The Compressive Property And Its Strengthening Mechanism In Beetle Elytron Plate

Beetle forewings(or elytra)are a kind of typical sandwich structure,which possess characteristics of high optimization,light weight and high strength.A large number of studies have been done regarding this excellent biological structure and some biomimetic models have been proposed.However,until now,the reason why the design method in natural beetle elytra structures in which the outer sides of the trabeculae are strengthened by chitin fibers and the central regions are filled with protein has not been investigated,and the function of trabecularhoneycomb core structure in beetle elytra also has not been illustrated.Thus,for answering these questions and further developing light-weight and high-strength biomimetic structure,firstly,the design method in trabeculae mentioned above is qualitatively explained from the view of mechanics,and it is predicted that beetle elytron plate(BEP for abbreviation,a type of biological sandwich plate inspired by beetle elytra)with hollow trabecular-honeycomb core structure would possess prominent mechanical properties,which are verified by direct comparison experiments between BEP,as a new concept,and conventional honeycomb plate,and at the same time,the strengthening mechanism of deformation form and compressive performance in BEP and its biological function achieved by trabecular structure is investigated.Secondly,by discussing the influential rule of trabecular number in a honeycomb unit to the compressive properties of BEP,this project illustrated the bionic process of BEP,and the definition of BEP is proposed explicitly combining with the biological structure of beetle elytra;also,by changing the trabecular radius,the synergistic mechanism of trabecular-honeycomb core structure in a BEP is further revealed,which provides the experimental and theoretical foundation for optimizing BEP's mechanical property.Finally,the mechanical stability of BEPs made of various materials is investigated.What's more,in order to accelerate the extensive application of BEP in practical engineering,this research develops a preliminary exploration for the properties of the element unit of core structure,which provides an inspiration for the calculation of BEP mechanical parameters and their equivalent model.The results indicate the followings:1)A shared mechanism of the trabecular structure is proposed,and the compression experiments have verified that the shared mechanism can constrain the buckling deformation of honeycomb walls,which brings out brilliant compressive strength,deformation ability and energy-absorption ability in BEPs when comparing with honeycomb plate.The reason lies in the fact that,in the honeycomb plate,the triangular columns located in intersection of walls are mainly dominated by torsion deformation,which produces a half-wave convex deformation(C type)in honeycomb walls;however,the closed-section hollow trabeculae in BEPs possess more powerful torsional rigidity,which can better avoid the torsion failure,and mainly produce three half-wave convex deformations(S type)in trabecular-honeycomb structure,so that the bearing capacity and elastoplasticity deformation of BEPs are effectively improved.What's more,the structural parameters in core layer are varied to investigate their influence on BEP's mechanical performances,which shows that the BEP can improve its mechanical properties by setting trabecular structure in core layer in the same material cost.Based on these findings,this study illustrates the intrinsic relationship between biological structure of a beetle elytron and its functions: lightweight and high strength sandwich structure formed by the elytra plays the prominent role of a defensing system for beetles to overcome natural disasters and enemies.2)With the growing number(N)of trabeculae in a honeycomb unit,when N is less than or equal to three,the bearing capacity of BEPs increases rapidly;when N is between four and six,the there is a plateau appeared in the stress-strain curve,which signifies a remarkable improvement in energy absorption ability.When N is equal to six,BEP has the best compressive performance,which verifies the rationality and validity of the structure's design mentioned above and provides a design foundation for the trabecular distribution of BEPs in engineering projects.The reason lies in the fact that,the synergistic mechanism between trabecular and honeycomb structures is revealed in BEPs,namely except for the constrain effect for the convex deformation of honeycomb walls from the trabeculae,conversely,honeycomb walls provide lateral support for trabeculae also.When N is equal to six and trabecular outer diameter is equal to the length of a honeycomb wall,S-type convex deformation will be mainly produced in the core structure,which is caused by the synergistic mechanism being fully played.At this case,BEPs possess the optimal compressive property.Based on these finds and combining with biological structures of elytra of A.dichotoma and P.inclinatus,this study proposes the definition of beetle elytra plate(BEP),which is shown as follows: the BEP is a type of sandwich structure as long as the core structure exists the hollow or solid trabeculae,where the trabeculae can be distributed either in the intersection of the honeycomb walls or in the walls or only the trabeculae are present without the honeycomb walls.3)In metal BEP,S-type compressive deformation predominantly occurs under the vertical load,while honeycomb plate generates a C-type half-wave deformation,which are consistent with deformation of sandwich plates made of resin materials,and indicates that BEPs can well keep their mechanical features for different materials.Besides,the stress-strain curve of metal honeycomb plates has only two stages: rise and fall stage.In contrast,the stress-strain curve of BEPs is highly consistent with the three stages of metal materials(rise,plateau and fall stages),particularly,the appearance of yielding plateau in BEPs curve promotes the full play of the mechanical property of metal materials.Besides,based on sandwich theory,characterized by trabecular structure,the element unit of core layer and its features are explicitly proposed,and the experiments have verified that the constraint condition of this element unit is almost unchanged compared to the whole core structure,thus possessing a relatively high independency and stability in mechanical properties.In other words,the yield plateau and variation tendency of the compressive strength after buckling of the elementary unit are highly consistent with the compressive properties of the entire structure,which will provide a further foundation for the establishment of equivalent model of the BEP and its trabecular-honeycomb core structure.