Matthias Scheiffele’s scientific contributions

For the development of advanced materials and structures with improved corrosion and abrasion resistance, a better understanding of the complex multiphase flow/structure interaction is necessary. Besides appropriate material development of ceramic matrix composites (CMC) materials concerning the harsh application conditions, a precise material characterization with respect to compatibility to relevant fuels on aging aspects and, especially, to performance on application-related combustion tests for ramjet and scramjet propulsion are of special interest. In order to test and evaluate different silicon carbide (SiC) contents on the surface of different C/C-SiC materials, two different materials of quality XS (standard) and an enhanced C/C-SiC material with SiC enriched surface and graded structural lay-up were developed, manufactured, characterized, and tested at DLR's test facility M11 at scramjet conditions. This facility is able to produce the boundary conditions typical of a scramjet/ramjet propelled flight at Mach 5.5 to Mach 6.0 flight at an altitude of 30 km in the connected pipe ground test configuration. It is capable of stagnation temperatures up to 1500 K, 25 bar stagnation pressure, and 5 kg/s hot gas mass flow rate. The material samples were exposed to the vitiated air in a scramjet model combustion chamber with lateral optical access and a wedge-shaped shock generator similar to flame holder geometries This publication gives both a detailed overview of the material and component development and an overview of the hot gas testing facility and its capabilities for testing materials and components. In addition, some typical results of tested C/C-SiC materials are presented.

Möglichkeiten und Grenzen von Faserpreformen zur Herstellung von Radomen wurden aufgezeigt Silica-Aerogele weisen exzellente Wärmeisolationseigenschaften bei gleichzeitiger hoher Radartransparenz auf SiC-reiche Kegelspitzen für Ram-jet-Lufteinläufe lassen sich auf der Basis von MICaSiC herstellen UHTCMC-Werkstoffe können durch Schmelzinfiltration eutektischer Metalllegierungen in C/C analog LSI-Prozess dargestellt werden Erste Versuchsergebnisse von Ablatormaterialien im Plasmawindkanal erweisen sich als vielversprechend Weitere Versuche in Vorbereitung Zukünftige neue Entwicklungsfelder für CMC-Werkstoffe in der Luft- und Raumfahrt: Radome mit signifikant verbesserter thermischer Isolation Bauteile für Raketenantriebe: Schubkammern, Einspritzköpfe, Düsenerweiterungen, Satellitentriebwerke etc.

For the development of advanced materials and structures with improved abrasion resistance a better understanding of the complex multiphase flow / structure interaction is necessary. Fibre reinforced ceramic matrix composites (CMC) combine the general properties of ceramic materials (abrasion and high temperature resistance as well as high temperature strength and hardness) with favourable properties of fibre reinforced composites (high damage tolerance in case of overloading). Due to their extreme thermal shock resistance and stability under high temperature load beyond 2000 °C they are ideal candidates for hot gas applications in rocket motor propulsion for aerospace. Liquid silicon infiltration (LSI) developed by DLR provides ideal requirements in order to manufacture cost-effective CMC components based on C/C-SiC, which are not feasible by other CMC manufacturing techniques (e.g. CVI) owing to complex component geometry, especially wall thickness. In order to be able to test erosion and high temperature stability of materials and components with respect to combustor and nozzle relevant conditions, a test facility was developed and erected at DLR M11 test complex: Abrasive Hot Gas Facility (HotGaF). This facility is able to produce particle and droplet laden hot gas flows with temperatures and area specific impulse densities of the condensed phase, similar to distinct smaller solid rocket motors. The hot abrasive jet wash is produced by the combustion of Al particle containing solid fuel tubes with a preheated and oxygen enriched air flow in a primary and a subsequent secondary combustion chamber. The production of the oxygen enriched hot vitiated air flow is conducted by making use of hydrogen/oxygen burners. Due to the design of this facility similar to a connected pipe ramjet combustor test facility, the time period, in which the abrasive jet wash attacks the samples, can be varied by the quick shut-down of the “air” heater at pre-selected times and the opening of a bypass valve. Thus “load” pulses of pre-selected time can be generated for the determination of abrasion histories. Here a solid fuel composition of HTPB/IPDI with 40 wt.-% Al particles was used. No chlorine containing additives were used in these test runs, because the primary goal of the conducted investigations was to show the direct influence of the condensed phase (Al2O3, Al, etc.) in a jet wash on the abrasion of the ceramic jet vane samples based on C/C-SiC. In order to measure pressure and temperature at various positions in the C/C-SiC nozzle, which is a prerequisite for the time-resolved erosion history of jet-vane samples, nine pressure and temperature ports were implemented. A 6 degree-of-freedom (6 DOF) thrust balance can be connected to the test facility for the determination of the changes of the forces and moments acting on the test specimen. Figure 1 shows as example two images from a typical test run at the abrasive hot gas facility. A C/C-SiC test specimen is positioned in the expansion part of the C/C-SiC nozzle. Tests under these conditions shall give information of contour erosion, which is relevant for material development of jet vanes. The left image shows the glowing of the upstream part of the sample and the nozzle wall during the test run. The right image presents a view into the nozzle after the test run, which shows the erosion of the test specimen. The proposed publication will give both a detailed overview of the material and component development based on C/C-SiC and an overview of HotGaF as well as its capabilities for testing of materials and components. In addition, some typical results of tested C/C-SiC materials (inlay in secondary combustor, nozzle as well as jet-vane samples) are presented.

Einleitung und Motivation Keramische Querschubdüsen für Heißgasuntersuchungen Aerogele für Wärmedämmung Radome aus WHIPOX-Werkstoffen mit Aerogol-Isolation Werkstoffentwicklung für Ablatormaterialien UHTCMC-Werkstoffe Zusammenfassung und Ausblick

The key step in the manufacture of C-fibre reinforced SiC composites (C/C-SiC) via liquid silicon infiltration of porous C/C structures is the manufacture of CFRP composites. In this step fibre matrix bonding (FMB) is determining the microstructure in C/C state: strong FMB leads to a block structure of dense C/C segments which are hardly accessible to complete reaction with liquid silicon, whereas weak FMB leads to a porous C/C structure which is easily accessible to reaction with liquid silicon. Consequently, different C/C-SiC materials with low and high SiC content, high and low fracture toughness as well as bending strength are obtained. Within the framework of fundamental research several novel C-precursors based on phenolic resins were selected, screened and thoroughly characterised with respect to their suitability of application within the LSI-process in order to obtain C/C-SiC with respect to microstructure and SiC content. Characterization includes thermal analysis and especially rheological investigations of precursors prior to composite manufacture. Furthermore, the effect of interaction of precursors with various C-fibres is investigated. Since processing routes like resin transfer moulding (RTM) or autoclave technique strongly influence matrix evolution and final SiC formation phenolic resins are investigated accordingly. Microstructure and properties are monitored along the complete processing chain from polymer infiltration via pyrolysis and resulting C/C phase to the final siliconised state. Microstructural composition is characterised by SEM and phase analysis. With these results it is expected that final composition as e.g. content of SiC can be defined accurately by the choice of precursors and adjustment of processing routes and parameters.