Surfaces are rough, unless special care is taken to make them atomically smooth. Roughness exists at all scales, and any surface-producing operation affects the roughness in certain degrees, specific to the production process. When two surfaces are brought close to each other, contact is established at many isolated locations. The number and size of these contact islands depend on the applied load, material properties of the surfaces and the nature of roughness. These contact islands affect the tribological properties of the contacting surfaces. The real contact area, which is the sum total of the area of contacting islands, is much smaller than the apparent contact area dictated by the macroscopic geometry of the contacting surfaces. Since the total load is supported by these contact islands, the local contact pressure will be very high, and dependent on the local microscopic geometry of the roughness. Thus understanding the deformation behaviour of the rough surfaces will lead to better understanding of friction and wear properties of the surfaces. In this work, the interaction of these contact islands with each other is studied when two surfaces are in contact and sliding past each other. Asperities can be thought of as basic units of roughness. The geometry and the distribution of heights of asperities can be used to define the roughness. For example, one of the earliest models of roughness is that of hemispherical asperities carrying smaller hemispherical asperities on their back, which in turn carry smaller asperities, and soon. In the present study the asperities are assumed to be of uniform size, shape and distribution. Normal and tangential loading response of these asperities with a rigid indenter is studied through elastic-plastic plane strain finite element studies. As a rigid indenter is loaded onto a surface with a regular array of identical asperities, initial contact is established at a single asperity. The plastic zone is initially confined within the asperity. When the load is increased ,the elastic-plastic boundary moves towards the free surface of the asperity, and the contact pressure decreases. The geometry and spacing are determined when the neighbouring asperities come into contact. The plastic zone in these asperities is constrained, and hence contact pressure sustained by these asperities is larger. As the indentation progresses, more asperities come into contact in a similar way. If a tangential displacement is now applied to the indenter, the von Mises stress contours shift in the direction of indenter displacement. As the tangential displacement increases, the number of asperities in contact with the indenter decreases gradually before reaching a steady sliding state. The tangential sliding force experienced by the indenter arises from two components. One is the frictional resistance between the contacting surfaces and the other is due to the plastic deformation of the substrate. If the surface is completely elastic, it has been seen that the sliding force is purely due to the specified friction coefficient. For the smooth surface, as the subsurface makes the transition from purely elastic to confined plastic zone, plasticity breaks out on the free surface, hence the sliding force increases. For surfaces with asperities, even at very small load, the asperities deform plastically and hence the sliding force is considerably higher. The frictional force is experimentally measured by sliding a spherical indenter on smooth and rough surfaces. These experimental results are qualitatively compared with two dimensional finite element results. It has been observed that for rough surface, sliding force is considerablyhigherthanthesmoothsurface,asisobservedinsimu-lations at lower loads. In contrast to the simulations, the sliding force decreases at higher loads for both the smooth and rough surfaces.

In the last decades, significant improvements regarding the design, materials and technology of rock drills have been made. Likewise, in sheet metal forming, forming tools experience very high contact pressures when processing high strength steel sheets. In both applications components operate under extremely tough contact conditions that result in an accelerated component failure. Enhancements on mechanical properties of components material subjected to extreme contact conditions are highly required in order to withstand the application loads and prevent severe wear. The present thesis was focused on understanding of machinery component damage mechanisms under severe contact conditions. A case study of worn components used in rock drilling and sheet metal cold work was carried out. Thread joints from rock drilling and punches from sheet metal pressing were selected for the investigation. For these components, sliding contact under high contact pressure is a common load condition under the components usage. Then, to understand and quantify the influence of contact parameters, load and surface quality on material performance, laboratory simulations were performed. The results were used for a comparative analysis of the typical damage mechanisms observed in the tests and the case study of the components. The case study results showed that the threaded surfaces underwent severe plastic deformation due to the high-pressure sliding contact. The microstructure beneath the worn surface was altered and surface cracks and delamination were frequently observed at the worn surface. The dominant damage mechanism found on the investigated punches was adhesive wear. Material transfer adds friction stresses at the punch surface and ultimately, with repeated punch strokes, it leads to initiation and propagation of fatigue cracks. Wear process in thread joint and punch wear was simulated using the SOFS. The worn specimens tested experimentally showed similar wear mechanisms obtained in the case study. The thread joint wear simulation showed that the total damage at the worn surface was a result of adhesive wear, plastic deformation, and initiation and propagation of fatigue cracks. In addition, the results showed that the type of motion had a significant influence on the worn volume and crack initiation, and more severe wear was observed at reciprocal motion. The punch wear simulation showed that the friction quickly increased as work material from metal sheets transferred to the disc surface. The rate of the material transfer was strongly dependent on the combination of sheet material and tool steel. Further, the present experimental simulations were applicable to characterize and predict wear of components in the application. / Components used in rock drilling and sheet metal forming operate under harsh contact conditions that result in an early-life component failure. Wear and fatigue are considered as the most common damage mechanism for these components. Commonly, the service life of a component is designed based on its fatigue life. However, wear might have a significant effect on the components life too. Wear results in a surface damage that in turn may cause a fatigue crack initiation. Therefore, knowledge about wear of materials and components is a key factor in design and prediction of the lifetime of the components. In order to predict wear of a certain component, a thorough understanding of the component with regards to its material properties, application loads and working environment, and damage mechanisms is required. The overall aim of the present work was to define the typical wear mechanisms occurred on machinery components used in rock drilling and sheet metal forming. A comparative analysis of the case studies and results from performed laboratory tests simulated wear mechanisms in the applications highlighted wear mechanisms and factors influencing severity of wear in the applications. Obtained information is crucial for ranking and selection of the best material in the applications. / <p>The presentation will will be via zoom. PhD student will together with the supervisors will be in Karlstad while the opponent is in Luleå. </p>

Ein Haupteinsatzgebiet der Großraummanipulatoren stellen Betonverteilermasten dar. Aufgrund der langen schmalen Armkonstruktionen fällt bei diesen Maschinen der Trend zum Leichtbau bezüglich der Dynamik besonders ins Gewicht. Um die Vorteile leichter Konstruktionen wie geringere Achslasten, geringerer Kraftstoffverbrauch und kleinere Antriebe nutzen zu können, werden Regelungen benötigt, die die Struktur stabilisieren und ein Schwingen der Mastspitze verhindern. Zur Systemanalyse und Regelungsauslegung wurde ein Mehrkörpermodell aus starren und elastischen Körpern sowie den notwendigen Hydraulikzylindern erstellt und durch Messungen validiert. Am Modell konnte gezeigt werden, dass die Regelung im letzten Gelenk die Schwingung an der Mastspitze maßgeblich beeinflusst und zur Schwingungstilgung eingesetzt werden kann. Hierfür wird die Bewegung des Verteilermastes durch eine Ausgleichsbewegung im letzten Gelenk kompensiert, sodass die Mastspitze keine starken Schwingungen ausführt. Die Schwingungen werden über Beschleunigungsmessung detektiert und nach entsprechender Filterung kann die Bewegung bestimmt werden. Mittels Sliding Mode Control erfolgt die Berechnung der schwingungsmindernden Zylinderkraft und garantiert somit Robustheit gegenüber Modellierungsungenauigkeiten und äußeren Störungen. Die Kraftregelung des Hydraulikzylinders wird anschließend über eine Integrator-Backstepping Regelung realisiert. Die resultierende Schwingungsminimierung beträgt in unterschiedlichsten Maststellungen bis zu 95%. / A special case of multi-link manipulators are truck mounted concrete pumps. Due to the lightweight design of the long and slender boom, it is vulnerable to vibrations. The advantages are smaller masses and therefore less actuation power which results in smaller actuators with less fuel consumption. In order to retain the advantages of lightweight design, special controllers are needed to stabilize the overall system and result in a vibration free motion of the boom tip. A multibody system with flexible bodies has been built in order to analyse the system's behaviour and to test and design appropriate control strategies. It could be demonstrated, that controlling only the last joint of the boom decisively effects the motion of the boom tip and is therefore suitable to suppress vibrations. The idea is to compensate the boom's motion by adjusting the last joint angle in a way, so that the boom tip stays at its initial position. In order to implement these findings and obtain a robust control three steps are necessary: the boom's motion must be measured and a vibration reducing force defined which has to be applied by the hydraulic actuator. The vibrations are detected by acceleration measurement and after appropriate filtering a joint angle trajectory can be determined. The cylinder force is found using Sliding Mode Control which guarantees robustness against modeling inaccuracies and external disturbances. A mathematical description of the last segment is necessary for the design of this nonlinear control strategy. The force control of the hydraulic cylinder is then implemented via backstepping control. The resulting vibration is minimized by this control by up to 95% at different boom positions.

Das Ziel dieser Forschungsarbeit ist die Bestimmung charakteristischer aerodynamischer Koeffizienten im Schwebeflug mit Hilfe von Strömungssimulationen. Diese Koeffizienten werden für eine modellbasierte Regelung eines vollaktuierten Multikopters benötigt. Für die Simulationen wird aufbauend auf vorangegangenen Arbeiten ein ‚Sliding-mesh‘-Modell optimiert und einem ‚Overset-mesh‘-Modell gegenübergestellt. Die Verfahren werden anhand von Mess- sowie Referenzdaten hinsichtlich ihrer Rechenzeit und Genauigkeit verglichen. Die Messdaten werden im Rahmen dieser Arbeit ausgewertet. Die Referenzdaten stammen aus älteren Untersuchungen. Das ‚Overset-mesh‘-Verfahren liefert bei viermal höherer Rechenzeit gleichwertige adäquate Ergebnisse. Aus diesen Gründen werden anknüpfende Untersuchungen des Zeitverhaltens der Rotorschubkraft bei Drehzahländerungen mit dem ‚Sliding-mesh‘-Modell durchgeführt. Es wird beobachtet, dass die Schubkraft innerhalb der Simulation den Messdaten bei Drehzahlsprüngen vorauseilt.:1 Einleitung 1.1 Motivation 1.2 Zielsetzung und Aufbau der Arbeit 2 Theoretische Grundlagen 2.1 Strömungsmechanik 2.1.1 Grundgleichungen 2.1.2 Zusätzliche Gleichungen 2.1.3 Navier-Stokes-Gleichungen 2.1.4 Laminare und turbulente Strömungen 2.1.5 Grenzschicht 2.2 Numerische Strömungsmechanik 2.2.1 Numerische Diskretisierung 2.2.2 Numerische Lösungsmodelle 2.2.3 Turbulenzmodelle 2.3 Rotorströmungen 2.3.1 Strahltheorie 2.3.2 Numerische Rotorsimulation 3 Stand der Technik 3.1 Motivation 3.2 Rotorströmung 3.3 Aeroelastizität 3.4 Nachlaufströmung 4 Umsetzung 4.1 Modellbildung 4.1.1 ‚Sliding-mesh‘-Verfahren 4.1.2 ‚Overset-mesh‘-Verfahren 4.2 Validierung 4.2.1 ‚Sliding-mesh‘-Verfahren 4.2.2 ‚Overset-mesh‘-Verfahren 4.3 Modifikationen 4.3.1 ‚Sliding-mesh‘-Verfahren 4.3.2 ‚Overset-mesh‘-Verfahren 4.4 Auswertung 4.4.1 ‚Sliding-mesh‘-Verfahren 4.4.2 ‚Overset-mesh‘-Verfahren 5 Messaufbau und Messauswertung 5.1 Messaufbau 5.2 Messauswertung 5.2.1 Schubkraftverlauf 5.2.2 Drehmomentenverlauf 6 Zeitverhalten 6.1 Modellbildung 6.2 Auswertung Schubkraftverlauf 6.2.1 Drehzahlsprung 1 6.2.2 Drehzahlsprung 2 7 Zusammenfassung und Ausblick 7.1 Zusammenfassung 7.2 Ausblick

Introduktion: Röntgenmottagningen på Universitetssjukhuset i Örebro (USÖ) undersökertraumapatienter med sliding gantry datortomografi (SGDT). I ett SGDT-system står bordet fastpå plats och det är istället gantryt som rör sig över patienten under bildtagningen. Detta öppnarupp för möjligheten till ett nytt arbetssätt vilket kan påverka både röntgensjuksköterskor ochpatienten. Syfte: Syftet med studien är att undersöka hur SGDT påverkar röntgensjuksköterskans arbete vidtrauma och akutverksamhet. Underlättar SGDT arbetsflödet för röntgensjuksköterskor? I sådanafall hur? Metod: Studien utfördes som en kvalitativ studie med semistrukturerade intervjuer. Tioröntgensjuksköterskor deltog i studien. För att koda material och skapa tema gjordes en kvalitativinnehållsanalys. Resultat: Fördelar med SGDT är att arbetsflödet blivit smidigare eftersom det finns en tydligareroll i traumarummet, det är bättre organiserat, samarbetet med traumateamet har blivit bättre ochröntgensjuksköterskorna återgår fortare till normala akutflödet. Nackdelen med SGDT är att detinte är anpassad till ett vanligt akutflöde på USÖ. Slutsats: SGDT underlättar arbetsflödet för röntgensjuksköterskan vid en traumasituation med ettförbättrat samarbete, kommunikation och organisering. Dock är SGDT inte optimal för detvanliga akuta flödet. / Introduction: The department of radiology at Örebro University Hospital (USÖ) examinestrauma patients with sliding gantry computed tomography (SGDT). A SGDT system incorporatesa stationary examination table with a gantry that passes over the patient during scanning. Thisnovel method has the potential to affect both the radiographer as well as patient care. Aim: The aim of the study is to ascertain how SGDT affects the work of radiographers in traumaand emergency care. Does a SGDT facilitate an improved workflow for radiographers? If so,how? Method: The study used a qualitative design with semi-structured interviews. Ten radiographersfrom USÖ participated in the study. A qualitative content analysis was performed to create codesand themes from the collected materials. Results: The foremost benefit of SGDT is that the radiographers’ workflow improved. This isdue to a clearer role in the trauma suite, improved organisation, better interprofessionalcooperation with the trauma team and the ability to return more quickly to regular acuteexaminations. A drawback with SGDT is that it is suboptimal for normal acute examinations. Conclusion: SGDT facilitates a better workflow for radiographers in trauma examinationsbecause of improved coordination, communication and organisation, with few drawbacks.

Silicon nitride on steel sliding contacts may provide advantageous tribological properties over traditional self-mated pairs, however the friction and wear behavior at high sliding speeds (>1 m/s) is not well understood. Previous studies at low sliding speeds (< 1 m/s) have found that the wear mechanisms change as a function of the operating parameters, e.g. atmosphere, sliding speed, load, and temperature, due to the formation of transition metal oxides such as Fe2O3 and Fe3O4. This study detected transient effects of the dry silicon nitride on steel contact over a range of sliding speeds to understand their relation to tribochemical reactions and the resulting tribological behavior. Two sets of dry silicon nitride on steel experiments were conducted at 1.45 GPa maximum Hertzian pressure. The first set were low sliding speed reciprocating experiments, conducted at an average of 0.06 m/s, conducted at variable operating temperature, ranging from 23 °C to 1000 °C. In the low sliding speed experiments, transitions of the wear mechanism from adhesive wear, to abrasive wear, then to oxidative wear was observed when the operating temperature increased. The second set were high sliding speed experiments, conducted at variable sliding speeds, ranging from 1 m/s to 16 m/s. In the high sliding speed experiments, a transition from adhesive wear to oxidative wear was observed when the sliding speed surpassed 4.5 m/s. The high sliding speed experiments were accompanied by in-situ instrumentation which detected the presence of a tribofilm which correlated to a reduction in friction, and its formation was linked to tribochemical reactions induced by high flash temperatures. Both sets of experiments had a maximum estimated contact temperature of 1000 °C where oxidative wear was prevalent. Although, the low sliding speed experiments underwent severe bulk oxidation and thermal softening effects, while the high sliding speed experiments experienced localized flash heating events with temperatures sufficient to form a semi-coherent tribofilm that was lubricious and significantly improved wear resistance. Therefore, the effects of transition metal oxides in sliding contacts are determined to be significantly influenced on their mechanisms of formation and interrelated to the operating parameters as found for dry sliding silicon nitride on steel contacts.

Evidence of networks in the resting-brain reflecting the spontaneous brain activity is perhaps the most significant discovery to understand intrinsic brain functionality. Moreover, subsequent detection of dynamics in these networks can be milestone in differentiating the normal and disordered brain functions. However, capturing the correct dynamics is a challenging task since no ground truths' are present for comparison of the results. The change points of these networks can be different for different subjects even during normal brain functions. Even for the same subject and session, dynamics can be different at the start and end of the session based on the fatigue level of the subject scanned. Despite the absence of ground truths, studies have analyzed these dynamics using the existing methods and some of them have developed new algorithms too. One of the most commonly used method for this purpose is sliding window correlation. However, the result of the sliding window correlation is dependent on many parameters and without the ground truth there is no way of validating the results. In addition, most of the new algorithms are complicated, computationally expensive, and/or focus on just one aspect on these dynamics. This study applies the algorithms and concepts from signal processing, image processing, video processing, information theory, and machine learning to analyze the results of the sliding window correlation and develops a novel algorithm to detect change points of these networks adaptively. The findings in this study are divided into three parts: 1) Analyzing the extent of variability in well-defined networks of rodents and humans with sliding window correlation applying concepts from information theory and machine learning domains. 2) Analyzing the performance of sliding window correlation using simulated networks as ground truths for best parameters’ selection, and exploring its dependence on multiple frequency components of the correlating signals by processing the signals in time and Fourier domains. 3) Development of a novel algorithm based on image similarity measures from image and video processing that maybe employed to identify change points of these networks adaptively.

The friction of rubber on ice and snow surfaces is complex. Deeper scientific understanding is important for optimising performance of tyres in winter. Rubber, ice and snow systems exhibit frictional behaviour which depends on their material properties. The viscoelastic nature of rubber results in a higher real contact area compared to most other solids. At temperatures close or below the glass transition temperature, the frictional behaviour of rubber changes and its hardness increases. Thus, the real area of contact decreases, while the dissipation in the bulk of the rubber increases. Sliding of rubber on ice or snow leads to a temperature increase at the interface because of frictional heating, this can cause the surface to melt which decreases friction significantly. In this study we measured the friction of rubber on ice and snow and related the behaviour to mechanisms that occur. Key parameters affecting friction were examined and quantified. For this work a cold room and a new linear tribometer were specially designed and constructed. The rubber samples were made from various compounds and had different geometries. Typically they were the size of a “tread block element”. The geometries were chosen systematically to investigate the effects of surface area, sharp/rounded edges and sipes (small slits in the tread block that are used on snow tyres). A significant part of the work was developing consistent and reproducible ice and snow surfaces. New protocols were devised for these. The ice surfaces were made of de-ionised water, tap water and de-ionised water with salt. For the snow surface production: artificial snow was made and then compacted in a specially manufactured press, resulting in hard packed snow tracks for testing. Static and dynamic friction were investigated. Both were affected by speed, load, temperature and ice composition. The dynamic friction behaviour on ice was explained in terms of melt-water formation and the real area of contact of the rubber. The static friction was significantly affected by the losses inside the rubber bulk, the adhesive forces at the interface, and the time of stationary contact before the test. The investigation of rubber sliding on snow showed some similarities with sliding on ice; the surface of the rubber block slides over snow particles resulting in similar mechanisms as are seen on ice. However with snow there can also be a “ploughing” effect, where snow is cut by the leading edge of a sharp tread block. This effect contributes to friction. Experiments were made with simple rounded edged samples to avoid ploughing; the results showed the same trends as seen on ice, i.e. lower friction with increased speed, load and temperature. Investigations of siped tread blocks showed the same friction at low speeds as tread blocks without sipes. At higher speeds siped blocks exhibited less, or no, decrease in friction; more sipes gave less friction decrease. Our industrial collaborator, Michelin, made vehicle tests on snow using whole tyres with similar tread blocks. The trends they found were identical to our tests despite the dynamics of the system being more complex. This indicates how powerful the approach of using simple systematic experiments is for generating deeper understanding of the processes involved in sliding on ice and snow.

This thesis aims to better understand the relationships between basal water pressure, friction, and sliding mechanisms at ice sheet scales. In particular, it develops a new subglacial hydrology model (Hydro) to explicitly predict water pressures in response to basal water production and water injection from the surface. Recent research suggests that the Greenland ice sheet (gis) is losing a substantial volume of ice through dynamic thinning. This process must be modelled to accurately assess the contribution of the gis to sea-level rise in future warming scenarios. A key control on dynamic thinning is the presence of water at the ice-bed interface; Zwally et al. (2002) highlight the importance of supraglacial lakes' impact on basal ice dynamics, a process now con rmed by Das et al. (2008) and Shepherd et al. (2009). Many studies focus on the effects of surface meltwater reaching the bed of the gis but the underlying processes are often ignored. Geothermal, strain, and frictional melting, which evolves with basal hydrology, provide the background basal pressure profile that surface meltwater perturbates. Without understanding how these heat terms affect the background profile it is difficult to define basal boundary conditions in models and therefore difficult to model the dynamic response of the gis to surface melting. Hydro tracks subglacial water pressures and the evolution of efficient drainage networks. Coupled with the existing 3D thermomechanical ice sheet model Glimmer, model outputs include effective pressure N and the efficient hydraulic area. Defining frictional heat flux and basal traction as functions of N allow the modelling of seasonal dynamic response to randomly draining supraglacial lakes. Key results are that frictional heat flux, as a function of N, caps potential runaway feedback mechanisms and that water converges in topographic troughs under Greenland's outlet glaciers. This leads to a background profile with low N under outlet glaciers. Therefore, outlet glaciers show a muted dynamic speedup to the seasonal surface signal reaching the bed. Land-terminating ice does not tend to have subglacial troughs and so has higher background N and consequently a larger seasonal response. This, coupled with effects of ice rheology, can explain the hitherto puzzling lack of observed seasonal velocity change on Jakobshavn Isbræ and other outlet glaciers.

The rolling-sliding dry-wear behaviour of a series of bainitic steels and a standard pearlitic rail steel have been compared over a range of contact stress and creepage conditions applicable to the British Rail network. A rolling-sliding wear machine has been constructed - LEROS - which allows very high contact stresses to be combined with high creepages under well controlled conditions. Materials were tested on LEROS and on an Amsler machine. Limited vibration analyses were carried out on both machines and compared with the frequencies of disc surface periodic undulations. No direct linkage was determined. Despite better standard mechanical properties, the wear resistance of lower carbon bainitic steels was inferior to that of the pearlitic steel. A bainitic steel with the same carbon content as the pearlitic steel wore a little less, but at considerable expense to the pearlitic wheel steel counter-material in the wear couple. The wear resistance of bainitic steels depends upon the volume fraction of hard phase, such as carbide and martensite-austenite phase, for rolling-sliding as well as other types of dry wear loading. Pearlitic steel performs exceptionally well under certain rolling-sliding conditions, such as the majority seen in these tests, since the lamellar microstructure is modified so as to present a greater area fraction of carbide hard phase at the wear surface, a fraction in excess of bulk volume fraction. Recommendations are made for the dry wear applicability of the steels.