Flexible Matrix Composite Skins for One-dimensional Wing Morphing

Abstract

Morphing aircraft wings require flexible skins that undergo large strains, have low in-plane stiffness, and high out-of-plane stiffness to carry aerodynamic loads. For some morphing applications deformation and low stiffness in the flexskin is required in one direction. In these cases, a flexible matrix composite (FMC) skin is proposed as a possible solution. A FMC comprises of stiff fibers embedded in a soft, high-strain capable matrix material. The matrix-dominated direction is aligned with the morphing direction. This allows the skin to undergo large strain at low energy cost. However, the high-stiffness in the fiber-dominated direction allows application of pretension along this direction, without rupture, and is critical for the membrane skin to carry out-of-plane pressure loads without excessive deformation. An analysis for a FMC skin panel is developed and validated against experiment. The analysis is used to conduct design studies. Comparison of the FMC skin to a matrix-only skin illustrates the importance of the fiber’s stiffness in tolerating pretension and limiting out-of-plane deformation under load. The other dominant parameter that limits out-of-plane deformation is panel size, with smaller lengths in the non-morphing direction proving beneficial. In general, fiber and matrix modulus has limited effect on out-of-plane deformation of flexskin panels.