The objective of the present study is the computational and analytical modelling of a stress and strain state of the composite laminated structures. The exact three dimensional solution is derived for laminated anisotropic thick cylinders with both constant and variable material properties through the thickness of a layer. The governing differential equations are derived in a such form that to satisfy the stress functions and are given for layered cylindrical shell with open ends. The solution then extended to the laminated cylindrical shells with closed ends, that is to pressure vessels. Based on the accurate three-dimensional stress analysis an approach for the optimal design of the thick pressure vessels is formulated. Cylindrical pressure vessels are optimised taking the fibre angle as a design variable to maximise the burst pressure. The effect of the axial force on the optimal design is investigated. Numerical results are given for both single and laminated (up to five layers) cylindrical shells. The maximum burst pressure is computed using the three-dimensional interactive Tsai-: Wu failure criterion, which takes into account the influence of all stress components to the failure. Design optimisation of multilayered composite pressure vessels are based on the use of robust multidimensional methods which give fast convergence. Transverse shear and normal deformation higher-order theory for the solution of dynamic problems of laminated plates and shells is studied. The theory developed is based on the kinematic hypotheses which are derived using iterative technique. Dynamic effects, such as forces of inertia and the direct influence of external loading on the stress and strain components are included at the initial stage of derivation where kinematic hypotheses are formulated. The proposed theory and solution methods provide a basis for theoretical and applied studies in the field of dynamics and statics of the laminated shells, plates and their systems, particularly for investigation of dynamic processes related to the highest vibration forms and wave propagation, for optimal design etc. Geometrically nonlinear higher-order theory of laminated plates and shells with shear and normal deformation is derived. The theory takes into account both transverse shear and normal deformations. The number of numerical results are obtained based on the nonlinear theory developed. The results illustrate importance of the influence of geometrical nonlinearity, especially, at high levels of loading and in case when the laminae exhibit significant differences in their elastic properties. / Thesis (Ph.D.)-University of Natal, Durban, 1995.

Rotor (helicopter/wind turbine) blades are typically slender structures that can be modeled as beams. Beam modeling, however, involves a substantial mathematical formulation that ultimately helps save computational costs. A beam theory for rotor blades must account for (i) initial twist and/or curvature, (ii) inclusion of composite materials, (iii) large displacements and rotations; and be capable of offering significant computational savings compared to a non-linear 3D FEA (Finite Element Analysis). The mathematical foundation of the current effort is the Variational Asymptotic Method (VAM), which is used to rigorously reduce the 3D problem into a 1D or beam problem, i.e., perform a cross-sectional analysis, without any ad hoc assumptions regarding the deformation. Since its inception, the VAM based cross-sectional analysis problem has been in a constant state of flux to expand its horizons and increase its potency; and this is precisely the target at which the objectives of this work are aimed. The problems addressed are the stress-strain-displacement recovery for spanwise non-uniform beams, analytical verification studies for the initial curvature effect, higher fidelity stress-strain-displacement recovery, oblique cross-sectional analysis, modeling of thin-walled beams considering the interaction of small parameters and the analysis of plates of variable thickness. The following are the chief conclusions that can be drawn from this work: 1. In accurately determining the stress, strain and displacement of a spanwise non-uniform beam, an analysis which accounts for the tilting of the normal and the subsequent modification of the stress-traction boundary conditions is required. 2. Asymptotic expansion of the metric tensor of the undeformed state and its powers are needed to capture the stiffnesses of curved beams in tune with elasticity theory. Further improvements in the stiffness matrix can be achieved by a partial transformation to the Generalized Timoshenko theory. 3. For the planar deformation of curved laminated strip-beams, closed-form analytical expressions can be generated for the stiffness matrix and recovery; further certain beam stiffnesses can be extracted not only by a direct 3D to 1D dimensional reduction, but a sequential dimensional reduction, the intermediate being a plate theory. 4. Evaluation of the second-order warping allows for a higher fidelity extraction of stress, strain and displacement with negligible additional computational costs. 5. The definition of a cross section has been expanded to include surfaces which need not be perpendicular to the reference line. 6. Analysis of thin-walled rotor blade segments using asymptotic methods should consider a small parameter associated with the wall thickness; further the analysis procedure can be initiated from a laminated shell theory instead of 3D. 7. Structural analysis of plates of variable thickness involves an 8×8 plate stiffness matrix and 3D recovery which explicitly depend on the parameters describing the thickness, in contrast to the simplistic and erroneous approach of replacing the thickness by its variation.

Metal organic frameworks (MOFs) and metal oxide-MOF composites were investigated for adsorption and oxidation of carbon monoxide. Metal oxides were successfully included in MOFs via both impregnation and encapsulation. UiO-66, a zirconium-based MOF, was impregnated with magnesium or cobalt oxide. Cobalt oxide in UiO-66 increases the room temperature CO capacity and shows increased adsorption at 65°C due to strong cobalt-CO interactions. Titania and magnetic nanoparticles were encapsulated in HKUST-1, a copper-based MOF. Including titania in HKUST-1 lowers the CO oxidation onset temperature by over 100°C compared with HKUST-1, and the composite reaches complete conversion by 250°C. HKUST-1 with magnetic nanoparticles shows enhanced structural stability and increased room temperature adsorption of CO and hexane. MOF-74, an isostructural family with coordinatively unsaturated metal centers of cobalt, magnesium, nickel, or zinc, was investigated for the metal center’s impact on stability and adsorption. Pre-treatment conditions to optimize accessibility were found that maximize solvent removal while retaining structural integrity. The impact of air exposure on equilibrium CO capacity was investigated, and these predictions were compared to dynamic conditions, separating CO from nitrogen or air at room temperature. The cobalt analog loses only 25% of its CO capacity with air exposure, retaining higher capacity than the other analogs under ideal conditions. Unlike cobalt, the magnesium analog does not follow the predicted trends with air exposure, having higher dynamic capacities with pre-exposed samples. Under all dynamic conditions, the nickel analog oxidized a portion of the carbon monoxide feed.

Terahertz radiation or T-rays or THz radiation refers to the region of the electromagnetic spectrum between approximately 100 GHz and 30 THz. This spectral region is often referred to as the THz gap as these frequencies fall between electronic (measurement of field with antennas) and optical (measurement of power with optical detectors) means of generation. THz measurements may yield useful information about the structural and chemical nature of the material inspected. Examples include detection of voids in materials and protein binding in biomolecules. This report provides an overview of THz measurements of defects in fiber composites. We find that it efficiently detects defects such as voids and delamination in glass fiber composites better than ultrasound, which was widely used for defect characterization in glass fiber earlier. Comparison of the existing methods with THz is presented in the report for characterization of defects.

The major goals of this thesis were to: (1) create a site-isolated aminosilica material with higher amine loadings than previously reported isolation methods, (2) use spectroscopic, reactivity, and catalytic (olefin polymerization precatalysts) probes to determine isolation of amine groups on these organic/inorganic hybrid materials, (3) synthesize an organic/inorganic hybrid material capable of activating Group 4 olefin polymerization precatalysts, and (4) synthesize a high amine loaded organic/inorganic hybrid material capable of reversibly capturing CO2 in a simulated flue gas stream. The underlying motivation of this research involved the synthesis and design of novel amine and sulfonic acid materials. Traditional routes to synthesize aminosilicas have led to the formation of a high loading of multiple types of amine sites on the silica surface. Part of this research involved the creation of a new aminosilica material via a protection/deprotection method designed to prevent multiple sites, while maintaining a relatively high loading. As a characterization technique, fluorescence spectroscopy of pyrene-based fluorophores loaded on traditional aminosilicas and site-isolated aminosilicas was used to probe the degree of site-isolation obtained with these methods. Also, this protection/deprotection method was compared to other reported isolation techniques with heterogeneous Group 4 constrained-geometry inspired catalysts (CGCs). It was determined that the degree of separation of the amine sites could be controlled with protection/deprotection methods. Furthermore, an increase in the reactivity of the amines and the catalytic activity of CGCs built off of the amines was determined for aminosilicas synthesized by a protection/deprotection method. The second part of this work involved developing organic/inorganic hybrid materials as heterogeneous Brønsted acidic cocatalysts for activation of olefin polymerization precatalysts. This was the first reported organic/inorganic hybrid sulfonic acid functionalized silica material capable of activating metallocenes for the polymerization of ethylene when small amounts of an alkylaluminum was added. Lastly, an organic/inorganic hybrid hyperbranched aminosilica material capable of capturing carbon dioxide from flue gas streams was synthesized. This material was determined to capture CO2 with capacities higher than currently reported aminosilica adsorbents.

This thesis addresses the results of an experimental and analytical investigation aimed at examining the static load-displacement response of braced plane frame structures composed of fiber reinforced polymeric (FRP) composite material structural members manufactured by the pultrusion process. In the experimental part of this investigation, eighteen full-scale lateral loading tests for FRP composite frames with different brace configurations and beam column connection types were performed. The load-displacement responses of such frames were measured and are reported herein. In the analytical part of this investigation, a frame analysis method that accounts for the anisotropic nature of FRP composite material structural members was investigated. The results from the experimental work are compared with the results from the analytical procedures. The effects of various structural parameters of the frame such as (1) effective mechanical material properties of members, (2) beam-column connection types, and (3) the influence of diagonal structural members on the lateral load-displacement response of the braced plane frames are also investigated. The numerical load-displacement results from the proposed FRP composite frames analysis procedure provided good agreement with the results from the full-scale laboratory tests.

The graphitic nature, continuous structure, and high mechanical properties of carbon nanotubes (CNTs) make them good candidate for reinforcing polymer fiber. The different types of CNTs including single-wall carbon nanotubes (SWNTs), few-wall carbon nanotubes (FWNTs), and multi-wall carbon nanotubes (MWNTs), and carbon nanofibers (CNFs) differ in terms of their diameter and number of graphitic walls. The desire has been to increase the concentration of CNTs as much as possible to make next generation multi-functional materials. The work in this thesis is mainly focused on MWNT and CNF reinforced polyacrylonitrile (PAN) composite fibers, and SWNT, FWNT, and MWNT reinforced poly(etherketone) (PEK) composite fibers. To the best of our knowledge, this is the first study to report the spinning of 20% MWNT or 30% CNF reinforced polymer fiber spun using conventional fiber spinning. Also, this is the first study to report the PEK/CNT composite fibers. The fibers were characterized for their thermal, tensile, mechanical, and dynamic mechanical properties. The fiber structure and morphology was studied using WAXD and SEM. The effect of two-stage heat drawing, sonication time for CNF dispersion, fiber drying temperature, and molecular weight of PAN was also studied. Other challenges associated with processing high concentrations of solutions for making composite fibers have been identified and reported. The effect of CNT diameter and concentration on fiber spinnability and electrical conductivity of composite fiber have also been studied. This work suggests that CNT diameter controls the maximum possible concentration of CNTs in a composite fiber. The results show that by properly choosing the type of CNT, length of CNTs, dispersion of CNTs, fiber spinning method, fiber draw ratio, and type of polymer, one can get electrically conducting fibers with wide range of conductivities for different applications. The PEK based control and composite fibers possess high thermal stability with almost no weight loss up to 500 degree C and negligible thermal shrinkage up to 200 degree C. The PEK based fibers showed high toughness which surpassed many of the high-performance fibers like Kevlar(R) and Zylon(R). The 10% FWNT containing fiber is unique in terms of high electrical conductivity and high toughness. The CNT based fibers may be used as structural material, fire-barrier/protection textile, electrode for electrochemical capacitor or fuel cells, and as a template for directional growth of tissues.

The goal of this research was to investigate the tensile fatigue behavior of a carbon fiber / epoxy composite material. Specifically, the stress levels at which cracks initiated in static and fatigue loading in the 90 degree plies of a "quasi-cross ply layup" [0/905]S was investigated. For layups which contain them, cracks in composite laminates initiate and propagate from 90 degree plies (including the ubiquitous "quasi-isotropic layup" 0/±45/90). Thus, this work provides valuable insight into the fatigue behavior of the plies which originate fatigue damage. Unidirectional off-axis 90 degree and 10 degree specimens were also tested, but the bulk of testing was done on the cross-ply laminates. The project sponsors, Boeing, were in the process of extending a failure model to the case of fatigue. The body of work presented here provided empirical data for that effort. Several different inspection techniques were used to investigate for cracking in the 90 degree plies, including: x-ray images, edge replicates, dye penetrants, and optical microscopy. Plots of the stress level at which crack initiation occurred will be presented, as well as images illustrating damage development in these layups. Comparisons are made to the experimental results of other investigations of this type of layup. Explorations of the effect of R-ratio (including R = 0.1 and 0.5), loading frequency (including 3, 10, and 30 Hz), and surface roughness (hand polished specimen edges to 1500 grit smoothness) on fatigue crack initiation were also performed. For the most damaging case (10 Hz, R = 0.1, no polishing), the crack initiation strain (0.00276) was one half of the strain at which cracks initiated in static monotonic loading (0.0054), and was 16% of the cross-ply specimen's (0 degree fiber dominated) ultimate strain value of (0.018).

Η διατριβή αποσκοπεί στην ανάπτυξη κατάλληλης μεθοδολογίας και των αντίστοιχων υπολογιστικών εργαλείων με σκοπό τον προσδιορισμό της αξιοπιστίας κατασκευών από σύνθετα υλικά, όταν λαμβάνεται υπόψη όχι μόνο η στοχαστικότητα της φόρτισης και των ιδιοτήτων αντοχής του ορθότροπου υλικού, αλλά και η μεταβλητότητα των ελαστικών του ιδιοτήτων και των συντελεστών θερμικής διαστολής. Ταυτόχρονα, στόχος της εργασίας είναι η μέθοδος που θα αναπτυχθεί να είναι ευκολόχρηστη και αρκετά ακριβής, ώστε να καταστεί πρακτική για χρήση σε σχεδιασμό τέτοιων κατασκευών όπου μέχρι το τελικό αποτέλεσμα απαιτούνται πολλές επαναληπτικές δοκιμές. Στην εργασία διερευνάται η μεταβλητότητα των μηχανικών ιδιοτήτων συνθέτων υλικών, κυρίως αυτών που χρησιμοποιούνται στην κατασκευή πτερυγίων Ανεμογεννητριών, η στατιστική μοντελοποίηση της, καθώς και μέθοδοι για τον προσδιορισμό της αξιοπιστίας της κατασκευής. Επικεντρώνοντας το ενδιαφέρον στον δομικό σχεδιασμό πτερυγίων ανεμογεννητριών αναπτύχθηκε κατάλληλο υπολογιστικό εργαλείο για την εκτίμηση της αξιοπιστίας του πτερυγίου υπό στατική φόρτιση, στο επίπεδο της στρώσης του υλικού λαμβάνοντας υπόψη την στοχαστικότητα των ελαστικών-θερμικών ιδιοτήτων και των ιδιοτήτων αντοχής του υλικού, ενώ από την πλευρά της φόρτισης περιλαμβάνεται η μεταβλητότητα τόσο των ορθών τάσεων όσο και των διατμητικών τάσεων που αναπτύσσονται στο επίπεδο της στρώσης, ξεκινώντας από την στοχαστικότητα της εξωτερικής φόρτισης του πτερυγίου. Οι προτεινόμενες μέθοδοι εκτίμησης της πιθανότητας αστοχίας του πτερυγίου ανεμογεννήτριας αποδεικνύονται εφαρμόσιμες και σε άλλες κατασκευές από σύνθετα υλικά, με κύριο γνώρισμά τους την παραλαβή της φόρτισης σε μεγάλο βαθμό από το σύνθετο υλικό. / The dissertation aim was to develop a suitable methodology and the relevant numerical tools for the determination of the reliability of composite materials structures, when not only the variability of loading and the orthotropic material strength properties but also the variability of the material's elastic properties and thermal expansion coefficients. In parallel, scope of the work is to develop a method that is easily applicable and relative accurate, so as to be practical for use during the design of such structures, for which a large numbers of iterations is required up to the design final solution. In the current work the variability of the mechanical properties of composite materials, focusing on materials used for manufacturing wind turbine blades, is studied, the statistical modeling of the structure, as well as methods for the estimation of the structural reliability. Concentrating the interest in the structural design of wind turbine blades an adequate numerical tool was developed for the estimation of the wind turbine blade reliability under static loading, at the layer level, taking into account the stochastic material elastic properties, thermal expansion coefficients and strength properties, while on the loading side both the variability of normal and shear stresses which are developed at the layer level is taken into consideration, starting at the variability of the blade's external loading. The proposed methods developed for the failure probability estimation of the wind turbine blade are proved applicable to other composite material structures, as well, for cases where the structural load is undertaken in the largest extend by the composite material.

Les structures constructives de type Gridshells sont réalisées à partir d'une grille régulière plane que l'on déforme élastiquement, puis que l'on rigidifie dans la position souhaitée. Les Gridshells en matériaux composites ont été développés et étudiés depuis plusieurs années au laboratoire Navier. La thèse propose, à travers un historique des réalisations Navier, un retour d'expérience. Elle identifie également les aspects à mieux maîtriser, d'un point de vue simulation numérique ou d'un point de vue matériau et technologie. La thèse détaille alors des développements numériques nouveaux permettant l'analyse ultime de la structure, prise en compte des ruptures de barres (robustesse), et permettant la prise en compte de la torsion dans des poutres anisotropes, c'est-à-dire à section quelconque. Dans le premier chapitre on traite ainsi du contexte dans lequel s'inscrivent les travaux sur les gridshells. La conception des gridshells au laboratoire Navier y est détaillée. En particulier, la méthode numérique historiquement utilisée, à savoir la méthode de relaxation dynamique, est présentée. Le second chapitre présente les réalisations du laboratoire Navier. Plusieurs prototypes ont été réalisés durant les dix dernières années. Les deux dernières structures, le gridshell de Solidays et la Cathédrale Ephémère de Créteil, ont été conçues et fabriquées pour accueillir du public. Les choix importants de conception et de fabrication de ces gridshells sont détaillés, avec un accent sur les avancées technologiques et sur les retours d'expérience. Le troisième chapitre traite du comportement des gridshells en matériaux composites. La démarche a été d'investiguer le comportement du gridshell pour comprendre les processus d'endommagement des gridshells. On montre que le flambement conditionne la robustesse des gridshells. En effet, les résultats de l'étude montrent que lorsque le gridshell a été bien dimensionné et que les risques de flambement de la structure sont écartés, la structure se comporte de manière robuste, du fait de sa forte redondance. Finalement, le dernier chapitre traite d'un nouveau modèle de poutre permettant de prendre en compte la torsion dans les poutres de section quelconque. Dans les précédents chapitres, il est souligné que la non prise en compte de la torsion peut-être préjudiciable pour diverses raisons, sous-estimation des contraintes, méconnaissance des efforts de jonctions, erreur sur la géométrie. Dans ce chapitre, le modèle de poutre est un modèle à quatre degrés de liberté, à la manière des travaux de Basile Audoly et Ethan Grinspun. La simulation numérique, à nouveau réalisée à l'aide d'un algorithme de relaxation dynamique, permet d'obtenir les configurations d'équilibre de structures fortement réticulées telles que les gridshells. Une des particularités de ce travail est que le modèle de poutre est développé en continu jusqu'à l'obtention des efforts intérieurs. Le modèle est ensuite discrétisé et implémenté de manière à pouvoir être utilisé. Une sous-étape permet d'ajouter des forces et des moments extérieurs. Pour des poutres de section rectangulaire, les résultats du modèle sont comparés à un logiciel élément fini et donnent de bons résultats en termes de précision et de temps de calcul. Finalement la méthode numérique est appliquée à des structures composées de poutres connectées. La transmission des efforts au niveau des connexions est implémentée. L'excentricité des connexions est également modélisée ce qui permet d'obtenir de précieuses informations sur les efforts transitant au sein des connexions. Grâce à ces travaux, il devient possible d'utiliser la richesse de forme que peuvent offrir les poutres élancées présentant deux inerties en flexion différentes / The structures like gridshells are structures made of a plane regular grid which is elastically deformed and then stiffened in the wished configuration. The composite materials gridshells have been developed and studied for several years at Navier laboratory. The thesis offer a feedback, through a history of Navier realisations. It also precise the points to improve, in numerical simulation or about materials or technological aspects. Then, the thesis explains the new numerical developments that make possible the ultimate analysis of the structure, taking account the ruptures of beams (robustness), and that makes possible the consideration of the torsion in anisotropic beams, that is to say beams with any cross-section. In the first chapter the context of the work is presented. This chapter explains how the Navier laboratory designs and builds gridshells. In particular, the numerical method historically used - the dynamic relaxation method - is presented. The second chapter presents the gridshell realisations of the Navier laboratory. Several prototypes have been built during the past ten years. The two last ones, the Solidays gridshell and the Ephemeral Cathedral of Creteil, have been designed to shelter public. The important choices during design and fabrication are detailed with an accent on technological progresses and feedbacks. The third chapter deals with the behaviour of composite materials gridhsells. The approach was to investigate the behaviour of the gridshell to understand the processes of damage. It is shown that buckling is particularly dangerous for the gridshell. The results of the study shows that when the gridshell has been well designed and in particular if buckling is avoided, the gridshell behave in a robust manner, thanks to its redundancy. Finally the last chapter deals with a new beam model, able to take into account torsion, for beams with any section. In the previous chapters it was underlined that the consideration of torsion aspects was lacking and has various consequences – incorrect estimation of stress, ignorance of forces and moments in connections, imprecision in geometry. In this chapter, the model of beams used is a four degrees of freedom model, similar to the ones presented by Basile Audoly and Ethan Grinspun. The numerical simulation, performed once again thanks to a dynamic relaxation algorithm, is able to provide equilibrium configurations of highly reticulated structures as gridshells. One of the particularity of this work is the fact that the model is a continuous model, only discretized for numerical simulations. The external forces and moments can be implemented. For beams with rectangular cross-section, the results of the model are compared to finite element modelling simulations. The results are satisfying in term of accuracy and computational time. Finally the numerical method is applied to structures made of interconnected beams. The connections are modelled and the efforts through them are provided by the model. This provides important information about how to design the connections. Thanks to these work it become possible to use the large possibility of shapes offered by slender beams whose flexural inertias are different