Ceramic Structures

Nose cap of the X38 experimental spacecraft as an example for a complex shaped C/C-SiC structure (740 mm x 640 mm x 170 mm).

Since monolithic ceramics typically offer no damage tolerance, they typically fail in a catastrophic way after overloading. Cracks initiated by flaws, e.g. pores and surface defects, cannot be stopped and therefore run through the complete part. Due to the fact that the number of flaws is increasing with the volume of the ceramic part, the failure probability of large structures is higher than that of small parts, leading again to a reduced allowable stress level and high wall thicknesses of structural parts. In contrast, fibre reinforced ceramics are characterized by a significantly higher damage tolerance and a quasi-ductile breaking behaviour. Emerging cracks can be stopped at the fibre/matrix interface and at micro pores. Therefore, the strength of CMC materials is independent from the component size, enabling the realization of mechanically and thermally extremely loaded, large sized and thin walled lightweight structures.

The institute of structures and design has achieved an internationally recognized status regarding the development and manufacture of CMC lightweight structures. In this area, the development work concentrates on computer assisted dimensioning (FEM, Ansys), on the material- and manufacture-oriented design with modern CAD tools (Unigraphics), as well as on the manufacture of full-scale prototypes for testing.
Thereby the entire process chain is available at DLR, from the inspection of incoming raw materials, up to the component qualification by non destructive and destructive evaluation at maximum temperatures of up to 1700 °C.

The main application fields for C/C-SiC materials are lightweight components in aerospace, e.g. hot structures and low thermal expansion structures. In this field, fibre reinforced ceramic materials represent a key technology and could already be introduced successfully for thermal protection systems of spacecraft, rocket propulsion systems and for telescope structures. In direct cooperation with industrial partners C/C SiC brake discs and brake pads as well as rocket motor components (jet vanes) have been developed successfully and were transferred to industrial partners for serial production.

Current development is focused on:

• Thermal protection systems from non oxide and oxide CMC materials.
• Low thermal expansion and highly stiff C/C SiC telescope structures. 
• Corrosion and abrasion resistant C/C SiC lightweight components for rocket motors.
• Hot gas liners for jet engines and stationary gas turbines. 
• Lightweight ceramic armour and high temperature heat exchangers based on biomorphic SiSiC materials. 
• Highly porous SiC structures for radiation heaters. 
• C/C SiC brake disks and friction pads as well as further spin off activities.