Bending characterization of axis and off-axis fiber-reinforced hinges at large deflection

High-strain composite materials, consisting of elastomer matrix materials and carbon fibers, offer an unconventional portfolio of mechanical properties. The highly anisotropic character allows their application in flexible and deformable compliant structures. The local integration of high-strain matrix materials between conventionally rigid matrix materials enables the creation of integral fiber-reinforced hinges [1]. The bending characteristics of such elements differ significantly from conventional composite materials due to local flexibility and large deflections. The paper presents a bending test device, which is able to overcome the deficits of existing test devices. The set-up allows to determine the correlation between bending moment and hinge opening for large hinge deflections, bending and unbending, cyclic loads, positive and negative bending angles and different hinge designs. Thick-walled (approximately 1.6 mm) fiber-reinforced hinges with 0°/90° and +/-45° dominated weave fiber-reinforcement and 30 mm long flexible hinge area are experimentally investigated. It is found that the fiber orientation influences the deflection and failure behavior. 0°/90° reinforcement orientations lead to stiff hinges with buckling and delamination failure at small deflections. The +/-45° reinforcement orientations show lower stiffness, no failure up to 90° deflection but significant perpendicular curvature in the hinge area. The initial results give evidence to the suitability of the developed testing device and establish the foundation for ongoing investigations of hybrid-matrix fiber-reinforced hinges.