| The design and development of energy-absorbing cushioning structures has become one of the key focuses of collision safety technology,especially the research on the crashworthiness of energy-absorbing and load-bearing components in the collision process.Commonly used cushioning energy-absorbing structures are thin-walled structures,and the next generation of research targets are lighter weight and higher energy absorption.With the development of additive manufacturing technology,lattice structures with lightweight and high strength characteristics have entered the researchers’ vision.Lattice structures can realize higher energy absorption and improve the designability of energy-absorbing structures.Therefore,this paper focuses on the innovative design of cushion energy-absorbing structures to conduct in-depth research,designed a variety of new lattice reinforced thin-walled cushion energy-absorbing structures,and carried out the research on the crashworthiness of the structures under multi-operating load conditions by means of theoretical analysis,engineering experiments,numerical simulation and multi-objective optimization.The main contents are as follows:(1)Novel point-reinforced thin-walled hybrid energy-absorbing structures were designed.The effects of geometrical parameters(including: porosity,morphology and gradient density configurations)on the crashworthiness of the hybrid structure under axial quasi-static and low-velocity impact loads were investigated by means of experiments and finite element numerical simulations.A theoretical prediction model for the average load of the hybrid structure was established and its validity was verified,based on which the average load and energy absorption performance of the structure were predicted and obtained.The designed hybrid energy absorber structure improves the specific energy absorption by 83.02% compared to thin-walled tubes and realizes a wide-domain tunable mechanical response.(2)An improved design of lattice reinforced thin-walled hybrid energy absorbing structure was carried out.A multi-cell hybrid structure with additional internal ribs in the lattice reinforced thin-wall cushion energy-absorbing structure is proposed,and crashworthiness analysis and multi-objective optimization are carried out.Based on quasi-static axial compression and oblique compression,the deformation mode and crashworthiness of the structure are investigated.By introducing the non-equal length design of the rib plate and the outer tube,the initial peak force under the axial load is effectively reduced and the structural stability under the oblique load is improved.In addition,based on the grey correlation method and multi-objective parameter optimization,a hybrid structure with maximum specific energy absorption and minimum peak force under complex working conditions is sought for the non-equal length design structure.(3)The buckling of point-reinforced multi-cell thin-walled hybrid structures is investigated.Based on experimental and finite element numerical analyses,the deformation modes and crashworthiness of the structure under three-point bending loads are investigated.The effects of thin-walled tube wall thickness,rib thickness,rib length,and lattice length on the impact resistance of the structure are parametrically analyzed.The crashworthiness performance of the designed structure is selected based on the multi-criteria decision-making technique,and then the optimal structure is subjected to multi-objective optimization to obtain the Pareto front surface about the optimal ensemble,which further improves the crashworthiness of the hybrid structure under three-point bending.A normalized bending force dimensionless semi-empirical formulation for multi-cellular hybrid structures is proposed,which can effectively predict the load-displacement curves of hybrid structures.(4)One-piece printing and split-assembly connection methods are proposed to address the problem of connecting hybrid structure lattice with thin-walled tubes.The deformation mechanism and crashworthiness of the hybrid structure with one-piece printing and split assembly under axial compression and lateral compression are investigated.The effects of wall thickness and lattice density on the crashworthiness of the hybrid structures with two connection methods are parametrically analyzed by means of a validated finite element model.The connection method is insensitive to the effect of axial load,but the transverse load leads to the separation of the lattice from the thin-walled tube,which affects the energy-absorbing effectiveness of the structure.Under the effect of transverse load,one-piece printing improves the energy absorption efficiency by 134.83%compared with the split-assembly connection mode.The deformation pattern and energy absorption performance of the one-piece printed structure under high-speed impact transverse loading are investigated.(5)A node-reinforced isotropic body-centered cubic thin-walled sandwich structure was designed,and the elastic properties of the novel lattice monoliths as well as the mechanical properties of their sandwich structure under compression and bending loads were investigated.The effect of relative density on the elastic properties and anisotropy of the lattice monoclinic was investigated,and the anisotropy decreased with the increase of relative density.The deformation of the structure under compressive loading is dominated by bending,and the deformation of the structure under shear and triaxial loading is dominated by tension.The stress concentration at the nodes is effectively improved by the equal-strength design,and a more uniform stress distribution is realized.The energy absorption of the sandwich structure under compressive loading was enhanced by up to79.76%,and the peak stress was reduced by 40.37%.The prediction formulas for the compressive strength and three-point bending capacity of the sandwich structure were proposed,and the failure modes of the structure were obtained based on experimental and theoretical analyses. |
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