Manufacture and test of C/C–SiC sandwich structures

Sandwich structures based on C/C–SiC composites (carbon fibre-reinforced carbon with silicon carbide matrix), manufactured using the liquid silicon infiltration (LSI) process and an in situ joining method, offer high specific stiffness and strength, low thermal expansion, high environmental stability, and temperature resistance. Potential application areas are thermal protection systems (TPS) for spacecraft, optical benches in satellites, and hot structures in aerospace. In this work, C/C–SiC sandwich parts of two different geometries, small sandwich samples and large sandwich structures, were manufactured and tested. Carbon fibre-reinforced polymer (CFRP) plates for the skin panels as well as for the cores were made via warm pressing of prepregs based on a 2D carbon (C) fibre fabric, preimpregnated with phenolic resin. After pyrolysis, carbon fibre-reinforced carbon (C/C) core structures were built up and joined to C/C skin panels. Finally, the resulting C/C sandwich preforms were infiltrated with molten silicon (Si), building up a silicon carbide (SiC) matrix. The resulting C/C–SiC sandwich parts were tested in four-point and three-point bending. The applied forces and the correspondent displacements and strain of the skin panels were determined. The bending and shear stiffness as well as bending moment were evaluated through analytical and finite-element (FE) simulation approaches. Furthermore, failure modes of the sandwich samples were analysed. Sandwich stiffness and ultimate bending moment obtained in the bending tests were close to the expected theoretical values, calculated on the basis of the material properties and the sandwich geometry.