Nonlinear flutter characteristics of graphene-reinforced porous folding wing-plate

The flutter research on folding wings is of crucial engineering significance for ensuring structural safety, aeroelastic stability, and suppressing nonlinear vibration behaviors under supersonic flight conditions. Taking the physical prototype of Lockheed Martin's folding-wing unmanned aerial vehicle as the research object, this paper establishes the aerodynamic force according to the first-order piston theory. Considering three porosity distribution patterns and three graphene distribution types, the dynamic governing equations of the graphene nanoplatelet-reinforced porous aluminum matrix sandwich (GNPs-PFMSC) folding wing-plate are derived using the first-order shear deformation theory (FSDT) and von Kármán large deformation assumption. The effects are systematically investigated for the porosity distribution, graphene distribution type, porosity coefficient, graphene mass fraction, folding angle and yaw angle on the critical flutter aerodynamic pressure (CFAP) of the structure. Moreover, the vibration responses of the system before and after the CFAP, especially the limit cycle oscillation (LCO) behavior, are analyzed. It is found that X-type and X-pattern distributions exhibit higher CFAP and smaller limit cycle amplitudes, indicating superior stiffness distribution and stronger flutter suppression capability. Increasing the porosity reduces the CFAP and increases the flutter amplitude, while increasing the graphene mass fraction enhances the CFAP and effectively suppresses the amplitude. A larger yaw angle significantly increases the CFAP and suppresses the vibration amplitude; as the folding angle increases, the CFAP first increases and then decreases, making the folding angle a dominant factor affecting flutter stability. This study provides important theoretical value and significance for the engineering practice of folding wings.