Shear Morphing Skins: Simulation and Testing of Optimized Design

NextGen’s work on the DARPA sponsored Next Generation Morphing Aircraft Structures (N-MAS) program [1]–[6] designed and successfully tested novel morphing wing designs that were enabled by “shear-morphing” skins capable of withstanding up to 400 psf air-loads while simultaneously undergoing shear strains in excess of 100%. These ad-hoc skin designs consisted of high-strain silicone facesheets supported by an intricate aluminum under-structure made of thin, closely-spaced aluminum ribbons glued to the facesheets and bounded by pin-jointed frames. While these performed well in wind tunnel and flight tests, two areas for improvement were identified: (1) reduction in manufacturing complexity, and (2) reduction in actuation force requirements. In this research program, through use of high-fidelity modeling (ANSYS) and in-house testing, a new design was obtained that met both of the desired objectives using novel materials and single-piece support structure fabrication. The optimization modeling code was designed to be adaptable to a range of design inputs, and as such can be used on future programs as well, at various scales from UAV to MAV. The thorough understanding of the design space gained from non-linear FEM modeling guided design, manufacturing and testing in the later portion of the research. Using the optimized design from analysis, as well as variations in facesheet prestrain, the ANSYS code was validated through manufacture and testing of panels. This report details the results of testing and compares them to both predictions of the ANSYS code and N-MAS baseline designs values through various test setups. Results presented include shear morphing forces/energy, out-of-plane displacement under air loading, and 3D photometric analysis of shearing panels for identification of stresses/strains and wrinkling initialization in the skin. Testing provided substantiation of the ANSYS code, matching the general predicted trends despite wide variability in material properties.