Dissertations / Theses on the topic 'Syntacic foams'

While hollow glass microspheres are commonly used in syntactic foam, their abrasive and brittle properties usually result in poor processability and have adverse effects on the foam performance. Therefore, a number of attempts have been made in the industry to replace hollow glass microspheres with polymeric foamed microspheres. Among many choices, expandable thermoplastic (ETP) microspheres filled syntactic foam has shown its high potential to become a novel class of engineering materials, especially for lightweight structural applications. However, conventional processing techniques for syntactic foam usually experience difficulties such as high processing viscosity, low loading of foam fillers, and ineffective microsphere expansion. To address these emerging issues, a microwave expansion process to produce thermoset-matrix syntactic foam containing thermoplastic foam beads was developed in this thesis work. In this process, unexpanded ETP microspheres were directly foamed in uncured thermoset matrix via microwave heating. Expandable polystyrene (EPS) microspheres and epoxy resin were chosen as a model material system. The resin viscosity and specific microwave energy are found to be the two primary control parameters determining the process window. Mechanical characterization showed that the syntactic foam can outweigh neat polymer in lightweight structural applications and was effectively toughened by foamed EPS. Furthermore, the microwave expansion process was found to be capable of molding syntactic foam parts of relatively sophisticated geometry with smooth surfaces. In order to broaden its impact, the microwave expansion process was extended to produce composite EPS foam. This process converts an expandable suspension into a composite foam with a honeycomb-like barrier structure. The suspension viscosity was found to highly influence the foam morphology. Results from mechanical tests showed that the existence of the barrier structure can considerably improve the mechanical performance of the composite foam. Fire-retardation tests demonstrated that the barrier structure can effectively stop the fire path into the foam, suppress toxic smoke generation, and maintain foam structure integrity. A general formulation was developed to model the EPS expansion to optimize the microwave expansion process. A semi-analytical solution was first obtained based on the case of a single bubble expansion in an infinite matrix. The dimensionless bubble radius and pressure are defined and found to be as exponential functions of dimensionless expansion time. The semi-analytical solution can qualitatively predict the radial expansion of EPS microsphere observed in a real-time experiment. To have an accurate prediction, a numerical solution was obtained to the model that couples the nucleation and expansion of multiple bubbles in a finite matrix. The results show that the numerical solution can quantitatively predict the radial expansion of EPS. A parameter sensitivity study was performed to examine the effect of each parameter over the expansion process.

In this study, aluminium matrix syntactic foams reinforced with several types of ceramic micro-sphere were produced by pressure infiltration. The mechanical properties of a range of aluminium matrix syntactic foams were investigated in order to optimise the composition and structure to find the best configuration in terms of high energy absorption capability, and to validate the finite element predictions against the corresponding experimental results. Initially, the compressive behaviour of six different types of aluminium matrix syntactic foam was evaluated. It was shown that the size of the ceramic micro-spheres, the grade of the aluminium matrix and the volume fraction of the aluminium matrix all have a significant influence on the compressive strength and energy absorption capability of the material. Then, the three-point bending and shear fracture properties of aluminium syntactic foams were evaluated. These tests indicated that density plays an important role in determining the stiffness, specific energy absorption and ultimate flexural strain. Here, it was found that the specific energy absorption related to shear was lower than that corresponding to flexure. Following this, the behaviour of the syntactic foams under low velocity impact was characterised and the underlying failure mechanisms were identified to evaluate their effective mechanical performance. It was found that the aluminium syntactic foams subjected to drop-weight impact have 20–30% higher plateau values than samples subjected to the equivalent level of quasi-static compression. Subsequently, the Split Hopkinson Pressure Bar technique was used to investigate the behaviour of the material at high strain-rates, which highlighted the material sensitivity of aluminium syntactic foams under high strain-rate loading. Following this, terminal ballistic tests were conducted to determine the perforation resistance of the aluminium syntactic foams. The results showed that the syntactic foams have the ability to prevent the perforation of projectile velocities up to 120 m/s. Finally, blast tests were performed to investigate the influence of the charge mass and sample thickness on the dynamic response of the syntactic foams. The results showed that syntactic foams with a thickness of 14 mm have the capability to sustain a blast load of 4.82 Ns. Finite element models were developed to simulate the structural behaviour of aluminium syntactic foams subjected to various quasi-static and dynamic loads. Here, an elasto-plastic model with both ductile and shear failure criteria was employed to predict the material performance. The rate-dependent response of the foam was considered by a stress-ratio based model to take strain-rate effects into account. The numerical simulations were compared with their corresponding experimental results with reasonably good correlation. In general, the essential features of the aluminium syntactic foams tested under different loading regimes were captured by the FE models, including load-displacement traces, deformation and failure modes.

Syntactic foams-composite materials consisting of hollow particles embedded in a host matrix-have many applications for manufactured products, including weight reduction, thermal insulation, and noise reduction. In this thesis, a certain variety of syntactic foam is investigated with regards to reducing fluid borne noise in hydraulic systems. Such a foam maintains stiffness at low hydrostatic pressures and becomes compressible as pressure increases. With this compressibility, the foam is potentially useful as a liner for a reactive noise control device, much like compressed gas style devices currently in use; but the syntactic foam additionally adds significant damping to the system. In order to predict device performance, a linear multimodal model is developed of a hydraulic suppressor, constructed as an expansion chamber lined with a syntactic foam insert. Material models are developed for various compositions of the foam liners, based on an inverse analysis matching the model to experimental results. Two model simplifications are considered, and it is found that a simplified bulk modulus model gives sufficiently accurate results to make approximate predictions of suppressor performance. Several optimizations are performed to predict the optimal material composition for hydraulic excavator work cycles. To help compare the prototype suppressor against commercially available bladder style suppressors, a model is developed for the bladder style silencer and is validated experimentally. Overall, this work both demonstrates the current and potential utility of syntactic foam as a device lining material, and contributes new models to the hydraulics noise control community.

Hollow glass microspheres have been used extensively in the automotive and marine industries as an additive for reducing weight and saving material costs. They are also added to paints and other materials for their reflective properties. They have shown promise for weight critical applications, but have thus far resulted in materials with low fracture toughness and impact resistance when combined with thermosetting resins in syntactic foam. The advent of commercially available microspheres with a wide range of crushing strengths, densities and adhesive properties has given new impetus to research into syntactic foam with better fracture behaviour. Current research suggests that the beneficial effects on fracture and impact resistance gained by the addition of solid reinforcements such as rubber and ceramic particles are not seen with the addition of hollow glass microspheres. The research presented in this paper has examined the mechanisms for fracture resistance in glass microsphere filled epoxy (GMFE) syntactic foams, as well as determined the effect microsphere crushing strength and adhesion strength has on the material???s fracture toughness. The flexural properties of various GMFE have also been determined. GMFE were manufactured with varying microsphere volume fraction up to 50%, and with variances in microsphere crushing strength and adhesion. The specimens were tested for Mode I fracture toughness in a three point single edge notched bending setup as described in ASTM D5045 as well as a three point flexural setup as described in ASTM D790-3. Fracture surfaces were inspected using scanning electron microscope imaging to identify the fracture mechanisms in the presence of microspheres. Results indicate a positive effect on fracture toughness resulting from new fracture areas created as tails in the wake of the microspheres in the fracture plane. Results also indicate a negative effect on fracture toughness resulting from weak microspheres or from interfacial disbonding at the fracture plane. These two effects combine to show an increase in GMFE fracture toughness as the volume fraction of microspheres is increased to between 10 ??? 20% volume fraction (where the positive effect dominates), with a reduction in fracture toughness as microspheres are added further (where the negative effect dominates).

L'installation de conduites pétrolières par la méthode de dépose en déroulé induit une flexion qui entraîne la rupture brutale de leur revêtement d'isolation thermique.Le matériau critique du revêtement est une mousse syntactique de polypropylène. Cette étude consiste à caractériser la réponse et la rupture de ce matériau sous divers états de contrainte. L'évolution de sa microstructure a été suivie emph{in-situ} en cours de déformation grâce à de la tomographie au synchrotron. Les mécanismes de décohésion sphères-matrice suivis de la coalescence avec les craquelures dans la matrice ont été mis en évidence pour amener à la rupture du matériau. Ces mécanismes ont été pris en compte dans la modélisation du comportement mécanique par une loi de comportement élasto-viscoplastique ajoutée de la porosité comme variable interne. Une modélisation fine par un procédé multi-échelles a permis de simuler l'évolution de la microstructure en lien avec une réponse macroscopique cohérente avec les données expérimentales. Les simulations numériques d'essais de laboratoire ont été utilisées pour identifier le maximum de la plus grande contrainte principale comme paramètre de chargement qui permet de localiser l'amorçage de la fissure. Des diagrammes associant ce paramètre de chargement à la vitesse de déformation locale ont été établie, selon la température d'essai. Ces diagrammes ont ensuite été comparés, avec succès, aux données issues d'essais de flexion sur tubes où le revêtement a rompu. Ainsi , la transférabilité des résultats des éprouvettes de laboratoire aux structures industrielles a donc été validée
The installation of oil&gaz pipelines using the reel-lay method induces bending which leads to a rapid cracking of their thermal insulation coating.The critical coating material consists of a syntactic glass polypropylene foam.This study deals with a comprehensive characterization of the mechanical response and the failure of this material under various stress conditions.The evolution of its microstructure was observed thanks to emph{in-situ} tensile tests using synchrotron tomography.The mechanisms of decohesion of microsphere-matrix, followed by coalescence with crazes in the matrix were highlighted, leading to the failure of the material.These mechanisms were taken into account in the constitutive relationships using an elasto-viscoplastic model with porosity added as an internal variable.Fine modelling using a multi-scale process was used to simulate the evolution of the microstructure in relation to the macroscopic response, which was consistentwith experimental data.Numerical simulations of laboratory tests were used to identify the maximum of the largest principal stress as a load parameter allowing the localization of the crack initiation.Temperature dependent diagrams associating this load parameter with the local strain rate were established.These latter diagrams were then successfully compared with data from bending tests on tubes where the coating had failed.The transferability of the results from laboratory tests to engineering structures was therefore validated

Excessive fluid-borne noise in hydraulic systems is a problem the fluid power industry has long struggled to address. Traditional noise control devices such as Helmholtz resonators, tuning coils, and Herschel-Quincke tubes are generally too large for fluid power systems unless the speed of sound in the device can be reduced. A compliant lining can achieve this effect, but compliance (and lossy compliance) has had little attention in noise control in general, and in fluid power in particular. One means to achieve compliance in these devices, especially at elevated pressures, is through a liner made of syntactic foam, which in this case is a urethane host matrix with embedded hollow, polymer microspheres. The material properties at elevated pressure are unknown by the liner manufacturer, but are known to be pressure- and temperature-dependent. Therefore, the effect of hydrostatic pressures from 2.1-21 MPa and temperatures from 20-45 C on the liner properties, thus the device performance, are studied. For a Helmholtz resonator, a theoretical model is fit to experimentally-measured transmission loss of the device using a least-squares routine, which solves the inverse problem for the complex bulk modulus of the liner. These material properties are used to compare a predictive model of a tuning coil to experimental data, and in a parameter study of a Herschel-Quincke tube. The compliance of the liner is found to lower the effective sound speed by an order of magnitude and decrease the volume of the cavity of a Helmholtz resonator by up to two orders of magnitude. This work is expected to result is more compact noise control devices for fluid power systems.

Syntactic foams are hollow particles-filled lightweight composites that are widely used in areas that require high strength while maintaining low weight and density. These foams are highly tailorable materials whose properties can be altered during the manufacturing process by changing various parameters like matrix and microballoon material type, size, distribution, as well as the volume fraction and wall thickness of microballoons. Therefore, understanding the effect of these parameter changes in the behavior of syntactic foams is very important to manufacture the foam for different applications. In the present study, syntactic foams of various volume fractions of microballoons were fabricated and different mechanical testing was conducted to study their elastic and viscoelastic behavior. Moreover, density, void content, and microstructure of the syntactic foam with varying volume fractions of microballoons were also studied to better characterize these foams. Results show that changes in the volume fraction of the microballoons had a significant impact on the elastic and viscoelastic behavior of the foams. The introduction of the microballoons into the epoxy resin decreased the density of the epoxy resin by up to 43.36% and at the same time increasing the specific modulus by up to 21.059%. In addition, representative 3D models of these syntactic foams were also developed to further study the elastic behavior of these materials which were found to be in good agreement with the experimental results. These findings will help in designing and optimizing the material properties of the syntactic foam required for different applications.

Les mousses polymères trouvent de nombreuses applications industrielles en tant qu’isolants thermiques, matériaux de structuration ou atténuateurs de choc. En effet, il s’agit de matériaux légers, possédant un excellent rapport masse / rigidité, et demandant de faibles coûts de production.Une des applications envisagées par le CEA est la protection de structures face à des chargements mécaniques générés lors d’irradiations laser ou lors d’impacts de débris micrométriques.L’objectif principal de cette thèse est d’évaluer la capacité d’atténuation d’une mousse expansée en polyuréthane rigide et d’une mousse syntactique à matrice époxy face à des sollicitations dynamiques extrêmement rapides (> 106 s−1) et intenses (> 10 GPa). Des essais quasi-statiques de compression / décompression et des expériences dynamiques ont ont été réalisés pour analyser le comportement de ces deux mousses pour des vitesses de déformation allant de 10−3 à 106 s−1. L’analyse des résultats expérimentaux montre que ces mousses polymères ont une phase de comportement élastique suivie d’une phase de compaction conduisant à des déformations irréversibles importantes. Les seuils de compaction sont estimés à 9 MPa pour la mousse polyuréthane et 30 MPa pour la mousse époxy en régime quasi-statique, et à 21 MPa pour la mousse polyuréthane et 72 MPa pour la mousse époxy lorsque la vitesse de déformation dépasse 104 s−1. Deux modèles physico-numériques sont développés pour représenter le comportement macroscopique de ces mousses à de telles vitesses de déformation. Les paramètres sont identifiés à partir des résultats d’expériences de compression dynamique (lanceur `a gaz, générateur de pression magnétique). La validité des modèles est testée en comparant les profils de vitesse calcul´es à l’aide d’un code dynamique explicite et les profils de vitesse mesurés lors des expériences. Ces modèles sont ensuite utilisés pour analyser les résultats obtenus lors d’expériences d’irradiation par faisceau d’électrons et de choc laser. Nous démontrons ainsi que les mousses polymères étudiées ont une forte capacité d’atténuation et que les modèles proposés sont valides à grande vitesse de déformation
Polymeric foams are widely used in many industrial applications as thermal insulators, structural materials or shock mitigators. Indeed, they are light weight materials with an excellent weight /stiffness ratio and low production costs. One of the applications which interests the CEA is the protection of structures against mechanical loadings generated by laser irradiation or high velocity impact of small debris.The main objective of this PhD thesis is to investigate the mitigation capability of an expanded polyurethane foam and an epoxy syntactic foam against extremely fast (> 106 s−1) and intense(> 10 GPa) dynamic loadings. Cyclic quasi-static tests and dynamic experiments have been performed to investigate the behavior of these two foams for strain rates ranging from 10−3 to 106 s−1. Analysis of the experimental results shows that these polymeric foams have an elastic behavior phase followed by a compaction phase with significant permanent sets. Compaction thresholds are about 9 MPa for the polyurethane foam and 30 MPa for the epoxy foam under quasi-static loadings and around 21 MPa for the polyurethane foam and 72 MPa for the epoxy foam for strain rates above 104 s−1.Two porous compaction models are developed to represent the macroscopic behavior of these foams for such strain rates. The parameters are identified from the results of dynamic compression experiments (gas gun, low inductance generator). The validity of the models is tested by comparing calculated velocity profiles with an explicit hydrocode and velocity profiles measured during the experiments. These models are then used to analyze the results obtained with electron beam irradiation and laser-driven shock experiments. We demonstrate that the studied polymeric foam shave high mitigation capabilities and that the models are valid for high strain rates

Utilisation de diverses approches pour analyser l'influence de la microstructure sur le comportement mécanique d'une mousse syntactique constituée de microbilles de verre creuses et de résine époxyde. Adaptation au modèle de Hashim. Exposition d'un modèle micromécanique. Application de la loi de Weibull. Loi d'évolution de l'endommagement

L’étude se situe dans le cadre de la recherche de gains de performance de structures d’isolations passives pour l’offshore profond. Le travail proposé a pour support des analyses expérimentales et numériques de tubes revêtus par des matériaux isolants utilisés en eau profonde pour transporter du fluide chaud. Le raboutage des tubes en acier, préalablement revêtus en atelier, nécessite un dégagement du revêtement aux extrémités pour réaliser l'opération d'assemblage (généralement par soudure). La partie dégagée est ensuite recouverte par un nouveau matériau pouvant être appliqué sur site. Ainsi l’isolation de cette partie du tube (Field Joint), qui est soumise à des chargements thermomécaniques en service, doit être optimisée pour assurer une durée de vie compatible avec les contraintes de l’exploitation offshore en eau profonde. Le travail comporte principalement quatre parties : - la modélisation du comportement thermique pour analyser l’évolution en temps et en espace de la température du matériau au cours de la fabrication, de la pose et en service sachant que pour les matériaux d’isolation le comportement mécanique est fortement dépendant de la température,- une partie expérimentale pour l’analyse du comportement des matériaux isolants en fonction de la température et en fonction de la pression hydrostatique qui est le principal chargement mécanique de ces structures en service,- la modélisation du comportement mécanique des isolants,- et une partie modélisation et simulation du comportement en service d'assemblages multi-matériaux de type industriel, avec prise en compte du comportement non-linéaire des constituants
Ultra deep offshore oil exploitation presents new challenges to offshore engineering and operating companies. Such applications require the use of pipelines with an efficient thermal protection. Passive insulation materials are commonly used to guarantee the thermal performance of the pipes, and syntactic foams are now the preferred material for this application. The mechanical behaviour of such insulation materials is quite complex, associating time-dependent behaviour of polymers with damage behaviour of glass microspheres. In order to allow an optimisation of such systems, while ensuring in-service durability, accurate numerical models of insulation materials are thus required. During the service life in deep water, hydrostatic pressure is the most important mechanical loading of the pipeline, so this study aims to describe the mechanical behaviour of the material under such loading. Using a hyperbaric chamber, the analysis of the evolution of the volumetric strain with time, with respect to the temperature, under different time-evolutions of the applied hydrostatic pressure is presented in this paper. Such experimental results associated with the mechanical response of the material under uniaxial tensile creep tests, allow the development of a thermo-mechanical model, so that representative loadings can be analysed

In der Arbeit wird die Entwicklung einer Herstellungstechnologie für Hohlkugeln (HK) und Schalen mit ihrem anschließenden Einsatz als Füllgut in einem syntaktischen Schaum mit Polymermatrix dargestellt. Die Technologie basiert auf einem Übergangsprozess der Erstarrung einer Zinnschmelze, in dem die Gestaltsgebung von HK durch die Wirkung eines Gasmediums stattfindet. Eine entsprechende Pilot-Anlage mit der Steuerung der Druck- oder Temperaturwerte wurde aufgebaut und unter verschiedenen technologischen Bedingungen getestet. Es wurde ein theoretisches Druck- und Temperaturmodell, die als Steuerfunktionen genutzt werden können, vorgeschlagen. Während der Entwicklungsstufe wurden die Konstruktion und die Simulation der relevanten physikalischen Prozesse durchgeführt und mithilfe von Nebenversuchen verifiziert. Zur qualitativen und quantitativen Bewertung der ermittelten Ergebnisse ist die statistische Versuchsplanung herangezogen worden. Anschließend sind die Erzeugnisse metallographisch und röntgenographisch untersucht worden.

The use of nano and microfillers in research and industrial areas have been increasing in recent decades. In material industry especially, the combination of specific nano and microparticles properties has been studying since they can offer a great contribution to the resolution of tough issues. One of these issues is the possibility to disassemble components for repairing, recycling or avoiding waste when errors occur in manufacturing processes. The disassembly of mechanical component is still an open issue and there are many technical problems that are involved in this process. For example, the possibility to have a clean surface of the separated component after the disassembly or the possibility to introduce damages to other linked components. This dissertation investigates the possibility to disassemble a hot-melt adhesive, used in automotive industries to join plastic components, by embedding iron nanoparticles, Fe3O4, that are sensitive to electromagnetic induction. This peculiarity makes the modified adhesives able to melt when an electromagnetic field is oriented on it and so the joint separation is possible. The mechanical and physical properties of these nanomodified adhesives, with different particles concentrations of iron oxide, were studied and compared with the pristine adhesive. This correlation was necessary in order to assess the possibility to use these modified adhesives in the vehicle assemblies since the pristine adhesive is already used by some car manufacturers for internal and external components. Separation tests of plastic joints were evaluated and the most sensitive factors were stated and analysed. The shape of the inductor coil, the diameter of the pipe coil, the frequency of the applied magnetic field and the applied current were found to be influencing factors of the induction heating process. The possibility to use cheaper particles, iron microparticles coupled with electromagnetic induction, together with the possibility to bond composite, glass fibre-reinforced plastics (GFRP), substrates were assessed as well. Composite components have been replacing many structural and non-structural components in automotive design in order to reduce the vehicle weight. The opportunity to disassemble adhesive with graphene nanoparticles embedded in the same hot-melt adhesive and coupled with microwave was assessed as well. The heating of this particles is possible by means of the π electron mechanism In recent decades, researchers and industries have been also investigating the possibility to make a material electrically conductive. In this PhD dissertation, the possibility to make a structural epoxy resin electrically conductive have been discussed as well. In order to make the material electrically conductive, different coatings of glass spheres with conductive GnPs were tried, as well, but in these cases, the coating results was not satisfactory. For these reasons the chosen filler concentration for these tests was set at 1% (volume fraction) for the conductive filler and 30% (volume fraction) for the hollow glass spheres. These were the maximum concentration that it was possible to embed in the epoxy matrix in order to obtain an easy processability of the material. The modified epoxy resins were not conductive they showed interesting mechanical properties especially under compressive load.

Les mousses syntactiques créées par l’association d’une matrice élastomère et de microsphères à paroi souple possèdent des propriétés acoustiques amortissantes intéressantes. Elles ouvrent de nouvelles perspectives dans la fabrication de sous-marins furtifs ou de navires, mais le principal frein à l’industrialisation de ces mousses est leur compressibilité : à haute profondeur, les mousses écrasées perdent leurs propriétés amortissantes. Nous nous intéressons donc à l’étude du renforcement de mousses syntactiques à matrice polyuréthanes. La littérature scientifique étant peu abondante sur ce sujet, une mousse syntactique modèle a été synthétisée en laboratoire pour permettre une meilleure caractérisation de ce matériau et de ses composants. En particulier, un moyen innovant de compression hydrostatique a été mis au point pour caractériser le comportement sous pression des microsphères et de la mousse. Les paramètres matériaux recueillis ont permis d’utiliser un modèle de la littérature qui a simulé l’influence de divers paramètres sur la compression de mousses syntactiques. Ce modèle a également pu prévoir les caractéristiques des composants d’une mousse dont la compressibilité répondrait à un cahier des charges préétabli. Ces différentes analyses ont démontré que le principal paramètre régissant la compression de mousses syntactiques est le module d’Young de la matrice. De plus, un renforcement en compression n’est obtenu qu’avec un renforcement chimique de la matrice ; la présence de charges (fibres, nanotubes de carbone) n’apporte pas de changements significatifs
Syntactic foams synthesized from an elastomeric matrix and soft-shell microspheres have shown interesting acoustical properties. They open new perspectives for the manufacturing of stealthy submarines or ships, but the industrialization of such material is held back by their great compressibility: hydrostatic pressure tends to crush the microspheres, which leads to a loss of the damping properties. We are therefore interested in studying the reinforcement of syntactic foams with polyurethane matrix. Scientific literature being scarce on this subject, a reference syntactic foam has been synthesized in the laboratory to allow a better characterization of this material and its components. In particular, an innovative test of hydrostatic compression has been developed to characterize the behavior under pressure of the microspheres and foam. A model of the literature simulating the compression of syntactic foams has been used thanks to the material parameters collected; it allowed us to test the influence of various parameters on this compression. This model could also predict the characteristics of the components of a foam whose compressibility would meet a set of specifications. These different analyses have shown that the main parameter governing the compression of syntactic foams is the Young's modulus of the matrix. In addition, a compression reinforcement can only be obtained using a chemical reinforcement of the matrix; the presence of fillers (fibers, MWCNTs) does not bring significant changes

Les matériaux aujourd'hui utilisés pour l'isolation thermique en milieu aquatique sous pression hydrostatique sont soit des mousses souples à base de caoutchoucs, soit des mousses rigides, notamment syntactiques, selon la profondeur. Ces matériaux souples ont été analysés par des tests mécaniques et thermiques classiques. Cependant, les protocoles et valeurs relevées ont été adaptés à l'usage final du produit, et plus particulièrement à l'environnement aquatique en surface et en profondeur. Les relations entre les différentes caractéristiques (structures et propriétés) de ces matériaux ont été étudiées afin de définir les propriétés adéquates selon des critères pertinents. Pour mettre en évidence les propriétés thermiques sous pression hydrostatique, un outil de test a de plus été développé : une enceinte de test hyperbare innovante, pour l'évaluation de la résistance thermique et de l'épaisseur sous pression d'eau entre 0 et 50 m de profondeur. Les points forts et faibles des matières classiquement utilisées ont été clairement établis. L'analyse de ces résultats a permis d'identifier un concept de matériau composite propre à l'usage défini. Une matière innovante a été conçue en fonction : une mousse syntactique. En variant le type de particules additionnées à une matrice thermoplastique élastomère, la structure cellulaire a été affinée pour obtenir un comportement identique en milieu aquatique, en surface comme en profondeur. En parallèle de sa production industrielle, cette matière a été testée afin d'identifier les relations entre structures et propriétés
Materials nowadays used for thermal insulation in aquatic environment under hydrostatic pressure are either rubber flexible foams or rigid foams, especially syntactic foams, depending on depth. These flexible materials were analyzed through classical mechanical and thermal tests. However, methods and results were adapted to the final usage of the product, particularly to the aquatic environment at the surface and under depth. Relationships between structures and properties characteristics were studied to define appropriate properties within relevant criteria. Moreover, to underline thermal properties under hydrostatic pressure, a testing instrument has been developed: an innovating hyperbaric test chamber, dedicated to under water pressure thermal resistance and thickness measurements, from 0 to 50 m depth. Strengths and weak points of these classical materials have been clearly established. Results analysis lead to a new concept of composite material for the defined usage. This innovating material, a syntactic foam, has been developed. By varying the particle type added to a thermoplastic elastomer matrix, the cellular structure has been refined in order to obtain a similar behaviour in aquatic environment, at the surface like in depth. This material has been tested, parallel to its industrial production, to identify relationships between structures and properties

Le projet de la thèse a consisté au développement et à l’évaluation des performances d’une mousse syntactique phénolique pour la réalisation d’un système sandwich multicouche (cœur/peau en matériau composite). Il permet d’assurer la protection thermique, mécanique et au feu en particulier contre l’impact d’un feu torche. Un feu torche peut survenir sur un site pétrochimique suite à l’inflammation d’une fuite de fluides inflammables sous pression pouvant être très dévastateur par son effet abrasif et le flux convectif et radiatif intense. Le travail s’est essentiellement axé sur l’étude de l’efficacité de la mousse syntactique phénolique à partir d’une analyse de la relation microstructure-propriété. Les exigences de mise en œuvre ont imposé une maîtrise de la formulation par une bonne compréhension de la réactivité de la résine, notamment par rapport aux différentes transformations physiques (gélification, vitrification) qui ont lieu pendant le processus de réticulation. Il s’agit alors d’optimiser le dosage des différents composés actifs et additifs vis-à-vis des contraintes de mise en œuvre afin de parvenir à des propriétés optimales du matériau final. L’efficacité de ce dernier dans les conditions normales d’utilisation a été déterminée par une phase d’expérimentation complète sur ses propriétés mécaniques, thermiques et thermomécaniques. Des tests au feu ont permis d’étudier son comportement au feu afin de vérifier ses propriétés protectrices sous l’impact d’une flamme issue d’un feu torche. Enfin, un essai instrumenté capable de reproduire en condition réelle une fuite de gaz de propane à haute pression a été mis au point pour évaluer la performance au feu torche d’un prototype industriel complet. En parallèle, un modèle numérique simplifié a été proposé afin de simuler l’impact d’un tel feu
This work consisted in the development and the evaluation of a phenolic syntactic foam performance for the production of a multilayer sandwich system (core/skin in composite material). It ensures thermal, mechanical and fire protection, in particular against the impact of a jet fire. A jet fire can occur on a petrochemical site resulting from the combustion of a fuel continuously released under pressure. It can be very devastating for its abrasive effect and intense convective and radiative flux. The work focuses mainly on the study of the effectiveness of the phenolic syntactic foam through the analysis of the relationship microstructure-propriety. The manufacturing process requirements imposed to control the elaboration via a good understanding of the reactivity of the resin, especially in relation to various physical transformations (gelation, vitrification) that take place during the curing mechanisms. That involves optimizing the proportions of the various active compounds and additives depending on the working conditions in order to achieve optimal properties of the final material. The effectiveness of this final material under normal conditions of use was determined by a complete testing phase on its mechanical, thermal and thermomechanical properties. Fire tests were also conducted to investigate the material burning behavior to ensure its protective properties under a jet flame impact. Finally, a large-scale instrumented test, reproducing in real conditions a propane gas leak at high pressure, was developed to evaluate the resistance to a jet fire of a complete industrial prototype. In parallel, a simplified numerical model was also proposed to simulate the impact of such a fire

Dans le cadre de la conception d'engins de recherche et d'exploitation en mer, profonde, nous nous interessons aux poutres composites a noyau leger gaine. Le noyau est constitue d'une mousse syntactique. La gaine est une enveloppe composite stratifiee. Cette etude comprend principalement deux grandes parties; une modelisation theorique et une analyse experimentale. La partie theorique est basee sur les hypotheses de navier-bernouilli pour les problemes de flexion et celles de vlassov pour les problemes de torsion et prend en compte les deformations de cisaillement introduites en valeurs moyennes entre deux sections droites voisines. Ce modele assure egalement la continuite des deplacements entre le noyau et la gaine. Nous modelisons un element "p. C. N. L. G" et nous introduisons les conditions aux limites, notamment des forces de liaison aux noeuds de cet element pour etablir la relation matricielle de comportement par l'application du principe des puissances virtuelles. L'analyse experimentale a pour objet de caracteriser les materiaux constituant la structure et de qualifier sur des modeles dits de "validation" le modele theorique dont on vient de definir les grandes lignes. L'element "p. C. N. L. G" permet d'analyser les structures en lignes ou des structures spatiales, necessitant neanmoins et ulterieurement la realisation d'un element de junction assurant l'assemblage des elements poutres. Les applications de cette etude peuvent etre developpees dans la conception des flotteurs, des tubes, des engins, etc. . .

Etude du vieillissement de polymeres renforces ou non de fibres de verre ou de mousses syntactiques immerges dans l'eau sous des pressions de 0 a 300 bars. Adsorption d'eau, proprietes mecaniques, eclatement des microspheres dans les mesures syntactiques

Research Doctorate - Doctor of Philosophy (PhD)
Advanced manufacturing of metal matrix syntactic foams (MSFs) is the focal point of the present thesis. In particular, the manufacturing of low-cost materials for potential commercialisation. The thesis investigates a novel pre-compaction process for the counter-gravity infiltration technique. This manufacturing step allows the casting of expanded perlite-aluminium syntactic foam with densities ranging from 0.74 to 1.06 g/cm³, without the changing of raw materials. The way in which the infiltration casting process influences the material properties of MSF is further analysed in contrast to the stir casting technique. Finally, the influences of filler particles and the metal matrix on the manufacturing and properties of MSF are compared. The choice of manufacturing technique influences the morphology of the foam. While infiltration casting yields open-cell morphologies, stir casting yields closed-cell MSF. The closed-cell morphology significantly improves strength. The open-cell morphology is mainly caused by low particle wettability and occurs because of a lack of infiltration of inter-particle voids. The wettability is influenced by the outer structure of the filler particles. Particles with an outer shell have an increased contact surface, which lowers the wettability between ceramic particles and melt. The tested porous particles (expanded glass and expanded perlite) have low mechanical strength and do not contribute significantly to the strength of the MSFs. Their benefit is in having lower prices than other established filler materials, such as synthetic hollow spheres. They are thus very attractive for future large-scale processes. This work further examines the influence of the matrix material on the manufacturing and the properties of the MSFs. Aluminium exhibits high specific strength and is affordable but shows limitations if exposed to loads at high temperatures. Zinc has the benefit of lower processing costs arising from a lower melting point but lacks in terms of achievable densities and is slightly more expensive than aluminium. This thesis introduces novel manufacturing techniques and contributes to the broader understanding of lightweight MSFs.

Highly damage tolerant hybrid syntactic foams are developed by using polydimethylesiloxane (PDMS) particles to modify the matrix microstructure in syntactic foams. Two different types of glass hollow particles (microballoons) with different densities are used to fabricate the foam samples. In this study, the effect of PDMS particle size (45μm, -200μm) at different volume fractions (3%, 5%, 7%and 10%) is being studied. First the volume content of filler is being optimized. The total volume of fillers is maintained at 40% in plain and hybrid syntactic foams. The plain and hybrid syntactic foams are characterized for mechanical properties. An increase in toughness is observed with the incorporation of PDMS in syntactic foams. The strength of micro balloons plays an important role in determining the fracture mode of plain and hybrid syntactic foams. Silicon microspheres are found to increase the energy absorption under the flexural loading conditions.

In this investigation, polymer precursor of syntactic foam has been reinforced with SiC nanoparticles to enhance mechanical and fracture properties. Derakane 8084 vinyl ester resin was first dispersed with 1.0 wt% of SiC particles using a sonic cavitation technique. In the next step, 30.0 wt% of microspheres (3M hollow glass borosilicate, S-series) were mechanically mixed with the nanophased vinyl ester resin, and cast into rectangular molds. A small amount of styrene was used as dilutant to facilitate mixing of microspheres. The size of microspheres and SiC nanoparticles were 20-30 um and 30-50 nm, respectively. Tension, compression, and flexure tests were conducted following ASTM standards and a consistent improvement in strength and modulus within 20-35% range was observed. Fracture toughness parameters such as KIC and GIC were also determined using ASTM E-399. An improvement of about 11-15% was observed. Samples were also subjected to various environmental conditions and degradation in material properties is reported
by Debdutta Das
Thesis (M.S.C.S.)--Florida Atlantic University, 2009
Includes bibliography
Electronic reproduction. Boca Raton, Fla., 2009. Mode of access: World Wide Web

Research Doctorate - Doctor of Philosophy (PhD)
In the last two decades a great deal of research has been focused on the development and characterisation of metallic foams for special purpose applications. Due to their high strength to weight ratios and highly porous structures, metallic foams have unique energy absorption, damping, and thermal properties. However, these materials have not yet been widely used in industry, simply because of their higher costs when compared to their polymeric competitors in the market. In recent years, researchers have shown considerable interest in metallic syntactic foams, which are produced by embedding hollow or porous low density heat resistant particles in a metallic matrix. Owing to their relatively simple manufacturing processes, metallic syntactic foams have lower costs when compared to other foams. However, the typical aluminium syntactic foams have significantly higher densities (reportedly more than 1.4 g/cm³). This is mainly due to the high densities of the filler particles (typically more than 0.6 g/cm³) and the failure of particles during the manufacturing process. In this thesis, the major limitations of the metallic syntactic foams, i.e., their high densities and relatively high costs, are addressed by introducing a novel light porous filler material, Expanded Perlite (EP). A large volume fraction of internal porosity (≥95%) reduces the density of this natural volcanic glass down to only 0.18 g/cm³. Being mined in large quantities, to the author’s knowledge EP has the lowest price when compared to its competitors. The large particle size range, from 300 μm to 6 mm, allows for the simple, cost efficient manufacture of foams with the desired properties. EP/A356 aluminium syntactic foams were successfully fabricated using a melt infiltration technique. Depending on the manufacturing parameters, the densities of the foams may vary between 0.7 and 1.05 g/cm³, which are the lowest among the typical syntactic foams. The produced foams were then subjected to a wide range of microstructural, structural, and mechanical testing for a comprehensive characterisation of the material. With a special focus on the energy absorption capabilities of the foams, attempts were made to improve the mechanical responses of the foams by adjusting their structures and microstructures. Heat treatment, a smaller EP particle size, and a higher sphericity of the particles were shown to be effective parameters which increase the mechanical strength and energy absorption capacities of the foams. The positive strain rate sensitivity of the compressive properties makes this foam attractive for crash cushioning applications. The foams also showed outstanding performances under cyclic compressive loading conditions. Following the major characterisations, an application of EP/aluminium syntactic foam, as the core of hollow steel tubes, was investigated. The compressive and bending properties of the foam filled tubes improved considerably when compared to empty tubes. A second novel filler material, with a higher density and crushing strength than those of expanded perlite, was employed for the manufacture of high strength syntactic foams, while maintaining a low price. Syntactic foams with a density of 1.5 g/cm³ were made by the infiltration of packed beds of pumice, a natural porous volcanic glass with a particle density of 0.75 g/cm³, with molten aluminium. The pumice/aluminium syntactic foams showed a 35% increase in their energy absorption capacities when compared to the EP/aluminium syntactic foams.

Research Doctorate - Doctor of Philosophy (PhD)
The graded structure of porous materials has attracted increasing research attention recently. Their tailored structure allows mechanical properties to be controlled throughout their deformation. In fact, the properties change selectively along one direction of a functionally graded material. The gradient in porous metals is also beneficial for some engineering applications, such as biomedical implants and energy absorbers in construction and automotive industries. Metal syntactic foams (MSFs) are considered a promising energy absorber material. Creating any gradient in the structure of MSFs permits controlling their energy absorption capability at different deformation stages. Therefore, it is essential to explore functionally graded metal syntactic foams (FG-MSFs), a novel material, to broaden the knowledge about the metallic foams field and their graded structures. The current study focuses on FG-MSFs to explore their processing as well as to investigate their physical and mechanical properties. For this purpose, various approaches, including the spatial arrangements of different filler particles, the partial pre-compaction of particles and the integration of the foam with a metal tube are considered to create a gradient in either the longitudinal or the radial directions of MSFs through the counter-gravity infiltration casting technique. Then, the mechanical properties of the FG-MSFs are determined according to ISO 13314. The deformation mechanisms of these samples are investigated through light photography and IR-thermal imaging under quasi-static and dynamic loadings, respectively. In addition, the cycling loading of the FG-MSFs is examined to determine their fatigue behaviour. The mechanical properties of uniform MSFs are also investigated and compared with those of FG-MSFs to identify differences between them. This study also characterises the physical properties of the manufactured FG-MSFs to determine the fraction of the matrix, particles and voids in their structures. Their physical properties provide a vision for comparing FG-MSFs with other engineering materials.

abstract: Due to increasing integration of renewable resources in the power grid, an efficient high power transmission system is needed in the near future to transfer energy from remote locations to the load centers. Gas Insulated Transmission Line (GIL) is a specialized high power transmission system, designed by Siemens, for applications requiring direct burial or vertical installation of the transmission line. GIL uses SF6 as an insulating medium. Due to unavoidable gas leakages and high global warming potential of SF6, there is a need to replace this insulating gas by some other possible alternative. Insulating foam materials are characterized by excellent dielectric properties as well as their reduced weight. These materials can find their application in GIL as high voltage insulators. Syntactic foam is a polymer based insulating foam. It consists of a large number of microspheres embedded in a polymer matrix. The work in this thesis deals with the development of the selection proce-dure for an insulating foam for its application in GIL. All the steps in the process are demonstrated considering syntactic foam as an insulator. As the first step of the procedure, a small representative model of the insulating foam is built in COMSOL Multiphysics software with the help of AutoCAD and Excel VBA to analyze electric field distribution for the application of GIL. The effect of the presence of metal particles on the electric field distribution is also observed. The AC voltage withstand test is performed on the insulating foam samples according to the IEEE standards. The effect of the insulating foam on electrical parameters as well as transmission characteristics of the line is analyzed as the last part of the thesis. The results from all the simulations and AC voltage withstand test are ob-served to predict the suitability of the syntactic foam as an insulator in GIL.
Dissertation/Thesis
Masters Thesis Electrical Engineering 2014

The present work is focused on the synthesis and study of the deformation behavior of epoxy resin/glass microballoonbased syntactic foams. Different densities syntactic foams with 0 to 40 volume percentages of glass microballoons were prepared by stir-casting method for the present investigation. The high viscosities of the resin-microballoons mixture (putty like consistency) beyond 40 volume percentage prevents processing of higher microballoon content syntactic foam. The effect of glass microballoon content on tensile, compression, flexural and impact properties were studied in detailes. The results show that specific tensile strengths of the foam was increased by about 34% along with the reduction in density (by about 38%), starting from pure resin to foams with 40% glass microballoon. It is also found that compressive strength of the foam decreases from 140 MPa (for pure resin) to 75 MPa (with 40 vol.% reinforcement). During tensile loading, deformation occurs predominantly through shear yielding of the resin matrix followed by debonding at the matrix-microballoon interface. The crushing of the glass microballoons and subsequent densification of the foams is responsible for large amount of plastic strain during compressive deformation. The erosion behavior of the syntactic foam is also investigated as a function of the different glass microballoons content. Three different erodent velocities (48, 70, 82 m sec-1) and three different angles of impingement (30o, 60o and 90o) are used as experimental parameters in the present investigation. The erosion rate is found to be highest for 40 vol.%reinforcementas compared to pure resin due to presence of larger amount of hollow glass microspheres.

Research Doctorate - Doctor of Philosophy (PhD)
Advanced porous materials are a new group of materials where the desired properties can be controlled and even tailored. These interesting materials offer a vast field of applications, thanks to their multi-functional abilities. Several types of advanced porous structures including cellular metals and ceramic porous materials are the focus of the present investigation. Corevo® foam and perlite metallic syntactic foam are investigated in this thesis and manufactured from infiltration casting. In addition, advanced pore morphology foam elements are addressed that are fabricated using thermal expansion of a thin wire-shaped precursor. Ceramic porous structures specially developed (via foam replication) for tissue engineering scaffolds are also studied within the scope of this work. Given the similarity of the geometrical structure of all these materials, the same mechanical characterisation approaches are adopted to assess their mechanical properties. The materials properties are determined for quasi-static and dynamic compression for both small and large strain deformation. Numerical simulations are performed by making use of the highly accurate models obtained from micro-computed tomography data. Where possible, numerical results are verified by the findings of experimental testing. Detailed analysis is included in each chapter elaborating the result from the numerical simulations and the compressive loading test. Versatile tools such as electron microscopy, image based geometry analyser software and IR-thermal imaging are utilised to assist the study. The results show that all cellular metals investigated in this thesis exhibit the characteristic stress-strain curve of metallic foams. This means that a linear slope is found in the beginning of the compression loading, this is followed by a long plateau region indicating energy absorption capability and ends with a steep slope at the end representing the densification. Corevo® foam exhibits a significant amount of mechanical anisotropy in casting direction under quasi-static compressive loading. The degree of mechanical anisotropy is considered mild for perlite metallic syntactic foam in the casting direction under the same loading condition. Foam materials (Corevo® and advanced pore morphology foam element) characterised under dynamic loading show a strain-rate dependence property. Last, but not least, a possible extension of the present research is proposed at the end of this thesis in the Conclusions and Outlook section.

The aim of the present thesis is to explore sustainable low cost environmentally friendly composite materials. It is a step by step experimental research. Firstly, taking under consideration the so far commercial available non-organic materials used as reinforcement and the petroleum based resins used as matrices, composite materials were fabricated and mechanically characterized. Different components in micro- and nano- scale were combined. Afterwards, the non-organic materials used as reinforcements were substituted by different types of non conventional natural-based fillers. The fillers (corn starch and olive pit granules) were in powder form, derived from agricultural local resources and additionally flax fabric used to produce laminated composites. All the semi-green epoxy composites were characterized by means of three-point bending testing. Moreover, the manufactured composites were induced in several sources of damage and their residual properties were extensively investigated. More precisely, the effect of the strain-rate and low velocity impact as well as of thermal fatigue, on the mechanical properties of the olive pit and the flax fabric reinforced resin was studied. Since, conventional and semi-green composite materials were fabricated and experimentally investigated, the final objective of the present thesis was to produce novel green composites materials by substituting the petroleum-based epoxy resin with a biodegradable derived from natural resources biopolyester. In order to accomplish this target, polylactic acid (PLA) was combined with olive pits in powder form at different concentrations. Olive pits, is almost unknown non-traditional filler to composites, obtained during the oil extraction process. It is a raw material characterized by its low cost and its abundance, since it consists a waste product of the olive oil industry. In order to successfully accomplish this part of research, experiments were taken place in France at the CMGD (Centre des Matériaux de Grande Diffusion) Institute of the École Nationale Supérieure des Mines d’ Alés, under the guidance of Prof. A. Bergeret within the framework of research cooperation with the main supervisor of this thesis, Prof. G. Papanicolaou. The most important feature of the present green composites is their satisfactory mechanical and thermal performance in combination with their complete biodegradability. The PLA/olive pit composites could be applied to various components with moderate strength such as automotive interiors, interior building applications, durable goods, serviceware and food packaging material The aim of this part of the study was to investigate the effect of three types of olive pit powder at different weights fractions on the physical and mechanical properties of polylactide (PLA) matrix composites. For the preparation of the powder, two different grinding procedures were applied, producing three types of olive pit powder. Various measurements were accomplished to determine characteristics such as the density and the size distribution and the shape of the powder. Different PLA/ olive pits powder composites were manufactured by extrusion and injection molding. A comparative study between the different composites was made in order to investigate the matrix-filler interactions, occurring between the PLA and olive pit granules and their overall physical, mechanical and thermomechanical properties were investigated by means of TGA, FT-IR, DSC, SEM, flexural and uni-axial tensile testing. Finally, theoretical predictive models were applied in most of the composite materials manufactured in the present work. These models making use of minimal number of experimental results can satisfactorily predict the residual properties of damaged materials, irrespectively of the type of the material investigated and the damage source. Namely, the Modulus Predictive Model (ΜPM), the Residual Properties Model (RPM) and the Residual Strength after Impact Model (RSIM), have been successfully applied. A big number of interesting conclusions have been derived from the present work. However, a general conclusion is that a totally green composite with useful properties and applications is a promising target for the humanity and the planet survivability.
Σκοπός της παρούσας διδακτορικής διατριβής είναι η κατασκευή και μελέτη συνθέτων υλικών χαμηλού κόστους ενισχυμένων με φυσικά υλικά, φιλικά προς το περιβάλλον. Η επίτευξη αυτού του στόχου πραγματοποιήθηκε σταδιακά. Αρχικά, πραγματοποιήθηκε μια εκτεταμένη μελέτη διαφορετικών συνθέτων υλικών τα οποία ήταν εξ’ ολοκλήρου κατασκευασμένα από ανόργανα και συνθετικά υλικά. Γι’ αυτό το σκοπό κατασκευάστηκαν και μελετήθηκαν οι μηχανικές ιδιότητες συνθέτων υλικών που έχουν ως μήτρα μια εμπορικά διαθέσιμη πετροχημική εποξειδική ρητίνη. Η εποξειδική ρητίνη ενισχύθηκε με ανόργανα υλικά σε μικρο- (συμπαγή και κενά σφαιρίδια γυαλίου) και νανο- (νανοσωλήνες άνθρακα πολλαπλού τοιχώματος) διαστάσεις. Στη συνέχεια, βασιζόμενη στο ήδη υπάρχον επιστημονικό υπόβαθρο, καθώς η μεταπτυχιακή μου εργασία ειδίκευσης ήταν στο ίδιο ερευνητικό πεδίο με το αντικείμενο της διδακτορικής μου διατριβής, γίνεται προσπάθεια περαιτέρω εξέλιξης της έρευνας που σχετίζεται με την μελέτη και κατασκευή συνθέτων φιλικών προς το περιβάλλον. Ως εκ τούτου, το επόμενο στάδιο της πειραματικής μελέτης στα πλαίσια εκπόνησης της διατριβής αυτής, ήταν η κατασκευή και χαρακτηρισμός, ως προς την μηχανική τους συμπεριφορά, συνθέτων υλικών πολυμερικής εποξειδικής μήτρας ενισχυμένης με διαφορετικού τύπου φυσικές ενισχύσεις και περιεκτικότητες. Οι φυσικές ενισχύσεις που επιλέχθηκαν να μελετηθούν ήταν τόσο σε μορφή κόκκων και μικρο-ινών, όσο και σε μορφή υφάσματος. Τα εγκλείσματα που χρησιμοποιήθηκαν ήταν σκόνη από κόκκους ελαιοπυρήνα και σκόνη αμύλου καλαμποκιού. Στα σύνθετα υλικά ενισχυμένα με κόκκους ελαιοπυρήνα, έγινε μελέτη της επίδρασης των διαφορετικών ρυθμών παραμόρφωσης στις μηχανικές τους ιδιότητες, ενώ στα σύνθετα υλικά ενισχυμένα με την σκόνη αμύλου μελετήθηκαν εκτενώς οι στατικές μηχανικές τους ιδιότητες. Επιπλέον, κατασκευάστηκαν πολύστρωτα σύνθετα υλικά χρησιμοποιώντας για τις διάφορες στρώσεις ύφασμα από ίνες λιναριού. Τα πολύστρωτα σύνθετα υλικά χαρακτηρίστηκαν ως προς τις μηχανικές τους ιδιότητες, υποβλήθηκαν σε θερμική κόπωση και υπέστησαν κρούση χαμηλής ενέργεια. Οι εναπομένουσες μηχανικές ιδιότητες των υλικών αυτών μελετήθηκαν τόσο πειραματικά όσο και θεωρητικά. Ο απώτερος στόχος αυτής της διδακτορικής διατριβής ήταν να γίνει η δυνατή η κατασκευή συνθέτων υλικών τα οποία να είναι πλήρως βιοδιασπώμενα και φιλικά προς το περιβάλλον. Για το σκοπό αυτό, το τρίτο και τελευταίο στάδιο της έρευνας που διεξήχθη στα πλαίσια της παρούσας διατριβής, ήταν η κατασκευή εξολοκλήρου φυσικών συνθέτων υλικών έχοντας ως μήτρα ένα βιοδιασπώμενο πολυεστέρα φυτικής προέλευσης, το πολύ (γαλακτικό οξύ), ενισχυμένο με σκόνη από κόκκους ελαιοπυρήνα. Ο ξηρός ελαιοπυρήνας που χρησιμοποιήθηκε, αποτελεί μέρος των αποβλήτων που προκύπτουν από την διαδικασία παραγωγής ελαιολάδου. Ο ελαιοπυρήνας σε αυτή την μορφή έχοντας μηδαμινό κόστος απαντάται σε εξαιρετικά μεγάλες ποσότητες και σε σημαντικό ποσοστό εναποτίθεται στους περιβάλλοντα χώρους των μονάδων παραγωγής του ελαιολάδου. Η ερευνητική εργασία που σχετίζεται με αυτό το αντικείμενο του διδακτορικού έλαβε χώρα στην Γαλλία στο École Nationale Supérieure des Mines d’ Alés, στο ερευνητικό ινστιτούτο CMGD (Centre des Matériaux de Grande Diffusion) υπό την επίβλεψη της καθηγήτριας A. Bergeret, στα πλαίσια ερευνητικής συνεργασίας του επιβλέποντα καθηγητή Γ. Παπανικολάου και της ερευνητικής του ομάδας. Τα πειράματα που διεξήχθησαν στο ερευνητικό ινστιτούτο CMGD, περιελάμβαναν αρχικά την προετοιμασία των κόκκων του ελαιοπυρήνα στην κατάλληλη μορφή για να είναι δυνατή η χρησιμοποίησή τους ως ενισχυτικό υλικό. Έγινε κονιορτοποίηση των κόκκων από την οποία προέκυψαν δύο τύπου σκονών που διέφεραν ως προς την διασπορά του μεγέθους των κόκκων, ενώ μια τρίτη σκόνη ελαιοπυρήνα είχε ήδη προετοιμαστεί με διαφορετική μέθοδο κονιορτοποίησης στο τμήμα Επιστήμης των Υλικών του Πανεπιστήμιου Πατρών. Έγινε εκτενής χαρακτηρισμός των φυσικών και μορφολογικών ιδιοτήτων όλων των σκονών ελαιοπυρήνα που χρησιμοποιήθηκαν για την κατασκευή των συνθέτων υλικών με μήτρα το PLA. Προσδιορίστηκαν διαφορετικού τύπου πυκνότητες και η διασπορά του μεγέθους των κόκκων. Έγινε θερμική ανάλυση με δοκιμή θερμοζυγού (TGA), μορφολογικός χαρακτηρισμός με χρήση ηλετρονικού μικροσκοπίου σάρωσης (SEM) καθώς και χαρακτηρισμός με φασματοσκοπία υπερύθρου με μετασχηματισμό Fourier (FT IR) και ακτίνων-Χ. Αφού ολοκληρώθηκε ο χαρακτηρισμός των ιδιοτήτων της ενισχυτικής φάσης, στη συνέχεια κατασκευάστηκαν σύνθετα υλικά μήτρας PLA ενισχυμένα με τους κόκκους ελαιοπυρήνα σε διαφορετικές περιεκτικότητες. Η προετοιμασία των σύνθετων αυτών υλικών πραγματοποιήθηκε σε δύο στάδια. Αρχικά έγινε μια πρώτη μορφοποίηση με εξώθηση (extrusion). Τα σύνθετα υλικά που προέκυψαν από την εξώθηση που ήταν στη μορφή δισκίων (pellets) χαρακτηρίστηκαν και αυτά με διάφορες τεχνικές (WAXD, DSC, TGA). Τα σύνθετα υλικά υπό μορφή δισκίων για να αποκτήσουν την τελική τους μορφή ως δοκίμια κατάλληλα για μηχανικές δοκιμές κατά τα πρότυπα ISO 527, μορφοποιήθηκαν με έγχυση (Injection molding). Τα σύνθετα υλικά στην τελική τους μορφή χαρακτηρίστηκαν με διάφορες τεχνικές (WAXD, DSC, TGA), έγινε χαρακτηρισμός των μηχανικών τους ιδιοτήτων και μορφολογική παρατήρηση των επιφανειών τους ύστερα από την μηχανική τους αστοχία (SEM). Τέλος, σε πολλά από τα σύνθετα υλικά που κατασκευάστηκαν και μελετήθηκαν πειραματικά, εφαρμόστηκαν διαφορετικά ημιεμπειρικά μοντέλα ανάλυσης και πρόβλεψης της μηχανικής τους συμπεριφοράς. Στο κυρίως κείμενο της διδακτορικής διατριβής, περιγράφεται σε ξεχωριστό κεφάλαιο το σύνολο των θεωρητικών μοντέλων που εφαρμόστηκαν στα πειραματικά αποτελέσματα. Στα επιμέρους κεφάλαια που παρουσιάζονται και αναλύονται τα πειραματικά αποτελέσματα, παρατίθενται η σύγκρισή τους με τις αντίστοιχες προβλέψεις που πρόεκυψαν από την εφαρμογή των θεωρητικών μοντέλων. Από τη σύγκριση αυτή παρατηρούμε ότι τα θεωρητικά μοντέλα που εφαρμόστηκαν που είναι το μοντέλο πρόβλεψης του μέτρου ελαστικότητας κοκκωδών υλικών, ΜPM (Modulus Predictive Model), το μοντέλο πρόβλεψης της υποβάθμισης ιδιοτήτων ύστερα από διαφορετικές είδους καταπονήσεις (θερμική κόπωση, κρούση χαμηλής ενέργειας και του ρυθμού παραμόρφωσης σε κάμψη τριών σημείων), RPM (Residual Properties Model) και το μοντέλο πρόβλεψης της υποβάθμισης της αντοχής των υλικών ύστερα από κρούση, Residual Strength after Impact Model (RSIM), έδωσαν ικανοποιητικές προβλέψεις για την μεταβολή των ιδιοτήτων κάνοντας χρήση ελάχιστων μόνο πειραματικών σημείων. Στην παρούσα διατριβή συνδυάστηκαν δύο διαφορετικού τύπου πολυμερικές ρητίνες με πληθώρα ενισχυτικών υλικών για την κατασκευή και μελέτη της μηχανικής τους συμπεριφοράς, τόσο πειραματικά όσο και θεωρητικά με την εφαρμογή ημιεμπειρικών μοντέλων πρόβλεψης και ανάλυσης. Για την κατασκευή των δοκιμίων, ανάλογα με τον τύπο του υλικού της μήτρας και της ενίσχυσης, εφαρμόστηκαν διαφορετικές τεχνικές και σύνθετες πειραματικές διαδικασίες. Ενώ, για την μελέτη των μηχανικών, θερμομηχανικών και μορφολογικών τους ιδιοτήτων εφαρμόστηκε σημαντικός αριθμός διαφορετικών τεχνικών χαρακτηρισμού.