Deutsches Zentrum

für Luft- und Raumfahrt e.V.German Aerospace Center

Germany

Institute of Structures and DesignPfaffenwaldring 38-4070569 Stuttgart

Dipl.-Ing.

Tel.: +49(0) 711/6862-Fax: +49(0) 711/6862-227E-mail:Internet: http://www.dlr.de

Sandrine Denis

720

sandrine.denis@dlr.de

Design and Finite Element Analysis ofCMC Components

DesignSince (are usually carried by conventional metallicparts, the main aspect of design anddimensioning is the integration of CMCcomponents in metallic structures. Inparticular, the large differences in thermalexpansion coefficients and servicetemperatures of CMC parts and metallicstructures have to be considered. Mountingsystems to surrounding metallic structureshave been developed e.g. for the C/C-SiCbrake disc and for CMC combustionchamber shingles.

Ceramic Matrix Composites CMCs)Numerical AnalysisNumerical analyses help to reduceexpensive routine testing. The FiniteElement Analysis (FEA) is used to modelCMC components and surroundingstructures.First of all a 2D or 3D model is generatedvia Unigraphics. Then the model is meshedusing the ANSYS-FEA software.In future, simulations of materials andcomponents whose structures weredetermined by computer tomography willbe intensified.ANSYS offers a variety of mesh elementssuitable to simulate CMC materials.Orthotropic materials like CMCs can berather easily simulated using e.g. the'Solid Elements' from ANSYS. The 'LaminarElements' make it possible to simulatelayers of CMC materials with different fibreorientations, like wound materials.After selecting the proper element type,material properties, loadings andboundary conditions are defined.The CMC material properties are obtainedfrom thermomechanical testing or fromalready existing databases.Thermal conditions, like in the case of thecombustion chamber shingle, can beimported from computational fluiddynamics (Fluent, ANSYS CFX). Thereforethe close collaboration and densenetworking of fluid and structrureengineers within the DLR is an importantkey factor.All boundary conditions have to be definedas realistic as possible. Additional testingcan deliver valuable informations (e.g.about acting forces, pressure and tem-perature distributions).Finally the FEA results are analysed usingdifferent failure criteria (e.g. maximumprincipal stress, Tsai Wu). Conclusiveexperiments at DLR-test facilities areperformed to validate the simulationresults.

Distribution of principal stresses in an oxid-CMC combustion chamber shingle

C/C-SiC brake disc with mounting concept for the metallic carrying structure

CMC combustion chamber with metallic carrying structure and a single curvedshingle