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Faserverbund-Kunststoffe: Werkstoffe - Verarbeitung - Eigenschaften
... 2 feature approximate maximum fibre diameters of 24, 10 and 30 µm, respectively [10][11][12][13]. Hahn [14] summarises the different modes of FRP compressive failure as illustrated in Fig. 1. ...
... Mode (a) is denoted by longitudinalsplitting and results from a transverse tension failure of the polymer matrix due to the different Poisson's ratios ν of the fibres and the polymer matrix [10]. Two possible alternatives depending on the stiffness of the polymer matrix exist: (i) in stiff matrices, the bond between fibres and polymer matrix fails and (ii) in soft matrices, the fibres bend until fibre bending failure occurs. ...
... FRP consist of fibres from various source materials. These fibres serve to carry the load and are coated by a polymer matrix binding them together and protecting them against environmental impacts and stresses perpendicular to the fibre axis [10,11]. Regarding the mechanical properties of FRP, a significant difference between the compressive and tensile strength of FRP is known from the literature [1,10,11]. ...
Internationally leading standards currently do not permit to consider the contribution of reinforcement made of fibre reinforced polymers (FRP) to a concrete member’s compressive load-bearing capacity due to a lack of reliable knowledge regarding FRP’s material properties in compression. Thus, there is a very high demand for carefully specifying an optimised test setup for FRP bar reinforcement that accounts for both theoretical considerations and established standards from other industry branches. This paper presents an extensive literature review on mechanical approaches to describe FRP material properties in compression, existing test setups from various industry branches as well as experimental studies that have been conducted in order to research the compressive material properties of FRP reinforcement. Based on experimental results from literature a database was compiled. Following a reasonable choice of a test setup based on the literature study, an experimental campaign was setup, in order to investigate the influence of different fibre materials (carbon, glass, basalt), polymer matrices and bar diameters on the compressive material properties of FRP reinforcement bars. In addition to the experimental determination of the material properties, the joint evaluation of the total sample size of n = 95 own experimental test results and the results from the database generated from literature allows for
statistical investigations. Thus, the determination of material scatter and the estimation of the distribution type by means of a statistical analysis applying the Kolmogorov-Smirnov test provides the basis for further research towards the reliability of concrete structures reinforced with FRP bars in compression.
... While composites were originally based on thermosets, we have observed a trend towards thermoplastic materials in recent years. 2 In the manufacturing of thermoset-based composites, fibers are typically impregnated with a non-polymerized material, usually a low-molecular-weight resin that has very low viscosity, penetrates easily into the fiber carpet, and thus facilitates efficient impregnation. 3 Polymerization and crosslinking are initiated and promoted by curing agents and catalysts during the curing process, which results in a hard but brittle polymer matrix. Since this chemical crosslinking reaction is irreversible, thermosets are difficult to recycle mechanically. ...
... Traveling at constant velocity, the carriage passes the first light barrier in the travel direction and thus sends a digital trigger signal (LVTTL 3.3 V) to the OCT main unit to start measurement (2). While moving at a constant velocity across the tape surface, a Python program in combination with the OCT sensor records the predefined number of A-scans needed (3). Computation of this number by int ...
Originally developed for biomedical applications and diagnosis, optical coherence to-mography (OCT) has recently been demonstrated to be a powerful non-destructive and non-invasive measurement method for detecting defects in glass-fiber reinforced polymer composites. While previous studies have focused mainly on the use of OCT in the analysis of thermoset composites, we were able to show in offline experiments that OCT can be used to quickly detect typical defects (e.g., dry fiber regions, gaps and fiber breakage) in thermoplastic unidirectional (UD) tapes at high resolution. To investigate the applicability of OCT to inline monitoring, we advanced our previously published approach in two major steps: First, we incorporated the OCT system into an industrial-scale UD-tape production line, and derived optimal settings for inline detection of dry region defects from a comprehensive design of experiments (DoE) to find an optimal balance between accuracy and data size for a stationary tape sample by varying A-scan sampling rate, A-scan averaging and OCT transverse travel velocity. Second, using these optimal settings, we went on to investigate moving tapes over a range of industrially relevant takeoff speeds. Microscopy was used for validation in both cases. We developed a fast and robust statistical analysis of B-scans that visualizes the quality of full cross-sections in an interpretable manner for potential use in a real-time setting. Within an industrially relevant production speed range of up to 15 m/min, we are thus now able to investigate 120 mm wide (and potentially wider) UD tapes inline at a transverse resolution of 22 μm, producing only 21 MB of data per measurement.
... These composites combine high-performance fibres like carbon, glass or aramid for load transfer along the fibre's length, along with a plastic matrix responsible for handling compressive and shear loads. [1][2][3] As a result, these composites exhibit exceptional anisotropic material properties with high specific tensile strength and stiffness in the direction of reinforcement. 4 The manufacturing process of these composites involves several stages, including textile semi-finished product fabrication, preforming, infiltration and consolidation. 5 Conventional preforming typically involves cutting textile reinforcement structures with homogeneous surface structures into sizeable portions. ...
... To ensure a constant fabric density along the produced fabric, the weave can alternatively be adjusted according to the changing fabric width. The theoretical density factor of the weave pattern p (see equation (2)) is calculated based on the existing warp yarn density, the desired constant fabric density and a fixed weft density. Corresponding weave patterns are then assigned. ...
Technical fabrics find extensive use as reinforcement in plastic components across various applications. Traditionally, these fabrics are produced using wide weaving machines with a constant fabric width and are then cut to achieve the desired component geometry, leading to significant waste generation. An effective approach to minimizing waste and conserving resources involves utilizing fabrics with outer contours that match the desired component geometry from the outset. Until now, the production of width-variable fabrics during the weaving process has not been achievable using wide weaving machines. Addressing this limitation, this paper introduces a novel reed design specifically developed for wide weaving machines. The paper presents the design concept of the new reed and elucidates the fabric development process associated with its implementation. Furthermore, the resulting fabric properties and physical relationships are demonstrated based on manufactured samples. By enabling the production of width-variable fabrics, this innovative approach aims to contribute to more sustainable manufacturing practices in the field of technical fabrics-reducing waste and optimizing resource utilization.
... In general, phenolic resins are too brittle for most structural applications, so the phenolic resin is toughened with the help of bisphenol-A (bisphenol A epichlorohydrin). Phenolic resins begin to degrade at temperatures of 280 to 300 °C [50][51][52]. ...
In this study, the influence of four different process parameters on hot gas welding of CF/epoxy fiber composites functionalized with a PA6 thermoplastic film is investigated. Additional experiments are carried out on specimens adorned with triangular beads of coupling material that are printed onto the plates, ensuring extra material within the joining zone. This approach offers a great advantage for compensating geometric tolerances. The parameters considered are common process parameters for regular two-step processes: Heating element temperature (THE), heating time (HT), welding force (F) and welding time (HTF). The design of experiments (DoE) is planned according to the Taguchi method. An orthogonal array is used to set up the experimental plan. Three factor levels of each welding parameter are considered. The test series are carried out with two sample variants. In the second sample variant, additional thermoplastic material is placed in the joining zone. The strength of the welded joints is investigated by tensile shear tests according to DIN EN 1465. The results show that the welding force has the greatest influence on the welding strength. Heating times of 20 s were found to be optimal. Within the first sample variant, a saturation behavior of the welding force can be observed at 500 N. Higher heating element temperatures (500 °C) and welding forces (1165 N) are advantageous using additional material. High welding temperatures result in a negative effect on the interdiffusivity of the polymer chains.
... After heating a sheet above melting temperature of the thermoplastic matrix, it is formable into the desired shape. This is usually achieved by placing the sheet between two heated metal molds in a process called thermoforming [7,8]. ...
The growing market for fiber-reinforced thermoplastics (FRTP) requires new flexible production processes for prototype and small series production, as conventional forming techniques involving molds are not cost efficient in these cases. Inspired by incremental sheet metal forming (ISF), an alternative manufacturing processes for the forming of FRTP with just two robot guided standard tools is outlined. To maintain a locally formed shape in the heated, flexible fabric, auxiliary wire mesh metal is used as it has similar deformation mechanisms, especially shearability, while being sufficiently self-supporting. Feasibility of the approach is discussed and investigated in basic experiments.
... Due to their superior physical-mechanical properties, chemical and temperature resistance, dimensional stability, versatility, and processability, they are especially used for applications with increased performance requirements [1][2][3][4]. This especially holds true for glass or carbon fiber reinforced composites used in aerospace, automotive, and sports industries where their higher specific strength is superior to metallic materials such as aluminum or steel [5,6]. The glass transition temperature (T g ) is considered a critical property for polymers because it is an important indicator of processing and performance properties such as stiffness, heat resistance, and adhesion. ...
The use of machine learning (ML) models to screen new materials is becoming increasingly common as they accelerate material discovery and increase sustainability. In this work, the chemical structures of 16 epoxy resins and 19 curing agents were used to build an ML ensemble model to predict the glass transition ( T g ) of 94 experimentally known thermosets. More than 1400 molecular descriptors were calculated for each molecule, of which 119 were chosen based on feature selection performed by principal component analysis. The quality of the trained model was evaluated using leave-one-out cross-validation, which yielded a mean absolute error of 16.15 ∘ C and an R 2 value of 0.86. The trained model was also used to predict T g for 4 randomly selected resin/hardener combinations for which no experimental data were available. The same combinations were then prepared and measured in the laboratory to further validate the ML model. Excellent agreement was found between experimental and predicted T g values. The current ML model was created using only theoretical features, but could be further improved by adding experimental or quantum mechanical properties of the individual molecules as well as experimental processing parameters. The results presented here contribute to improving sustainability and accelerating the discovery of novel materials with desired target properties.
Graphical Abstract
... Einen innovativen Lösungsansatz stellen funktionalisierte Bewehrungsstäbe aus glasfaserverstärktem Kunststoff (GFK) mit einem im Kernquerschnitt integrierten Heizleiter dar. Grundlegende Untersuchungen zu GFK-Bewehrungen sowie zu deren Verhalten unter Temperaturbeanspruchung von außen finden sich u. a. in [5][6][7][8][9][10][11][12]. Diese Stäbe erfüllen die Aufgabe einer statisch wirksamen Bewehrung im Betonbau und ermöglichen zugleich die Einspeicherung von Wärme in Betonbauteile in Form einer Widerstandsheizung. ...
Durch die Vorgaben des Erneuerbare‐Energien‐Gesetzes wird Strom aus Erneuerbaren Energien vorrangig in das elektrische Netz eingespeist. Zur Vermeidung von Überlastungen im Stromnetz muss diese Einspeisung temporär reduziert werden. Die elektrische Energie, die in diesen Zeiträumen technisch erzeugt werden kann, aber nicht wird, wird als Ausfallarbeit bezeichnet. Diese fällt zum größten Teil in der Heizperiode an und kann zur Beheizung von Gebäuden genutzt werden. Ein Ansatz für die effiziente Einbindung von Erneuerbaren Energien eröffnet die Nutzung der Gebäudetragstruktur zur Wärmespeicherung. Im Rahmen dieses Beitrags wird eine Lösung vorgestellt, mit der elektrische Energie in Wärme umgewandelt, in Betonbauteilen gespeichert und zur Beheizung von Gebäuden genutzt wird. Die Einspeicherung von Wärme erfolgt über eine neuartige, funktionalisierte Faserkunststoffbewehrung mit einem Heizdraht in Querschnittsmitte. Um das Ziel der Reduktion von Ausfallarbeit zu erreichen, wird ein Modell benötigt, welches abhängig von der Beladedauer und der ‐spannung die Temperatur im Bauteil vorhersagt. Das mithilfe von Messungen entwickelte Modell erlaubt dies für Beladedauern bis zu 12 h. Zudem werden die im Bauteil gespeicherte Wärme sowie die resultierende Heizleistung prognostiziert. Im untersuchten Beispiel werden Leistungen von bis zu 174 W/m ² und Temperaturänderungsraten von rd. 1 K/h erreicht.
... Due to the complex plant environment and the available measuring systems on the market, quality assurance of the component during the curing process is hardly possible. However, the properties of a CFRP component only become established during the process and can vary from component to component [7]. Due to the complex components, systems and processes, inhomogeneous temperature distributions can occur during manufacturing which may affect the component either being not fully cured or with different properties. ...
Based on the missing cure monitoring in the manufacturing of structural components, the degree of automation and thus the increase in production cannot be improved. Since much more airplanes per month have to be produced promptly, a higher degree of automation is indispensable.
Especially in the field of Fibre Metal Laminates (FML), there is a high potential. The development of a new production line that will allow automated fuselage production is the focus of the studies within the joint project AUTOGLARE. In order to ensure the optimal processing of the reinforced adhesive, a process monitoring system has been developed for the in-situ process monitoring of the manufacturing process within an autoclave. The simultaneous measurement of the resin’s temperature and electrical resistance allows for the real-time prediction of the viscosity, the degree of cure and the glass transition temperature (Tg). The curing of the polymer adhesive was modelled in the lab and its electrical properties were correlated to its Tg. Finally, the cure monitoring system was installed in the autoclave and several trials and an entire fuselage were executed. The continuous measurement of the temperature and resistance in all sensors was quite smooth and accurate while the ORS system provided successfully the evolution of the Tg at four critical locations.
The present scientific publication shows that the use of a process monitoring system can provide a reliable means to achieve online and accurate Tg estimation during the FML manufacturing in an autoclave with a potential to decrease the curing time by 50%.
... Adhesive bonding is known as a weight saving and material conform joining method for aerospace structures made of carbon fiber reinforced plastics (CFRP). Besides the common use of thermoset (epoxy) matrices, also high-performance thermoplastic matrices are of growing interest [1][2][3][4]. ...
This study investigates the role of surface functionalization to increase adhesion forces on polymers. The effects of two different physical pre-treatment methods (oxygen low-pressure plasma - LPP, vacuum-UV - VUV) are investigated on four different polymer matrices (polyetheretherketone - PEEK, polyetherimide - PEI, poly- ethersulfone - PES and the epoxy resin RTM6). Polymer surfaces were additionally washed after surface treat- ment with different polar solvents. Surface chemistry, wettability, and topography were investigated before pre- treatment, after pre-treatment and after washing of the samples using x-ray photoelectron spectroscopy (XPS), contact angle measurements and atomic force microscopy (AFM).
The results show, that washing of the samples after pre-treatment lead to a chemical surface condition similar to the initial surface. Interestingly, the tensile bond strength of centrifugal adhesion tensile test (CATT) speci- mens however remained high. In consequence, the thus far widely accepted understanding of surface functio- nalization as the dominating factor for adhesion promotion on polymers has to be re-evaluated.
... Die den Nasspressprozess kennzeichnenden Verfahrensschritte sind in Bild 5 dargestellt. [31]. Im Bereich dieser Kanten wird die Faserstruktur stark komprimiert, was zu einer Erhöhung des Fließwiderstandes führt und somit das Harz am Austreten aus dem Formraum hindert. ...
Ziel der Arbeit war die Realisierung des Trockentiefziehens, da Schmierstoffe und Reinigungsmittel oft umweltschädliche Substanzen enthalten und eine längere Prozesskette zum Beölen sowie zum Reinigen der umgeformten Bauteile nötig ist. Motiviert durch die ökologischen und ökonomischen Potentiale wurde in Umformversuchen die Konsequenzen des Schmierstoffverzichts für einen verzinkten Tiefziehstahl sowie zwei Aluminiumlegierungen analysiert. Erhöhte Reibung und Adhäsionsneigung führte besonders beim direkten Kontakt der Aluminiumlegierungen mit dem Werkzeug zu Verschleiß und Schäden auf der Blechoberfläche. Zur Reibungsreduktion wurden die Werkzeuge unterschiedlich bearbeitet und mit verschiedenen amorphen Kohlenstoffschichten versehen. In Streifenzieh- und Trockentiefziehversuchen wurde gezeigt, dass eine niedrige Werkzeugrauheit unabhängig vom Blechwerkstoff zu vorteilhaftem tribologischen Verhalten führt. Eine Wolframdotierung der Schichten wirkt hingegen negativ auf das Verschleißverhalten. Der Einfluss lasergenerierter Mikrostrukturen hängt von deren Tiefe und Flächendeckungsgrad ab. Es wurden tribologische Wirkzusammenhänge unter trockenen Kontaktbedingungen abgeleitet und gezeigt, dass Trockentiefziehen abhängig von Kontaktpartnern und Oberflächenmodifikationen realisierbar ist.
Wood–Textile Composites (WTCs) are a new type of composite material based on willow wood strips and polypropylene that combines the properties of classic natural-fiber-reinforced polymers with an innovative textile wood design. While the basic quasi-static properties have already been investigated and described, there is a lack of knowledge about the behavior of the material under dynamic-cyclic and dynamic-impact loading as well as in relation to basic wood construction parameters. The present study is intended to contribute to the later use of the developed material, e.g., in architecture. For this purpose, fatigue tests, dart drop tests (impact and penetration), impact bending tests, and embedment tests were carried out. It was shown that embedding wood fabrics in a thermoplastic matrix leads to a significant increase in resistance to impact loads compared to the neat basic materials. It was also shown that the ratio of the failure stress in the fatigue test to the tensile strength of the WTC corresponds to that of other fiber-reinforced thermoplastics at around 70%. The embedment tests showed that WTC has good values compared to neat wood.
Wood Textile Composites (WTCs) represent a new and innovative class of materials in the field of natural fiber composites. Consisting of fabrics made from willow wood strips (Salix americana) and polypropylene (PP), this material appears to be particularly suitable for structural applications in lightweight construction. Since the threads of the fabric are significantly oversized compared to classic carbon or glass rovings, fundamental knowledge of the mechanical properties of the material is required. The aim of this study was to investigate whether WTCs exhibit classic behavior in terms of fiber composite theory and to classify them in relation to comparable composite materials. It was shown that WTCs meet all the necessary conditions for fiber-reinforced composites in tensile, bending, and compression tests and can be classified as natural-fiber-reinforced polypropylene composites. In addition, it was investigated whether delamination between the fiber and matrix can be simulated by using experimentally determined mechanical data as input. Using finite element analysis (FEA), it was shown that the shear stress components of a stress tensor in the area of the interface between the fiber and matrix are responsible for delamination in the composite material. It was also shown that the resistance to shear stress depends on the geometric conditions of the reinforcing fabric.
A thorough knowledge and understanding of the structure–property relationship between thermal conductivity and C-fiber morphology is important to estimate the behavior of carbon fiber components, especially under thermal loading. In this paper, the thermal conductivities of different carbon fibers with varying tensile modulus were analyzed perpendicular and parallel to the fiber direction. Besides the measurement of carbon fiber reinforced polymers, we also measured the thermal conductivity of single carbon fibers directly. The measurements clearly proved that the thermal conductivity increased with the tensile modulus both in fiber and perpendicular direction. The increase is most pronounced in fiber direction. We ascribed the increase in tensile modules and thermal conductivity to increasing anisotropy resulting from the orientation of graphitic domains and microvoids.
Graphical abstract
Fiber-reinforced thermoplastics are an important construction material for lightweight applications. The increasing use of especially glass fiber-reinforced plastics leads to growing amounts of not recyclable composite materials, which is commonly disposed of by landfilling. Hence, there is a need for a recycling concept for glass-fiber-reinforced plastics that enables their complete reuse over many recycling cycles. In this paper, such a recycling concept is presented, which is based on the idea of melting the whole glass-fiber-reinforced component without prior size reduction. The fiber-reinforced melt will be pressed through a nozzle in order to achieve a strand with highly oriented fibers that can then be applied in new components via a tape-like laying process. The feasibility of the recycling concept is proved in this paper. Therefore, investigations on the reorientation of fibers in the melt by pressing through a rectangular nozzle have been carried out with different nozzle diameters, shear rates and melt temperatures. The investigations result in a stable process, which enables an increase in fiber orientation of about 37% up to a mean fiber orientation of 67% in the flow direction. These findings are independent of the initial fiber orientation.
Cracked concrete members with fiber-reinforced polymer (FRP) reinforcement generally suffer from increased deflections compared to steel-reinforced members due to FRP reinforcements' lower modulus of elasticity. An approach to counteract this problem can be the prestressing of the FRP reinforcement, which can significantly reduce member deflections. However, time-dependent prestress losses occur due creep and shrinkage of the concrete and relaxation of the prestressing tendons. Within the first part of this article, mathematical approaches to determine relaxation rates from creep tests are introduced. Subsequently , short-term and long-term tensile tests under sustained load on glass and basalt FRP reinforcement bars are presented. Based on the experimental data and the mathematical model, relaxation rates for the investigated specimens are derived. In addition, using an approach based on logarithmic extrap-olation, the relaxation rates at 1 million hours (end of service life) are calculated, and the experimentally determined residual tensile properties are evaluated.
A broader application of biocomposites still faces many challenges regarding structural integrity, environmental resistance, and biodegradability. These issues are particularly important when their marine applications are considered. Therefore, this paper seeks to address the hygroscopicity, mechanical properties, and biofouling resistance of biocomposites made of epoxy resin with 28 m% bio-based carbon content reinforced with flax and hemp fibers. A series of experiments are performed to acquire water absorption rates, saturation limits, mass increase, tensile and flexural properties, interlaminar shear strength, impact resistance, and mass gain due to biofouling. All tests of mechanical properties are conducted before and after immersion in seawater. The acquired saturation limits of flax/epoxy and hemp/epoxy biocomposites amount to 7.5% and 9.8%, respectively. The water uptake causes the tensile and flexural properties to decrease by 26–74%, while interlaminar and impact strength increase for flax/epoxy and decrease for hemp/epoxy biocomposites. In addition, it is observed that in almost all cases, flax/epoxy has superior properties compared with hemp/epoxy biocomposites. It is expected that this research will motivate naval architects and classification societies to consider biocomposites as prospective hull materials that provide both structural integrity and environmental sustainability.
Für Bauwerke wird in der Regel eine Lebensdauer von mehreren Jahrzehnten angestrebt. Entsprechend dauerhaft leistungsfähig müssen die verwendeten Materialien sein. Kapitel 9 beginnt mit einer kurzen Einführung in die Grundlagen des Ermüdungsverhaltens von Werkstoffen. Anschließend werden das Dauerstand‐ und das Ermüdungsverhalten von Carbon und Beton sowie des Komposits Carbonbeton und von Bauteilen aus Carbonbeton erläutert. Abschließend werden Hinweise zur Bemessung gegeben.
Serious environmental pollution, increasing energy consumption and greenhouse gas emissions as well as raw material resources scarcity are huge challenges in our today’s society. In order to realize sustainable development and preserve the environmental balance, the 3R rule is applied, which corresponds to reduce, reuse and recycle. In materials development, this rule needs to be also considered for the sustainable development. In the present study, we used different rCFs to manufacture PEEK-based tribocomposites. The results demonstrate that rCFs, independent of their recycling histories, can serve as excellent candidates for preparing high-performance tribocomposites. The friction and wear performance is much better than that of a commercially available product, which is quite close to the best tribological performance of distinct high-performance tribomaterials reported in the literature.
This study considers the influence of different irradiation scenarios on the thermal degradation of carbon fibre-reinforced polymers (CFRP). Real threats are simulated, such as fires with long-lasting low heat fluxes and nuclear heat flashes with short-lasting high heat fluxes. For this purpose, coated and uncoated quasi-isotropic samples of the commercially available CFRP HexPly® 8552/IM7 are thermally irradiated from one side by an electrical heater of a cone calorimeter and a xenon short-arc lamp of a laboratory heat flash simulator with heat fluxes between 5 and 175 W/cm² at varying time intervals. The specimens’ temperature is recorded on the front and back side as well as at different laminate depths. The CFRP are analyzed with ultrasonic testing (UT), infrared spectroscopy (ATR-FTIR), scanning electron microscopy (SEM) and micro-focused computed X-Ray tomography (μCT). Destructive tests are performed to determine the mechanical properties in terms of interlaminar shear, compressive and tensile strength. When samples of CFRP are exposed to higher heat flux, high temperatures and temperature gradient values occur along the cross-section. As a result, extreme damage gradients appear in the material, leading to changes in damage behavior and loss of mechanical properties within seconds. However, to ensure the safety of the material in case of thermal exposure, loading limits are introduced, indicating the threshold for strength collapse. In addition, with the application of coatings, thermal degradation of CFRP can be delayed. Finally, the time-heat flux superposition principle is established to predict the residual strength under different loading scenarios.
Die vorliegende Arbeit befasst sich mit der Darstellung und Anwendung von mechanochemisch funktionalisierten Mehrlagengraphenen (MFG) aus Graphit. Es wurden deren Synthese durch Mahlen mit einer Planetenkugelmühle, die Eignung von MFG als Trägermaterial für die Polyethylen-Katalyse und die Verwendung als Füllstoff für Nanokomposite untersucht. Bei der Herstellung der hochgefüllten Komposite wurden die synergetischen Effekte von kohlenstoffbasierten Füllstoffen und die selbstverstärkende Wirkung von PE-Reaktorblends (RB) in Kompositen aufgezeigt. Im letzten Teil konnten zusätzlich über den mechanochemischen Ansatz Polystyrol (PS) und Polyethylen (PE) kovalent an MFG angebunden werden.
Die Darstellung der kantenfunktionalisierten MFG erfolgte über eine einstufige und lösungsmittelfreie Synthese bei der Graphit in verschiedenen Gasatmosphären (Ar und CO2) vermahlen wurden. Dadurch war es möglich Funktionalisierungsart (Hydroxyl- und Carboxylgruppen) und Morphologie der Partikel (sphärisch und plättchenartig) zu variieren. Über die Rotationsgeschwindigkeit (167 bis 250 U∙min-1) konnten zudem der Funktionalisierungsgrad, die Exfolierung, die Partikelgröße und die spezifische Oberfläche eingestellt werden. Ebenso wurden bei der Variation des Füllgrads der Mahlkammern (8 bis 32 %) in Kombination mit verschiedenen Rotationsgeschwindigkeiten (300 und 400 U∙min-1) und Mahldauern (24 und 48 h) die Effekte auf die Größe, die Oberfläche und die Sauerstofffunktionalisierung der MFG charakterisiert und verschiedene Korrelationen aufgezeigt.
Die MFG wurden als Träger für die heterogene Mehrzentrenkatalyse zur Synthese von multimodalen PE-RB untersucht, wobei sie gute Aktivitäten ohne Anzeichen für Katalysator-Leaching zeigten. Dabei konnten mit den Katalysatoren Cr1, FeBIP und CrBIP maßgeschneiderte Materialien mit frei einstellbaren Anteilen von kurzkettigem PE-Wachs und langkettigem, ultrahochmolekularem PE synthetisiert werden. Ebenso konnten der Einfluss der Partikelgröße, der Funktionalisierungsart und des Funktionalisierungsgrads der vier Trägermaterialien auf die PE-Synthese bestimmt werden.
Bei der Verarbeitung der MFG zu hochgefüllten Polymer-Nanokompositen mittels Spritzguss konnten Füllstoffgehalte von 40 Gew.-% compoundiert werden. Das resultierende Eigenschaftsprofil zeigte perkolierende Netzwerke, die eine elektrische Leitfähigkeit von bis zu 6,0∙10 4 S∙cm-1 erzeugten und Mechaniken mit einer gesteigerten Steifigkeit (+240 %) und Festigkeit (+50 %), bei gleichzeitigen Einbußen in der Zähigkeit ( 55 %) und Bruchdehnung (-97 %). Die Barrierewirkung des Komposits konnte zusätzlich um bis zu 60 % gesteigert werden.
Durch den gleichzeitigen Einsatz von kohlenstoffbasierten Füllstoffen und eines RB (bis 50 Gew.-%) mit 9 Gew.-% UHMWPE wurden Synergieeffekte erzielt. Die selbstverstärkende Wirkung des RB resultierte in einer weiter verbesserten Mechanik, d.h. Steifigkeit (+350 %), Festigkeit (+535 %) und Zähigkeit (+280 %) bei reduzierter Bruchdehnung (-97 %). Die Effekte gingen deutlich über das Maß der Verstärkung durch RB oder Füllstoff hinaus. Gleichzeitig verloren die RB-MFG-Komposite jedoch ihre Leitfähigkeit und Barrierewirkung. Durch die Charakterisierung der Morphologie konnten die signifikanten, mechanischen Verbesserungen der selbstverstärkenden Wirkung des UHMWPE und der Ausbildung von faserartigen Überstrukturen zugeordnet werden. Zusätzlich wurde die schichtartige Orientierung der plättchenartigen Füllstoffe, bedingt durch die Verarbeitung, aufgezeigt.
Eine weitere Form der kovalenten Funktionalisierung von MFG stellte die mechanochemische Pfropfung mit Monomeren und Polymeren dar. Erstmals wurden sowohl die radikalische Synthese von Styrol als auch die kovalente Bindung von PS und PE auf MFG in einem einstufigen, mechanochemischen Prozess aufgezeigt. Dabei wurden die Unterschiede zwischen der Adsorption der Polymere bei der Trockenvermahlung mit Graphit und der kovalenten Anbindung bei der Nassvermahlung im Detail untersucht und analysiert. Durch die Polymeranbindung konnte die Dispersionsstabilität der MFG-Partikel um ein Vielfaches gesteigert werden. Die Verwendung der polymerfunktionalisierten MFG in Kompositen erzielte eine Verbesserung der Steifigkeits- und Festigkeitsbilanz zu Lasten der Zähigkeit und Dehnbarkeit der Komposite.
The further development of composite manufacturing methods is characterized by the progress of their mechanical properties which are widely used in many applications as automotive, aerospace, and marine industries. The automated composite production techniques are as follows: automatic tape layering, automatic fiber placement, and filament winding methods used in many industries. Photopolymerized composites and their additive manufacturing methods are promising with new advances in technology. This method for printing continuous fiber-reinforced plastic composite parts by a six-axis industrial robotic arm is based on fused deposition modeling technology. The objective of this work is to obtain a better understanding of the mechanical properties of robotic three-dimensional printed photopolymer resin continuous fiberglass–reinforced composites (CFGRCs) as a function of different printing speeds (10, 20 and 30 mm/s), fiber densities (45, 55 and 65%), and fiber orientations (0, 0/90 and ±45°). This work infers that mechanical properties are significantly affected by the fiber density and fiber orientation of CFGRC. With this method, approximately 300 MPa tensile strength can be obtained and structurally preferred instead of ferrous materials in many areas.
The level of energy consumption in renovation activities of buildings has huge advantages over the demolition of old buildings and the construction of new structures. Such renovation activities are usually associated with the simultaneous strengthening of their elements, such as externally bonded carbon fibre reinforced polymer (CFRP) lamellas or sheets on vertical and horizontal surfaces as structural reinforcements. This means the process of refurbishing a building, as well as the raw materials themselves have a significant impact on CO2 emissions and energy consumption. This research paper demonstrates possibilities of replacing state of the art, highly energy-intensive CFRP lamellas with basalt fibre reinforced plastics as energy-efficient structural reinforcements for building constructions. The mechanical and thermal properties of basalt fibre reinforced polymer (BFRP) composites with variable matrix formulations are investigated. The article considers macro- and microstructures of innovative BFRP. The investigations focus on fibre–matrix interactions with different sizing formulations and their effect on the tensile strength, strain as well as modulus of elasticity.
The functionality of products increases when more sensors are used. This trend also affects future automobiles and becomes even more relevant in connected and autonomous applications. Concerning automotive lightweight design, carbon fibre-reinforced polymers (CFRP) are suitable materials. However, their drawbacks include the relatively high manufacturing costs of CFRP components in addition to the difficulty of recycling. To compensate for the increased expenditure, the integration of automotive sensors in CFRP vehicle structures provides added value. As a new approach, established sensors are integrated into fibre-reinforced polymer (FRP) structures. The sensors are usually mounted to the vehicle. The integration of sensors into the structure saves weight and space. Many other approaches specifically develop new sensors for integration into FRP structures. With the new approach, there is no need for elaborate development of new sensors since established sensors are used. The present research also showed that the range of applications of the sensors can be extended by the integration. The present paper outlines the functional behaviour of the integrated sensor utilized for crashing sensing. First of all, the integration quality of the sensor is relevant. Different requirements apply to the usual mounting of the sensor. The self-sensing structure must fulfil those requirements. Moreover, unfamiliar characteristics of the new surrounding structure might affect the sensing behaviour. Thus, the sensing behaviour of the self-sensing composite was analyzed in detail. The overarching objective is the general integration of sensors in products with reasonable effort.
In this study, optically transparent glass fiber-reinforced polymers (tGFRPs) were produced using a thermoset matrix and an E-glass fabric. In situ polymerization was combined with liquid composite molding (LCM) techniques both in a resin transfer molding (RTM) mold and a lite-RTM (L-RTM) setup between two glass plates. The RTM specimens were used for mechanical characterization while the L-RTM samples were used for transmittance measurements. Optimization in terms of the number of glass fabric layers, the overall degree of transparency of the composite, and the mechanical properties was carried out and allowed for the realization of high mechanical strength and high-transparency tGFRPs. An outstanding degree of infiltration was achieved maintaining up to 75% transmittance even when using 29 layers of E-glass fabric, corresponding to 50 v. % fiber, using an L-RTM setup. RTM specimens with 44 v. % fiber yielded a tensile strength of 435.2 ± 17.6 MPa, and an E-Modulus of 24.3 ± 0.7 GPa.
Near-infrared spectroscopy (NIR) was implemented in the resin transfer molding (RTM) process to inline monitor the degree of curing of a bio-based epoxy resin, which consists of epoxidized linseed oil (resin) and citric acid (hardener), respectively. A NIR micro-spectrometer was used for the development of robust calibration models using partial least squares (PLS) regression. Since the micro-spectrometer offers a smaller wavelength range compared with conventional NIR devices, and typical absorbance peaks are not directly involved in the captured data range, the results show new insights for the utilization of this technology. Different pre-treatments of the spectroscopic data have been tested, starting with different reference spectra, i.e., uncured resin and polytetrafluorethylene (PTFE), and followed by chemometrical algorithms. As a reference method for the degree of curing, direct current (DC) supported by differential scanning calorimetry (DSC) was used. The results show the potential of these cost-efficient and compact NIR micro-spectrometers for the intended inline monitoring purpose to gain relevant information feedback during the process.
Kein modernes Transportmittel kommt heute ohne technische Textilien aus und der Anteil dieser textilen Materialien mit speziellen technischen und funktionellen Eigenschaften nimmt stetig zu. Die Anwendungsbereiche der technischen Textilien sind dabei vielfältig. Je nach Anwendungsbereich stehen unterschiedliche Eigenschaften der Faserrohstoffe sowie der Faden- und Flächenkonstruktionen im Vordergrund. Gerade Letztere eröffnen für den Chemieunterricht eine neue Perspektive auf das Thema Kunst- und Naturstoffe. Im Beitrag werden zentrale fachliche Aspekte vermittelt und Anregungen für den Einsatz im Unterricht vorgestellt.
Unterricht Chemie, Heft 184, Juli 2021
https://www.friedrich-verlag.de/chemie/stoffe-ihre-eigenschaften/von-der-faser-zum-verbundwerkstoff-9541
Additive manufacturing by material extrusion such as the widespread fused filament fabrication is able to improve 3D printed part performance by using short fiber reinforced composite materials. Fiber alignment is critical for the exploitation of their reinforcing effect. This work investigates the influence extrusion parameters have on the fiber alignment by conducting set of experiments on the process parameters determining whether the flow under the nozzle is convergent or divergent. A strong impact of flow conditions during extrusion line shaping on the fiber alignment is observed and two extremes are tested which show a large difference in strength, stiffness and strain at break in tensile testing along the extrusion lines. From highest to lowest fiber alignment, strength is reduced by 41% and stiffness by 54%. Fiber misalignment also leads to inhomogeneous strain fields in the layers when tested perpendicular to the extrusion lines. It is demonstrated that material flow after the nozzle has a high impact on the material properties of short fiber reinforced 3D printed parts and needs to be considered in process design.
Kap. 2 präsentiert den Stand der Technik zu hybriden Werkstoffen. Nach einer kurzen Einführung (Abschn. 2.1.1) zu allgemeinen Anwendungen von Hybridlaminaten stellen die teilnehmenden Partner ihre projektrelevanten laufenden oder bereits abgeschlossenen Forschungsarbeiten vor (Abschn. 2.1.2). Grundlegende Aspekte, die das Projekt TroPHy2 im Folgenden berücksichtigt, sind die Fügetechnik (Abschn. 2.1.3), die Anbindung zwischen Faserkunststoffverbunden (FKV) und Metallen (Abschn. 2.1.4) und das Eigenspannungs- sowie Verformungsverhalten in Hybridlaminaten (Abschn. 2.1.5). Recherchen zu Simulationsmethoden (Abschn. 2.1.6) sowie die Fertigung von Hybridlaminaten (Abschn. 2.1.7) insbesondere im Rollformverfahren (Abschn. 2.1.8) liefern weiteren wichtigen Input für das Projekt.
The present study is focused on the characterization of cyclic loads on the fiber matrix adhesion of regenerated cellulose fibers (RCF) and glass fibers (GF) in a PP matrix with varying contents of maleic anhydride-grafted polypropylene (MAPP). Glass fibers were used for reference purposes. By means of the cyclic loaded single fiber pull-out test (SFPT) the interfacial shear strength (IFFS) and the critical fiber length (lc) are determined as a function of the applied loads, the number of cycles and the MAPP content. The results of the material-specific reduction of the IFSS were extrapolated to approximately predict the fatigue behavior of the composites.
The investigations show the influence of cyclic loads in the single fiber pull-out test on the fiber-matrix adhesion for the first time. On the one hand, the results show that cyclic loading of the embedded single fibers leads to a significant reduction of fiber-matrix adhesion. On the other hand, it becomes clear that the number of cycles has the greatest effect on IFSS and thus on fatigue, while the various investigated setups (test speeds and forces) show the least effect.
The transfer of the resulting findings to the integral fatigue properties of composites can contribute to a much more precise property and failure prediction in the future.
Nanoparticles are proven to enhance the material characteristics of carbon fiber reinforced composites. But these scientific findings are only verified at a lab-scale level. This chapter investigates the extent to which the material performance of nanoparticle-modified resins can be transferred from the coupon level to a larger-scale component. To this end, L-brackets and C-frames are manufactured and the corresponding mechanical performance and matrix-induced distortions are compared. The results for the L-brackets reveal a reduction of the spring-in by 17 wt.% by adding boehmite nanoparticles. This results mostly from the decrease of the matrix’s chemical shrinkage. The effect can also be found for the C-frame, but here standard deviations are high and negate the positive effect of the particles. Even though clear evidence is missing, for larger components it seems likely that deviations in fiber volume content and defects in the fiber orientation are more relevant than the impact of the particles. The analysis of the mechanical performance involved 4-point bending tests of impacted C-frames. This was carried out to investigate the upscaling effects of compression after impact tests. Interestingly, the C-frames with nanoparticles show significant decrease in damage areas after impact in comparison to the unmodified specimen. However, this difference does not result in increased mechanical performance in the bending test. The most likely explanation is that the known enhancements of the matrix material only play a subordinate role in case of abrupt structural stability failure without a preceding period of rising damage.
Short glass fiber reinforced plastics (SGFRP) offer superior mechanical properties compared to polymers, while still also enabling almost unlimited geometric variations of components at large-scale production. PA6-GF30 represents one of the most used SGFRP for series components, but the impact of injection molding process parameters on the fatigue properties is still insufficiently investigated. In this study, various injection molding parameter configurations were investigated on PA6-GF30. To take the significant frequency dependency into account, tension–tension fatigue tests were performed using multiple amplitude tests, considering surface temperature-adjusted frequency to limit self-heating. The frequency adjustment leads to shorter testing durations as well as up to 20% higher lifetime under fatigue loading. A higher melt temperature and volume flow rate during injection molding lead to an increase of 16% regarding fatigue life. In situ Xray microtomography analysis revealed that this result was attributed to a stronger fiber alignment with larger fiber lengths in the flow direction. Using digital volume correlation, differences of up to 100% in local strain values at the same stress level for different injection molding process parameters were identified. The results prove that the injection molding parameters have a high influence on the fatigue properties and thus offer a large optimization potential, e.g., with regard to the component design.
Hohlprofile stellen ideale Strukturen für Leichtbaukonstruktionen mit hohen Widerständen gegen Biege-, Torsions- und Druckbelastung bei geringer Masse dar. Darüber hinaus kann das Leichtbaupotential aufgrund der klar definierten Kraftflüsse innerhalb der Profilstruktur durch die Ausnutzung der Anisotropie von Verbundwerkstoffen zusätzlich erhöht werden. Große Herausforderungen bestehen bei der Gestaltung von Krafteinleitungsbereichen und funktionalen Bereichen, wie etwa tribologisch beanspruchten Oberflächen. Dementsprechend werden diese im Sinne des Multi-Material-Designs meist als metallische Anschluss-, Befestigungs- oder Funktionselemente ausgeführt. In Erweiterung zu klassischen Verbindungstechnologien wie Kleben, Verpressen und Nieten bieten Konturverbindungen ein vielversprechendes Potential für FVK/Metall-Hohlstrukturen, welche intrinsisch gefügt werden können. In diesem Kapitel werden für das Schleuder- und das Schlauchblas-Integral-Verfahren die theoretischen und technologischen Grundlagen zur ressourceneffizienten Fertigung dieser Strukturen dargestellt und deren Verfahrensgrenzen ermittelt. Dabei liegt der Fokus neben der Prozessgestaltung auf der Herstellung, Auslegung und experimentellen Untersuchung des multiskalenstrukturierten Fügebereiches zur Erhöhung der Verbindungsfestigkeit. Anhand von Demonstratorstrukturen wird das realisierbare Bauteilspektrum aufgezeigt.
Concrete infrastructure is deteriorating at a fast pace because of corrosion issues inherent to traditional black steel reinforcement bars (rebars). Alternative non-corrosive reinforcement materials for concrete structures have been developed and rebars made from fiber reinforced polymers (FRP) are one of the most predominantly used non-corrosive materials for internal reinforcement. This research focused on Basalt FRP rebars as this technology is still in development for the U.S. market and no standard specifications are available, yet. In an effort to develop basalt specific acceptance criteria, two commonly available BFRP rebar sizes from five different sources and two different production lots were tested to quantify the tensile strength and stress-strain behavior of this emerging rebar technology. The obtained results were used to evaluate the performance of each rebar type in a relativistic comparison to existing benchmark values for Glass FRP rebars given in AC454. The tensile strengths were consistent for all rebar types and the recorded values surpassed the strength measurements generally reported for comparable GFRP rebars. It was found that No. 3 rebars measured guaranteed tensile strengths between 760 MPa and 1266 MPa (110 ksi and 184 ksi), while No. 5 rebars ranged between 836 MPa and 1074 MPa (129 ksi and 131 ksi). Though the fiber-to-resin ratio of all tested rebar types was similar, the tensile strength of these rebars varied due to differences in the raw materials and production. The elastic moduli were calculated according to AC454}, and it was noted that this property varied significantly between the different rebar types because of irregular cross-sectional dimensions and the various proprietary (not standardized) manufacturing processes. It was determined that acceptance criteria for BFRP rebars can be conservatively defined according to the currently available GFRP values, but more specific criteria can be developed through further research to take advantage of the additional load capacity and potential improved stiffness of BFRP rebars.
Polymer based composite materials have a great potential for applications in tribology as dry lubricants since the components comprising the composition may be chosen to fit to various tribological requirements. It is however well known that heat transfer and thermal effects are important for such systems. Systematic experimental studies of temperature effects are time consuming and expensive. In this work, we use a numerical homogenization approach in order to study the principal influence of key composite descriptors of fiber and particle reinforced PEEK on the homogenized heat conductivity. It turns out that the sensitivity of this key parameter on the descriptors can be nicely fitted to a regression model and thus allows for interpolation in the sense of a structure-property-relationship.
Aufgrund zunehmender Bemühungen thermoplastische faserverstärkte Kunststoffe (engl. CFR-TP) in Flugzeugstrukturen der kommenden Generationen einzusetzen steht die Untersuchung von Fügeverfahren für diese Werkstoffe im Fokus der aktuellen Forschung. Thermoplastische Faserverbundwerkstoffe zeigen gegenüber duromerer Faserverbundwerkstoffe Vorteile bei der Fügetechnologie, da diese z. B. eine Gewichtsreduktion aufgrund wegfallender Bolzen, kürzere Assemblyzeiten und dünnere Lagenaufbauten der Einzelstrukturen aufgrund einer Neudefinition der Laminatschichtung mit wegfallenden Lochleibungslaminaten ermöglicht. Das elektrische Widerstandsschweißen gilt als vielversprechender Fügeprozess für CFR-TPs, da bei diesem die Wärme direkt in der Fügezone generiert wird, ohne dass die gesamte Struktur aufgeschmolzen werden muss. Um große Strukturen wie Rumpfhalbschalen zu Fügen, bedarf es einer Skalierung von bisherigen Schweißversuchen auf Probenniveau hin zu Prozessen für reale Bauteile. Die Skalierbarkeit des statischen Widerstandsschweißprozesses ist jedoch durch Anforderungen an die elektrische Schweißleistung und den Konsolidierungsdruck begrenzt. Für große Strukturen mit langen Fügenähten ergibt sich deshalb die Notwendigkeit einer Unterteilung des Schweißvorgangs in kleine Teilschritte. Dies kann durch die Verwendung eines kontinuierlich geführten Prozesses, der sich flexibel an die Geometrie der Fügeteile anpassen lässt, erreicht werden. Zu diesem Zweck werden im Rahmen dieser Arbeit unterschiedliche Konzeptansätze zur Umsetzung eines kontinuierlichen Schweißverfahrens erarbeitet sowie durch experimentelle Untersuchungen bewertet und verglichen. Aus den Konzepten wird das Design für einen Endeffektor abgeleitet, der komplexe Fügenähte auf einem Roboter- oder Gantrysystem im kontinuierlichen Verfahren verschweißt. Zum Einsatz kommt dabei eine Kombination aus rollenden Kontakt- und flächiger Konsolidierungseinheiten. Die Einsatzfähigkeit des Endeffektors wird durch Schweißversuche validiert und der Einfluss von Prozessparametern auf die Ergebnisse diskutiert.
Forming processes of continuous fiber reinforced thermoplastic materials are oftentimes limited to high volume production due to the high costs for tooling and processing machines. This study suggests the combined use of a cold and simple tool and high forming speeds to reduce tooling and processing costs and enable the usage of common stamping machines. Half sphere samples are produced from single and two-layer polypropylene and glass fiber organo-sheets in a custom built drop tower and analyzed for their geometry, degree of re-consolidation, surface quality and potential fiber damage using a variety of microscopy techniques. While only mediocre degrees of re-consolidation and limited surface qualities can be achieved with the combination of a cold tooling and state-of-the-art forming speeds of 0–0.5 ms⁻¹, the usage of a higher forming speed of 3 ms⁻¹, vastly improves surface qualities and the degree of re-consolidation without any detectable fiber damage. This effect is more pronounced in the dual layer material. Extensive knowledge on the forming behavior of continuous fiber reinforced thermoplastics at high cooling rates and high speeds of deformation is required for sufficient process control and future studies need to further elaborate and quantify the influencing factors and limits of high-speed forming of continuous fiber reinforced thermoplastics.
Im Leichtbau gilt mittlerweilen die Philosophie, immer den richtigen Werkstoff für den richtigen Anwendungsfall (Multi-Material-Design). Dies setzt voraus, dass der Leichtbauer einen breiten Überblick über die technologisch relevanten Werkstoffe hat. Vor diesem Hintergrund wird im Weiteren ein Überblick über typische Leichtbauwerkstoffe gegeben.
Mit Hilfe eines neuen, gesamtheitlichen Lösungsansatzes zur automatisierten Montage von Flachleiterkabeln auf Fahrzeugmodulen, lässt sich die exemplarisch nachvollzogene Montageprozesskette für Pkw-Türaggregateträger erheblich verkürzen und vollständig automatisieren. Dadurch ist es möglich, die lange und teure Logistikkette in europäische Niedriglohnländer aufzulösen und eine flexible Modulmontage mit kurzen Reaktionszeiten in der Nähe der Automobilhersteller in Deutschland aufzubauen.
Thermoforming is one of the most important processes in polymer processing. In the packaging industry, thermoformed parts such as blister packs are manufactured from amorphous plastics such as polystyrene (PS) or polyvinyl chloride (PVC). In the field of semi-crystalline thermoplastics, mainly standard thermoplastics, such as, for example, polypropylene (PP), polyethylene (PE), or polyethylene terephthalate (PET), are used. There is limited literature dealing with the thermoforming of thin filled systems. Filler bonding, in particular, represents a major challenge in strain rheology. Electron irradiation is a way to generate improved filler-matrix bonding. In this study, the influence of fillers and radiation-crosslinking on the elongation behaviour and on the wall thickness distribution was investigated. At higher areal draw ratios, an enormous benefit of radiation-crosslinking of thin filled sheets is shown. While non-crosslinked specimens could not be formed, it was possible to thermoform radiation-crosslinked sheets filled with 10 vol.% glass fibres. Furthermore, with the higher areal draw ratio, the influence of the filler orientation on the stretching behaviour became more apparent.
Despite intensive research on material properties of non-metallic technical textiles for internal reinforcement in concrete, the long-term durability is not yet fully understood. In this work, results of preloaded long-term durability tensile tests on carbon-reinforced concrete specimens under environmental factors of stress, temperature, moisture and alkalinity are presented. Based on investigations of non-metallic glass fiber reinforcements with polymer matrices, where strength losses occur over time, it was planned to derive a time to failure curve and to determine a reduction factor for the tensile strength of the carbon textile reinforcement. However, no loss of strength was discovered in residual capacity tests due to the high material resistance and therefore no reduction factor due to the environmental factors could be derived. After more than 5000 h of testing, the residual capacity tests showed an increase in the ultimate failure stress in comparison with the short-term tests. In addition to the long term-durability tests, the influence of the preloading was investigated. The preload was applied to the long-term tests and led to a straighter alignment and loading of the filaments and thus to an increase in the ultimate capacity.
Nowadays, the use of fiber reinforced polymers increases continuously. Endless carbon fiber reinforced polymers are used primarily for products, which require high stiffness and strength while having a minimum weight. The increasing use of these materials results in the issue of production and after lifetime waste recycling. Due to the high costs for carbon fibers the recycling is reasonable from the economic point of view. Currently there are different strategies to reuse carbon fibers. One of them is processing carbon fiber waste in twin screw compounders for the production of short fiber reinforced polymers. One of the main issue during this process is the distributive mixing of the fibers and the fiber degradation of carbon fiber waste which is mostly available as cutted fabric.
In order to achive higher fiber lengths while having evenly distributed fibers in the polymer matrix, a new type of compounding machine typically used for recycling of domestic plastic waste is investigated. In a first step the flow region of the machine is calculated numerically. With a particle tracking method that is based on the numerical flow calculation the distributive mixing behavior is determined. In the experimental part the compounding of glass fibers (chopped strands) in a Polypropylene matrix is investigated. Different pre-mixtures of granulate and fibers with fiber proportions of 20%, 30% and 40% are prepared and processed using different parameter settings. For every processing point the fiber length distribution and the fiber mass proportion in the produced granulate is measured. By analyzing the different results the homogeneity and the fiber breakage is determined. Finally there is a comparison between the material properties of the conventionally produced material in the twin screw process and the material produced with the aforementioned machine.
248 7.1.2 Unidirektional verstärkte Schicht (UD-Schicht)
- Hookesches . . . . Gesetz Bei Ebenem Spannungszustand
Hookesches Gesetz bei ebenem Spannungszustand..........248
7.1.2
Unidirektional verstärkte Schicht (UD-Schicht)....................250