Les matériaux cimentaires tels que le béton, le ciment et le plâtre sont largement utilisés dans la construction, les matières premières dont ils sont faits étant abondantes sur Terre. Cette tendance ne devrait pas changer dans les prochaines décennies. Mais ces matériaux subissent l'impact du fluage. Le fluage des matériaux cimentaires est une problématique complexe. D'une part, dans les matériaux cimentaires, le fluage est souvent couplé avec d'autres phénomènes tels que le séchage, l'hydratation et la fissuration, et peut être influencé par différents paramètres comme la température, le niveau de contrainte, la teneur en eau et la formulation. D'autre part, la mesure du fluage par un test macroscopique traditionnelle du fluage requiert du temps (il est recommandé de réaliser l'essai de fluage du béton sur plusieurs mois afin de donner une caractérisation fiable du fluage à long terme) et s'avère fastidieuse, puisque les paramètres expérimentaux doivent être bien contrôlés sur de longues périodes de temps. Cette thèse étudie la micro indentation à l'échelle de la pâte de ciment ou du plâtre pour évaluer les propriétés de fluage propre à long terme des matériaux cimentaires, en comparant les fonctions de fluage obtenues par des tests de micro indentation de quelques minutes avec celles obtenues par des expériences macroscopiques de fluage réalisées pendant de longues années. Pour la pâte de ciment, la comparaison a été faite à l'échelle du béton à l'aide d'une certaine homogénéisation. L'étude a validé le fait que un test de micro indentation de quelques minutes peut fournir une mesure des propriétés à long terme de matériaux cimentaires. Une fois validée la technique d'indentation, nous avons étudié l'effet de la microstructure (c'est-à-dire la distribution des phases) et celui de l'eau sur le fluage propre à long terme des matériaux cimentaires. L'effet de la microstructure a été étudiée sur des matériaux tels que des pâtes de C3S et de C2S ainsi que sur des compacts de C-S-H synthétique, de portlandite (CH) et leurs mélanges préparés par compression de poudres. Une attention particulière a été consacrée à créer des compacts avec de grandes fractions volumiques de phase cristalline. Pour tous les échantillons examinés, nous avons identifié le bon modèle micromécanique qui permette de prédire les résultats. Le choix du modèle micromécanique concorde avec les observations microstructurales. L'effet de l'humidité relative a été étudié par le conditionnement et l'indentation de certains de ces matériaux (par exemple la pâte de C3S, de compact de C-S-H et de compact de CH) dans différentes humidités relatives allant de 11% à 94%. L'humidité relative a eu un effet significatif sur le fluage : pour tous les matériaux testés, une plus grande humidité a conduit à un fluage plus important. Le compact de portlandite fut le plus sensible à l'humidité relative, sans doute parce que le fluage se produit au niveau des interfaces entre les cristaux de portlandite. Pour la pâte de C3S, une relation simple a été identifiée entre les propriétés de fluage à long terme et la teneur en eau. Enfin, nous avons proposé des modèles micromécaniques qui permettent la prédiction des propriétés de fluage à long terme de matériaux cimentaires avec une large gamme de fraction volumique de phase cristalline et sur une gamme d'humidités relatives étendue / Cementitious materials such as concrete, cement and gypsum are widely used in construction, as the raw materials of which they are made are abundant on Earth. Such trend is unlikely to change in the coming decades. But these materials suffer from creep. The creep of cementitious materials is a complex issue. On one hand, in cementitious materials creep is often coupled with other phenomena such as drying, hydration and cracking, and can be influenced by various parameters such as temperature, level of stress, water content and mix design. On the other hand, measuring creep by traditional macroscopic creep testing is time-consuming (creep test on concrete is recommended to be carried out over several months in order to provide a reliable characterization of long-term creep) and tedious, since experimental parameters need to be well controlled over extensive periods of time. This thesis studied microindentation at the scale of cement paste or gypsum plaster for the assessment of long-term basic creep properties of cementitious materials, by comparing creep functions obtained by minutes-long microindentation testing with those obtained with macroscopic creep experiments which lasted up to years. For cement paste, the comparison was made at the scale of concrete with the aid of upscaling tools. The study validated that minutes-long microindentation testing can provide a measurement of the long-term creep properties of cementitious materials. With the validated indentation technique, we studied the effect of microstructure (i.e., the distribution and the spatial organization of phases) and of water on long-term basic creep of cementitious materials. The effect of microstructure was studied on materials such as C3S pastes and C2S pastes as well as on compacts of synthetic C-S-H, portlandite (CH) and their mixtures prepared by compaction of powders. For all samples considered, we identified the right micromechanical model that allows predicting the results. The choice of micromechanical model was consistent with microstructural observations. The effect of relative humidity was studied by conditioning and testing some of those materials (i.e., C3S paste, compact of C-S-H, and compact of CH) in various relative humidities ranging from 11% to 94%. Relative humidity had a significant effect on creep: for all materials tested, a greater humidity led to a greater creep. The compact of portlandite was the most sensitive to relative humidity, probably because creep occurs at interfaces between portlandite crystals. For C3S paste, a linear relation was identified between long-term creep properties and water content at relative humidities ranging from 11% to 75%.Finally, we proposed micromechanical models that allow predicting long-term basic creep properties of cementitious materials with a wide range of volume fraction of crystalline phase and over a wide range of relative humidities

Recent work has shown the capability of spherical nanoindentation to capture local structure-property relationships in polycrystalline cubic metals by measuring indentation stiffness and yield strength from stress-strain curves as a function of the local microstructure in the indentation zone. However, these protocols capture structure-property relationships at only one level of the material hierarchy (e.g., single grains). Thus it is still very difficult to infer bulk structure-property relationships using these indentation protocols, which is mainly due to a lack of understanding indentation length scale effects and the important role played by structural hierarchy (i.e., unique structural features at different length scales). It is the goal of this work to extend these protocols to systematically study length scale effects of mechanical properties (e.g., indentation stiffness and yield strength) in titanium alloys. Alpha-beta titanium alloys were chosen because they display a rich variety of two phase microstructures and structural hierarchy and are well documented in literature. Firstly, nanoindentation protocols are extended to characterize the elastic and plastic anisotropy of a hexagonally close packed metal (alpha titanium in commercially pure and alloy Ti-6Al-4V) and a two phase microstructure (alpha-beta colony in Ti-6Al-4V). Secondly, spherical microindentation stress-strain protocols are developed and employed to characterize polycrystalline volumes in three titanium alloys (commercially pure, Ti-6Al-4V, and Ti18). The results of these major advances in indentation protocols and systematic study of length scale effects on the mechanical properties in Ti-6Al-4V will be presented and discussed along with applications demonstrating their high throughput nature to rapidly explore alloy development.

Liquid Metal (LM) Composites are a rapidly expanding field within function materials research. Composed of isolated LM droplets dispersed in an elastomer, these composites can exhibit properties that include electrical conductivity, thermal conductivity, and programmable and anisotropic mechanical properties. Microindentation is a material characterization technique that can be used to study the micron-scale droplet-droplet interactions between the inclusions in these composites. Because most microindentation systems are incapable of producing plastic/elastic deformation volumes large enough to measure the interaction between inclusion and matrix or inclusion and inclusion in these systems, a specialized microindenter is designed and detailed here. The indenter is then used to test various droplet size, spacings, and matrix material combinations to view the mechanical and electrical implications of these variables. These materials were analyzed with a basic fracture energy scaling formula. It was also found that resistivity can decrease by up to seven orders of magnitude after droplet rupture, with as little as a 20μm elastomer film separating droplets before rupture. Continued studies of these phenomena will allow us to exploit the properties of these materials in new and interesting ways. / Master of Science / When a metal which is a liquid at room temperature (eutectic gallium-indium) is dispersed inside a soft, stretchable material such as a silicone rubber, it creates a unique functional material. These materials go beyond their typical uses by having new and exciting properties such as the ability to conduct heat and electricity. Not only do these materials have these properties, but we can also control them through specific manufacturing steps. These materials are called liquid metal composites or liquid metal embedded elastomers. These materials can be used to create flexible wiring for soft electronics and robots which can bend and stretch to suit their environment. One component of the interactions that lead to these properties is the interaction between pairs of droplets of liquid metal inside of the silicone. To study these interactions, we utilize micro-indentation which produces very small and precise deformations in a material. By slowly pressing on the material, and measuring forces, displacements, and electrical resistance, we can gain a closer insight into how the interactions of droplets and rubber produce these properties. These materials can be modeled using an analysis of fracture energy, and pairs of droplets decrease electrical resistance by over 10 million times when droplets combine. By studying these interactions, we gain a greater sense of how to control the properties of these materials, and can create new wearable devices that can bend and stretch with the human body's movements.

Les systèmes barrières thermiques protégeant les aubes de turbine sont des multicouches constitués d’une couche céramique isolante appliquée sur un superalliage par l’intermédiaire d’une couche de liaison qui, dans les systèmes actuels est à base de NiAl(Pt). Pour en comprendre et décrire le comportement thermomécanique, il est nécessaire de connaître le comportement de chaque couche, en particulier celui de la couche de liaison dont le rôle est critique. Nous avons employé une technique originale, la microindentation instrumentée à chaud (jusqu’à 850°C), pour obtenir des informations sur le comportement mécanique de matériaux de couches de liaison. Il a fallu d’abord fiabiliser le dispositif pour minimiser les effets d’oxydation et caractériser la stabilité thermique pour s’assurer de la validité et la reproductibilité des résultats. Un second volet a consisté à mettre en place une méthode de traitement de données et une méthode d’analyse inverse des résultats associant une approche analytique et une simulation de l’essai par éléments finis. Les essais menés sur des matériaux massifs élaborés sous forme de couples de diffusion pour explorer une large gamme de compositions ont permis de déterminer la loi de comportement élastoviscoplastique du composé NiAl(Pt) sous forme [bêta] et sous forme martensitique. Des propriétés mécaniques ont été également été déterminées sur les composés NiAl(Ru) et NiAl(Zr) envisagés pour des systèmes futurs. L’influence des divers éléments (Al, Pt et Ru) a pu ainsi être mise en évidence. Finalement des essais ont été effectués sur des couches de liaison de barrière thermique et les résultats corrélés à ceux obtenus sur matériaux massifs / Thermal barrier systems, which protect turbine blades, are multilayers constituted of an insulating ceramic layer applied on a metallic bondcoat itself in contact with the superalloy substrate. A widely used bondcoat is composed of a NiAl(Pt) compound. In order to understand and describe the thermomechanical behaviour of such systems, it is required to know the mechanical behaviour of each layer, in particular that of this bondcoat whose role is critical for maintaining the integrity of the systems. In this study, we have employed an original technique – high temperature instrumented microindentation, up to 850°C – to extract information on the mechanical behaviour of bondcoat materials. A preliminary phase consisted in improving the experimental procedure - in particular to minimise oxidation phenomena - and in characterising the thermal stability of the equipment at high temperature to ensure the reliability, validity and reproducibility of the results obtained. We have then developed a systematic data treatment and an inverse problem analysis combining analytical approaches and a FEM simulation of the experiment to extract a mechanical behaviour law of the materials investigated. Tests performed on bulk diffusion couples, selected to explore a wide range of compositions representative of aging bondcoats, permitted to extract an elastic viscoplastic behaviour law of NiAl(Pt), both in the B2 phase and in the martensitic phase. Some mechanical properties could also be determined on NiAl(Ru) and NiAl(Zr) systems. Finally the results of a few tests performed on thermal barrier bondcoats could be correlated with the results obtained on bulk materials

De nos jours, l’étude biomécanique des structures osseuses représentent un enjeu pour différents domaines: accidentologie, prise en charge des pathologies osseuses, confort des personnes âgées, conception de prothèses innovantes, etc. Le but de cette thèse est de fournir des valeurs de référence représentatives de la qualité de l'os enfant en caractérisant des propriétés mécaniques et morphométriques du tissu osseux en croissance à différentes échelles. Les propriétés mécaniques ont été mesurées à 2 échelles différentes – mésoscopique et microscopique – selon 2 modalités expérimentales – spectroscopie à résonance ultrasonore et microindentation. Un autre volet de cette thèse concerne le développement d’une procédure d’analyse morphométrique adaptée au tissu osseux pour le traitement d’images obtenues par micro-tomographie (RX). Mieux connaître le tissu osseux juvénile est indispensable pour développer des modèles dédiés et ainsi mieux comprendre les mécanismes pathologiques caractéristiques de l'os en croissance (fracture en bois vert) pour améliorer le diagnostic et adapter les choix thérapeutiques pour les jeunes patients. / Nowadays, the biomechanical study of bone structures is a challenge for different fields: accidentology, management of bone pathologies, comfort for the elderly, design of innovative prostheses, etc. The aim of this thesis is to provide reference values representative of the quality of child bone by characterizing the mechanical and morphometric properties of growing bone tissue at different scales. Mechanical properties were measured at 2 different scales - mesoscopic and microscopic - in 2 experimental modalities – resonant ultrasound spectroscopy and microindentation. Another part of this thesis concerns the development of a morphometric analysis procedure adapted to bone tissue for the treatment of images obtained by micro-tomography (RX). A better knowledge of juvenile bone tissue is essential to develop dedicated models and thus better understand the pathological mechanisms characteristic of growing bone (greenstick fracture) to improve diagnosis and adapt therapeutic choices for young patients.

Cementitious materials such as concrete, cement and gypsum are widely used in construction, as the raw materials of which they are made are abundant on Earth. Such trend is unlikely to change in the coming decades. But these materials suffer from creep. The creep of cementitious materials is a complex issue. On one hand, in cementitious materials creep is often coupled with other phenomena such as drying, hydration and cracking, and can be influenced by various parameters such as temperature, level of stress, water content and mix design. On the other hand, measuring creep by traditional macroscopic creep testing is time-consuming (creep test on concrete is recommended to be carried out over several months in order to provide a reliable characterization of long-term creep) and tedious, since experimental parameters need to be well controlled over extensive periods of time. This thesis studied microindentation at the scale of cement paste or gypsum plaster for the assessment of long-term basic creep properties of cementitious materials, by comparing creep functions obtained by minutes-long microindentation testing with those obtained with macroscopic creep experiments which lasted up to years. For cement paste, the comparison was made at the scale of concrete with the aid of upscaling tools. The study validated that minutes-long microindentation testing can provide a measurement of the long-term creep properties of cementitious materials. With the validated indentation technique, we studied the effect of microstructure (i.e., the distribution and the spatial organization of phases) and of water on long-term basic creep of cementitious materials. The effect of microstructure was studied on materials such as C3S pastes and C2S pastes as well as on compacts of synthetic C-S-H, portlandite (CH) and their mixtures prepared by compaction of powders. For all samples considered, we identified the right micromechanical model that allows predicting the results. The choice of micromechanical model was consistent with microstructural observations. The effect of relative humidity was studied by conditioning and testing some of those materials (i.e., C3S paste, compact of C-S-H, and compact of CH) in various relative humidities ranging from 11% to 94%. Relative humidity had a significant effect on creep: for all materials tested, a greater humidity led to a greater creep. The compact of portlandite was the most sensitive to relative humidity, probably because creep occurs at interfaces between portlandite crystals. For C3S paste, a linear relation was identified between long-term creep properties and water content at relative humidities ranging from 11% to 75%.Finally, we proposed micromechanical models that allow predicting long-term basic creep properties of cementitious materials with a wide range of volume fraction of crystalline phase and over a wide range of relative humidities

La prise en compte du développement des couches de corrosion d'armature dans les calculs de durée de vie d'ouvrage en béton armé nécessite une bonne connaissance des propriétés mécaniques de ces produits. Ce travail est consacré à la caractérisation des propriétés mécaniques de ces couches de produits de corrosion. L'approche adoptée consiste en une identification des propriétés de la microstructure complétée par des calculs d'homogénéisation en élasticité linéaire afin de calculer un comportement mésoscopique des couches de produits de corrosion. L'étude comprend une série de campagnes expérimentales à l'échelle de la microstructure. Des essais de microindentation Vickers analysés par une approche de modèle de mélanges gaussien ont permis l'acquisition de duretés et modules d'élasticité locaux. Une analyse des principaux composants est réalisée par microspectrométrie Raman. L'étude à l'échelle microscopique fournit les informations morphologiques et mécaniques nécessaires aux calculs d'homogénéisation en élasticité linéaire. La première approche a consisté en des calculs d'homogénéisation des milieux aléatoires par des schémas autocohérent et autocohérent généralisé. Dans une deuxième approche, et d'après les hétérogénéités importantes observées pour la microstructure qui ne présente pas de motif régulier, des calculs de modules effectifs ont été réalisés en employant la méthode des éléments finis sur des images 2D prises au microscope optique. Le corpus étant composé d'échantillons de provenances et d'âges divers, leurs microstructures ont été comparées

The aim of this study is to investigate the deterioration in mechanical integrity of the collagen network in bovine bone with aging, which are related to fracture toughness. Age-related changes in collagen molecular structures formed by non-enzymatic glycation were examined and indentation fracture technique was used as a method for measuring the microstructural toughness of cortical bone. Microcrack propagation characteristics of bone for fragility were also studied. Young and old group of bovine cortical bone specimens were grouped into 2 as ribosylated and non-ribosylated which were rested in solutions for four weeks. Series of indentations were made on bone specimen groups for each of five masses 10g, 25g, 50g, 100g and 200g for 10 sec to detect the effect of applied indentation load. The applied load was increased to 300g, 500g, 1000g and 2000g for 10 sec to be able to make microcracks. Series of indentations were made on bone specimen groups for each of five durations 5sec, 10sec, 20sec, 30sec for 100g to study the effect of indentation duration. Specimens were examined in the wet and dry state while studying the factors effecting microhardness measurement. Microhardness values measured by 10g of load for 10sec were indifferent between the ribosylated and non-ribosylated groups in the young and old bovine bone pointing that this load is not indicative of the structural collagen changes. Loads of 25g, 50g, 100g and 200g for 10 sec were able to differ ribosylated bone from non-ribosylated bone for the young and old bovine bones. Degree of microhardness increased with increased incubation period. Microhardness of dry specimens being either ribosylated or non-ribosylated were found to be statistically higher than wet specimens in young and old bone except for 10g for 10sec. It has been shown that the calculated fracture toughness measured by the indentation method is a function of indentation load. Additionally, effect of indentation size might have resulted in a higher toughness measurement for higher indent loads with longer cracks even if the toughness is not actually higher.Methods using indentation technique has difficulty in relating the resistance to crack growth to the Mode I fracture toughness definition.Indentation fracture toughness allows sampling only one point on the R&shy / curve methods and was not considered as successful for assessing materials with rising R&shy / curve. Toughness is ranked incorrectly among riboslated and non-ribosylated bovine bone by this technique. Presence of extrinsic toughening mechanisms including crack bridging due to uncracked ligaments and collagen fibers were directly observed by scanning electron microscope. Ribosylated bone was found to have lower number of collagen bridging compared ton on-ribosylated bovine bone.As a summary, indentation fracture method by Vickers indentation in bone is a method for measuring the fracture toughness.

The nanostructure, physical properties and mechanical performance of C-S-H, 1.4 nm tobermorite, jennite, and ettringite were studied. C-S-H of variable stoichiometries was examined as a model system in comparison with that produced in the hydration of Portland cement. The current Master’s thesis is comprised of four research papers designed to improve the current understanding of the nanostructure and engineering properties of C-S-H systems and modified C-S-H systems. Many of the controversial issues in cement science were identified and were addressed in a comprehensive research study, which examined the key features of the C-S-H systems at the nano-structure level. In Chapter 4, each paper presented new evidence for a number of mechanical aspects of C-S-H materials. Numerous advanced analytical tools were used in order to verify the observations made in each section. The major achievements of the current work are mentioned briefly as follows: 1. It was determined that microindentation is a useful method for determining the creep behavior of C-S-H of various stoichiometries, 1.4 tobermorite, jennite, and ettringite. 2. Microindentation parameters i.e. creep modulus, indentation modulus and indentation hardness are porosity dependent. 3. Microindentation creep measurements on C-S-H (C/S = 0.80 and 1.20) demonstrated that creep modulus, indentation modulus, and indentation hardness are all dependent on mass-loss from the 11%RH condition. 4. Evidence was presented that the nanostructural role of interlayer water in C-S-H has a significant influence on the creep process.

Fiber sizings are used to improve the performance of fiber-reinforced polymer composites made from low-cost fiber and matrix materials. Evaluation of three sizings, poly(vinylpyrrolidone) (PVP), a carboxyl modified polyhydroxyether (PHE), and a standard industrial sizing (G'), have revealed tremendous improvements in static mechanical and enviro-mechanical properties. The focus of this work is to determine if these improvements in performance can be ascertained from a micromechanical test for interfacial shear strength (IFSS) on as-processed materials. The accomplishment of this goal would create more information with fewer experiments and a need for less experimental materials. In this study, a nanoindenter uniquely outfitted with a blunt tip is effectively used to obtain microindentation results where the debond load is extracted directly from the experimental load-deflection curve. Shear lag and finite element analyses are used to evaluate the mechanics of the system, but both methods show limitations with regard to determining interfacial stresses in an experimental system. In the results obtained, the PHE and Gâ materials outperform the PVP in IFSS, but the bulk properties for PVP and PHE outperform the Gâ material, suggesting the presence of another dominant mechanism. Despite better retention of bulk properties after hygrothermal exposure, PHE experiences degradation in IFSS that PVP does not. The PHE loses 10% of its original IFSS after 576 hours of 65ºC moisture exposure, while PVP improves by 25%. The tensile strengths for PHE and PVP decrease 7% and 10% respectively at 576 hours exposure. Finite element modeling shows that matrix swelling due to moisture absorption increases interfacial shear stresses, a finding supported by a comparison of wet and dry specimens subjected to equivalent aging times. Matrix swelling is not, however, responsible for the increase in IFSS of the PVP material. The relationship between tensile strength and IFSS proves to be small as predicted by a tensile strength model, but processing defects and other failure processes that are not included in the tensile strength model appear to have strong influences over the experimental results. IFSS is important in composite materials, but in the case of the G', PHE and PVP materials, other factors dominate fiber direction tensile performance. Therefore, this one simple micromechanical test provides significant insight into the composite material behavior, but it does not provide the same magnitude of information as from bulk composite experiments. / Master of Science