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Structural assessment procedures for existing concrete bridges : Experiences from failure tests of the Kiruna BridgeBagge, Niklas January 2017 (has links)
Assessing existing bridges is an important task in the sustainable management ofinfrastructure. In practice, structural bridge assessments are usually conducted usingtraditional and standardised methods, despite knowledge that these methods oftenprovide conservative estimates. In addition, more advanced methods are available, suchas nonlinear finite element (FE) analysis, that are used for research purposes and cansimulate the structural behaviour of bridges more accurately. Therefore, it would beuseful to develop practical and reliable procedures for refined assessments using theseadvanced techniques.Focusing on the ultimate load-carrying capacity of existing concrete bridges, this thesispresents a procedure for structural assessments. The fundamental idea is to improve theassessment successively, as necessary to predict bridges’ structural behaviour adequately.The procedure involves a multi-level assessment strategy with four levels of structuralanalysis, and an integrated framework for safety verification. At the initial level (Level 1)of the multi-level strategy, traditional standardised methods are used, no failures arecovered implicitly in the structural analysis and action effects are verified using localresistances calculated using analytical models. In the subsequent enhanced levels (Levels2 – 4), nonlinear FE analysis is used for stepwise integration of the verification of flexural,shear-related and anchorage failures into the structural analysis. The framework for safetyverifications includes partial safety factor (PSF), global resistance safety factor (GRSF) andfull probabilistic methods. Within each of these groups, verifications of desired safetymargins can be conducted with varying degrees of complexity.To demonstrate and evaluate the proposed structural assessment procedure, comparativestudies have been carried out, based on full-scale tests of a prestressed concrete bridge.This was the Kiruna Bridge, located in the northernmost city in Sweden, which was duefor demolition as part of a city transformation project, necessitated by large grounddeformations caused by the large nearby mine. Thus, it was available for destructiveexperimental investigation within the doctoral project presented in this thesis. The bridgehad five continuous spans, was 121.5 m long and consisted of three parallel girders with a connecting slab at the top. Both the girders and slab were tested to failure to investigatetheir structural behaviour and load-carrying capacity. Non-destructive and destructivetests were also applied to determine the residual prestress forces in the bridge girders andinvestigate the in situ applicability of methods developed for this purpose. The so-calledsaw-cut method and decompression-load method were used after refinement to enabletheir application to structures of such complexity. The variation of the experimentallydetermined residual prestress forces was remarkably high, depending on the sectioninvestigated. There were also high degrees of uncertainty in estimated values, and thusare only regarded as indications of the residual prestress force.Level 1 analysis of the multi-level assessment strategy consistently underestimatedcapacity, relative to the test results, and did not provide accurate predictions of the shearrelatedfailure observed in the test. With linear FE analysis and local resistance modelsdefined by the European standard, Eurocode 2, the load-carrying capacity wasunderestimated by 32 % for the bridge girder and 55 % for the bridge deck slab. At theenhanced level of structural analysis (Level 3), nonlinear FE analyses predicted thecapacities with less than 2 % deviation from the test results and correctly predicted thefailure mode. However, for existing bridges there are many uncertainties, for instance,the FE simulations were sensitive to the level of residual prestressing, boundaryconditions and assumed material parameters. To accurately take these aspects intoaccount, bridge-specific information is crucial.The complete structural assessment procedure, combining the multi-level strategy andsafety verification framework, was evaluated in a case study. Experiences from theprevious comparative studies were used in an assessment of the Kiruna Bridge followingthe Swedish assessment code. The initial assessment at Level 1 of the multi-level strategyand safety verification, using the PSF method, indicated that the shear capacity of one ofthe girders was critical. The most adverse load case (a combination of permanent loads,prestressing and variable traffic loads) was further investigated through enhancedstructural analyses implicitly accounting for flexural and shear-related failures (Level 3).Nonlinear FE analysis and safety evaluation using the PSF method, several variants of theGRSF method and the full probabilistic analysis for resistance indicated that the permittedaxle load for the critical classification vehicle could be 5.6 – 6.5 times higher than thelimit obtained from the initial assessment at Level 1. However, the study also indicatedthat the model uncertainty was not fully considered in these values. The modeluncertainty was shown to have strong effects on the safety verification and (thus)permissible axle loads. The case study also highlighted the need for a strategy forsuccessively improving structural analysis to improve understanding of bridges’ structuralbehaviour. The refined analysis indicated a complex failure mode, with yielding of thestirrups in the bridge girders and transverse flexural reinforcement in the bridge deck slab,but with a final shear failure of the slab. It would be impossible to capture suchcomplexity in a traditional standardised assessment, which (as mentioned) indicated thatthe shear capacity of the girder limited permissible axle loads. However, nonlinear FEanalyses are computationally demanding, and numerous modelling choices are required.Besides a strategy for rationally improving the analysis and helping analysts to focus oncritical aspects, detailed guidelines for nonlinear FE analysis should be applied to reduce the analyst-dependent variability of results and (thus) the model uncertainty. Clearly, toensure the validity of bridge assessment methods under in situ conditions, theirevaluations should include in situ tests. This thesis presents outcomes of such tests, therebyhighlighting important aspects for future improvements in the assessment of existingbridges.
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Potential and application fields of lightweight hydraulic components in multi-material designUlbricht, Andreas, Gude, Maik, Barfuß, Daniel, Birke, Michael, Schwaar, Andree, Czulak, Andrzej January 2016 (has links)
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).
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Investigation of a carbon fibrereinforced plastic grinding wheel for high-speed plunge-cut centreless grinding applicationHänel, Albrecht, Teicher, Uwe, Pätzold, Holger, Nestler, Andreas, Brosius, Alexander 04 November 2019 (has links)
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.
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Development of Dynamic Test Method and Optimisation of Hybrid Carbon Fibre B-pillarJohansson, Emil, Lindmark, Markus January 2017 (has links)
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.
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Wickelverstärkte HybridrohreLohaus, Ludger, Markowski, Jan 21 July 2022 (has links)
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]
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Studies on the Effects of Carbon Nanotubes on Mechanical Properties of Bisphenol E Cyanate Ester/Epoxy Based Resin Systems and CFRP CompositesSubba Rao, P January 2016 (has links) (PDF)
The search and research for high performance materials for aerospace applications is a continuous evolving process. Among several fibre reinforced polymers, carbon fibre reinforced polymer (CFRP) is well known for its high specific stiffness and strength. Though high modulus and high strength carbon fibre with structural resin systems have currently been established reasonably well and are catering to a wide variety of aerospace structural applications, these properties are generally directional with very high properties along the fibre direction dominated by fibres and low in other directions depending mainly on the resin properties. Thus, there is a need to enhance the mechanical properties of the resin systems for better load transfer and to improve the resin dominated properties like shear strength and properties in directions other than along the fibre. Use of carbon nanotubes (CNTs) with their extraordinary specific stiffness and strength apparently has great potential as an additional reinforcement in resin for development of CNT-CFRP nanocomposites. However, there are several issues that need to be addressed such as compatibility of a particular resin with CNTs, amount of CNTs that can be added, uniform dispersion of these nanotubes, surface treatment and curing process etc., for optimal enhancement of the required properties.
Epoxy and cyanate ester resin systems are finding applications in aerospace structures owing to their desirable set of properties. Of these, bisphenol E cyanate ester (BECy) resin of low viscosity with its low moisture absorption, better dimensional stability, and superior mechanical properties can establish itself as potential structural resin system for these applications. BECy in particular has the advantage of being more suitable for out of autoclave manufacturing process such as Vacuum Assisted Resin Transfer Molding (VARTM). Literature shows that, significant work has been carried out by various researchers reporting improvements using CNTs in epoxy resins along with various associated problems. However, studies on effects of addition of CNTs /fCNTs to BECy-CFRP composite system are not well reported.
Thus, objective of this work is to study the effects of adding pristine and functionalized CNTs to low viscosity cyanate ester as well as epoxy resin systems. Further, to study the effects on mechanical properties of nanocomposites with carbon fibre reinforcement in these CNT dispersed resin system through a combination of experimental and computational approaches.
Multiwall carbon nanotubes (CNTs) without and with different chemical functionalization are chosen to be added to epoxy and BECy resins. The quantity of these CNTs /fCNTs is varied in steps up to 1% by weight. Different methods of mixing such as shear mixing, ultrasonication and combined mixing cycles are implemented to achieve uniform dispersion of these nanotubes in the resin system. Standard test samples are prepared from these mixtures of nanotubes in resin systems to study the variation in mechanical properties. Further, these nanotubes added resin systems are used in fabricating CFRP laminates by VARTM process. Both uni-directional and bi-directional laminates are made with the above modified resin systems with CNTs/fCNTs. Series of experimental investigations are carried out to study various aspects involved in making of nanocomposites and the effects of the same on different mechanical properties of the nanocomposites. Standard specimens are cut out from these laminates to evaluate them for tension, compression, flexure, shear and interlaminar shear strength. The main parameters investigated are the effects of varied quantity of CNTs and functionalized CNTs in the resin mix and in CFRP nanocomposites, effect of different mixing / curing cycles etc. on the mechanical properties of the nanocomposites. The investigations have yielded very interesting and encouraging results to arrive at optimum quantity of CNTs to be added and also the effects of functionalization to achieve enhanced mechanical properties. In addition, correlation of mechanical property enhancements with failure mechanisms, dispersion behaviour and participation of CNTs / fCNTs in load transfer are explained with the aid of scanning electron microscope images.
Computational studies are carried out through atomistic models using computational tools to estimate the mechanical properties, understand and validate the effects of various parameters studied through series of experimental investigations. An atomistic model is built taking into consideration the nanoscale effects of the single wall carbon nanotubes (SWCNTs) and its reinforcement in the BECy resin. Using these atomistic models, mechanical properties of individual SWCNT, BECy polymer resin, polymer with different quantities of added SWCNT, and the CFRP laminates with improved resin are computed. As the interaction of CNT with the polymer is only at the outermost layer and the mechanical properties of either MWCNTs or SWCNTs are too high compared to resin systems, it is not expected to have any difference in the final outcome whether it is MWCNT or SWCNT. Hence, only SWCNTs are considered in computational studies as it helps in reducing the complexity of atomistic models and computational time when coupled with polymer resin. This is valid even for functionalized CNT as functionalization is also a surface phenomenon.
To start with, the mechanical behaviour of SWCNT is studied using molecular mechanics approach. Molecular mechanics based finite element analysis is adopted to evaluate the mechanical properties of armchair, zigzag and chiral SWCNT of different diameters. Three different types of atomic bonds, i.e., carbon-carbon covalent bond and two types of carbon-carbon van der Waals bonds are considered in the carbon nanotube system. The stiffness values of these bonds are calculated using the molecular potentials, namely Morse potential function and Lennard-Jones interaction potential function respectively and these stiffness values are assigned to spring elements in the finite element model of the SWCNT. The importance of inclusion of Lennard-Jones interactions is highlighted in this study. Effect of these non-bonded interactions is studied by making the numerical stiffness of these bonds to negligible levels and found that they significantly reduce the mechanical properties. The effect of non-bonded Lennard-Jones atomic interactions (van der Waal interactions) considered here is a novelty in this work which has not been considered in previous research works. The finite element model of the SWCNT is constructed, appropriate boundary conditions are applied and the behaviour of mechanical properties of SWCNT is studied. It is found that the longitudinal tensile strength and maximum tensile strain of armchair SWCNTs is greater than that of zigzag and chiral SWCNTs and its value increases with increasing SWCNT diameter. The estimated values of the mechanical properties obtained agree well with the published literature data determined using other techniques.
As the systems become more complicated with the inclusion of polymers, molecular dynamics (MD) method using well established codes is more adoptable to study the effect of SWCNTs on BECy. Hence, it is used to model and solve the nanosystems to generate their stress-strain behavior. Further, MD approach followed here can effectively include interfacial interaction between polymer and the CNTs as well. Mechanical properties of SWCNT functionalized SWCNT (fSWCNT), pure BECy resin and that of the CNT nanocomposite consisting of specific quantity of SWCNT / fSWCNT in BECy are estimated using MD method. Atomistic models of SWCNT, fSWCNT, BECy, BECy with specific quantities of CNT / fSWCNT are constructed.
A monomer of BECy is modelled and stabilized before its usage as a building block for modelling of BECy resin and to compute its properties. A cell of specific size containing monomers of BECy and another cell of same size with SWCNT at centre surrounded by BECy monomer molecules are built. The appropriate quantity of SWCNT in resin is modelled. This model captures the required density of the composite resin. The models so constructed are subjected to geometric optimization satisfying the convergence criteria and equilibrated through molecular dynamics to obtain a stable structure. The minimized structure is subjected to small strain in different directions to calculate the Young’s modulus and other moduli of the CNT-BECy resin composite. The process is repeated for different quantities of SWCNT in BECy resin to obtain their moduli. Further, tensile and shear strengths of CNT-BECy are obtained by subjecting the equilibrated structure to a series of applied strains from 0 to 10% in steps of 1%. The stress values corresponding to each strain are obtained and a stress – strain curve is plotted. From the stress- strain curve, the strengths of the CNT -BECy which is the stress corresponding to the modulus after which the material starts to soften are determined. Effects of functionalization on mechanical properties of SWCNT are observed. Further, effects of functionalization of SWCNT are studied with a specific quantity of fSWCNT on different moduli and strengths of BECy are investigated.
The properties of enhanced CNT–BECy nanocomposite resin with different quantities of added CNT obtained through MD are used to estimate the mechanical properties of the CNT-BECy-CFRP nanocomposite using micromechanics model. Further, validation with experimental results is attempted comparing the trends in enhancement of properties of the CNT-BECy resin and CNT-BECy-CFRP nanocomposite system.
The outcome of this research work has been significantly positive in terms of
i) Development of an appropriate process establishing different parameters for dispersing CNTs in the resin system, mixing, curing cycle for making of nanocomposites demonstrating significant and consistent enhancement of mechanical properties of BECy based resin system and CFRP nanocomposites using optimum quantity of CNTs /fCNTs through a series of well planned and executed experimental investigations. Evaluation of mechanical properties for each of the cases has been carried out experimentally.
ii) Establishing a computational methodology involving intricate atomistic modelling and molecular dynamics of nanosystems for estimation of mechanical properties of BECy polymer resin and to study the effects by addition of SWCNT / functionalized SWCNT on the properties. Results obtained through series of experimental investigations have been validated through this computational study. This could be an important step towards realising the potential of this resin system for high performance aerospace applications.
Thus, in brief, detailed experimental work combined with computational studies performed as presented in this thesis resulted in achieving structurally efficient cyanate ester based nanocomposites which is unique and not reported in open literature.
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Beitrag zur Entwicklung neuartiger hybrider Werkstoffverbunde auf Polymer/Keramik-BasisTodt, Andreas 08 September 2017 (has links)
Kohlenstofffaserverstärkter Kohlenstoff weist ausgezeichnete thermische, mechanische und chemische Eigenschaften auf. Aufgrund seiner Faserarchitektur und Porosität zeigt dieser eine mit metallischen und polymeren Werkstoffen vergleichbar hohe Schadenstoleranz. Die Herstellung komplexer Leichtbaustrukturen aus C/C-Verbunden ist jedoch zeit- und kostenintensiv. Ein neuer Ansatz stellt die Integration geometrisch simpler C/C-Verbunde in komplexe, problemlos zu realisierende polymere Strukturen dar. Ein derartiges Werkstoffkonzept vereint die Vorteile seiner Komponenten in einem ganzheitlichen Werkstoffsystem. Einen Nachteil stellt jedoch die geringe wechselseitige Adhäsion seiner Komponenten dar. Die Innovation dieses Beitrags stellt sich einerseits der Herausforderung die mechanischen Eigenschaften der C/C-Verbunde in Abhängigkeit der intrinsischen Porosität zu beeinflussen. Dies geschieht durch Veränderung der chemischen und physikalischen Vernetzungsbedingungen des Matrixprecursors. Andererseits soll die dadurch herrührende inhärente Porosität zur Vergrößerung der wirksamen äußeren Oberfläche und zur gezielten Verbesserung der Adhäsion zum Polymer führen. Es wird ein Kohlenstoffprecursor mit variabler offener
Porosität entwickelt und daraus neuartige verschiedenporöse C/C-Verbunde hergestellt und untersucht. Im Anschluss werden die verschiedenporösen C/C-Verbunde mit ausgewählten Polymeren unter definierten Konsolidierungsparametern thermisch gefügt und deren wechselseitiges Adhäsionsverhalten bewertet.:ABKÜRZUNGEN UND FORMELZEICHEN I
ABBILDUNGSVERZEICHNIS VI
TABELLENVERZEICHNIS XI
I EINLEITUNG UND MOTIVATION 1
II STAND DER TECHNIK 3
II 1 Hybride Polymer/Keramik - Werkstoffverbunde 3
II 1.1 Grundlagen zur Adhäsion 3
II 1.1.1 Adhäsionsmodelle 3
II 1.1.2 Keramik/Polymer-Grenzflächentypen 7
II 1.2 Konstruktionsprinzipien 8
II 1.2.1 Differentialbauweise 8
II 1.2.2 Integralbauweise 8
II 1.2.3 Mischbauweise 8
II 1.2.4 Hybridbauweise (hybride Werkstoffverbunde) 8
II 1.3 Fertigungsverfahren 9
II 1.3.1 Klassifizierung 10
II 1.3.2 In-situ-Fügetechnik (In-Mould Assembly) 11
II 1.3.3 Ex-situ-Fügetechnik (Post-Mould Assembly) 11
II 1.4 Aspekte zur Interfaceoptimierung 12
II 1.5 Versagensverhalten von einfachen hybriden Werkstoffverbunden 13
II 1.6 Fazit zu hybriden Polymer/Keramik - Werkstoffverbunden 14
II 2 Grundlagen zu Keramik/Matrix-Verbundwerkstoffen 15
II 2.1 Grundlagen zur Verstärkung keramischer Werkstoffe 15
II 2.1.1 Einteilung keramischer Werkstoffen 15
II 2.1.2 Versagensverhalten unverstärkter Monolithkeramik 15
II 2.1.3 Verstärkung keramischer Matrices 19
II 2.1.4 Verstärkungskomponenten und deren Wirkungsweise 20
II 2.2 Klassifizierung faserverstärkter Keramik/Matrix Verbundwerkstoffe 25
II 2.2.1 Weak Interface Composite – CMCs (WIC-CMC) 25
II 2.2.2 Weak Matrix Composite – CMCs (WMC-CMC) 25
II 2.3 Rissfortschrittsverhalten in faserverstärkten CMCs 26
II 2.3.1 Rissablenkung an der F/M-Grenzfläche 27
II 2.3.2 Rissausbreitung und sukzessives Versagen der Faser/Matrix-Domänen 28
II 2.3.3 Rissabschirmung und -ablenkung in porösen Matrices 28
II 2.4 Versagensverhalten faserverstärkter CMCs 29
II 2.4.1 Lastübertragungsverhalten an Faser/Matrix-Grenzflächen 29
II 2.4.2 Mikromechanisches Versagensverhalten 30
II 2.4.3 Makromechanisches Versagensverhalten 31
II 2.5 Fazit zu Keramik/Matrix-Verbundwerkstoffen 34
II 3 Kohlenstofffaserverstärkter Kohlenstoff 35
II 3.1 Kohlenstofffaserbasierte Verstärkungskomponenten 35
II 3.1.1 Kohlenstofffasern 35
II 3.1.2 Textile Flächengebilde 39
II 3.2 Kohlenstoffmatrix-bildende Precursoren und Verfahren 40
II 3.2.1 Allgemeine Verfahrensweisen 40
II 3.2.2 Grundlagen zu Phenolharzen 41
II 3.2.3 Polymerpyrolyse 46
II 3.2.4 Intrinsische Entwicklung der Porosität 49
II 3.3 Herstellung von PF-Novolak-basierten C/C-Verbunden 50
II 3.3.1 Herstellung der CFK- Produktzwischenstufe 50
II 3.3.2 Herstellung der C/C-Produktendstufe 51
II 4 Fazit zu kohlenstofffaserverstärktem Kohlenstoff 53
II 5 Thermoplastische Kunststoffe 54
II 5.1 Synthese 54
II 5.2 Klassifizierung von Polymeren 54
II 5.3 Thermoplastisches Ethylen-Vinylacetat (EVA) 55
II 5.4 Verarbeitung mittels Thermoplast-Spritzgießen 56
II 5.5 Mechanisches Verhalten 57
II 5.6 Fazit zu thermoplastischen Kunststoffen 58
II 6 Folgerungen und Zielsetzung 59
III EXPERIMENTELLER TEIL 61
III 1 Methodische Vorgehensweise 61
III 2 Versuchsbeschreibung und –durchführung 63
III 2.1 Charakterisierende Verfahren 63
III 2.1.1 Prozessbegleitende Untersuchungen 63
III 2.1.2 Dynamische Differenz-Kalorimetrie und Thermogravimetrie 64
III 2.1.3 ATR Spektroskopie 65
III 2.1.4 Röntgendiffraktometrie (XRD) 66
III 2.1.5 Raman Spektroskopie 67
III 2.1.6 Gefüge- und Phasenanalyse 68
III 2.1.7 Oberflächenanalyse der C/C-Verbunde 68
III 2.1.8 3-Punkt-Biegeprüfung 69
III 2.1.9 Haftabzugversuch 70
III 2.2 Entwicklung und Untersuchung des Matrixprecursors 71
III 2.2.1 Validierung des Matrixprecursors 71
III 2.2.2 Komposition der Harz / Härter-Gemische 71
III 2.2.3 Vernetzungsverhalten der Vorkondensate 72
III 2.2.4 Kohlenstoffausbeute der Resite 73
III 2.2.5 Phasengenese des generierten Matrixkohlenstoffs 74
III 2.2.6 Mikrostrukturentwicklung der Resite und Matrixkohlenstoffe 75
III 2.3 Entwicklung und Untersuchung der CFK-Produktzwischenstufe 76
III 2.3.1 Beschreibung zur Herstellung 76
III 2.3.2 Gefüge- und Phasenanalyse 78
III 2.3.3 Untersuchungen zum mechanischen Verhalten 78
III 2.4 Entwicklung und Untersuchung der C/C-Produktendstufe 79
III 2.4.1 Beschreibung zur Herstellung 79
III 2.4.2 Gefüge- und Phasenanalyse 80
III 2.4.3 Untersuchungen zum mechanischen Verhalten 80
III 2.5 Entwicklung und Untersuchung hybrider EVA/(C/C)-Werkstoffverbunde 81
III 2.5.1 Herstellung der C/C-Verbundwerkstoffkomponenten 81
III 2.5.2 Untersuchung der Oberflächenmorphologien der porösen C/C-Verbunde 81
III 2.5.3 Herstellung der hybriden EVA/(C/C)-Werkstoffverbunde 82
III 2.5.4 Gefüge und Phasenanalyse am hybriden Interface 84
III 2.5.5 Untersuchungen zum mechanischen Verhalten 84
III 3 Ergebnisse 85
III 3.1 Untersuchung des Matrixprecursors 85
III 3.1.1 Validierung des Matrixprecursors 85
III 3.1.2 Vernetzungsverhalten der Vorkondensate 85
III 3.1.3 Kohlenstoffausbeute der Resite 91
III 3.1.4 Phasengenese des generierten Matrixkohlenstoffs 92
III 3.1.5 Porositätsentwicklung der Resite und Matrixkohlenstoffe 94
III 3.2 Mikrostrukturentwicklung der Verbundwerkstoffe 98
III 3.2.1 Gefüge- und Phasenanalyse der CFK-Verbunde 98
III 3.2.2 Gefüge- und Phasenanalyse der C/C-Verbunde 103
III 3.3 Untersuchung der Faser/Matrix-Adhäsion 107
III 3.3.1 Einflüsse auf die Faser/Matrix-Adhäsion der CFK-Verbunde 107
III 3.3.2 Einflüsse auf die Faser/Matrix-Adhäsion der C/C-Verbunde 109
III 3.4 Mechanisches Verhalten der Verbundwerkstoffe 110
III 3.4.1 3-Punkt-Biegefestigkeiten der Verbunde bei einem Härtedruck von 15 bar 110
III 3.4.2 3-Punkt-Biegefestigkeiten der Verbunde bei einem Härtedruck von 60 bar 111
III 3.5 Untersuchung der hybriden EVA/(C/C)-Werkstoffverbunde 113
III 3.5.1 Entwicklung der Oberflächenmorphologie ausgewählter C/C-Verbunde 113
III 3.5.2 Mikrostrukturelles Adhäsionsverhalten am hybriden Interface 115
III 3.5.3 Mechanisches Adhäsionsverhalten am hybriden Interface 117
III 4 Diskussion der Ergebnisse 119
III 4.1 Vernetzungsverhalten der Resite 119
III 4.1.1 Netzwerkgenese der Vorkondensate und Degradation des Härters 119
III 4.1.2 Einfluss des Härtermassenanteils auf das Vernetzungsverhalten der Resite 121
III 4.1.3 Zur Phasengenese der generierten Matrixkohlenstoffe 122
III 4.1.4 Fazit zum Vernetzungsverhalten der Resite 122
III 4.2 Ausbildung der Porenmorphologie 124
III 4.2.1 Porenmorphologie der Resite 124
III 4.2.2 Porenmorphologie der Matrixkohlenstoffe 126
III 4.2.3 Fazit zur Ausbildung der Porenmorphologie 127
III 4.3 Mikrostrukturentwicklung der Verbundwerkstoffe 128
III 4.3.1 Mikrostrukturentwicklung der CFK-Produktzwischenstufe 128
III 4.3.2 Mikrostrukturentwicklung der C/C-Produktendstufe 128
III 4.3.3 Porositätsentwicklung der CFK- und C/C-Verbunde 129
III 4.3.4 Fazit zur Mikrostrukturentwicklung der Verbundwerkstoffe 130
III 4.4 Mechanisches Verhalten der Verbundwerkstoffe 131
III 4.4.1 Einfluss der Härtermassenanteils 131
III 4.4.2 Einfluss des Härtedrucks 131
III 4.4.3 Einfluss des Temperns 131
III 4.4.4 Einfluss des Pyrolyseschrumpfes 131
III 4.4.5 Fazit zum mechanischen Verhalten der Verbundwerkstoffe 132
III 4.5 Hybride EVA/(C/C)-Werkstoffverbunde 133
III 4.5.1 Entwicklung der Oberflächenmorphologie ausgewählter C/C-Verbunde 133
III 4.5.2 Mikrostrukturelles Adhäsionsverhalten am hybriden Interface 133
III 4.5.3 Mechanisches Adhäsionsverhalten am hybriden Interface 134
III 4.5.4 Fazit zur Realisierung der hybriden Werkstoffverbunde 134
IV SCHLUSSFOLGERUNGEN 135
V ZUSAMMENFASSUNG UND AUSBLICK 139
VI LITERATURQUELLEN 140
ANLAGEN / Fibre-reinforced ceramic matrix composite materials are characterized by excellent thermal, mechanical and chemical properties. Their high tolerance regarding damaging is a result of the intrinsic fibre structure and porosity. Due to this fact, they offer outstanding dampening characteristics, as is the case for polymeric materials. The production of complex structures is very time consuming and expensive. The integration of simple geometric ceramic composite materials in complex polymeric structures is regarded as a new approach for the production of these materials. These easy-to-produce hybrid ceramic/polymer compound materials combine the advantages of ceramics and polymers in one material system. However, one main disadvantage of these materials is the mutual adhesion of the two components. This article deals with the challenge of the manipulation of the mechanical properties of the C/C composites depending on the intrinsic porosity. This is realized by altering the physical and chemical wetting/coating conditions of the matrix precursor. In addition, the inherent porosity is supposed to increase the effective outer surface and specifically improve the adhesion. For this purpose, a novel carbon precursor with an adjustable open porosity is developed and investigated further. During this different versions of the CFRP and various C/C materials of different production steps are produced and examined. The variation of the precursors is supposed to take place in the polymeric state. The different C/C composites are subsequently thermally bonded with selected polymers and defined consolidation parameters. The mutual joining and connection behaviour is investigated further.:ABKÜRZUNGEN UND FORMELZEICHEN I
ABBILDUNGSVERZEICHNIS VI
TABELLENVERZEICHNIS XI
I EINLEITUNG UND MOTIVATION 1
II STAND DER TECHNIK 3
II 1 Hybride Polymer/Keramik - Werkstoffverbunde 3
II 1.1 Grundlagen zur Adhäsion 3
II 1.1.1 Adhäsionsmodelle 3
II 1.1.2 Keramik/Polymer-Grenzflächentypen 7
II 1.2 Konstruktionsprinzipien 8
II 1.2.1 Differentialbauweise 8
II 1.2.2 Integralbauweise 8
II 1.2.3 Mischbauweise 8
II 1.2.4 Hybridbauweise (hybride Werkstoffverbunde) 8
II 1.3 Fertigungsverfahren 9
II 1.3.1 Klassifizierung 10
II 1.3.2 In-situ-Fügetechnik (In-Mould Assembly) 11
II 1.3.3 Ex-situ-Fügetechnik (Post-Mould Assembly) 11
II 1.4 Aspekte zur Interfaceoptimierung 12
II 1.5 Versagensverhalten von einfachen hybriden Werkstoffverbunden 13
II 1.6 Fazit zu hybriden Polymer/Keramik - Werkstoffverbunden 14
II 2 Grundlagen zu Keramik/Matrix-Verbundwerkstoffen 15
II 2.1 Grundlagen zur Verstärkung keramischer Werkstoffe 15
II 2.1.1 Einteilung keramischer Werkstoffen 15
II 2.1.2 Versagensverhalten unverstärkter Monolithkeramik 15
II 2.1.3 Verstärkung keramischer Matrices 19
II 2.1.4 Verstärkungskomponenten und deren Wirkungsweise 20
II 2.2 Klassifizierung faserverstärkter Keramik/Matrix Verbundwerkstoffe 25
II 2.2.1 Weak Interface Composite – CMCs (WIC-CMC) 25
II 2.2.2 Weak Matrix Composite – CMCs (WMC-CMC) 25
II 2.3 Rissfortschrittsverhalten in faserverstärkten CMCs 26
II 2.3.1 Rissablenkung an der F/M-Grenzfläche 27
II 2.3.2 Rissausbreitung und sukzessives Versagen der Faser/Matrix-Domänen 28
II 2.3.3 Rissabschirmung und -ablenkung in porösen Matrices 28
II 2.4 Versagensverhalten faserverstärkter CMCs 29
II 2.4.1 Lastübertragungsverhalten an Faser/Matrix-Grenzflächen 29
II 2.4.2 Mikromechanisches Versagensverhalten 30
II 2.4.3 Makromechanisches Versagensverhalten 31
II 2.5 Fazit zu Keramik/Matrix-Verbundwerkstoffen 34
II 3 Kohlenstofffaserverstärkter Kohlenstoff 35
II 3.1 Kohlenstofffaserbasierte Verstärkungskomponenten 35
II 3.1.1 Kohlenstofffasern 35
II 3.1.2 Textile Flächengebilde 39
II 3.2 Kohlenstoffmatrix-bildende Precursoren und Verfahren 40
II 3.2.1 Allgemeine Verfahrensweisen 40
II 3.2.2 Grundlagen zu Phenolharzen 41
II 3.2.3 Polymerpyrolyse 46
II 3.2.4 Intrinsische Entwicklung der Porosität 49
II 3.3 Herstellung von PF-Novolak-basierten C/C-Verbunden 50
II 3.3.1 Herstellung der CFK- Produktzwischenstufe 50
II 3.3.2 Herstellung der C/C-Produktendstufe 51
II 4 Fazit zu kohlenstofffaserverstärktem Kohlenstoff 53
II 5 Thermoplastische Kunststoffe 54
II 5.1 Synthese 54
II 5.2 Klassifizierung von Polymeren 54
II 5.3 Thermoplastisches Ethylen-Vinylacetat (EVA) 55
II 5.4 Verarbeitung mittels Thermoplast-Spritzgießen 56
II 5.5 Mechanisches Verhalten 57
II 5.6 Fazit zu thermoplastischen Kunststoffen 58
II 6 Folgerungen und Zielsetzung 59
III EXPERIMENTELLER TEIL 61
III 1 Methodische Vorgehensweise 61
III 2 Versuchsbeschreibung und –durchführung 63
III 2.1 Charakterisierende Verfahren 63
III 2.1.1 Prozessbegleitende Untersuchungen 63
III 2.1.2 Dynamische Differenz-Kalorimetrie und Thermogravimetrie 64
III 2.1.3 ATR Spektroskopie 65
III 2.1.4 Röntgendiffraktometrie (XRD) 66
III 2.1.5 Raman Spektroskopie 67
III 2.1.6 Gefüge- und Phasenanalyse 68
III 2.1.7 Oberflächenanalyse der C/C-Verbunde 68
III 2.1.8 3-Punkt-Biegeprüfung 69
III 2.1.9 Haftabzugversuch 70
III 2.2 Entwicklung und Untersuchung des Matrixprecursors 71
III 2.2.1 Validierung des Matrixprecursors 71
III 2.2.2 Komposition der Harz / Härter-Gemische 71
III 2.2.3 Vernetzungsverhalten der Vorkondensate 72
III 2.2.4 Kohlenstoffausbeute der Resite 73
III 2.2.5 Phasengenese des generierten Matrixkohlenstoffs 74
III 2.2.6 Mikrostrukturentwicklung der Resite und Matrixkohlenstoffe 75
III 2.3 Entwicklung und Untersuchung der CFK-Produktzwischenstufe 76
III 2.3.1 Beschreibung zur Herstellung 76
III 2.3.2 Gefüge- und Phasenanalyse 78
III 2.3.3 Untersuchungen zum mechanischen Verhalten 78
III 2.4 Entwicklung und Untersuchung der C/C-Produktendstufe 79
III 2.4.1 Beschreibung zur Herstellung 79
III 2.4.2 Gefüge- und Phasenanalyse 80
III 2.4.3 Untersuchungen zum mechanischen Verhalten 80
III 2.5 Entwicklung und Untersuchung hybrider EVA/(C/C)-Werkstoffverbunde 81
III 2.5.1 Herstellung der C/C-Verbundwerkstoffkomponenten 81
III 2.5.2 Untersuchung der Oberflächenmorphologien der porösen C/C-Verbunde 81
III 2.5.3 Herstellung der hybriden EVA/(C/C)-Werkstoffverbunde 82
III 2.5.4 Gefüge und Phasenanalyse am hybriden Interface 84
III 2.5.5 Untersuchungen zum mechanischen Verhalten 84
III 3 Ergebnisse 85
III 3.1 Untersuchung des Matrixprecursors 85
III 3.1.1 Validierung des Matrixprecursors 85
III 3.1.2 Vernetzungsverhalten der Vorkondensate 85
III 3.1.3 Kohlenstoffausbeute der Resite 91
III 3.1.4 Phasengenese des generierten Matrixkohlenstoffs 92
III 3.1.5 Porositätsentwicklung der Resite und Matrixkohlenstoffe 94
III 3.2 Mikrostrukturentwicklung der Verbundwerkstoffe 98
III 3.2.1 Gefüge- und Phasenanalyse der CFK-Verbunde 98
III 3.2.2 Gefüge- und Phasenanalyse der C/C-Verbunde 103
III 3.3 Untersuchung der Faser/Matrix-Adhäsion 107
III 3.3.1 Einflüsse auf die Faser/Matrix-Adhäsion der CFK-Verbunde 107
III 3.3.2 Einflüsse auf die Faser/Matrix-Adhäsion der C/C-Verbunde 109
III 3.4 Mechanisches Verhalten der Verbundwerkstoffe 110
III 3.4.1 3-Punkt-Biegefestigkeiten der Verbunde bei einem Härtedruck von 15 bar 110
III 3.4.2 3-Punkt-Biegefestigkeiten der Verbunde bei einem Härtedruck von 60 bar 111
III 3.5 Untersuchung der hybriden EVA/(C/C)-Werkstoffverbunde 113
III 3.5.1 Entwicklung der Oberflächenmorphologie ausgewählter C/C-Verbunde 113
III 3.5.2 Mikrostrukturelles Adhäsionsverhalten am hybriden Interface 115
III 3.5.3 Mechanisches Adhäsionsverhalten am hybriden Interface 117
III 4 Diskussion der Ergebnisse 119
III 4.1 Vernetzungsverhalten der Resite 119
III 4.1.1 Netzwerkgenese der Vorkondensate und Degradation des Härters 119
III 4.1.2 Einfluss des Härtermassenanteils auf das Vernetzungsverhalten der Resite 121
III 4.1.3 Zur Phasengenese der generierten Matrixkohlenstoffe 122
III 4.1.4 Fazit zum Vernetzungsverhalten der Resite 122
III 4.2 Ausbildung der Porenmorphologie 124
III 4.2.1 Porenmorphologie der Resite 124
III 4.2.2 Porenmorphologie der Matrixkohlenstoffe 126
III 4.2.3 Fazit zur Ausbildung der Porenmorphologie 127
III 4.3 Mikrostrukturentwicklung der Verbundwerkstoffe 128
III 4.3.1 Mikrostrukturentwicklung der CFK-Produktzwischenstufe 128
III 4.3.2 Mikrostrukturentwicklung der C/C-Produktendstufe 128
III 4.3.3 Porositätsentwicklung der CFK- und C/C-Verbunde 129
III 4.3.4 Fazit zur Mikrostrukturentwicklung der Verbundwerkstoffe 130
III 4.4 Mechanisches Verhalten der Verbundwerkstoffe 131
III 4.4.1 Einfluss der Härtermassenanteils 131
III 4.4.2 Einfluss des Härtedrucks 131
III 4.4.3 Einfluss des Temperns 131
III 4.4.4 Einfluss des Pyrolyseschrumpfes 131
III 4.4.5 Fazit zum mechanischen Verhalten der Verbundwerkstoffe 132
III 4.5 Hybride EVA/(C/C)-Werkstoffverbunde 133
III 4.5.1 Entwicklung der Oberflächenmorphologie ausgewählter C/C-Verbunde 133
III 4.5.2 Mikrostrukturelles Adhäsionsverhalten am hybriden Interface 133
III 4.5.3 Mechanisches Adhäsionsverhalten am hybriden Interface 134
III 4.5.4 Fazit zur Realisierung der hybriden Werkstoffverbunde 134
IV SCHLUSSFOLGERUNGEN 135
V ZUSAMMENFASSUNG UND AUSBLICK 139
VI LITERATURQUELLEN 140
ANLAGEN
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