Rapid prototyping has in the last few years gained an ever increasing central role in projects thanks to its agile benefits. Because of that, boundaries regarding what can be accomplished can be pushed and new techniques for achieving goals can be explored at a reasonable cost. A challenge that remains though, is to be able to prototype rapidly with advanced materials such as fibre composites, in a cost effective and reliable manner. The Maritime Robotics Laboratory at KTH Royal Institute of Technology is developing an unmanned fixed-wing aerial vehicle that is also submersible and takes off from the water surface. The design for the craft is completely novel in order to meet the necessary requirements.  The goal of this master's thesis is to assist with the design of the craft in order to ensure its manufacturability. When the design was finished, a structural analysis of said design was performed, utilizing finite element software. This ensured that the correct amount of material was used, where it was needed. Lastly, and the main scope of this thesis, is the manufacture of the components which make up the craft. Several options were considered during the manufacturing process, like vacuum infusion and prepreg due to the varying size and complexity of all the components which are to be manufactured.  More conventional materials (such as medium density fibreboard) was decided upon when manufacturing the molds for the main airframe of the craft due to its sheer size. The method which was decided upon for building all auxiliary components was to use inexpensive 3D-printed polylactic acid molds, coated with glass fibre reinforce adhesive polytetrafluoroethylene film, in conjunction with a low-temperature prepreg. The trials eventually turned out successful and the components which were built using this technique came out according to their specified dimensions that were provided and in accordance to the structural analysis which was conducted. This is promising for rapid prototyping in where only entry-level composites manufacturing equipment is accessible. / "Rapid prototyping" (Snabb prototyptillverkning) har under de senaste åren fått en allt mer central roll i projekt tack vare dess agila fördelar. På grund av detta kan gränser för vad som kan åstadkommas tänjas på och nya tekniker för att uppnå mål kan undersökas till en rimlig kostnad. En utmaning som dock kvarstår är att snabbt kunna ta fram prototyper med avancerade material som fiberkompositer på ett kostnadseffektivt och pålitligt sätt. Maritime Robotics Laboratory vid KTH utvecklar en drönare som är nedsänkbar under vatten och lyfter från vattenytan. Designen för detta är helt ny för att uppfylla den önskade kravspecifikation. Målet med detta examensarbetet är att hjälpa till med utformningen av drönaren för att säkerställa dess tillverkbarhet. Designarbetet omfattar en strukturanalys med användning av finita elementmetoder. Detta för att säkerställa att rätt mängd material används där det behövs. Slutligen, och huvuduppgiften för detta projekt, är tillverkningen av de komponenter som utgör drönaren. Flera alternativ övervägdes under tillverkningsprocessen, som vakuuminjektion och prepreg på grund av den varierande storleken och komplexiteten hos alla komponenter som ska tillverkas. Mer konventionella material (som t.ex. medium density fibre, fiberspånskiva) valdes vid tillverkning av formarna för drönarens skrov på grund av dess stora storlek. Metoden som beslutades för att bygga alla hjälpkomponenter var att använda billiga 3D-printade polylaktid-formar, belagda med glasfiberarmerade självhäftande polytetrafluoreten-film, i kombination med en lågtemperatur prepreg. Försöken blev så småningom framgångsrika och komponenterna som byggdes med dessa metoder blev producerade enligt deras angivna dimensioner som gavs och i enlighet med den strukturella analys som utfördes. Detta är lovande för snabb prototyping där utrustning för produktion med kompositmaterial är begränsad till inträdesnivå.

The physical and mechanical characteristics of carbon fiber reinforced polymers (CFRP) and Ti6Al4V make them widely used in the aerospace industry. The hybrid structure of CFRP/ Ti6Al4V material has been used in the new generation of aircraft manufacturing. The drilling process of these materials is often associated with unfavorable machining defects such as delamination, burr formation, reduced surface integrity, and tensile residual stresses. These machining defects are attributed to high thermal load, continuous chip morphology, and poor chips evacuation efficiency. Vibration-assisted drilling (VAD) uses an intermittent cutting process to control the uncut chip thickness and chip morphology. VAD has potential advantages include low thermal load, high chips evacuation effectiveness, and longer tool life. This thesis presents an experimental investigation into the effect of VAD machining parameters on the cutting energy, CFRP delamination, surface integrity, geometrical geometry, Ti6Al4V burr formation, induced residual stresses, and tool wear during the drilling process of CFRP, Ti6Al4V, and CFRP/Ti6Al4V stacked materials. Moreover, a kinematics model is developed to link the observed results to the independent machining parameters (i.e., cutting speed, feed rate, modulation amplitude, and modulation frequency). The experimental work covers a wide range of machining parameters using four levels of frequencies (83.3, 125, 1500, and 2150 Hz). The VAD results show up to 56 % reduction in the cutting temperature with a significant enhancement in the CFRP entry and exit delamination, geometrical accuracy, surface integrity, and burr formation. The use of VAD also generates compressive stresses, hence improving the part fatigue life. / Thesis / Doctor of Philosophy (PhD)

La thématique de recherche proposée se présente comme une étude préliminaire en vue de minimiser le cout des opérations de perçage de multi-matériaux CFRP/Al et CFRP/Ti. Cette minimisation passe par la compréhension des mécanismes d'usure des outils de coupe ainsi que par la compréhension des phénomènes engendrant les différents défauts pouvant amener à la non-conformité de la pièce. Dans ce sens, des essais de perçages ont été mis en place. Leur instrumentation nous permet d'accéder aux efforts et aux températures générées lors de la coupe.En parallèle de cela, les moyens d'analyse mis en place permettent l'accès à la qualité des trous. L'identification de mécanisme d'usures subis par l'outil est réalisée à l'aide de visualisations au microscope électronique à balayage. L'usure du foret est aussi quantifiée par l'utilisation d'un microscope numérique pouvant mesurer le profil de l'arête de coupe de l'outil.Les champs de température au voisinage de l'interface outil/copeau influent de façon importante sur la durée de vie de l'outil. Difficile d'accès par l'expérimentation, ces champs de température sont toutefois accessibles par la simulation numérique des sollicitations thermiques appliquées à la pièce. Le modèle développé dans ce projet permet, par méthode inverse, de déterminer la température appliqué sur la paroi du trou à partir des mesures expérimentales réalisé à 4mm de celle-ci. Celui-ci à permis de visualiser l'étendu des zones affectées thermiquement et de confirmer les tendances observées expérimentalement

Fibre reinforced polymers (FRPs) have gained considerable popularity as a building and repair material. In particular, FRPs have been an economical means of extending the life of structures. As time passes, an increased number and variety of new and old structures are incorporating FRPs as reinforcement and for rehabilitation. Perhaps most common are their applications for bridge structures. Much of the reluctance towards the inclusion of FRP as primary reinforcement or as a rehabilitation measure in building structures is due to its poor performance in fires. In order to move forward with an understanding of how FRP may overcome its temperature-related short comings, it is important to explore the behaviour of FRP, and structures which utilize FRP for reinforcement, at elevated temperatures. The results of a testing program including eleven high temperature, two room temperature intermediate-scale, FRP-strengthened, and one unstrengthened reinforced concrete beam tests are presented. The elevated temperature tests were conducted on both un-post-cured and post-cured FRP strengthening at temperatures up to 211°C. The tests also utilized a novel method for heating and post-curing FRP-strengthening in place. The strengthened beams exhibited strength gains above the unstrengthened reference beam, and it has been demonstrated that post-curing of an FRP system can be effective at increasing an FRP’s performance at elevated temperatures. Exposed to constant temperatures, un-post-cured specimens still exhibited substantial FRP strength at exposure temperatures up to Tg+79°C. Post-cured specimens exhibited similar performance at temperatures of Tg+43°C. The transient temperature tests resulted in ii beam failure at an average temperature of 186°C and 210°C for un-post-cured and post-cured FRP strengthening respectively at a constant applied load level 93% of that of the room temperature strengthened control beam. The results of this testing program demonstrate that FRP strengthening can remain effective when exposed to temperatures well above the measured value of Tg. / Thesis (Master, Civil Engineering) -- Queen's University, 2013-02-28 15:14:31.336

As traffic demand on bridges increases, loading cycles on critical components will increase, reducing their service life. Modular bridge expansion joints, which are imperative to allowing the bridge superstructure to move, are susceptible to fatigue damage at their field splice. These splices are used to connect segments of the total joint, during staged construction. Current splice designs are either bolted or welded connections, which allow stress concentrations to induce pre-mature fatigue failure. This thesis examines the use of a hybrid FRP/steel design under fatigue loading for use as a splice detail. The splice detail consists of steel plates bolted to steel beam webs and CFRP pultruded plates adhesively bonded to the underside of the steel beam flanges. Two different moduli of CFRP were examined: Normal Modulus and Ultra High Modulus. Two beams of each modulus were tested under static conditions and six under constant amplitude fatigue loading. A testing rig was used to simulate similar bending moments experienced in bridge joints. In the static tests, slippage of the web plates caused considerable stiffness loss and the slippage load varied drastically between CFRP moduli. For the fatigue tests, the intention was to reach two million cycles at the different constant load ranges. Stiffness degradation was noticed during the fatigue process, and was likely due to bolt pre-tension loss and/or plastic deformation of the adhesive. Specimens that reached two million cycles were monotonically loaded to failure. Once the CFRP had failed, a secondary mechanism was observed for reserve load capacity. Simple beam mechanics were used to create prediction models for the initial spliced beam stiffness and peak CFRP load. Flexural and shear deformations of the spliced system were considered for beam stiffness. For the CFRP failure load prediction, a design peak strain in the CFRP was used to account for shear lag effects in the material and variability of the splice detail. While the model was inaccurate for beam stiffness, it provided a good approximate of the peak CFRP load. Based on the presented test data, the Normal Modulus CFRP hybrid splice detail showed better fatigue performance than conventional steel connection details. / Thesis (Master, Civil Engineering) -- Queen's University, 2013-07-24 11:28:19.728

Laminated carbon fibre-reinforced polymer (CFRP) composites are already well established in structural applications where high specific strength and stiffness are required. Damage in these laminates is usually localised and may involve numerous mechanisms, such as matrix cracking, laminate delamination, fibre debonding or fibre breakage. Microstructures in CFRPs are non-uniform and irregular, resulting in an element of randomness in the localised damage. This may in turn affect the global properties and failure parameters of components made of CFRPs. This raises the question of whether the inherent stochasticity of localised damage is of significance for application of such materials. This PhD project is aimed at developing numerical models to analyze the effect of material randomness on delamination damage in CFRP materials by the implementation of the cohesive-zone model (CZM) within the framework of the finite-element (FE) method. Both the unidirectional and cross-ply laminates subjected to quasi-static loading conditions were studied. The initiation and propagation in delamination of unidirectional CFRP laminates were analyzed. The CZM was used to simulate the progress of that failure mechanism in a pre-cracked double-cantilever beam (DCB) specimen loaded under mode-I employing initially, a two-dimensional FE model. Model validation was then carried out comparing the numerical results with experimental data. The inherent microstructural stochasticity of CFRP laminates was accounted for in the simulations, and various statistical realizations for a half-scatter of 50% of fracture energy were performed, based on the approximation of that parameter with the Weibull s two-parameter probability density function. More detailed analyses were undertaken employing three-dimensional DCB models, and a number of statistical realizations based on variation of fracture energy were presented. In contrast to the results of two-dimensional analyses, simulations with 3D models demonstrated a lower load-bearing capacity for most of the random models as compared to the deterministic model with uniform material properties. The damaged area and the crack lengths in laminates were analyzed, and the results showed higher values of those parameters for random realizations compared to the uniform case for the same levels of applied displacement. The effect of material randomness on delamination in CFRP cross-ply laminates was also investigated. Initially, two-dimensional finite-element analyses were carried out to study the effect of microstructural randomness in a cross-ply laminate under bending with the direct introduction of matrix cracks with varying spacings and delamination zones. A considerable variation in the stiffness for cases with different crack spacings suggested that the assumption of averaged distributions of defects can lead to unreliable predictions of structural response. Three-dimensional uniform, deterministic cross-ply laminate models subjected to a tensile load were analyzed to study the delamination initiation and propagation from the tips of a pre-existing matrix crack. The material s stochasticity was then introduced, and a number of random statistical realizations were analyzed. It was observed that by neglecting the inherent material randomness of CFRP laminates, the initiation conditions for delamination as well as the character of its propagation cannot be properly detected and studied. For instance, the delamination crack length value for all the simulated random statistical realizations predicted its higher magnitudes compared to the uniform (deterministic) case for the same value of applied strain. Furthermore, the location of delamination initiation was shown to be different for different random statistical realizations. Another aspect, emphasizing the importance of microstructural randomness, was the scatter in the magnitudes of global strain at the instance of initiation and subsequent propagation of delamination. In summary, the material randomness in CFRPs can induce randomness in localised damage and it can affect the global properties of laminates and critical failure parameters. These effects can be investigated computationally through the use of stochastic cohesive-zone elements.

The main aim of this research was to investigate the behaviour of adhesive joints exposed to repeated low-velocity impact i.e. impact fatigue (IF), and to compare this loading regime with standard fatigue (SF), i.e. non-impacting, constant amplitude, sinusoidal loading conditions. Two types of lap joint configuration using rubber toughened modified epoxy adhesives were used and exposed to various loading conditions in order to determine the fatigue behaviour of the joints for each load conditions. The fatigue life was investigated using bonded aluminium alloy (7075-T6) single lap joint (SLJ) specimens, where it was seen that IF is an extremely damaging load regime compared to SF. Different trends were visible in force-life plots for these two types of loading. In SF a gradual decrease in the fatigue life with increasing load was observed, whereas, in IF a significant decrease in life was seen at relatively modest levels of maximum force after relatively few cycles. Comparisons of the fatigue life show a considerably earlier failure in IF than in SF for comparable levels of force and energy. Additionally, it was demonstrated that the maximum force per cycle, loading time, stiffness and strength decreased as a result of damage generated in the sample during IF.

The application of composites has been increasing dramatically in aerospace structures recently, for example, composites have contributed over 50 percent of the structure mass of large transport airplanes Boeing 787 and Airbus 350XWB. However, the further usage has been restricted because of the high material and manufacturing costs. Hence, it is essential to utilize cost estimation tools for accurate cost estimation in the early design stages, and then efficient decisions and design optimizations could be made to reduce the cost of composite products. This research project aims to develop a cost model for aerospace carbon fibre reinforced plastic (CFRP) composites, which will help designers and cost engineers with the cost estimation for composites manufacturing in the early development stages. The main objectives of the research are to: (i) recognise the standard manufacturing stages and activities of CFRP components; (ii) identify the cost drivers of composites manufacturing; (iii) identify the cost estimation relationships; (iv) develop a cost model that can assist designers and engineers with manufacturing cost estimation for CFRP components; (v) validate the developed cost model through case studies and expert judgements. The process of model development was carried out through four main steps: firstly, conducting an integrated understanding of cost modelling for composites manufacturing; secondly, collecting data for cost modelling from industry and existing literature and databases; thirdly, developing the cost model with several function modules and databases; and finally, taking a validation of the developed model. The developed cost model consists of several modules: material selection, process planning, cost estimation, cost reporting and a user friendly interface. Moreover, the selection and planning modules are combined with databases including material and process. The developed model enables the user to estimate the manufacturing cost and process time of CFRP composites, and it can also help designers realize the impact of design changes on the manufacturing cost. The process planning can efficiently help estimators with manufacturing process understanding and accurate time estimation. Quality control activities are time consuming and investment sensitive in composites manufacturing.

La fatigue représente la deuxième cause d’endommagement des structures métalliques anciennes après la corrosion. Celle-ci se manifeste par l’apparition de fissures, dans les zones fortement sollicitées présentant des concentrations de contraintes importantes, et peut mener à terme à la ruine de l’ouvrage. Dans le cas des structures métalliques anciennes, les fissures de fatigue s’amorcent généralement au droit des trous de rivets rendant difficile leur détection par les techniques de contrôle non destructif conventionnelles. De même, les matériaux métalliques anciens de la construction, et notamment le fer puddlé, limitent l’utilisation de certaines techniques. Dans le cadre de ce travail de thèse, l’objectif principal est d’étudier l’efficacité d’un renforcement par composites collés dans le cas de fissures de fatigue émanant de trous de rivets. Pour cela, des éprouvettes de petites dimensions, présentant un perçage central et une unique fissure de fatigue en bord de perçage, ont été considérées. De même, deux matériaux métalliques, acier doux et fer puddlé, ainsi que deux procédés de renforcement PRFC (polymères renforcés de fibres de carbone), à Module Normal et à Ultra Haut Module, sont étudiés. Pour chaque procédé de renforcement, différentes configurations de renforcement ont été testées et notamment la mise en précontrainte du plat composite MN avant collage. Cela a permis de mettre en évidence l’efficacité de la technique de collage de plats PRFC pour un renforcement à la fatigue de matériaux métalliques anciens. Par ailleurs, les expressions analytiques simples proposées pour le facteur d’intensité de contraintes pourront par la suite être utilisés pour une application aux structures rivetées en tenant compte de la présence du rivet ainsi que celle des plaques assemblées. / After corrosion, fatigue phenomenon is the main cause of damage in old metallic structures. Fatigue cracks appear in stress concentration area subject to high stresses, and can lead to the ruin of the bridge. In old metallic structures, fatigue cracks mainly occur at the edge of the rivet hole and are thus difficult to detect with the common non-destructive inspection technique (NDI). Moreover, due to the poor quality of the old metallic materials, particularly puddled iron, some of the NDI techniques cannot be used. The main objective of the present work is to study the effectiveness of carbon fibre reinforced polymer (CFRP) laminates in reinforcing fatigue crack emanating from the rivet hole. Thus, investigations on small-scale specimens were done. These specimens consist of metallic plates with center hole from which one single crack emanates. Two metallic materials, puddled iron and mild steel, and two reinforcement processes were used. These reinforcement processes consist of Normal Modulus (NM) and Ultra High Modulus (HHM) CFRP laminates. Furthermore, symmetrical and un-symmetrical reinforcement configurations are considered as well as pre-stressing NM laminates before application. The experimental results showed firstly the efficiency of the different studied reinforcement configurations in slowing down crack propagation. In conclusion of this work, the achieved results, particularly those in terms of Stress Intensity Factor, could be used for reinforcement of riveted structures by CFRP bonding, taking into account the presence of rivets as well as the presence of the others elements of the assembly.

Civil engineers are presently faced with the challenge of strengthening and repairing many existing structures to assure or increase their structural safety. The reasons for this include changes in the use of structures, and increased traffic loads on bridges. In Iraq, for example, several highway bridges needed to accommodate increased axle load during the transportation of huge turbines for electricity generating stations. The requirement for structural strengthening and repair methods is, however, driven by the worldwide need to ensure the safety and sustainability of our aging infrastructure which is deteriorating at a rate faster than it can be renovated. The ever increasing damage caused by environmental effects and the corrosion of steel and deterioration of concrete, reduce structural safety and lead to disruption for the users, which can have serious economic consequences. In a plate girder bridge, the plate girders are typically I-beams made up from separate structural steel plates (rather than rolled as a single cross-section), which are welded or, in older bridges, bolted or riveted together to form the vertical web and horizontal flanges of the beam. The two primary functions of the web plate in a plate girder are to maintain a relative distance between the top and bottom flanges and to resist the induced shear stresses. In most practical ranges of plate girder bridges’ spans, the induced shear stresses are relatively low compared to the bending stresses in the flanges induced by flexure. As a result the web plate is generally chosen to be much thinner than the flanges. The web panel consequently buckles at a relatively low shear force. For steel girder structures dominated by cyclic loading, as is the case with repeated vehicle axle loads on bridges, this can lead to the so-called ‘breathing’ phenomenon; an out-of-plane buckling displacement that can induce high secondary bending stresses at the welded plate boundaries. In the current work, a novel FRP strengthening technique using bonded shapes is applied to resist these out of plane deformations, and hence reduce the breathing stresses, and improve the fatigue life of the plate girder which is very different to the majority of applications of FRP strengthening that exploit the FRP for its direct tensile strength and stiffness. The objective of the current experimental programme is to strengthen thinwalled steel girders against web shear buckling using a corrugated CFRP or GFRP panel bonded externally along the compression diagonal of the web plate. The programme was divided into three main phases, including: (1) the development of a new preformed corrugated FRP panel, and (2, 3) testing its performance in two main experimental series. The initial series involved tests on 13 steel plates strengthened with the proposed preformed corrugated FRP panel and subjected to in-plane shear loading using a specially manufactured “picture-frame” arrangement designed to induce the appropriate boundary conditions and stresses in the web plates. This initial test series investigated the performance of different forms of strengthening under static load, in preparation for another series of cyclic tests to investigate their fatigue performance. The test variables included FRP type (CFRP or GFRP), form of FRP (closed or open section), number of FRP layers, and orientation of GFRP fibres used to produce the FRP panel. In the second series, six specimens were manufactured to simulate the end panel of a plate girder. These were strengthened with the optimized FRP panel from the initial series and tested for shear buckling under repeated cyclic loading with a stress range 40-80% of the static ultimate capacity. A considerable increase in the stiffness of the strengthened specimens is evident in the observed reductions of the maximum out-of-plane displacement. The stiffness of the strengthened specimens is assessed to be increased by a factor ranging between 3 to 9 times the stiffness of the corresponding unstrengthened specimen, depending upon the type of the FRP panel used and the aspect ratio of the tested specimens. The breathing phenomena is also significantly reduced, consequently the surface, membrane and secondary bending stresses are reduced. The 45° strengthening scheme succeeded the best both in reducing the breathing stresses and increasing the ultimate shear capacity of the specimen by 88%. Fatigue analyses indicated that the proposed strengthening technique is able to considerably elongate the life expectancy of the strengthened plate girders by a factor ranging between 2.5 and 7 depending on the applied cyclic load amplitude. In addition, the proposed strengthening technique did not show any debonding or delamination under both static and cyclic loading which makes it a good candidate for strengthening thin-walled structural members, especially, when ductility is a concern. In fact, the proposed strengthening technique succeeded in improving the energy absorption capacity of the strengthened specimens by a factor ranging between 1.5 and 2.5 times the corresponding control specimen which means that the ductile failure type associated with shear buckling of steel plate girders is not only maintained, but it was improved as well. This type of ductile failure is not common in other types of FRP strengthening techniques. Finally, a geometrical and material non-linear finite element model is presented both for the steel and composite sections which showed very good correlation with test results and was capable of predicting both the strength and deformational behaviour of the tested specimens. This numerical model is used for a parametric study to support the proposed design method.