Properties of large scale ultra-high temperature ceramic matrix composites made by filament winding and spark plasma sintering

In this paper, for the first time, we report the manufacturing and characterization of large UHTCMCs discs, made of a ZrB2/SiC matrix reinforced with PyC-coated PAN-based carbon fibres. This work was the result of a long term collaboration between different institutions and shows how it is possible to scale-up the production process of UHTCMCs for the fabrication of large components. 150 mm large discs were produced by filament winding and consolidated by spark plasma sintering and specimens were machined to test a large set of material properties at room and elevated temperature (up to 1800 °C). The extensive characterization revealed a new material with mechanical behaviour similar to CMCs, but with intrinsic higher thermal stability. Furthermore, the scale-up demonstrated in this work increases the appeal of UHTCMCs in sectors such as aerospace, where severe operating conditions limit the application of conventional materials

Processing of UHTCMCs

There is an increasing demand for advanced materials with temperature capability in highly corrosive environments for aerospace. Rocket nozzles of solid/hybrid rocket motors must survive harsh thermochemical and mechanical environments produced by high performance solid propellants (2700-3500°C). Thermal protection systems (TPS) for space vehicles flying at Mach 7 must withstand projected service temperatures up to 2500°C associated to convective heat fluxes up to 15 MWm-2 and intense mechanical vibrations at launch and re-entry into Earth’s atmosphere. The combination of extremely hot temperatures, chemically aggressive environments and rapid heating/cooling is beyond the capabilities of current materials. As indicated by the previous talk, the main purpose of C3HARME is to design, develop, manufacture, test and validate a new class of out-performing, reliable, cost-effective and scalable Ultra High Temperature Ceramic Matrix Composites (UHTCMCs) based on C fibre preforms enriched with ultra-high temperature ceramics (UHTCs) and capable of in-situ repairing damage induced during operation in severe aerospace environments. Two main applications are envisaged: near-ZERO erosion rocket nozzles that must maintain dimensional stability during firing in combustion chambers, and near-ZERO ablation thermal protection systems enabling hypersonic space vehicles to maintain flight performance. This talk aims at providing an indication of progress to date within Work Package 2, which is focused on the processing of Cf-ZrB2 UHTCMCs. Four primary routes are being investigated, these include: green forming of fibre reinforced UHT ceramics followed by spark plasma sintering; radio-frequency enhanced chemical vapour infiltration of UHTCMCs; reactive melt infiltration of UHTCMCs and polymer infiltration and pyrolysis of UHTCMCs. All four approaches will be outlined and conclusions drawn, plus there will be a brief mention of ongoing work into atomistic modelling of processes at materials interfaces and nanoparticle dispersion with a view to imparting self-healing properties. Acknowledgements: This work has received funding from the European Union’s Horizon 2020 “Research and innovation programme” under grant agreement N°685594 (C3HARME

Metabolic shift induced by synthetic co-cultivation promotes high yield of chain elongated acids from syngas

Bio-catalytic processes for sustainable production of chemicals and fuels receive increased attention within the concept of circular economy. Strategies to improve these production processes include genetic engineering of bio-catalysts or process technological optimization. Alternatively, synthetic microbial co-cultures can be used to enhance production of chemicals of interest. It remains often unclear however how microbe to microbe interactions affect the overall production process and how this can be further exploited for application. In the present study we explored the microbial interaction in a synthetic co-culture of Clostridium autoethanogenum and Clostridium kluyveri, producing chain elongated products from carbon monoxide. Monocultures of C. autoethanogenum converted CO to acetate and traces of ethanol, while during co-cultivation with C. kluyveri, it shifted its metabolism significantly towards solventogenesis. In C. autoethanogenum, expression of the genes involved in the central carbon- and energy-metabolism remained unchanged during co-cultivation compared to monoculture condition. Therefore the shift in the metabolic flux of C. autoethanogenum appears to be regulated by thermodynamics, and results from the continuous removal of ethanol by C. kluyveri. This trait could be further exploited, driving the metabolism of C. autoethanogenum to solely ethanol formation during co-cultivation, resulting in a high yield of chain elongated products from CO-derived electrons. This research highlights the important role of thermodynamic interactions in (synthetic) mixed microbial communities and shows that this can be exploited to promote desired conversions.The research leading to these results has received funding from the Netherlands Ministry of Education, Culture and Science and from the Netherlands Science Foundation (NWO) under the Gravitation Grant nr. 024.002.002 and Programme ‘Closed Cycles’ with Project nr. ALWGK.2016.029.info:eu-repo/semantics/publishedVersio

The 'Octoberfest Bubble' and other statistical phenomena of the official Bavarian web server

This paper presents in detail statistical data of the official Bavarian web server (http://www.bayern.de/ target=NewWindow> http://www.bayern.de/ ). We identify and discuss a number of acces phenomena related to the first three months of its operation, which are in part due to its regional appeal. These phenomena are likely to be found as well with other sites of similar importance and - in conjunction with more data sets of this kind - can possibly help to derive rules of thumb to predict development of bandwidth requirements and contents appeal of new web sites. (orig.)SIGLEAvailable from TIB Hannover: RR 8166(95-11) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekBayerische Forschungsstiftung, Muenchen (Germany)DEGerman

Compressive strength of a 3-D C/C composite - measurements at temperature up to 1800 degree

A compression testing device for Carbon Fibre-Reinforced Carbon materials was developed following the main features of the ASTM-arrangement. All parts are made of Carbonmaterials which allows testing up to 2000 degree Celsius under vacuum or inert gases. Using this device compressive strengths of a 3-D Carbon/Carbon composite which is protected against oxidation, were determined in the range between room temperature and 1800 degree Celsius. Specimens with two different orientations of the reinforcement were tested, i.e. in direction of the fibers and 22.5 degree off-axis. The strengths increase remarkably with increasing temperature and reach their maxima at about the same level for both orientations between 1400degree Celsius and 1600 degree Celsius

Mechanical properties of Ti-6Al-4V fabricated by electron beam melting

Powder bed additive manufacturing of titanium components offers several advantages. The high freedom of design enables the fabrication of structurally optimized, lightweight parts. Complex geometries may serve additional functions. The use of additive manufacturing has the potential to revolutionize logistics by dramatically reducing lead time and enabling a high degree of customization. Manufacturing near net shape parts reduces the loss of expensive material.For the application in safety relevant parts certainty about static and fatigue strength is critical. A challenge arises from complex influences of built parameters, heat treatments and surface quality. Ti-6Al-4V specimen built by electron beam melting (EBM) were subjected to heat treatments adapted to various employment scenarios. The results of tensile and fatigue testing as well as crack propagation and fractography will be compared to titanium manufactured conventionally and by selective laser melting (SLM). The mechanical behavior will be correlated to the microstructural evolution caused by the heat treatments