Wing twisting by elastic instability: A purely passive approach

The design of morphing structures requires attaining concurrently light-weight, load-carrying and shape adaptable systems that minimize complexity, actuation requirements and part count. Exploiting the external loads to produce local stiffness variations induced by elastic instabilities offers the potential to activate shape deformations purely passively. Following this approach, we present the structural response study of wings capable of attaining compliant buckling-induced twisting deformations. The structure is designed such that a specific level of aerodynamic load triggers the elastic instability in a shear web part of the wing box. The buckling-induced variation in effective shear stiffness, resulting from the development of a stable, reversible diagonal tension field, leads to a twisting deformation. The structural behaviour is characterized by two drastically different mechanical responses, delimited by the onset of elastic instability. The influence of the buckling component design on the attainable change in spanwise angle of attack is investigated for the specific case of a finite composite wing structure under aerodynamic loads. The type of composite material, its thickness, and the fibre orientation are the considered design parameters. The buckling-induced variation in twist angle, and the corresponding aerodynamic pressure redistribution on the wing, is exploited for achieving load alleviation, reducing the global lift coefficient and decreasing the wing root bending moment.