Cyclic Testing of C/C-SiC Sandwich Structures and Interfaces

Kurzfassung

In a new design approach, sandwich structures made of ceramic matrix composites (CMC) have been realized by using the liquid silicon infiltration (LSI) process. Due to their high specific stiffness and strength, low thermal expansion, high environmental stability and temperature resistance, as well as due to economic manufacturing processes, these so-called C/C-SiC sandwich structures offer a high potential for the application in dimensionally stable structures, like optical benches in satellites. Carbon fibre reinforced polymer (CFRP) preforms for both, skin plates and core plates, were manufactured by autoclave technique using prepregs, based on a 2D carbon fibre fabric, preimpregnated with phenolic resin. Skin and core plates were individually converted to C/C panels by pyrolysis. Slit webs were cut out of the thin walled (0.6 mm) core plates and assembled to a grid core. Skin plates and grid core structure were joined to a sandwich structure, using an adhesive based on phenolic resin and amorphous C powder. Finally, this C/C sandwich was infiltrated with molten Si and both, the SiC matrix and the SiC joining area, were built up by a chemical reaction of Si and C, leading to a permanently joined C/C-SiC sandwich structure. Sandwich and interface coupons were manufactured and tested in 4-point bending and tension, respectively. In order to demonstrate the mechanical stability, compliance tests with increasing load levels were performed. The results from testing and FEM simulation were correlated and it could be shown that the real structural behaviour was reproduced closely. The manufacture of C/C-SiC sandwich structures as well as the results from simulation and mechanical testing will be presented in detail.