Titanium is well known for its excellent properties, such as high strength-to-weight ratio and outstanding corrosion resistance. However the high cost of this metal has confined its applications to those mostly within the aerospace and military industries. The high purchase price of titanium is primarily driven by the need for intricate metal extraction processes, as well as the sensitivity towards conventional metal working operations. Among the potential solutions, powder metallurgy (P/M) technology provides an economical approach to bring down the price of finished titanium products. However, there are still many problems, such as the residual porosity in the sintered body, that need to be overcome. In this thesis, a fundamental study was carried out focusing on the P/M press-and-sinter technique, using commercially pure titanium (CP Ti) as well as two binary titanium alloys, namely Ti-Ni and Ti-Sn. The influence of several processing parameters including compaction pressure, lubricant type/concentration, sintering time/temperature were performed on both the CP and binary systems. The principal tools utilized for mechanical characterization were hardness and tensile testing, whereas optical microscopy, x-ray diffraction (XRD), and scanning electron microscopy were employed to identify the microstructural features present. Press-and-sinter P/M strategies were successfully developed for all of the blends studied. For CP-Ti, a maximum tensile strength >750MPa and near full theoretical density (~99%) were achieved. Transitions in the size and the size distribution of pores and ?-Ti grains were also observed and quantified. It was found these transitions, as well as the powder impurities present (i.e. oxygen and carbon), greatly influenced the final mechanical properties. In the case of the binary alloys, it was shown that liquid phase sintering (LPS) significantly improved the sintered density for the Ti-10%Ni composition, when sintered at l100°C. A eutectic microstructure (CP-Ti + Ti2Ni), coupled with grains of CP-Ti, were identified as the principal phases present. On the other hand, the Ti-Sn alloys only showed a modest increase in sintered density compared to the CP-Ti, owing to the high solubility of Sn in Ti. In terms of crystal structure, XRD highlighted that the Sn containing samples were fully CP-Ti.

This research has investigated the behaviour of synthetic turf pitches for field hockey. A combination of mechanical and perceived data collection methods were used to provide an increased understanding of pitch behaviour. A methodology was developed to elicit perceptions from elite field hockey players. Part of the method was an inductive analysis of players responses during a participant led interview. This enabled the development of a 'structured relationship model' which Illustrated five general dimensions. Each general dimension was part of a hierarchical structure formed from base themes via players responses. Based on characteristics identified in the 'structured relationship model' a questionnaire was designed to quantify the Importance and preferences of certain playing characteristics for elite field hockey players. It was found that players thought 'surface consistency' and 'the ability to demonstrate deft skills' as the most Important surface characteristics it was also identified that given a choice the majority of players would like to play on a fast, low bouncing surface conducive to deft stickwork with 'high' underfoot grip, no ball spin and with a moderate hardness Monitoring during the construction of a world class water-based synthetic turf hockey pitch has shown the influence each layer on the overall pitch system. Novel equipment to the sports Industry was used to evaluate each layer during construction and a large amount of variability was identified across the pitch. it was identified that if the subgrade had a weak area of low stiffness then the subsequent layers above were also vulnerable to low measurements. This highlighted the Importance of quality control during construction A laboratory investigation using a combination of shockpad and carpet samples identified the Influence different systems had on the playing surface. During the investigation testing was conducted on the laboratory floor and in a prepared box constructed to Simulate a 'typical' pitch. it was identified that the layers below the shockpad had little Influence on the measurements. Conditions were monitored and it was identified the Importance water has on the behaviour of the surface lt was found to significantly reduce ball rebound height and rotational traction A series of site investigations using mechanical tests has shown the variability between pitches even at elite standard Six pitches were evaluated and a range of results were obtained and compared with the requirements from the international governing body for field hockey. A correlation between the artificial athlete Berlin and 2.25 kg Clegg impact hammer demonstrated that the Clegg hammer could be a valuable tool for surface assessment. A comparison of players perceptions and the mechanical measurements of six pitches were evaluated. lt was found that the perceived behaviour of ball rebound, underfoot traction and surface hardness correlated well with measured data. However, it was shown that players perceptions of surface pace did not correspond to measurements of ball roll distance. The three main sections of work comprising site data collection, laboratory testing and elicitation of players perceptions have been used together to provide a much greater understanding of the behaviour of synthetic turf pitches for field hockey.

In the process of developing cast iron and cast aluminium components, the co-operation between product development and production is important. On the engineering level, this co-operation is limited already in the product development phase e.g. by the lack of established methods to consider the mechanical behaviour of the completed component. This thesis aims to increase the possibilities for co-operation in the product realisation process between product development and production by enabling the use of predicted local mechanical behaviour in structural analyses of cast components. A literature review on existing simulation methods and a work on characterization of mechanical behaviour from microstructural features are performed to identify important knowledge gaps. A simulation strategy is formulated that is able to predict local mechanical behaviour throughout the entire component and incorporate the behaviour into a Finite Element Method (FEM) simulation of the structural behaviour of the component. In the simulation strategy, the component specific microstructure-based mechanical behaviour is predicted using a casting process simulation. A computer program is developed to create FEM material definitions that capture the local variations in mechanical behaviour throughout the component. The relevance of the simulation strategy is demonstrated for a ductile iron component. It is found that the local variations in mechanical behaviour result in a stress-strain distribution in the component that a homogeneous material description fails to express. Residual stresses affect the mechanical behaviour at low loads. At higher loads, however, the accuracy of the simulation is determined by the local variations in mechanical behaviour. Using a material reduction technique, the local mechanical behaviour can be incorporated without increasing the FEM simulation time.

Avec l’augmentation de la pression de confinement, le comportement mécanique des calcairespasse d’un comportement fragile à un comportement ductile. Le régime fragile estcaractérisé par une compaction élastique suivie d’une dilatance macroscopique due à despropagations de fissures. Lorsque les fissures coalescent, la rupturemacroscopique est reliéeà une chute de contrainte. Le régime ductile est caractérisé par une compaction élastiquesuivie d’une déformation macroscopique diffuse. La déformation est accommodée par uneplasticité intracristalline (dislocations, macles) et/ou une fracturation des grains. L’objectif decette thèse est d’examiner expérimentalement les paramètres influant sur le comportementmécanique des calcaires de porosité intermédiaire et de modéliser ce comportement. Lesexpériences ont été réalisées sur le calcaire de Tavel (porosité de 14.7%). / The mechanical behaviour of limestones is brittle at low confining pressure and becomesductile with the increase of the confining pressure. The brittle behaviour is characterisedby a macroscopic dilatancy due to crack propagation, leading to a stress drop when crackscoalesce at failure. The ductile behaviour is characterised by a a diffuse deformation due tointra-crystalline plasticity (dislocation movements and twinning) and microcracking. The aimof this work is to examine the influence of temperature, pore fluid, strain rate, and time onthe mechanical behaviour. Triaxial deformation experiments were performed on white Tavellimestone (porosity 14.7%). The macroscopic behaviour is then modelled.Constant strain rate triaxial deformation experiments and stress-stepping creep experimentswere performed. Elastic wave velocities were inverted in term of axial crack densities. Themechanical behaviour is brittle for constant strain rate deformation experiments performed atPc · 55 MPa. In this case, inelastic deformation is due to cracks propagation. For Pc ¸ 70 MPa,elastic compaction is followed by an inelastic compaction. Porosity collapse is due to intracrystallineplasticity and micro-cracking. After some inelastic compaction, volumetric strainturns to dilatancy because crack nucleate at dislocation pile-ups and their contribution to thestrain becomes predominant compared to plastic pore collapse. In the brittle regime, watersaturationdecreases the differential stress at the onset of crack propagation and enhancesmacroscopic dilatancy. Temperature decreases the confining pressure at the brittle-semibrittle(ductile) transition. A model describing the macroscopic behaviour is derived from (1) a crackpropagation law, (2) a plasticity law for a porous medium, and (3) a law for nucleation of newscracks due to local dislocation pile-ups. The model predicts the volumetric strain, the stresstensor, and the evolution of damage, as a function of applied deformation. Theoretical resultsare in good agreement with experimental observations.

Dans les travaux de cette thèse, des fibres extraites de la plante de chanvre et des agro-composites polypropylène renforcés par des fibres courtes ont été étudiés. Des essais de caractérisations expérimentales alliés à une modélisation numérique ont permis de comprendre et de déterminer leurs comportements mécaniques en tenant compte des considérations géométriques, des défauts naturels ainsi que la taille des fibres. De part leur nature, les fibres unitaires et les faisceaux de chanvre ont une structure, une forme et une composition complexe influençant leur comportement et leurs propriétés mécaniques. Les études menées dans cette thèse ont montré l’influence des conditions de cultures et de la variété de chanvre sur les propriétés des fibres et des agro-composites. Concernant l’agro-composite, d’autres méthodes expérimentales à la fois optique et macroscopique ont été utilisées pour la caractérisation de son comportement. La méthode de corrélation d’images sous diverses sollicitations mécaniques a mis en lumière l’hétérogénéité du comportement local de ces matériaux, montrant ainsi la non-homogénéité des propriétés mécaniques. Une étude complémentaire a montré l’influence de la répartition des fibres et du processus de fabrication des agro-composites sur l’endommagement et la rupture du matériau / In this thesis, fibres extracted from hemp plant and bio-composites polypropylene reinforced by short hemp fibres was investigated. Experimental studies coupled to numerical modelling have enabled to understand and determined their mechanical behaviour taking into account the geometrical shape, the natural defects and the size of hemp fibres. Microscopic experimental method has enabled to characterize the unitary fibre behaviour independently of fibre bundles. Due to their vegetal origins, hemp unitary fibres and bundles present a complex morphology and structure which have an impact on the mechanical properties of composite. Studies carried out the effect of the growing conditions and hemp variety on the fibre behaviour.For the bio-composite material, optical and macroscopic experimental characterization methods were used in order to determine the behaviour of a polypropylene PP reinforced by hemp fibres. The imaging correlation method is also used to analyse the local behaviour showing the heterogeneity of PP/hemp fibres reinforced material. Moreover, complementary work showed the impact of the fibre distribution and the manufacturing process on the composite properties and the damage initiation and growth

Aujourd’hui, les modèles numériques sont couramment utilisés dans le monde de la recherche, mais aussi de l’industrie, de la santé, de la finance, etc… La qualité du résultat sera toujours liée à la finesse et à la précision avec laquelle l’ingénieur est capable de formaliser les phénomènes physiques rencontrés. Dans le cadre plus spécifique de la modélisation biomécanique, énormément de paramètres rentrent en compte, rendant très compliquée la standardisation des modèles. Cette thèse s’inscrit donc dans une démarche d’amélioration de la qualité des modèles numériques du crâne humain au travers de plusieurs études ayant pour objectif d’analyser les paramètres morphologiques du crâne et de les utiliser pour la personnalisation d’un modèle morpho-mécanique. La méthode de scan par micro-tomographie a été utilisée pour scanner plus de 360 échantillons prélevé sur 10 crânes, puis des essais mécaniques de compression quasi-statiques et dynamiques ont été menés sur une partie de ces échantillons. Les résultats obtenus ont permis de développer une carte d’évolution d’un certain nombre de paramètres morphologiques du crane basés sur un modèle polynomiale. Une étude comparative statistique a permis de mettre en évidences les liens existants entre la morphologie et le comportement mécanique de ces échantillons. Au final, la liaison de ces deux études a permis de proposer un modèle morpho-mécanique personnalisable, puis de le valider pour différentes simulations éléments finis sur des échantillons osseux et sur une voute crânienne complète. / Today, the digital models are usually used in the world of research, but also in industry, health, finance, etc.… The quality of the results will always be connected to the accuracy with which the engineer is able of formalizing the physical phenomena. More specifically in the biomechanical modelling, working with a high number of parameters, making very complicated the standardization of the models. This thesis has an approach of improvement in the quality of the digital models of the human skull through several studies having for aim the analysis of the morphological parameters of the skull and their use for the personalization of a morpho-mechanical model.The method of scan by micro-tomography was used to scan more than 360 samples taken from 10 skulls, and then mechanical tests of compression in quasi-statics and dynamics were led on a part of these samples. The results we obtained allowed us to develop a card of evolution of a number of morphological parameters of the skull based on a polynomial model. A statistical comparative study allowed to highlight the existing links between the morphology and the mechanical behaviour of these samples. Finally, the connection of these two studies allowed to propose a customizable morpho-mechanical model, and to validate it for various finite elements simulations on bones samples and on complete human skull.

The natural soils and sedimentary rocks are typically formed by deposition and progressive consolidation of marine sediments. Consequently, they are characterized by the presence of closely spaced bedding planes, resulting in anisotropy in their mechanical behaviour. Among anisotropic rocks, the group of sedimentary rocks known as shales is of a particular interest as it is often the host rock in nuclear waste storage and oil industry. The Tournemire shales are anisotropic in terms of deformability and the failure mode, which means that complex constitutive models should be used to describe their mechanical response. In this thesis a pragmatic methodology based on the notion of a microstructure tensor, as suggested by Pietruszczak and Mroz (2001), has been employed for the description of orientation dependent characteristics of Tournemire shale. This has been combined with a plasticity framework that incorporates an anisotropic deviatoric hardening. The formulation requires identification of several parameters including strength descriptors associated with the failure criterion and constants that are involved in describing the anisotropy and strain hardening. All the material functions/parameters have been identified here based on the experimental results reported by Niandou et al. (1997). Using those parameters, the numerical simulations of a number of triaxial tests were conducted and the results compared with the experimental data in order to verify the performance of the model. After the verification stage, the formulation was incorporated in a commercial FE code (Abaqus/standard) using the UMAT interface and was then applied to a numerical analysis of a tunnel excavation within the anisotropic rock mass. The numerical results, including the distribution of the damage and vertical/horizontal displacements, have been compared for different orientations of the bedding planes. / Thesis / Master of Applied Science (MASc)

Titanium is a widely applied material in industries and characterized by highly anisotropic mechanical behaviour. To study the special property of titanium, many kinds of mechanical loading tests have been conducted. Moreover, researchers attempted to reproduce these experiments with numerical methods. This paper will present an overview about the deformation mechanisms and related representative studies of titanium. Among the numerical methods, Taylor type and self-consistent crystal plasticity models are two of the most common ones seen in literature. Simulation of some mechanical loading tests using visco-plastic self-consistent model was carried out and compared with the results given by Taylor type model. It has been found that self-consistent model prevails in the reproduction of stress-strain response and texture evolution. During the calculation of self-consistent model, there are totally 4 kinds of self-consistent schemes available for linearization process. The author investigated 4 groups of simulation works using different self-consistent schemes. But no evident distinction has been observed. The application of visco-plastic self-consistent model in commercial purity titanium is studied at the end. The simulation results successfully captured the general features of 9 mechanical loading tests. / Thesis / Master of Applied Science (MASc)

Yes / This paper focuses on monitoring the evolution of lime-clay reactions using geotechnical parameters as a function of lime content and environmental temperature. Lime contents of 5, 7, 9, 11 and 13% by dry weight of expansive clay powder were added to prepare lime-clay specimens. The specimens were prepared at the same dry unit weight of 12.16 kN/m3 and moisture content of 40% except for tests aimed at the determination of dry unit weight as a function of mellowing period. Prepared specimens were mellowed or cured at two different ambient temperatures of 20 °C and 40 °C. Results attained from Unconfined Compressive Strength and permeability tests were employed to assess the impact of lime content on the mechanical and hydraulic properties of lime treated expansive clays. The results revealed that at the beginning, the rate of strength gain is remarkably fast for a particular period of time which is dependent on lime content. Furthermore, the strength gain on specimens cured at 40 °C is 8 times higher than that observed on specimens cured at 20 °C which highlights significant effect for the environmental temperature on accelerating the chemical reactions. Reduced dry unit weight due to increased resistance to compactability is observable with increasing lime content and higher environmental temperature. Accelerated pozzolanic reaction at higher environmental temperature resulted in permeability coefficient of specimens mellowed for 24 h at 40 °C to be higher than those mellowed at 20 °C. The results also highlighted that the permeability coefficient would be relatively stable when expansive clays were treated with small amounts of lime e.g. 5%.

Ce travail de thèse, s'inscrit dans un accord co-tutelle entre l’École Polytechnique de Thiès du Sénégal, et de l'Université de Franche-Comté. Il a été réalisé au Département de Mécanique Appliquée de l'institut FEMO-ST à Besançon (France). [...]L'objectif de cette thèse est de contribuer à la caractérisation du comportement thermo-hygro-mécaniques des fibres libériennes élémentaires issues du chanvre. Les fibres élémentaires testées dans ce travail ont des diamètres extérieurs moyens d'environ 20µm et des longueurs utiles de l'ordre de 10mm. Des essais couplant des chargements mécaniques, hygroscopiques et thermiques sont réalisés afin d'apporter des éléments de compréhension sur le comportement des fibres et de collecter une base de données sur leurs performances mécaniques.Trois types de comportement sont identifiés sur les fibres en traction quasi statique en fluage pour les différents niveaux hygro-thermique testés. Une rigidification de la fibre est révélée sous chargements cycliques progressifs dans des conditions environnementales constantes. Une chute du module d' Young initial de la fibre est remarquée quand l'humidité relative augmente. Une accélération de la vitesse de déformation différée de la fibre est obtenue en fluage lorsque des cycles d'humidité relative sont appliqués. Une baisse des propriétés mécaniques des fibres sous l'effet de la température est également observée. Elle dépend directement du niveau de la durée de l'exposition à la température. / The thesis work joins in the framework in joint supervision between the Polytechnic school in Thies (Sénégal) and the University of Franche-Comté (France)[...]The aim of this thesis is to contribute to the characterization of thermo-hygro-mechanical behaviour of elementary hemp fibres. These fibres used in this work have an average diameter approximately 20µm and useful length of only 10 mm. The méchanical, hygroscopic and thermal coupling testing are realized to provide some understanding of the behaviour of the hemp fibres and to collect details from a database on their mechanical performance.From the uniaxial quasi static tensile tests and creep tests, three categories of behaviours are measured and observed. How ever subject to constant environmental conditions, a fibre hardening is observed under cyclic tensile loading. It was also found that a drop of the initial Young 's modulus of the hemp fibres when the relative humidity gradually increases. Thus, the strain rates measured on the fibres during creep exhibited a speeding up relative humidity cycles are imposed . We found also that the mechanical properties of the fibres decrease under temperature effects. It depends directly on the level and exposure time to temperature