This dissertation focuses on quantitative subsurface and mechanical properties imaging potential of AFM probes. Extensive modeling of AFM probes are presented for thorough understanding of capabilities and limitations of current techniques, these models are verified by various experiments, and different methods are developed by utilizing force-sensing integrated read-out active tip (FIRAT), which is an active AFM probe with broad bandwidth. For quantitative subsurface imaging, a 3-D FEA model of AFM tip-sample contact is developed and this model can simulate AFM tip scan on nanoscale-sized buried structures. FIRAT probe, which is active and broadband, is utilized for interaction forces imaging during intermittent contact mode and mechanical characterization capability of this probe is investigated. It is shown that probe dynamics, stiffness, stiffness ambiguity, assumed contact mechanics, and noise are important parameters for the accuracy of mechanical properties imaging. An active tip control mechanism is introduced to limit contact forces during intermittent contact mode. In addition to these, a combined ultrasonic AFM and interaction forces imaging method is developed and modeled to solve the reduced elasticity measurement sensitivity on composite materials. This method is capable of imaging a broader range of elasticity on combination samples such as metal nanoparticles in polymers at nanoscale.

Os ligamentos são estruturas estabilizadoras estáticas das articulações e desempenham um papel importante na junção mecânica. Podem ser influenciadas por fatores de diversas naturezas, inclusive adaptações sofridas durante o período puerperal. Na gravidez existem grandes modificações hormonais que preparam o organismo materno para o desenvolvimento do embrião e feto, bem como para a parturição. Assim, sob ação hormonal os ligamentos e a sínfise púbica têm suas características mecânicas alteradas preparando a mãe para o parto. Este trabalho teve por objetivo caracterizar mecanicamente as modificações sofridas na sínfise púbica e no ligamento cruzado anterior do joelho, durante a gestação e na fase final. Para o estudo foram utilizadas 44 ratas da raça Wistar, com massa corporal inicial média de 301.1 / 8,1g e idade aproximada de 100 dias. Os animais foram divididos em três grupos experimentais: o grupo controle, grupo prenhez I e o grupo prenhez II. Para constituição do grupo prenhez I e II, fêmeas férteis foram acasaladas com machos e o coito foi comprovado pela presença de espermatozóides no lavado vaginal obtido da fêmea. Confirmando a prenhez, os animais foram mantidos em gaiolas até o décimo sexto dia para o grupo prenhez I e sacrificados, para o grupo prenhez II foi esperado até o vigésimo dia de gestação e sacrificados, sendo coletados a pelve e os joelhos de ambos os grupos. Após preparo, a sínfise púbica e o ligamento cruzado anterior do joelho foram ensaiados mecanicamente em tração, com obtenção dos seguintes parâmetros: carga no limite máximo e rigidez. Os resultados comparados com as fêmeas controles não prenhes mostraram que para a sínfise púbica houve aumento da rigidez e diminuição da carga no limite máximo. Para o ligamento cruzado anterior não houve diferença significativa entre os grupos / Ligaments are static stabilizer structures of the joints and play an important role in the mechanical junction. They may be influenced by factors of several natures, including adaptations suffered during the puerperal period. There are in pregnancy big hormonal modifications that prepare the maternal organism for the embryo and fetus development, as well to parturition. Thus, under hormonal actions the ligaments and the pubic sinfisis have their mechanical features shifted preparing the mother for the labor. This paper aimed to point out the shifts occurred by the pubic sinfisis and by the knee anterior cruciate ligament during pregnancy and in the final phase. For the study were used 44 mice Wistar breed, corporal average mass of 301,1 / 8,1g and approximated age of 100 days. They were divided into 3 experimental groups: control group, pregnancy I group and pregnancy II group. For the disposition of the control group, the animals were expected to complete 120 days, then sacrificed and collected the pelvis and the knees. For pregnancy group I and II, fertile females were mated with males and the coitus was proved with the presence of spermatozoids in the vaginal washed obtained from the female. Once confirmed pregnancy, the animals were kept in cages until the 16th day for pregnancy group I and so only collected the animal’s pelvis. For pregnancy group II was expected until the 23rd day of pregnancy and sacrificed, being collected the pelvis and the knees. After preparing, the pubic sinfisis and the anterior cruciate ligament of the knee were mechanically tested in traction, obtaining the following parameters: load in maximum border line and stiffness. The results compared with non pregnant females showed that to the pubic sinfisis there was an increase of stiffness and a load in maximum border line decrease. For the anterior cruciate ligament there was no significant difference between the groups

PTMO-urethane and urea diacrylates (UtDA, UrDA) were synthesized from a two-step reactions of bis (4-isocyanatocyclohexyl) methane (HMDI) with either α,Ï -hydroxy-terminated poly (tetramethylene oxide) (PTMO Mn 250, 1000, 2000 and 2900 g/mol) or α,Ï -aminopropyl-terminated PTMO and 2-hydroxyethyl acrylate (HEA). PTMO-based ester precursors (EtDA) were also synthesized from α,Ï -hydroxy-terminated PTMO (Mn 1000 and 2000 g/mol). Two bis acetoacetates were synthesized from acetoacetylation of 1,4-butanediol and 250 g/mol hydroxy-terminated PTMO with tert-butyl acetoacetate. ¹H NMR spectroscopy confirmed the structure and average molecular weights (Mn)of diacrylates. Mn of these precursors were in the range of 950 to 3670 g/mol by ¹H NMR. The rheological properties of diacrylates were studied and activation energies for flow were calculated. Activation energies increased with increasing Mn and hydrogen-bond segment content. Michael carbon addition was employed to covalently crosslink the precursors resulting in networks with gel fractions better than 90%. DSC and DMA experiments revealed that networks had a broad distribution of glass transition temperatures depending on Mn and degree of hydrogen bonding present in the diacrylates. Their Tg's varied from -61 ºC to 63 ºC depending on the crosslinking density and hydrogen-bonding segment content. TGA revealed that UtDA and UrDA networks had an improved thermal stability compared to their EtDA counterparts. Tensile properties showed a variation depending on the structure and Mn of diacrylate and BisAcAc precursors. The storage moduli of networks precursor change from 25.3 MPa to 2.0 MPa with increasing Mn of the urethane diacrylate Elongation at break increased from 255% to 755 % for the same networks. The Young's moduli increased from 3.27 MPa for EtDA 2000 to 311.1 MPa for UrDA 2000 which was attributed to increasing degree of hydrogen-bonding. Acid functionalization of C70 P Baytubes multiwalled carbon nanotubes (MWCNT) generated acid-functionalized nanotubes (MWCNT-COOH). Suspension of MWCNT-COOH in organic solvents (chloroform, toluene, THF, DMF and 2-propanol) were prepared. DLS indicated average particle diameters of MWCNT-COOH in DMF and in 2-propanol were 139 nm and 162 nm respectively. FESEM of suspensions revealed aggregate free dispersion of MWCNT-COOH in DMF and 2-propanol. MWCNT-COOH containing composite networks were prepared. FESEM images of fracture surfaces of UtDA showed MWCNT-COOH were well-dispersed in the composites. DMA showed an increase in the rubbery plateau modulus which correlated with the MWCNT-COOH content in the networks. Tensile testing also revealed a relationship between MWCNT-COOH content and young's moduli and strain at break of networks. Storage moduli of networks increased from 25 MPa to 211 MPa with increasing MWCNT-COOH content whereas elongation at break decreased from 255 % to 146 %. UtDAs and pentaerythritol tetraacrylate (PETA) were crosslinked under UV radiation (6 passes, 1.42 ± 0.05 W.cm2 for each pass) in the presence of 2,2-dimethoxy-2-phenylacetophenone (DMPA) (1 wt. % of the mixture) UV initiator. DMA demonstrated the presence of broad glass transition regions with a range of Tg's which varied from -60 °C to -30°C. Tensile testing also revealed the relationship between Young's moduli, strain at break and the molecular weight of the diacrylates. The increasing molecular weight of urethane diacrylate precursors caused a drop in the storage moduli of networks from 15.8 MPa to 1.4 MPa and an increase in elongation at break from 76 % to 132 %. / Master of Science

Among the commercial aluminum alloys, aluminum 319 (Al-7wt%Si-4wt%Cu) type alloys are popularly used in automobile engine parts. These alloys have good casting characteristics and excellent mechanical properties resulting from a suitable heat treatment. To get a high strength in the 319 type alloys, grain refining, reducing the porosity, solid solution hardening, and precipitation hardening are preferred. All experimental variables such as solidification condition, composition, and heat treatment are influence on the precipitation behavior; however, precipitation hardening is the most significant because excess alloying elements from supersaturated solid solution form fine particles which act as obstacles to dislocation movement. The challenges of the 319 type alloys arise due to small size of precipitate and complex aging response caused by multi components. It is important to determine the chemical composition, crystal structure, and orientation relationship as well as precipitate morphology in order to understand the precipitation behavior and strengthening mechanism. In this study, the mechanical properties and microstructure were investigated using transmission electron microscopy and three dimensional atom probe tomography. The Mn and Mg effects on the microstructure and mechanical properties are discussed with crystallographic study on the iron intermetallic phases. The microstructural evolution and nucleation study on the precipitates in the low-Si 319 type aluminum alloys are also presented with sample preparation and analysis condition of TEM and 3DAP tomography.

This study aimed to extend the knowledge on player and surface loading by contributing new data in relation to a greater range of movements, relevant in-game scenarios and on carefully controlled third generation artificial turf surfaces. This was done by selecting soccer relevant movements and in-game scenarios for a player movement study with the help of a player focus group and questionnaire. Furthermore, four surfaces were created with surface hardness and rotational traction values at the upper and lower limits of the standards set by FIFA. The study showed that both the surface hardness and rotational traction properties can affect the human movement dynamics, though these effects were mainly present during the stop and turn manoeuvre. During the stop and turn manoeuvre the soft and high traction surfaces conditions led to increased frontal plane moments as well as increased average ground reaction forces during mid-stance. In combination with decreased ground contact times it appeared that the players were able to decelerate / accelerate faster and generate a larger force on the soft and high traction surfaces. During peak push off it appeared that the players were able to generate a larger force on the hard surfaces, which also led to a significant increase in plantar flexion moment. While some parameters showed an effect for surface hardness and / or rotational traction across all four surface conditions, for others such as the knee valgus, hip extension and hip internal rotation moment showed only a significant effect between two of the four surfaces. At the same time the other surfaces showed either no effect or the opposite effect. This suggests that the effects of the surface hardness can be influenced by the rotational traction properties, and vice versa. Regarding the jumping / heading manoeuvre the effects of the surface conditions were limited. This may have been related to the high demands of the movement, or to limitations of the mechanical measurement methods. In addition to the effects of surface properties on human movement dynamics the study also showed that the mechanical measurement methods may not be representative of the human loading. The impact force conditions of the advanced artificial athlete were substantially different to that of the stop and turn and jumping / heading manoeuvre. Whereas for the rotational traction test the study showed that the rotation of the foot during the ST was substantially less than the minimum 45° required by the FIFA guidelines. Regarding the inclusion of in-game scenarios the study showed that both the simulated opponent used for the stop and turn manoeuvre, and heading a ball during a maximal vertical stop jump manoeuvre can affect the human movement dynamics. During the stop and turn with a simulated opponent the frontal plane moments in the lower limbs were significantly increased. However, this increase in joint loading could not be related to any changes in movement strategy. During the landing after heading a ball during a maximal vertical stop jump the players used a different landing strategy by landing in a more upright position and increasing the ankle plantar flexion ankle just before lading. This allowed for a larger change in the ankle plantar / dorsi flexion angle to absorb the impact of the landing. In addition to this, the heading manoeuvre also led to a significant increase in the frontal plane joint moments of the lower limbs. For future studies it is recommended that a combination of surface properties is used to gain insight into how these affect each other regarding the effects they have on human movement dynamics. In addition, they should provide detailed information on the surface design as well as the properties. Regarding the quantification of the properties it is recommended that in addition to industry standards the surfaces are also quantified using conditions closer to those expected within the study. It is also recommended that future studies incorporate in-game scenarios in order to gain more insight into the effects of interventions that simulate actual match situations.

[pt] No presente trabalho foi estudado o comportamento mecânico do concreto reforçado com fibras de aço na escala do material e estrutural. A caracterização da matriz foi realizada por meio de ensaios de compressão para diferentes idades. Foram realizados ensaios de flexão em três pontos, e ensaios de tração direta em corpos de prova no formato de dog bone, tanto para a matriz quanto para concretos reforçados com fibras de aço. As fibras eram providas de ganchos nas extremidades, com comprimentos de 30, 35 e 60 mm e diâmetros de 0,62, 0,55 e 0,75 mm, respectivamente. As frações volumétricas adotadas foram 0,25, 0,5 e 1,0 por cento. A adição de fibras promoveu aumento na tenacidade e na resistência residual do concreto tanto nos ensaios de flexão quanto tração direta. Ensaios de tração direta em tirantes de concreto armado foram conduzidos para a matriz e para concretos reforçados com 1,0 por cento das fibras de 35 e 60 mm de comprimento. Foi observado que a adição de fibras controlou a abertura de fissuras, aumentou a rigidez pós fissuração e a aderência barra-concreto. Na escala estrutural, ensaios de momento negativo no meio do vão foram conduzidos em dormentes de concreto protendido sem reforço e com 0,5 por cento de fibras de comprimento 35 e 60 mm. O momento de primeira fissura, momento último e a tenacidade foram incrementadas com a adição de fibras no dormente. Os resultados experimentais foram verificados por cálculo teórico. O incremento no momento último pela adição de fibras seguiu o mesmo padrão apresentado experimentalmente. / [en] This work presents an evaluation of the mechanical behavior of steel fiber reinforced concrete on a material and structural scale. The characterization of the matrix was performed by compression tests for different ages. Three-point bending tests and direct tensile tests on dog bone specimens were performed for the matrix and for concrete reinforced with steel fibers. The fibers had hooked-end geometry, were 30, 35 and 60 mm long and had diameters of 0.62, 0.55 and 0.75 mm, respectively. The volume fractions were 0.25, 0.5 and 1.0 per cent. The addition of fibers promoted an increase in toughness and residual strength of the concrete in both the flexural and direct tensile tests. Tension stiffening tests were conducted on the matrix and on concretes reinforced with 1.0 per cent of the 35 and 60 mm long fibers. It was observed that the addition of fibers controlled the crack opening, increased post-cracking stiffness and bar-concrete adhesion. In the structural scale, negative bending moment tests at mid span were conducted on reinforced concrete sleepers with 0.5 per cent of the 35 and 60 mm long fibers. The first crack strength, ultimate strength and toughness were increased with the addition of fibers on the sleeper. The experimental results were verified by theoretical calculations. The increment ratio of the ultimate moment by the fiber addition was the same for the theoretical and experimental analysis.

Le remplacement des alliages durs à base cobalt par des alliages à base fer suscite un intérêt croissant pour la protection anti-usure des pièces métalliques fonctionnant dans le circuit primaire d’une centrale nucléaire. Dans le cadre de cette thèse, une étude métallurgique détaillée a été effectuée sur des dépôts épais en Norem 02™ élaborés par le procédé de projection laser.Un affinement significatif de la microstructure du Norem 02™ a été obtenu après optimisation des paramètres du procédé (puissance laser, vitesse de balayage et débit de poudre), par rapport à un procédé concurrent par Plasma à Arc Transféré. Les essais tribologiques montrent que l’amélioration de la microstructure n’empêche cependant pas l’apparition du grippage à 300°C.La deuxième partie de cette étude a été consacrée à l’amélioration du Norem 02™ avec ajout de différents éléments chimiques. Le choix de ces ajouts adéquats a été validé grâce aux tests de frottement réalisés sur des échantillons en Norem 02™ modifié, sous haute contrainte mécanique (1 GPa) et à haute température (300°C). Parmi une dizaine d’éléments d’ajouts testés, l’ajout de titane a permis une transformation complète de la microstructure du Norem 02™. Cette transformation métallurgique a amélioré son comportement tribologique avec un faible coefficient de frottement (<0.3) à 300°C.L’origine de cette amélioration du comportement mécanique du Norem 02-Ti a été étudiée et expliquée par différentes analyses microstructurales (MO, MEB, EDS, EBSD) ainsi que des essais de traction sur des éprouvettes extraites des revêtements épais. / This study aims to substitute the cobalt-based hardfacing alloys with iron-based hardfacing alloys to protect mechanical parts operating in the primary circuit of a pressurized water reactor (PWR)Firstly, a detailed metallurgical study was carried out to characterize a thick deposit on Norem 02™ produced by the laser process (Direct Metal Deposition - DMD). Compared with a classical PTA process, a microstructure refinement was achieved after an optimization of process parameters (laser power, scanning speed and powder flow-rate). However, wear tests show that the improvement of the microstructure does not prevent the occurrence of galling at 300 ° C.The second part of this study is dedicated to Norem 02™ improvement with the addition of various chemical elements. The appropriate additions to this application have been validated by wear tests under high mechanical stress (1 GPa) and at high temperature (300°C). Among a dozen samples of modified Norem 02 ™, the addition of titanium was shown to provide a complete transformation of the initial Norem 02™’s microstructure. This metallurgical transformation improved its tribological behavior with a low friction coefficient (<0.3) obtained at 300 °C.Last, the origin of the mechanical behavior improvement of Norem 02-Ti was studied and explained by microstructural analysis (MO, MEB, EDS, EBSD) and tensile tests on specimens extracted from thick coatings.

Nickel-based superalloys, an alloy system bases on nickel as the matrix element with the addition of up to 10 more alloying elements including chromium, aluminum, cobalt, tungsten, molybdenum, titanium, and so on. Through the development and improvement of nickel-based superalloys in the past century, they are well proved to show excellent performance at the elevated service temperature. Owing to the combination of extraordinary high-temperature mechanical properties, such as monotonic and cyclic deformation resistance, fatigue crack propagation resistance; and high-temperature chemical properties, such as corrosion and oxidation resistance, phase stability, nickel-based superalloys are widely used in the critical hot-section components in aerospace and energy generation industries. The success of nickel-based superalloy systems attributes to both the well-tailored microstructures with the assistance of carefully doped alloying elements, and the intently developed manufacturing processes. The microstructure of the modern nickel-based superalloys consists of a two-phase configuration: the intermetallic precipitates (Ni,Co)3(Al,Ti,Ta) known as γ′ phase dispersed into the austenite γ matrix, which is firstly introduced in the 1940s.  The recently developed additive manufacturing (AM) techniques, acting as the disruptive manufacturing process, offers a new avenue for producing the nickel-based superalloy components with complicated geometries. However, γ′ strengthened nickel-based superalloys always suffer from the micro-cracking during the AM process, which is barely eliminated by the process optimization. On this basis, the new compositions of γ′ strengthened nickel-based superalloy adapted to the AM process are of great interest and significance. This study sought to design novel γ′ strengthened nickel-based superalloys readily for AM process with limited cracking susceptibility, based on the understanding of the cracking mechanisms. A two-parameter model is developed to predict the additive manufacturability for any given composition of a nickel-based superalloy. One materials index is derived from the comparison of the deformation-resistant capacity between dendritic and interdendritic regions, while another index is derived from the difference of heat resistant capacity of these two spaces. By plotting the additive manufacturability diagram, the superalloys family can be categorized into the easy-to-weld, fairly-weldable, and non-weldable regime with the good agreement of the existed knowledge. To design a novel superalloy, a Cr-Co-Mo-W-Al-Ti-Ta-Nb-Fe-Ni alloy family is proposed containing 921,600 composition recipes in total. Through the examination of additive manufacturability, undesired phase formation propensity, and the precipitation fraction, one composition of superalloy, MAD542, out of the 921,600 candidates is selected. Validation of additive manufacturability of MAD542 is carried out by laser powder bed fusion (LPBF). By optimizing the LPBF process parameters, the crack-free MAD542 part is achieved. In addition, the MAD542 superalloy shows great resistance to the post-processing treatment-induced cracking. During the post-processing treatment, extensive annealing twins are promoted to achieve the recrystallization microstructure, ensuring the rapid reduction of stored energy. After ageing treatment, up to 60-65% volume fraction of γ′ precipitates are developed, indicating the huge potential of γ′ formation. Examined by the high-temperature slow strain rate tensile and constant loading creep testing, the MAD542 superalloy shows superior strength than the LPBF processed and hot isostatic pressed plus heat-treated IN738LC superalloy. While the low ductility of MAD542 is existed, which is expected to be improved by modifying the post-processing treatment scenarios and by the adjusting building direction in the following stages of the Ph.D. research. MAD542 superalloy so far shows both good additive manufacturability and mechanical potentials. Additionally, the results in this study will contribute to a novel paradigm for alloy design and encourage more γ′-strengthened nickel-based superalloys tailored for AM processes in the future. / <p>Additional funding agencies: Agora Materiae Graduate School for multidisiplinary PhD students at Linköping University, and Stiftelsen Axel Hultgren.</p>

<p><a>Aluminum (Al) alloys have been widely used in </a>industry as light-weight structural materials. However, the mechanical strength of the strongest Al alloys is still much lower than most high-strength steels. This thesis aims to investigate the fabrication and mechanical behaviors of nanotwinned high-strength Al alloys and multilayers.</p> <p>Twin boundaries are special grain boundaries with mirror symmetry. Twin boundaries can generate slip discontinuity and block the transmission of dislocations, and serve as dislocation sources to accommodate plasticity. However, twinning in Al is rare due to its high stacking fault energy and low unstable stacking fault energy. In this thesis, we used multiple methods to introduce high-density twins into Al and achieve outstanding mechanical properties and thermal stability. </p> <p>Certain type of solutes can greatly increase the twin density in Al by decreasing the stacking fault energy of Al and retarding the detwinning process. Nanotwinned Al-Ni and Al-Ti binary alloys fabricated by magnetron sputtering show high strength, good deformability, and unique deformation mechanisms. Furthermore, deformation and thermal stability of binary nanotwinned Al alloys can be enhanced by adding a third or fourth solute element. </p> <p>Interfaces can facilitate twin formation in Al as well. High-density twins and stacking faults were introduced into Al by using Al/Ti layer interfaces. Nanotwinned Al/Ti multilayers have ultra-high strength, superb deformability and thermal stability. This thesis provides promising pathways to fabricate Al alloys and composites with high strength and good thermal stability.</p>

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