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Previous modeling of wood materials has included many assumptions of unknown mechanical properties associated with the hierarchical structure of wood. The experimental validation of previous models did not account for the variation of mechanical properties present in wood materials. Little research has explored the uncertainties of mechanical properties in earlywood and latewood samples as well as wood strands. The goal of this study was to evaluate the effect of the intra-ring properties and grain angles on the modulus of elasticity (MOE) and ultimate tensile strength (UTS) of different orientation wood strands and to analyze the sensitivity of the MOE and UTS of wood strands with respect to these variables. Tension testing incorporating digital image correlation (DIC) was employed to measure the MOE and UTS of earlywood and latewood bands sampled from growth ring numbers 1-10 and growth ring numbers 11-20. A similar technique adjusted for strand size testing was also applied to measure the MOE and UTS of different orientation wood strands from the two growth ring numbers. The stochastic finite element method (SFEM) was used with the results from the earlywood and latewood testing as inputs to model the mechanical property variation of loblolly pine wood strands. A sensitivity analysis of the input parameters in the SFEM model was performed to identify the most important parameters related to mechanical response. Modulus of elasticity (MOE), Poisson ratio, and ultimate tensile strength (UTS) from earlywood and latewood generally increased as the growth ring number increased except for the UTS of latewood, which showed a slight decrease. MOE and UTS from radial, tangential, and angled grain orientation strands increased as the growth ring numbers increased while MOE and UTS from cross-grain strands decreased as the growth ring number increased. Shear modulus of wood strands increased as the growth ring number increased while shear strength decreased as the growth ring number increased. Poisson ratio from radial and angled grain strands decreased as the growth ring number increased while Poisson ratio from tangential and cross grain orientation strands increased as the growth ring number increased. The difference of average MOE from different grain strands between experimental results and SFEM results ranged from 0.96% to 22.31%. The cumulative probability distribution curves from experimental tests and SFEM results agreed well except for the radial grain models from growth ring numbers 11-20. From sensitivity analysis, earlywood MOE was the most important contributing factor to the predicted MOE from different grain orientation strand models. From the sensitivity analysis, earlywood and latewood participated differently in the computation of MOE of different grain orientation strand models. The predicted MOE was highly associated with the strain distribution caused by different orientation strands and interaction of earlywood and latewood properties. In general, earlywood MOE had a greater effect on the predicted MOE of wood strands than other SFEM input parameters. The difference in UTS between experimental and SFEM results ranged from 0.09% to 11.09%. Sensitivity analysis showed that grain orientation and growth ring number influenced the UTS of strands. UTS of strands from growth ring numbers 1-10 showed strength indexes (Xt, Yt, and S) to be the dominant factors while UTS of strands from growth ring numbers 11-20 showed both strength indexes and stress components (Ï 1, Ï 2, and Ï 12) to be the dominant factors. Grain orientations of strands were a strong indicator of mechanical properties of wood strands. / Ph. D.

The genus Chrysopelea encompasses the "flying" snakes. This taxon has the ability to glide via lateral aerial undulation and dorsoventral body flattening, a skill unique to this group, but in addition to other functions common to all colubrids. The skin must be extensible enough to allow this body shape alteration and undulation, and strong enough to withstand the forces seen during landing. For this reason, characterizing the mechanical properties of the skin may give insight to the functional capabilities of the skin during these gliding and landing behaviors. Dynamic and viscoelastic uniaxial tensile tests were combined with a modified particle image velocimetry technique to provide strength, extensibility, strain energy, and stiffness information about the skin with respect to orientation, region, and species, along with viscoelastic parameters. Results compared with two other species in this study and a broader range of species in prior studies indicate that while the skin of these unique snakes may not be specifically specialized to deal with larger forces, extensibility, or energy storage and release, the skin does have increased strength and energy storage associated with higher strain rates. The skin also has differing properties with respect to dorsoventral location, and regional differences in strength in the circumferential orientation. This may indicate that, although the properties of the skin may not be different, the rate at which the skin is strained in the different species may vary, thus altering the apparent properties of the skin during specific behaviors. / Master of Science

Full 360 degree 3D finite element models are the most complete representation of Oil Country Tubular Goods (OCTG) premium threaded connections. Full 3D models can represent helical threads and boundary conditions required to simulate make-up and service loading. A methodology is developed to create a 360 degree full 3D parametric finite element model with helical threads as an effective design and analysis tool. The approach is demonstrated with the creation of a metal-to-metal seal integral joint full 3D model with manufacturer supplied geometry. The premium connection is decomposed into smaller parts to generate parametric geometric features. A controlled parametric meshing scheme is developed to manage mesh density in contact regions to effectively represent the mechanics in regions of interest while minimizing total element count. The scripted parametric approach allows for efficient geometric and mesh updates. Several methods to reduce and manage model runtimes are presented. An elastic-plastic material model is created with material coupon tensile tests results. Digital Image Correlation (DIC) is used to measure full-field displacement and strain data on the surface of the box. Experimental set up and data processing procedures are discussed. Error metrics are developed to correlate the finite element model results with the DIC experimental data. The DIC make-up experimental results are used to reconcile the finite element model to develop a minimum error make-up model relative to the pin rotation. The friction coefficient is estimated and the make-up torque-turn behavior is verified. The calibrated 3D finite element model is validated with ISO_13769 load series B axial and internal pressure loading experimental DIC data. Metal-to-metal seal metrics of contact pressure and seal length are evaluated. / Master of Science

The application of fracture mechanics to engineering design has provided significant advances in understanding of the causes and mechanisms of failure and crack growth. Despite this, there are still some aspects that remain incompletely understood, such as the crack closure/crack shielding effect. The presence of crack closure/shielding acts to reduce . The mechanisms of crack closure/shielding are complicated, and have not been fully understood. This work focuses on the plasticity-induced crack tip shielding mechanism and presents a novel approach to characterise the elastic stress fields under the influence of the plastic enclave surrounding the crack tip. The model is successfully applied to determine the four stress parameters experimentally using full-field photoelastic stress analysis on polycarbonate CT specimens, following studies of the effect of the crack tip position and the valid data collection zone giving the best fit between the model predictions and the experimental data. The predicted values from the model demonstrate good data repeatability, and exhibit sensible trends as a function of crack length and load ratio that are interpretable in terms of physically meaningful changes to the plastic enclave. In addition, the model is proven to describe the stress field around a crack more accurately than classic Williams‟ stress solution. The model is also extended to AL 2024-T3 specimens using a full-field displacement measurement technique, digital image correlation. Using the Sobel edge detection method to identify the crack tip from the displacement fields with a rectangular shaped data collection zone employed in the current study, reasonable trends were again demonstrated in the experimental results as a function of crack length.

Les techniques de mesure de champs, et en particulier celles basées sur la Corrélation d’Images Numériques (CIN), sont matures et reconnues pour la détermination de déplacements d’objets quelconques, en deux ou trois dimensions. Ces travaux ont pour objet le développement d’essais et de techniques d’identification associées, en s’appuyant sur les méthodes de mesure par CIN, pour permettre l’évaluation des caractéristiques mécaniques d’un liner en titane T35, développé pour des applications spatiales. Des essais de traction uniaxiale sont tout d'abord utilisés pour déterminer le comportement élastoplastique du T35. Plusieurs méthodes d'identification sont comparées. En particulier, il est proposé d'étendre la corrélation d'image dite "intégrée" aux cas élastoplatiques. Cette méthode permet d'évaluer à la fois les déplacements du solide observé et les paramètres mécaniques des matériaux le constituant. Elle est comparée à une méthode de recalage de référence. L'étude se porte ensuite sur l'analyse de l'amorçage des fissures dans le liner. Les chargements cycliques du réservoir imposent à la tôle une déformation biaxiale cyclique en traction-compression de quelques pourcents, qui a été reproduite expérimentalement dans une machine multiaxiale. Cette partie a notamment nécessité le développement d’un essai triaxial à rapport de charge négatif sur tôle mince. Une estimation de la limite d'amorçage a été obtenue pour les niveaux de déformation visés. Enfin, la fissuration du liner a été étudiée par des techniques d'analyse dédiées. Certaines de ces techniques sont comparées quantitativement, afin d'étudier leurs capacités et limitations respectives. Des lois de propagation de type Paris ont été identifiées directement à partir d'images du voisinage de la fissure. / Field measurement techniques, and more particularly those based on Digital Image Correlation (DIC), are mature techniques for the determination of displacements of two or three-dimensional objects. The goal of this work is to develop test and associated identification DIC-based techniques to identify the mechanical behavior of a commercially-pure titanium liner, conceived for spatial applications. Uniaxial tensile teste are first used to identify the elasto-plastic behavior of this material. Several identification methods are compared. It is especially proposed to extend said "integrated" Digital Image Correlation to elasto-plastic cases. This methods allows to identify directly the displacement of the observed solid and the mechanical parameters of the constituting material. It is compared to a reference updating method. The crack initiation is then studied in this material. Some zones of the liner will be submitted to a plastic cyclic deformation, that has to be reproduced experimentally. A dedicated test has been conceived, allowing to apply a negative load ratio to the thin sheet. An estimation of the initiation limit has been obtained for this material. Finally, the crack propagation in the liner has been studied, using dedicated techniques. Some of these have been quantitatively compared, to study their respective capabilities. Paris' propagation laws have been identified directly from a set of raw images of the crack tip vicinity.

Depuis ces dernières décennies, les matériaux composites sont de plus en plus utilisés dans l'aéronautique. Notamment, les composites tissés 3D présentent des caractéristiques matériau hors-plan intéressantes par rapport aux stratifiés. Cette technologie est développée pour les aubes FAN des moteurs d'avion. La difficulté réside dans l'identification et la validation du modèle orthotrope élastique macroscopique du pied d'aube. En effet, l'hypothèse de séparation des échelles pour l'obtention des paramètres matériau macroscopique par homogénéisation n'est pas clairement vérifiée au sein du pied d'aube comportant plusieurs zones matériau. Le composite tissé 3D formant le pied d'aube est un matériau multi-échelle complexe. Les travaux de thèse ont donc été menés afin de proposer une identification des paramètres du modèle basée sur la mesure de champs de déplacements par Corrélation d'Images Numériques (CIN) et sur la méthode d'identification de recalage de modèles éléments finis (FEMU). Cette identification a pris en compte l'influence du bruit du capteur CCD présent sur les images servant à la CIN sur l'identification des paramètres matériau. Du fait du grand nombre de paramètres matériau à identifier et des éventuels couplages entre ceux-ci, il apparaît que quelques uns ne peuvent pas être identifier à travers l'essai de traction étudié. Par conséquent, une régularisation de la FEMU a été proposée basée sur la connaissance a priori des valeurs nominales et de leur incertitude. Celle-ci consiste en une pondération intelligente vis-à-vis des données issues de l'essai afin de faire tendre les paramètres non identifiables vers leur valeur nominale. Finalement, la qualité de l'identification a été quantifiée grâce aux incertitudes sur les paramètres matériau identifiés et grâce aux cartes de résidus d'identification basées sur les images. Ces cartes traduisent la capacité du champ de déplacement calculé par le modèle éléments finis identifié à corriger l'image déformée pour la recaler sur l'image de référence, images sur lesquelles la mesure par CIN est effectuée. Ces cartes de résidus et les incertitudes obtenues permettent ainsi de valider le modèle éléments finis proposé et le cas échéant de mettre en lumière ses insuffisances. Remettre en cause les valeurs nominales ou la modélisation (par exemple le zonage matériau) pour aboutir à une description compatible avec l’expérience reste du ressort de l’ingénieur. Le travail présenté ici lui permet d’éclairer au mieux ses choix. / In recent decades, composite materials are increasingly used in aerospace. Particularly, 3D woven composite present interesting out-of-plan characteristics compared to laminates. This technology is developed for FAN blades of aircraft engines. The difficulty lies in the identification and validation of the macroscopic elastic orthotropic model of the FAN blade root. Indeed, the assumption of scales separation to obtain the macroscopic parameters by homogenization is not clearly verified in the blade root containing multiple zones. The 3D woven composite forming the blade root is a complex and multi-scale material. The thesis work has been carried out to propose an identification of model parameters based on measurement of displacement fields with Digital Image Correlation (DIC) and the identification method of finite element model updating (FEMU) . This identification has taken into account the influence of noise, coming from the CCD sensor and present on the images utilized for the DIC, on the identification of material parameters. Because of the large number of material parameters to identify and the possible couplings between them, it appears that some of them can not be identified through the tensile test studied. Therefore, a regularization was proposed based on a priori knowledge of the nominal values &#8203-&#8203-and their uncertainty. This consists in a smart balance regarding the data obtained through the test in order to force the unidentifiable parameters to their nominal value. Finally, the quality of the identification was quantified using the uncertainties on the identified material parameters and residual maps after identification based on images. These maps reflect the ability of the calculated displacement to match the corrected deformed image on the reference image, images with which the DIC is performed. These residual maps and uncertainties on material parameters allow to validate the finite element model and propose an appropriate tool to highlight its shortcomings. Challenging nominal or modeling (eg material zones) to achieve a description consistent with the experience remains the responsibility of the engineer. The work presented here allows him to enlighten its choices.

Orientador: Aparecido Augusto de Carvalho / Resumo: O desenvolvimento de sistemas capazes de monitorar e controlar informações estão sendo cada vez mais utilizados, permitindo maior refinamento e confiança nos resultados. Na área instrumental de laboratório, existem situações que exigem maior controle sobre o ensaio. Com o atual avanço na área de microprocessadores, microcontroladores, sensores inteligentes, entre outros, têm impulsionado a utilização dos mesmos na melhoria e confiabilidade de processos mecânicos, químicos, físicos, biológicos, de inteligência artificial, de melhoria de qualidade de vida de pessoas com deficiência. Os processos podem ser melhorados utilizando equipamentos que possuem sistemas embarcados capazes de processar informações e fazer o controle a partir de sistemas operacionais que antes só eram possíveis nos computadores. Na área das grandes estruturas de concreto não é diferente, deve-se monitorar algumas variáveis que resultam em uma manifestação patológica conhecida como reação álcali-agregado, que é um fenômeno de expansão que afeta a durabilidade e a resistência mecânica do concreto, este fenômeno está ligado à algumas variáveis, a umidade relativa interna é umas delas. Existem várias pesquisas no sentido de inibir as reações álcali-agregados, e é sabido que um importante passo antes do acontecimento da reação álcali-agregado em obras hidráulicas, como as usinas hidroelétricas é o monitoramento da umidade e da temperatura no interior do concreto e, acompanhamento das fissuras inerentes do proce... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: The development of systems able to monitor and control information is increasingly being used, allowing greater refinement and confidence in results. In the instrumental area of the laboratory, there are situations that require greater control over the test. With the current progress in the area of microprocessors, microcontrollers, intelligent sensors, among others, have encouraged the use of these in the improvement and reliability of mechanical, chemical, physical, biological, artificial intelligence, improving the quality of life of people with deficiency. Processes can be improved by using equipment that has embedded systems that can process information and control from operating systems that were previously only possible on computers. In the area of large concrete structures is not different, it is necessary to monitor some variables that result in a pathological manifestation known as alkali-aggregate reaction, which is an expansion phenomenon that affects the durability and the mechanical resistance of the concrete, this phenomenon is connected to some variables, the relative humidity is one of them. There are several researches to inhibit alkali-aggregate reactions and is known that an important step before the occurrence of the alkali-aggregate reaction in hydraulic works such as hydroelectric plants is the monitoring of humidity and temperature inside the concrete and, the inherent fissures of the expansion process. The present work implemented a low cost, temperat... (Complete abstract click electronic access below) / Doutor

Memoria para optar al título de Ingeniero Civil Mecánico / Capturar las vibraciones de un objeto usando cámaras estereoscópicas de alta velocidad posibilita la determinación en campo completo de su geometría y desplazamiento en tres dimensiones, ya que permiten medir un elevado número de grados de libertad simultáneamente. Disponer de datos de medición de campo completo de una estructura es de interés para la aplicación de metodologías de identificación de daño centradas en la respuesta vibracional. El objetivo de este trabajo de título es desarrollar e implementar indicadores de daño basados en la deformación, curvatura y en derivadas de orden superior de los modos de vibración, que sean capaces de identificar daño por delaminación en un panel compuesto tipo panal de abeja usando un sistema de correlación de imágenes digital de alta velocidad (DIC). Las muestras consistieron en paneles de geometría plana tipo sándwich con núcleos del tipo panal de abeja, y se diferenciaron según su composición y según distintos escenarios de daño por delaminación. Las muestras fueron excitadas a rangos cercanos de sus respectivas frecuencias naturales, esta vibración se captó por el sistema DIC y se identificaron un determinado número de modos de vibración para cada muestra. Se procesó la información recabada por las cámaras, se les aplicó un algoritmo de suavizado y se construyeron indicadores de daño basados en la deformación, curvatura, y en la tercera y cuarta derivada parcial del desplazamiento normal a la superficie modal. Finalmente, a los indicadores resultantes se les aplicó un tratamiento estadístico de selección de datos (asociados a daño) y se les comparó mediante un algoritmo evaluador de predicción. Se utilizaron dos técnicas distintas para la estimación de los parámetros vibracionales de deformación, curvatura y derivadas de orden superior: diferencias finitas y point least-squares (PLS). Luego, en conjunto con la metodología \textit{Gapped Smoothing} (GSM) se construyeron los indicadores de daño. Se concluyó que aquellos indicadores basados en parámetros estimados mediante diferencias finitas presentaron ser sensibles al ruido experimental y por tanto poco confiables. En cambio, los indicadores basados en parámetros estimados mediante point least-squares presentaron ser sensibles al daño y robustos ante la presencia de ruido experimental. En particular, los indicadores de daño basados en la deformación, curvatura y tercera derivada del desplazamiento normal a la superficie de los modos estimadas mediante point least-squares presentan las mejores predicciones de detección según el algoritmo evaluador. Además, la detección de delaminaciones pequeñas fue realizada de mejor manera por el indicador basado en la curvatura estimada mediante point least-squares. / FONDECYT