The Flexural Properties And Reinforcement Mechanics Of Beetle Elytron Plate (BEP)

In recent years,with the rapid development of economy and the growth of population,the contradiction between human and nature has become increasingly intensified.And the problem of material and resources’lackness has become more and more serious.Therefore,how to live in harmony with nature and how to implement economic development more effectively and sustainably has become a topic of great concern.Under this background,honeycomb sandwich structure has been widely phrased for its advantages of light weight,high strength,sound insulation and heat insulation.And now,it has been widely used in lots of fields,including aerospace,construction,transportation and many others.Professor Chen started to study the structure and mimic of beetle’s fore wing from about twenty years ago.And he found that the biological prototype of honeycomb structure should be beetle’s fore wing rather than honeycomb.The core structure of beetle’s fore wing is more ingenious and excellent than traditional honeycomb.Then in 2016,the bionic model of beetle’s fore wing was named beetle elytron plate,on the base of exploration of the strengthening mechanism of compressive mechanical properties.Our research group has carried out a series of studies on its static compressive mechanical properties.Thus,in this paper,the bending properties,reinforcement mechanism and problems of two kinds of beetle elytron plates were investigated for the first time.In addition,the core structure characteristics of ladybird and differences among ladybird’s and two other beetles’core structure of fore wings were compared.The results are listed as follows:(1)Three-point bending experiments were carried out on three kinds of plates with equal wall thickness or equal volume.These three kinds of plates have different core structures,the first one with honeycomb walls and trabeculae in the joint of walls(EBEP),the second one with only trabeculae(TBEP),and the last one with only honeycomb walls(traditional honeycomb structure,HP).And the results showed that the bending properties and ductility of EBEP were the best.In addition,the strengthening mechanism was also studied.In TBEP,the honeycomb walls and trabeculae connected together.This can not only help the skin to bear part of the tension,but also reinforce the skin.At the same time,compared with the Y-shaped column in HP,the hollow closed circular column in EBEP not only shortened the width of honeycomb walls,but also restrained the deformation of honeycomb walls effectively by its excellent torsional performance.The bending performance of TBEP was worse than HP.The columns in the core were pulled up completely from the roots when destroyed.However,in beetles’forewing,the trabeculae are always connected with skins by a chamfer.Thus,adding chamfers may be helpful for TBEP to overcome the weakness.These findings laid a foundation for targeted research in future and the popularization and application of EBEP in engineering more reasonably and effectively.(2)The setting of chamfer can improve the bending properties of these three kinds of plates to a certain degree.However,under the experimental condition of this paper,it can not completely reverse the relationship between the advantages and disadvantages of them.After adding chamfer,the bending performance of TBEP was obviously improved,while in HP,the improvement was smaller.As for EBEP,the function of chamfer was only reducing the dispersion of experimental results.Beyond that,the strengthening mechanism of chamfering on bending properties of these plates has been researched.For TBEP,the addition of chamfer made the weak position much more centered.For HP,the chamfer enhanced the restraint of honeycomb walls slightly,which made it less prone to buckling.So,the bending strength of HP increased a little.As for EBEP,though the existence of chamfer can restrain the walls,yet,because of the great restraint effect of the hollow closed circular column and the synergistic effect between the columns and the honeycomb walls,the function of chamfer was only reflected in dispersion reduction of the results.It provides a useful reference for the design of sandwich structure with chamfer in the following work.(3)The core structure and characteristics of ladybird(Harmonia axyridis)fore wing was observed.And by comparing the inter structure photos of two other kinds of beetles,Allomyrina dichotoma and Prosopocoilus inclinatus,which were studied before,the similarities and differences among these three kinds of beetles,which are different in shapes and body sizes,were studied.It was found that there was foam and trabeculae in ladybird forewing.And trabecula was also found existing in the frame.The parametersλ_t,the ratio of the cross-sectional area of the trabeculae to the effective area of trabecular distribution,N,the total number of trabeculae in each forewing were determined for the first time.The trabeculae size of ladybird is the smallest.However,it has the highest trabecular density of 84 per square millimeter.Theλ_t values for H.axyridis,A.dichotoma and P.inclinatus are approximately 1.0%,1.5%and10.5%,respectively.The total numbers of trabeculae in the forewings of H.axyridis,A.dichotoma and P.inclinatus are 1.4,1.7 and 3.7 thousand,respectively.Based on these findings,a biomimetic model of the ladybird forewing is proposed,which is characterized by a core structure with a high-density distribution of thin trabeculae surrounded by a foam-like material.This elucidation of the structural characteristics and design of the ladybird forewing is intended to establish a new direction of new beetle elytron plates and its structural parameters optimization.