Designing with C/C-SiC Composites

Abstract

Designing with C/C-SiC materials, manufactured by Melt Infiltration (MI), principally follows the same rules and requirements as exist for other fibre reinforced composites. However, due to the high temperatures during their fabrication and their heterogeneous microstructure, some specific characteristics must be taken into account for a suitable design of C/C-SiC components. The matrix shrinkage during the pyrolysis step can either lead to residual stresses within the component or results in dimensional changes. Generally, these effects are determined by the fibre orientation and volume fraction of the fibre preform. Short fibre reinforcements with a random orientation show a rather isotropic shrinkage, whereas bi-directionally reinforced components only shrink transverse to the fabric layers. As almost all dimensional changes within the C/C-SiC components are complete after the pyrolysis step, the manufacturing of complex components is possible through modular construction. Ceramic joints can be produced in situ by converting molten silicon to silicon carbide within the joints which bond the surfaces together. This paper deals with the correlation between microstructure and experimental results and describes some applications where these design aspects have been used successfully.