Bending mechanics of cylindrical skins for morphing aerospace applications

Abstract

Shape-changing aerospace structures explore the trade-offs between aerodynamic performance and actuation efficiency. Herein, a morphing cylinder is optimized to minimize both its work to actuate in bending as well as radial deviations. Based on derived linear elastic mechanics of a cylindrical shell in bending, it was determined that favorable designs have high circumferential and low axial stiffnesses. We investigate circumferentially reinforced composites that limit radial displacement and allow for out-of-plane bending. Designs of flexible skins with embedded or underlying reinforcement were modeled, fabricated, and compared to unreinforced skins. Finite element analyses predicted the bending kinematics and structural responses. Digital image correlation used during the bending of physical prototypes generated strain contour plots of cylinder surfaces. Strong agreement between model predictions and experimental measurements was observed. The dimensions of each archetype were systematically varied via finite element modeling to obtain a set of nondominated designs capable of 25° of bending without buckling or large radial displacements. For the examined designs, it was determined that flexible skins reinforced with embedded rings were optimal at low (8–15 N·m) and high (>250 N·m) values for the work to articulate while flexible skins reinforced with underlying helical springs were optimal at moderate values (15–250 N·m). Keywords: Morphing structures, Digital image correlation, Finite element analysis, Kinematic design