Ce travail vise à étudier le comportement à la rupture des composites tissés C/PPS à haute températureT > Tg/c/pps. Des analyses fractographiques et des observations microscopiques des faciès de rupture ont permis d'appréhender les mécanismes d'endommagement qui existent dans les stratifiés C/PPS à haute température (HT) en présence de fissure. Pour les stratifiés quasi-isotropes (comportement élastique fragile), plusieurs techniques ont été utilisées afin d'étudier la ténacité à l'initiation et à la propagation. En particulier, l'émission acoustique semble pertinente car elle permet de détecter l'initiation, la propagation de la fissure mais aussi de suivre l'évolution de l'endommagement. Pour les stratifiés à plis croisés (comportement ductile), une approche basée sur le calcul de l'intégrale J en utilisant la méthode de séparation de charge a été utilisée. Cette méthode a montré sa capacité à fournir les courbes J-R des composites à comportement très ductile à HT pour différents rapports longueur d'entaille initial sur la largeur de l'éprouvette a/W. Numériquement, un modèle viscoélastique spectral linéaire et un modèle viscoplastique de Norton généralisé ont été utilisés pour tenir compte du comportement dépendant du temps des composites C/PPS à HT. Pour évaluer précisément les paramètres de rupture dans les stratifiés à base TP, une étude sur le type de maillage et son raffinement a été réalisée. Enfin, en se basant sur le maillage sélectionné et en utilisant le code de calcul aux éléments finis Cast3m, la méthode Gθ a été appliquée afin de tester sa capacité à déterminer J pour différents niveaux de chargement. / The present work was aimed at investigating the fracture mechanics in woven-ply TP (PPS) based laminates at T > Tg/c/pps. A fractography analysis and microscopic observations of fracture surfaces were used to apprehend the damage mechanisms in C/PPS at high temperature (HT) in the presence of a crack. For quasi-isotropic laminates (elastic brittle behavior), several techniques were used to investigate the tenacity at initiation and propagation. In particular, the acoustic emission showed to be particularly relevant as it allows to detect the crack initiation, propagation but also to follow the evolution of the damage. For cross-ply laminates (ductile behavior), an approach based on the calculation of integral J using the load separation method was used. This method showed its capability to provide the J-R curves of composites with very ductile HT behavior for different crack length over specimen width ratios a/W. Numerically, a linear spectral viscoelastic model and a generalized Norton viscoplastic model were used to account for the time-dependent behavior of C/PPS composite laminates at HT. To precisely evaluate the fracture parameters in TP-based laminates, a study on the mesh type and its refinement was carried out. Finally, based on the selected mesh and using the finite element code Cast3m, the Gθ method was applied in order to test its capability to determine J for different loading levels.

Les composites à matrice organique et renforcés par des préformes textiles (CMORT) sont en passe d’être déployés sur les véhicules de grandes séries pour réduire leur poids. Lorsqu’ils sont soumis à des impacts basse vitesse ces matériaux présentent des comportements complexes qui doivent être précisément modélisés et prédis au moyen de simulations par éléments finis. Dans ce but, un modèle matériau a été développé et implémenté dans un code éléments finis commercial. Soumis à un impact basse vitesse, un CMORT présente quatre mécanismes physiques majeurs qui altèrent la rigidité initiale du matériau : fissuration matricielle intralaminaire, rupture des fibres, délaminage et sensibilité à la vitesse de déformation. L’endommagement matriciel est modélisé grâce à un modèle constitutif reposant sur la mécanique de l’endommagement des milieux continus. Basé sur l’Onera Damage Model, il prend en compte les mécanismes de friction aux abords des fissures. La sensibilité à la vitesse de déformation est introduite au moyen d’un modèle de Maxwell généralisé. Ensuite, un critère de rupture est utilisé pour prédire l’initiation de la rupture des fibres et l’endommagement des fibres qui en découle est régularisé par l’utilisation d’un modèle de rupture progressive. Finalement, afin de prédire précisément le comportement hors-plan d’un stratifié, le calcul d’une distribution de déformation réaliste à travers l’épaisseur est réalisé au niveau du modèle matériau. Cette modélisation est capable de prendre en compte les effets du délaminage en utilisant seulement un élément coque. De plus, l’intégralité du modèle est formulé suivant la description Lagrangienne totale afin d’assurer l’objectivité et la cohérence matérielle durant la simulation. La procédure d’identification, ainsi que les tests de validation et les corrélations essais/simulations sont décrits pour chaque mécanisme physique. Enfin, le modèle est évalué au travers de la prédiction du comportement d’une structure automobile industrielle. / Carbon Fabric Reinforced Polymers (CFRP) will soon used in high volume automotive production in order to reduce the vehicle weight. For safety and design reasons, their complex behaviours under low-speed impacts, such as pedestrian impacts, need to be accurately modelled and predicted by finite element simulations. For this purpose, a material model dedicated to explicit finite element simulations has been developed and implemented in a commercial finite element code. Subject to low-speed impacts, the CFRP shows four different physical mechanisms which alter the initial stiffness of the material: intralaminar matrix cracks, fibre failure, delamination and strain-rate sensitivity. The intralaminar damage is modelled through constitutive equations based on the continuum damage theory. It is based on the Onera Damage Model, but with the consideration of friction mechanisms between crack lips in order to represent the hysteresis loops in case of cyclic loading. The strain-rate sensitivity is introduced by means of the rheological generalised Maxwell viscoelastic model. Regarding the fibre damage, a failure criterion based on the strain of the fibre direction is introduced. The energy release due to the fibre failure is also regularised thanks to a smeared crack approach. Finally, in order to welldescribed the out-of-plane behaviour, such as bending, of a laminated CFRP material, a recomputation of a realistic strain field through-the thickness of the laminate is introduced at level of the material model. Based on strain energy equilibrium between usual shell element theory and higher-order zigzag theory, this formulation is able to consider delamination at ply interfaces by using only one shell element through-the-thickness of a laminate. In addition, the model is placed in a total Lagrangian framework to ensure both objectivity and material coherence. The identification procedure, with the needed experimental tests, as well as validation tests and experimental/numerical correlations are given for all physical mechanisms previously described. Finally, this model is evaluated through the behaviour prediction of an industrial structure.

In vielen technischen Anwendungen werden Faserverbundwerkstoffe mit Hochleistungsfasern aus Carbon und AR-Glas eingesetzt, die aufgrund ihrer physikalischen und chemischen Eigenschaften ein hohes Festigkeitspotential aufweisen. Damit eröffnen sich neue Anwendungsgebiete, z. B. als textile Bewehrungen für Betonbauteile. Die Garnmaterialien müssen hohe sicherheitstechnische Anforderungen erfüllen. Dazu gehören u. a. eine ausreichende Tragfähigkeit unter Dauerlastbeanspruchung und eine hohe Temperaturbeständigkeit im Brandfall. Zur Spezifizierung dieser Eigenschaften wurden experimentelle Untersuchungen durchgeführt, deren Ergebnisse nachfolgend vorgestellt werden. / Due to their strong mechanical and chemical properties, fiber composite materials composed of high performance carbon and AR-glass fibers lend themselves to many technical applications. Potentially new and innovative application fields should be considered, such as textile reinforcements for concrete components. The yarn materials must meet high technical and safety standards, specifically sufficient load-bearing capabilities under long-term conditions and acceptable strength at high temperatures should fire occur. Research was conducted to document these characteristics. The results are presented in this paper.

Thin cylindrical shell structures may provide an interesting breakthrough for deployable  structures for small satellites. Its bi-stable behaviour allows two different stable configurations: coiled and deployed. Several projects worldwide are using tape springs for satellites and for the SEAM project, at KTH, 1 meter long tape springs will be used for booms. This thesis investigates the energy stored inside the tape spring according to its layup configuration and the different fiber orientations. With a thickness around 0.3 mm and a length of one meter, the booms will deploy sensors with a quite low deployment speed in order to minimize the shock load during the deployment phase. A Matlab code is written to compare the stored strain energy. Another aim is to find an adequate layup all along the tape spring, it means change the fiber orientation to decrease the energy released, but also generating main manufacturing issue.

No description available.

Phononic crystals are structures composed of periodically arranged scatterers in a background medium that affect the transmission of elastic waves. They have garnered much interest in recent years for their macro-scale properties that can be modulated by the micro-scale components. The elastic properties of the composite materials, the contrast in the elastic properties of the composite materials, and the material arrangement all directly affect how an elastic wave will behave as it propagates through the sonic structure. The behavior of an elastic wave in a periodic structure is revealed in its transmission bandstructure, and modification of any the elastic parameters will result in tuning of the band structure. In this dissertation, a phononic crystal with properties that can be modulated using electromagnetic radiation, and more specifically, radio-frequency (RF) light will be presented.

Composite layups have been continuously used over many years in various applications. It is necessary to optimize its composition by studying various parameters influencing the mechanical properties and studying the failure behavior. In this master thesis, the objective was to test five different plies manufactured using thick and thin plies and various combinations of thick and thin laminates called hybrid laminates. Bearing tests are performed for five layups with each layer has its thickness varying from 40μm to 130μm, and a combination called hybrid laminate, and the results from the tests are investigated. The resulting system has a good performance with onset damage above 700 MPa and an ultimate failure above 1130 MPa, using fibers' full potential. Also, the different failure modes like fiber kinking, matrix crack, delamination, and their effect on the layup's strength are investigated using fractography. This paper also investigates the influences of the thickness of the laminate on the strength of hybrid composites jointed using different mechanisms, and its failure modes are checked. Results from this experiment are used to validate in the form of FEM model, which is a part of an internal project at RISE SICOMP AB. This thesis is suitable for an engineering student in mechanical engineering, material science interested in composite materials and fractography.

Thesis submitted in fulfilment of the requirements for the degree Doctor of Technology: Chemistry in the Faculty of Applied Sciences at the Cape Peninsula University of Technology 2013 / In this present study, the physicochemical properties, nature and morphology of prepared composite materials involving activated carbon, fly ash, nFe3O4, nSiO2 and nZnO in the 1:1 ratio for two components composite materials and 1:1:1 for three components composite materials were investigated. The nature, morphology and elemental characterizations of these materials were carried out by means of modern analytical methods such as scanning electron and transmission electron microscopy (SEM and TEM), x-ray diffraction (XRD), x-ray fluorescence (XRF), inductively coupled plasma mass spectrometry (ICP-MS), inductively coupled plasma atomic emission spectroscopy (ICP-AES) and Fourier transform infrared spectroscopy (FTIR). Other physicochemical characterizations undertaken were CNH analysis, ash content, pH, point of zero charge and surface area and porosity determination by Brunauer, Emmett and Teller (BET). The precursors and composite materials were then applied to the sorption (remediation) of tributyltin (TBT) and triphenyltin (TPT) from artificial seawater and wastewater and the adsorption efficiencies for the precursors and the composites compared. The adsorption of TBT and TPT onto these materials as a function of adsorbent amount, contact time, pH, stirring speed, initial adsorbate concentration and temperature was investigated. Maximum organotin adsorption was recorded within the pH range of normal saline water (pH 8). Approximately 99.95 %, 95.75 %, 96.78 %, 99.88 %, 96.96 %, 99.98 %, 99.99 %, 99.99 % and 99.99 % TBT were removed from 25 mL of 100 mg/L TBT-contaminated artificial seawater using 0.5 g adsorbents at a contact time of 60 min, pH 8, stirring speed 200 rpm and temperature of 80 oC by activated carbon, fly ash, nFe3O4, nSiO2, nZnO, fly ash/activated carbon, nFe3O4/activated carbon, nSiO2/activated carbon and nZnO/activated carbon composite, respectively and the adsorption of TBT onto these adsorbents was endothermic. Approx. 99.99 %, 96.54 %, 95.50 %, 96.92 %, 97.14 %, 99.99 %, 98.44 %, 98.98 % and 99.66 % TPT were also removed from 25 mL of 100 mg/L TPT-contaminated artificial seawater using 0.5 g adsorbents at a contact time of 60 min, pH 8, stirring speed 200 rpm and a temperature of 20 oC by the activated carbon, fly ash, nFe3O4, nSiO2, nZnO, fly ash/activated carbon, nFe3O4/fly ash, nSiO2/fly ash and nZnO/fly ash composite, respectively. The adsorption of TPT onto activated carbon and fly ash/activated carbon composite from TPT – contaminated artificial seawater was endothermic while TPT adsorption onto fly ash, nFe3O4, nSiO2, nZnO, nFe3O4/fly ash, nSiO2/fly ash and nZnO/fly ash composites from TPT – contaminated artificial seawater was exothermic. The adsorption of TBT and TPT onto nFe3O4/fly ash/activated carbon and nSiO2/fly ash/activated carbon composites from TBT – and TPT – contaminated water, respectively were endothermic and approx. 99.98 % and 99.99 % of TBT and TPT, respectively were removed from the initial concentration of 100 mg/L OTC by the composites at a temperature of 80 oC, 60 min contact time, pH 8 and a stirring speed of 200 rpm. The adsorption kinetics of all the precursors and composite materials fitted well with the pseudo second-order kinetic model while the adsorption isotherm data could be well described by the Freundlich isotherm model except TBT adsorption onto nZnO/activated carbon and nFe3O4/activated carbon composite from TBT contaminated artificial seawater, TPT adsorption onto activated carbon and fly ash/activated carbon from TPT contaminated artificial seawater, and TPT sorption onto nSiO2/fly ash/activated carbon composite from TPT – contaminated water which could be described by both the Freundlich and Dubinin-Radushkevich (D-R) isotherm models. Optimal conditions for the adsorption of TBT and TPT from artificial seawater were further applied to TBT and TPT removal from TBT – and TPT – contaminated natural seawater obtained from Cape Town harbour and the results obtained show that 99.71 %, 79.23 %, 80.11 %, 82.86 %, 80.42 %, 99.75 %, 99.88 %, 99.83 % and 99.88 % TBT were removed from TBT – contaminated natural seawater by activated carbon, fly ash, nFe3O4, nSiO2, nZnO, fly ash/activated carbon, nFe3O4/activated carbon, nSiO2/activated carbon and nZnO/activated carbon composite, respectively while 99.90 %, 96.44 %, 95.37 %, 96.75 %, 97.03 %, 99.92 %, 98.42 %, 98.92 % and 99.58 % TPT were removed from TPT – contaminated natural seawater by activated carbon, fly ash, nFe3O4, nSiO2, nZnO, fly ash/activated carbon, nFe3O4/fly ash, nSiO2/fly ash and nZnO/fly ash composite, respectively. Experimental results therefore show that the composite materials present higher organotin adsorption efficiency than the precursors due to the nature and improved properties of the composite materials and can therefore be utilized for the remediation of organotin contamination from industrial and/or shipyards process wastewater to > 99 % reduction before discharge into the environment.

The issue of accurately determining the effective properties of composite materials has received the attention of numerous researchers in the last few decades and continues to be in the forefront of material research. Micromechanics models have been proven to be very useful tools for design and analysis of composite materials. In the present work, a versatile micromechanics modeling framework, namely, the Variational Asymptotic Method for Unit Cell Homogenization (VAMUCH), has been invented and various micromechancis models have been constructed in light of this novel framework. Considering the periodicity as a small parameter, we can formulate the variational statements of the unit cell through an asymptotic expansion of the energy functional. It is shown that the governing differential equations and periodic boundary conditions of mathematical homogenization theories (MHT) can be reproduced from this variational statement. Finally, we employed the finite element method to solve the numerical solution of the constrained minimization problem. If the local fields within the unit cell are of interest, the proposed models can also accurately recover those fields based on the global behavior. In comparison to other existing models, the advantages of VAMUCH are: (1) it invokes only two essential assumptions within the concept of micromechanics for heterogeneous material with identifiable unit cells; (2) it has an inherent variational nature and its numerical implementation is shown to be straightforward; (3) it calculates the different material properties in different directions simultaneously, which is more efficient than those approaches requiring multiple runs under different loading conditions; and (4) it calculates the effective properties and the local fields directly with the same accuracy as the fluctuation functions. No postprocessing calculations such as stress averaging and strain averaging are needed. The present theory is implemented in the computer program VAMUCH, a versatile engineering code for the homogenization of heterogeneous materials. This new micromechanics modeling approach has been successfully applied to predict the effective properties of composite materials including elastic properties, coefficients of thermal expansion, and specific heat and the effective properties of piezoelectric and electro-magneto-elastic composites. This approach has also been extended to the prediction of the nonlinear response of multiphase composites. Numerous examples have been utilized to clearly demonstrate its application and accuracy as a general-purpose micromechanical analysis tool.

abstract: An orthotropic elasto-plastic damage material model (OEPDMM) suitable for impact simulations has been developed through a joint research project funded by the Federal Aviation Administration (FAA) and the National Aeronautics and Space Administration (NASA). Development of the model includes derivation of the theoretical details, implementation of the theory into LS-DYNA®, a commercially available nonlinear transient dynamic finite element code, as material model MAT 213, and verification and validation of the model. The material model is comprised of three major components: deformation, damage, and failure. The deformation sub-model is used to capture both linear and nonlinear deformations through a classical plasticity formulation. The damage sub-model is used to account for the reduction of elastic stiffness of the material as the degree of plastic strain is increased. Finally, the failure sub-model is used to predict the onset of loss of load carrying capacity in the material. OEPDMM is driven completely by tabulated experimental data obtained through physically meaningful material characterization tests, through high fidelity virtual tests, or both. The tabulated data includes stress-strain curves at different temperatures and strain rates to drive the deformation sub-model, damage parameter-total strain curves to drive the damage sub-model, and the failure sub-model can be driven by the data required for different failure theories implemented in the computer code. The work presented herein focuses on the experiments used to obtain the data necessary to drive as well as validate the material model, development and implementation of the damage model, verification of the deformation and damage models through single element (SE) and multi-element (ME) finite element simulations, development and implementation of experimental procedure for modeling delamination, and finally validation of the material model through low speed impact simulations and high speed impact simulations. / Dissertation/Thesis / Doctoral Dissertation Civil, Environmental and Sustainable Engineering 2019