Morphological Characteristics And Mechanical Properties Of Insect Wings With Typical Rigid-flexible Coupling Structures Formed By Vein And Membrane

Fatigue is restricted component service life, the important technical problems of production quality and efficiency improvement. For a long time, domestic and international scientists have made many studies about the fatigue theory and technology exploration. Howeve, due to the complexity of problem, the increasing requirement, and the limitations of research methods, fatigue research has always been difficulties for engineering sector. Currently, anti-fatigue research is still largely dependent on improving the material composition and manufacturing process, implementing surface strengthening technology, rarely considering the impact of surface geometry and internal physical structure and other factors. In nature, many insect wings have excellent properties and perform remarkable capabilities in resisting crack and anti-fatigue properties. Such insect wings made of soft membrane and hard veins connecting together by appropriate mean show the typical structure of rigid-flexible coupling. Insect wings are ideal biological models for the study of biomimetic anti-fatigue. Exploring the morphology and mechanical properties regularity of Insect Wings with typical rigid-flexible coupling structures formed by vein and membrane is an important biological basis of bionics. Revealing insect wing crack arrest and anti-fatigue mechanism of insect wings will provide new principles, new ways and new support for bionic anti-fatigue research in engineering.In this thesis, the research backgrounds on the demand of crack arrest and anti-fatigue mechanical components in engineering area, we take three typical rigid-flexible coupling structures insect(Pantala flavescens Fabricius, Locusta migratorias, Apis cerana Fabricius)(hereinafter referred to as dragonflies, grasshoppers, and bee) wings as the research object, analyze the macro/micro and micro/nano as well as 2D/3D geometry and structures of the insect wings by using different testing methods, analyze the mechanical properties of the vein-membrane rigid-flexible coupling structures acted on crossing scale analyzed through the macro tensile experiments and nanoindentation experiments and studies the dynamic variation of crack initiation and propagation of insect wings under mechanical loading by high speed cameras. The effects of the rigid units and flexible units to whole mechanical properties have been studied by finite element simulation.The main conclusions of this thesis are as follows:(1) The main components of the rigid-flexible coupling structures “vein” and “membrane” are all non-smooth structure. The membrane connects with the vein by coating and formed as one-level rigid-flexible coupling structures together. The connection styles can be divided as movably connection and fixed connection, the distribution and proportion of different connections have a big difference in different types of insects as well as their position of the wings. Optimization of connection styles not only guarantee the connection strength of the wing, but also greatly improve the deformation of flexible wings.(2) Veins are a hollow tubular structure, and the vein wall is a typical “sandwich” multilayer structure. Chitin layers wrappers the intermediate layer forming the two-level rigid-flexible coupling structures in microcosmic. The membrane of dragonflies wing and bees wing can be divided into two layers, but locusts wing membrane contains special middle fibrous layer beside two layers, the special middle layer play an important role in trimmer pressure. Folds of insect wings are the most notable features(3D structure). Folding size of insect wing gradually decrease from the wing root to the wing tips; the same result can be taken place from leading edge to trailing edge.(3) A rigid unit vein and flexible unit wing membrane have same chemical compositions which are the organic composition of protein and chitin. But the content of the chemical element are different. Compared with the wing membrane, Vein contains much more minerals like Ca, this minerals can improve the hardness and intensity of the vein wall.(4) Different insect wings have different mechanical properties due to their different living conditions and different load types. The average tensile strength and the elongation rate of the dragonfly costa are 209.8MPa and 5.45% respectively; The average tensile strength and the elongation rate of the locusts costa are 136.4MPa and 5.51%; The average tensile strength and the elongation rate of the bee costa are 375.4MPa and 2.48%.The vein structure and the material content of each component are the main reason for the difference of static mechanical properties of insects.(5) The change law of the elastic modulus and the maximum hardness of the leading edge on different insect wings are Bee> Dragonfly> Locust, the nanomechanical properties were not related with the size changing but the material of the vein and the microstructures, the change law of the mechanical property is consistent with the result of the macroscopic tensile test.(6) The grid structure of rigid unit “vein” distribution affects the mechanical properties of the whole structure. It is found by finite element simulation analysis that the comprehensive strength and stiffness of quadrilateral structure with no nodes dislocation are optimal, Hexagon model’s comprehensive strength and stiffness are followed, the comprehensive strength and stiffness of quadrilateral structure with nodes dislocation are the worst, and the existence of nodes dislocation result in a decline in the strength and stiffness, the greater the dislocation, the worse the resistance, the more easily deformed. The addition of flexible wing membrane has a significant effect on enhancing strength and stiffness of the whole structure.(7) Rigid unit “vein” and flexible unit “membrane” play different roles in stopping and preventing crack propagation. The vein is taken a role as support and strength to enhance the fatigue strength as well as stop the crack propagation. The membrane can bear the bending and torsion deformation which acted on the wing.