Study Of Energy Absorption Characteristics And Optimal Design Of Bionic Hierarchical Thin-Walled Square Tubes

Due to the high operating speed and large passenger mass of the train,the consequences of a collision are very serious.Thin-walled structures are widely used as energy-absorbing devices for rail vehicles,so it is crucial to design thin-walled structures with high energy absorption efficiency for passive safety of trains.Natural organisms have evolved their own structures with excellent mechanical properties through hundreds of millions of years of selection and elimination.In recent years,bionic design has become a hot research topic in the field of engineering.In order to further improve the energy absorption efficiency of traditional multi-cell thin-walled square tube structure,this paper is inspired by the microscopic trabeculae structure of beetle wing sheath,and adopts the principle of structural bionics and the idea of hierarchy to design a new bionic hierarchical thin-walled square tube,and the energy absorption characteristics of the bionic hierarchical thin-walled square tube are studied through theoretical analysis and numerical simulation,and the parameter analysis and optimal design of the bionic hierarchical thin-walled square tube with better energy absorption characteristics are carried out.The main research contents are as follows:（1）A Bionic Hierarchical Thin-walled Square Tube（BHST）was designed by simulating the microstructure of beetle wing sheaths,based on the traditional multi-cell square tube,combined with the hierarchy idea.Based on the super folding element theory,a theoretical model of the mean crushing force under axial impact of the bionic hierarchical thin-walled square tube is established.The axial energy absorption characteristics of the bionic hierarchical thin-walled square tube and the first-order conventional multi-cell square tube were analyzed by the nonlinear finite element software LS-DYNA.The results show that the theoretical predictions agree with the numerical simulation results,and the relative errors are within 7%.The bionic hierarchical thin-walled square tubes have excellent axial energy absorption characteristics.The energy absorption performance of the structure increases significantly with the increase of the layers,and the optimal energy absorption characteristics are achieved when the structure level is third order.（2）The energy absorption characteristics of the bionic hierarchical thin-walled square tubes under different working conditions in the axial and oblique directions were analyzed by the finite element method.A complex proportional assessment method（COPRAS）was used to comprehensively evaluate the energy absorption characteristics of bionic hierarchical thin-walled square tubes,and the structure of 4BHST3-1 was determined to be the best design.Then the influence of structural parameters on the 4BHST3-1 structure was investigated.The results show that the bionic hierarchical thin-walled square tube shows progressive folding deformation under both axial（θ=0^?）and small angle（θ=10^?）oblique loading conditions,and has a large specific energy absorption and crushing force efficiency.With the increase of the oblique loading angle,the structure shows bending deformation,which reduces the energy absorption performance of the structure.Compared with the third-order square tube edge length,the second-order square tube edge length and wall thickness have more significant effects on the energy absorption properties of the structure.（3）A radial basis function（RBF）agent model and a non-dominated ranking genetic algorithm（NSGA-II）were used for the multi-objective optimization of the 4BHST₃-1structure,and the Pareto fronts of the 4BHST₃-1 structure under different working conditions were obtained,and the optimal design parameters of the structure were obtained using the minimum distance method,and then the energy absorption characteristics of the optimized structure and the initial design structure were compared and analyzed.The results show that the optimized structure exhibits excellent energy absorption characteristics under different impact conditions.The bionic hierarchical design and optimization method used in this paper can provide new ideas for designing thin-walled square tubes with excellent energy absorption characteristics.