Obtaining an enhanced lifespan for mechanical transmissions has become a challenge in diverse application sectors. Micropitting as a contact fatigue mechanism has seriously jeopardized the well-being of rolling-sliding elements present for instance in gearboxes. Additivation through copper nanoadditives has demonstrated promising results in preventing contact fatigue. There is a need to assess the influence of copper nanoadditives on micropitting and mild wear before contemplating employing them in real transmission gearboxes. Consequently, this research work aims to acquire knowledge of the tribological behavior of rolling-sliding contacts additivated with a copper nanoadditive, emphasizing the influence of two different copper nanoadditive concentrations (0.3% and 3%) on wear and micropitting as failure mechanisms. Tests were performed using a micropitting test rig. Micropitting and wear were analyzed at different slide-to-roll ratios (1%, 5%, and 30%), different load conditions (1.5 GPa and 2.5 GPa), and different temperatures (60 °C and 100 °C), for all versions of the studied lubricant. There was no change in friction behavior between the versions of the oil additivated with the copper nanoadditive and its original version. Furthermore, it was found a reduction of micropitting for the 3% version of the studied oil in some operating conditions, and a reduction of the average wear volume for this same concentration in all studied operating conditions. On the other hand, it was found that the 0.3% version of the studied oil promoted wear with an increasing slide-to-roll ratio when compared with the original version of the studied oil. A higher reduction in wear was obtained for the 0.3% version of the studied oil with an increasing temperature when compared with the 3% version. These results indicate that copper nanoadditives exhibit the potential to reduce micropitting in non-conformal rolling-sliding contacts typically found in gears and rolling-element bearings.

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<p dir="ltr">Fretting wear occurs when two contacting bodies under load are subjected to small amplitude oscillatory motion. Depending on the applied normal load, displacement amplitude, coefficient of friction and resulting shear force, two types of fretting wear regimes exist – (i) partial slip and (ii) gross slip. At displacement amplitudes higher than gross slip condition, sliding wear regime prevails. Fretting wear becomes dominant in machine components subject to vibrations such as bearings, dovetail joints, etc. whereas sliding wear is observed in brakes, piston-ring applications, etc. The work in this dissertation primarily focuses on characterizing the material response of various machine components subjected to fretting and sliding wear regimes.</p><p dir="ltr">At first, the friction and fretting wear behavior of inlet ring and spring clip components used in land-based gas turbines was investigated at elevated (<a href="" target="_blank">500°C</a>) temperature. In order to achieve this objective, a novel high-temperature fretting wear apparatus was designed and developed to simulate the conditions existing in a gas turbine. The test apparatus was used to investigate fretting wear of atmospheric plasma sprayed (APS) Cr₃C₂-NiCr (25% wt.), high-velocity oxy-fuel (HVOF) sprayed Cr₃C₂-NiCr (25% wt.), HVOF sprayed T-800 and APS sprayed PS400 coated inlet rings against HVOF-sprayed Cr₃C₂-NiCr (25% wt.) coated spring clip. The PS400 coated inlet rings demonstrated a significant reduction in friction and wear. A finite element (FE) framework was also developed to simulate fretting wear in HVOF-sprayed Cr₃C₂-NiCr composite cermet coating. The material microstructure was modelled using Voronoi tessellations with a log-normal distribution of grain size. Moreover, the individual material phases in the coating were randomly assigned to resemble the microstructure from an actual SEM micrograph. A damage mechanics based cohesive zone model with grain deletion algorithm was used to simulate debonding of the ceramic carbide phase from the matrix and resulting degradation from repeated fretting cycles. The specific wear rate obtained from the model for the existing material microstructure was benchmarked against experiments. Novel material microstructures were also modeled and demonstrated to show less scatter in wear rate.</p><p dir="ltr">Following, a three-dimensional (3D) continuum damage mechanics (CDM) FE model was developed to investigate the effects of fretting wear on rolling contact fatigue (RCF) of bearing steels. In order to determine the fretting scar geometry, a 3D arbitrary Lagrangian-Eulerian (ALE) adaptive mesh (AM) FE model was developed to simulate fretting wear between two elastic bodies for different initially pristine fretting pressures (0.5, 0.75 and 1 GPa) and friction coefficients (0.15, 0.175 and 0.25) resulting in stick zone to contact width ratios, c/a = 0.35, 0.55 and 0.75. The resulting wear profiles were subjected to various initially pristine RCF pressures (1, 2.2 and 3.4 GPa). The pressure profiles for RCF were determined by moving the contact over the fretted wear profiles in 21 steps. These pressure profiles were then used in the CDM-FE model to predict the RCF life of fretted surfaces. The results indicate that increased fretting pressure leads to more wear on the surface, thereby reducing RCF life. As the RCF pressure increases (P_RCF ≥ 2.2 GPa), the effect of fretting on RCF life decreases for all fretting pressures and c/a values, indicating that life is primarily governed by the RCF pressure. The results from CDM-FE model were used to develop a life equation for evaluating the L₁₀ life of fretted M-50 bearing steel for the range of tested conditions.</p><p dir="ltr">Lastly, the sliding wear characteristics of pitch and poly-acrylonitrile based carbon-carbon (C/C) composites were investigated in air and nitrogen environment by designing and developing a disc brake test rig. It was found that the temperature of the disc, the surrounding environment, the supplied energy flux as well as the type of composite play a critical role in determining whether C/C composites operate in normal wear or dusting wear regime. Further analysis of wear mechanisms revealed interface and matrix cracking with fiber breakage from tests in air environment, whereas in nitrogen environment, particulate and layered debris played a prominent role.</p>

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No description available.

Every moment of every day, at least hundreds of thousands of tires roll across a surface throughout the world. Tires are indisputably important in our daily life. The tire's primary component is rubber, which consumes energy when it rotates on a substrate due to the viscoelastic material's internal friction: a phenomenon referred to as rolling resistance. The interaction between the tire and the road surface is one of the most intricate and crucial phenomena in an automobile, because it is responsible for creating forces, moments, and deformation in the tire. Additionally, the road's roughness interacts with the tire and contributes significantly to its performance. This dissertation aims to develop a comprehensive physics-based model for predicting the rolling resistance of a viscoelastic material due to dynamic deformations caused by tire rotation using an analytical approach. The model was developed by proposing a Gaussian wave function propagating across a tire circumference's viscoelastic medium. The wave function was selected to describe the displacement field produced by tire-road interaction. Additionally, by adopting a multi-scale modeling technique, the model was upgraded to estimate rolling resistance while taking into account surface roughness at all length scales, from macroscopic to microscopic. Additionally, another mathematical model was developed using the Fourier series approach to evaluate the steady-state stress response and energy dissipation for any harmonic and non-harmonic periodic strain signals. Additionally, the dissertation strove to build a continuum damage mathematical model using a combined testing/modeling methodology to predict the aging of Styrene-Butadiene Rubber (SBR) after continuous exposure to the atmosphere. The obtained model was developed through the implementation of optimization techniques while formulating a mathematical model, which was then combined with a physics-based model to predict rolling resistance while taking into account rubber aging. Calibration of hyperelastic and viscoelastic material models with testing data was performed using an optimization technique that yielded sufficient results. The results of all mathematical models obtained in this dissertation are reported subsequently. The stress response of a viscoelastic material under harmonic and non-harmonic strain input yielded good agreement with the FEA model obtained using ABAQUS. The rolling resistance behavior under various operating conditions, including texture and aging effects, was reported, and the results aligned with the experimental results found in the literature. / Doctor of Philosophy / Every moment of every day, hundreds of thousands of automobile tires roll across a surface somewhere in the world. A tire is an undeniably important part of everyday life. Rubber is the tire's main component, and when it rotates on a surface, it loses energy, resulting in a force that resists motion, known as rolling resistance force. The contact between the tire and the road is one of the most complicated and important phenomena that happens in an automobile because it is responsible for the vehicle's dynamic performance in areas such as acceleration, stopping distance, and stability. Another factor that affects tire and car performance and should be taken into account is the road's roughness. This dissertation used an analytical method to come up with an accurate physics-based model for predicting the rolling resistance force of a viscoelastic material caused by tire rotation. The model was developed by assuming a Gaussian wave function would move across the tire circumference. Additionally, using a multi-scale modeling technique, the model was improved so that it could calculate the value of rolling resistance force considering surface roughness in all lengths of scale. This project also developed an additional mathematical model using the Fourier series method to determine how the stress response and energy dissipation would behave for any harmonic and nonharmonic periodic strain signals. Additionally, the dissertation presents the developing of a continuum damage mathematical model that could predict the material property of styrene-butadiene rubber (SBR) after being exposed to the air for a long time (i.e., aged). The model was developed based on experimental data and optimization techniques. This model was then combined with a physics-based model to predict rolling resistance force while taking aging into account. The material models were defined using an optimization method that yielded good results. The stress response of a viscoelastic material when it was subjected to harmonic and non-harmonic strain was in good agreement with the Finite Element Analysis (FEA) model made with ABAQUS. Rolling resistance behavior was observed, and the results were consistent with those found in the literature.

Wellen sind essentielle Maschinenelemente zur Übertragung von Kräften und Momenten in Getrieben. Die Forderung der Industrie nach Leistungssteigerung in der Antriebstechnik erfordert höhere Festigkeiten der Wellen. Zur Steigerung der Tragfähigkeit können einerseits höherfeste Werkstoffe und andererseits mechanische Oberflächenverfestigungsverfahren genutzt werden. Das effektive und kostenschonende Verfahren des Festwalzens wird am kritischen Querschnitt des Bauteils zur lokalen Festigkeitssteigerung durchgeführt. Bekannte Auslegungskonzepte, wie die DIN 743 oder auch die FKM Richtlinie berücksichtigen die aus dem Prozess eingebrachten Druckeigenspannungen jedoch nicht oder nur unzureichend. In diesen Auslegungsrichtlinien wird die Tragfähigkeitssteigerung mittels Diagrammen zum Einflussfaktor der Oberflächenverfestigung KV abstrahiert. Es wird davon ausgegangen, dass der Faktor KV die Tragfähigkeitsreserven festgewalzter Bauteile unterschätzt. Der vorliegende Beitrag zeigt auf, wie mittels numerischer Methoden der Einfluss von Druckeigenspannungen auf die Festigkeit von wellenartigen Bauteilen beschrieben werden kann. Dies ermöglicht die Abschätzung und Erschließung vorhandener Tragfähigkeitsreserven. Auf Basis eines mittels röntgenographischer Eigenspannungsmessungen validierten Simulationsmodells für das Festwalzen ungekerbter Bauteile, werden die numerisch ermittelten Eigenspannungen in Festigkeitssimulationen sowohl auf einer Kleinteilprobe als auch einer Bauteilprobe aufgeprägt. Es erfolgt eine elastisch-plastische Simulation des lokalen Beanspruchungszustandes im Bereich dauerfest ertragbarer Lasten entsprechend der Versuchsergebnisse. Ausgewertet werden das Spannungs- und Dehnungsverhalten am kritischen Querschnitt während der Lastwechsel sowie der Eigenspannungsabbau. Abschließend werden die Simulationsergebnisse mit den experimentellen Ergebnissen verglichen. / Shafts are essential machine elements for the transmission of forces and moments in gearboxes. The industry's demand for increased performance in drive technology requires higher fatigue strengths. The effective and cost-saving process of deep rolling is carried out on the critical cross-section of the component to increase fatigue strength locally. However, known design concepts such as DIN 743 or the FKM guideline do not or only insufficiently take into account the residual compressive stresses introduced by the process. In these design guidelines, the increase in fatigue strength is abstracted by means of diagrams on the influence factor of surface condition KV. It is assumed that the factor KV underestimates the fatigue strength reserves of deep rolled components. This article shows how numerical methods can be used to describe the influence of residual compressive stresses on the fatigue strength of shaft-type components. This enables the estimation and utilisation of existing fatigue strength reserves. Based on a simulation model for deep rolling of unnotched components validated by means of X-ray residual stress measurements, the numerically determined residual stresses are applied to a specimen as well as a component in strength simulations. This is followed by an elastic-plastic simulation of the local stress distribution with ultra-high-cycle fatigue loads according to the experimental results. The stress and strain behaviour at the critical cross-section during the load cycles and the residual stress reduction are evaluated. Finally, the simulation results are compared with the experimental results.

Les pieds d’aubes de soufflantes de turboréacteurs étant soumis à des sollicitations de type fretting, l’introduction de matériaux composites dans la nouvelle génération de moteur d’avion a rendu nécessaire le développement d’outils permettant de modéliser le contact entre des matériaux hétérogènes. En particulier, le comportement tribologique et l’endommagement de ces matériaux est encore mal compris. La mise en place de méthodes numériques capable de prédire les endommagements dans le contact permettrait de mieux prédire la durée de vie des pièces en service et de garantir la sécurité des passagers. Cette thèse porte sur le développement de méthodes semi-analytiques pour la modélisation de l’endommagement dans des conditions de fretting et de roulement. / The blade/disk interface in turbofan is subject to fretting loading. Fan blade of the new generation of aircraft engines are made of woven composite materials. The introduction of these new kind of materials create the need for a new numerical tool able to simulate the contact between heterogeneous materials. The tribological behavior and the damage mechanism associated with these kind of material are still not well understood. The developpment of new numerical tool able to model the damage in the contact area would allow to predict the life of engines parts and to guarantee the security of passengers. This PhD is about the developpment of semi-analytical methods for modeling the damage in fretting and rolling contact conditions with some applications to heterogeneous materials.

I detta examensarbete användes olika bildbehandlingstekniker för detektion och kvantifiering av DNA-mikrobollar, mer specifikt rolling circle amplification-produkter, på mikroskopibilder. Avsikten med detta arbete var att hjälpa Countagen AB utforska pipelines för bildbehandling för sin produkt där de analyserar utfallet av genredigeringsförsök på ett billigare och snabbare sätt än dagens konventionella sekvenseringsmetoder. Två olika metoder för objektdetektion användes i detta arbete. Big-FISH, som bygger på Laplacian of Gaussian och detektion av lokala maxima, samt LodeSTAR, en single-shot, self-supervised djupinlärningsmodell. Förbehandling av bilder var också en central del av detta projekt. DeepSpot, en djupinlärningsmodell för framhävning av punkter, användes för att framhäva mikrobollarna så att de lätt kunde upptäckas, och en top-hat-transform användes för att filtrera bort bakgrunden från bilderna. De olika metoderna utvärderades på ett dataset med manuellt annoterade bilder, en spädningsserie av prover samt prover med samma koncentration. Detta för att få värden på precision, recall och F1-score samt mäta hur robust modellen är när det gäller att detektera punkter. Den modell som presterade bäst var LodeSTAR, med en F1-score på 83% på det annoterade datasetet. / In this thesis project, different image processing techniques were utilized for the detection and quantification of DNA microballs on fluorescence microscopy images. These microballs consisted of rolling circle amplification products, of regions of interest. This was done to aid Countagen AB in exploring image processing pipelines for their product where they analyze gene editing efficiency in a cheaper and faster manner than today's conventional sequencing methods. Two different object detection methods: Big-FISH, which builds on Laplacian of Gaussian and local maxima detection, and LodeSTAR, a single-shot, self-supervised deep learning model, were evaluated for this task of detection and quantification. Image preprocessing was a central part of this project. DeepSpot, a deep learning model for spot enhancement was used to highlight the microballs, and a white top-hat transform was applied to the images for background subtraction. The different methods were evaluated on a test set of manually annotated images, a dilution series of samples, and samples with the same concentration to obtain precision, recall, and F1 scores, as well as gauge the robustness of the model in detecting spots. The best-performing model was LodeSTAR, with an F1-score of 83% on the test set.

В работе проведен обзор основных технологий производства холоднокатаных листов низкоуглеродистых сталей для изготовления изделий методом холодной штамповки и эмалирования. Проанализированы химические составы, структура, кристаллографическая текстура образцов листов, и их влияние на возможности производства бытовых изделий (ванн, моек, поддонов). Рассмотрены вопросы улучшения качества листов низкоуглеродистых сталей, используемых для холодной штамповки и эмалирования. / The paper reviews the main technologies to produce cold-rolled sheets of low-carbon steels for the manufacture of products by cold stamping and enameling. The chemical compositions, structure, crystallographic texture of sheet samples, and their influence on the possibility of manufacturing household products (bathtubs, sinks, and pallets) are analyzed. The issues of improving the quality of low-carbon steel sheets used for cold stamping and enameling are considered.