AN APPLICATION OF THE RELATIVE WARPS ANALYSIS TO PROBLEMS IN HUMAN PALEONTOLOGY - WITH NOTES ON RAW DATA QUALITY

This study investigates the use of geometric morphometrics as well as methodological aspects specifically related to its application in paleoanthropology. Based on lateral photographs taken from a fossil sample of 58 specimens, a relative warps analysis was computed in order to assess the variation of cranial shape among various hominin groups. The fossil sample represents Middle and Late Pleistocene populations commonly assigned to H. erectus, H. neanderthalensis, archaic H. sapiens as well as anatomically modern H. sapiens. The preliminary results indicate that several fossil skulls considered as belonging to archaic H. sapiens have a distinct shape compared to modern humans. The results suggest that these hominins are not as closely related to modern humans as previously thought. Instead, their morphometric affinities suggest that they are as distinct from modern humans as are the Neandertals. Methodological aspects, such as raw data accuracy and the use of type 2 and 3 landmarks that are directly related to this type of quantitative analysis and that potentially affect their results, are discussed

Manufacture and thermomechanical characterization of wet filament wound C/C‐SiC composites

The paper presents manufacture of C/C‐SiC composite materials by wet filament winding of C fibers with a water‐based phenolic resin with subsequent curing via autoclave as well as pyrolysis and liquid silicon infiltration (LSI). Almost dense C/C‐SiC composite materials with different winding angles ranging from ±15° to ±75° could be obtained with porosities lower than 3% and densities in the range of 2 g/cm3. Thermomechanical characterization via tensile testing at room temperature and at 1300°C revealed higher tensile strength at elevated temperature than at room temperature. Thus, C/C‐SiC material obtained by wet filament winding and LSI‐processing has excellent high‐temperature strength for high‐temperature applications. Crack patterns during pyrolysis, microstructure after siliconization, and tensile strength strongly depend on the fiber/matrix interface strength and winding angle. Moreover, calculation tools for composites, such as classical laminate and inverse laminate theory, can be applied for structural evaluation and prediction of mechanical performance of C/C‐SiC structures.German Ministry of Defenc

Development of Advanced CMC Materials for Dual-bell Rocket Nozzles

The main goal of sub-project D7 is the development of advanced ceramic matrix composites (CMCs) for a dual-bell application. These CMCs are characterized by continuous carbon filaments which are embedded in a silicon carbide matrix (SiC). The process route used for the manufacture of the so called C/C-SiC material is the Liquid Silicon Infiltration (LSI), also called Melt Infiltration (MI). The CMC material is favorable to replace conventional high-density engine alloys due to their outstanding high temperature properties. In a liquid-fueled rocket engine the material must withstand extreme conditions, e.g. high gas temperatures and high mechanical loads. In a first step the specifications and requirements of a CMC nozzle material have been defined and also the thermal and mechanical loads of a typical launcher system engine (e.g.Vulcain 2-Ariane 5) were described prior to the further development of C/C-SiC. A central part of the development is the integration of the filament winding process into the LSI route and the characterization of specimens in terms of thermo-mechanical properties by variation of fibre orientation. The analysis of permeability to hot gases and a study on oxidation behavior is planned in the upcoming year. The manufacturing process and the concept of characterizing the CMC material are presented and discussed

Development, Manufacture and Characterization of C/C-SiC Components based on Filament Winding

In this contribution development, manufacture and characterization of C/C-SiC tubes based on different winding angles is described. Therefore, CFRP tubes were made by wet-winding of C-filaments using thermoset resins with high char yield and, in a second step were converted to C/C tubes via pyrolysis. Then, the porous tubes were infiltrated by liquid silicon providing C/C-SiC tubes which were characterized by their microstructure and mechanical properties. Mechanical testing was performed under tensile loading in axial and circumferential direction (burst test). In addition, a correlation of mechanical properties to the winding angle will be presented

Oxide CMC Components Manufactured via PIP Processing Based on Polysiloxanes

For a long time polysiloxanes have been used to build up an oxidation and corrosion resistant matrix (SiOC) in damage tolerant ceramic matrix composites (CMC) using polymer infiltration and pyrolysis (PIP) processing. These oxide CMCs are reliable candidates for aeronautics applications, such as turbine inlets for future jet engines. Another interesting feature of these materials is the transparency for radar waves in front structures of air vehicles (e.g. radomes). State of the art is the infiltration of fibre preforms with polysiloxanes and pressure less curing. At DLR, pressure-assisted infiltration and curing via resin transfer moulding (RTM) as well as warm-press technique was developed further in order to use systems curing via polycondensation. In a second process step, the pyrolysis, the “dense” polymer matrix is transferred into a porous ceramic matrix due to shrinkage. Further densification of the matrix to an open porosity < 10 vol-% can be efficiently performed by RTM route or near-vacuum infiltration in a resin bath. In this contribution the variety of manufacturing methods of oxide CMC components based on OXIPOL (oxide CMC based on polymers) is described. Therefore, oxide fibres (Nitivy or Nextel) and commercial polysiloxanes were chosen. In order to obtain high damage tolerance, based on weak fibre/matrix bonding, a fugitive coating was used. Therefore, a phenolic resin solution was applied on fabrics with a Foulard machine prior to composite manufacture. After the last pyrolysis step the carbon (ex-phenolic resin layer) on the fabrics was removed via oxidation at 700 °C in air for 20 h. Depending on the design and application needs of the component, several industrial processes, such as RTM, pressing of fibre performs as well as wet filament winding of rovings, were applied. Moreover, different kind of fibre types, fibre orientation, liquid or solid polymers and coating thicknesses were used. In addition, some first application tests are presented

CMC with a Graded Lay-up Manufactured via LSI-Process

Ceramic matrix composites (CMC) armed by long fibres are promising candidates for structural applications due to their damage tolerance even at very high temperatures. Since CMC based on SiC fibres are still very costly most cost-efficient CMC are based on carbon fibres. Among the processing routes for CMC most common for industrial applications is the liquid siliconization infiltration process (LSI) developed by DLR. In this three-step-process (CFRP manufacture, pyrolysis, siliconization) the fibre matrix bonding is determining the final microstructure, SiC content, mechanical properties and damage tolerance as well as oxidation and abrasion resistance. In general, higher SiC content enhances oxidation and abrasion resistance, however, lowers mechanical properties and damage tolerance significantly. For components applied in severe environments it is thus, desirable to have a SiC rich outer layer bearing a core being capable to carry high mechanical loads. Another possibility to obtain CMC with a graded lay-up concerning mechanical properties can be achieved by filament winding using a combination of selected winding angles, especially on tubes. In this paper several methods to manufacture CMC with a graded lay-up as well as properties and potential applications are presented

Oxidation resistant fibre coatings on the basis of lanthanum phosphate for CMCs

This internship report of second year study in engineering school deals with Ceramic Matrix Composite manufactured by polymer infiltration and pyrolysis process (PIP). In order to improve the behavior of CMCs in oxidizing atmosphere a new coating based lanthanum phosphate is investigated and described in detail. Firstly parameters of the coating process are analyzed like the influence of the sizing, the duration of the firing and the temperature of the firing. In the second part more temperatures are investigated as some parameters are fixed thanks to the first study. In the third part the influence of a second coating is tested. In the fourth part the coated fibers are put in conditions of a plate production. All these investigations were made thanks to scanning electron microscopy (SEM), mass measurements and calculation of the coating thickness. Due to conclusions, a new protocol for lanthanum phosphate coating was made and will be used in order to produce CMCs