Lors de la sollicitation mécanique des roches, la propagation de fissures provoque l'émission d'une onde acoustique (EA) ainsi qu'une modification des propriétés élastiques du matériau. L'EA est donc un moyen direct pour étudier l'évolution de l'endommagement, depuis le stade diffus jusqu'à celui où il se localise pour former une discontinuité macroscopique. L'EA est également considérée comme un modèle à petite échelle de la sismicité induite par les travaux souterrains ou de celle de la croûte terrestre. En effet, on observe à ces différentes échelles des distributions en loi puissance (exposant b) qui indiquent une invariance d'échelle.<br />La première partie de ce travail est consacrée à une étude expérimentale de l'EA du granite du Sidobre en compression triaxiale. Nous montrons que l'EA est liée à un comportement macroscopique non linéaire et peut être utilisée comme un estimateur de l'endommagement. L'augmentation de la pression de confinement rend le comportement mécanique plus ductile et fait diminuer l'exposant b.<br />Nous proposons, dans la deuxième partie, un modèle numérique basé sur l'endommagement élastique et sur la méthode des éléments finis. Ce modèle permet de simuler les principales observations concernant l'EA et le comportement des roches. En particulier, il permet de simuler un comportement macroscopique allant du fragile avec un endommagement localisé au ductile avec un endommagement diffus avec un seul paramètre de contrôle : l'angle de frottement interne. En utilisant des valeurs expérimentales de ce paramètre, nous parvenons à simuler les transitions fragile-ductile et localisé-diffus observées lorsque la pression de confinement augmente.<br />La troisième partie concerne l'étude de la sismicité induite dans une mine. Le caractère critique de la distribution de la taille des séismes est proposé comme un critère de surveillance du risque sismique. La relation entre l'exposant b et la dimension de corrélation spatiale des sources sismiques est étudiée.

As hard rock mining progresses into higher stress mining conditions through either late stage extraction or mining at depth, the rock mass is driven not just to the peak strength, but often well into the post-peak until complete ‘failure’ occurs and easier mining conditions become evident. Limited research has been accomplished in identifying the transition of the rock mass and its behaviour into the post-peak and this research investigates this behaviour in detail. As the rock mass progressively fails, fractures are initiated through intact rock and extension and shear failure of these and pre-existing features occurs. Associated with this failure are microseismic events, which can be used to give an indication of the strength state of the rock mass. Based on an analogy to laboratory testing of intact rock and measurement of acoustic emissions, the microseismicity can be used to identify, fracture initiation, coalescence of fractures (yield), localization (peak-strength), accumulation of damage (post-peak) and ultimate failure (residual strength) leading to aseismic behaviour. The case studies presented in this thesis provide an opportunity to examine and analyse rock mass failure into the post-peak, through the regional and confined failures at the Williams and the Golden Giant mines, both in the Hemlo camp in Northern Ontario, Canada. At the Williams mine, the progressive failure of a sill pillar region into the post-peak was analysed; relating the seismic event density, combined with numerical modelling and a spatial and temporal examination of the principal components analysis (PCA), to characterize the extent, trend and state of the yielding zone, which formed a macrofracture shear structure. Observations of conventional displacement instrumentation, indicates regional dilation or shear of the rock mass occurs at or prior to the point of ‘disassociation’ (breakdown of stable PCA trends) when approaching the residual strength. At the Golden Giant mine, the complete process from initiation to aseismic behaviour is monitored in a highly stressed and confined pendent pillar. The PCA technique, numerical modelling and focal mechanism studies are used to define significant stages of the failure process, in which a similar macrofracture structure was formed. Temporal observations of key source parameters show significant changes prior to and at the point of coalescence and localization.

Made available in DSpace on 2016-12-08T15:56:19Z (GMT). No. of bitstreams: 1 Ricardo Kirchhof Unfer.pdf: 99775 bytes, checksum: 27709fdea77151b3e21cfdaf92146d6e (MD5) Previous issue date: 2015-08-28 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The new contributions of present thesis are an alternative experimental waviness method and a new theoretical model for evaluation of limit strains of sheet metal forming in the automotive industry, employing the analysis of roughness and waviness parameters evolution with the equivalent plastic strain and a new ductile rupture criterion as function of stress triaxiality. For validation of proposed experimental waviness method and rupture criterion, specimens of IF steel sheet of thickness 0.72mm, 0.82mm and 0.85mm were tested under tensile test and Nakazima sheet forming test with Marciniak flat punch. The specimens were deformed in incremental steps in different strain path such as: balanced biaxial stretching, plane strain, uniaxial tension and pure shear. Present proposed method consider that roughness and waviness parameters are important surface quality index and useful as indicator of onset of visible local necking and should be monitored in sheet metal forming. Thus, a Waviness Limit Curve, WLC, is proposed to be plotted in Map of Principal Limit Strains (MDLC) of sheet metal as an alternative to the forming limit strain curve, FLC. Various parameters of roughness and waviness such as arithmetic average roughness (Ra), maximum peak-valley roughness (Rt), arithmetic average waviness (Wa), total heigth peak-valley waviness (Wt), maximum peak height waviness (Pp) and maximum valley depth waviness (Pv) were measured during the uniaxial and biaxial testing. Tensile test of IF steel specimens at 0º, 45º and 90º to the rolling direction, RD, and Nakazima type of IF steel specimens at 0º RD only, in which a mesh of 2.5mm circles were printed, were employed. During the uniaxial and biaxial testing, the following plastic deformations were calculated in each straining step from the printed circles in the sheet surface: major true strain (&#61541;1) and minor true strain (&#61541;2). Parameters of roughness and waviness versus equivalent plastic strain curves were plotted to obtain a phenomenological equation of 4th and 3rd degree polynomials, using the Hill 1979 yield stress criterion. Furthermore, the growth rate of parameters Wa and Wt with equivalent plastic strain were calculated. From the growth rate, it was possible to conclude that the sheet 12 thickness imperfections, measured by Wa and Wt, evolve during material deformation, being possible to predict with accuracy the influence of equivalent plastic strain in the onset of local necking. From the experimental analysis, it was concluded that the maximum peak-valley waviness parameter (Wt) was the best option to chacaracterized the beginning of local necking in IF steel sheet forming. Thus, from the analysis of waviness growth rate parameters, Wa and Wt, during plastic strains, it was possible to propose a criterion of local necking inception. This allowed to obtain and plot an experimental Waviness Limit Curve (WLC) in the map MDLC: the beginning of local necking was established when the normalized parameter Wt* (=Wt/Wto) attained a critical value Wt*= 2.5, but with distinct values of equivalent strains. A second mathematical model was proposed for local necking criterion to obtain the FLC of IF steel sheets, employing stress triaxiality analysis and the Hill 1979 yield stress criterion. 2nd degree polynomials were obtained from plotted and adjusted phenomenological curves in graphs of equivalent strain at rupture versus stress triaxiality, considering the different plastic strain path in the formability testing. The IF steel specimens showed ductile rupture, according to scanning electronic microscope examinations, which showed that rupture occurred due to formation, growth and coalescence of large quantity of pores in many specimens of balanced biaxial (BB) and plane strain (DP). Also, mixed rupture of ductile type due to shear mechanisms in certain regions of tensile test (TS) and Nakazima uniaxial tension (UTN) specimens were shown. / As propostas de ineditismo da presente tese foram mostrar um método experimental alternativo de rugosidades e um modelo teórico de ruptura novo para se avaliar as deformações limites de conformação de chapas metálicas da indústria automobilística, empregando-se uma análise da evolução dos parâmetros de ondulação da rugosidade com a deformação plástica equivalente e um critério de ruptura dúctil em função da triaxialidade das tensões. Para validação do método experimental de rugosidades e do critério de ruptura propostos, utilizou-se corpos de prova de chapas de aço IF de 0,72mm, 0,82mm e 0,85mm de espessura, que foram submetidas aos ensaios de tração simples e ensaio de estampagem tipo Nakazima com punção plano de Marciniak. As amostras foram sujeitas a deformação incremental em diferentes trajetórias de deformação, tais como: estiramento biaxial balanceado, deformação plana, estiramento uniaxial e cisalhamento puro. O presente método proposto considera que parâmetros de rugosidade e ondulação são índices importantes de qualidade da superfície e servem como indicador preciso do início da estricção local visível e devem ser monitorados na conformação de chapas metálicas. Portanto, propõe-se traçar uma Curva Limite de Ondulação da Rugosidade, CLOR, no Mapa das Deformações Principais Limite de Conformação (MDLC) das chapas metálicas como alternativa da curva limite de conformação, CLC. Vários parâmetros do perfil de rugosidade e da ondulação da rugosidade tais como a rugosidade média aritmética (Ra), altura máxima pico-vale (Rt), ondulação média aritmética (Wa), a altura máxima da ondulação pico-vale (Wt), altura máxima de pico da ondulação (Pp) e profundidade máxima de vale (Pv) foram medidos durante os ensaios uniaxiais e biaxiais. Foram utilizados corpos de prova de aço IF em tração simples a 0º, 45º e 90º da direção de laminação, DL, e corpos de prova tipo ensaio Nakazima de aço IF somente a 0º DL nos quais foram impressos uma malha de círculos de 2,5 mm de diâmetro. Durante os ensaios uniaxiais e 10 biaxiais, as seguintes deformações plásticas foram calculadas em cada etapa a partir da malha de circulos impressos na superficie da chapa: a deformação verdadeira longitudinal maior (&#61541;1) e a deformação verdadeira transversal menor (&#61541;2). Curvas dos parâmetros de rugosidade e ondulações versus deformação plástica equivalente, empregando-se o critério de escoamento plástico de Hill (1979), foram traçados para se obter equações fenomenológicas do tipo polinomial de 4° e 3° graus. Além disso, foram calculadas as taxas de crescimento dos parâmetros Wa e Wt com a deformação plástica equivalente. A partir das curvas de taxas crescimento, foi possível concluir que as imperfeições na espessura da chapa, medidas por meio de Wa e Wt, evoluem durante a deformação do material, sendo possível prever com precisão a influência da deformação plástica equivalente no início do surgimento da estricção local. Concluiu-se então que o parâmetro da altura máxima total pico-vale das ondulações (Wt) é a melhor opção para caracterizar o início da estricção local em chapas de aço IF. Portanto, a partir da análise das taxas de crescimento dos parâmetros de ondulação, Wa e Wt, durante as deformações plásticas, foi possível propor um critério para o surgimento da estricção local. Isto permitiu obter e traçar a curva experimental de Limite de Ondulação da Rugosidade, (CLOR), no Mapa MDLC: o início da estricção local foi quando o parâmetro normalizado Wt* (=Wt/Wto) atingiu o valor crítico Wt*=2,5, mas com valores distintos da deformação equivalente. Um segundo modelo matemático foi proposto como critério de estricção local para obtenção da CLC de chapas de aço IF, empregando-se análise da triaxialidade de tensões e o critério de escoamento plástico de Hill (1979). Foram obtidos polinômios de 2º grau por meio de curvas fenomenológicas ajustadas e traçadas nos gráficos de triaxialidade de tensões versus deformação equivalente de ruptura, considerando-se as diferentes trajetórias da deformação plástica dos ensaios de conformabilidade. As amostras de chapa de aço IF mostraram ruptura dúctil conforme exame no microscópio eletrônico de varredura, o qual mostra que a fratura ocorreu devido a formação, crescimento e coalescência de uma grande quantidade de espaços vazios ou poros na maioria dos corpos de prova tipo Biaxial Balanceado (BB) e Deformação Plana (DP). Também, as amostras apresentaram fraturas mistas do tipo dúcteis e com mecanismos de cisalhamento em determinadas regiões das amostras fraturadas em Tração Simples (TS) e Tração Uniaxial de Nakazima (UTN).

Submitted by ISABELA ATILIO null (isabelaatilio@hotmail.com) on 2017-10-31T16:58:11Z No. of bitstreams: 1 Dissertação Final - Isabela Atilio.pdf: 12968588 bytes, checksum: 24d1b58efcf37a8ffc0d9ed1afc4d7d4 (MD5) / Approved for entry into archive by LUIZA DE MENEZES ROMANETTO (luizamenezes@reitoria.unesp.br) on 2017-11-10T19:48:34Z (GMT) No. of bitstreams: 1 atilio_i_me_guara.pdf: 12968588 bytes, checksum: 24d1b58efcf37a8ffc0d9ed1afc4d7d4 (MD5) / Made available in DSpace on 2017-11-10T19:48:34Z (GMT). No. of bitstreams: 1 atilio_i_me_guara.pdf: 12968588 bytes, checksum: 24d1b58efcf37a8ffc0d9ed1afc4d7d4 (MD5) Previous issue date: 2017-09-18 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / O aumento da demanda por petróleo e seus derivados tem instigado o desenvolvimento de materiais para dutos com elevadas tenacidade à fratura e resistência mecânica, como os aços de alta resistência e baixa liga (ARBL) pertencentes às classes API. Aliada à utilização destes aços, a aplicação do processo de soldagem por resistência elétrica de alta frequência (HF/ERW) tem conquistado maior interesse no setor. Entretanto, defeitos nas juntas soldadas constituem uma das principais causas de falhas em dutos, principalmente quando associados às condições externas de operação, o que tem sido motivo para estudos relacionados à integridade estrutural destes tubos. O objetivo deste trabalho foi estudar a tenacidade à fratura de um tubo de aço API 5L X70 soldado pelo processo HF/ERW, a partir de dados obtidos com ensaios CTOD de espécimes de flexão por três pontos, tipo SE(B) “gull wing”. A metodologia proposta envolveu ensaios de CTOD a variadas temperaturas, incluindo a região de transição dúctil-frágil, a fim de avaliar a integridade estrutural do material em condições críticas de operação. Os ensaios foram realizados com base nas normas ASTM E1820 e BS7448, e consistiram na utilização de corpos de prova retirados diretamente da parede do tubo, com posterior planificação. De forma geral, as amostras de material base apresentaram uma boa tenacidade à fratura em todas as temperaturas de ensaio, o que não aconteceu com as amostras de material de solda, que apresentaram baixa tenacidade. Os resultados de tenacidade obtidos mostraram que a metodologia empregada para o estudo da integridade estrutural por meio de ensaios CTOD com amostras extraídas diretamente da parede do tubo, com posterior planificação, mostrou-se adequada. Embora as normas ASTM E1820 e BS7448 adotem diferentes parâmetros para a determinação do valor de CTOD, observou-se que os valores de CTOD foram bem próximos. / The increasing demand for oil and its products has driven the development of materials for ducts with high fracture toughness and high mechanical strength, such as high strength low alloy (HSLA) steels, appertaining to the API classes. In addition to the use of these steels, the application of the high frequency resistance welding process (HF/ERW) has gained greater interest in the sector. However, defects in the welded joints are one of the most causes of failures in pipelines, especially when they are associated with external operating conditions, which has been the reason for studies related to the structural integrity of these tubes. The aim of this work was to study the fracture toughness of an API 5L X70 steel tube welded by the HF/ERW process, from data obtained with CTOD tests bending specimens by three points, type SE (B) gull wing. The proposed methodology involved CTOD tests at various temperatures, including the ductile-brittle transition region, in order to assess the structural integrity of the material under critical operating conditions. The tests were performed based on the ASTM E1820 and BS7448 standards, and consisted of the use of specimens taken directly from the wall of the tube, with subsequent planning. In general, the base material samples showed good fracture toughness at all test temperatures, which did not occur with the samples of welded material, which presented low toughness. The toughness results obtained showed that the methodology used for the study of structural integrity by means of the CTOD tests with samples drawn directly from the wall of the tube, with subsequent planning, was adequate. Although the ASTM E1820 and BS7448 standards adopt different parameters for the determination of the CTOD value, it was observed that the CTOD values were very close.

Caracterizar propriedades de resistência à propagação de trinca em materiais dúcteis é um elemento central em métodos de avaliação de integridade estrutural de dutos destinados ao transporte de gás, petróleo e seus derivados que utilizam os aços ARBL. Sendo assim, o objetivo deste trabalho foi estudar as propriedades de fratura dúctil do aço API 5L X80, através da obtenção da curva de resistência à propagação estável de defeitos (curvas J-R) do material. O ensaio de tenacidade à fratura para obtenção da curva J-R foi conduzido utilizando a técnica do corpo-de-prova único (single specimen) empregando o método da flexibilidade no descarregamento (unloading compliance), segundo a norma de ensaios ASTM E1820-96. Os corpos-de-prova compactos C(T) apresentaram espessura B=15mm, largura W=2B e uma relação aproximada entre o tamanho de trinca (a) e a largura, a/W=0,6. O ensaio foi conduzido numa máquina universal de ensaios (MTS) servo-controlada e capacidade máxima de 250kN. Adicionalmente, foram conduzidos ensaios convencionais de tração (limite de escoamento – 550MPa, limite de resistência – 676MPa e alongamento total em 50mm – 27%), ensaios de impacto Charpy (energia absorvida de 220J à 0ºC – sentido longitudinal) e análises metalográficas (microestrutura refinada composta por ferrita, colônias de perlita e presença do constituinte MA). Tais caracterizações permitirão uma maior precisão na comparação da curva J-R do aço API 5L X80 em estudo com estudos futuros de tenacidade à fratura. / Assessments of crack growth resistance in ductile materials play a key role in structural integrity procedures for high strength, low alloy (HSLA) pipeline steels commonly employed in gas and petroleum trasmission systems. This work presents an investigation of the ductile tearing properties for an API 5L X80 pipeline steel using experimentally measured crack growth resistance curves (J-R curves) for the material. Testing of the X80 pipeline steel employed compact tension (C(T)) fracture specimens to determine the J-R curves based upon the unloading compliance method using a single specimen technique in accordance with the ASTM E1820 standard procedure. The C(T) specimens have thickness B=15mm, width W=2B and a ratio between crack size (a) and width, a/W=0,6. The experimental tests utilized a 250 kN MTS universal machine. Conventional tensile tests were also performed to determine the tensile properties for the tested material: yield strength of 550MPa, tensile strength of 676MPa and elongation of 27% (gage length of 50 mm). The Charpy V-notch impact tests also provided and absorbed energy of 220J at 0ºC. The metallographic analysis showed colonies of perlite and MA constituent islands in a ferrite matrix. This experimental characterization provides additional toughness and mechanical data against which the general behavior of X80 class pipeline steel can be compared.

Des méthodes micromécaniques spécifiques ont été développées pour la détermination du comportement effectif de matériaux cellulaires dotés d’une architecture discrète à l’échelle microscopique. La méthode d’homogénéisation discrète a été appliquée à des structures tissées monocouches ainsi qu’à l’os trabéculaire. La topologie discrète initiale de ces milieux est remplacée à l’échelle mésoscopique par un milieu effectif anisotrope micropolaire, qui rend compte des effets d’échelles observés. Ces méthodes d’homogénéisation permettent d’accéder à des propriétés classiques et non classiques dont la mesure expérimentale est souvent difficile. Des modèles 3D ont été développé afin de décrire la rupture fragile et ductile de l’os trabéculaire, incorporant des effets de taille des surfaces d’écoulement plastique. Nous avons construit par des analyses éléments finis de la microstructure de l’os trabéculaire un milieu de substitution 3D homogène, orthotrope de type couple de contraintes, sur la base d’une équivalence en énergie. Les tissus osseux ont la capacité d’adapter leur densité locale et leur taille et forme aux stimuli mécaniques. Nous avons développé des modèles de remodelage interne et externe dans le cadre de la thermodynamique des processus irréversibles, aux échelles cellulaire et macroscopique. Finalement, le remodelage interne anisotrope a été couplé à l’endommagement de fatigue, dans le cadre de la théorie continue de l’endommagement / A methodology based on micromechanics has been developed to determine the effective behavior of network materials endowed with a discrete architecture at the microscopic level. It relies on the discrete homogenization method, which has been applied to textile monolayers and trabecular bones. The initially discrete topology of the considered network materials results after homogenization at the mesoscopic level in anisotropic micropolar effective continuum, which proves able to capture the observed internal scale effects. Such micromechanical methods are useful to remedy the difficulty to measure the effective mechanical properties at the intermediate mesoscopic level scale. The bending and torsion responses of vertebral trabecular bone beam specimens are formulated in both static and dynamic situations, based on the Cosserat theory. 3D models have been developed for describing the multiaxial yield and brittle fracture behavior of trabecular bone, including the analysis of size-dependent non-classical plastic yield. We have constructed by FE analyses a homogeneous, orthotropic couple-stress continuum model as a substitute of the 3D periodic heterogeneous cellular solid model of vertebral trabecular bone, based on the equivalent strain energy approach. Bone tissues are able to adapt their local density and load bearing capacities as well as their size and shape to mechanical stimuli. We have developed models for combined internal and external bone remodeling in the framework of the thermodynamics of irreversible processes, at both the cellular and macroscopic levels. We lastly combined anisotropic internal remodeling with fatigue continuum damage

The effect of Laves phase (Fe2Nb) formation on the Charpy impact toughness of the ferritic stainless steel type AISI 441 was investigated. The steel exhibits good toughness after solution treatment at 850°C, but above and below this treatment temperature the impact toughness decreases sharply. With heat treatment below 850°C the presence of the Laves phase on grain boundaries and dislocations plays a significant role in embrittlement of the steel whereas above that temperature, an increase in the grain size from grain growth plays a major role in the impact embrittlement of this alloy. The toughness results agree with the phase equilibrium calculations made using Thermo–Calc® whereby it was observed that a decrease in the Laves phase volume fraction with increasing temperature corresponds to an increase in the impact toughness of the steel. Annealing above 900°C where no Laves phase exists, grain growth is found which similarly has a very negative influence on the steel’s impact properties. Where both a large grain size as well as Laves phase is present, it appears that the grain size may be the dominant embrittlement mechanism. Both the Laves phase and grain growth, therefore, have a significant influence on the impact properties of the steel, while the Laves phase’s precipitation behaviour has also been investigated with reference to the plant’s manufacturing process, particularly the cooling rate after a solution treatment. The microstructural analysis of the grain size shows that there is a steady increase in grain size up to about 950°C, but between 950°C and 1000°C there is a sudden and rapid 60 % increase in the grain size. The TEM analysis of the sample that was annealed at 900°C shows that the Laves phase had already completely dissolved and cannot, therefore, be responsible for “unpinning of grain boundaries” at temperatures of 900°C and higher where this “sudden” increase in grain size was found. The most plausible explanation appears to be one of Nb solute drag that loses its effectiveness within this temperature range, but this probably requires some further study to fully prove this effect. During isothermal annealing within the temperature range of 600 to 850°C, the time – temperature – precipitation (TTP) diagram for the Laves phase as determined from the transformation kinetic curves, shows two classical C noses on the transformation curves. The first one occurring at the higher temperatures of about 750 to 825°C and the second one at much lower temperatures, estimated to possibly be in the range of about 650 to 675°C. The transmission electron microscopy (TEM) analyses show that there are two independent nucleation mechanisms that are occurring within these two temperature ranges. At lower temperatures of about 600°C, the pertaining nucleation mechanism is on dislocations and as the temperature is increased to above 750°C, grain boundary nucleation becomes more dominant. Also, the morphology of the particles and the mis-orientation with the matrix changes with temperature. At lower temperatures the particles are more needle-like in shape, but as the temperature is increased the shape becomes more spheroidal. The effect of the steel’s composition on the Laves phase transformation kinetics shows that by lowering the Nb content in these type 441 stainless steels, had no significance effect on the kinetics on precipitation of the Laves phase. However, a Mo addition and a larger grain size of the steel, retard the formation of the Laves phase, although the optimum values of both parameters still need further quantification. The calculation made for the transformation kinetics of the Laves phase, using the number density of nucleation sites No and the interfacial energy, as the fitting parameters in this work, demonstrated a reasonable agreement with experimental results. / Thesis (PhD)--University of Pretoria, 2010. / Materials Science and Metallurgical Engineering / unrestricted

Previous thread rolling methods for the plastic limit are shown to be inadequate and inaccurate. Alternative methods for the plastic limit are shown to be imprecise and unreliable. The strength-based concept and use of the fall-cone test to determine the plastic limit are shown to be flawed. An apparatus that replicates Atterberg’s rolling technique, devised and developed by the author, is described, referred to as the Barnes Apparatus. A thread of soil is rolled between two plates configured to permit extrusion and reduction of diameter with much less operator interference than with the standard test and judgement of the crumbling condition is eliminated. Using a loading device nominal stresses are derived and from dial gauge readings diametral strains are determined for each rolling traverse of the soil thread. Toughness has previously only been studied in an empirical or qualitative manner. From plots of nominal stress vs. strain the workability or toughness of the plastic soil is determined as the work/unit volume. The apparatus and test are appropriate to a wide range of soils. Threads are tested over a range of water contents from near the sticky limit to the brittle state. Good correlations between toughness and water content display an abrupt ductile-brittle transition and give an accurate definition of the plastic limit. From the correlations useful properties are obtained such as the maximum toughness at the plastic limit, the toughness limit, the water content at zero toughness, the stiffness transition, the toughness coefficients, the toughness index and the workability index. An investigation into the significance of the soil thread diameter of 3 mm in the standard plastic limit test has found that as the water content of a soil reduces it undergoes a transition from fully plastic, to cracked, to brittle, largely regardless of the diameter of the thread. It is recommended that the 3 mm diameter requirement is withdrawn from the standard test procedure as unnecessary and emphasis placed on observing the behaviour of the soil thread as it is rolled by hand. A review of the relationship between the clay matrix and the granular particles in a soil has found that the linear law of mixtures and activity index are appropriate only at high clay contents. The terms granular spacing ratio and matrix porosity are introduced to explain the effect of the granular particles on the toughness and plastic limit. An analysis confirms that with small diameter soil threads large granular particles affect the results disproportionately. An aggregation ratio term is introduced to explain the change in toughness in the clay matrix as its water content reduces towards the plastic limit. To assess the effect of granular particles in a clay matrix on the toughness and plastic limit the results of tests conducted on mixtures of a high plasticity clay and silt, and sand particles of two different sizes are discussed. Smaller particle sizes are found to have a greater effect on reducing the toughness and the plastic limit of the clay. In the ceramics industry mixing different clays together to obtain suitable properties is common. The toughness and plastic limits of two pairs of mixed clays do not follow the linear law of mixtures but are dependent on the total clay content and the content of a dominant clay mineral.

Wood structural elements are more vulnerable to blast loading due to the inherent brittle nature and low density of the material, as demonstrated by recent significant research efforts on the behaviour of timber elements subjected to the effect of blast loading. These studies showed that wood performs poorly under blast loading. A way of improving this performance is to provide additional ductility or energy absorption capabilities to wooden elements. Recently, there was interest in investigating and developing energy-absorbing connections (EAC) to improve timber assemblies’ ductility and energy absorption capabilities. Although some research effort has been made to investigate the use of EACs to enhance the ductility of reinforced concrete or structural steel members, only limited work is available on this topic about timber elements. The current study aims to systematically investigate the use of various shapes of EACs to be used to enhance the post-peak performance of timber assemblies. Preliminary finite element analysis led to selecting nine steel EACs with varying geometries for further experimental investigation. A total of eighteen specimens were tested statically. In comparison, a total of eighteen specimens were tested dynamically in the shock tube facility of the University of Ottawa to simulate the effects of far-field blast explosions. The experimental results showed that decreasing the leg length or increasing the thickness of EACs manufactured with steel angles and reducing the diameter of EACs manufactured with circular HSS caused an increase in yield load and elastic stiffness while reducing the densification displacement. Connections with angles and a centre weld, and connections with 90-degree arcs from circular HSS, were identified as unsuitable for the application of EACs. The experimental program also showed that EACs manufactured from angles offer a well-defined plateau able to absorb a large quantity of energy, making them particularly suitable for blast mitigation. EACs manufactured from multiple circular HSS were shown to achieve multiple load-displacement plateaus and present an interesting option for systems with multiple failure modes occurring at different levels. SDOF analysis and FEA were conducted to predict the experimental behaviour with some success. The importance of the weld type was also highlighted from both the analytical and experimental results. A methodology for developing idealized load-displacement curves from experimental results of EACs was also proposed and evaluated.

The diploma thesis is aimed to assesment of the influence of the specimen orientation during the Small Punch Tests (SPT). Steel ČSN 41 0214, or its equivalent steel RFe80, W.-Nr. 1.104 was chosen for experiments. Resulting records from SPT were evaluated using already known correlations which are reported in literature. The correlation values were compared with values obtained by the standard tests like Charpy impact test and tensile test. The influence of axial, radial and tangential test specimens orientation is discussed in relation to Ductile-to-Brittle fracture behaviour of the steel.