Bionic Investigation On Mechanical Mechanism Of Dragonfly Wings Functional Characteristics

Dragonfly is one of the most excellent nature’s flyers, and its wings possess nearlyperfect functional characteristics including flying, self-cleaning, anti-fatigue, vibrationelimination and noise reduction. It had been already verified the excellent functionalcharacteristics of Dragonfly wings were resulted from the coupling of morphology,configuration, structure and materials. Furthermore, these characteristics of dragonfly wingshave closely interactive relationship with each other. Among those, flying is one of theprimary functional characteristics of dragonfly wings, the other functional characteristicssuch as self-cleaning, anti-fatigue, vibration elimination and noise reduction also playimportant supporting role in flying founction implementation. Dragonfly wings which canwithstand sorts of different alternating load during flapping, gliding, hovering have goodmechanical properties, and show the superior flying performance.The biological characteristics of dragonfly wings are systematically analyzed in thisthesis, and the excellent functional characteristics including flying, self-cleaning, anti-fatigue,vibration elimination and noise reduction are sufficiently exhibited through the intercouplingand cooperation of morphology, configuration, structure and materials of the wings from thepoint of biological coupling. Tensile testing and fatigue testing are conducted to study themechanical properties of dragonfly wings. Comprehensive analysis of various factors whichhad effect on mechanical properties of dragonfly wings is also carried. Based thecharacteristic of network morphology and section configuration, the bionic models of eachnetwork and section were established. Combining finite element analysis and experimentaltest, the mechanism between mechanical properties and coupling cell is investiagted in orderto establish a firm foundation for the coupling bionic design of dragonfly wings. The mainwork, conclusions and progresses of the thesis are as follows:(1) Based on the study of the geometric parameters, configuration, surface morphology, structure and materials of dragonfly wings, tt is found the mass of fore and hind wings ofPantala flavescens Fabricius is4.88%of its total mass, areas of fore and hind wings arebasically the same, the fore wing has a bigger area but a lower aspect ratio than the hindwing. The leading edge and trailing edge of dragonfly wing are in streamline form, thespanwise is sharp-pointed and formed a strong3D truss-like configuration; Wing surfacesare covered by longitudinal and transverse veins, forming by different network morphologysuch as triangle, quadrangle, pentagon and hexagon. Corrugation structure is found in thecross section of the whole wing. Meanwhile, cavity structure of multilayer compositematerial is also existed in the wing; Membrane is structed by three composite layers. Thevein-joints are divided into fixed and mobilizable junctions. The mobilizable flexiblevein-joints can make the whole wing produce buckling deformation, which could improvethe wings deformability. The vein is mainly composed of chitin, protein, and fiber, butmembrane is mainly composed of chitin and protein.(2) The excellent functional characteristics of dragonfly including flying, self-cleaning,anti-fatigue, vibration elimination and noise reduction sufficiently perform through theintercoupling and cooperation of morphology, configuration, structure and materials of thewings. The coupling cell plays different roles in different functional characteristics.(3) The results obtained by tensile test show that the main veins are beneficial tobearing load and play an important role in the flight. The configuration of cross section hasimportant influence on its force bearing ability. The main vein of dragonfly wings plays thesimilar role as a beam, bearing greater force than other veins. Also, the configuration andsize of main veins diameter are the key factors for the mechanical properties of dragonflywings.(4) The results obtained by qualitative fatigue test indicate that the membrane has littleresistance to the fatigue crack growth, but the vein can reduce or even restrain the fatiguecrack growth through the coupling and synergy of structure and material.(5) The network morphology characteristics and misalignment relations between eachnode of dragonfly wings are analyzed. Based on the results, network morphology models of dragonfly wings are established, and the influence of the network morphology and nodelocation on the deformation ability and stress distribution are also studied through numericalsimulation and experiment test.a) In the condition of bioderection uniform tension, the crisscrossed quadranglenetwork model Ⅲ has the greatest resistance to tensile; Hexagon network model andquadrangle network modelⅠ with great node displacement are the easiest to deforme; Thedeformation ability enhances when the node displacement increases.b) In the condition of a single-ended uniform compression, the crisscrossed quadranglenetwork model Ⅲ has better resistance to be deformed, Hexagon network model andquadrangle network modelⅠ with great node displacement are easier to deforme; The forcetransfer becomes greater and the stress distribution becomes more symmetrical when nodedisplacement increases.(6) On the main longitudinal veins of dragonfly wings, the section configuration ofdifferent locations from the wing root to the wing tip is not the same. The cross sectionconfiguration of the leading edge and trailing edge is triangle, and other sectionconfiguration of main longitudinal veins is similar to calabash in different thickness andradius. Based on cross section configuration characteristics of the dragonfly longitudinalveins, bionic models of each section are established. In order to study the mechanism ofspecial configuration, equal-radius section models and equal-thickness section models ofdragonfly vein are established. In order to study the mechanical properties of differentcross-section configuration, equal-area section models are established based on the bionicsection configuration models.(7) Finite element analysises of27models stress and deformation under the effect ofbilateral tension on9different locations of dragonfly vein are conducted to reveal theresistance mechanism of the bionic section configuration models, equal-radius sectionmodels and equal-area section models to tensile. Under the same loads, bionic sectionconfiguration models has bigger deformation than equal-radius sections and equal-areasection models, and the thickness between upper and lower parts of the cross section have a greater impact on the deformability than the radius in the same conditions.(8) Through the finite element analysis and examination test under the condition ofbilateral tension of equal-area section model, the results show that the section configurationhas influence on the section stress. That implies, the deformation will become smaller andthe stress distribution will become more symmetrical when the radius thickness of upper andlower part of cross section becomes more symmetrical.(9) Based on the bionic section configuration models, equal-radius section models andequal-area section models of dragonfly veins, the bionic straight bar models, equal-radiusstraight bar models, equal-thickness straight bar models of different location on veins areconstructed. Through numerical simulation and experimental tests, the results show that thesection configurations have important influence on the bionic bars, equal-radius bars andequal-thickness bars. That is, the unequal of radius and thickness of upper and lower parts ofthe cross section can both increase the deformation of bars, improving the deformationability of bars. The section thickness is greater than the section radius in influencing thedeformation of bars.(10) Through the finite element analysis of the bionic bars in9different locations, weresearch the rule of deformation resistance ability of bionic bars in the wingspan directionand the direction perpendicular to wingspan direction. The results show that for the bionicbars of different locations of veins, the bars near wing root location have better resistance todeform, the bars staying away from wing root location have better flexibility. For the crosssection perpendicular to the direction of wingspan, the bionic bars corresponding to thelocation of wein R1have better deformation resistance ability than the bionic bars in thelocation of other veins.(11) Based on the equal-area section models of dragonfly veins, the equal-area straightbar models in different locations of dragonfly veins are established. Through the numericalsimulation and experimental tests, the influence of section configuration on deformationresistance of straight bars is obtained in the equal area condition. The results show that thedeformation resistance ability increases when the radius and thickness between upper and lower parts of the cross section become more and more symmetrical.(12) Combing with the bar common used in engineering, the equal-area circular tubeand cylinder are designed and processed. Through the numerical simulation andexperimental tests, the rules of section configuration which have effect on circular tube,column, bionic bar in the equal area condition are obtained. It shows that in the condition ofequal-area loads, the hollow circular tube has the smallest deformation, while the solidcylinder has the biggest deformation, and the deformation of bionic bar is between the two.Compared with hollow circular tube and solid cylinder, the bionic bar which sectionconfiguration is similar to calabash is more suitable for the dragonfly veins.