Flexible fiber composites for space structures

Flexible fiber composites are those in which fibres reinforce (highly) flexible matrix materials like urethane, silicone or similar. In this chapter basics of flexible fiber composites are given focusing on carbon fiber-reinforced silicone (CFRS) composites. Specific methods are addressed for manufacturing, testing, and analysis of unidirectional CFRS laminate as well as CFRS of both biaxially and triaxially woven fabric (TWF). A method of homogenization of material properties of TWF flexible composites is given in detail. For this a derivation procedure is developed and discussed for a 9 x 9 ABD stiffness matrix of an equivalent laminate, which is based on micromechanical finite element analysis of a repeated unit cell of the composite. Using an effective beam finite element model, 3D deformability of the cell is fully accounted for. The resulting properties include tensile and flexural as well as transverse shear stiffnesses, which are particularly needed for characterizing the flexible fiber composites. It is concluded that TWF composites behave as transversely (quasi) isotropic materials according to the calculated homogenized properties. After addressing possible space applications like large deployable reflectors and large membrane structures, a focus is given on shape variable space structures using the flexible fiber composites as reflecting morphing skins. The prospective of the use of CFRS in shape morphing structures opens new challenging application direction for this material.