1,029 research outputs found

    Infusion Simulation of Graphene-Enhanced Resin in LCM for Thermal and Chemo-Rheological Analysis

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    The present numerical study proposes a framework to determine the heat flow parameters—specific heat and thermal conductivity—of resin–graphene nanoplatelets (GNPs) (modified) as well as non-modified resin (with no GNPs). This is performed by evaluating the exothermic reaction which occurs during both the filling and post-filling stages of Liquid Composite Moulding (LCM). The proposed model uses ANSYS Fluent to solve the Stokes–Brinkman (momentum and mass), energy, and chemical species conservation equations to a describe nano-filled resin infusion, chemo-rheological changes, and heat release/transfer simultaneously on a Representative Volume Element (RVE). The transient Volume-of-Fluid (VOF) method is employed to track free-surface propagation (resin–air interface) throughout the computational domain. A User-Defined Function (UDF) is developed together with a User-Defined Scaler (UDS) to incorporate the heat generation (polymerisation), which is added as an extra source term into the energy equation. A separate UDF is used to capture intra-tow (microscopic) flow by adding a source term into the momentum equation. The numerical findings indicate that the incorporation of GNPs can accelerate the curing of the resin system due to the high thermal conductivity of the nanofiller. Furthermore, the model proves its capability in predicting the specific heat and thermal conductivity of the modified and non-modified resin systems utilising the computed heat of reaction data. The analysis shows an increase of ∼15% in the specific heat and thermal conductivity due to different mould temperatures applied (110–170 °C). This, furthermore, stresses the fact that the addition of GNPs (0.2 wt.%) improves the resin-specific heat by 3.68% and thermal conductivity by 58% in comparison to the non-modified thermoset resin. The numerical findings show a satisfactory agreement with and in the range of experimental data available in the literature

    Steigerung der thermischen Stabilität von warm- und kaltgewalztem Wolfram durch Kalium-Dotierung für die Fusionsenergietechnik

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    Fusionskraftwerke der Zukunft stellen enorme Materialanforderungen, beispielsweise in Bezug auf Hitzeresistenz an Plasmakontaktzonen der inneren Reaktorwand und des Divertors. Als abschirmendes Material stellt Wolfram nach aktueller Konzeption die mit Abstand beste Alternative dar. Nachteilig ist dabei jedoch dessen hohe Spröd-duktil-Übergangstemperatur (BDTT), welche aufgrund thermischer und mechanischer Belastungszyklen zu katastrophalem Risswachstum führen kann. Zwar kann die BDTT durch starkes Kaltwalzen drastisch abgesenkt werden, das dabei entstehende, feinkörnige Gefüge ist jedoch thermisch instabil, wodurch es bei relativ niedrigen Temperaturen wiederum zu einer Erhöhung der BDTT kommt. Neben einer Untersuchung der zu einer solchen Versprödung führenden mikrostrukturellen Restaurationsprozesse, wurde daher in der vorliegenden Arbeit das Potential zur Stabilisierung der Mikrostruktur durch eine Dotierung mit Kalium (K) umfassend analysiert, durch welche die Migration von Korngrenzen und Versetzungen mittels fein verteilter K-Blasen unterdrückt wird. Zwar wird K-Dotierung bereits seit mehr als 100 Jahren bei der industriellen Herstellung von Glühlampendrähten angewendet, die Kombination des Verfahrens mit hochgradiger Walzumformung von Wolfram stellt jedoch einen neuartigen Ansatz dar. Grundlage der Studie war zunächst die erfolgreiche Herstellung zweier äquivalent gewalzter Blechserien von technisch reinem Wolfram (Referenz) und K-dotiertem Wolfram mit bis zu sehr hohen logarithmischen Umformgraden von 4,7 bzw. 4,6 durch Warm- und Kaltwalzen. Anhand beider Materialserien wurde eine detaillierte Analyse der verformungsbedingten Evolution von Mikrostruktur (durch REM und EBSD), mechanischer Eigenschaften (durch Härteprüfung, Zugversuche und Untersuchungen der Risszähigkeit) und Verteilung von K-Blasen (durch REM) nach den Walzschritten erstellt. Als weiteres Kernstück der Arbeit wurde die Mikrostruktur nach isochronen, isothermen und aufheizratenkontrollierten Wärmebehandlungsreihen zwischen 600 °C und 2400 °C mittels Härteprüfung und REM-Analysen hinsichtlich aufgetretener Restaurationsprozesse in unterschiedlichen Temperaturregimen systematisch untersucht. Es ist herauszustellen, dass nach höchstem Umformgrad sowohl bei reinem als auch K-dotiertem Wolfram eine nochmals niedrigere BDTT unterhalb von −80 °C im Vergleich zu bisherigen Studien an reinen Wolframblechen vorgefunden wurde. Die Analyse ergab weiterhin, dass die verformungsbedingte Evolution der Mikrostruktur zwischen beiden Blechserien annähernd gleich verlief. Allerdings traten in den K dotierten Blechen mit geringerem Umformgrad mikrometerdicke Lagen auf, die jeweils einzelnen Texturkomponenten zuzuordnen sind und nahezu ausschließlich Kleinwinkelgrenzen enthalten. Da sich dieses Phänomen mit einer hohen BDTT der besagten Bleche in Verbindung bringen ließ, könnte dessen Vermeidung ein wichtiges Qualitätskriterium bei zukünftigen Materialproduktionen darstellen. Weitere mechanische Eigenschaften, wie Mikrohärte, Zugfestigkeit und Dehngrenze, ließen sich in Anlehnung an die Hall-Petch-Beziehung mit der Korngröße korrelieren, wobei in den kaltgewalzten Blechen ein signifikanter Einfluss durch Kleinwinkel-grenzen festgestellt wurde, welche oftmals in einer Hall-Petch-Beziehung nicht berücksichtigt werden. Die Mechanismen, welche die Dispersion der K-Blasen und damit die Zener-Kräfte gegenüber Erholung, Rekristallisation und Kornwachstum beeinflussen, wurden tiefgreifend analysiert. Maßgeblich ist dabei der Umformgrad der Bleche, der zu einer Streckung der Blasen führt, sowie die Parameter einer darauffolgenden Wärmebehandlung, die den Aufbruch der gestreckten Blasen ähnlich einer Plateau-Rayleigh-Instabilität bewirkt. Die theoretischen Grundlagen dieser Aufbruchskinetik wurden mit den experimentellen Ergebnissen in Einklang gebracht und das Modell für den Grenzfall von Blasen mit geringem Streckungsverhältnis weiterentwickelt. Eine nanoskalige Analyse der chemischen Zusammensetzung zeigte erstmals in-situ eine heterogene Elementverteilung innerhalb des Volumens von K-Blasen aus einer aluminiumreichen und einer volatilen, kaliumreichen Phase sowie erhöhte Gehalte von Silizium und Sauerstoff. Es konnte zudem eine Instabilität dieser chemischen Zusammensetzung nach einer Wärmebehandlung im Bereich von ca. 2400 °C nachgewiesen werden, welche bei Hochtemperaturanwendungen von Relevanz sein kann. Die Analyse wärmebehandelter Proben ergab, dass Bleche mit geringem Umformgrad in einem niedrigen Temperaturregime nur schwache mikrostrukturelle Änderungen durch Erholung zeigten. Bleche mit hohem Umformgrad offenbarten jedoch drastische Änderungen durch sogenannte erweiterte Erholung (auch als kontinuierliche Rekristallisation bezeichnet), welche einen maßgeblichen Grund für die Versprödung dieser Bleche darstellt. Durch K-Dotierung konnte eine nur geringfügig retardierende Wirkung gegenüber erweiterter Erholung nachgewiesen werden. Erst in einem mittleren Temperaturregime bewiesen K-dotierte Bleche eine deutlich retardierende Wirkung gegenüber der dabei stattfindenden Rekristallisation in Blechen mit geringem Umformgrad bzw. in Blechen mit hohem Umformgrad gegenüber der fortschreitenden erweiterten Erholung mit direktem Übergang zu Kornwachstum. Zudem ergaben sich durch die Dotierung deutliche Unterschiede in der Texturentwicklung, welche den weiteren Verlauf der Restauration durch Kornwachstum beeinflusst. In einem hohen Temperaturregime bewirkte die Dotierung eine nahezu vollständige Stabilisierung gegenüber normalem und abnormalem Kornwachstum bei geringem Umformgrad, bei hohem Umformgrad jedoch besonders starkes abnormales Kornwachstum. Auch etwaige Einflüsse durch unterschiedliche Aufheizraten von 1 K/s und 200 K/s unter Berücksichtigung einer thermischen Aktivierungsäquivalenz wurden an den dicksten Blechen untersucht, jedoch kein aufheizratenbedingter Effekt festgestellt. Dieses Ergebnis steht im Widerspruch zu bisherigen Studien, in denen eine thermische Aktivierungsäquivalenz nicht berücksichtigt wurde. Die komplexen Zusammenhänge von thermomechanischer Behandlung reiner und K-dotierter Wolframmaterialien und der daraus resultierenden mikrostrukturellen Evolution wurden abschließend einander gegenübergestellt. Aufgrund der gewonnenen Erkenntnisse scheint K-dotiertes Material mit geringem Umformgrad die meisten Vorteile für die Anwendung in Fusionsreaktorkomponenten aufzuweisen, insbesondere durch die enormen Auswirkungen der K-Dotierung auf Kornwachstum sowie der deutlichen Retardierung von Rekristallisation, aber auch durch einen geringeren Herstellungsaufwand im Vergleich zu hochgradig umgeformtem Wolfram

    An Overview of the Measurement of Permeability of Composite Reinforcements

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    Liquid composite molding (LCM) is a class of fast and cheap processes suitable for the fabrication of large parts with good geometrical and mechanical properties. One of the main steps in an LCM process is represented by the filling stage, during which a reinforcing fiber preform is impregnated with a low-viscosity resin. Darcy’s permeability is the key property for the filling stage, not usually available and depending on several factors. Permeability is also essential in computational modeling to reduce costly trial-and-error procedures during composite manufacturing. This review aims to present the most used and recent methods for permeability measurement. Several solutions, introduced to monitor resin flow within the preform and to calculate the in-plane and out-of-plane permeability, will be presented. Finally, the new trends toward reliable methods based mainly on non-invasive and possibly integrated sensors will be described

    The effect of embedded blobs irregularities on the characteristics of 3D printed panels with dissimilar materials

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    Abstract: 3D printed panels with embedded blobs or irregularities can significantly affect the mechanical properties and overall characteristics of the 3D printed panels, depending on the materials used and the location. These irregularities can lead to weak spots or inconsistencies in the panel, affecting its strength, durability, and overall performance. Additionally, the use of dissimilar materials in the panel can also affect its properties, as the different materials may have varying thermal expansion coefficients, melting points, and other properties that can impact the panel's performance. The finite element model adopted in this research is used to investigate the impact of defects on the mechanical properties of 3D-printed composite sandwich panels. The study examines various parameters such as the interfacial position, size, material properties, and location of defects along the panel, and how they might affect the failure mechanism. The results of the study show that defects can have a significant influence on the mechanical properties of the panel, particularly in the middle section and at the edges where the tension concentration is highest. Additionally, the study adopted a linear elastic behavior using the ANSYS simulation program to analyze the panel's behavior under stress. In the intact situation, the deformation is found to be zero at the ends of the panel and highest in the middle of the composite. The shear stress is also most significant in the center of the panel and decreases as you move toward the edges. Additionally, the endpoints where support responses are present have large maximum shear stresses which can degrade the material's overall mechanical properties. This increase in maximum principal stresses at the end support is likely due to the reaction of the fixed support, which aims to counteract the applied flexural load, causing the maximum principal stresses to rise.Communication présentée lors du congrès international tenu conjointement par Canadian Society for Mechanical Engineering (CSME) et Computational Fluid Dynamics Society of Canada (CFD Canada), à l’Université de Sherbrooke (Québec), du 28 au 31 mai 2023

    Beam scanning by liquid-crystal biasing in a modified SIW structure

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    A fixed-frequency beam-scanning 1D antenna based on Liquid Crystals (LCs) is designed for application in 2D scanning with lateral alignment. The 2D array environment imposes full decoupling of adjacent 1D antennas, which often conflicts with the LC requirement of DC biasing: the proposed design accommodates both. The LC medium is placed inside a Substrate Integrated Waveguide (SIW) modified to work as a Groove Gap Waveguide, with radiating slots etched on the upper broad wall, that radiates as a Leaky-Wave Antenna (LWA). This allows effective application of the DC bias voltage needed for tuning the LCs. At the same time, the RF field remains laterally confined, enabling the possibility to lay several antennas in parallel and achieve 2D beam scanning. The design is validated by simulation employing the actual properties of a commercial LC medium

    Systemic Circular Economy Solutions for Fiber Reinforced Composites

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    This open access book provides an overview of the work undertaken within the FiberEUse project, which developed solutions enhancing the profitability of composite recycling and reuse in value-added products, with a cross-sectorial approach. Glass and carbon fiber reinforced polymers, or composites, are increasingly used as structural materials in many manufacturing sectors like transport, constructions and energy due to their better lightweight and corrosion resistance compared to metals. However, composite recycling is still a challenge since no significant added value in the recycling and reprocessing of composites is demonstrated. FiberEUse developed innovative solutions and business models towards sustainable Circular Economy solutions for post-use composite-made products. Three strategies are presented, namely mechanical recycling of short fibers, thermal recycling of long fibers and modular car parts design for sustainable disassembly and remanufacturing. The validation of the FiberEUse approach within eight industrial demonstrators shows the potentials towards new Circular Economy value-chains for composite materials

    Application of Particle Transfer by Dipping Using Polymer Binder

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    The demand for particle transfer is increasing in various industries, such as manufacturing, metal joining, microfluidics, roller lubrication process, fuel cells, super-capacitors, hybrid coating, and protective layer applications. As a result, the importance of efficient transfer of solid micron-size particles is becoming more crucial. Submicron-sized particles can easily adhere to solid substrates due to negligible gravitational force, while micron-sized or larger particles require a binder to overcome the gravitational effects. This thesis aims to investigate the interactions between microparticles and polymer thin film on cylindrical substrates using particle transfer methods. The process parameters are optimized and demonstrated two applications of this process: sorting particles based on their size from poly-disperse particle mixtures and controlling the friction force of the rods. To transfer particles into a substrate, a density-mismatching heterogeneous suspension is utilized, where kinetic energy is supplied by a magnetic stirrer’s rotation to keep the particles suspended during transfer. Initially, the effect of magnetic stirrer rotation and binder concentration on the optimal particle transfer was investigated. As a result of optimizing process parameters, a novel technique was developed for filtering poly-disperse particles from density mismatching heterogeneous mixtures at the solid-liquid interface (submerged condition) using entrapment instead of the conventional entrainment approach used in dip-coating processes. The polymer layer thickness formed over the substrate is controlled by controlling the binder concentration in the suspension. The binder concentration is varied from ϕb = 1% to ϕb = 13% at different intervals and the particle concentration is kept fixed ϕp = 10%. The viscosity is measured at room temperature (25 ºC) to observe the behavior of the suspension using a rotational rheometer. The variation in the polymer layer thickness controls the size of the entrapped particles. This work successfully showed the size-based separation of particles from a poly-disperse particle mixture. Another aspect of this thesis involved the systematic control of frictional forces between elastic rods in contact by transferring particles via dip-coating. Non-spherical particles adhere to the rods using a polymeric binder. A custom continuous dip-coating setup was constructed in the laboratory to coat the elastic rods. The particle delivery over the rods is regulated by controlling the concentration of particles in the suspension. Particle concentration in the suspension is varied from ϕp = 1% to ϕp = 13% at different intervals to observe the effect of variation of particle concentration keeping the binder concentration fixed (ϕb = 5%). The coated rods are dried in the oven to overcome the effect of the solvent during the friction force measurement. Table-top experimental setup with a push-pull digital force gauge is used to measure the variation friction force at different pulling lengths of overhand knots with a variety of unknotting numbers. This work successfully demonstrates a novel method of controlling the friction force of elastic rods by controlling the particle concentration in the suspension

    Adaptive position control of DC motor for brush-based photovoltaic cleaning system automation

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    In this paper, we have developed an automatic brush-based PV cleaning system to control and synchronize the 3 motors together with a smooth periodic of cleaning while moving it horizontally over the PV surface. The mechanical design involved installing linear guides at the top and bottom of the rail to support the aluminium plate that holds the carrier motors and rotating brush. Two different movements of translational and rotational motion of the motors are managed by an algorithm programmed in Arduino Mega. In investigating the performance of motor parameters and dust removal rate, we conducted an experiment by spreading dry sand over the PV surface. Results showed that the torque of the cleaning brush motor increases with the increase in load. The obtained torque of the carrier motor was found to be 9.167 Nm (> stall torque, 9.8 Nm) with a full load of 18 brushes. The torque is inversely proportional to the speed but directly proportional to power. The required power to move the 2.93 kg of cleaning system was 19.20 W with 3.015 Nm of torque. The system achieved 86.8% of the dust removal rate from the four cycles of cleaning operation

    Effect of process parameters on the mechanical properties of carbon fiber epoxy composites by wet compression molding

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    In recent years, due to growing environmental concerns, composite materials have emerged as a promising lightweight alternative for metals in structural applications in automobiles. Among composite manufacturing processes, Wet Compression Molding (WCM) is a new method of producing Carbon Fiber Reinforced Polymer (CFRP) components. For similar processes like RTM, operating conditions are always one of the factors that impact the mechanical performance of CFRP parts. Thus, this thesis aimed to investigate the effects of operating conditions, including resin temperature, mold temperature, resin set time, gap closure speed, and mold curing time on the mechanical property of the composite parts. In addition, the relationship between the initial resin application and the quality of the final parts was evaluated in this research. Flat plaques of carbon-fiber composites in an epoxy matrix were fabricated using WCM equipment, and the flexural property (Young’s Modulus) of the final parts were measured. Through statistical analysis, experimental results revealed that the part\u27s mechanical property was significantly affected by the mold temperature, resin temperature, and resin set time. Moreover, at the higher level of the significant factors, the quality of the parts was lower, and the optical microscope test confirmed voids formation during the WCM process (air entrapment), which was the primary reason for the poor quality of the final parts. In addition, statistical results exhibited no correlation between the initial resin distribution and the mechanical property of the final parts
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