published_or_final_version / Mechanical Engineering / Doctoral / Doctor of Philosophy

The interference-fit joint is widely used in machine design to connect two cylindrical machine elements. Its popularity comes from the simplicity of the assembly and the low cost of the production process. Even so, no study has examined the boundary non-linearities in the assembly of these joints. Moreover, the contact stresses and the stress concentration factors in interference-fit joints under torsional loads have not yet been examined in detail. In addition, the interface stresses and stress concentration factors in interference-fit joints subjected to bending loads have not been approached theoretically before. The sugar-mill roller is one of the oldest and most important examples of the interference-fit joints. The frequent fatigue failure of the sugar-mill rollers under reversed bending causes costly emergency line-shut downs. The versatility of the finite element method and the capability of the point-matching technique in handling contact problems have been combined, in the present work, to produce a surface-matching technique. It has been found that the complete-cohesion contact assumption may be acceptable for coefficients of friction ≥ 0.2, which is the case for most of the normally machined surfaces. An approach combining the semi-inverse displacement finite element method and the surface-matching technique has been developed to perform the torsional analysis. It has been found that the governing non-dimensional quantities are the ratio of the cohesion-length to the interface-length and the coefficient of friction divided by the load-level. The load-level is the ratio between the angle of twist of the shaft per unit length when the torque acts on the shaft alone and the amount of the diametral interference divided by the shaft diameter. A finite element model, using 8-noded solid elements together with linear interface elements, has been employed to locate the cohesion and slippage-zones in the sugar-mill roller under bending. The contact pressure increases along the compression side and decreases along the tension side. On the contrary, the interface shear decreases along the compression side due to bending and increases along the tension side. Subsequently, a larger slippage-length has been detected along the tension side.

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Titanium (Ti) alloys have been commonly used in the aerospace industry, not only because they have a high strength-to-weight ratio (comparing to the steels) but also their satisfactory corrosion resistance. Furthermore, they can be assembled with the carbon fibre composite parts. However, conventional manufacturing methods cause high material scrap rate and require lots of machining to obtain the final shape and size, which increases both the manufacturing time and cost. In order to improve the efficiency and reduce the cost of Ti parts, Additive Manufacturing (AM) has been developed. Rolled Wire and Arc Additive Manufacturing (rolled WAAM) is one of the AM processes. The main characteristics of this technology is the reduced β grain size to refine the alloy's microstructure. Both the ultimate tensile strength and yield strength of Ti alloy made by rolled WAAM are at least 10% higher than traditional wrought Ti. This project is to investigate the fatigue crack growth rates of the Ti-6Al-4V built by rolled WAAM process in both the longitudinal and transverse orientations to study the effect of rolling on fatigue crack growth rate of WAAM processed Ti. The project was carried out by testing the fatigue crack growth rates for 4 compact tension specimens. The test results of different orientations were compared with each other, and scatters in fatigue life and fatigue crack growth rate were found. Fatigue crack growth rate is lower in the longitudinal specimens. The results are also compared with those of the unrolled WAAM specimens tested in a previous project. It was found that rolling can significantly improve the fatigue crack growth behaviour in WAAM processed Ti, and can reduce the difference between the two orientations, i.e. achieving better isotropic material properties. Recorded scatters may be caused by the process induced residual stresses, error in measurement, and the test machine load range being much higher than the applied loads. More specimens can be tested to validate above observations further.

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.

In this thesis, nondestructive surface wave measurements are presented for characterization of dynamic modulus and layer thickness on different pavements and cement concrete slabs. Air-coupled microphones enable rapid data acquisition without physical contact with the pavement surface. Quality control of asphalt concrete pavements is crucial to verify the specified properties and to prevent premature failure. Testing today is primarily based on destructive testing and the evaluation of core samples to verify the degree of compaction through determination of density and air void content. However, mechanical properties are generally not evaluated since conventional testing is time-consuming, expensive, and complicated to perform. Recent developments demonstrate the ability to accurately determine the complex modulus as a function of loading time (frequency) and temperature using seismic laboratory testing. Therefore, there is an increasing interest for faster, continuous field data evaluation methods that can be linked to the results obtained in the laboratory, for future quality control of pavements based on mechanical properties. Surface wave data acquisition using accelerometers has successfully been used to determine dynamic modulus and thickness of the top asphalt concrete layer in the field. However, accelerometers require a new setup for each individual measurement and are therefore slow when testing is performed in multiple positions. Non-contact sensors, such as air-coupled microphones, are in this thesis established to enable faster surface wave testing performed on-the-fly. For this project, a new data acquisition system is designed and built to enable rapid surface wave measurements while rolling a data acquisition trolley. A series of 48 air-coupled micro-electro-mechanical sensor (MEMS) microphones are mounted on a straight array to realize instant collection of multichannel data records from a single impact. The data acquisition and evaluation is shown to provide robust, high resolution results comparable to conventional accelerometer measurements. The importance of a perfect alignment between the tested structure’s surface and the microphone array is investigated by numerical analyses. Evaluated multichannel measurements collected in the field are compared to resonance testing on core specimens extracted from the same positions, indicating small differences. Rolling surface wave measurements obtained in the field at different temperatures also demonstrate the strong temperature dependency of asphalt concrete. A new innovative method is also presented to determine the thickness of plate like structures. The Impact Echo (IE) method, commonly applied to determine thickness of cement concrete slabs using an accelerometer, is not ideal when air-coupled microphones are employed due to low signal-to-noise ratio. Instead, it is established how non-contact receivers are able to identify the frequency of propagating waves with counter-directed phase velocity and group velocity, directly linked to the IE thickness resonance frequency. The presented non-contact surface wave testing indicates good potential for future rolling quality control of asphalt concrete pavements. / <p>QC 20170209</p>

Rock’n’roll has specific aesthetic — a set of invisible rules that each young rock musician accepts as a given. If one examines the history of rock’n’roll starting from 1950s, one will notice that there was a clear division in rock that separates the rock’n’roll of 1950s from rock of the second half of the 1960s and beyond—the rock that we know today. This thesis investigates how the visual aesthetic of rock’n’roll evolved from its origins in the 1950s blues tradition, how it was formed in the second half of the 1960s, and how it was modified in the first half of the 1970s. In particular, it focuses on the role played by the British band Rolling Stones as mediators between the 1950s early rock aesthetics rooted in the blues tradition and the Beats’ ideology and the subsequent generations of American rockers who emerged in the 1970s, such as the band New York Dolls. The final section of the thesis investigates how the New York Dolls adopted and transmitted the aesthetics of authenticity pioneered by the Stones to the new wave of punk and grunge bands. Although the thesis considers the music produced within this milieu, its primary focus is on the visual presentation and promotion of the new aesthetic through stage performances, publicity and the medium of television.

During this thesis work a coupled thermo-mechanical finite element model (FEM) was builtto simulate hot rolling in the blooming mill at Sandvik Materials Technology (SMT) inSandviken. The blooming mill is the first in a long line of processes that continuously or ingotcast ingots are subjected to before becoming finished products. The aim of this thesis work was twofold. The first was to create a parameterized finiteelement (FE) model of the blooming mill. The commercial FE software package MSCMarc/Mentat was used to create this model and the programing language Python was used toparameterize it. Second, two different pass schedules (A and B) were studied and comparedusing the model. The two pass series were evaluated with focus on their ability to healcentreline porosity, i.e. to close voids in the centre of the ingot. This evaluation was made by studying the hydrostatic stress (σm), the von Mises stress (σeq)and the plastic strain (εp) in the centre of the ingot. From these parameters the stress triaxiality(Tx) and the hydrostatic integration parameter (Gm) were calculated for each pass in bothseries using two different transportation times (30 and 150 s) from the furnace. The relationbetween Gm and an analytical parameter (Δ) was also studied. This parameter is the ratiobetween the mean height of the ingot and the contact length between the rolls and the ingot,which is useful as a rule of thumb to determine the homogeneity or penetration of strain for aspecific pass. The pass series designed with fewer passes (B), many with greater reduction, was shown toachieve better void closure theoretically. It was also shown that a temperature gradient, whichis the result of a longer holding time between the furnace and the blooming mill leads toimproved void closure.

Les matériaux ODS (Oxide Dispersion Strengthened), mis au point par métallurgie des poudres, sont la solution de référence pour le gainage du combustible nucléaire des nouveaux réacteurs de génération IV à fort taux de combustion. Ils présentent une résistance au gonflement sous irradiation augmentée par rapport aux aciers austénitiques et une grande stabilité dimensionnelle en fluage induite par une dispersion homogène de nano-particules stables à haute température. Après co-broyage de la poudre d'alliage maître avec une poudre d'oxydes d'yttrium, le matériau est consolidé par filage à chaud, puis mis en forme à froid par laminage à pas de pèlerin. Les matériaux ODS sont caractérisés par une faible ductilité et une dureté élevée à température ambiante. Les passes de laminage doivent être entrecoupées par des traitements thermiques intermédiaires afin de restaurer le tube et éviter tout endommagement pendant la gamme de transformation.Cette étude vise à identifier les points clés pour la maîtrise de la gamme de transformation à froid de deux nuances ODS : une nuance ferritique Fe-14Cr-1W et une nuance martensitique Fe-9Cr-1W. Les relations entre les traitements thermomécaniques et la microstructure sont étudiées à partir de caractérisations multi-échelles. La compréhension des mécanismes d'évolution de la microstructure permet de proposer, pour chaque nuance, une gamme de transformation à froid robuste. Pour la nuance ferritique Fe-14Cr-1W, la déformabilité est assurée par une croissance des grains à haute température suivant un mécanisme de type Strain Induced Boundary Migration (SIBM). Des optimisations s'appuyant sur une recristallisation primaire sont envisagées. Pour la nuance martensitique Fe-9Cr-1W, la gamme mise en œuvre permet d'obtenir un matériau dont la déformabilité et les caractéristiques mécaniques à chaud sont équivalentes voire meilleures que celles des nuances de la littérature. Des évolutions des gammes et de la composition chimique sont proposées pour améliorer la résistance à la corrosion et au fluage. / Oxide dispersion strengthened steels, elaborated by powder metallurgy, are considered as reference materials for high burn up cladding tubes for future Sodium Cooled Fast reactors. They present superior radiation resistance compared with austenitic steels and high creep strength due to reinforcement by the homogeneous dispersion of hard nano-sized particles. After mechanical alloying of the matrix powder and the yttrium oxides, ODS steels are consolidated by hot extrusion and manufactured by using cold pilgerin process. ODS steels are usually characterized by a low ductility and a high hardness at room temperature. The cold-rolling passes have to be punctuated by intermediate heat treatments in order to soften the raw tube and avoid any damage in the course of manufacturing.The aim of this study is to identify the key points for the control of the manufacturing of two grades: a Fe-14Cr-1W ferritic grade and a Fe-9Cr-1W martensitic grade. The relationship between thermomechanical treatments and microstructure is studied by multi-scale characterizations. The understanding of the microstructure evolution permits the determination of robust fabrication routes for both grades. The deformability of the ODS Fe-14Cr-1W ferritic grade is ensured by grain growth at high temperature following a Strain Induced Boundary Migration (SIBM) mechanism. Optimizations through primary recrystallization are proposed. Fabrication route of ODS Fe-9Cr-1W martensitic grade permits to obtain a material characterized by deformability and high temperature mechanical properties similar or even better than those of literature grades. Fabrication routes evolutions and chemical composition optimization are proposed to improve the corrosion and thermal creep resistance.

O aço 10B06 é utilizado na produção de fio máquina para trefilação. Por ser produzido em aciaria elétrica, o teor de nitrogênio desse aço tende a ser elevado, o que pode causar o fenômeno de envelhecimento, resultando em aumento de resistência e queda de ductilidade. Reduzir o teor de nitrogênio livre é uma forma de minimizar esse efeito, o que é realizado pela adição de boro. Dessa forma, o presente trabalho teve como objetivo estudar o efeito do boro no aço 10B06. Foram utilizadas amostras de fio máquina, diâmetro 5,50mm, e arame trefilado com teores de boro variando de 55 a 112ppm. Os dois principais fatores que influenciam a microestrutura e propriedades mecânicas do material são a composição química e o processo produtivo. Por esse motivo, inicialmente foi avaliada a etapa de resfriamento durante a laminação do fio máquina, por meio de uma análise termográfica. Foi encontrada a temperatura de 767ºC no início do resfriamento do material, valor próximo de Ac1, limite inferior do intervalo intercrítico. Esse fato favorece o enriquecimento da austenita em carbono, facilitando a formação de martensita e/ou austenita retida. Os resultados da análise metalográfica com Nital revelaram microestrutura composta de aproximadamente 88% de ferrita e 12% de perlita. Já o reagente Le Pera identificou ilhas de martensita e/ou austenita retida (MA), o que foi comprovado por análises de microscopia eletrônica de varredura. Os resultados de microdureza mostraram uma tendência de queda com o aumento do teor de boro. As medições de nanodureza confirmaram a presença do microconstituinte MA. A ferrita apresentou dureza na faixa de 280 - 320 HV, enquanto o MA ficou no intervalo de 349 - 424 HV. Comparando-se o limite de resistência obtido no fio máquina com menor teor de boro (55ppm - 434MPa) com o de maior (112ppm - 394MPa), observasse uma redução de 40MPa para um acréscimo de 57ppm de boro, confirmando o efeito esperado para esse elemento pela formação de BN. Utilizando os dados da curva tensão versus deformação foram obtidos os coeficientes de encruamento dos fios máquina, que apresentaram uma tendência de crescimento com o teor de boro, sendo que o material com 101ppm de boro mostrou o melhor valor para aplicação em processos de conformação. As análises fractográficas revelaram que os mecanismos de fratura presentes em todos os materiais foram a formação e coalescimento de microvidades. Considerando-se todas as análises realizadas nesse trabalho foi possível evidenciar o efeito do boro na redução do efeito do envelhecimento provocado pelo nitrogênio. Entre os testes realizados, os que apresentaram as melhores relações B/N foram os de teores 109 e 112ppm de boro. Essas relações estão próximas do valor máximo indicado de 0,8. / The 10B06 steel grade is applied to the production of wire rod for drawing. The steel is produced in an Electric Arc Furnace and this process can lead to higher nitrogen levels that cause strain aging resulting in an increase of the strength and ductility loss. The reduction of free nitrogen content through boron addition is one way to minimize this effect that can be done through boron addition. In this way, the present work aims to study boron effect on 10B06 steel. It was used wire rod, diameter 5,50mm and a cold-drawn wire rod with chemical composition from 55 to 112ppm of boron. The main factors that influence the microstructure and mechanical properties of the material are the chemical composition and the productive process. For this reason, initially, the cooling treatment was analyzed using thermography and it was found at the beginning of the cooling process a temperature of 767oC in the material, close to Ac1, lower limit of the intercritical interval. This temperature can facilitate the enrichment of carbon in the austenite, making easier martensite and/or retained austenite formation. The metallographic analysis with Nital etchant showed a microstructure composed of about 88% ferrite and 12% perlite, and Le Pera etchant identified martensite and/or retained austenite (MA), what was confirmed by scanning electron microscope analysis. Furthermore, nanohardness measurements confirmed the presence of the microconstituent MA, as ferrite presented hardness from 280 to 320 HV and MA from 349 to 424 HV. Microhardess results decreased with increasing boron content. A decrease of 40MPa in the tensile strength was observed between the wire rod with boron content of 55ppm (434MPa) and the one with 112ppm (394MPa), in agreement with the expected effect of the BN formation. It was possible to obtain hardening coefficient of the wire rod using the data of the stress versus strain curve, which increased with boron content, and the material with 101ppm of boron showed the best value for forming application. Fractographic analysis revealed that the fracture mechanisms in all the materials were the development and coalescing of microcavity. Considering all the analysis of this study it was possible to confirm boron\'s effect to reduce strain aging caused by nitrogen. Materials with 109 and 112ppm of boron presented the best B/N ratio, with values close to the maximum indicated, 0,8.