The Piston Ring - Cylinder Liner (PRCL) contact is the single largest contributor to frictional losses in an internal combustion (IC) engine, causing 20-40% of all mechanical losses. If these mechanical losses can be reduced by 10% then vehicle fuel efficiency could be increased by approximately 1.5-2.5%. In todays automotive industry fuel efficiency is one of the most important factors in vehicle design due to increasing concerns about energy security, increasing fuel prices and climate change. The objective of this project is to optimise the cylinder surface texture, which when referring to cylinder liners in this work means the cross-hatch grooves left by the honing process.This work focuses on simulation techniques that can be used to help optimize cylinder liner surface texture to reduce friction while at the same time minimizing oil consumption and wear. Cylinder liner surface topography is investigated with a range of measurement techniques in order to reveal all the important features of the existing surface. Different ways of characterizing surface topography based on both traditional height averaging parametersand functional parameters calculated for a range of different surface measurements are discussed. The different characterization techniques are compared to find the most appropriate way of quantitatively describing surface topographies.A full engine cycle simulation of the PRCL contact has been developed. A homogenization technique was implemented for solving the Reynolds equation. This is a two scale approach where surface roughness is treated on the local scale and surface texture plus global geometry on the global scale. A method for generating artificial surface topography based on real surface measurement data was developed. This allows for the possibility of simulating a wide range of new surface topographies in order to investigate their potential for reducing friction and minimising oil consumption and wear.

Rolling element bearings contain seals to keep lubricant inside and contamination outside the bearing system. These bearings are more often lubricated with grease rather than oil. Much knowledge is available on oil lubricated seals but a good understanding of grease lubricated seals is lacking.In this thesis, first the lubrication, pumping and sealing mechanisms of oil and grease lubricated radial lip seals have been discussed. The first paper reviews the public literature. This review has shown that very little is known on grease lubrication in radial lip seals. The primary lubrication, sealing and pumping mechanisms found for oil lubricated seals are micro-elastohydrodynamic lubrication between the seal and shaft roughness and tangential deformations of the seal surface for a pumping action. These mechanisms are important but it is felt that other effects have to be included for explaining differences seen in grease lubricated radial lip seals. One effect in grease lubrication is the normal stress effect which is described in the second paper. It is shown that the grease rheology and especially the normal stress effect play a significant role in film formation in grease lubricated seals. The model predicts that 50 to 60% of the load carrying capacity can be generated by the normal stress effect for a low contact pressure bearing seal depending on the operating conditions. The oil bleed model presented in the third paper describes the release of oil from the grease. This model is based on viscous flow through the porous soap microstructure and the driving force is the pressure gradient resulting from centripetal forces. It is shown that the soap fibre distribution has to become anisotropic during oil bleed and the model has been validated with experiments at different temperatures and rotating speeds. The model can be used with good confidence for longer periods of time and can be used as input for replenishment models.

In recent years, the use of ultra high-strength steels (UHSS) as structural reinforcements and in energy-absorbing systems in automobiles has increased rapidly; mainly in view of their favourable strength to weight ratios. However, due to their high strength, the formability of UHSS is poor, thus complex-shaped UHSS components are invariably produced through hot-metal forming processes. The use of hot stamping or press hardening, which was developed during the 1970’s in northern Sweden, has become increasingly popular for the production of ultra high strength steels. In hot stamping, different tribological problems arise when the tool and work-piece interact during the forming process at elevated temperatures. Wear and surface damage of forming tools can be detrimental to the quality of the final product and these can also have an adverse impact on the process economy due to frequent maintenance or replacement of tools. In this work, a literature review pertaining to tribology of hot sheet metal forming has been carried out. This review has revealed that the awareness of tribology and its application in metal forming processes at high temperature has increased in the recent years. A considerable amount of work has been done to enhance the understanding of the response of different materials and parameters involved and also to improve the process itself. However, despite these developments, there exist major gaps in knowledge pertaining to the occurrence of friction and wear in hot sheet metal forming. Extensive experimental studies have thus been undertaken to bridge some of the knowledge gaps related to tool wear and failure mechanisms in the hot stamping process. These studies have involved both the systematic analysis of actual worn tools as well as parametric tribological investigations in the laboratory. The analysis of worn tools showed that friction is a crucial parameter in their operating life. It was observed that severe mechanical stresses are generated due to high friction during the work-piece/tool interaction. As a result of the cyclic thermal and mechanical loads imposed during the hot forming process, the stresses generated eventually lead to the occurrence of fatigue damage at the tool surface. Another important mechanism observed was material transfer from the work-piece to the tool surface. This is particularly common and detrimental in hot forming of coated work-piece material. The most common coating applied to the ultra high strength steel is a hot dip aluminium based coating, commonly referred to as Al-Si coating. The parametric studies carried out were aimed at understanding of the initiation mechanisms of material transfer from the Al-Si coated steel to the tool material. The results showed that severe galling occurs by accumulation and compaction of wear debris and becomes enhanced in tools having rough surfaces. The roughness defects on the surface promote accumulation of wear particles. Furthermore, high contact pressure also enhances the compaction of wear debris and consequently the severity of material transfer. It was observed that the severity of galling can be reduced by the use of smooth and hard surfaces. Additionally, the use of different PVD coatings on the tool steels showed an increased tendency on adhesion, causing a severe material transfer onto the tool surface.

Traditionally rolling contact fatigue observed in bearing field applications was subsurface initiated. However, despite the improvement of steel properties, some factors such as downsizing in bearing design, extreme loading of the bearings as well as demanding application conditions (start up-stop cycles) have led to an increase on the cases of surface damage related to surface initiated fatigue, that comes basically from surface distress. Possible causes leading to surface initiated fatigue are: material and surface properties, marginal lubrication and lubricant chemical composition. Lubricants are formulated products composed of base oil, and an additive package designed for a specific application. Extreme-pressure (EP) and antiwear (AW) additives are chemically active additives, they react with the steel surfaces in contact to form a protective additivederived layer, thus reducing friction and controlling wear. However, certain EP/AW additives that increase the performance of other machine elements, such as gears, can be detrimental for the bearings running in the same lubrication environment. In order to identify the plausible mechanisms that govern the detrimental effect of EP/AW additives on bearing performance, it is necessary to study closely the interactions occurring in the system form by the base oil, the additives present and the steel surface, as well as the influence of operating conditions. The focus of the present work is to identify the parameters affecting the additive-derived layer formation, as it is directly related to the additive reactivity towards the surface, and the tribological properties of the layer, that will determine the tribological performance. Zinc dialkyldithiophosphate (ZDDP), and two low viscosity model oils with different polarity were selected. The influence of base oil polarity on the additive performance was studied in the nanoscale using Atomic Force Microscopy and the tribological performance was evaluated using a ball-on-disc test rig under mixed rolling-sliding conditions in the boundary lubrication regime. An in-situ interferometry technique was used to monitor the additive derived reaction layer formation, and the chemical composition, morphology and nanomechanical properties were studies using X-ray Photoelectron Spectroscopy, Atomic Force Microscopy and Nanoindentation respectively. It was found that base oil polarity determines the transport of additives to the surface thereby controlling the maximum reaction layer thickness, friction and wear, as well as the morphology and nanomechanical properties of the additive-derived reaction layer. However the reaction layer chemical composition is not determined by the base oil polarity. Among the operating conditions, shear was identified as a fundamental parameter on the activation of additives on rubbing steel surfaces and the properties of the derived reaction layer.

Polymer composites research designed for orthopaedic applications are commonly focused on Ultra high molecular weight polyethylene (UHMWPE) reinforced by a variety of different nanoparticles. However, the high melt viscosity of UHMWPE renders conventional melt mixing techniques impossible for composite manufacturing. Either solvents that are often difficult to extract from the finished composite or addition of high density polyethylene is necessary in order to use conventional melt mixing techniques. Therefore, solid state mixing is convenient option for manufacturing of UHMWPE based nanocomposites.The aim of this work is to optimize manufacturing parameters (rotational speed and mixing time) for CNT and ND reinforced UHMWPE prepared by planetary ball milling. Many reports have previously been presented, where UHMWPE has been reinforced by CNTs through ball milling, but typically, only mixing time is presented as the crucial variable in ball milling and the movement of the vials, size of the balls, ball-to-powder mass ratio, mixing media and even rotational speed are often overlooked.During this work, both multi walled carbon nanotubes (MWCNTs) and nanodiamonds (NDs) as reinforcement in UHMWPE have been studied. Beginning with the optimal speed in a planetary ball mill for CNT reinforcement and continuing to time and mixing media for NDs. Scanning electron microscopy (SEM) has been used to study the dispersion of nanoparticles using an extreme high resolution SEM (XHR-SEM). Differential scanning calorimetry (DSC) was used to study the thermal properties of the nanocomposite and X-ray diffraction (XRD) was used to complement the crystallinity measurements obtained by DSC. The water contact angles were measured using the sessile drop method. The results showed changes in morphology on UHMWPE powder due to ball milling, such as flattening, welding of powder and changes in powder particle size. The ball milling procedure also negatively affected the crystallinity of the powder, however the crystallinity of the sintered material did not show this negative trend for all composites. Furthermore, thermal analysis did not show any changes in melting temperatures, which indicates that any thermal effects on the powder due to ball milling is only temporary. SEM analysis also showed that a higher speed and longer mixing times more effectively distribute and break down nanoparticle clusters, but at the expense of flattening of the powder and reduced powder crystallinity. It was also shown that wet mixing with ethanol was more efficient and less detrimental to powder morphology compared to dry mixing. Water contact angles were overall increased for composites compared to UHMWPE.

Metal-to-metal seals are critical components as their failure can lead to leakage of hazardous fluids to the environment or to fatal failure of the systems they operate on. Most systems are subjected to increasingly more demanding conditions and deeper knowledge about how different parameters affect the leakage is necessary to design seals with the desired performance. Fundamental knowledge can be obtained by means of numerical simulations, since it can provide in-situ information which would be extremely difficult, if not impossible, to obtain by means of physical experiments only. Moreover, in the virtual experiments it is possible isolate the effect of variations in a single parameter. However, no model that can serve as a predictive tool and thus has been tested against experimental results has been found in literature. The reason for this is the complexity in accounting for both the multi-scale nature of surface roughness and its intrinsic randomness. This lack have defined the main objective of this work, i.e., to develop a model for the leakage through metal-to-metal seals, which can output quantitative results that can be used for comparison against experimental work. This has been accomplished by including the stochastic nature of the surface topography explicitly in a two-scale method. The model constructed following this approach fulfills the requirement of giving a quantitative prediction of metal-to-metal seals. Moreover, it also provides new insight on the expected variability in leakage introduced by the stochastic nature of the roughness.A secondary objective has been to investigate the seal behaviour during unloading, i.e., when the applied load is gradually released after having caused significant plastic deformation. The reason for assessing this topic is that metal-to-metal seals subjected to a certain load cycle exhibit, at any given load, a significantly larger leakage during the first loading than it does during the subsequent unloading for the same load. The numerical simulations of the seal behavior during unloading also confirmed the smaller leakage during unloading. Moreover, it was observed that a substantial load release was required before a significant leakage increase could be detected and that the leakage remained nearly constant up to that point. This is an important finding that can be used when designing seals in order to account for stress relaxation during service live.

In the automotive industry, press hardening is usually employed to produce safety orstructural components from advanced high–strength steels. This hot forming process, andthermomechanical forming processes in general, is highly dependent on friction betweentool and workpiece as friction affects and controls the deformation of the workpiece.However, friction is also directly associated with wear of the forming tools. Tool wear isa complex system response depending on contact conditions and is a serious issue whenit comes to process economy as it reduces the service life of the tool. Therefore, it isnecessary to enhance the durability of thermomechanical forming tools by studying theinfluence of parameters such as contact pressure, cyclic thermal loading, repetitive mech-anical loading and others on tool wear. Then, computational mechanics can be utilised tonumerically simulate and optimise the thermomechanical forming process by predictingwear of the tools.Dry sliding tests were carried out on a high temperature reciprocating friction andwear tester. The aim was to identify the occurring wear mechanisms and determine thetribological behaviour of prehardened hot work tool steel when sliding against 22MnB5boron steel. A normal load of 31 N, which corresponds to a contact pressure of 10 MPa, asliding speed of 0.2 ms −1 and temperatures ranging from 40◦Cto800◦ C were employed.It was found that the coefficient of friction and the specific wear rate decreased at elevatedtemperature because of the formation of compacted wear debris layers on the interactingsurfaces.Increasing material and energy expenses, rising demands for process flexibility andstability as well as requirements for minimal trial and error have led to a growing interestin numerical simulation of wear phenomena. Finite element simulations of a strip drawingtest were conducted to explore the possibility of predicting tool wear in press hardening.The focus laid on unveiling the contact conditions on the forming tools through numericalsimulation. The influence of high temperature on wear was studied and the results wereimplemented in Archard’s wear model to introduce temperature dependence. Further-more, another wear model used for warm forging was also considered. It was found thatthe extreme contact conditions occurred at tool radii and that the different wear modelsled to similar wear depth profiles on the radii but with different orders of magnitude.Standard high temperature tribometers allow fundamental tribological studies to becarried out in order to investigate the tribological behaviour of the materials in contact.However, the conditions prevalent during the interaction of the hot workpiece and toolsurfaces in thermomechanical forming are not adequately simulated in these tribometers.A novel high temperature tribometer has been employed in order to more closely simulatethe interaction between tool and workpiece at elevated temperatures during thermomech-anical forming. It was found that a higher load led to a lower and more stable coefficient

Moving machine assemblies are increasingly exposed to extreme operating conditions involving high temperatures owing to demands on higher power densities, high performance/efficiency and extreme environments. The changes in surface and near surface properties of contacting surfaces caused by exposure to high temperature and deformation govern the occurrence of friction, wear and material transfer of the tribological system. However, these changes have not been thoroughly investigated. In order to enable development of new products and processes, there is a need for new knowledge pertaining to tribological phenomena occurring at elevated temperatures.One of the most commonly used engineering materials is steel as it offers a good compromise between performance and cost even at high temperatures. For example, prehardened (quenched and tempered) tool steels are commonly used in hot forming dies can also be employed in other technological applications involving elevated temperatures. Although the research pertaining to hot stamping, and high temperature tribology in general, has significantly grown during the last years there are still knowledge gaps that need to be bridged. Adhesion and abrasion have been identified as the most dominant wear mechanisms in high temperature tribological systems but the detailed understanding of the mechanisms is still inadequate.The objective of this work is therefore to obtain a deeper understanding of the tribological phenomena associated with adhesion and abrasion that takes place at high temperatures. Unidirectional sliding wear tests have been conducted in order to investigate the influence of contact pressure and temperature on the wear and friction characteristics of tool steel and boron steel pair. Tribological studies involving boron steel, tool steels and heat-treated high-Si steels in a three body abrasive environment were also carried out with a view to explore the effect of temperature on the wear rate, wear mechanisms and to correlate this with material properties like hot hardness and toughness.The results from the unidirectional sliding tests showed that the frictional behaviour of tool steel and boron steel is load and temperature dependent. In general the friction coefficient decreases as both temperature and load are increased as a result of the formation of oxide layers. At temperatures above 200 °C, the compaction and sintering of these layers led to the formation of a wear protective glaze layer. Consequently, the wear rate for both materials decreased at elevated temperatures. Additionally, a friction and wear mechanisms map was developed for the investigated materials.In the case of abrasive wear tests, the results showed that the main wear mechanism presented for each material varied with temperature. In general, a transition from micro-ploughing to a combination of micro-cutting and micro-ploughing was present. The tool steels and boron steel showed a decrease in wear rate in the range of 100 to 400 °C compared to that at room temperature. This was attributed to the toughness in case of the tool steel and the formation of a protective tribolayers for the boron steel. Above 400 °C the wear rate increased for these three materials mainly due to the recovery and recrystallization processes. The wear rate of the high-Si steels increased with testing temperature. At 500 °C, these steels had the same hardness and the differences in wear were attributed to the changes in the material toughness.

In order to predict and optimize energy efficiency, fuel consumption and service life, friction and wear need to be predetermined with higher accuracy than what is possible today. This prediction and optimization is crucial for the development of sustainable mechanical components and systems with excellent environmental performance.Better and more reliable models for predicting friction, wear and scuffing risk in boundary lubricated contacts will be developed in this project. This includes a model for asperity-asperity collision with components of contact mechanics, thermodynamics and physics.In the boundary lubricated contact, loads are mostly carried by asperities. This makes the real area of contact is so different from the nominal contact area, a small fraction of the nominal contact area supporting the load will cause high contact stress and large deformation. Surfaces of machine components operating under high stress in long period can easily cause damage. Therefore, an elastoplastic analysis of asperity collision was conducted with the Finite Element Method. The contact area and contact stress were studied based on the change of parameters as adhesive friction coefficient, interference and collision velocity. The plastically deformed area and residual stress after collision were also depicted in figures.Friction will generate heat in the sliding contact, and eventually cause a temperature rise. Due to the heat is generated at asperities, heat flux is not continuous and the temperature both increase to a relatively high value and decrease to a small value in very short time. This kind of temperature is often called flahtemperature, and it is important to study because it can affect the viscosity of the lubricant, the formation of tribolayer and in turn it will affect the mechanical properites of the surface. The flash temperature was analyzed based on the previous study of the elastoplastic asperity collision, the times for flash temperature to reach maximum value were given and thermal expansion was also included.The FEM model can conduct a study regardless of the geometry and material properties of the surface asperity, but due to the very fine mesh required at the interface, it is not suitable to carry out an analysis of the rough surface contact. Therefore the Boundary Element Method was adopted to have a thorough study of the rough surface contact. The features of the analysis coudcuted in the FEM model, such as strain hardening and friction, should be replicable in the BEM model. In the end, an Engineering tool for the rough surface contact will be developed.

With today’s striving towards reduction of fuel consumption it is moreimportant than ever to understand how different components in theinternal combustion engine function. There is a need for tools that canbe used to investigate and predict the result of specific design changesmade on the components. In this work, the mechanics and the tribologyof the power cylinder unit and more specifically the operation of thetwin land oil control ring (TLOCR) is investigated. In heavy duty dieselengines (HDDE), TLOCR are typically used. The TLOCR plays a veryimportant role in the engine since it is supposed to distribute the correctamount of oil on the liner to lubricate the other rings. It is importantthat the TLOCR does not leave too much oil on the liner for the twotop rings since it could lead too high oil consumption. In a HDDE thepiston assembly is the largest contributor to frictional losses where thepiston ring pack accounts for the major part of this. The oil control ringhas the largest contribution to frictional losses in the piston ring packtherefore making it very interesting to study from a fuel consumptionperspective. The objective of this thesis is to develop a simulation toolthat can be used to quantify design changes to the TLOCR. Such as thedimensions of the ring itself but also ring tension, running land profileand out of roundness of the cylinder liner.The model developed in this work accounts for the tribological interfaceof the TLOCR against the cylinder liner and piston ring groove aswell as the elastic deformation of the ring and the ring dynamics withinthe piston ring groove. The actual ring cross section is modelled in orderto account for the full three dimensional elastic deformation of the ring.By solving all of these problems as a coupled system it is believed thatthe entire operation of the oil control ring could be understood in a betterway than earlier and open up new optimisation possibilities for theTLOCR. The full ring is modelled in order to account for out of roundcylinder liners. Since the cylinder liner in an engine will always havesome deviation from perfectly round this is important. The model cantherefore be used to investigate the effect on oil distribution by reducedring tension which will affect the frictional losses of the system.