A verticalização de molares inferiores é indicada quando ocorre inclinação mesial dos segundos molares, atribuídas à ausência do primeiro molar. Existem inúmeras metodologias para realização de tal movimento. O objetivo do estudo foi analisar e comparar in vitro, por meio de fotoelasticidade, a distribuição de tensões nos segundos molares inferiores geradas por diferentes métodos de verticalização. Foram avaliados quatro modelos com as seguintes mecânicas: mini-implante, cantiléver, mola em T e mola aberta. As regiões do segundo molar selecionadas para avaliação foram: cervical da raiz mesial, apical da raiz mesial, cervical da raiz distal e apical da raiz distal. A resultante das forças aplicadas foi aferida por meio da quantificação das franjas isocromáticas. Os valores de franjas foram descritos com uso de média e desvio padrão e verificada a concordância/reprodutibilidade entre as avaliações com uso do coeficiente de correlação intraclasse com os respectivos intervalos com 95% de confiança e calculadas as medidas de repetibilidade. Os diferentes tipos de mecânicas foram comparados com uso de teste não paramétrico e quando o teste apresentou significância estatística foram realizadas comparações múltiplas não paramétricas para medidas pareadas com o intuito de verificar entre quais tipos de mecânicas ocorreram diferenças nas ordens das franjas. Os valores diferiram estatisticamente entre os tipos de mecânica utilizados (p < 0,05), exceto na região cervical distal, onde apresentaram-se estatisticamente iguais nos quatro tipos de mecânica (p = 0,112). Na técnica utilizando mini-implante, as maiores tensões foram encontradas na região cervical distal, seguidas de apical da raiz mesial e apical da raiz distal. Na região cervical mesial não foram detectadas tensões. Utilizando o cantiléver, as maiores tensões localizaram-se na região cervical mesial, seguidas de apical da raiz mesial e região cervical distal. Não foram detectadas tensões na apical da raiz distal. Na mola em T, as maiores tensões foram observadas na apical da raiz mesial, seguidas de região cervical da raiz mesial, apical da raiz distal e região cervical distal. Na mola aberta, as maiores tensões foram constatadas na apical da raiz mesial, seguidas de região cervical mesial, região cervical distal e apical da raiz distal. Ao compararem-se as técnicas, foi possível concluir que o mini-implante é a técnica que apresentou as menores tensões e o cantiléver as maiores tensões nas regiões estudadas. / Lower molars uprighting is indicated when mesial inclination of second molars occurs due to the lack of first molars. There are many methodologies to perform such movement. The goal of this research study was to in vitro analyze and compare, by means of photoelasticity, the strain distribution in lower second molars caused by several uprighting methods. Four models with the following mechanics have been evaluated: miniscrews, cantilever, T- loop spring and open coil spring. The second molar areas selected for the evaluation were the following ones: mesial-cervical area, apical area of the mesial root, distal-cervical and apical areas of the distal root. The resultant of forces applied was measured by quantifying isochromatic fringes. The fringe values were described using the mean and the standard deviation values and the agreement/reproducibility among the assessments were verified applying the intraclass correlation coefficient in the respective intervals with 95% confidence. Repeatability measures were calculated. The different types of mechanics were compared applying the nonparametric test and, when the test showed statistical significance, nonparametric multiple comparisons were carried out for paired measurements, aiming at checking in which mechanics fringe differences occur. Values statistically differed among the types of mechanics applied (p < 0.05), except in the distal-cervical area, in which the values were statistically the same for the four types of mechanics (p = 0.112). In the technique using miniscrews, the highest strain values were found in the distal-cervical area, followed by the apical area of the mesial root and the apical area of the distal root. No strain was found in the mesialcervical area. With the cantilever, the highest strains were found in the mesialcervical area, followed by the apical area of the mesial root and the distal-cervical area. No strain was found in the apical area of the distal root. In the T-loop spring, the highest strains were found in the apical area of the mesial root, followed by the cervical area of the mesial root, the apical area of the distal root and the distalcervical area. With the open coil spring, the highest strains were found in the apical area of the mesial root, followed by the mesial-cervical, the distal-cervical and the apical areas of the distal root. When comparing the techniques, it was concluded that the miniscrew showed the lowest stresses and the cantilever the highest stresses in the study regions.

[pt] Tubos de aço de grande diâmetro, baixa espessura e alta resistência mecânica, possuem tendência à formação de rugas no lado compressivo do curvamento (intrados) ao serem curvados a frio. A presente dissertação descreve os principais códigos de projeto nacionais e internacionais, quanto à presença de rugas provenientes desse tipo de curvamento em dutos, e propõe um ângulo para o qual há a formação do enrugamento. Os códigos internacionais mostram-se conservadores quanto à presença de rugas nos tubos curvados, uma vez que o enrugamento é uma mudança geométrica que, a princípio, gera concentração de tensões e susceptibilidade à ocorrência de falhas por fadiga. Esta dissertação faz uso do método de elementos finitos para modelar a formação do enrugamento e determinar fatores de concentração de tensões, nestas regiões, para carregamentos de pressão interna. Os fatores encontrados são comparados com resultados encontrados na literatura e utilizados no cálculo contra a fadiga por meio de diferentes métodos: Markl, inclinações universais de Manson e ASME seção VIII divisão 2. Neste estudo foram utilizados tubos de aço estrutural API X70 com razão diâmetro espessura (D/t) variando de 20 a 100, modelados por meio do software Abaqus(r). Foram obtidas curvas com ângulo de 4°/diâmetro e enrugamentos severos, com razão entre a altura da ruga e o diâmetro do tubo (d/D) da ordem de 6,5% e fator de concentração de tensão chegando a 1,89. Os modelos de tubo enrugado não apresentaram falha na resistência mecânica à pressão interna aplicada, quando esta é suficiente para obtenção de tensão circunferencial nominal equivalente a 100% do limite de escoamento do material. Os resultados de vida em fadiga para os diferentes métodos aplicados variam de acordo com o método utilizado, mas todos apresentam redução na vida do tubo com presença de enrugamento severo. O estudo propõe que se utilize para o cálculo da vida em fadiga um procedimento conservador que associa o fator de concentração de tensão determinado por Rosenfeld com o método de cálculo contra a fadiga recomendado pelo código ASME VIII. O estudo sugere ainda, que sejam realizadas novas análises de forma a considerar o efeito Bauschinger e a instabilidade à flexão do modelo não avaliados no presente trabalho. / [en] Large diameter, thin walled, high mechanical resistance steel pipe has a tendency to wrinkle on the compressive side (the intrados) of the bend when it is cold bent. This dissertation describes the principal national and international design codes that apply to wrinkling resulting from pipe cold bending, and it proposes an angle at which such wrinkling occurs. The international codes prove to be conservative regarding wrinkling in bent pipe, since a wrinkle is a geometric change, which at first causes a stress concentration and susceptibility to fatigue failure. The dissertation uses the finite element method to model the formation of wrinkling and to determine stress concentration factors in these areas for internal pressure loading. The resulting factors are compared with the results found in the literature and are utilized in calculating fatigue life by means of the following methods: Mark1, Mansons universal inclinations and ASME Section VIII Division 2. In this study API X70 structural pipe with a diameter thickness (D/t) ratio varying from 20 to 100 was utilized, and modeled using Abaqus(r) software. Bends with an angle of 4°/diameter and severe wrinkling resulted, with a ratio between the peak of the wrinkle and the diameter of the pipe (d/D) of about 6.5% and a stress concentration factor nearing 1.89. The wrinkled pipe models did not reveal any lack of mechanical resistance to the applied internal pressure when it is sufficient for obtaining a nominal circumferential stress equivalent to 100% of the yielding limit of the material. The fatigue life results for the different methods varied according to the method that was utilized, but all displayed a reduction in pipe life if there was severe wrinkling. The study proposes a conservative procedure to be utilized for calculating fatigue life. This procedure associates the stress concentration factor determined by Rosenfeld with the method for calculating fatigue recommended by the ASME VIII code. Furthermore, the study suggests that new analyses may be performed in order to consider the Bauschinger effect and the model bend instability, which the study did not evaluated.

No description available.

Composite materials hold numerous advantages over conventional aircraft grade metals. These include high stiffness/strength-to-weight ratios and beneficial stiffness coupling typically used for aeroelastic tailoring. Due to the complexity of modeling composites, designers often select safe, simple geometry and layup schedules for their wing/blade cross-sections. An example of this might be a box-beam made up of 4 laminates, all of which are quasi-isotropic. This results in neglecting more complex designs that might yield a more effective solution, but require a greater analysis effort. The present work aims to show that the incorporation of complex cross-sections are feasible in the early design process through the use of cross-sectional analysis in conjunction with Timoshenko beam theory. It is important to note that in general, these cross-sections can be inhomogeneous: made up of any number of various materials systems. In addition, these materials could all be anisotropic in nature. The geometry of the cross-sections can take on any shape. Through this reduced order modeling scheme, complex structures can be reduced to 1 dimensional beams. With this approach, the elastic behavior of the structure can be captured, while also allowing for accurate 3D stress and strain recovery. This efficient structural modeling would be ideal in the preliminary design optimization of a wing structure. Furthermore, in conjunction with an efficient unsteady aerodynamic model such as the doublet lattice method, the dynamic aeroelastic stability can also be efficiently captured. This work introduces a comprehensively verified, open source python API called AeroComBAT (Aeroelastic Composite Beam Analysis Tool). By leveraging cross-sectional analysis, Timoshenko beam theory, and unsteady doublet-lattice method, this package is capable of efficiently conducting linear static structural analysis, normal mode analysis, and dynamic aeroelastic analysis. AeroComBAT can have a significant impact on the design process of a composite structure, and would be ideally implemented as part of a design optimization. / Master of Science

A complete solution of thermoelastic dilatational waves in an elastic, heat conducting, homogeneous, and isotropic medium has been obtained for both the steady and unsteady states. Discussions of the solution for a wide range of frequencies and various values of the coefficient of rise (or decay) have been made and the result has been applied to the explanation of the unusual seismic waves recorded from an underground atomic explosion of September 19, 1957, in Nevada. Reflection and retraction of plane waves at plane boundary and plane interface between two media have been studied. The surface waves have also been studied. The solutions of spherical and cylindrical dilatational waves have been found. / Ph. D.

A single piece of optical fiber can be utilized to sense both strain and temperature simultaneously. To develop such a sensor, we sandwich a section of two-mode elliptical core (e-core) fiber between two partially reflecting mirrors. This configuration can be considered as an intrinsic Fabry-Perot interferometer, in which the two-mode, e-core fiber serves as the resonant cavity. Two different types of phase modulation can be extracted under perturbations of strain and temperature on the fiber. These phase changes are due to the two-mode interference and intrinsic Fabry-Perot interference, respectively. The relationship between the phase information and the two physical measurands, i.e. strain and temperature, can be established using two coupled equations, in which the strain and temperature are considered as two unknowns. By solving these two coupled equations, we can simultaneously determine the strain and temperature. The waveguide theory and the Cross sensitivity analysis of this sensor are presented. The descriptions of four independent experiments that have been used to determine the coefficients of the two coupled equations are given. The resolutions of the strain and temperature measurements have been obtained to be 31 μm/m and 4.5 °C, respectively. / Master of Science

No description available.

This study develops new quantitative thermoelastic stress analysis (TSA) techniques for fracture and fatigue damage analysis of composite materials. The first part deals with the thermo-mechanical derivation of two quantitative TSA techniques applied to orthotropic composites with and without a transversely-isotropic surface coating layer. The new TSA test procedures are derived in order to relate the thermal infrared (IR) images with the sum of in-plane strains multiplied by two newly defined material constants that can be experimentally pre-calibrated. Experiments are performed to verify the TSA methods with finite element (FE) numerical results along with available anisotropic elasticity solution. The second part of this study applies the quantitative TSA techniques together with the Lekhnitskii's general anisotropic elasticity solution to calculate mixed-mode stress intensity factors (SIFs) in cracked composite materials. The cracked composite coupons are subjected to off-axis loadings with respect to four different material angles in order to generate mixed-mode SIFs. A least-squares method is used to correlate the sum of in-plane strains from the elasticity solution with the measured TSA test results. The mode-I and mode-II SIFs are determined from eccentrically loaded single-edge-notch tension (ESE(T)) composite specimens. The FE models and virtual crack closure technique (VCCT) are utilized for comparisons. In the third part, a new stochastic model is proposed to generate S-N curves accounting for the variability of the fatigue process. This cumulative damage Markov chain model (MCM) requires a limited number of fatigue tests for calibrating the probability transition matrix (PTM) in the Markov chain model and mean fatigue cycles to failure from experiments. In order to construct the MCM stochastic S-N curve, an iterative procedure is required to predict the mean cycles to failure. Fatigue tests are conducted in this study to demonstrate the MCM method. Twenty-one open-hole S2-glass laminates are fatigue-cycled at two different stress levels. The coupon overall stiffness and surface-ply TSA damage area have been used as two damage metrics. The MCM can satisfactorily describe the overall fatigue damage evolution for a limited number of coupons (less than 6) subjected to a given specific stress level. The stochastic S-N curve can be constructed using at least two sets of fatigue tests under different stress levels. Three available fatigue tests for different E-glass laminates from the literature are also investigated using the proposed MCM approach. The results show the MCM method can provide the stochastic S-N curves for different composite systems and a wide range of fatigue cycles.

Le traitement thermochimique de nitruration des aciers conduit à l'augmentation de leur durée de vie en fatigue comme conséquence de l'amélioration de la résistance à la fatigue du matériau due au durcissement superficiel et à la génération d'un champ de contraintes résiduelles de compression. Il a été possible d'effectuer un calcul original de la variation locale de volume à partir de la répartition des différents types de précipités qui ont été déterminés en utilisant un calcul thermodynamique direct. A partir d'une modélisation utilisant un modèle micromécanique, l'étude montre que les contraintes résiduelles dans les différentes phases, présentes dans la couche nitrurée, sont différentes des contraintes moyennes dans le matériau. Ce modèle a été confronté à l'expérimentation qui a permis de déterminer les contraintes dans la matrice en utilisant la diffraction des rayons X et les contraintes moyennes dans le matériau en employant la méthode du trou incrémentale. Parallèlement, une analyse des profils de diffraction complétée par une étude microscopique a permis de remarquer que les déformations plastiques résiduelles dans la couche nitrurée sont très faibles et localisées autour des précipités et que la largeur intégrale des pics de diffraction semble être principalement une indication de la taille des domaines cohérents de diffraction. Cette étude a été complétée par l'analyse de la relaxation des contraintes résiduelles en fonction du temps et de la température. Le phénomène de relaxation correspond à la poursuite de la diffusion de l'azote et les contraintes sont stables thermiquement. Par ailleurs, l'application du modèle dans le cas d'une plaque mince nitrurée d'un seul côté a permis de confirmer que les contraintes dans la ferrite ne sont pas égales aux contraintes moyennes. Ce type d'éprouvette peut constituer un moyen de contrôle industriel en donnant une indication sur l'intensité de nitruration (dépôt de brevet en cours).

No description available.