Numerical and Experimental Modal Analysis Applied to the Membrane of Micro Air Vehicles Pliant Wings

Abstract

Hyperelastic latex membrane is an integral structure of micro air vehicles and plays an important role in their wings performance. This paper presents finite element analysis (FEA) models for characterizing latex hyperelastic membrane at both static and dynamic loadings, validated by experimental results. The membrane at different pre-tension levels are attached with a circular steel ring and statically loaded using steel spheres of different sizes placed at the center of the membrane. The deformation of the membrane is measured by visual image correlation (VIC), a non-contact measurement system and strain energy is calculated based on Mooney-Rivlin material model. It is found that the deflection and strain energy of the membrane computed by experimental and FEA models are correlated well, although discrepancy is expected among experimental and FEA results within reasonable limits due to the variation of the thickness of the membrane. The experimental modal analysis is conducted by imposing a structural excitation to the ring for investigating the membrane vibration characteristics at both atmospheric pressure and reduced pressure in a vacuum chamber. The three-dimensional shape of the membranes during a burst-chirp excitation at different pre-tension levels is dynamically measured and recorded and the natural frequencies are computed by performing the fast Fourier transform of the out-of-plane displacement at several points of the circular membrane. Experimental results show that the natural frequencies increase with mode and pre-tension of the membrane, but decrease due to increase in ambient pressure. A preliminary FEA model is developed for the natural frequencies of the membrane at different isotropic and nonisotropic pre-tension levels at vacuum environment.