In this thesis, new methods for shear strength are proposed and backed up through extensive experimentation, ABAQUS models and data analysis of Titanium welds of three different alloys. The results are compared with those obtained by using the procedure outlined by AWS B4 for calculating Shear Strength in the transverse and longitudinal directions; this equation is widely used by the American Welding Society (AWS) and all those in search of more efficient designs involving welding. It is a well-documented issue that the equation provided by AWS yields a large discrepancy between the values for shear strength of longitudinal and transverse welds.

Most of the water fed into a paper machine is removedmechanically in the forming and press sections. One of thefactor which has an important influence on mechanicaldewatering, i.e. in both forming and pressing, is thestress-strain behaviour of the fibre network. The focus of this thesis is on the development of improvedmathematical descriptions of the stress-strain behaviourexhibited by fibre networks in the forming and press sections.The first part of the thesis presents a physically based modelof the forming and densification of fibre mats in twin-wireformers. The model can calculate the ecect of the applicationof a varied load through the forming section. It was developedfrom mass and momentum balances of the fibre and liquid phases,the fibre mat stress-porosity relation and an expression forthe permeability as a function of the porosity. The fibre-matstress-porosity relation used is rate-independent and presentshysteresis. Simulations have been conducted to study theeffects of roll pressure, blade pulses, wire tension andbeating. The effect of sequential blade pressure pulses afterthe forming roll on the dewatering and the concentrationgradients could be characterised. The simulations alsoexhibited rewetting by expansion when the fibre mats left theforming roll. Increasing wire tension resulted in increaseddewatering, but the rate of increase diminished rapidly withincreasing tension. The simulation results also indicated thatbeating has a large influence on dewatering. The second part of the thesis presents two models of therate-dependent stress-strain behaviour of the fibre networkthat is observed in wet pressing. The first model was based onthe approach pioneered by Perzyna (1966) for strain-ratedependent plasticity and was quite satisfactory for calculatingthe stress-strain behaviour of the fibre network in singlepress nips. It was successfully applied for studyingdensification and dewatering in both normal wet pressing andhigh temperature wet pressing. However, the first model onlyincludes rate dependence in the compression phase of thecompressionexpansion cycle; the expansion phase is treated asbeing rate independent The second model of the stress-strain behaviour of the fibrenetwork treats both compression and expansion as being ratedependent, according to experimental observations. It is basedon the idea that the wet fibre web may be conceived as alayered network of restricted swelling gels. A swollen fibre isa restricted gel, the inner swelling pressure in a swollenfibre wall being balanced by the stresses in the fibre wallstructure. The observed rate dependence of wet webs in bothcompression and expansion phases was attributed to the flow ofwater out of and into the fibre walls. The second model gavepredictions that are in good agreement with results fromuniaxial experiments using pressure pulses of arbitrary shapefor both a single pulse and a sequence of pulses. It maytherefore be used as a general model for the rheologicalbehaviour of the wet fibre network in wet pressing, providedthe model parameters are estimated from experimental data withsmall experimental error. KEYWORDS:Paper, modelling, dewatering, forming, wetpressing, fibre network stress, rheology, hysteresis,intra-fibre water, compressibility, structural stress,stress-strain, restricted gels, swelling. / <p>QC 20161026</p>

O estudo da resistência à compressão e da deformabilidade de paredes de alvenaria de blocos de concreto é de fundamental importância para a caracterização desse material e o desenvolvimento de análises de estruturas compostas por esse tipo de painel. Este trabalho trata desse tema, objetivando prever com maior acuidade os principais parâmetros de deformação e de resistência de paredes de alvenaria de blocos de concreto, a saber: resistência à compressão e módulo de elasticidade longitudinal nas direções paralela e perpendicular à junta de assentamento. Foi desenvolvido um trabalho experimental para estimar a influência da resistência dos blocos, da resistência da argamassa e da direção de aplicação de forças no comportamento mecânico da alvenaria de blocos de concreto não-grauteada, quando submetida a esforços de compressão. Para tanto, realizaram-se ensaios de laboratório em blocos, argamassas, prismas de três blocos e paredinhas com dimensões de 80 cm x 80 cm. Por inferência estatística não foram obtidas correlações aceitáveis entre as variáveis estudadas. Porém, obtiveram-se tendências de comportamento dos corpos de prova estudados, confirmando a influência das características da argamassa e do bloco no comportamento estrutural da alvenaria quando submetida a esforços de compressão / The study of strength and the curved stress/strain relationship of blockwork masonry walls is basic for the material characterization and the development of structural analysis of blockwork walls. This work deals with that subject, aiming at the evaluation of the main elastic parameters and the strength of concrete blockwork walls: the compressive strength and modulus of elasticity for masonry in two orthogonal directions, parallel and perpendicular to bed joints. An experimental program was developed to evaluate the influence of the strength of blocks and mortar, and the load application direction on the mechanical behavior of ungrouted concrete block masonry under compression. A series of laboratory tests was carried out with blocks, mortar, prisms of three blocks and wallets (80 cm x 80 cm). It was impossible to obtain acceptable correlations of the defined variables, using statistical inference. However, tendencies of the specimens behavior were obtained, confirming the influence of mortar and block properties on the structural behavior of concrete blockwork walls under compression

O trabalho é um estudo experimental do comportamento tensão-deformação, em argila adensada unidirecionalmente, após mistura com água. Para sua execução, foram desenvolvidos equipamentos para adensamento de grandes quantidades de Lama, e medidores eletrônicos específicos para deformações volumétricas e radiais, usados em ensaios de compressão triaxial. O modelo da teoria clássica elasto-linear, para solos com comportamento anisotrópico é utilizado, após desenvolvimento algébrico, na obtenção dos parâmetros da argila. Nos cálculos, são aplicados processos estatísticos de regressões polinomiais. São analisadas as correlações dos parâmetros elásticos iso e anisotrópicos (Módulos de Elasticidade, Coeficientes de Poisson e Módulos de Elasticidade Transversal), com as tensões confinantes dos ensaios triaxiais, e com os Índices de pré-adensamento OCR das Lamas. / This work is an experimental study of the stress-strain behavior on clay one-dimensionally consolidated, after mixing with water. A consolidation equipment designed for great mass of mud and specific electronic apparatus for volumetric and lateral displacements on the triaxial tests were developed for this study. The classical theory of elasto-linear model for anysotropic soils is used, after algebraic manipulation, to obtain clay parameters. Multiple regressions are used for variables computations. Iso and anysotropic elastic parameters (Young modulus, Poisson ratio and shear modulus) are correlated with the confinant stresses and the over-consolidation-ratios (OCR).

La loi de comportement est un élément essentiel de la caractérisation mécanique des matériaux. Pour pouvoir identifier le comportement d'un matériau, il existe plusieurs méthodes expérimentales (traction statique, barres d'Hopkinson) qui permettent d'obtenir des lois mécaniques applicables dans des conditions bien définies et le plus souvent sur des matériaux massifs homogènes. La plupart de ces essais sont de plus couteux et exigent le plus souvent des géométries d'échantillons spécifiques. L'utilisation de ces tests reste limitée et ne permet pas d'analyser tous les types de matériaux comme les revêtements ou les matériaux poreux... par exemple. Or ces matériaux eux aussi nécessitent aujourd'hui une connaissance fine de leurs propriétés afin de permettre une simulation au plus juste de leur comportement en service. Les lois de comportement établies à l'échelle d'un matériau massif ne répondent également que partiellement aux besoins de modélisation de certains procédés detraitement mécanique de surface comme par exemple le grenaillage, car elles ne prennent pas en compte les effets de la surface. L'objectif principal de cette étude est de développer une méthode à la fois rapide et facile pour pouvoir identifier le comportement local des matériaux sous condition dynamique, afin de pouvoir caractériser les surfaces soumises à des sollicitations de type chocs. Pour atteindre cet objectif, une méthode inverse a été développée pour identifier le comportement des matériaux à l'aide d'une combinaison d'approche expérimentale et numérique d'essais d'impacts répétés. Les lois decomportements obtenues à l'aide de cette méthode inverse restent sujettes à caution car difficile à comparer à des valeurs de référence par manque de données dans la littérature. Pour cette raison ces lois seront ensuite comparées avec une méthode analytique inspirée de la théorie de l'indentation. Afin de valider l'efficacité de la méthode inverse et de la méthode analytique, des essais numériques à l'aveugle ont été menés, ensuite des applications sur des matériaux modèles et industriels ont été réalisées pour déterminer les limites des méthodes. / The behavior law is an essential element of the mechanical characterization of materials. To identify the material behavior several experimental methods can be used such as (static traction, Hopkinson bars ...) that allow to obtain mechanical laws applied under well-defined conditions, i.e. on homogeneous and bulk materials. However, do to the rising cost of these tests and their specific sample geometry, their use is limited and does not allow to probe and measure all types of materials (like coatings or porous materials....). Moreover, a broad knowledge of their properties allows a more accurate simulation of their behavior in working process. Behavior laws appropriate for bulk material do not always fit to process modeling shot peening, due to surface deformation. The main objective of this study is to develop a simple, rapid method for identifying the local behavior of materials under dynamic conditions, in order to characterize surfaces under impact loading. An inverse method has been developed to identify the behavior of materials using a combination of numerical and experimental approaches of repeated impact tests. The behavior laws obtained by the inverse method must be further investigated due to missing comparison data in literature. A comparison with an analytical method based on the theory of indentation must be carried out for more accuracy. In order to validate the efficiency of the inverse method and the analytical method, numerical blind tests wereconducted, then applications on industrial and ideal materials have been carried out to determine the limits.

Stress-strain relations for unconfined and confined concrete are proposed to overcome some shortcomings of existing commonly used models. Specifically, existing models are neither easy to invert nor integrate to obtain equivalent rectangular stress-block parameters for hand analysis and design purposes. The stress?strain relations proposed are validated for a whole range of concrete strengths and confining stresses. Then, closed form expressions are derived for the equivalent rectangular stress-block parameters. The efficacy of the results is demonstrated for hand analysis applied for deriving the moment-curvature performance of a confined concrete column. Results are compared with those obtained from a computational fiber-element using the proposed stress-strain model and another widely used model; good agreement between the two is observed. The model is then utilized in the development of a new structural system that utilizes the positive attributes of timber and concrete to form a parallel. Timber has the advantage of being a light weight construction material, easy to handle, is environmentally friendly. However, large creep deflections and significant issues with sound transmission (the footfall problem) generally limit timber use to small spans and low rise buildings. Concrete topping on timber sub-floors mitigate some of these issues, but even with well engineered wood systems, the spans are relatively short. In this study, a new structural system called structural boxed-concrete, which utilizes the positive attributes of both timber and reinforced concrete to form a parallel system (different from timber-concrete composite system) is explored. A stress-block approach is developed to calculate strength and deformation. An analytical stress-block based moment-curvature analysis is performed on the timber-boxed concrete structural elements. Results show that the structural timber-boxed concrete members may have better strength and ductility capacities when compared to an equivalent ordinary reinforced concrete member.

In this thesis, the effects of size and stress on permeability, deformability and strength of fractured rock masses are investigated. A comparison study was carried out to examine the effects of considering, or not considering, the correlation between distributions of fracture apertures and fracture trace lengths on the hydro-mechanical behavior of fractured rocks. The basic concepts used are the fundamental principles of the general theory of elasticity, Representative Elementary Volume (REV), the tensor of equivalent permeability, and the strength criteria of the fractured rocks. Due to the size and stress dependence of the hydro-mechanical properties of rock fractures, the overall effective (or equivalent) hydro-mechanical properties of the fractured rocks are also size and stress-dependent. However, such dependence cannot be readily investigated in laboratory using small samples, and so numerical modeling becomes a necessary tool for estimating their impacts. In this study, a closed-form relation is established for representing the correlation between a truncated lognormal distribution of fracture apertures and a truncated power law distribution of trace lengths, as obtained from field mapping. Furthermore, a new nonlinear algorithm is developed for predicting the relationship between normal stress and normal displacement of fractures, based on the Bandis model and the correlation between aperture and length. A large number of stochastic Discrete Fracture Network (DFN) models of varying sizes were extracted from some generated large-sized parent realizations based on a realistic fracture system description from a site investigation programme at Sellafield, UK, for calculating the REV of hydro-mechanical properties of fractured rocks. Rotated DFN models were also generated and used for evaluation of the distributions of directional permeabilities, such that tensors of equivalent permeability could be established based on stochastically established REVs. The stress-dependence of the permeability and the stress-displacement behaviour were then investigated using models of REV sizes. The Discrete Element Method (DEM) was used for numerical simulation of the fluid flow, deformability properties and mechanical strength behavior of fractured rocks. The results show significant scale-dependency of rock permeability, deformability and strength, and its variation when the correlation between aperture and trace length of fractures are concerned, with the overall permeability and deformability more controlled by dominating fractures with larger apertures and higher transmissivity and deformability, compared with fracture network models having uniform aperture. As the second moment of aperture distribution increases, a fractured rock mass shows more discrete behavior and an REV is established in smaller value of second moment with much larger model size, compared with the models with uniform fracture aperture. When the fracture aperture pattern is more scattered, the overall permeability, Young’s modulus and mechanical strength change significantly. The effect of stress on permeability and fluid flow patterns in fractured rock is significant and can lead to the existence or non-existence of a permeability tensor. Stress changes the fluid flow patterns and can cause significant channeling and the permeability tensor, and REV may be destroyed or re-established at different applied stress conditions. With an increase in the confining stress on the DEM models, the strength is increased. Compared with the Hoek-Brown criterion, the Mohr-Coulomb strength envelope provides a better fit to the results of numerical biaxial compression tests, with significant changes of the strength characteristic parameters occurring when the second moment of the aperture distribution is increased. / QC 20100702

Stress-strain relations for unconfined and confined concrete are proposed to overcome some shortcomings of existing commonly used models. Specifically, existing models are neither easy to invert nor integrate to obtain equivalent rectangular stress-block parameters for hand analysis and design purposes. The stress?strain relations proposed are validated for a whole range of concrete strengths and confining stresses. Then, closed form expressions are derived for the equivalent rectangular stress-block parameters. The efficacy of the results is demonstrated for hand analysis applied for deriving the moment-curvature performance of a confined concrete column. Results are compared with those obtained from a computational fiber-element using the proposed stress-strain model and another widely used model; good agreement between the two is observed. The model is then utilized in the development of a new structural system that utilizes the positive attributes of timber and concrete to form a parallel. Timber has the advantage of being a light weight construction material, easy to handle, is environmentally friendly. However, large creep deflections and significant issues with sound transmission (the footfall problem) generally limit timber use to small spans and low rise buildings. Concrete topping on timber sub-floors mitigate some of these issues, but even with well engineered wood systems, the spans are relatively short. In this study, a new structural system called structural boxed-concrete, which utilizes the positive attributes of both timber and reinforced concrete to form a parallel system (different from timber-concrete composite system) is explored. A stress-block approach is developed to calculate strength and deformation. An analytical stress-block based moment-curvature analysis is performed on the timber-boxed concrete structural elements. Results show that the structural timber-boxed concrete members may have better strength and ductility capacities when compared to an equivalent ordinary reinforced concrete member.

Das Tragverhalten von Textilbeton ist stark nicht-linear und der Verlauf der Spannungs-Dehnungs-Beziehung hängt von zahlreichen Parametern ab. Unter einaxialer Zugbelastung existieren bereits umfangreiche experimentelle Untersuchungen und theoretische Modelle zur Beschreibung des Tragverhaltens. In vielen Anwendungen, z. B. bei Querkraft- und Torsionsbeanspruchung, sind die Beanspruchungen jedoch nicht einaxial und/oder nicht axial zur Bewehrungsrichtung, und es kommt zu Interaktionen der beiden Bewehrungshauptrichtungen, primär infolge des Einflusses zweier Risssysteme in den beiden Hauptrichtungen. Das Tragverhalten textiler AR-Glas- und Carbonbewehrungen unter zweiaxialen Zugbeanspruchungen wurde experimentell untersucht, um diese Einflüsse qualitativ und quantitativ beschreiben zu können. In diesem Beitrag werden erste Ergebnisse vorgestellt.

A model is presented to use normalized multi-linear tension and compression material characteristics of strain-hardening textile reinforced concrete and derive closed form expressions for predicting moment-curvature capacity. A set of design equations are derived and simplified for use in spreadsheet based applications. The model is applicable for both strain-softening and strainhardening materials. The predictability of the simplified model is checked by model calibration and development of design charts for moment capacity and stress developed throughout the cross section of a flexural member. Model is calibrated by predicting the results of Alkali Resistant Glass and Polyethylene fabrics. A case for the flexural design of Glass Fiber Reinforced Concrete (GFRC) specimen as a simply supported beam subjected to distributed load is used to demonstrate the design procedure.