Additive Manufacturing (AM) has revolutionized manufacturing processes by enabling the realization of custom products with intricate geometric features that were either too complex or even intractable for subtractive manufacturing processes. Yet, functional surfaces generated in AM have to be often finish machined because of their relatively inferior roughness. The first phase of this research worked around this limitation by tailoring the topography of an AM surface in-process to entail textures that further enhance certain functionalities in a process called Additive Texturing (AT). In this context, the Selective Laser Melting (SLM) process ability to realize intricate surface microfeatures was explored experimentally, evaluating its geometrical limitations. Utilizing such limitations, various patterns comprising pillars, channels, and re-entrant structures were printed to control the wetting behaviour of SLM stainless steel. AT's efficacy is demonstrated in its capability to generate hydrophobic AM surfaces with water contact angles exceeding 140°. Similarly, other texturing patterns comprising dimples, linear, V-shaped, and X-shaped grooves were investigated to tailor the tribological response of textured surfaces under dry sliding conditions. Evidently, a specific wear rate and coefficient of friction reduction of 80% and 60%, respectively, demonstrated another potential for AT. The undesirable tensile Residual Stresses (RS) that inevitably accumulate during the SLM process's rapid heating and cooling cycles were investigated in the second phase of this research. Laser Peening (LP) was utilized to post-process the printed samples to eliminate the initial tensile RS and induce near 500 Mpa compressive RS. Moreover, the LP parameters were explored and optimized to enhance RS, surface roughness, hardness, and wear resistance. / Thesis / Doctor of Philosophy (PhD)

Doctor of Philosophy / The control systems installed in modern vehicles lack crucial information regarding the interaction between the tires and the road surface. This knowledge gap significantly impacts the safety and control of the vehicle. Thus, to address this issue, this research introduces a novel fusion approach to estimate friction at the tire-road contact interface. This hybrid fusion friction estimation algorithm employs techniques like signal processing and machine learning, backed up by information from various vehicle and tire dynamics models, to develop algorithms that estimate the level of friction between the tire and the road. This fusion approach enables more precise estimations of the friction coefficient in both normal driving situations and scenarios involving sudden changes in speed or road conditions. Therefore, this research aids in enhancing vehicle safety and control by providing improved information about such tire-road interactions.

Friction and wear have been concerns to industrialists, scientists and environmentalist for several decades. Many robust models have been developed to address friction and wear and their dependency on various parameters. Numerous experiments have been conducted in the past to model friction and wear. In order to get the experimental results as close as to the real world, the construction of the scientific instrument has to be precise as well. There are several factors that influence the experimental results such as setup of the experiment, dynamics of the instruments etc. These need to be analysed, characterised and suppressed their influence on the experiments. The dynamics of the tribometer when two surfaces are in sliding contact consist of friction induced vibrations and vibrations that influence friction. It is highly complex to device a model which defines interplay of friction and vibrations together. To understand the effect of dynamics of tribometer on sliding contact, vibrations signals were examined. The data was collected by mounting vibrations sensors on the tribometer and the stiffness of the tribometer was modified by changing the spring fixed in the tribometer. The vibrations signals and coefficient of friction data were analysed. The result showed that changing the stiffness of the tribometer did not influence vibrations and coefficient of friction to observable extent, in fact, the vibrations signals were the interaction between the sliding surfaces. The coefficients of friction and vibrations signals for several experiments were similar. The interplay between the vibrations and friction was observed and the vibrations were more like induced vibrations rather than vibrations in the tribometer affecting the sliding contact. The results of experiments comply with by the previously established theories. As the sliding speed decreases, vibrations also decrease and coefficient of friction increases because of increment in the area of contact. This also shows that as vibrations reduces, coefficient of friction increases. The roughness of the pins after the experiments with 40 N/mm spring constant were higher than the ones with 20 N/mm and 120 N/mm, even though the experiment with 20 N/mm were run for a fewer hour. The roughness of the disc for experiment with 120 N/mm were higher than that of the 40 N/mm and 20 N/mm. The experiment with 20 N/mm is higher than 40 N/mm because experiment ran for fewer number of hours than 40 N/mm and 120 N/mm. The roughness results did not have observable patterns and therefore it was concluded that changing one of the components of the tribometer do not influence the experiment at microscale. / Friktion och slitage har varit bekymmer för industrimän, vetenskapsmän och miljöpartister i flera decennier. Många robusta modeller har utvecklats för att hantera friktion och slitage och deras beroende av olika parametrar. Många experiment har utförts tidigare för att modellera friktion och slitage. För att få de experimentiella resultaten så nära den verkliga världen, måste konstruktionen av det vetenskapliga instrumentet också vara exakt. Det finns flera faktorer som påverkar de experimentella resultaten såsom experimentets uppställning, instrumentens dynamik etc. Dessa behöver analyseras, karaktäriseras och undertrycka deras inverkan på experimenten. Tribometerns dynamik när två ytor är i glidkontakt består av friktionsinducerade vibrationer och vibrationer som påverkar friktionen. Det är mycket komplucerat att skapa en modell som definierar samspelet mellan friktion och vibrationer. För att förstå effekten av tribometerns dynamik på glidkontakten undersöktes vibrationssignaler. Data samlades in genom att montera vibrationssensorer på tribometern och tribometerns styvhet modifierades genom att byta fjäder som var fixerad i tribometern. Vibrationssignalerna och friktionskoefficientdata analyserades. Resultatet visade att ändring av tribometerns styvhet inte påverkade vibrationer och friktionskoefficient i en observerbar utsträckning, i själva verket var vibrationssignalerna interaktionen mellan glidytorna. Friktionskoefficienterna och vibrationssignalerna för flera experiment var likartade. Samspelet mellan vibrationerna och friktionen observerades och vibrationerna var mer som inducerade vibrationer snarare än vibrationer i tribometern som påverkade glidkontakten. Resultaten av experiment överensstämmer med de tidigare etablerade teorierna. När glidhastigheten minskar minskar också vibrationerna och friktionskoefficienten ökar på grund av ökningen i kontaktområdet. Detta visar också att när vibrationerna minskar så ökar friktionskoefficienten. Stiftarnas grovhet efter försöken med 40 N/mm fjäderkonstant var högre än de med 20 N/mm 120 N/mm, även om försöket med 20 N/mm kördes i färre timmar. Råheten hos skivan för experiment med 120 N/mm var högre än den flr 40 N/mm och 20 N/mm. Experimentet med 20 N/mm är högre än 40 N/mm eftersom experimentet pågick under färre antal timmar än 40 N/mm och 120 N/mm. Ojämnhetsresultate§n hade inga observerbara mönster och därför drogs slutsatsen att förändring av en av komponenterna i tribometern inte påverkar experimentet i mikroskala.

This work investigates the velocity-dependent coefficient of friction between concrete and 300 Maraging steel over short displacements. A modified torsional Hopkinson bar is utilized for rotating thin-walled steel rings in contact with a concrete disk under static precompression. Rotational velocity is varied between tests to determine the velocity dependence of the friction coefficient. Normal force is varied between certain tests to determine the pressure dependence of the friction coefficient between the concrete and steel. Three different types of concrete are tested to deduce any composition effect on the friction coefficient. Dry and greased conditions’ impact on the friction coefficient are also evaluated. Lastly, the displacement dependence (fade) is considered for the concrete with regards to the steel. Discussion of the usefulness of this data in modeling and experimentation of impact between concrete and steel is disclosed.

Previous research has shown that with advancing age, there are increasing incidences of slip and fall injuries. Understanding mechanisms associated with gait adjustments across a known slippery surface may help in proactively avoiding slips and falls. The primary goal of this study involved examination of gait parameters and muscle activity characteristics of the lower extremities during two different walking conditions. Research has shown that both physical and mental changes accompany the aging process in humans. Moreover, research has shown that emotions and physiological responses are related. A secondary goal of this study was to examine the relationships of fear of falling with gait parameters and muscle activity. This study consisted of exposing 14 younger and 14 older participants to controlled slippery conditions safely, while studying normal and adjusted gait characteristics (friction requirement, heel contact velocity, and step length) and muscle activity characteristics (Integrated EMG). First, a baseline measure was done to study normal gait prior to any exposure to slipping. A second measure was done following a slip from a contaminated floor surface, but before the initiation of a second slip. The results indicate that there were significant gait parameter differences between younger and older participants for both walking conditions. Results also indicate that there were differences in muscle activity between to the two age groups for the adjusted condition. Findings suggest that older individuals require an additional step to properly adjust gait for a contaminated walking surface. / Master of Science

En 1970, George K. Batchelor suggérait que la connaissance des lois de l'hydrodynamique rendait possible la dérivation de propriétés rhéologiques macroscopiques telle la viscosité, à partir de la connaissance de la microstructure d'une suspension de particules. Quarante ans plus tard, ses espoirs ne se sont pas concrétisés et la rhéologie des suspensions,notamment en régime concentré, reste un domaine de recherche très actif.Considérant des suspensions modèles de particules non colloïdales dans un liquide newtonien, le travail expérimental réalisé au cours de cette thèse s'est d'abord attaché à unifier les concepts classiquement définies en rhéologie des suspensions et ceux issus des récentes avancées sur les écoulements granulaires. Dans ce but, un dispositif original de cisaillement à pression imposée a été développé et a permis une caractérisation claire des équations constitutives en régime très dense.Par la suite, des configurations d'écoulements à surface libre ont été utilisées pour la mesure des deux différences de contraintes normales.Enfin, la mise en cohérence de l'ensemble des résultats expérimentaux donne une formulation complète et cohérente de la rhéologie des suspensions non colloïdales. / In 1970, George K. Batchelor suggested that the knowledge of the laws of hydrodynamics made ​​possible the derivation of macroscopic rheological properties such as the effective viscosity, from the knowledge of the microstructure of a suspension of particles. Forty years later, his hopes have not materialized and the rheology of suspensions, particularly in the concentrated regime, remains an area of ​​active research. Considering suspensions of non-colloidal particles in a Newtonian liquid, the experimental work in this thesis was first attached to unify the concepts traditionally defined rheology of suspensions and those from recent advances on granular flows. For this purpose, an original of shear imposed pressure was developed and showed a clear characterization of constitutive equations in the dense regime. Subsequently, the configurations of free surface flows have been used for the measurement of both normal stress differences. Finally, the coherence of all the experimental results gives a complete and consistent formulation of the rheology of non-colloidal suspensions.

Na maioria dos equipamentos mecânicos há movimento relativo entre componentes, e como resultado desse deslizamento relativo, as forças de atrito na superfície geram deformação plástica e/ou remoção de massa (ou volume) do material. Nos motores de combustão interna a geração da potência é realizada pela transformação da energia química em calor por meio da combustão do combustível com o ar, gerando o movimento alternativo de mecanismos (pistões, biela, virabrequim). Já no caso dos motores flex-fuel, o etanol como combustível aumenta a potência, levando a maiores carregamentos termomecânicos e, consequentemente, tribológicos nos seus componentes. Um dos sistemas do motor mais afetado pela mudança no combustível é o par válvula-sede, motivo pelo qual é necessário investigar os mecanismos de desgaste, os efeitos dos parâmetros de operação no comportamento frente ao atrito, e escolher apropriadamente pares deslizantes de materiais que apresentem baixas perdas de massa (taxas de desgaste) e coeficientes de atrito. Ensaios do tipo reciprocating tinham sido empregados para realizar estudos tribológicos de materiais de válvulas e com tratamentos superficiais. As condições de ensaio mais representativas são de operação do motor. Portanto, a seleção de parâmetros como carga, velocidade e temperatura não é fácil: para alguns equipamentos de teste, as variáveis não são independentes. Além disso, devido à complexidade do sistema tribológico, a interação entre as variáveis afeta os resultados. O objetivo deste trabalho de pesquisa foi dividido em duas frentes. A primeira, analisar isoladamente o efeito da temperatura, força normal e velocidade no coeficiente de atrito e no desgaste. O tribômetro SRV-4 do tipo reciprocating foi usado com uma esfera de aço AISI 52100 e distintos materiais de disco (aços e ligas intermetálicas sinterizadas de Nb). A segunda parte consistiu na caracterização dos mecanismos de desgaste de válvulas e sedes de motores distintos, após diferentes tipos de ensaios (dinamômetro e campo em veiculo). O coeficiente de atrito (?) e a perda de massa foram medidos para determinar o desempenho tribológico dos sistemas estudados. Além disso, as superfícies das marcas de desgaste tanto no disco quanto na esfera, assim como das válvulas e sedes foram analisadas por microscopia óptica (MO), microscopia eletrônica de varredura (MEV) com espectroscopia de energia dispersiva de raios-X (EDS) e espectroscopia Raman. Para as distintas ligas intermetálicas de Nb ensaiadas com esfera de aço AISI 52100, encontrou-se que os mecanismos de desgaste nas superfícies após uma análise de MEV-EDS foram particularmente abrasão, adesão e oxidação. Já no caso dos motores que foram avaliados, muitos dos danos observados estavam presentes em ambas as válvulas e sedes de admissão e escape; no entanto, a oxidação ocorreu apenas nas válvulas de escape, provavelmente produzido pela alta temperatura durante a operação do motor. / In most of the mechanical assemblies there is relative motion between components, and as a result of this relative sliding action, frictional forces on the sliding surface result in removal or displacement of mass (or volume) of the material. The power generation of internal combustion engines comes from chemical energy transformation into heat through air fuel combustion with further expansion of gases generating the reciprocating movement of power cell (pistons, rod and crankshaft). For flex fuel engines, the ethanol increases power, leading to higher thermo-mechanical forces and consequently higher friction between its components. The valve/valve seat pair is one of the most affected system due to this change, leading to the need of more accurate analysis of its wear mechanisms, its operating parameters effects and his behavior regarding the friction so making possible to choose properly materials with lower mass loss (wear rate) and coefficient of friction. Reciprocating tests had been used to tribological studies of valve materials with surface treatment purpose. The most important test boundary conditions are the engine operating conditions. Therefore, the load, speed and temperature parameters definition is not easy since for some test equipment those variables are not independent. Besides due to tribological system complexity the variable interaction affects its results. The present research goal was divided in two groups. The first one analyzes the normal force, frequency and temperature effect on friction coefficient and wear, independently of each other. It was used a SRV-4 reciprocating tribometer with a sphere (AISI 52100 steel) against several disc materials (steel and sintered intermetallic alloys of Nb). The second one consisted in the characterization of wear mechanisms of valve/valve seat from different engines that were submitted to different test (engine dynamometer test bench and vehicle). The coefficient of friction (?) and mass loss were measured in order to define the studied systems tribological performance. Besides the both disc and sphere wear scars such as valve/valve seat were analyzed using optical microscopy (OM), scanning electron microscopy (SEM) with energy dispersive spectroscopy of X-ray (EDS) and Raman spectroscopy. For the tested intermetallic alloys of Nb with AISI 52100 sphere it was found the following wear mechanisms after SEM-EDS analyses: abrasion, adhesion and oxidation. In the case of the evaluated engines, several damages were observed in both intake and exhaust valves/valve seats; however, the oxidation occurred only on exhaust valves, probably due to high operating temperature.

This research conducts tribological investigation in three areas. The first area of research is to obtain basic understanding of tribological properties of high performance Inconel alloys. Pin-on-disk testing was conducted through a range of applied normal loads and sliding velocities in an unlubricated condition. Average friction coefficient, friction work, and specific wear rates were calculated from the data and microscopy techniques were used to observe and characterize wear mechanisms. Experimental results show a dependence of average coefficient of friction as a function of frictional work. Also shown is the wear rate dependence on frictional work, predicated by a wear mechanism change. This research gives a tribological baseline for high performance alloys. The second area of research is in the in situ spatial study of friction, complemented by monitoring changes in electrical contact resistance (ECR). Pin-on-disk testing of samples was done under low normal loads and velocities. Friction and electrical contact resistance measurements were taken spatially in the wear track during each friction cycle, giving a spatial evolution of friction and resistance change, in situ. Results show a lowering in the ECR under increased friction cycles, which was closely related to a change in the friction coefficient of the material. Using surface profilometry and X-ray Photoelectron Spectroscopy, we determined that the lowering of resistance is a result of surface modification through wear and development of a friction induced conductive tribo-film. This research provides a simple method for in situ monitoring of friction and solidifies a fundamental relationship between friction and contact resistance. The third area of research is the design of a variable force tribometer, incorporating the fundamental results demonstrated in the first two experiments. The creation of a novel testing apparatus to test materials under dynamic tribological conditions is given in detail. Simple experiments were performed on an Inconel sample and preliminary results show how dynamic normal and tangential forces affect the friction coefficient. These early results utilizing the variable force tribometer will lay the groundwork for more advanced research into the dynamic nature of friction.

O atrito na interface entre a peça e a ferramenta tem considerável importância em operações de estampagem de chapas, são necessários conhecimentos precisos sobre processos de conformação de chapas para a análise e projeto de novas peças e ferramentas, assim como para validação de uma simulação numérica. Este trabalho usa o método de determinação do coeficiente de atrito em estampagem através do ensaio de dobramento sob tensão e avalia sua precisão com o uso do software de elementos finitos LS-DYNAFORM, específico para esse processo de fabricação. Como existem seis equações que calculam o coeficiente de atrito para o mesmo ensaio de dobramento sob tensão, foram testadas todas as equações com o objetivo de verificar se existe variação entre os resultados. O material de estudo foi o alumínio comercialmente puro, liga AA1100. Os resultados indicam que há certa variação para cada equação usada, principalmente para aquelas que consideram o torque no pino. É observada também uma tendência do software a se distanciar dos resultados práticos por considerar o atrito como uma constante ao longo do processo. A pressão de contato entre o pino e a chapa no ensaio de dobramento sob tensão também foi avaliada através de um filme que tem a capacidade de registrar a pressão aplicada juntamente com a medição da força vertical aplicada ao pino. Os resultados indicam que a força vertical é mais precisa para se definir a pressão de contato ao uso de equações pré-estabelecidas e que a área de atuação da chapa no pino é sempre menor que a área calculada geometricamente. Por fim, para se saber qual é o comportamento do atrito para altas pressões, o ensaio de dobramento sob tensão foi feito com força variável e constatou-se que o atrito diminui com o aumento das pressões. No entanto, os valores iniciais da curva de atrito versus pressão de contato não foram obtidos pois nesse caso seria necessário usar uma máquina diferente da usada nesse estudo, ou seja, que não use pressão de óleo para acionamento e movimentação da chapa. / Friction at the interface of workpiece and tooling has a considerably importance in sheet metal forming operations. It is necessary an accurate knowledge for the analysis and design of new workpieces and tooling, as well as for the validation of a numeric simulation. This work uses the bending under tension test to determining the friction coefficient in sheet metal forming and evaluates its accuracy using the finite element software LS-DYNAFORM, specific to this manufacturing process. Since there are six equations that calculate the coefficient of friction for the same bending under tension test, all equations were tested in order to verify if there is much variation between the results. The material used in these work was pure commercial aluminum alloy AA1100. The results indicate that there is some variation for each equation used, especially for those that consider the torque on the pin. It was also observed a tendency for software to distance themselves from practical results considering friction as a constant throughout the process. It is also observed a tendency for the software to generate curves away from the tests as the friction increases. The contact pressure between the pin and the sheet in the bending under tension test was also evaluated through a film that has the ability to measure the pressure applied, together with the measurement of the vertical force applied to the pin. The results indicate that the vertical force is more accurate to define the contact pressure than equations previously established for this and that the contact area between the sheet and the pin is always smaller than the area calculated geometrically. Finally, to know the behavior of the friction at high pressures, the bending under tension test was done with variable forces and it was found that the friction decreases with increasing the pressure, which is in full agreement with the theory.

Submitted by Viviane Lima da Cunha (viviane@biblioteca.ufpb.br) on 2017-07-20T11:05:50Z No. of bitstreams: 1 arquivototal.pdf: 3752282 bytes, checksum: 05ec02c81a4866e4202382045165f792 (MD5) / Made available in DSpace on 2017-07-20T11:05:50Z (GMT). No. of bitstreams: 1 arquivototal.pdf: 3752282 bytes, checksum: 05ec02c81a4866e4202382045165f792 (MD5) Previous issue date: 2015-09-25 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / Pressure drawdown in oil producing fields can lead to reservoir compaction, surface subsidence and cementation/casing failure. The study and understanding of these effects can imply financial and environmental risks reduction. In order to analyze and predict these problems some models were built using the finite element software ABAQUS due to its flexibility in treatment of geometry and topological heterogeneity, use of external routines and plugins. This study describes, through axisymmetric models, the influence of 'depletion' and "coefficient of friction" on reservoir compaction, surface subsidence, von Mises stresses in the casing and slip between cement/casing was analyzed. A central composite rotatable design (CCRD) 22 with four axial points and a center point was made to analyze the significance of the variables through the response surface method. In addition to the quantitative variables, as indicated, it was also analyzed the influence of qualitative variable type of reservoir rock. It was concluded that depletion is a significant variable for the answers "Mises stress", "reservoir compaction" and "subsidence" while the variable coefficient of friction is significant for the answers "Mises stress" and "slip." The type of reservoir rock influences directly the Mises stress, compaction and subsidence. For the same depletion more rigid is the rock, less is the von Mises stress, compaction and subsidence. Also to realize a reduction in the maximum active tension in the coating, for the same level of depletion, friction coefficient and type of reservoir rock when concentric coatings run, due to increased structural capacity. Also was realize, for the same level of depletion, friction coefficient and type of reservoir rock, a reduction in the maximum active stress in the casing, when was used concentric casings, due to increased structural capacity. / Em reservatórios subterrâneos de petróleo, a diminuição da pressão de poros devido à produção pode ocasionar a compactação do reservatório e a consequente subsidência da superfície, além de falhas na cimentação e no revestimento. O estudo e entendimento destes efeitos implicam na redução dos riscos econômicos e ambientais dos projetos de exploração. A fim de analisar e prever estes problemas foram construídos alguns modelos através do simulador de elementos finitos ABAQUS, devido à sua flexibilidade no tratamento da geometria e heterogeneidade topológica, uso de rotinas externas e plugins. Este estudo descreve, através de modelos axissimétricos, a influência das variáveis quantitativas depleção e coeficiente de atrito entre a formação rochosa e a pasta de cimento nas seguintes respostas: compactação do reservatório, subsidência da superfície, estado de tensões de von Mises no revestimento e deslizamento/abertura (falha adesiva) na interface formação rochosa-pasta cimentícia. Com o objetivo de tratar estatisticamente as respostas, foi realizado um delineamento composto central rotacional (DCCR) 22 com quatro pontos axiais e um ponto central, que possibilitou analisar a significância das variáveis através de superfícies de respostas. Além das variáveis quantitativas, já indicadas, foi analisada também a influência da variável qualitativa tipo de rocha reservatório. Concluiu-se que a depleção é uma variável significativa para as respostas tensão de Mises, compactação e subsidência, enquanto a variável coeficiente de atrito é significativa para as respostas tensão de Mises e deslizamento. O tipo de rocha reservatório influencia diretamente nas respostas tensão de Mises, compactação e subsidência. Quanto mais rígida a rocha, menor as tensões atuantes, compactação e subsidência para uma mesma depleção. Percebeu-se, também, uma redução na tensão máxima atuante no revestimento, para um mesmo nível de depleção, coeficiente de atrito e tipo de rocha reservatório, quando são executados revestimentos concêntricos, devido o aumento da capacidade estrutural.