Surfaces of carbon fibre roving were modified by means of a low temperature plasma treatment to improve their bonding with mineral fines; the latter serving as an inorganic fibre coating for the improved mechanical performance of carbon reinforcement in concrete matrices. Variation of the plasma conditions, such as gas composition and treatment time, was accomplished to establish polar groups on the carbon fibres prior to contact with the suspension of mineral particles in water. Subsequently, the rovings were implemented in a fine concrete matrix and their pull-out performance was assessed. Every plasma treatment resulted in increased pull-out forces in comparison to the reference samples without plasma treatment, indicating a better bonding between the mineral coating material and the carbon fibres. Significant differences were found, depending on gas composition and treatment time. Microscopic investigations showed that the samples with the highest pull-out force exhibited carbon fibre surfaces with the largest areas of hydration products grown on them. Additionally, the coating material ingresses into the multifilament roving in these specimens, leading to better force transfer between individual carbon filaments and between the entire roving and surrounding matrix, thus explaining the superior mechanical performance of the specimens containing appropriately plasma-treated carbon roving.

Ordinary concrete is the most commonly used building material, but nowadays the requirements for low energy consumption, durability of structures together with their easy diagnostics as well as ecological production raises. This thesis deals with cement and aluminosilicate composites with content of conductive fillers, which allows to monitor the change in electrical properties, most commonly electrical resistance in dependence on mechanical stress. In the experimental part of the thesis, test beams were produced based on alkali-activated slag with content of carbon nanotubes, graphite powder, carbon black and carbon fibre. The beams were subjected to flexural loading in a three-point bending configuration and the shift in electrical resistance was monitored.

Dans un composite stratifié, les plis orientés à 0° par rapport à la direction du chargement pilotent souvent la rupture sous chargement de traction. Les fibres procurent l’essentiel de la rigidité et la résistance de ces plis. Dans ces travaux de thèse, le comportement en fatigue des plis à 0° est analysé dans des stratifiés unidirectionnels (UD) et multidirectionnels, au moyen d’essais de fatigue multi-instrumentés. Un protocole expérimental est mis en place pour éviter les ruptures prématurées typiques des essais sur UD. L’évolution en fatigue des ruptures de fibres est identifiée par leur émission acoustique. Les mécanismes de fatigue dominés par la rupture des fibres sont analysés par un modèle aux éléments finis développé à l’échelle des constituants. / Under quasi-static and fatigue tension loads, the failure of a carbon fibre reinforced polymer laminate (CFRP) is usually driven by 0° plies. Carbon fibres give most of the stiffness and strength of these plies. In this work, the fatigue behaviour of 0° plies inside unidirectional (UD) and multidirectional laminates is analysed via multi-instrumented tension-tension fatigue tests. A numerical and experimental study is addressed to perform fatigue tests without the typical premature failures of the UD laminates. The acoustic emissions technique is used to identify the evolution law of fibre breaks. A finite element model is developed at the microscale (fibres and matrix) to analyse the fibre-driven fatigue mechanisms.

Hydraulic systems are used in many fields of applications for different functions like energy storage in hybrid systems. Generally the mass of hydraulic systems plays a key role especially for mobile hydraulics (construction machines, trucks, cars) and hydraulic aircraft systems. The main product properties like energy efficiency or payload can be improved by reducing the mass. In this connection carbon fiber reinforced plastics (CFRP) with their superior specific strength and stiffness open up new chances to acquire new lightweight potentials compared to metallic components. However, complex quality control and failure identification slow down the substitution of metals by fiber-reinforced plastics (FRP). But the lower manufacturing temperatures of FRP compared to metals allow the integration of sensors within FRP-components. These sensors then can be advantageously used for many functions like quality control during the manufacturing process or structural health monitoring (SHM) for failure detection during their life cycle. Thus, lightweight hydraulic components made of composite materials as well as sensor integration in composite components are a main fields of research and development at the Institute of Lightweight Engineering and Polymer Technology (ILK) of the TU Dresden as well as at the Leichtbau-Zentrum Sachsen GmbH (LZS).

Nowadays, thin-walled load bearing structures can be realised using textile reinforced concrete (BRAMESHUBER and RILEM TC 201-TRC [1]). The required tensile strength is achieved by embedding several layers of textile. By means of the laminating technique the number of textile layers that can be included into the concrete could be increased. To further increase the first crack stress and the ductility as well as to optimize the crack development, fine grained concrete mixes with short fibres can be used. By a schematic stress-strain curve the demands on short fibres are defined. Within the scope of this study, short fibres made of glass, carbon, aramid and polyvinyl alcohol are investigated in terms of their ability to fit these requirements. On the basis of these results, the development of hybrid fibre mixes to achieve the best mechanical properties is described. Additionally, a conventional FRC with one fibre type is introduced. Finally, the fresh and hardened concrete properties as well as the influence of short fibres on the load bearing behaviour of textile reinforced concrete are discussed.

Mit zunehmendem Alter zeigt das Verbundverhalten von Multifilamentgarnen aus alkaliresistentem Glas (AR-Glas) oder Kohlenstoff in Abhängigkeit von der Zusammensetzung der zementgebundenen Matrix eine sehr unterschiedliche Entwicklung. Während bei AR-Glas teilweise drastische Verluste des Leistungsvermögens zu verzeichnen sind, treten diese bei Kohlefasern nicht auf. Zur Untersuchung der Phänomene wurden beidseitige Garnauszugversuche durchgeführt und die Interphase zwischen Filamenten und Matrix im Rasterelektronenmikroskop (ESEM) untersucht. Die unterschiedlichen mechanischen Eigenschaften stehen in Zusammenhang mit verschieden ausgeprägten Mikrostrukturen der Interphasen. Welche Ursachen die unterschiedliche morphologische Entwicklung der Interphasen hat, ist Gegenstand aktueller Arbeiten.

High-speed plunge-cut centreless grinding opens up enormous potential for the manufacturing of difficult-to-machine materials and to improve the surface quality while reducing the grinding forces. For this investigation, a new grinding wheel base body of carbon fibre-reinforced plastic (CFRP) was developed to achieve grinding wheel speeds up to 150 m/s in plunge-cut centreless grinding of hardened shafts. For evaluation of the performance characteristics, the grinding forces and the surface quality of different grinding tools were detected. These experiments were conducted using a newly developed measuring system to analyse the grinding forces in the workrest blade. The experimental results are described and discussed in this article.

The strive for lower fuel consumption and downsizing in the automotive industry has led to the use of alternative high performance materials, such as fibre composites. Designing chassis components with composite materials require accurate simulation models in order to capture the behaviour in car crashes. By simplifying the development process of a B-pillar with a new dynamic test method, composite material products could reach the market faster. The setup has to predict a cars side impact crash performance by only testing the B-pillar in a component based environment. The new dynamic test method with more realistic behaviour gives a better estimation of how the B-pillar, and therefore the car, will perform in a full-scale car side impact test. With the new improved tool for the development process, the search for a lighter product with better crash worthiness is done by optimising a steel carbon fibre hybrid structure in the B-pillar. The optimisation includes different carbon fibre materials, composite laminate lay-up and stiffness analysis. By upgrading simulation models with new material and adhesive representation physical prototypes could be built to verify the results. Finally the manufactured steel carbon fibre hybrid B-pillar prototypes were tested in the developed dynamic test method for a comparison to the steel B-pillar. The hybrid B-pillars perform better than the reference steel B-pillar in the dynamic tests also being considerably lighter. As a final result a hybrid B-pillar is developed that will decrease fuel consumption and meet the requirements of any standardized side impact crash test. / Strävan efter lägre bränsleförbrukning och minimalistiskt tänkande inom bilindustrin har lett till användning av alternativa högpresterande material, såsom fiberkompositer. Vid design av chassi-komponenter utav kompositer krävs noggranna simuleringsmodeller för att fånga upp bilens beteende vid en krock. Genom att förenkla utvecklingsprocessen för en B-stolpe med en ny dynamisk testmetod kan produkter bestående av fiberkompositer nå marknaden snabbare. Provuppställningen skall förutse bilens prestanda vid ett sidokrocktest genom att endast testa B-stolpen i en komponentbaserad miljö. Den nya dynamiska testmetoden med ett mer realistiskt beteende skall ge en bättre uppskattning om hur B-stolpen, och därmed bilen, kommer att prestera i ett fullskaligt sidokrocktest. Med utvecklingsprocessens nya förbättrade verktyg kan strävan mot lättare produkter med bättre krocksäkerhet utvecklas genom optimering av en hybrid B-stolpe i stål och kolfiber. Optimeringen innefattar olika kolfibermaterial, laminatvarianter och styvhetsanalyser. Genom att uppgradera simuleringsmodeller med nya material och adhesiva metoder kunde fysiska prototyper tillverkas för att verifiera resultaten. Slutligen testades de tillverkade prototyperna utav stål och kolfiber i den nyutvecklade dynamiska testmetoden för jämförelse mot den ursprungliga stål B-stolpen. Hybrid B-stolparna presterade bättre än referensstolpen utav stål i de dynamiska provningarna och är samtidigt betydligt lättare. Det slutgiltigt resultatet är en utvecklad hybrid B-stolpe som både ger minskad bränsleförbrukningen och uppfyller kraven för ett standardiserat sidokrocktest.

Dieses Projekt widmete sich einer neuen Bauweise für stabförmige Drucktragglieder aus ultrahochfestem Beton (UHFB), die - als UHFB-Rohre mit Stahlrohren ummantelt - hier als Hybridrohre bezeichnet werden. Durch eine äußere Wickelverstärkung aus kohlenstofffaserverstärktem Kunststoff (CFK) werden die beiden, für sich alleine betrachtet ausgeprägt spröden Hochleistungsmaterialien UHFB und CFK so kombiniert, dass sie zu besonders leichten Bauteilen hoher Tragfähigkeit mit ausgeprägt duktilem Versagensverhalten zusammengefügt werden. [Aus: Motivation und Zielsetzung] / This project was dedicated to a new construction method for rod-shaped support elements made of ultra-high performance concrete (UHPC), which - as UHPC tubes coated with steel sheets - are called hybrid tubes in this report. Through an exterior wrapping-reinforcement made of carbon fibre reinforced plastic (CFRP), the two high-performance materials UHPC and CFRP, which are distinctly brittle when viewed on their own, are combined in such a way that they form particularly light components of high load-bearing capacity with profound ductile failure behaviour. [Off: Motivation and objective]

It is in the nature of the human species to find solutions of complex technical problems and always strive for improvements. The development of new materials is not an exception. One of the many man-made materials is carbon fibre (CF). Its excellent mechanical properties and low density have made it attractive as the reinforcing agent in lightweight composites. However, the high price of CF originating from expensive production is currently limiting CF from wider utilisation, e.g. in the automotive sector.   The dominating raw material used in CF production is petroleum-based polyacrylonitrile (PAN). The usage of fossil-based precursors and the high price of CF explain the strong driving force of finding cheaper and renewable alternatives. Lignin and cellulose are renewable macromolecules available in high quantities. The high carbon content of lignin is an excellent property, while its structural heterogeneity yields in CF with poor mechanical properties. In contrast, cellulose has a beneficial molecular orientation, while its low carbon content gives a low processing yield and thus elevates processing costs.   This work shows that several challenges associated with CF processing of each macromolecule can be mastered by co-processing. Dry-jet wet spun precursor fibres (PFs) made of blends of softwood kraft lignin and kraft pulps were converted into CF. The corresponding CFs demonstrated significant improvement in processing yield with negligible loss in mechanical properties relative to cellulose-derived CFs. Unfractionated softwood kraft lignin and paper grade kraft pulp performed as good as more expensive retentate lignins and dissolving grade kraft pulp, which is beneficial from an economic point of view.   The stabilisation stage is considered the most time-consuming step in CF manufacturing. Here it was shown that the PFs could be oxidatively stabilised in less than 2 h or instantly carbonised without any fibre fusion, suggesting a time-efficient processing route. It was demonstrated that PF impregnation with ammonium dihydrogen phosphate significantly improves the yield but at the expense of mechanical properties.   A reduction in fibre diameter was beneficial for the mechanical properties of the CFs made from unfractionated softwood kraft lignin and paper grade kraft pulp. Short oxidative stabilisation (&lt;2 h) of thin PFs ultimately provided CFs with tensile modulus and strength of 76 GPa and 1070 MPa, respectively. Considering the high yield (39 wt%), short stabilisation time and promising mechanical properties, the concept of preparing CF from lignin:cellulose blends is a very promising route. / Det ligger i människans natur att hitta lösningar på komplexa tekniska problem, samt att alltid sträva efter förbättringar. Utvecklingen av nya material är inget undantag. Ett av flera material utvecklade av människan är kolfiber. Dess utmärkta mekaniska egenskaper samt låga densitet har gjort det attraktivt som förstärkningsmaterial i lättviktskompositer. Det höga priset på kolfiber, vilket härstammar ur en kostsam framställningsprocess, har förhindrat en mer utbredd användning i exempelvis bilindustrin.   Det dominerande råmaterialet för kolfiberframställning är petroleumbaserad polyacrylonitril (PAN). Användandet av fossila råvaror och det höga priset på kolfiber förklarar den starka drivkraften att hitta billigare och förnyelsebara alternativ. Lignin och cellulosa är förnyelsebara makromolekyler som finns tillgängliga i stora kvantiteter. Det höga kolinnehållet i lignin gör det mycket attraktivt som råvara för kolfiberframställning, men dess heterogena struktur ger en kolfiber med otillräckliga mekaniska egenskaper. Däremot har cellulosa en molekylär orientering som är önskvärd vid framställning av kolfiber, men dess låga kolinehåll ger ett lågt processutbyte som i sin tur bidrar till höga produktionskostnader.             Det här arbetet visar att många av de problem som uppstår med kolfiber från respektive råvara kan kringgås genom att utgå från blandningar av desamma. Prekursorfibrer från blandningar av kraftlignin och kraftmassa från barrved tillverkade med luftgapsspinning konverterades till kolfiber. Utbytet för kolfibrerna som framställdes var mycket högre än vid framställning från endast cellulosa. Ofraktionerat barrvedslignin och kraftmassa av papperskvalitet presterade lika bra som de dyrare retentatligninen och dissolvingmassan, vilket är fördelaktigt ur ett ekonomiskt perspektiv.   Stabilisering är det mest tidskrävande processteget i kolfibertillverkning. I det här arbetet visades det att prekursorfibrerna kunde stabiliseras på kortare än två timmar, eller direktkarboniseras utan någon sammansmältning av fibrerna. Detta indikerar att en tidseffektiv produktion kan vara möjligt. Impregnering av prekursorfibrerna med ammoniumdivätefosfat ökade utbytet avsevärt, men med lägre mekaniska egenskaper som bieffekt.           Kolfibrernas mekaniska egenskaper ökade vid en diameterreduktion. En kort oxidativ stabilisering under två timmar i kombination med tunna prekursorfibrer gav kolfiber med en elasticitetsmodul på 76 GPa och dragstyrka på 1070 MPa. Att göra kolfiber från blandningar av lignin och cellulosa är ett lovande koncept om det höga utbytet (39%), den korta stabiliseringstiden samt de lovande mekaniska egenskaperna tas i beaktande. / <p>QC 20190226</p>