Bionic Optimization Method Of Sandwich Structure Based On Biological Strategy Of Light-weight And High-strength And Study Of Out-of-plane Mechanical Properties Of Sandwich Structure

Sandwich structures are widely used in agricultural machinery,transportation,aerospace,protective engineering and other fields.However,in the face of increasing functional diversification and complex working conditions,it is of important scientific and engineering significance to improve its load bearing capacity and impact resistance on the basis of ensuring the original advantages of sandwich structure.In this paper,based on the study of lightweight and high-strength strategies for two biological structures,seagull feather shaft and ladybird elytron,the structural bionics method is adopted to map the biological structure features to the design of the panel and core,so as to improve the strength of the bionic sandwich structure,and reveal the mechanism of panel performance improvement and core energy dissipation.According to the characteristics of light-weight and strength,the seagull feather rachis is selected as the biological prototype.Macro and micro structure analysis shows that the it is composed of the outer cortex and the inner medulla.Axial compression tests and nano-indentation test show that the cortex is the main load-bearing part.According to the characteristics of high strength and mass,the ladybird elytra is selected as the biological prototype.The structural analysis shows that the elytra consist of upper lamination,middle layer and lower lamination.The upper lamination is composed of at least 5 fiber layers with different angles(48°/-45°/33°/0°/75°).The middle layer consists of trabeculae that connect and support the upper and lower lamination.The lower lamination can be divided into protein layer and fiber layer,but the angle of fiber layer is not clear.Nano-indentation test,nano-three point bending test,tensile test and composition analysis provide key parameter and material parameter reference for the establishment of finite element model.In order to determine the significant effect of structural characteristics on mechanical properties,the seagull feather rachis and ladybird elytra are scanned with3 D X-ray microscopy,the models are reconstructed with Mimics and Geomagic Studio.The model of feather rachis is based on the cortical model,which has the characteristics of the cross section,grooves and wall thickness,confirming the influence of the section characteristics on the axial compression performance.An accurate ladybird elytra model is established.The structural characteristics are explored by using the control variable method through simulation.The influence of the structural characteristics on the mechanical properties of tensile and bending is explored from the angle of fiber layer,the thickness of each layer and the number of trabeculae.Based on the correlation model between structural characteristics and mechanical properties,a bionic optimization design method for panel and core is proposed.Inspired by the cross-distribution characteristics of multi-layer fibers of ladybird Elytra,the bionic panel is cured by epoxy resin and carbon fiber with different layering angles.The bionic core selects the center line of the cross section of the primary feather shaft,which is simplified and described quantitatively by sine curve,as the design basis of the center line of the single cell section.The 3D printing and nylon material are used to process the bionic core.Finally,an epoxy resin binder is used to fix the panel and core,the autoclave is applied to curing molding.The influences of loading speed,wall thickness of the core and number of cells on the mechanical properties of the bionic sandwich structure under out-of-plane quasi-static compression are explored,the stiffness and peak force of the sandwich structure under different thickness of the upper and lower panels and impact energy are analyzed.Aiming at the damage of carbon fiber composite laminates under load,a 3D progressive failure model based on Hashin and Yeh failure criteria is used.The stiffness matrix and elastic constants are calculated according to the balance equation of the laminates.The improvement of the mechanical properties of the bionic panels is revealed theoretically.Finally,the non-dominant sorting genetic algorithm II is used to optimize the panels.In view of the plastic deformation behavior of the core,the simplified super-folded element theory is used to reveal it,the high-precision simulation model is verified by experiments.The parameters of wall thickness,sinusoidal amplitude and cell number are analyzed.Finally,the bionic core is sorted and optimized by complex proportional assessment and Central Composite Design.The overall performance of the core with 5 rows and 5 columns is better,the peak load can be reduced by 11.08% when the amplitude is 5 and the wall thickness is 1.347 mm.Compared with the combination sandwich structure of conventional panel and honeycomb core,the mass of the optimized combination sandwich structure of bionic panel and bionic core is controlled at the same level,the peak force is reduced by10.26%,the mean force is increased by 4.30%,the specific energy absorption is increased by 4.65%.From the perspective of structural bionics,a new sandwich structure according to the lightweight and high-strength of the seagull feather shaft and the ladybird elytra is proposed in this paper.Its feasibility is verified through experiments,simulations and theories,optimization based on multiple objectives is carried out.This paper provides theoretical basis and technical reference for the design and optimization of sandwich structure.