Fibre Reinforced Polymer Composites are extensively used in aircraft structures because of its high specific stiffness, high specific strength and tailorability. Though Fibre Reinforced Polymers offer many advantages, they are not free from problems. The damage of different nature, e.g., service mechanical damages, fatigue damage or environmental damage can be observed during operating conditions. Among all the damages, manufacturing or service induced, delamination related damage is the most important failure mechanisms of aircraft-composite structures and can be detrimental for safety. Delamination growth under fatigue loading may take place due to local buckling, growth from free edges and notches such as holes, growth from ply-drops and impact damaged composites containing considerable delamination. Delamination growth can also occur due to interlaminar stresses, which can arise in complex structures due to unanticipated loading. The complex nature of composite failure, involving different failure modes and their interactions, makes it necessary to characterize/identify the relevant parameters for fatigue damage resistance, accumulation and life prediction. An effort has been made in this thesis to understand the fatigue behavior of carbon fibre reinforced epoxy laminates under aircraft wing service loading conditions. The study was made on laminates with different lay-up sequences (quasi-isotropic and fibre dominated) and different geometries (plain specimen, specimen with a hole and ply-drop specimen). The fatigue behaviour of the composite was analyzed by following methods: . Ultrasonic C-Scan was used to characterize the delamination growth. . Dynamic Mechanical Analysis (DMA) was done to study the interfacial degradation due to fatigue loading. In this analysis, the interfacial strength indicator and interfacial damping were calculated. The DMA also provides the storage modulus degradation under fatigue loading. . Scanning electron microscope examination was carried out to understand the fatigue damage mechanisms. . A semi-empirical phenomenological model was also used to estimate the residual fatigue life. This research work reveals that the Carbon Fibre Reinforced Polymer laminates are in the safe limit under service loading conditions, except the specimen with a hole. The specimen with a hole showed delaminations around the hole due to stress concentration and higher interlaminar stresses at the hole edges and this delamination is found to be associated with fibre breakage and fibre pullout. The quasi-isotropic laminate is found to show poorer fatigue behaviour when compared to fibre dominated laminate and ply-drop also shows poor performance due to high stress concentration in the ply-drop region.

Este trabalho trata das falhas que podem ocorrer em uniões e juntas de materiais compósitos unidas mecanicamente por parafusos. O compósito de fibra de carbono (tecido) embutido em resina epoxy foi estudado neste trabalho devido ao amplo uso em estruturas de vários segmentos da indústria. O trabalho apresenta vários critérios de falha, demonstrando as vantagens e desvantagens de cada um para materiais compósitos. A fabricação dos corpos de provas e os ensaios necessários para obtenção de parâmetros e validação de estruturas são descritos. A resistência da junta mostrou-se muito menor do que a da estrutura de compósito, demonstrando a importância de estudos assim. Criou-se um modelo numérico utilizando critérios de falhas como o critério de Hashin e o de máxima tensão. Os resultados da simulação de elementos finitos tiveram uma boa relação com os ensaios experimentais e o modelo foi então validado e considerado representativo. / This work shows failures that can occur in composite mechanically fastened joints. The composite carbon fiber embedded in epoxy resin, used in this study, was chosen due to it\'s wide use in structures of any segment of the industry. Many failure criteria, showing the advantages and disadvantages for each, regarding composite structures are presented in this work. Test specimens\' manufacturing is described along with required tests for parameter definition and structures validation. The countersunk fastened joint strength is much lower than the composite structure itself, demonstrating the necessity of studies like this. A numerical model using criteria like Hashin and maximum stress was created. The finite elements\' simulation results had a close response to the experimental results and the model was validated and considered representative.

Diese Dissertation beschreibt die Synthese und Charakterisierung neuartiger Hyperstern-Polymere (HSP) und deren Funktion als Reaktivbinder in Epoxy- bzw. PUR-Harzen. Hyperstern-Polymere sind Hybride aus hochverzweigten (hvz) und linearen Polymeren. Sie können über ihre reaktiven OH-Gruppen als multifunktionelle hochverzweigte Quervernetzer kovalent in ein kationisch härtendes Epoxyharz einbinden und thermische sowie thermomechanische Eigenschaften verbessern.:Theoretischer Teil Einleitung und Aufgabenstellung Grundlagen 1 Polymeraufbau 1.1. Radikalische Polymerisationen 1.1.1. Kontrolliert radikalische Polymerisation 1.1.2. NMRP 1.1.3. ATRP 1.1.4. RAFT 1.2. Anionische Polymerisation 1.3. Kationische Polymerisation 1.3.1. CROP von Oxazolinen 1.4. Koordinative Polymerisationen 2 Verzweigte Polymerarchitekturen 2.1. Dendritische Polymere 2.1.1. Dendrimere 2.1.2. Hochverzweigte Polymere 2.1.2.1 SCVP 2.1.3. Dendrigrafts 2.1.4. Dendronisierte Polymere 2.2. Spezielle Polymerarchitekturen 2.2.1. Hyperstern-Polymere (HSP) 3 Lacke 3.1. Lösungsmittelhaltige Lacke 3.1.1. Chemisch härtende Lacke 3.1.2. Physikalisch trocknende Lacke 3.2. Wässrige Lacke 3.3. Lösungsmittelfreie Lacke 3.3.1. Strahlenhärtende Lacke 3.3.2. Pulverlacke 3.4. Aliphatische Epoxylacke 3.4.1. UV-Härtung 3.4.2. Thermische Härtung 3.4.3. Thermische Härtung klassischer 2K-Polyepoxid-Lacke 3.5. 2K-PUR-Lacke 3.6. Aktuelle Herausforderungen 3.7. Wissenschaftliche Konzepte zur Schlagzähmodifizierung von Lacken Diskussion und Ergebnisse 4 Synthese hochverzweigter Makroinitiatoren 4.1. Polyester-Makroinitiatoren PE-MI1 und PE-MI2 4.1.1. Polyester-Kern (PE-OH) 4.1.2. Makroinitiatoren für die Oxazolinpolymerisation (PE-MI1) 4.1.3. Makroinitiatoren für die ATRP von Methacrylaten (PE-MI2) 4.2. Poly(vinylbenzylchlorid)-Makroinitiator (PVBC) 5 Hypersterne mit POxa-Armen 5.1. Lineare Polyoxazolin-Modellverbindungen (POxa) 5.1.1. Test der Initiatorfunktionen 5.1.2. Einfluss der Mikrowelle 5.1.3. Terminierung (Capping) 5.1.4. Polymerisation OH-tragender Oxazoline 5.1.5. Adamantan-funktionalisierte Polyoxazoline 5.2. Hypersterne aus Polyester-Kern sowie Polyoxazolin-Armen: PE-g-POxa 5.2.1. Einführung von OH-Gruppen über die Terminierung 5.2.2. Einführung von OH-Gruppen über die Wiederholeinheiten 5.3. Hypersterne aus Polyvinylbenzylchlorid-Kern sowie Polyoxazolin-Armen: PVBC-g-POxa 5.3.1. Modellinitiatoren 5.3.2. Einführung von OH-Gruppen über die Wiederholeinheiten 5.4. Ausblick: Arm first-Strategie 6 Hypersterne mit Polymethacrylat-Armen 6.1. Hypersterne aus Polyvinylbenzylchlorid-Kern sowie Polymethacrylat-Armen: PVBC-g-PHEMA 6.2. Hypersterne aus Polyester-Kern sowie Polymethacrylat-Armen: PE-g-(PMMA-b-HEMA) 7 Hypersterne als Quervernetzer-Additive in Lacken 7.1. PVBC-g-POxa in Epoxyharz 7.1.1. Thermische Härtung 7.2. PE-g-P(MMA-b-HEMA) in Epoxyharz 7.2.1. UV-Härtung 7.2.2. Thermische Härtung 7.3. PE-g-P(MMA-b-HEMA) in 2K-PUR-Harz Zusammenfassung – Ausblick Experimenteller Teil 8 Geräte, Methoden und Chemikalien 9 Synthesen 9.1. Monomere, Capper, Niedermolekulare Substanzen 9.2. Lineare Polyoxazoline 9.2.1. Niedermolekulare CROP-Initiatoren 9.2.2. Lineares Poly(2-methyloxazolin) (PMeOxa) 9.2.3. Adamantan-funktionalisierte Poly(2-methyloxazoline) 9.2.4. Lineare Poly(2-ethyloxazoline) 9.2.5. NMR-Modellverbindungen für PVBC-Kern 9.3. Hochverzweigte Polymere und Makroinitiatoren 9.4. Hyperstern-Polymere mit POxa-Armen 9.5. Hyperstern-Polymere mit PAlkMA-Armen 9.6. Lackproben Abkürzungsverzeichnis Literaturverzeichnis Publikationsliste

Carbon fibre reinforced composites are known for their high specific strength-to-weight ratio and are of great interest to the aerospace industry. Incorporating these materials into the fuselage, like in Boeing's 787 "Dreamliner", offers considerable weight reduction which increases flying efficiency, and reduces the cost of flying. In flight, aircraft are often subject to lightning strikes which, in the case of composites, can result in localized melting given the high resistive nature of the material. Aerospace carbon fibre composites often incorporate a metallic mesh or foil within the composite layers to dissipate the electrical charge through the large aircraft. The damage to the aircraft is minimized but not always eliminated. This research aims to elaborate a practical technique to deposit thin layers of conductive material on the surface of aerospace grade composites. Using Cold Gas Dynamic Spray (CGDS), such coatings could be used to repair damaged components. An experimental research approach was used to develop metallic coated composites. Using the CGDS equipment of Centerline (SST-P), specific parameters (such as gas temperature and stagnation pressure) were determined for each type of metallic coating (tin-based & copper-based). The use of bond coats was explored in order to attain the desired coatings. Once optimized, these coatings were evaluated with respect to their corrosive, adhesive, and electrical properties following industry standards.

Parmi les nouvelles technologies pour l’énergie inscrites dans un contexte de développement durable, les piles à combustible à membrane échangeuse de protons (PEMFC) présentent des aspects séduisants. Toutefois, pour rendre cette technologie compatible avec une application à grande échelle, elle doit répondre à des exigences strictes en termes de coût, performance, et durabilité. Alors que les plaques bipolaires métalliques sont pénalisées par leur résistance à la corrosion et celles en graphite par leurs propriétés mécaniques et leur coût (dû aux phases d’usinage des canaux), les plaques bipolaires composites apparaissent attrayantes en raison de leurs propriétés et performances et de leur coût. Cette thèse s’inscrit dans ce cadre, en proposant un matériau composite à matrice organique de type époxy et charges conductrices de graphite. L’objectif de notre étude consiste à mettre au point un matériau thermodurcissable à base d’une formulation époxyde solide (permettant de contrôler sa chimie et plus particulièrement sa réactivité) fortement chargée en graphite. Deux formulations différentes sont étudiées. La première est à base de prépolymère époxy appelé DGEBA et de dicyandiamide (DDA) comme durcisseur. L’autre formulation étudiée est constituée de DGEBA et de durcisseur : le 3,3’,4,4’-benzophénone dianhydride tétracarboxylique (BTDA). Ces deux formulations ont la particularité d’être très réactives à haute température (180-200°C) caractérisées par des temps de gel très courts (plus petit que 1min) afin d’avoir un temps de cycle de réticulation court pour une industrialisation de la fabrication. De plus, ces mêmes matrices ont montré une bonne stabilité chimique à température ambiante ainsi qu’une bonne stabilité thermique du système réticulé compatible avec la température d’utilisation des piles en fonctionnement. Concernant les réseaux composites résultant de la polymérisation DGEBA/BTDA et DGEBA/DDA, le module au plateau caoutchoutique est dominé par le taux de charge qui est très élevé (85%), celui-ci est ainsi très proche d’un réseau à l’autre et reste supérieur à 1 GPa. Nous constatons une viscosité relativement élevée pour les systèmes fortement chargés, point à prendre en compte lors du procédé de transformation. Enfin, la dernière partie des travaux réalisés concerne l’étude de mélange constitué de la matrice thermodurcissable (DGEBA/DDA/urée) modifiée par un thermoplastique (PEI). L’originalité et l’intérêt de ce travail résident dans l’incorporation de charges conductrices afin que celles-ci puissent se disperser dans la phase continue ou co-continue époxyde-amine lors de la séparation de phase pour limiter la proportion de charges et ainsi la viscosité des systèmes chargés. L’autre intérêt est d’améliorer les propriétés de résistance à la rupture du réseau époxyde TD final grâce à la présence de la phase thermoplastique séparée. / Among the new technologies for energy for sustainable development, PEM fuel cells offer seducing aspects. However, in order to make this technology fit large scale application requirements, it has to comply with stringent cost, performance, and durability criteria. While metal bipolar plates are penalized by their corrosion resistance and those based on graphite by their mechanical properties and cost (due to machining phases of the channels), the composite bipolar plates appear attractive because of their properties, performance and their cost. In such a frame, the goal of this PhD was to propose a composite material based on an epoxy matrix and graphite conductive fillers.The aim of our study was to develop a thermosetting material based on a solid epoxy formulation (to control its chemistry and in particular its reactivity) highly filled with graphite. Two different formulations were studied. The first was based on the epoxy prepolymer DGEBA and dicyandiamine (DDA) as a hardener. The other formulation studied was composed of DGEBA and curing agent: 3,3’,4,4’ benzophenone tetracarboxylic dianhydride (BTDA). Both formulations have the particularity to be very reactive at high temperature (180-200 °C) characterized by very short gel time (less than 1min) to have a short curing cycle for the industrialization of the production. In addition, these matrixes have shown good chemical stability at room temperature and good thermal stability of cross-linked system compatible with the operating temperature of the fuel cell. On composite network resulting from the polymerization DGEBA / BTDA and DGEBA / DDA, the rubbery modulus appears to be dominated by the loading rate, very high (85%), and is above 1 GPa. We see a high viscosity for highly filled systems, point to consider during the process of transformation. The final part of the work concerned the study of blend of the thermosetting matrix (DGEBA / DDA / urea) modified with a thermoplastic (PEI). The originality and interest of this work is the incorporation of conductive fillers so that they can be dispersed in the continuous or co-continuous structure during the phase separation to limit the proportion of charges and and the viscosity of filled systems. The other interest is to improve the properties of tensile strength of the thermosetting epoxy network with the presence of the thermoplastic phase.

En vue de vectoriser de façon ciblée des microcapsules de parfum vers un substrat textile pour des applications lessivielles, ce travail de thèse s’est consacré à la modification chimique de la surface de ces microcapsules en milieu aqueux par des polysaccharides ayant des affinités particulières pour les substrats de cellulose (agent d’aide au dépôt). Pour ce faire, une approche mettant en jeu des fonctionnalités époxy a été développée en deux étapes : fonctionnalisation de la surface des microcapsules par des molécules relais, puis greffage covalent d’un polysaccharide via la fonctionnalité époxy. Après chaque étape de greffage covalent en surface des microcapsules, différentes stratégies de caractérisations ont été mises en place (spectroscopies infrarouge, RAMAN, RMN du solide, XPS, ATG, mesure du potentiel zêta, gravimétrie, microscopie optique et fluorescente). Des expériences témoins ont également été réalisées pour prouver la non-adsorption des greffons de surface sur les microcapsules. La synthèse et le greffage de polysaccharides marqués avec des sondes fluorescente, alcyne et méthacrylate nous ont également permis d’appuyer nos conclusions. Afin d’envisager des modifications chimiques en milieu aqueux, la stabilité des composés époxy dans l’eau a dû être étudiée de façon précise par spectroscopie RMN en solution et nous avons abouti avec succès à une meilleure compréhension des phénomènes réactionnels époxy-amine et époxy-hydroxyle en milieu aqueux.Enfin, une enzyme (la lipase) a également pu être greffée de façon covalente via la fonctionnalisation époxy tout en conservant son activité catalytique. / Colloidal suspensions are of paramount significance in industrial applications. They are employed in various domains like paintings, inks, pigments, pharmacology, cosmetics, food,textile, composite materials or waste water treatment. Properties of colloids strongly depend on parameters such as the chemical composition, dimensions or morphology. To confer additional features to the colloids, i.e. stability, compatibilization, targeting, stealth properties and so on, it is also crucial to tailor their surface functionalization. In this work, we intend to develop a methodology allowing for tuning the surface properties of highly cross-linked fragrance microcapsules to graft polysaccharides. To do so, the first objective of this work is to identify functionalities at the surface (of the colloids) amenable to post-modifications. Based on this crucial insight, suitable surface chemistries are further explored to impart new properties to the colloids. Thus the presence of amine functions is highlighted by ninhydrine tests and then exploited to incorporate new functionalities at the surface of colloids.Incorporation of fluorescent tags (such as  Rhodamine Isothiocyanate, RITC), intermediate polymer epoxy chains (α,ω-epoxy functionalized polyethylene glycol or PGMA) are performed. Depending on the nature of the moieties to be grafted, the resulting colloids are subsequently characterized by Confocal Laser Scanning Microscopy (CLSM), FTIR, XPS, and RAMAN Spectroscopy. After this first step of functionnalization, epoxy rings at the surface are used to postgraft polysaccharides.

No description available.

M. Tech. (Department of Mechanical Engineering, Faculty of Engineering and Technology), Vaal University of Technology. / Sisal is a vegetable fibre extracted from the leaves of Agave Sisalana. The fibre is long, bold and creamy white in colour besides being exceptionally strong. It can be used for making agricultural and parcelling twines of various kinds as well as ropes, sacks, carpet and upholstery. The primary purpose of this research was to study and evaluate the use of sisal as a reinforcing fibre in both treated and untreated forms with epoxy resin matrices. The casting process employed during the composite production was the the vacuum infusion. The effects of both the treated sisal fibre-epoxy resin composites and the untreated sisal fibre-epoxy resin composites on the tensile strength and stiffness, flexural strength and stiffness, impact toughness, shear strength, compression strength and hardness were evaluated. Finally, the occurrence of transverse matrix fracture and fibre pull-out were also studied. It was found that the quasi-static mechanical properties of both the treated sisal fibre-epoxy resin composites and the untreated sisal fibre-epoxy resin composites improved with increases in reinforcement weight fractions. Further, fibre surface treatment on the sisal fibres and the attendant increase in the interfacial bond also resulted into improved quasi-static mechanical properties of the treated sisal fibre-epoxy resin composites when compared to untreated sisal fibre-epoxy resin composites.

Master of Science / Department of Grain Science and Industry / Xiuzhi Susan Sun / Plant oil-based raw materials have become more attractive alternatives in polymer industry as fossil resources depletion and environmental concerns continue to arise. Camelina (camelina sativa L.) seed contains about 45% of oil and about 90% of the oil is unsaturated fatty acids such as linoleic acid, α-linolenic acid, and erucic acids. It also provides the advantages of low cost and low fertilizer demand. Functionalized oils such as epoxidized camelina oil (ECO) and di-hydroxyl camelina oil (DCO) can be used for resins, adhesives, coatings, etc. The objectives of this work were to synthesize and characterize ECO and DCO from camelina oil. The epoxidation reaction of camelina oil was completed with formic acid and hydrogen peroxide. Catalyst ratio, reaction time, and temperature effects on the epoxidation reaction were studied. The optimum epoxy content of 7.52 wt% with a conversion rate of 76.34% was obtained from camelina oil using excess hydrogen peroxide and a molar ratio of formic acid of less than 1 for 5 hours in 50 °C. Camelina oil yields higher epoxy content (7.52 wt%) than soybean oil (6.53 wt%); however, soybean oil had a higher conversion rate of 80.16% compared to camelina oil because of uniform fatty acids distribution. In this study, we found that epoxidation efficiency is significantly affected by fatty acids composition, structure, and distribution. DCO was synthesized from ECO with different reaction parameters. The ring opening of ECO was performed with water, perchloric acid, and THF as proton donor, catalyst, and solvent respectively. Hydroxyl value of DCO was measured, and the maximal hydroxyl value was 369.24 mg KOH/g. physical properties of DCO were characterized by acid value and moisture content; thermal properties of DCO were obtained using different scanning calorimeter (DSC), thermalgravimetric analysis (TGA). Amount of solvent and acid catalyst addition affected the hydroxyl value and residual acid in DCO. Heat capacity, phase transition temperatures, and thermal stability of DCO were obtained and showed higher values than ECO’s. The DCO showed higher peel adhesion when it was formulated with epoxidized soybean oils through UV curing because camelina oil allows higher epoxy content, which results in higher hydroxyl values.

The AHRLAC aircraft is a high performance light aircraft that is developed and manufactured in South Africa by Aerosud ITC in partnership with Paramount. This aircraft is the first of its kind to originate from South Africa. The aircraft has a twin boom, tandem pilot seating configuration, with a Pratt and Whitney turbine-propeller engine in a pusher configuration. The main structure of the aircraft is a conventional metallic structure, while the fairings and some secondary structures are composite. This study will focus on the design and development of the composite ventral fin of the first prototype aircraft, the experimental demonstrator model (XDM). It is crucial to ensure that the ventral fin can function safely within the design requirements of the aircraft under the loads which the fin is likely to encounter. Preceding the design process, a critical overview of composite materials used in aircraft applications is provided. This will include the materials, manufacturing methods, analysis and similar work done in this field of study. The literature will be used in the study for decision-making and validation of proven concepts and methodologies. The first part of this study entailed choosing a suitable composite material and manufacturing method for this specific application. The manufacturing method and materials used had to suit the aircraft prototype application. The limitations of using composite materials were researched as to recognize bad practice and limit design flaws on the ventral fin. Once the material and manufacturing methods were chosen, ventral fin concepts were evaluated using computer aided finite element analysis (FEA) with mass, stiffness and strength being the main parameters of concern. The load cases used in this evaluation were given by the lead structural engineer and aerodynamicist. The calculations of these loads are not covered in detail in this study. The FEA input material properties used, were determined by material testing by the relevant test methods. The ventral fin concept started as the minimal design with the lowest mass. The deflections, composite failure and fastener failure were then evaluated against the required values. The concept was modified by adding stiffening elements, such as ribs and spars, until satisfactory results were obtained. In this way a minimal mass component is designed and verified that it can adequately perform its designed tasks under the expected load conditions. Each part used in the ventral fin assembly was not individually optimized for mass, but rather the assembly as a whole. The final concept was modelled using the computer aided design software, CATIA. This model used in combination with a ply book made it possible to manufacture the ventral fin in a repeatable manner. A test ventral fin was manufactured using the selected materials and manufacturing methods to validate the design methodology. In the next step the selected load cases were used in static testing to validate the FEM through comparison. The result of the study is a composite ventral fin of which the mass, stiffness and strength are suitable to perform its function safely on the first prototype AHRLAC aircraft. The study concludes on the process followed from material selection to FEA and detail design, in order for this same method to be used on other AHRLAC XDM composite parts. / M (Mechanical Engineering), North-West University, Potchefstroom Campus, 2015