Lightweight Design of Composite Sandwich Structures

Abstract

Since a long time lightweight sandwich structures were used in the design of aircraft components. But the more recent use of composites allows even lighter components with outstanding special features. Beginning in the early 60 s sandwich rotor blades (e.g. for the helicopter BO 105) were designed with composite face skins and mainly foam for the support of the skins in order to prevent the skins from local buckling failure. The design of the BO 105 cross section, the blade cross section of the EMMEN wind tunnel, the DNW wind tunnel blade are shown in the presentation of this paper. The foam support allows an improved local stability of the skins. The stability strength is dependent on the longitudinal stiffness of the face skins and the transverse and shear stiffness of the supporting foam. Carbon- or Glass-fibers are used for the blade skins. Extreme light and stiff sandwich carbon composite designs are used since the early 70 s for space satellite solar arrays. The design consists of carbon face skins which are filament winded open nets. The solar cells are isolated to the carbon filaments by thin Capton foils. For the needed high bending stiffness, extremely high modulus carbon fibers are used. Again wrinkling strength is the critical failure mode, due to high dynamic acoustic noise produced by the space-craft booster. The noise level and thus the load can be reduced with the help of “Helmholtz-Resonators” integrated in the multifunctional design. This kind of sandwich design can also be used for light weight fuselage structures. Multifunctional features, such as damping elements can be included in the design.