| Buffer structure is widely used in aviation,aerospace and national defense industries,and its energy absorption characteristics directly affect the safety of personnel and equipment.It is of great practical significance to design a buffer energy absorption structure with good energy absorption characteristics and light weight.Based on the principle of engineering bionics,this paper takes the natural straw with high strength and light weight as the bionic prototype,and adopts the method of combining theory and experiment to carry out the bionic optimization design of the thin-walled structure,the foam-filled structure and the honeycomb structure,so as to provide a new idea and theoretical basis for the lightweight design of the energyabsorbing structure:Firstly,according to the similarity analysis,the light-weight and high-strength sorghum and reed stem were selected as the bionic prototype of the optimal design of energy absorption structure.The macroscopic and microstructural analysis of sorghum and reed stalks showed that the two stalks exhibited a tapered structure with varying wall thickness,and the node characteristics were distributed regularly.From top to bottom of the stem,the wall thickness and diameter increased gradually,while the internodal distance increased first and then decreased.The cross-section characteristics of the two stalks are also different.The circular cross-section of reed stalks is different from that of sorghum stalks.The cross-section of sorghum stalks is a progressive noncircular structure with groove.Microscopically,both stems are composed of fibrous tissue layer,inner pith core and large and small vascular bundle clusters,and the basic tissues are porous structures with gradient changes.The difference is that the vascular bundle tissue forms are different to some extent.Secondly,through the analysis of the static and dynamic mechanical properties of sorghum and reed stems,it is found that the node characteristics play an important role in the stability of stems.It shows negative effects under tensile loading,and enhanced effects under compression,bending and impact load.The axial compressive strength,radial compressive strength and bending strength of sorghum and reed with nodes are4.1/4.4,0.66/13 and 8.4/5.3 times higher than those of the specimens without nodes,respectively.The dynamic impact tests show that the peak axial impact resistance load of the specimens with nodes is 2.1,1.9,1.6,1.8 times higher than that of the specimens without nodes,and the impact toughness is 5/4.5 times higher.The impact toughness of the samples with high moisture content was up to 15.9 times higher than that of the samples with low moisture content.The mechanical tests show that the node feature can effectively improve the bearing capacity of stem,and the reinforcement of the node feature plays a leading role in the hollow structure of reed stem.As for the solid structure of sorghum stem,the combined action of pith core and node makes its mechanical properties better.In order to clarify the effect of node characteristics on stem enhancement,a digital model of node characteristics and vascular bundle structure of sorghum and reed stalks were established based on Micro-CT technology,and CT and CAD finite element models of sorghum and reed stalks were established based on mechanical tests and transversally isotropic material constitutive relations.The simulation results show that compared with the simplified CAD model,the simulation results of CT reconstruction model are closer to the real experimental phenomenon,and the minimum error of CT model is 10.77% compared with the simulation and experimental values.At the same time,the strengthening effect of the node and diaphragm on the stem was analyzed,and the critical compression stress and shear stress for the radial compression of the node and diaphragm structure in the sorghum and reed stem were deduced theoretically.According to the macroscopic gradient characteristics and microscopic porous characteristics of sorghum and reed stems,the design of thin-wall structure,foam-filled structure and honeycomb structure were optimized.According to the non-circular structure characteristics of sorghum stems,the design method of bionic grooved tube was proposed.The experimental and simulation results show that the specific energy absorption,bending strength and crushing force efficiency of the bionic pipe are increased by 93.10%,50.97% and 15.05%,respectively,and the mass of the bionic tube is reduced by 2%,compared with the ordinary tube.Based on sorghum and hollow reed stem,grooves,and section characteristics,of foam-filling structure bionic optimization design was carried out.The experimental results show that in the series of bionic foamfilled structures,the foam-filled structure obtained by the taper hole bionic design method has the lightest weight.The specific energy absorption of the foam-filled carbon fiber reinforced tubes is 32% higher than that of the fully filled carbon fiber reinforced tubes,and the mass of the foam-filled carbon fiber reinforced tubes is 29.01% lower than that of the fully filled carbon fiber reinforced tubes;According to the porous structure and gradient characteristics of the two kinds of stem micro layer,a variety of design methods of bionic honeycomb cell and edge structure were proposed.The simulation analysis and verification tests showed that three methods and six structures performed better than traditional hexagonal honeycomb structure.Compared with hexagonal honeycomb structure,the energy absorption of pentagon-circular composite honeycomb tube is 41.06% higher and 39.98% higher than that of hexagonal honeycomb structure.Finally,this paper proposes a bionic three-stage buffer structure for the lander’s energy absorbing leg.According to the simulation analysis,the mass of the biomimetic three-stage buffer structure is reduced by 27.5% compared with the traditional threestage buffer structure,and it is higher than the energy absorption by 27.7%.The singleleg quasi-static test shows that compared with the traditional three-leg cushion structure,the mass of the bionic three-leg cushion structure decreases by 22.37%,and the energy absorption ratio increases by 15.94%.The landing impact test shows that the bionic three-stage cushion structure can effectively eliminate the overload effect of 52.3% in the hard ground impact test,which is 18.06% higher than the traditional three-stage cushion structure.In the soft ground impact test,the bionic three-stage cushion structure can effectively eliminate the overload effect of 45.9%,which is 27.15% higher than the traditional three-stage cushion structure.Through the systematic macro and micro structure analysis and mechanical properties test of natural light-weight and high-strength bony stem,the bionic optimization design of thin-walled structure,foam-filled structure and honeycomb structure was carried out.The design method and thought can be the theoretical basis and technical guidance for the lightweight and crashworthiness design of energy absorbing structure. |
