Commingled composites are stronger than those manufactured with the standard manufacturing method. The objective of the thesis is to answer why that is, to investigate the microstructure of the composites, to model composite strength and compare experimental values with theoretical for composites having poly lactic acid (PLA) as matrix material and composites having poly propylene (PP) as matrix material. X - Ray micro - computed tomography was used to investigate the micro structure of the composites. Input from X - Ray micro - computed tomography was used to show that commingled PLA composites are stronger than standard PLA composites because the fibers are longer and more of them are orientated closer to the loading direction. Composites having PP as matrix material have lower strength than composites with PLA as matrix material. The strength for these composites is pretty much the same regardless of manufacturing method but still a little higher for commingled PP composites. Theoretical strength is modelled with the modified rule of mixture and correlates well with experimental values, having an R2 value of 0.95 for average composite strength.

The production of bio-based and biodegradable nanocomposites has gained attention during recent years for environmental reasons; however, the large-scale production of these nanocomposites still poses challenges. The objective of this work has been to prepare bio-based and biodegradable nanocomposites via liquid-assisted extrusion and to gain a deeper understanding of the process and the relationship between the process, composition, structure and properties. Extrusion is a common industrial process and thus, the development of this technique for the preparation of bionanocomposites can promote the commercialization of these materials in future. In this work, nanocomposites based on polylactic acid (PLA), cellulose nanofibers (CNF), cellulose nanocrystals (CNC), and chitin nanocrystals (ChNC) with varying nanomaterial content were prepared via liquid-assisted extrusion using a plasticizer as a dispersing and processing aid. This process consists of dispersing the nanomaterial in a liquid composed of water, a plasticizer and/or a solvent, and then feeding this suspension directly into the extruder during the process. To be able to carry out this process successfully, parameters such as the amount of liquid, the liquid feeding rate or the water-to-solvent ratio, among others, should be taken in account. CNF and ChNC were produced from banana rachis waste and crustacean waste, respectively, whereas CNC were available as a commercial product. Glycerol triacetate (GTA) and triethyl citrate (TEC) were used as plasticizers, dispersing and processing aids. The effects of the liquids used during extrusion, the plasticizers and the nanomaterials in the PLA properties were studied. Furthermore, the effects of the cooling rate during the compression molding and the solid-state drawing on the properties of the PLA nanocomposites were investigated. Additionally, the effect of ChNC on the processing and properties of blown films was evaluated. The results presented in this work demonstrated that the use of water and a solvent during the liquid-assisted extrusion did not decrease the molecular weight of the PLA. It was also found that the feeding of nanomaterials in aqueous or aqueous/solvent suspension resulted in PLA micro-composite with lower mechanical properties than PLA. However, when a nanomaterial was fed together with a plasticizer, its dispersion and distribution into the PLA were progressively improved with increasing plasticizer content. The plasticized PLA nanocomposites showed improved properties compared to their respective counterpart without nanomaterials when the plasticizer content was ≥7.5 wt%. Furthermore, it was demonstrated that the properties of PLA can be tailored through the composition of the nanocomposite or during the processing. It was observed that the modification of PLA with only plasticizer in high amounts (20 wt%) resulted in enhanced elongation at break and toughness but it had negative effects on the thermal and mechanical properties; however, the incorporation of nanomaterials minimized these effects. The addition of a small amount of nanomaterial (1 wt%), either CNF, CNC or ChNC, to plasticized PLA resulted in enhanced mechanical properties. It was also demonstrated that the cooling rate during compression molding and the solid-state drawing significantly affected the crystallinity of the PLA nanocomposites and, thus, their final properties. The fast cooling rate during compression molding resulted in more flexible and transparent materials than when a slow cooling rate was used, and as a result, PLA films with different mechanical properties were obtained. The drawing of the PLA/CNF nanocomposite at a drawing temperature slightly above the Tg, a high draw speed and at the highest drawing ratio, resulted in the highest mechanical properties. It was also found that the increased toughness after adding CNF to the plasticized PLA or after drawing the PLA/CNF nanocomposite, was attributed to the occurrence of massive crazing effect as a result of the presence of CNF and its effect on the crystallinity and/or on the spherulite growth. Finally, 6 kg of plasticized PLA nanocomposite with 5 wt% of ChNC was prepared and used as a masterbatch to produce bio-nanocomposite blown films. The nanocomposite material showed easier processability during the film-blowing process when compared with the reference material without nanocrystals. In addition, the nanocomposite blown films exhibited higher tear and puncture strength, lower fungal activity and lower electrostatic attraction properties, which are favorable in packaging applications.  In conclusion, this thesis shows that the liquid-assisted extrusion process is an excellent approach for producing PLA nanocomposites using cellulose and chitin nanomaterials. The results indicated that the addition of these nanomaterials, together with a plasticizer and further processing, can result in PLA nanocomposites with varied properties that can be used for packing applications. It was also shown that the processing technique presented can be a step forward for the large-scale production of bionanocomposites.

Sammanfattning  Inom flygindustrin blir komposit allt vanligare, framförallt på primära strukturdelar. Syftet med arbetet har varit att få en bild av de problem och utmaningar som finns för kompositer inom flygindustrin idag. Denna rapport har ett underhållsperspektiv och en analys har gjorts för att ta reda på vilka utmaningar och problem som användandet av kompositer kan medföra. Även för- och nackdelar har undersökts samt en jämförelse mellan komposit och aluminium har genomförts. För att ta reda på vilka utmaningar och problem som kan kopplas till komposit har intervjuer med kunniga personer inom flygbranschen gjorts. Dessa intervjuer har varit kvalitativa med öppna frågor för att på detta sätt ge intervjudeltagarna större chans till egna reflektioner och synvinklar inom ämnet. För att komplettera och få fördjupade kunskaper inom främst komposit samt aluminium har artiklar, handböcker och internethemsidor använts. Som ett resultat av intervjuerna samt inhämtning av fakta har problemformuleringen besvarats. Där fördelar med komposit visats vara viktbesparing, mindre korrosion samt mindre underhållskrävande. Däremot finns nackdelar som svårare att inspektera, dyrare material och det kräver andra kunskaper än vad aluminium gör. Samtidigt finns utmaningar som reparation av skada, mer resurskrävande vid reparation samt planeringsutmaningar. Framtida utmaningar för komposit är bland annat att identifiera skador, något som redan idag är ett problem. Samtidigt ser den tekniska utvecklingen ut att gå framåt för att kunna möta de problem som finns med kompositer. Arbetet har enbart beaktat det civila flygperspektivet i frågan, därmed har varken militära eller privata perspektiv tagits upp. De personer som har intervjuats är ingenjörer eller tekniker, inga tillverkare eller beslutfattare högre upp i flygbolagen har kontaktats. I framtiden kommer kanske kombinationer av nya aluminiumlegeringar samt komposit användas för att optimera flygplanet. / Abstract Within the aircraft industry composite becomes more common, especially on primary structures. The purpose of this thesis has been to get a picture of the problems and challenges that exist today related to composite. This report has a maintenance perspective and an analyse have been done to find problems and challenges that the use of composite can result in. Advantages and disadvantages between aluminium alloys and composite have been investigated as well as a general comparison. Interviews have been performed with people of knowledge within the airline industry to find out the challenges and problems connected to particularly composite. Qualitative and open questions have been used in the interviews, the people who were interviewed had an opportunity to tell their own perspective. In addition to interviews a collection of information about aluminium alloys and composite have been done in articles, handbooks and web pages. As a result of the interviews and the gathering of facts, the problem formulation has been answered. The benefits with composite are shown to be a saving in weight, less corrosion and less demanding maintenance. On the other hand, there are disadvantages like harder to inspect, more expensive material and it require different skills compared to aluminium. At the same time, there are challenges like the repair of damage, more demanding of resources when repairing and difficulties with planning. Future challenges for composite is among other things to identify damages, this is something that is already a problem today. At the same time, it looks like the technical development is going forward to meet the problems that are with composite. This thesis has only observed the perspective of the civil aircraft, the perspective of the military and the private sector have not been investigated. The people who have been interviewed are engineers and technicians, aircraft manufacturers or people high up in the airline who makes decisions have not been contacted. I the future there may be a combination of new aluminium alloys and composite on the aircraft to optimize the construction.

Målet med projektet är att undersöka om det med matematiska modeller eller datorsimulationer går att förutsäga hur fibermängd mellan 20 kg/m³ och 60 kg/m³ i stålfiberarmerad sprutbetong med tjocklek mellan 5 cm och 15 cm påverkar attenuering av RFID signaler. Detta är intressant att undersöka eftersom RFID är en möjlig teknik att använda för mätning av betongtjocklek. Stålfibrernas påverkan på RFID signalen tillsammas med de möjligheter som finns att förutsäga densamma bestämmer i stor grad RFID-teknikens lämplighet att användas för mätning av betongtjocklek. I rapporten undersöks homogenisering med hjälp av Maxwell-Garnetts blandningsformel tillsammans med en analytisk metod som jämförs med en datorsimulation i CST Microwave studio. Utöver det utförs ytterligare en datorsimulation i CST där stålfiberarmerad betong modelleras som inhomogen bestående av stålfiber och betong. Mätdata från experiment som utförts på stålfiberarmerade betongblock presenteras och jämförs med de simulerade och beräknade fallen. Av de metoder som undersöks i projektet har ingen validerats. Beräkningarna för varje metod ger ofta olika resultat, varav inga är direkt jämförbara med den data som uppmätts experimentellt. Fibrernas påverkan på signalen verkar däremot vara signifikant och bidra med stora mätosäkerheter och förluster. Enligt den inhomgena simulationen är Maxwell-Garnetts blandningsmetod olämplig för syftet. Den tagg som testas verkar inte vara lämpad för detta användningsområde. Svårigheter med radiokommunikation genom betong identifieras och förslag ges på hur en tagg kan konstrueras för att fungera bättre i miljön.

The interlaminar region is a contributing factor to the limited electrical conductivity of carbon fiber/epoxy composites. Consisting of electrically insulating epoxy matrix between conductive layers of carbon fiber, the interlaminar region prevents electrical interaction between the carbon fiber layers and electrical conduction in the through thickness direction.The interlaminar region in thin [0,0] carbon fiber/epoxy composites has been reinforced by carbon nanotubes (CNT) by two methods. First by aligned CNT forests from N12 Technologies and secondly by self-produced Buckypapers, porous CNT films, of different areal densitites. Two batches of laminates modified by aligned CNTs, having different curing conditions, and laminates modified with Buckypapers were manufactured. The laminates were evaluated by their electrical conductivity and electromagnetic interference shielding efficiency (EMI SE). The addition of external pressure to the laminates during curing brought an increase in longitudinal conductivity, a consequence of higher fiber packing. Also, both reinforcement methods increased the longitudinal conductivity through improved electrical interaction between the carbon fiber layers. However, only the Buckypaper reinforcement augmented the transversal conductivity significantly, acting as a highly conductive route in the interlaminar region. Both batches of aligned CNT modified laminates exhibited equal EMI SE, questioning the influence of the conductivity of the laminate on its EMI SE. Also, the increase in EMI SE brought by the aligned CNT forests were negligible compared to the reference. However, the reinforcement by Buckypapers proved successful, reaching -45/-50 dB at 1000 MHz, improving from 30 dB of the unmodified reference at the same frequency.

State-of-the-art aircraft engine manufactures aim to reduce theirenvironmental impact steadily. Thereby they attempt to increase engineefficiency, use new renewable fuel sources and most importantly aim toreduce component weight. While Titanium, Aluminum and continuousfiber reinforced thermosetting composites and superalloys prevail in thecurrent material selection, the present work desires to raise awareness fora novel group of materials; short carbon fiber reinforced thermoplasticcomposites (SCFRTPs). In this kind of composite short fibers givedimensional stability and strength while the thermoplastic matrix ensuresthe physical properties, even at temperatures up to 300°C.Even though in some applications these materials offer great potential tosave weight and cost, it is not clear if their properties suffice to be used indemanding areas of the aero engine and if they are still able provide costand weight reductions there.The present work therefore investigated potential aero-engine componentsthat could be replaced by SCFRTPs. With literature, manufacturer data andmaterial and process modelling approaches, it is shown that SCFRTPsmechanical and physical properties suffice for the selected component.Further it is shown that cost reductions up to 77% and weight savings upto 67% compared to the Ti-6Al-4V baseline component are possible.

Since its beginnings, the aerospace industry has been interested in lowering the weight of aircraft. Moving from performance and economic drivers to environmental design parameters, the weight has continuously been a major focus for this industry. A possible option to reduce weight is to use lighter materials such as fibre reinforced polymer composites (FRPC). This type of material has the potential to be used into cold or moderate high-temperature sections of aero-engines. One major obstacle that hinders composite insertion into aero-engines is the lack of predictive models. In recent years, there has been increasing interest in multiscale modelling as a possible approach to reliably predict composite behaviour. This modelling refers to the simulation of a material’s behaviour through multiple scales, passing on information from one scale to another. The purpose of the present work is to use a commercially available software tool (Altair Multiscale Designer™) to virtually characterize an FRPC made from a non-crimp fabric reinforcement based on its individual constituent properties. The studied composite was a carbon fibre and epoxy system developed by GKN Aerospace. In order to achieve this, a well-characterized unidirectional (UD) carbon fibre prepreg composite was used to calibrate the software. After calibration and verification, different repetitive unit cells were created to capture the non-crimp fabric (NCF) architecture where the effect of fibre waviness was studied. The calibration step allowed for fairly accurate and acceptable results when testing unidirectional or ±45 laminates with different tested UD prepreg material systems. The higher deviation from experimental values was up to 20% with these laminates’ configurations. When simulating more complex layups, such as quasi-isotropic ones, the simulations resulted in over-predicting up to 40% of the composite strength in comparison to experimental data. The study of NCF composites appeared to be more complicated than anticipated. Their complex architecture exhibits complicated failure modes, which could not be captured by the software tool. Large inaccuracy up to 100% were observed between simulation and experimental values of the laminate strengths. In spite of its limitations, the study of NCF composites allowed for a deeper understanding of the software functionalities and findings on the fibre waviness impact onto the predicted stiffness, while the strength of the laminate did not show dependency with the fibre waviness.

In this thesis, UN-U3Si2 nuclear fuel was fabricated using spark plasma sintering and characterized to analyze the microstructure and crystal structure of the resulting pellets. This work was done in collaboration with accident tolerant fuel research, an effort which aims at developing nuclear fuel with superior safety and performance compared to currently used oxide fuels. Uranium silicide was manufactured by arc melting to produce U3Si2 and uranium mononitride was synthesized by using the hydriding-nitriding method. They were mixed in varying compositions (5 wt%, 10 wt%, 20 wt%, and 25 wt% U3Si2) in order to create composite fuel pellets. Characterization of the resulting pellets showed an apparent ternary phase of U-N-Si, prompting fabrication of four more pellets at varying temperatures (1200 °C, 1300 °C, 1400 °C, and 1500 °C) to try and identify the temperature of phase formation. The presence of a probable ternary U-N-Si phase was confirmed to be present in all fuel pellets. Therefore, further investigation into the thermodynamic behavior of the ternary U-N-Si system is suggested before this fuel can be recommended for use in a reactor.

QC 20120131 / MOJO

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