The purpose of this thesis is to summarize the research carried out that led to the development of measurement techniques which measure the water content of lubricating grease. A simple and effective grease mixing method for preparing grease samples was developed and tested for repeatability. Calcium sulphonate complex (CaS-X) grease was used in all experiments. The water content of these samples were also tested with time and temperature as added variables to study if and how much water will evaporate from the samples. Additionally, two measurement techniques were investigated: optical attenuation in the visible and near-infrared (NIR) region and with a dielectric measurement method. The optical attenuation investigation found that the attenuation ratio of two wavelengths of light appear to approximate the water content of grease samples with an acceptable coefficient of determination. Additionally, aged and oxidized grease were measured as well and were not found to affect the measurement results. The dielectric method uses the temperature dependence on the dielectric properties of water-contaminated grease to approximate the water content of the grease samples. An additional parameter of incomplete fill/coverage of the sensor has been investigated as a prestudy. Both methods were found to provide measurements of water content in the prepared grease samples (ranging from 0.22% to 5.5% added water). The dielectric measurement is likely going to be better for applications requiring the possibility of measuring a larger bulk of the grease within the bearing. It shows promise for providing an accurate and robust system for monitoring grease condition as well as the amount of grease contained. The optical measurement will likely provide additional information; however, it will only measure small point samples within the bearing instead of the larger bulk. This could be of use though, because the sensors could be small (in the several millimeter scale) and could measure where water damage is determined to be most important to detect at.

Conformal contacts like those found in journal or inclined slider bearings are widely encountered in various types of machines from small engines to large turbines. These contacts involve convergent gaps that are used to separate the surfaces in relative motion and generate pressure in the lubricant film. The contacts have to carry a load while keeping friction as low as possible. Environmental and economic concerns require the machines to operate with minimal power loss. A number of design modifications have been proposed over the years in order to decrease bearing power consumption. There are indications that surface topography can have a significant and positive influence on hydrodynamic performance. Texturing of a load carrying surface is a process that would be beneficial in lubricated conformal contacts as it would be possible to obtain thicker films and reduced frictional losses. Textured lubricated contacts are analysed with Computational Fluid Dynamics (CFD) code through different geometries. The effects of the texture on hydrodynamic performance of the contact are investigated. For the simulations performed, the full Navier-Stokes equations are solved under steady-state conditions. The flow is taken to be laminar and two- dimensional. A journal bearing with several dimples created on the stationary part is firstly investigated. A realistic multiphase flow cavitation model is introduced and successfully validated. It is shown that the coefficient of friction can be reduced if dimples of suitable depth are introduced. This can be achieved either in the region of maximum hydrodynamic pressure for a bearing with high eccentricity ratio or just downstream of the maximum film for a bearing with low eccentricity ratio. A new effect of pressure build-up, generated by the surface texture, has been identified at low eccentricity ratios. This pressure build-up effect is more extensively investigated through the study of an inclined slider bearing with a texture located at the inlet part of the contact, i.e. just downstream of the maximum film. The governing mechanism at the origin of an optimum in load carrying capacity for a smooth slider bearing is analysed and the effects of the texture on the pressure build-up and load carrying capacity are explained. The energy received by the fluid from the moving wall is converted into pressure in the first part of the converging contact and into losses in the second part. Convergence ratio can be increased until the limit where flow recirculation begins to occur is reached in order to get the greatest pressure gradient. The texture appears to reach its maximum efficiency when its depth is such that the velocity profile is stretched at its maximum without incoming recirculating flow. Thus, the wall profile shape controlling the velocity profile can be optimized for many hydrodynamic contacts. For such contacts, heat is usually produced due to shearing of the flow and the lubricant is subjected to temperature variations. Since the dynamic viscosity of the lubricant is temperature dependent, variation of the viscosity as well as frictional losses and load carrying capacity is expected. Thermal effects are analysed for different shear rates in this inlet textured slider bearing. Shear losses and subsequent heating reduce load carrying capacity compared with isothermal conditions. Texture has a positive effect in a parallel surface contact when thermal effects are considered. It has been found that for the different convergence ratios considered, the texture enables the sustaining of a load only until a certain critical shear rate is reached. This critical shear stress depends on a number of factors such as the convergence ratio and lubricant parameters including the viscosity-temperature coefficient and the reference dynamic viscosity. / <p>Godkänd; 2007; 20070320 (ysko)</p>

Rail grinding has been employed since the 1980s in maintaining optimal rail profile as well as in the elimination of surface defects such as corrugations and head-checks. Likewise, the wheel sets also require re- turning to remove surface defects and restore the desired profile. The influence of surface roughness in the wheel/rail contact has been a concern for railway owners since the introduction of rail grinding as a maintenance strategy. Presently, there are no scientifically derived guidelines regarding the surface topographies of ground rails and re-turned wheels. There is thus a need to establish well defined guidelines regarding the surface topographies for new surfaces on the rails and wheels in order to minimize grinding cost/time and improve wheel/rail performance. This thesis concerns the influence of surface roughness of wheel/rail surfaces on running-in behaviour, wear, friction and resultant surface damage. The results presented in this thesis are based on both field measurements and experimental simulations in the laboratory. A two-disc rolling/sliding test machine has been used in the experimental work to simulate the wheel/rail contact. The test specimens were manufactured from actual wheel/rail parts. The maching/finishing parameters were chosen in such a way as to obtain different surface roughness on the test specimens. A Design of Experiment approach (DOE) has been used to conduct experiments and to analyse the results. Results obtained from the field measurements show that the surface roughness of a newly ground rail changes rapidly during the initial stages following grinding. It was also concluded that there is a considerable variation of the surface roughness of re-turned wheels depending on which workshop performed the turning operation. Experimental results show that the surface roughness of the test specimens in certain material pairs do influence wear, friction and resultant surface damage. There is also a significant difference in the tribological behaviour of tests run in dry conditions and those run with water lubrication. / <p>Godkänd; 2007; 20070820 (pafi)</p>

In this work, the tribological behaviour of different sealing elastomers has been studied. The influence of aging of a sealing elastomer in different lubricants on its tribological behaviour has been investigated. Tribological behaviour of sealing elastomers in dry condition and the mechanisms occurring in run-in period have been studied. Further studies pertaining to the influence of lubrication on the abrasive wear of a sealing elastomer have also been carried out. / <p>Godkänd; 2007; 20071128 (ysko)</p>

Interacting surfaces are found in mechanical systems and components. Since engineered surfaces are not perfectly smooth, only a fraction of the nominal surface area is actually in contact. This fraction is denoted as the real area of contact, Ar, and is formed by the sum of the contact spots between the two touching surfaces. If these contacting surfaces are sliding, then friction and wear occur in these actual contacts. Friction and wear may be controlled by lubrication: depending on the operating conditions different types of lubrication regime exist. When the surfaces are completely separated by the fluid film and load is carried by hydrodynamic action, contacts operate in hydrodynamic regime. When the load is carried by the lubricating fluid and asperity contact, the regime becomes mixed lubrication. In boundary lubrication, surfaces are in contact and the load is carried by surface asperities. In many cases this is the critical lubrication regime that governs the life of the components. Due to the complexity of thin film boundary lubrication, design of lubricated interfaces is still a trial-and-error process. The mechanism of formation and rupture of oxide layers and boundary layers is not completely known and a reliable model for rough surfaces in boundary lubrication is currently lacking. This study focuses on boundary lubrication regime: the effect of surface roughness on the real area of contact is investigated and a numerical model for the sliding interaction between two asperities in sliding contact is developed. Numerical simulations of normal, dry, friction free, linear elastic contact of rough surfaces are performed. A variational approach is followed and the FFT-technique is used to speed up the numerical solution process. Five different steel surfaces are measured using a Wyko optical profilometer and several 2-D profiles are taken. The real area of contact and the pressure distribution over the contact length are calculated for all the 2-D profiles. A new slope parameter is defined. An artificial neural network is applied to determine the relationship between the roughness parameters and the real area of contact. Boundary lubrication mechanism is usually controlled by the additives present in the oil that form low friction, protective layers on the wearing surfaces. Chemical reactions between the lubricant molecules and the asperity surface may take place. These reactions are activated by certain values of pressure and temperature. Fundamental research on the influence of surface roughness on contact conditions is hence required and is a key factor in understanding the wear mechanism in boundary lubrication condition since pressure distribution, shear stresses, frictional heating, mechanical wear highly depends on surface topography. Modelling boundary lubrication requires knowledge in many fields: contact mechanics, thermodynamics, surface chemistry etc, thus different sub-models interacting each other must be created. It is complicated and may be not feasible within a foreseeable time period to take into account all the different parameters and evaluate them. Artificial intelligence is a way to overcome the problem and determine the relationship between input parameters and desired outputs. An elasto-plastic analytical model is used to determine the variation of pressure distribution and shear stress during the collision process of two asperities in sliding contact. The outputs of the elasto-plastic model are inputs of the thermal model that calculates the temperature rise during the collision process. The desorption of the adsorbed layer is determined by using existing adsorption theories and finally the probability of wear is computed at each time step of the collision process. Different results obtained using different adsorption theories and different input parameters are compared. / <p>Godkänd; 2008; 20080512 (ysko)</p>

Wet clutches are used in a variety of different machinery. Wet clutches and brakes are frequently used to distribute torque in vehicle drive-trains. The clutches can be located in e.g. automatic transmissions or limited slip differentials. Their frictional behavior is of great importance for the overall vehicle behavior and has to be thoroughly investigated when designing new wet clutch applications. Frictional behavior is normally investigated in test rigs where complete friction discs are tested under similar working conditions as for the clutches in the drive-train. However, it is today possible to simulate the clutch behavior and not limited ourselves to only use testings as a help in the design of the wet clutches. This is an advantage because it is possible to simulate behavior that is not possible to measure in test rigs. Another advantage is the faster and more cost efficient design process than when all tests are carried out in a laboratory.The torque transferred by the clutch during engagement can be roughly divided into full film torque and boundary lubrication torque. Full film torque originates from the part of the engagement where the friction discs are completely separated by a lubricant film and the friction surfaces are not in contact, whereas boundary lubrication torque occurs when the lubricant film is so thin that the surfaces of the friction discs are in direct contact. The distribution between these two types of torque is different for different types of wet clutches and engagements. When the clutch works in full film regime, it is possible to simulate the friction quite well, whereas the friction in the boundary regime is much more difficult to model and simulate, since it is very additive dependent.The most common use of wet clutches is in automatic transmissions for vehicles. Hence, most research in wet clutch testing and simulations are performed on wet clutches suitable for these applications. Here, the wet clutch is often used to brake a rotating shaft to standstill and the total engagement will have a duration of fractions of a second. During most of the engagement the clutch will be working in full film lubrication.In this investigation, the focus is on wet clutches working under limited slip conditions, i.e. the clutches will have a limited slip during a long duration without any lock-up. During this kind of engagement the clutch will work mainly in boundary lubrication and generate much heat. Such clutches can be found in, e.g. limited slip differentials.The optimum when designing a new wet clutch would be to simulate the clutch during the whole engagement without having to do any measurements in the laboratory. This, however, is not yet possible but an efficient way to design clutches can be obtained by combining fast friction measurements with efficient computer simulations. In this work, a simple friction measurement technique for wet clutches working in boundary lubrication is developed, based on pin on disc measurements. These friction measurements are combined with a temperature simulation of a wet clutch, where the lubricant cooling flow, dependent of the surface groove pattern, is simulated. This method makes it possible to allow a wet clutch working in boundary lubrication to be optimized for given working conditions regarding lubricant, friction material and surface groove pattern. The simulations are validated by measured data from a test rig in which whole friction discs are investigated with the same working conditions. / Godkänd; 2006; 20061204 (parmar)

The lubricants of the future have to be more environmentally adapted, have a higher level of performance, and lower total life cycle cost (LCC) than commonly used lubricants today. Since we live on a planet with finite resources, we have to think about coming generations and work for a sustainable development in the field of tribology. To be able to formulate those lubricants, the properties of the base fluids have to be well known. Base fluid properties that influence the formulated lubricant performance could be divided in to three different groups. These groups are; physical, chemical and film formation properties. In this study are properties from all of these groups investigated to improve the understanding on there influence on base fluid overall performance. There are more or less environmentally adapted base fluids available for formulation of lubricants. They could be divided in to different groups, mineral, semi synthetic and synthetic fluids. Synthetic fluids could be of different type: PAO (poly alpha olefins), Synthetic ester, Poly glycols and others. The most interesting group for formulation of environmentally adapted lubricants are the synthetic esters. In this thesis the properties for a large number of environmentally adapted ester base fluids are studied in detail. The tested properties relate to the macroscopic / molecular behaviour and include: viscosity-temperature-pressure-effects, thermal conductivity, and heat capacity per unit volume. The film formation capability in EHD contacts is also studied. Different connections between the molecular structure and the performance for the fluids are discussed. As an example, it is found that a large number of carboxylate groups in the ester molecule are improving the thermal properties, and thereby a thicker lubricating film could be maintained in highly loaded, high slip contacts. / Godkänd; 2004; 20070128 (ysko)

This work investigated the wear mechanisms of turbocharger components in heavy duty diesel engines. By understanding the wear mechanisms that are occurring in turbochargers the life time of the turbocharger components can be improved. For better understanding, as to why the components are worn out, an analysis of several turbocharger components and tribological tests were carried out.   The contact surfaces between turbocharger and sealing rings were analysed. Surfaces are analysed by several methods, including chemical composition of the surface. Influence of different parameters such as contact pressure, sliding velocity, temperature, and distance on friction and wear behaviour are established by performing tribological tests. Pin on disc sliding wear tests were carried out at both room temperature and at high temperature of 300˚C. The pin and the disc, that were used during the tribological tests, were made of the same materials that are used in turbocharger components.   Analysis of pins and discs from tribo-tests and turbocharger components (turbine sealing rings and shafts) show abrasive and adhesive wear on the worn surfaces of the components, from both the tribological tests and the turbochargers respectively. An increase of the temperature resulted in a reduced friction due to the formation of oxide layers on the sliding surfaces of pins and discs. In the turbocharger, traces of lubricant between the sliding surfaces was found, in addition to plastic deformations on the worn surfaces of the shafts and adhesive and abrasive wear on both worn surfaces that were in contact with each other. On the other hand, on the worn surfaces of the turbine sealing rings some cracks were observed that were perpendicular to the sliding direction, which indicates presence of a fatigue process. The presence of fatigue cracks is probably due to the way the trucks were operated, the increase and decrease of temperature and pressure in the turbocharger is probably the cause of these cracks.   To minimize the wear mechanisms that occurs in turbocharger components such as sealing rings and shafts, there are some parameters such as contact pressure between the sliding surfaces of the components that can be minimized. By minimizing the contact pressure between the sliding surfaces, the lifetime of turbocharger can be improved. A better surface finishing and geometry of the contacting surfaces can also improve the sealing rings and shafts lifetime. To minimize the relaxation of turbine sealing rings, materials that can better keep the mechanical properties of the sealing rings at high temperatures must be used.

The following report conducted with collaboration of the University of Halmstad and ABSandvik Coromant.The focus of the project is characterizing the surface topography of different surface treatmentvariants before and after chemical vapor deposition (CVD).As a part of improving the knowledge about the surface area characterization and accomplisha better knowledge and understanding about surfaces and its relation to wear of uncoatedWC/Co cutting tools The project initiated in February 2016 and end date was set to May2016.The methodology used in this thesis based on the statistical analysis of surface topographicalmeasurements obtained from interferometer and SEM by using Digital-Surf-MountainsMapsoftware.The finding from this thesis showed that Mean and Standard deviation method, Spearman’scorrelation analysis and Standard deviation error bar followed by ANOVA and T-test areeffective and useful when comparing between different variants.The thesis resulted in a measurement approach for characterizing different surfacetopographies using interferometer and SEM together with statistical analysis.Keywords: 3D-Surfaces Texture, CVD coating inserts, Interferometer, Spearman’s correlation andANOVA &amp; T-test.

Godkänd; 1984; 20070424 (ysko)