Un nouveau procédé d’élaboration de CMC par voie liquide a été développé ; il met en œuvre l’utilisation de charges réactives afin d’obtenir un composite à bas coût. Afin de préserver le renfort en fibres Nicalon, ces charges doivent réagir sous azote à une température inférieure à 1100°C. Deux charges réactives répondant ces critères et présentant une prise de volume intéressante ont été identifiées : AlB2 et TiSi2.Le broyage planétaire de ces charges a été étudié afin d’évaluer l’influence de l’affinement de la microstructure sur les propriétés. Des poudres de surface spécifique élevée et de granulométrie proche l’échelle nanométrique ont été obtenues. La nitruration des charges a été analysée et un effet de taille a pu être mis en évidence sur la réactivité du TiSi2.Les poudres broyées ont été mises en suspension pour être imprégnées au sein de préformes. Les échantillons ont ensuite subi une étape de nitruration à 1100°C, cruciale pour la cohésion de la matrice. Un cycle PIP a ensuite été réalisé pour diminuer la porosité résiduelle.L’oxydation des matériaux obtenus a été étudiée dans des conditions correspondant à l’application aéronautique visée. Les propriétés mécaniques des composites élaborés ont été évaluées par des essais de flexion 3 points. La combinaison de l’utilisation de la charge réactive TiSi2 et d’un polysiloxane a permis d’obtenir un composite dont la contrainte à rupture est remarquable compte tenu du faible nombre d’étapes nécessaires à son élaboration par voie liquide. / A new CMC manufacturing process has been developped ; the active filler technique is used in order to obtain a low cost composite. Active fillers must react under nitrogen atmosphere at a temperature below 1100°C so that the Nicalon fiber reinforcement is not damaged. Two active fillers meeting these criteria and offering an interesting volume expansion have been identified : AlB2 et TiSi2.The planetary milling of these fillers has been explored in order to assess the influence of microstructure refinement on properties. Powders with high specific surface areas and of granulometry close to the nanometric scale were obtained. The nitridation of the active fillers was examined and a size effect on TiSi2 reactivity was displayed.Milled powders were used in colloidal suspensions in order to be impregnated in preforms. Samples were subsequently nitrided at 1100°C ; this step was crucial for matrix cohesion. A PIP cycle was eventually performed in order to reduce residual porosity.The oxydation behaviour of materials was studied in conditions corresponding to the considered aeronautics application. Mechanical properties of composites were estimated by 3 point bending tests. Combining the use of TiSi2 and of a polysiloxane enabled to obtain a composite whose maximum bending stress was remarkable considering the limited number of steps required for its processing.

The interface between aggregate grains and matrix in cementitious composites is their weakest element. The topic is particularly significant in the case of high performance and high strength concrete technology for which the eliminination or reduction of these weak links are necessary. The aim of this thesis is to determine the influence of the interface on the fracture behaviour of the cementitious composites. The fracture experiments were performed for this purpose and were complemented by the nanoindentation’s results and scanning electron microscopy results. Numerical model was created in ANSYS software on the basis of these data and the fracture toughness values of the interface were evaluated by means of the generalized fracture mechanics principles. Conclusion of the thesis is proof that the interface properties have a significant influence on the fracture behaviour of cementitious composites.

Bulk magnesium materials produced nowadays via powder metallurgy are based on a vastly extensive technological spectrum, which makes it possible to create a wide range of materials. This work focuses on the preparation of bulk materials from magnesium powder by cold pressing and hot pressing, sintering and field assisted sintering. The bulk materials were prepared in a series of compacting pressures from 100 MPa to 500 MPa and the sintering temperatures were selected in the range of 300 ° C to 600 ° C in order to characterize the influence of the manufacturing conditions and technology on the final properties of bulk materials. Prepared materials were evaluated in terms of microstructure, hardness, microhardness, three-point bend test, and fractography. From the hot pressed materials, the samples prepared at 400 and 500 MPa and 400 °C had the highest strength and hardness. The classic sintering of magnesium in the furnace with argon atmosphere proved to be ineffective due to the oxide layer on the surface and the presence of oxygen in technical argon. The SPS sintering (Spark Plasma Sintering) was the more effective with the lower applying pressure used to make the preforms and with the higher applied pressure during the SPS process itself. Highest strength and hardness were achieved in this case of materials sintered at 600 ° C prepared from free powder and the most porous preform (100 MPa). The bulk materials were prepared using all methods used, but the properties of these materials varied considerably depending on the technology used.

This work is focused on the application of advanced elasto-plastic material model intended for shotcrete. Spatial mathematical models of two laboratory tests are created, where this model is used. The first test is a three-point bending concrete specimen. Next, the behavior of the material is analyzed, in which input parameters are entered. Consequently, two reverse analyzes of the available data are analyzed where a match between prediction and measurement can be obtained. The second test is a modified tensile test, where is describe the material behavior in changing of input parameters. Subsequently, reverse data analysis is created, where an acceptable match between prediction and measurement is possible. In every study, the stress waveform in the fracture process zone is analyzed to more detail.

Tato Diplomová práce se zabývá vlivem vyztužení na mechanické vlastnosti materiálu pro přípravu snímatelných náhrad. Pro testování byly použity tři sady vzorků: PMMA pryskyřice, PMMA pryskyřice s Dentapreg Mesh výztuží a PMMA pryskyřice vyztužena zesilující síťkou z nerezové oceli.Pro měření chování vzorků při statickém a dynamickém namáhání byl použit třibodový ohybový test a Charpy rázové kladivo. Viskoelastické vlastnostzi byly měřeny dynamicko-mechanickou analýzou (DMA). Skenovací elektronová mikroskopie (SEM) byla použita k charakterizaci lomových ploch. Během statického namáhání vzorků výztuž nehraje důležitou roli v porovnání s nevyztuženou pryskyřicí. Nicméně byl pozorován opačný trend při dymanickém namáhání, kde efekt výzruže rostl v řadě PMMA pryskyřice – síťka z nerezové oceli – Dentapreg Mesh.

Disertační práce se zabývá mechanickou odezvou vrstevnatých kompozitů pro stomatologické aplikace. Různé skladby vrstev a různé částicové a vláknové kompozity jsou studovány v tříbodovém ohybu za pokojové teploty. Tyto výsledky jsou korelovány s výstupy dynamické termomechanické analýzy (DMTA) a optické analýzy (vysokorychlostní video záznam, SEM). Exeprimentální data byla použita pro srovnání s výsledky analytických a numerických modelů s cílem určit nejvhodnější model pro predikci základních mechanických vlastností vrstevnatých kompozitů. Na základě těchto analýz jsou navržena základní pravidla pro klinické použití vrstevnatých kompozitů ve stomatologických aplikacích jako jsou minimálně invazivní můstky nebo stabilizační dlahy.

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The master thesis is focused on analysis of stress field in the vicinity of stress concentration of stainless steel IPE beam loaded in tree point bending. Theoretical part includes introduction to fracture mechanics with basic terms, principles and variables used to describe fatigue behaviour of material. It concludes teoretical grounds of fracture tests which are future focus of the thesis, methodes used by numerical softwares and methodes used to obtain numerical results. Practical part includes comparision between two and three dimensional numerical models in three point bending, IPE model with different crack front shapes and plastic zone size. Numerical modelling was processed in Ansys Mechanical APDL. Thesis also involves results of experimental testing evaluated using numerical model.

Aerospace research for next-generation travel increasingly focuses on the use of advanced composites to reduce weight and cost while retaining strength. One subset of materials with great potential is based on the combination of resin matrix and glass-fiber reinforcement. This research explores the application of a candidate nanopaper coating with a given composite. Prior research applied a set of given heat fluxes to the top surface of the composite for a set of given periods of time, and subsequently performed a 3-point flexural test to determine the elastic modulus for both the coated and uncoated composite for all of the combinations of heat flux and time. A finite element (FE) model is developed using the ANSYS general purpose finite element analysis (FEA) software that models the degradation in strength/stiffness properties based on heating condition and with the goal of predicting cracking using the element death feature in ANSYS. This thesis describes the prior research suggesting both the need for and novelty of this model, and the procedures used to form the model. The loading conditions of the 3-point flexural test are replicated, and four measures of accuracy are developed based on the force versus displacement curve of the test and the FE model. It is envisioned that continuum-level models developed as a part of these research be applied for design of next-generation space components These measurements are used to verify the FE model, and this model is then employed to extrapolate beyond the context of experimental conditions.

[pt] Materiais feitos com microestruturas arquitetadas possuem propriedades mecânicas ajustáveis e podem ser usados na obtenção de estruturas leves e, ao mesmo tempo, com máxima rigidez. Em estruturas celulares formadas por rede de treliças, por exemplo, pode-se variar o tipo de topologia e porosidade de modo que o material seja eficientemente distribuído no domínio de projeto. Devido às geometrias complexas destas estruturas, projetá-las usando ferramentas de desenho assistido por computador é uma tarefa desafiadora. Neste trabalho, foi desenvolvida uma modelagem paramétrica no programa Rhinoceros usando a extensão Grasshopper para auxiliar na construção de modelos de sólidos celulares com estrutura interna treliçada de densidade variável. A modelagem paramétrica desenvolvida permite definir a topologia e o diâmetro das barras das treliças que simplificam em muito a geração de modelos de sólidos porosos. Modelos de microestrutura foram gerados e fabricados em poliamida 12 por meio de sinterização seletiva a laser para avaliar se é viável imprimir as treliças a partir dos parâmetros estabelecidos. O problema de uma viga biapoiada com carga concentrada no centro foi resolvido utilizando-se o método de otimização topológica e o campo de densidades foi usado para geração do modelo de densidade variável. Considerando a mesma massa final dos modelos otimizados, modelos com densidade constante foram gerados e fabricados juntamente com os modelos de densidade variável. Foram realizadas análises experimentais por meio de ensaios de flexão em três pontos e os resultados mostram que a solução usando densidade variável tem um grande aumento da rigidez quando comparadas com as soluções com densidade uniforme. / [en] Materials made with architected microstructures present tunable mechanical properties and can be used to obtain light structures and, at the same time, with maximum stiffness. In lattice structures, for example, the type of topology and porosity can be varied so that the material is efficiently distributed in the design domain. Due to the complex geometries of these structures, designing them using computer-aided design tools is a challenging task. In this work, a parametric modeling was developed in the Rhinoceros program using the Grasshopper extension to assist in the construction of models of lattice structures with varying truss diameters. The developed parametric modeling allows defining the topology and the diameter of the truss bars, which greatly simplifies the generation of models of porous solids. Microstructure models were generated and manufactured in polyamide 12 through selective laser sintering to assess whether it is feasible to print the trusses from the established parameters. The problem of a simply supported beam with a concentrated load at the center was solved using the topology optimization method and the density field was used to generate the variable density model. Considering the same final mass of the optimized models, models with constant density were generated and manufactured together with the models with variable density. Experimental analyzes were carried out using three-point bending tests and the results show that the solution using variable density has a large increase in stiffness when compared to solutions with uniform density.