Due to their excellent stiffness-to-weight ratio, sandwich structures have been widely used in aerospace, automotive and construction industries. Compared to traditional sandwich structures made of cardboard, aluminum, polymer (polypropylene or polycarbonate) or fibre reinforced composites, sandwich structures based on ceramic matrix composites (CMC) can achieve significantly higher service temperatures above 2000 °C, longer lifetime and considerable increase of specific strength and stiffness compared to solid structures. At the Institute of Structures and Design of German Aerospace Center (DLR) in Stuttgart, C/C-SiC sandwich structures based on continuous fiber reinforced fold cores and skin panels have been realized via liquid silicon infiltration (LSI) and in situ joining method. The resulting lightweight structures offer a high potential in various application areas, like optical benches in satellites or charging racks for high temperature furnaces.
A major impediment for the new development and practical application of ceramic sandwich structures is the lack of know-how of characterization and simulation of their mechanical properties. In this study, experimental investigations, analytical calculations and numerical models of four point bending tests on C/C-SiC sandwich structures are proposed. Several types of sandwich composite with different fiber orientations (0°/90° and +-45°) in the core structure were manufactured and analysed. The mechanical properties of different sandwich structures were analytically calculated and implemented in numerical (finite element) simulation. The results obtained by modeling of four point bending were compared with experimental results and the comparison showed good correlation. Therefore, the presented method is able to determine and simulate the mechanical properties of C/C-SiC sandwich structures and seems to be applicable for further product development.