90. The galling formation on milled and ground surfaces showed similar behaviour to cast steel and it increased with higher workpiece temperatures. The shot-blasted surfaces showed less build-up of transferred material on the surface but folding of asperities and entrapment of Al-Si particles within surface defects generated during shot-blasting.

Dans ce manuscrit, nous parlons des matériaux composites à matrice céramiques (CMCs) qui sont envisagés pour intégrer les chambres de combustion de futurs moteurs aéronautiques civils. Pour faire face des conditions extrêmes, ces matériaux possèdent la particularité de s’auto-protéger vis-à-vis de l’oxydation par la formation d’un oxyde passivant qui limite la diffusion des espèces oxydantes au sein des fissures matricielles. Nous modélisons l’écoulement d’un oxyde dans une fissure par l’équation de Navier-Stokes, puis les mettons sous forme non dimensionnelles, et les dérivations de deux types de modèles sont intéressantes : les modèles de Saint-Venant et les modèles de lubrification. Ensuit nous nous engageons à chercher l’existence de solution faible de l’approximation de lubrification d’ordre 4 obtenue précédent dans le cas uni-dimensionnel. Enfin nous précisons la limite entre les équations de Saint-Venant et l’équation de lubrification. / In this work, we are interested in the ceramic matrix composite materials(CMCs) who will be used to integrate the combustion chambers of future civil aeronautical engines. To face extreme conditions, these materials possess the peculiarity to auto-protect itself towards the oxidation by the formation of an oxide passivate which limits the distribution of the oxidizing species within the matrix cracks. We model the flow of an oxide in a crack by the Navier-Stokes equation, then put them under an asymptotic analysis in order to get two types of asymptotic models : models of Saint-Venant (Shallow water model) and lubrication models. Next we are interested in looking for the existence of weak solution to the one-dimensional approximated lubrication equation of order 4 obtained before. Finally we talk about the limit between the Saint-Venant equations and the lubrication equation.

This dissertation is focused on the effects of both artificially produced and real roughness features on mixed lubrication film formation during start-up and reversal of non-conformal contacts operated under rolling/sliding conditions. The start-up operation of mixed lubricated contacts represents one of the transient conditions that bring the risk of the surface damage because of asperities interactions. Chromatic interferograms captured by CMOS high-speed camera during start up of the motion enabled to observe the detailed changes in lubrication film caused by surface features. The observation of the effects of surface dents artificially produced on the ball surface helped to understand better the behaviour of real surface topography. It was found that the presence of shallow surface features can help to separate mixed lubricated rubbing surfaces more efficiently than it could be suggested from the results obtained with smooth surfaces. It can be suggested from the obtain results that properly designed topography of the rubbing surfaces can help to reduce the asperities interactions under transient operational conditions.

This dissertation thesis deals with elastohydrodynamic lubrication (EHL) of surfaces with real roughness. Systematic study of surface harmonic components behaviour, during their passage of the EHL contact, by other authors led to retrieval of a uniform principle according which individual harmonic components deform inside the contact. Although the amplitude attenuation model can provide rapid tool for more accurate surface assessment in design process it has not been validated on real surfaces till now. The thesis represents pioneering work on quantitative analysis of real surfaces EHD measurements. It contains original and new results with real and model roughness features that in many cases confirm theoretical expectations. Deeper understanding of surface roughness behaviour inside EHL contact, which is typical for machine parts like bearings, gears, cams etc., can help to improve design process of the components and ultimately enable machines and equipment to work with lower energy requirements and higher durability.

This PhD thesis deals with elastohydrodynamic lubrication (EHL) under the conditions that occur between mated hypoid gear teeth. The aim is to describe experimentally the behaviour of lubricating film and mechanisms of its formation. The focus is mainly placed on clarifying the influence of direction and magnitude of sliding velocity in circular and elliptical contacts. Generally, it is still assumed that the direction of sliding velocity has no effect on the resulting lubricant film. In this study optical interferometry is used to determine distribution of lubricant film thickness. This work includes new and original results which clarify the studied problem. It was found that the direction of sliding velocity affects shape of the film at high speeds. This relates to the effect on heat flow through the contact. The results have an impact on the development of general EHL theory and provide knowledge applicable in film thickness prediction in the design of real tribological nodes.

Laserpåsvetsning och laserytimpregnering är additiva tillverkningsmetoder som kan användas för att förlängakomponenters livslängd och specialanpassa ytor med avseende på friktions-, slitage- och korrosionsegenskaper.Duroc Laser Coating i Luleå är störst i Sverige på laserytbehandlingar men saknar objektiv data på friktionsoch nötningsegenskaperna hos de laserpåsvetsade materialen vilket har varit det huvudsakliga målet med dettaarbete att ta fram.Tolv material, varav tre referensstål för jämförelse, har testats enligt en något modifierad ASTM G132 standard avseende tvåkroppsabrasion. Resultaten visade att det abrasiva nötningsmotståndet ökade med ökandehårdhet. Tre material med karbidpartiklar i ytskiktet uppvisade överlägset högst nötningsmotstånd. Ytornahar undersökts med svepelektronmikroskop och ytprofileringsmätningar efter testerna för att karakterisera debakomliggande nötningsmekanismerna.Materialens mikrostruktur, hårdhet och deformationshärdning närmast ytan efter abrasiv nötningsprovninghar undersökts. De mjukaste materialens mikrostruktur hade deformerats i glidriktningen medans resterandematerials mikrostruktur var opåverkad. Koboltlegeringarna uppvisade högst deformationshärdning.Åtta material, varav två referensstål, har testats enligt ASTM G99 i en pin-on-disk uppställning för att undersöka adhesivt nötningsmotstånd och friktionsegenskaper med lagerstål som mötande material. Resultatenvisade att de tre koboltbaserade legeringarna som testades hade lägst och stabilast friktion med minst materialöverföring, medans ett brons som testades hade högst friktion och materialöverföring. Ett rostfritt stål hadelägst nötning.Målen med arbetet har uppnåtts och den tribologiska prestandan har kartlagts för de material som ingått iarbetet. Metodiken som tagits fram under arbetets gång kan även användas för att göra ytterligare materialkarakterisering i framtiden.

This study aims to develop coatings which show wear resistant behaviour along with multiple functions such as improved ice adhesion, better freezing delay etc which help in improving the effectiveness of the wind turbine efficiency. The significance of anti-icing/de-icing solutions for wind turbines is emphasized since ice accretion can cause serious issues in generation of power and might lead to damage of blades. The use of active and passive anti-icing/de-icing technologies in wind turbine blade applications is reviewed. The discrepancy between passive anti-icing, which depends on surface treatment, coatings, de-icing fluids and active anti-icing, which uses heating devices, sensors such as actuators, transducers, is explored along with the current challenges in industry. In this study we’ve developed interesting methods for improving the anti-icing/de-icing capabilities of wind turbine blades by using gelcoat coatings in which are filler particles (boron nitride and graphene) and oils (vegetable and paraffin oil) are incorporated. Evaluating the impacts of type of fillers, oils, their concentrations on anti-icing efficacy, as well as the prospects for this technique to enhance wind energy production's reliability and productivity will be explored. In summary, this study aims to develop multi-functional polymer coatings for anti-icing/de-icing application in wind turbine blades. The coatings with boron-nitride and graphene showed an increase in the surface roughness and contact angles, while there’s no change in the chemical composition in comparison with pure gelcoat. The thermal conductivity of the coatings was increased with addition of fillers. For the wear test, the operating parameters chosen are a load of 5N and 1Hz frequency of slider, which is run for a duration of 10 min. The COF for both the coatings is lesser than baseline coatings whereas graphene provided better wear resistance. The hardness was increased for boron-nitride coatings and it remained almost same for graphene coatings. The ice adhesion strength, freezing delay and thermal analysis (TGA) for these coatings showed better performance than pure gelcoat. Whereas for coatings with vegetable and paraffin oils, the contact angles were increased and surface roughness was increased in case of paraffin oil coatings whereas it reduced for vegetable oil coatings. Both the coatings offered better wear resistance and reduced COF, whereas the hardness was reduced. The ice adhesion strength and freezing delay improved drastically and are much better than both pure gelcoat as well as coatings with boron-nitride and graphene. There is slight increase in the glass transition temperature than pure gelcoat coating.

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