An understanding of the atomic-scale features of chemical and physical processes taking place behind the shockwave front will help in addressing some of the major challenges in energetic materials research. The high pressure shockwave environment can be simulated using computational techniques to predict mechanical and chemical properties of a shocked material. Density functional theory calculations were performed to investigate uniaxial compressions of diamond and both hydrostatic and uniaxial compressions of TATB and NEST-1. For diamond, we calculated shear stresses for uniaxial compressions in the , , and directions and discovered the anomalous elastic regime which is responsible for the significant delay of plastic deformation behind a shockwave. For TATB, the hydrostatic equation of state, bulk modulus, and equilibrium structure were calculated using an empirical van der Waals correction. The principal stresses, shear stresses, and energy change per atom calculated for uniaxial compressions in the directions normal to the {001}, {010}, {011}, {100}, {101}, {110}, and {111} planes show highly anisotropic behavior. A similar study was performed for the newly synthesized energetic material NEST-1 in order to predict mechanical properties under uniaxial compression. From the similarities in the calculated principal stresses for each compression direction we conclude that NEST-1 is likely to exhibit relatively isotropic behavior as compared to other energetic materials. Finally, reactive molecular dynamics of shock-induced initiation chemistry in detonating PETN was investigated, using first-principles density functional theory, in order to identify the reaction mechanisms responsible for shock sensitivities in energetic materials. The threshold collision velocity of initiation for each orientation was determined and correlated with available experimental data on shock sensitivity. The production of NO2 was found to be the dominant reaction pathway in every reactive case. The simulations show that the reactive chemistry of initiation occurs at very short time scales ~10E?¹³ s at highly non-equilibrium conditions, and is driven by dynamics rather than temperature.

The electric potential changes under uniaxial loading in some minerals and rocks have long been recognized. To daylight the electrical response of some minerals and rocks against applied stress, both theoretical studies and laboratory experiments are conducted. Some theories are also proposed by different researchers, in order to explain the electric potential variations. However, the mechanisms leading to electrical potential generation have not been fully explained yet. In the explanation of electric potential changes observed in rocks, type of the observed rock and the rock forming minerals in the rock fabric play an important role. One theory is based on the fundamentals of piezoelectricity only. However the relation between the stress state and the electric generation is not fully understood. This thesis aims to make a further contribution to the studies on understanding the electric potential change in rocks, containing quartz, which is a common piezoelectric mineral, under uniaxial loading conditions. Three types of rocks, namely quartz-sandstone, granite and granodiorite, are tested, and the stress and electric potential (EP) variations are recorded during the uniaxial loading experiments in a continuous manner. The experiments are conducted at three different loading rates, in order to investigate the effect of loading rate on the electrification mechanism. Also step loading experiments are conducted. Results indicated that, application of uniaxial stress creates a clear change in the EP responses of three quartz bearing rock types. The possible relationships between the EP generation and the level of applied stress are investigated based on the initial and final potential values (EPinitial, EPfinal), the potential just before the time of failure (EPUCS), the spike-like potential jump at the time of failure (&amp / #8710 / V), which are derived from the recorded data of the experiments.

L’objectif principale de cette thèse est de procéder à une identification paramétrique d’un modèle rhéologique de matériau métallique à chaud en utilisant des données expérimentales issues d’une presse industrielle. Dans le premier chapitre, le principe de l’identification paramétrique est exposé. Des essais de compressions uniaxiale faites sur machine d’essais spécialisés y servent alors comme cas d’étude. Les notions de choix de la fonction-coût, du plan d’expérience et du modèle y sont alors abordées ainsi qu’une analyse de sensibilité. Le chapitre suivant présente l’outillage utilisé pour faire les expériences sur presse. Enfin, une évaluation des échanges thermiques et des frottements que subis la pièce lors de l’essai est faite. Le troisième chapitre se concentre sur l’identification paramétrique proprement dite. Ainsi, des simulations par élément fini de la compression sont faites et comparées aux essais expérimentaux. Les résultats de l’identification sont discutés et comparés à ce que proposait initialement la base de données du logiciel FORGE® ainsi que les paramètres identifiés pour le même matériau au chapitre 1. Une simulation d’une pièce complexe avec ces différents jeux de paramètres est ensuite comparée avec le forgeage réel de cette pièce. Le quatrième chapitre reprend les acquis du troisième en faisant une identification paramétrique pour la rhéologie d’Inconel 625. Une tentative d’identification d’un modèle de microstructure pour l’Inconel à partir d’essais industriel termine ce manuscrit. / The main objective of this thesis is to identify the parameters of a hot metal rheology model by using experimental data from an industrial press. In the first chapter, the principle of parameter identification is exposed. Uniaxial compression testing done on specialized devices serves as a case study. The notions of cost function, experimental design and rheological model are examined. A sensitivity analysis is also performed. The next chapter present the experimental tools used on the industrial press. Finally, the friction and thermal exchange that will happen during the tests are evaluated. The third chapter is about the inverse analysis on industrial press. Finite elements modelling of the compression is made and compared with the experiments. The identification results are then compared with the FORGE® software database and the material parameters found in chapter 1. A complex part is then simulated with these different parameters and compared with a real forging of this part. The fourth chapter uses the same methods as in chapter 3 to perform an identification on the rheological parameters of an Inconel 625. A microstructural model for the Inconel is then identified with industrial testing as reference.

Models (both physical and numerical) of the friction stir (FS) welding process are used to develop a greater understanding of the influence of independent process parameters on dependent process output variables, such as torque, power, specific weld energy, peak temperature, cooling rates and various metallurgical factors (e.g., grain size and precipitates). An understanding of how the independent process parameters influence output variables and ultimately their effect on resultant properties (e.g., strength, hardness, etc..) is desirable. Most models developed have been validated primarily for aluminum alloys with relatively small amounts of experimental data. Fewer models have been validated for steels or stainless steels, particularly since steels and stainless steels have proven more challenging to friction stir than aluminum alloys. The Gleeble system is also a powerful tool with the capability to perform thermomechanical simulations in a known and controlled environment and provide physical representation of resultant microstructure and hardness values. The coupling of experimental data and physical simulated data can be extremely useful in assessing the capabilities of friction stir numerical process models. The overall approach is to evaluate Isaiah an existing three-dimensional finite element code developed at Cornell University by comparing against experimental and physically-simulated data to determine how well the code output relates to real FS data over a range of nine processing conditions. Physical simulations replicating select thermomechanical streamline histories were conducted to provide a physical representation of resultant metallurgy and hardness. Isaiah shows promise in predicting qualitative trends over a limited range of parameters and is not recommended for use as a predictive tool but rather a complimentary tool, Once properly calibrated, the Isaiah code can be a powerful tool to gain insight into the process, strength evolution during the process and coupled with a texture evolution model may also provide insight into microstructural and texture evolution over a range for which it is calibrated.

This thesis has discussed both properties and geometry of concrete slabs used in bridges. It gave understanding on behavior of concrete in both tension and compression zones and how crack propagates in specimens by presenting both theory of fracture and performing concrete tests like tension splitting, uniaxial compression and uniaxial tension tests. Furthermore, it supported experimental tests with finite elements modelling for each test, and illustrated both boundary conditions and loads. The thesis has used ARAMIS cameras to observe crack propagations in all experimental tests, and its first study at LNU that emphasized on Brazilian test, because of importance of this test to describe both crushing and cracking behavior of concrete under loading. It’s an excellent opportunity to understand how concrete and steel behave individually and in combination with each other, and to understand fracture process zone, and this has been discussed in theory chapter. The geometry change that could affect stresses distributions has also described in literature and modelled to give good idea on how to model slabs in different angles in the methodology chapter. Thus, thesis will use finite elements program (Abaqus) to model both experimental specimens and concrete slabs without reinforcement to emphasize on concrete behavior and skewness effect. This means studying both properties of concrete and geometry of concrete slabs. This thesis has expanded experimental tests and chose bridges as an application.

Made available in DSpace on 2017-07-10T19:24:51Z (GMT). No. of bitstreams: 1 Almiro Weiss.pdf: 7452787 bytes, checksum: 197399ca28d2e0c6c30badfe29ff070b (MD5) Previous issue date: 2005-07-01 / The compaction of the agricultural soils has worldwide importance because of the increasing of the farm with machinery resulting in the increasing of heavy machines for cultivation system, mainly, in the developed countries. The term, soils compaction refers to the compression carried out on the non-saturated soil, during which an increase of bulk density exists, producing the reduction of its volume of pores like a consequence. The excessive compaction has damaging consequences for the agriculture and environmental. For this reason, the state of soils compacting has received enough attention from researchers and agricultural farmers. The uniaxial compression has been used for predicting the agricultural soils compaction with so much efficiency. In accordance to the previous exposure, in this paper aimed the to develop an apparatus of uniaxial compression of the soil for testing in laboratory and evaluating its performance. The apparatus is composed by a pneumatic press, where the sample of soil is packaged in a metallic volumetric ring (made in steel carbon - ABNT 1020), with thickness of wall of 0,2 cm, internal diameter of 7,0 cm and two options of height of 2,4 cm and 4,8 cm. Cyclical loads of compression were applied to the sample in order to verify the variation of the soil deformation. A lineal transducer detects the samples behavior during the compression and uncompression (relaxation) uniaxial indicating in the digital counter s display the variations of measure of the sample deformation. Successive loads of 150, 200, 300, 400, 500, 600, 700 and 800 kPa were applied in periods of 60 s for compression and 120 s for uncompression of the sample. The results allowed conclude that the system presents answers with good precision and greater versatility with the variation of de samples size for compression. / A compactação dos solos agrícolas tem importância mundial em função do crescimento das áreas mecanizadas, acarretando o aumento de máquinas pesadas nos sistemas de cultivo, principalmente, nos países desenvolvidos. O termo compactação do solo refere-se a sua compressão realizada no solo não saturado, durante a qual existe um aumento de densidade produzindo como conseqüência redução de seu volume de poros. A excessiva compactação tem conseqüências danosas para a agricultura e para o meio ambiente. Por essas razões, o estado de compactação do solo tem recebido bastante atenção de pesquisadores e produtores agrícolas. O ensaio de compressão uniaxial tem sido utilizado para determinar a compactação dos solos agrícolas com muita eficiência. Face ao exposto, este trabalho estabeleceu como objetivo desenvolver um aparelho de compressão uniaxial do solo para ensaio em laboratório e avaliar o seu desempenho. O aparelho é composto por uma prensa pneumática, em que a amostra de solo fica acondicionada em um anel volumétrico metálico (feito em aço carbono - ABNT 1020, cromado), com espessura de parede de 0,2 cm, com diâmetro interno de 7,0 cm e com duas opções de altura de 2,4 cm e 4,8 cm. Cargas cíclicas de compressão foram aplicadas na amostra para verificar a variação da deformação do solo. Um transdutor linear detecta o comportamento da amostra durante a compressão e descompressão (relaxamento) uniaxial indicando no display do contador digital as variações de medida da deformação da amostra. Cargas seqüenciais de 150, 200, 300, 400, 500, 600, 700 e 800 kPa foram aplicadas em intervalos de tempo de: 60 s para compressão e 120 s para descompressão da amostra. Os resultados permitiram concluir que o sistema apresenta respostas com boa precisão e maior versatilidade, com variação do tamanho das amostras para compressão.

Made available in DSpace on 2017-05-12T14:48:14Z (GMT). No. of bitstreams: 1 Almiro Weiss.pdf: 7452787 bytes, checksum: 197399ca28d2e0c6c30badfe29ff070b (MD5) Previous issue date: 2005-07-01 / The compaction of the agricultural soils has worldwide importance because of the increasing of the farm with machinery resulting in the increasing of heavy machines for cultivation system, mainly, in the developed countries. The term, soils compaction refers to the compression carried out on the non-saturated soil, during which an increase of bulk density exists, producing the reduction of its volume of pores like a consequence. The excessive compaction has damaging consequences for the agriculture and environmental. For this reason, the state of soils compacting has received enough attention from researchers and agricultural farmers. The uniaxial compression has been used for predicting the agricultural soils compaction with so much efficiency. In accordance to the previous exposure, in this paper aimed the to develop an apparatus of uniaxial compression of the soil for testing in laboratory and evaluating its performance. The apparatus is composed by a pneumatic press, where the sample of soil is packaged in a metallic volumetric ring (made in steel carbon - ABNT 1020), with thickness of wall of 0,2 cm, internal diameter of 7,0 cm and two options of height of 2,4 cm and 4,8 cm. Cyclical loads of compression were applied to the sample in order to verify the variation of the soil deformation. A lineal transducer detects the samples behavior during the compression and uncompression (relaxation) uniaxial indicating in the digital counter s display the variations of measure of the sample deformation. Successive loads of 150, 200, 300, 400, 500, 600, 700 and 800 kPa were applied in periods of 60 s for compression and 120 s for uncompression of the sample. The results allowed conclude that the system presents answers with good precision and greater versatility with the variation of de samples size for compression. / A compactação dos solos agrícolas tem importância mundial em função do crescimento das áreas mecanizadas, acarretando o aumento de máquinas pesadas nos sistemas de cultivo, principalmente, nos países desenvolvidos. O termo compactação do solo refere-se a sua compressão realizada no solo não saturado, durante a qual existe um aumento de densidade produzindo como conseqüência redução de seu volume de poros. A excessiva compactação tem conseqüências danosas para a agricultura e para o meio ambiente. Por essas razões, o estado de compactação do solo tem recebido bastante atenção de pesquisadores e produtores agrícolas. O ensaio de compressão uniaxial tem sido utilizado para determinar a compactação dos solos agrícolas com muita eficiência. Face ao exposto, este trabalho estabeleceu como objetivo desenvolver um aparelho de compressão uniaxial do solo para ensaio em laboratório e avaliar o seu desempenho. O aparelho é composto por uma prensa pneumática, em que a amostra de solo fica acondicionada em um anel volumétrico metálico (feito em aço carbono - ABNT 1020, cromado), com espessura de parede de 0,2 cm, com diâmetro interno de 7,0 cm e com duas opções de altura de 2,4 cm e 4,8 cm. Cargas cíclicas de compressão foram aplicadas na amostra para verificar a variação da deformação do solo. Um transdutor linear detecta o comportamento da amostra durante a compressão e descompressão (relaxamento) uniaxial indicando no display do contador digital as variações de medida da deformação da amostra. Cargas seqüenciais de 150, 200, 300, 400, 500, 600, 700 e 800 kPa foram aplicadas em intervalos de tempo de: 60 s para compressão e 120 s para descompressão da amostra. Os resultados permitiram concluir que o sistema apresenta respostas com boa precisão e maior versatilidade, com variação do tamanho das amostras para compressão.

The goal of this research is to investigate the fundamentals of fracturing processes in heterogeneous materials such as concrete using geophysical methods and dynamic micromechanical models. This work describes how different aspects of fracture formation in concrete can be investigated using a combination of Acoustic Emission (AE) techniques, ultrasonic wave velocity imaging, and high resolution Computed Tomography (CT). Fracture formation and evolution were studied during shear failure of large reinforced concrete beams and compressive failure of concrete samples. AE analysis includes studying complex spatial and temporal fracture development that precedes shear failure. Predominant microcrack mechanisms were analyzed at different stages of fracture formation. CT images were used to investigate the influence of concrete microstructure on fracture topography. Combined AE and CT damage evaluation techniques revealed different aspects of fracture development, thus expanding our understanding of AE events and their mechanisms. These images show how aggregate particles influence fracture nucleation and development. An emphasis has been placed on the role of coarse aggregates during the interlocking of fracture surfaces at transferring shear stresses. Ultrasonic wave velocity and AE techniques have been applied to uniaxial compression tests of concrete with various aggregate sizes and strengths similar to that of the concrete beams. AE parameters, p-wave velocities, and stress-strain data have been analyzed concurrently to image damage evolution under compression. Influence of material composition on microcracking and material state changes during loading has been investigated in detail. The results of compressive tests were used as building blocks for developing realistic micromechanical numerical models of concrete. The models were designed using a distinct element code, where material is modelled through the combination of bonded particles. A number of procedures were developed to transfer the exact microstructure of material incorporating its visual representation into the model. The models’ behaviour has been verified against experimental data. It was shown that these models exhibit realistic micromechanical behaviour. The results of the experimental investigation of concrete fracturing were expanded by modelling more cases with aggregate size and strength variations. It was shown that geophysical imaging techniques, along with advanced micromechanical numerical modelling, can help us understand damage formation and evolution.

The goal of this research is to investigate the fundamentals of fracturing processes in heterogeneous materials such as concrete using geophysical methods and dynamic micromechanical models. This work describes how different aspects of fracture formation in concrete can be investigated using a combination of Acoustic Emission (AE) techniques, ultrasonic wave velocity imaging, and high resolution Computed Tomography (CT). Fracture formation and evolution were studied during shear failure of large reinforced concrete beams and compressive failure of concrete samples. AE analysis includes studying complex spatial and temporal fracture development that precedes shear failure. Predominant microcrack mechanisms were analyzed at different stages of fracture formation. CT images were used to investigate the influence of concrete microstructure on fracture topography. Combined AE and CT damage evaluation techniques revealed different aspects of fracture development, thus expanding our understanding of AE events and their mechanisms. These images show how aggregate particles influence fracture nucleation and development. An emphasis has been placed on the role of coarse aggregates during the interlocking of fracture surfaces at transferring shear stresses. Ultrasonic wave velocity and AE techniques have been applied to uniaxial compression tests of concrete with various aggregate sizes and strengths similar to that of the concrete beams. AE parameters, p-wave velocities, and stress-strain data have been analyzed concurrently to image damage evolution under compression. Influence of material composition on microcracking and material state changes during loading has been investigated in detail. The results of compressive tests were used as building blocks for developing realistic micromechanical numerical models of concrete. The models were designed using a distinct element code, where material is modelled through the combination of bonded particles. A number of procedures were developed to transfer the exact microstructure of material incorporating its visual representation into the model. The models’ behaviour has been verified against experimental data. It was shown that these models exhibit realistic micromechanical behaviour. The results of the experimental investigation of concrete fracturing were expanded by modelling more cases with aggregate size and strength variations. It was shown that geophysical imaging techniques, along with advanced micromechanical numerical modelling, can help us understand damage formation and evolution.

Les grandes quantités d’eaux usées générées par l’activité humaine doivent être traitées pour minimiser le risque sanitaire et l’impact sur les milieux récepteurs. Les boues résiduaires sont le principal coproduit de ce traitement. Afin de les valoriser, des transformations sont mises en œuvre dans les stations d’épuration pour réduire leur volume et améliorer leur qualité sanitaire. Des problèmes d’écoulement et de mottage sont fréquemment rencontrés par les opérateurs. La caractérisation du comportement rhéologique de ce mélange hétérogène d’eau, microorganismes, fibres, particules colloïdales et non colloïdales, polymères organiques, etc., représente encore de nos jours un challenge scientifique et technique, en particulier lorsque la concentration massique en solides excède 20%. Dans ce travail, une méthodologie complète, associant mesures et modélisation, a été développée afin de caractériser les propriétés rhéologiques, l’adhérence et la cohésion des boues résiduaires. Elle s’adresse à des boues dont le comportement, évalué par un test d’affaissement, s’apparente à celui d’un solide mou et elle peut être mise en œuvre tant que le matériau n’a pas dépassé la limite de plasticité mesurée selon la norme ASTM D 4318, relative aux sols. Dans cette étude, elle a été appliquée à des boues centrifugées, dont la teneur massique en solides était proche de 20%. La méthode expérimentale inclut des essais mécaniques en compression uniaxiale (à très grande déformation, à petite déformation avec un ou plusieurs cycles de charge/décharge) sur un texturomètre de Lloyd Instruments et des essais en cisaillement réalisés sur un dispositif spécialement conçu au laboratoire pour quantifier les propriétés adhésive et cohésive des boues. Ces essais permettent d’identifier le seuil de fracturation du matériau, les ordres de grandeur du module élastique, de la viscosité et du seuil de plasticité, la résilience, les contraintes maximales d’adhésion et de cohésion et, enfin, les énergies d’adhésion. Un modèle mécanique analogique a ensuite été établi. Le comportement viscoélastique et visco-élasto-plastique des boues sous une sollicitation uniaxiale de charge-décharge a pu être simulé par un modèle conceptuel, dit ‘Burgers-Ludwik’, à 7 paramètres rhéologiques. Ce modèle est basé sur les lois mécaniques fondamentales de Hooke, de Newton et sur l'équation de Ludwik pour décrire le comportement plastique d'écrouissage. L’optimisation des paramètres du modèle avec Matlab® a été réalisée avec une méthode de régression multiple non linéaire à plusieurs étapes, ainsi que les calculs des bassins d'attraction et des intervalles de confiance. La sensibilité de la méthodologie à mettre en évidence des changements de propriétés induits par des procédés ou par un stockage a ensuite été évaluée. Il s'est ainsi avéré qu"un malaxage rend le matériau plus adhésif et plus facile à déformer, avec une diminution du seuil et de la rigidité du matériau, et qu’un stockage rend les boues moins cohésives et aussi plus faciles à déformer. / Human daily activities generate a large quantity of wastewater that should be treated in order to minimise the sanitary risk and impacts on the environment. Sewage sludge is the main co-product of the wastewater treatment. Specific processes are implemented to reduce its volume and improve its sanitary quality before valorisation. As dewatered sludge is a mixture of water, microorganisms, fibres, colloidal and non-colloidal particles, organic polymers, etc., with the increase of its solid content, difficulties in pumping, conveying or discharging handling are frequently encountered during these treatments. The rheological characterisation of this heterogeneous material still remains a scientific and technical challenge, especially when solid mass content exceeds 20%. In this work, an entire methodology linking experimental measurements and modelling has been developed to characterise the rheological properties and the stickiness of sewage sludge. This methodology is suitable for sludge behaving as a soft solid (evaluated by slumping test) and as long as the material stays below its plastic limit (by the ASTM D 4318 initially standardized for soils). In this dissertation, the methodology is applied to dewatered sludge of total solid content around 20% by weight. This method includes uniaxial compression tests (from very large deformation to small one with single or two cycles of loading-unloading) using a universal materials testing machine of Lloyd Instrument and shearing tests using a device designed and fabricated in our laboratory for quantifying the sticky properties of sludge. These tests can identify the bioyield of the material, the orders of magnitude of the elastic modulus, viscosity, yield stress and resilience, the maximum adhesive and cohesive stresses, and finally the energy of adhesion. An analogical mechanical model is then established. The viscoelastic and visco-elasto-plastic behaviours under uniaxial cyclic compression can thus be simulated with this conceptual model of 7 parameters, named “Burgers-Ludwik”. This model is based on the fundamental mechanical laws of Hooke, Newton and the equation of Ludwik for simulating plastic hardening of material. A multi-step program based on non-linear multiple regressions is coded to optimize the model parameters with Matlab®. The sensibility of this methodology is highlighted by testing the changes in rheological properties of sewage sludge induced by processing or storage. Mixing makes the sludge more adhesive while storage makes it less cohesive. Both make the sludge easier to deform.