Structural Composite Elements with Special Behaviour

Abstract

The properties of composites allow outstanding new designs with unknown features. Composite structures with fibre reinforced elements are widely used in the design of aerospace structures. In 1967, the BO 105, a product of the former helicopter division of MBB, now Eurocopter Deutschland GmbH, flew for the first time. This innovative helicopter was equipped with the first serial “hinge- less” rotor system. The fibre composite blades were attached to the head with the help of the “lug” element. This made possible the simple design of the rotor without damper elements. The shear stiffness is very low for unidirectional composites. In the metal world the shear modulus G is high and linked to the Young's modulus and the Poisson's ratio by the formula G = E/2(1 + υ). The low shear stiffness of composites allowed the “Flexbeam design” of the EC 135 with a “bearingless” and “hingeless” concept. The shear modulus G and as a consequence the torsional stiffness are the important features of this paper, they allow the given different design concepts. The mechanical behaviour of composite materials allows the design of outstanding basic structural elements such as plates and shells having a high range of different stiffnesses, in plane and out of plane. These elements are often used for the attachment of vibration absorbing structures. In this paper several applications of anisotropic structures are described and possible use is shown.