Diffraction strain/stress analysis has been widely used in the determination of residual and applied stresses in the surface layers and bulk volumes of materials for a long time. The technique has been used for almost 100 years. However, there are still issues that have not been yet addressed.In this dissertation, we address these issues. The basic theory of diffraction strain/stress analysis is extensively reviewed and the weaknesses of the analysis are explained carefully. The current definitions that have been used for describing residual stresses are unified under this expanded analysis. In addition, the homogeneous continuum analysis is extended to the polycrystalline materials under various loading types. To search for answers to the questions asked in this dissertation, finite element modeling. was used. This approach provides both local and global stress and strain information at all locations of a virtual specimen. The results show that St. Venant regions such as edges, voids, or geometric constraints cause local inhomogeneous strain/stress distribution which can cause deviations from linear deformation theory. Even if the far-field load region is sampled by X-rays, the representative volume element should be determined by preliminary experiments because almost all single-phase polycrystalline materials (with the exception of tungsten) are composite materials within which variations of elastic moduli are observed along with sample directions. In the multiphase polycrystalline materials, this problem becomes more serious due to the differential deformation of each phase with respect to each other. Therefore, an experimenter needs to be careful during the experiment, in acquiring representative data; this requires significant preparation and material characterization. With the findings of the dissertation, a set of rules are written for users and experimenters to apply during or before the experiments to collect accurate and representative data.

Recent advances in the use of thermal proxies provide a window into how faults slip during earthquakes. Faults have a similar large-scale structure with a fault core, where earthquakes nucleate, and a surrounding damage zone, but complexities in fault zone architecture and rheology influence earthquake propagation. For example, changes in thickness of slipping layers in the fault core, compositional heterogeneity, and fault surface topography can influence fault strength and either facilitate or arrest a rupture. A further barrier to our understanding of earthquake behavior is in constraining the frictional energy that goes into the earthquake energy budget. Earthquakes can propagate when the energy available at the rupture tip is greater or equal to the energy being expended through radiation of seismic waves, permanent deformation within the process zone, and heat through friction. By quantifying the total energy involved in coseismic slip we can gain a more complete picture of the energy required for rupture propagation and how this may vary across faults. Although fracture and radiated energy can be constrained seismologically, thermal energy requires quantification by other means, and up until recently only few estimates existed for frictional energy. In this thesis I utilize biomarker thermal maturity to quantify temperature rise across multiple faults and explore what this can tell us about earthquake behavior. In chapters two through four, I focus on three large faults of varying structural and rheological complexity. Beginning with the Muddy Mountain thrust of southeast Nevada in Chapter two, I identify thermal evidence of coseismic slip in principal slip zones (PSZs) along this exhumed fault. I show that considerable heterogeneity in the thickness of slipping layers occurs a long a fault and that this has a large effect on coseismic temperature rise and hence fault strength, due to the effect of high temperature dynamic weakening mechanisms. In Chapter three, I move on to the creeping central deforming zone of the San Andreas fault, and show that it has experienced many large earthquakes that are clustered in a 4 m-wide zone adjacent to an actively creeping region. This work shows that the central San Andreas fault and other creeping faults can host seismic slip and should be included in seismic hazard analyses. Furthermore, I demonstrate the potential of K/Ar dating as a tool to constrain the age of earthquakes and find that these central San Andreas fault events are as young as ~3.3 Ma. In Chapter four, I focus on the Hikurangi Subduction zone, which has hosted large earthquakes and regular slow slip events in the past. Here, using drill core collected through the Pāpaku fault, a splay fault of the Hikurangi megathrust, I find evidence of temperature rise in the fault zone and deep hanging wall. Coupled forward models of heat generation and biomarker reaction kinetics estimate that displacement during these earthquakes was likely 11-15 m. These and other splay faults along the margin may pose considerable seismic and tsunami hazard to near-shore communities in the North Island of New Zealand. In Chapter five I explore what we have learned about fault behavior from biomarkers and other thermal proxies. I include measurements from five new faults and compile observations and measurements from past studies to explore how coseismic slip is localized across fault zones and put together a database of frictional energy estimates. Coseismic slip can broadly be described by two different scales of earthquake localization and that this is a function of total displacement, and to a lesser extent, material contrast across the fault. I see that frictional energy is relatively similar across faults of different displacement, depth, and maturity, and conclude that frictional energy is limited by the onset of dynamic weakening. Finally, I put together constraints on the energies involved in the budget to produce the first complete view of the earthquake energy budget and provide estimates of the total energy required for earthquake rupture across different faults.

As crucial infrastructure systems remain in service up to and beyond their originally intended service lives, there has been a significant increase in efforts to quantify their current strength and remaining life span. Suspension bridges are of particular concern due to their impact on commerce, low repairability, and high replacement cost. As such, quantification of the performance of suspension bridge main cables at elevated temperatures is necessary for a holistic safety assessment. These cables are the primary load-carrying members, and are susceptible to vehicular fires near the midspan and anchorage where the cable sweeps low to the deck. Due to the dearth of empirical data regarding the thermomechanical properties of main cables, previous studies were forced to rely on thermomechanical properties derived for different materials, geometries, and scales. It is the chief goal of this dissertation to fill this void in high-temperature empirical data. First, the high temperature stress-strain behavior of the constituent ASTM A586 wires is examined. The coldworked wires are highly susceptible to recovery at elevated temperatures, which has the power to undo the primary strengthening mechanism. Large decreases in elastic modulus, yield stress, and ultimate stress are observed at elevated temperature. The high temperature stress-strain curves are fully parameterized, and a procedure for generating stress-strain curves at temperatures between 22°C and 724°C is provided. Next, the post-fire performance of the wire is quantified. Wires are heated to various temperatures up to 842°C and then allowed to cool before being tensile tested. The results of this testing show that a significant portion of the high-temperature strength-loss observed in the in-situ tests persists after cool-down. Exposure to elevated temperatures reduces strength and fundamentally alters the shape of the stress-strain curves of the heated and cooled wires. These post-fire stress-strain curves are fully parameterized, and a procedure for recreating them between 22°C and 842°C is provided. Next, the metallurgical underpinnings for the observed changes in mechanical behavior at and after high-temperature exposure are explored using neutron diffraction techniques. Two engineering beamline experiments generate peak-narrowing data that sheds light on the evolving dislocation density and crystallite size in this wire during and after heating. Results confirm that the decreases in wire strength that persist after cool-down are the product of recovery; temperatures in excess of 700°C decrease wire dislocation density to values similar to those of undeformed structural materials. Finally, the thermal conductivity of the main cable is addressed. The air voids and point contacts between the wires create a complex (and anisotropic) heat transfer situation within main cables. A one-to-one, 8200 kg mock-up of a panel of a suspension bridge main cable is constructed, instrumented, and heated. The data provided by the internal temperature sensors is used to tune the thermal conductivity of a representative finite element via a gradient descent algorithm. The resulting temperature-dependent thermal conductivity function allows the complex internal heat transfer of the main cable to be accurately approximated by a monolithic section with conductivity tuned to the measured behavior of a physical main cable. Cumulatively, the results of these studies shows that the thermomechanical properties of main cables are not well represented by previous approximations that are based on other materials and applications. The properties derived herein will facilitate more accurate performance estimates of suspension bridges subjected to fires than previously possible.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / It was objectified in this dissertation to analyze the distribution of the stress and displacements in the bone-implant interface, using the finite element method. The implants had been analyzed in two distinct situations: put directly in the two bone layers, cortical and trabecular, simulating the situation of immediate load, previous to osseointegration, and with the implants involved by a denser bone layer simulating the occurrence of the osseointegration. The geometry of the bone layers was obtained by means of computerized cat scan and the format of the implants and the prosthetic components had been supplied by the Neodent (Curitiba, Brazil). The variables analysed had been: geometry of the implants (cylindrical and taper), abutment (internal hexagon and morse taper) and the positioning of the implants in relation to the alveolar bone boards (buccaly and palatine). With this, 16 groups of analysis were formed, for which bidimensional models of the alveolus of extration of an upper central incisor had been constructed, simultaneously with the geometry of the implants, for the numerical simulation. The results of bigger relevance had been: the Von Mises stresses, principal stress (maximum and minimum) and the shear stresses, as well as the relative displacements presented by the bone-implant structure. Through the analyses, one concluded that different implant geometries adjust themselves better to each situation (immediate load and osseointegrated implant), and that the Titamax CM implant, of cylindrical format with prosthetic connection, morse taper, in palatine position was the one that best adapted itself. The found values can lead to a better understanding of the biomechanics around the implants. Despite of being a preliminary study, the work supplies subsidies for the accomplishment of future researches, since the methodology used can be applied in a variety of similar cases found in the Implantology. / Objetivou-se nesta dissertação analisar a distribuição das tensões e deslocamentos na interface osso-implante, utilizando o método dos elementos finitos. Os implantes foram analisados em duas situações distintas: assentados diretamente nas duas camadas ósseas, cortical e trabecular, simulando a situação de carga imediata, anterior a osseointegração; e com os implantes envolvidos por uma camada óssea mais densa simulando a ocorrência da osseointegração. A geometria das camadas ósseas foi obtida por meio de tomografia computadorizada. O formato dos implantes e componentes protéticos foram fornecidos pela Neodent (Curitiba, Brasil). As variáveis analisadas foram: geometria dos implantes (cilíndrico e cônico), pilar (hexágono interno e cone morse) e o posicionamento dos implantes em relação às tábuas ósseas alveolares (vestibularizado e palatinizado). Com isto formou-se 16 grupos de análise, para os quais foram construídos modelos bidimensionais do alvéolo de extração de um incisivo central superior, conjuntamente com as geometrias dos implantes, para a simulação numérica. Os resultados de maior relevância foram: as tensões de Von Mises, tensões principais (máximas e mínimas) e as tensões cisalhantes, bem como os deslocamentos relativos apresentados pela estrutura osso-implante. Por meio das análises concluiu-se que, diferentes geometrias de implantes se ajustam melhor a cada situação (carga imediata e implante osseointegrado), e que o implante Titamax CM, de formato cilíndrico com conexão protética cone morse posicionado palatinizado, foi o que melhor adaptou-se. Os valores encontrados podem levar a um melhor entendimento da biomecânica ao redor dos implantes. Apesar de ser um estudo preliminar, o trabalho realizado fornece subsidio para a realização de pesquisas futuras, pois a metodologia utilizada pode ser empregada em uma variedade de casos similares encontrados na implantodontia. / Mestre em Engenharia Mecânica