Study On Energy Absorption Characteristics Of Lotus Root Multicelluar Structure And Its Application In The Collision Safety Of Vehicles

The rapid development of automobile industry and the increasing of car ownership have brought a serious traffic safety problem and environment pollution problem.The new four modernizations of automobiles,represented by intelligence,networking,and electrification and sharing,are considered as the main measures to solve the problems of safety and environmental protection.Due to the failure of the control system in the intelligent net-connected vehicle,which will bring driving safety and loss of life and property to drivers and passengers.With the rapid development of the production and sales of electric vehicles,electric vehicles are gradually accepted by consumers.Therefore,this paper will carry out the research on the structural safety design of electric vehicle based on the multi-collision accident conditions.For the purpose of meeting the requirenments of collision safety performance under the condition of multicollision accident patterns and the structural characteristics of electric vehicles,this paper presents a novel filled structure which uses a bionic structure mimicking lotus root,which can effectively improve the energy absorbing efficiency of the front-end energy absorbing parts.The design problem of both lightweight design and safety design in the process of electric vehicle crash safety design is solved,and the safety performance of electric vehicle crash in the form of multiple collision accidents is improved.The energy absorption performance of lotus root multicellular structure,energy absorption characteristics of lotus root multicellular filled crash box,multi-objective optimization design of lotus root multicellular filled crash box,and the application of lotus root multicellular filled crash box in the multi-collision accident of electric vehicles are studied systematically.The main contents and innovations of this study are as follows:1.The collision safety design concept of electric vehicle under multi-collision condition is proposed.Due to the vulnerability of intelligent net-connected electric vehicles to remote attack by hackers,there is a risk of braking system failure,which will lead to a variety of vehicle collision safety accidents.According to the characteristics of intelligent connected vehicle,a variety of collision accident forms are deduced,mainly including two types of accidents caused by error information interference and braking system failure.Then,taking a certain micro-electric vehicle as an example,finite element simulation analysis is carried out on the collision conditions under different accident modes,and the safety performance of frontal collision of electric vehicles under multiple collision modes is studied.The results show that the failure of information security brings greater challenges to the safety design of automobile structure,and the existing body structure is difficult to meet the safety performance in the form of multi-collision accident.2.A novel filled structure which uses a bionic structure mimicking lotus root was proposed.The relative density and mechanical properties of the novel filled structure and the mechanical model are studied.It is found that the relative density of the novel filled structure is related to the geometric size of the cellular structure,such as height,thickness,the connection length between the celluar.The relative density of the novel filled structure will vary widely with the change of these five parameters.By changing the geometry of cell structures,the relationship between the static properties of lotus root multicellular structures and the geometric parameters of cellular structures is studied.Then,the energy absorption characteristics of the lotus root multicellular structure are studied,including the relationship between the geometric parameters of the cell structure and the energy absorption characteristics under axial crushing condition,and the relationship between different crushing angles and the energy absorption characteristics under oblique crushing condition.The research results show that the change of cell geometry has great influence on the energy absorption characteristics and deformation mode under the condition of axial crushing.The energy absorption level and peak force of lotus root multicelluar structure in oblique crushing is less than in the condition of the axial crushing,and the crushing angle has important influence on the energy absorption and peak force of the structure.With the increasing of crushing angle gradually,the energy absorption and peak force of the novel filled structure will increases gradually,and the change of cell geometry has little effect on the absorption energy and peak force of the structure.3.The energy absorption characteristics of the lotus root multicelluar filled crash box under the multi-collision Angle were studied.Firstly,the mechanical properties of the basic thin-walled structure(BT),aluminum foam-filled thin-walled structure(FFT)and lotus root multicelluar filled thin-walled structure(LFT)were studied.With the same quality of energy absorption structure and loading conditions,the energy absorption efficiency of the LFT is higher than that of the FFT,while the energy absorption efficiency of the BT is the lowest.Secondly,the relationship between the mechanical properties of the LFT and the total number of filled columns is studied.It is found that the energy absorbed is positively correlated with the total number of filled columns,while the peak collision force is inversely correlated with the total number of filled columns.Finally,the relationship between the energy absorption characteristics of the LFT and the geometric parameters of the cell structure is studied,It is found that the relation between the energy absorption effect and the angle of cell structure is quadratic parabola when the mass of crash boxes are constant.The results show that under both axial and oblique crushing conditions,the LFT can reduce the peak force of collision under the condition of good energy absorption effect,and the deformation mode is more stable than the BT.4.An optimal design method of lotus root multicellular filled structure and a novel crash box which can improve the safety performance of multi-collision accident are proposed.The novel crash box consists of lotus root multicellular filled structure and a basic crash box.Firstly,According to the engineering design requirements of high energy absorption effect and low peak force target of the energy absorption structure,the sensitivity of each geometric parameter of the new energy absorption box is analyzed to find out the parameters that have a great influence on the energy absorption effect.To determine the optimal geometric parameters,multiobjective design optimization(MDO)is performed by integrating optimal Latin hypercube sampling(OLHD),response surface method(RSM)and non-dominated sorting genetic algorithm-II(NSGA-II).Then,the optimized lotus root multicellular structure was applied to the electric vehicle,and the peak acceleration of the vehicle was reduced by 3g under the condition of frontal collision.Finally,the multi-collision condition of the electric vehicle with the lotus root multicellular filled crash box is analyzed,including oblique collision of different angles and front collision of different speed.The results show that the acceleration peak and the deformation of battery pack frame are improved under different frontal impact conditions,and the lotus root multicellular structure has a good effect on improving the safety performance of frontal impact of the vehicle under the condition of multi-collision accident.5.An efficient multi-objective robust design method with adaptive importance sampling(AIS)is proposed.This method can balance accuracy and computational efficiency,and solve the problem of multi-objective robust design for the lightweight and collision safety of electric vehicles.In the process of multi-objective optimization design,the influence of design variables on random noise and fluctuation is ignored,which often results in the optimal solution violating the constraint boundary conditions and becoming a non-feasible solution.Therefore,in the process of optimizing the design of multi-objective robustness of electric vehicle with the lotus root multicellular filled crash box,the influence of variable uncertainty on the optimization result should be considered to improve the robustness of the results.The research results show that the AIS based robust optimization design method is suitable for the optimization of large nonlinear collision cases,and can greatly improve the optimization efficiency on the premise of ensuring the accuracy of optimization results.