| The thin-walled structure is a simple and efficient energy dissipation structure that gradually dissipates external energy in a relatively smooth manner through the formation of periodic plastic folds during the crushing process.As a typical lightweight porous material,aluminum honeycomb can maintain the platform crush stress in a relatively stable range while forming plastic large deformation in axial crush,which plays an important role in the impact protection of various high-speed delivery equipment and weaponry.Single structural form of energy-absorbing elements often need to have a large volume to meet the high-energy collision process of the object crashworthiness requirements.However,the structure is often limited by space and weight in practical engineering applications.Therefore,the design and preparation of efficient and lightweight composite structures to improve the crashworthiness of structures is gradually becoming an effective method that has gained extensive research interest from scholars at home and abroad.Honeycomb-filled structures are often designed to cope with different load-bearing and energy-absorbing requirements,and can take advantage of both structures while improving space utilization.The diversity of honeycomb core layers and combined structural forms enhances the designability of the structure,however,simply combining two energy-absorbing structures together may not achieve the expected results.In this paper,experimental and numerical simulations combined with theoretical analysis are used to explore the axial crush behavior of the proposed random honeycomb column-shell structure and its influencing factors,the interaction mechanism between the components of the combined structure,and the wave propagation characteristics under dynamics,in order to provide guidance for the design of lightweight composite structures for crashworthiness.The main research contents and results of this paper are as follows.(1)Based on the two-dimensional random Voronoi structure,a three-dimensional random honeycomb column-shell structure was constructed by a convolution algorithm and the STL file program required for this geometric model to be used for the preparation of specimens by additive manufacturing technology was prepared.The fused-deposition 3D printing technology was used to prepare random honeycomb structures with different fine structures of polylactic acid(PLA).3D printing can meet the requirements of the accuracy of the parameters(irregularity,relative density)of the lightweight random honeycomb shell structure well,and realize complex fine structures with a single variable.(2)Quasi-static loading tests were conducted on the 3D printed lightweight random honeycomb column-shell structure,and the effects of core irregularity and relative density on its quasi-static crush performance were analyzed.The results show that the deformation mode of the lightweight random honeycomb column-shell structure is dominated by the irregularity of the cell elements,and the average crush load depends on the relative density and increases exponentially with the relative density in a power form.Quasi-static load tests were further conducted on the sandwiched circular tube structure filled with this honeycomb column-shell structure to analyze the effects of the core irregularity and relative density as well as the inner and outer tube geometric parameters on its quasi-static crush performance.The results show that the deformation modes of the inner and outer tubes of the random honeycomb sandwich circular tube structure are influenced by the combined dimensions of the inner and outer tubes and the fine-scale structural parameters of the honeycomb core layer,and the interaction between the core layer and the tube wall enhances the energy absorption performance of the structure.By controlling the fine view structural parameters of the random honeycomb core layer,the strength of the interaction between the core layer and the tube wall during the collapse process of the sandwich structure is influenced,thus changing its macroscopic mechanical property performance.(3)Further,the axial crushing behavior of the metallic lightweight random honeycomb column-shell structure under quasi-static loading was investigated using finite element simulations.The results show that increasing the thickness-to-diameter ratio can improve the radial stability of the structure,and the deformation pattern and average crushing load of the metallic lightweight random honeycomb shell structure are similar to those of the PLA material honeycomb shell structure mainly affected by the cellular irregularity and relative density.By introducing a rigid,ideal plastic hardening model(R-PH)applicable to porous materials,the relationship between the crushing load and the crushing strain of the random honeycomb column-shell structure is studied quantitatively,and the variation of the crush performance with the relative density of the metallic lightweight random honeycomb column-shell structure is given.(4)Based on the experiments,the effects of the thin-walled tube size and core layer fine structure parameters on its crushing performance under quasi-static axial loading were investigated based on the finite element model of the fine view.Further,the effect of the fine structure parameters of the core layer on its crushing performance under high-speed impact was also numerically analyzed.The results show that the deformation mode of the inner and outer tubes of the sandwich round tube structure with large irregularity and relative density of the honeycomb core layer tends to non-axisymmetric deformation mode,and the smaller the diameter and wall thickness of the inner tube,the larger the wall thickness of the outer tube also tends to axisymmetric deformation mode.Under high speed impact loading,the deformation of the sandwich round tube structure develops from the impact end to the support end,so that the deformation of the inner and outer tubes tends to be more axisymmetric and the trend of the influence of the core layer parameters on the deformation mode of the structure is the same as quasi-static.The increase of irregularity of the core layer structure under high speed impact load has little effect on the average impact load of the sandwich circular tube structure but the specific mass energy absorption has a tendency to decrease,the greater the relative density of the core layer structure the greater the average impact load of the sandwich circular tube structure but the effect of the relative density is not obvious when the relative density exceeds 0.15.Based on finite element simulation,thin-walled circular tube,random honeycomb column-shell structure and the theory of porous structure filled circular tube structure proposed a quasi-static average crush load of random honeycomb sandwich circular tube structure depends on the theoretical prediction formula of the relative density of the core structure.(5)The deformation patterns and crush performance of the gradient random honeycomb column-shell structure and its sandwich tube structure at different impact velocities were investigated.The results show that for gradient random honeycomb column-shell structures,the location and development of shear zones appear differently for different gradients and loading velocities,and there are differences in the crushing force and change trends between the support and impact ends.The higher the velocity the more favorable the energy absorption of the negative gradient structure.Based on the deformation law of density gradient random honeycomb column-shell structure under high speed impact combined with shock wave theory,a theoretical prediction model of the force acting on the end of the γ≥0 density gradient random honeycomb column-shell structure is proposed.The gradient random honeycomb sandwich circular tube structure has good energy absorption effect at quasi-static time for uniform gradient random honeycomb sandwich circular tube structure,good energy absorption effect at medium speed impact for negative gradient random honeycomb sandwich circular tube structure,and the energy absorption performance of gradient random honeycomb sandwich circular tube structure at high speed impact is better than that of uniform honeycomb sandwich structure and the positive gradient structure shows more excellent performance. |
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