Realization and Dynamic Studies of CNTs-PDMS Membranes for Biomimetic Flapping Wing Applications

摘要

Aerial and aquatic animals including bats, insects and fish use their wings/fins to generate propulsive forces. Natural fliers deform their wings, actively and/or passively, in bending and twisting modes to generate lift and thrust. Within a flapping cycle, wing skin interacts with surrounding fluid and transfers dynamic loads to the internal stiffening structure. Biomimicking of such complex natural flapping wings is possible if the development involves both materials and structural aspects. In the present study, thin PDMS films are chosen for developing the skin of the biomimetic flapping wings. The films are first characterized for dynamic mechanical properties (storage modulus, loss modulus and loss factor) using a dynamic mechanical analyzer. The tests are done in frequency and strain sweep modes to analyze the effect of strain-rates and strain-amplitudes on the dynamic mechanical properties and generate experimental data for constitutive modeling. The dragonfly and cicada wings are taken as the bioinspiration for developing the biomimetic wings. The fabrication of wing skeletons and their integration with the PDMS membranes are achieved through advanced manufacturing techniques including laser micromachining, photolithography and casting. Two types of composite materials are used for making the wing skeletons, i.e., carbon nanotubes (CNTs)/polypropylene (PP) nanocomposite sheet for cicada inspired wing and carbon fiber/epoxy composite strands for dragonfly inspired wing. Structural dynamic analysis of such light, flexible and small size biomimetic structures are interesting and useful for evaluation of biomimicking performance of used materials and manufacturing methods, but difficult to perform. A real-time high-speed non-contact dynamic testing method based on DIC-FPGA coupling (3D digital image correlation technique coupled with real-time data acquisition system, developed at our lab) is used for determining the natural frequencies and corresponding mode shapes of fabricated wings.