Thermoset Composite Welding (TCW) is a process designed specifically for joining composite materials, developed by the Cooperative Research Centre for Advanced Composite Structures (CRC-ACS). The TCW manufacture process is carried out at higher temperatures than those used in service, causing thermal residual (TR) stresses to develop in the joints. An investigation of the strength of single-lap shear joints (SLJs), and the development of laminate free edge microcracks (LFEMs) is presented in this thesis. The reported investigations are primarily experimental. Finite element analysis has been used to understand observations where appropriate. The effect of TR stresses on static failure of TCW SLJs and Cytec FM1515 thin film epoxy adhesive SLJs over the temperature range of -55??C to 71??C is investigated. At temperatures where the joining material is ductile, plastic flow results in the redistribution of TR stresses within the joints, reducing their effect on the failure strength. No such stress redistributions occur at lower temperatures when the joining material is brittle; hence, the TR stresses cause strength reductions. These results were used to propose a method of shear strength improvement by initiating plastic flow in the joint at the time of manufacture. Microcracks are common at the free edges of thermoset composites. These develop preferentially near the weld material interface in TCW laminates, and are termed laminate free edge microcracks (LFEMs) in this study. MicroCT scanning was used to find and characterise LFEMs in TCW joints. The results indicated that TR stresses combined with the free edge sectioning process cause their development outside the joint overlap regions. Microcracks developed within the joint overlaps during mechanical fatigue cycling. LFEMs were also found in FM1515 joints. A fatigue life study is presented for TCW and FM1515 SLJs at -55??C, in which the effect of LFEMs is considered. TCW is a new process. This investigation is the first dealing with the effect of thermal residual stresses on the strength of TCW joints, and the development and effect of LFEMs. The shear strength improvement method is also a novel concept for joints.

Thermoset Composite Welding (TCW) is a process designed specifically for joining composite materials, developed by the Cooperative Research Centre for Advanced Composite Structures (CRC-ACS). The TCW manufacture process is carried out at higher temperatures than those used in service, causing thermal residual (TR) stresses to develop in the joints. An investigation of the strength of single-lap shear joints (SLJs), and the development of laminate free edge microcracks (LFEMs) is presented in this thesis. The reported investigations are primarily experimental. Finite element analysis has been used to understand observations where appropriate. The effect of TR stresses on static failure of TCW SLJs and Cytec FM1515 thin film epoxy adhesive SLJs over the temperature range of -55??C to 71??C is investigated. At temperatures where the joining material is ductile, plastic flow results in the redistribution of TR stresses within the joints, reducing their effect on the failure strength. No such stress redistributions occur at lower temperatures when the joining material is brittle; hence, the TR stresses cause strength reductions. These results were used to propose a method of shear strength improvement by initiating plastic flow in the joint at the time of manufacture. Microcracks are common at the free edges of thermoset composites. These develop preferentially near the weld material interface in TCW laminates, and are termed laminate free edge microcracks (LFEMs) in this study. MicroCT scanning was used to find and characterise LFEMs in TCW joints. The results indicated that TR stresses combined with the free edge sectioning process cause their development outside the joint overlap regions. Microcracks developed within the joint overlaps during mechanical fatigue cycling. LFEMs were also found in FM1515 joints. A fatigue life study is presented for TCW and FM1515 SLJs at -55??C, in which the effect of LFEMs is considered. TCW is a new process. This investigation is the first dealing with the effect of thermal residual stresses on the strength of TCW joints, and the development and effect of LFEMs. The shear strength improvement method is also a novel concept for joints.

Metallic robotic arms, or manipulators, currently dominate automated industrial operations, but due to their intrinsic weight, have limited usefulness for large-scale applications in terms of precision, speed, and repeatability. This thesis focuses on exploring the feasibility of using polymeric composite materials for the construction of long-reach robotic arms. Different manipulator layouts were investigated and an ideal design was selected for a robotic arm that has a 5 [m] reach, 50 [kg] payload, and is intended to operate on large objects with complex curvature. The cross-sectional geometry of the links of the arm were analyzed for optimal stiffness- and strength-to-weight ratios that are capable of preserving high precision and repeatability under time-dependent external excitations. The results lead to a novel multi-segment link design and method of production. A proof-of-concept prototype of a two degrees-of-freedom (2-DOF) robotic arm with a reach of 1.75 [m] was developed. Both static and repeatability testing were performed for verification. The results indicated that the prototype robot main-arm constructed of carbon fiber-epoxy composite material provides good stiffness-to-weight and strength-to-weight ratios. Finite element analysis (FEA) was performed on a 3-D computer model of the arm. Successful verification led to the use of the 3-D model to define the dimensions of an industrial-sized robotic arm. The results obtained indicate high stiffness and minimal deflection while achieving a significant weight reduction when compared to commercial arms of the same size and capability.

Cette thèse s’inscrit dans le cadre d’un vaste programme visant à établir un premier retour d’expérience sur des structures aéronautiques en fin de vie. L’objectif des travaux présentés ici est donc de caractériser le vieillissement et les propriétés résiduelles de pièces provenant d’avions après démantèlement, et donc après service. Plus précisément, deux matériaux de nature différente sont considérés : un alliage d’aluminium 2024-T351, constitutif d’une voilure d’A320 ; et un composite carbone/époxy T300/914, prélevé sur les voilures d’un Falcon X et d’un ATR.Pour les voilures composites, les travaux ont porté sur les effets de l’eau des stratifiés. L’évolution de la température de transition vitreuse en DMA a été étudiée en fonction du taux d’humidité présente dans le stratifié. Les résultats d’essais de sorption set de désorption ont été confrontés à différents modèles de diffusion. Les propriétés résiduelles ont été évaluée au travers de divers essais mécaniques. Il ressort de cette étude un très bon comportement du composite après service.Les travaux concernant la voilure métallique se focalisent sur les propriétés résiduelles en fatigue de l’alliage de voilure. Les résultats montrent qu’un durcissement structural apparaît en service, et qu’un léger abattement de la durée de vie en fatigue est observable. Cependant, le comportement à la fissuration est inchangé en comparaison avec un matériau « neuf ».Au final, ce premier retour d’expérience est positif. Il peut maintenant permettre aux avionneurs de vérifier les règles utilisées lors de la conception ou d’optimiser certains dimensionnements, mais aussi de justifier des extensions de durée de vie des avions. / The thesis is part of a larger program aimed at establishing a first feedback on structural health of aeronautical structures at the end of life. The aim of the work presented here is to characterize the residual properties after aging of parts from aircraft after teardown, and therefore after service. Specifically, two different types of materials are considered: an aluminum alloy 2024 T351, constituting the underside of an A320 wing, and a composite carbon/epoxy T300/914, taken from the wing of a Falcon X and the wing of an ATR.Concerning the composite wings, the study focused on the effects of water on laminated composites. The evolution of the glass transition temperature by DMA has been studied as function of moisture present in the composite. The results of sorption and desorption tests were confronted to different diffusion models. Residual properties were evaluated through various mechanical tests. It is clear from this study a very good behavior of the composite after service.The work on the metal wing is focused on the residual fatigue properties of these alloys. The results show that hardening occurs in service, and a slight reduction of the fatigue life is observed, the number of cycles to failure ranging between 104 and 106. However, the fatigue crack growth resistance is unchanged in comparison with a “virgin” material.Finally, this initial feedback is positive: It can now enable manufacturers to check the design rules or to optimize the design, but also to justify aircraft life extensions.

Highly crosslinked epoxy resin systems are essential in aerospace applications due to the high operating temperatures. Although highly crosslinked epoxy resins have the required glass transition temperature (Tg) for the application, they are inherently brittle and matrix toughness is improved by incorporation of a second phase. Previous studies have focused mostly on toughening of lightly crosslinked epoxy systems, whereas this study investigates toughening of a highly crosslinked epoxy resin system using thermoplastic toughners poly(ether sulfone) (PES) and a poly(methyl methacrylate)-b- poly(butyl acrylate)-b-poly(methyl methacrylate) (MAM) block copolymer (BCP).

This work is devoted to the computational modeling of a lightning strike electric arc discharge induced air plasma and the material response under the lightning strike impact. The simulation of the lightning arc plasma has been performed with Finite element analysis in COMSOL Multiphysics. The plasma is regarded as a continuous medium of a thermally and electrically conductive fluid. The electrode mediums, namely the cathode and anode, have also been included in the simulation in a unified manner, meaning that the plasma and electrode domains are simulated concurrently in one numerical model. The aim is to predict the lightning current density, and the heat flux impinged into the anode's material surface, as well as the lightning arc expansion and pressure and velocity of the plasma flow. Our predictions have been validated by the existing experimental data and other numerical predictions reported by former authors.

Cette thèse s'est déroulée dans le cadre du projet TOLEDO (Tolérance aux dommages par impact des réservoirs hyperbares) piloté par Air Liquide en partenariat avec le CEA Le Ripault et l'institut PPRIME.L'hydrogène est stocké au sein de réservoirs de type IV à une pression de service de 700 bar.Ces structures composites présentent comme particularités d'être épaisses (> 30 mm), d'avoir une forte courbure et d'être préchargées en pression lors d'un éventuel impact.Notre travail a montré que ces particularités modifient le type, la quantité et la localisation des différents endommagements couramment observés (rupture de fibres, délaminage et fissuration matricielle).Les endommagements ont pu être quantifiés par le biais de méthodes simples et originales.L'influence des particularités sur le comportement à l'impact a pu être déterminée par l'utilisation de deux dispositifs expérimentaux conçus et réalisés au cours de cette thèse.Le premier permet de précontraindre en tension uniaxiale des plaques composites épaisses.Le second permet de précharger en état de membrane un tube composite ce qui a permis de montrer que le cas d'impact le plus critique vis-à-vis des réservoirs est lorsque ces derniers sont vides.Cette étude a permis de mettre en évidence la criticité des ruptures de fibres sur les pertes de performance au sein des réservoirs hyperbares.Un modèle numérique prenant en compte la dispersion des contraintes à rupture et des différents types d'endommagements a été développé.Il permet d'introduire un endommagement initial et a confirmé certains résultats expérimentaux. / This thesis took place within the framework of the project TOLEDO (Tolerance in the damage by impact of the hyperbaric reservoirs) managed by Air Liquide in partnership with the CEA Le Ripault and PPRIME institute.The hydrogen is stored within the type IV vessel at a servive pressure of 700 bar.These composite structures present as peculiarities to be thick (> 30 mm), to have a strong curvature and to be precharged in pressure during a possible impact.Our work showed that these peculiarities modify the type, the quantity and the localization of the various usually observed damages (fiber breakage, délamination and matrix cracking).The damages were able to be quantified by means of simple and original methods.The influence of the peculiarities on the behavior in the impact was able to be determined by the use of two experimental devices designed and realized during this thesis.The first one allows to preload a thick composite plates in uniaxial tension thick composite plates.The second allows to preload in state of membrane a composite pipe and allowed to show that the most critical impact towards reservoirs is when they are empty.This study allowed to highlight the criticality of the fiber breakage on the loss of performance within the hyperbaric reservoirs.A digital model taking into account the dispersal of the failure stress and various types of damages was developed.It also allows to introduce an initial damage and confirm some experimental results.

Unidirectional carbon fiber and fiberglass epoxy composite elements consolidated with aramid sleeves were radially impacted at 5 J (3.7 ft-lbs) and 10 J (7.4 ft-lbs), tested under compression, and compared to undamaged control specimens. These structural elements represent local members of open three-dimensional composite lattice structures (e.g., based on isogrid or IsoTruss® technologies). Advanced three-dimensional braiding techniques were used to continuously fabricate these specimens. The unidirectional core specimens, 8 mm (5/16 in) in diameter, were manufactured with various sleeve patterns. Bi-directional braided sleeves and unidirectional spiral sleeves ranged from a nominal full to half coverage. These specimens were tested for compression strength after impact. This research used an unsupported length of 50.8 mm (2.0 in) specimens to ensure a strength-controlled compression failure. Compression strength of undamaged unidirectional carbon fiber and fiberglass epoxy composites is virtually unaffected by sleeve type and sleeve coverage. Fiberglass/epoxy configurations exhibited approximately 1/2 and 2/3 reduction in compression strength relative to undamaged configurations after impact with 5 J (3.7 ft-lbs) and 10 J (7.4 ft-lbs), respectively. Increasing aramid sleeve coverage and/or increasing the interweaving of an aramid sleeve (i.e., braid vs. spiral) increases the damage tolerance of fiberglass/epoxy composite elements. Damaged carbon/epoxy composites exhibited an approximate decrease in strength of 70% and 75% after 5 J and 10 J of impact, respectively, relative to undamaged configurations. The results verify that an aramid sleeve, regardless of type (braid or spiral), facilitates consolidation of the carbon fiber and fiberglass epoxy core. Not surprisingly, full coverage configurations exhibit greater compression strength after impact than half coverage configurations.

A l'heure actuelle le stockage de l'hydrogène sous forme gazeuse, comprimée à haute pression, apparaît comme la solution le plus mature présentant le meilleur compromis en termes de masse, de pression de service mais aussi de volume des réservoirs. Cependant pour un développement plus large et sécurisé, l'amélioration des performances et la réduction des coûts des réservoirs restent des enjeux prioritaires. C'est dans ce contexte que nous avons étudié le stockage de l'hydrogène dans des réservoirs de type IV, en composites fibres de carbone/époxy. Ce travail a eu pour objectif d'accroitre la fiabilité du dimensionnement. Dans un premier temps, une étude expérimentale de caractérisation des matériaux constitutifs du réservoir a été réalisée. Pour améliorer la fiabilité des calculs, un modèle probabiliste a été proposé pour décrire le comportement de la partie composite du réservoir, principalement la rupture des fibres. Des calculs multiéchelles ont été mis en place basés sur les propriétés mécaniques et physiques des fibres. Les autres modes de dégradations, décollement entre plis, liaison embase-liner ont aussi été pris en compte dans les calculs de comportement du réservoir jusqu'à son éclatement. Enfin des recommandations de dimensionnement du réservoir ont été proposées afin d'améliorer les performances tout en minimisant la masse de composite dans un objectif de réduction des coûts. / Presently, the compressed hydrogen storage under high pressure appears to be the most sophisticated solution regarding to a compromise of mass, service pressure and also volume of pressure vessels. However, the challenges of pressure vessels nowadays are their performance improvement as well as their cost reduction. In this context, we studied the type IV hydrogen storage pressure vessel in carbon fibre/epoxy composites. This work aims to obtain a reliable pressure vessel design. Firstly, an experimental study of associated materials and pressure vessel characterisation has been carried out. Then, we proposed a probabilistic model for a composite which is dedicated in particular to fibre breakage using multi-scale simulations in accordance with its mechanical and physical properties. Once this model joined with damage criteria dedicated separately to the others damage mechanisms are integrated into the pressure vessel simulations. Finally, recommendations on composite pressure vessels have been proposed in order to improve their performances and to decrease the mass of composite directly corresponding to the reduction of composite pressure vessels cost.

Compression tests were performed on damaged and undamaged rods and tubes made from unidirectional carbon/epoxy composite and lightweight core materials. Tested samples represent local members in an open, three-dimensional, composite lattice structure. Testing was performed in order to establish effective core materials to use in order to increase the buckling length of local IsoTruss® members while maintaining low weight. Members were formed from T700SC-12K-50C carbon fiber with UF6639-100 resin. Core materials consisted of 3/8-inch (0.953 cm) outside diameter Teflon® rods, Teflon® tubes, nylon rods, nylon tubes, Ertalyte® rods, and Duratron® rods. All 3/8-inch (0.953-cm) cores were each surrounded by 50 tows of carbon/epoxy prepreg. Control samples were also created with 50 carbon/epoxy prepreg tows. Half-inch (1.27 cm) outside diameter copper tubes were used as core materials for tubes consisting of 100 carbon/epoxy prepreg tows. Control samples to compare against samples with copper cores were also created with 100 tows of carbon/epoxy prepreg. Impact damage was inflicted using a cylindrical tup with 20 ft-lb impact energy.In undamaged specimens, nylon tube showed the highest structural efficiency. Nylon showed structural efficiencies much higher than other materials when comparing undamaged samples. In damaged specimens Ertalyte® rods showed the highest structural efficiency. Core stiffness appeared to control the level of absorbed impact energy with stiffer cores absorbing and dissipating more energy than softer equivalents during impact.