# Design and Shear Analysis of an Angled Morphing Wing Skin Module
###### Abstract  
Morphing wing skin can greatly improve the performance of aircraft by adjusting the shape of the wings according to different flight conditions. However, it is a challenge to maintain a smooth aerodynamic wing skin surface during the deformation process. Here, we propose an angled morphing wing skin module based on a silicon rubber matrix reinforced by carbon-fiber-reinforced polymer rods, which takes advantage of the tensile stress generated during shear to prevent it from wrinkling under large shear deformation. Experiments conducted on a series of wing skin modules with varying initial angles indicate that by starting from an angled configuration, the skin module can withstand a pure shear deformation of 92\({}^{\circ}\) without wrinkling, 53% larger than existing designs. A parametric analysis was also conducted to analyze the effects of geometric and material parameters on the wrinkle-free deformation range. Finally, a theoretical model based on the energy method was developed to unveil the underlying wrinkle prevention mechanism and to estimate the critical wrinkling angle of the skin. The proposed design can potentially greatly expand the shear morphing capability of aircraft wings, leading to larger variation in sweepback angle and therefore superior aerodynamic performance. a 202214 March 202214 March 202217 March 202214 March 20221  
This kind of design provides large deformation and sufficient out-of-plane stiffness. However, the surface is not smooth and continuous, and thus not able to maintain a seamless aerodynamic surface for the aircraft [6]. Honeycomb structures supported by a membrane to form a seamless surface have been studied for the skin design [13; 14]. Honeycomb structures are able to maintain a high out-of-plane stiffness to carry aerodynamic pressure while the in-plane stiffness is low to reduce actuation [15]. However, limited by the elastic limit of the base material (metal or plastic), they can only achieve a small range of stretch, torsion, and sweep deformation [16; 17]. The corrugated structures are considered a good candidate for morphing applications due to the high out-of-plane stiffness and in-plane transverse compliance [18]. [PERSON] et al. [19]. proposed a corrugated wing skin reinforced by unidirectional carbon-fiber-reinforced polymer rods, but only for bend and stretch deformation, rather than sweep deformation. As a result of the development of smart materials, shape memory polymers (SMPs) are increasingly applied to the design of the skins. SMPs have the characteristics of large deformation and adjustable stiffness under external excitation [20; 21], and are widely applied in the research of sweep, torsion, and bend deformation [22; 23; 24]. Nevertheless, many studies have shown that dynamic control problems, including uneven temperature distribution during heating [25], peeling of the hot wire and shape memory polymer [26], and cracking of the SMPs after multiple cycles of heating and deformation [27], have not been overcome. Finally, rubber can realize various forms of deformation [28; 29] due to its high elasticity, but it tends to wrinkle during the deformation process. To address this issue, [PERSON] et al. [30]. achieved a 45\({}^{\circ}\) shear deformation without wrinkling by applying pre-straining to the rubber, but this posed the problem of creep. [PERSON] et al. [31]. designed a kind of rubber matrix composite skin reinforced by carbon-fiber-reinforced polymer (CFRP) rods and Kevlar-fiber-reinforced polymer (KFRP) without pre-straining, and achieved shear deformation over 60\({}^{\circ}\). However, wrinkling is still prone to occur at a large shear angle, thus limiting the deformability of the morphing wing skin. In this paper, we propose a new angled wing skin based on reinforced rubber to achieve smooth and large shear deformation. By designing the initial angle of the skin, the tensile stress generated during a shear process is used to delay the occurrence of wrinkling and thus expand the deformation range.