Multi-disciplinary Optimization Of A Novel Negative Poisson’s Ratio Bumper System

The bumper system located in the front of the car has a very important position in the field of automobile safety.In the design of the bumper system,on the one hand,the crashworthiness should be considered,thus the bumper system must have enough stiffness and strength so as to protect the vehicle body and occupants.On the other hand,in order to reduce the damage to pedestrian in the vehicle-to-pedestrian collision,pedestrian protection should be paid great attention.In this paper,taking into account the crashworthiness and pedestrian protection at the same time,a novel bumper system is designed based on negative Poisson’s ratio structure(NPR)with the characteristics of lightweight and high energy absorption.Furthermore,it is parameterized optimization of bumper system by means of improved multidisciplinary collaborative optimization method.The main contents of this paper are as follows:Firstly,in order to improve the performances of crashworthiness and pedestrian lower legform protection,the negative Poisson’s ratio(NPR)structure is introduced in the design of vehicle bumper system,which mainly includes the NPR absorber and NPR bumper beam.On the basic of the inner hexagonal cellular structure,the novel bumper system model,pedestrian lower legform model and the vehicle collision models are established.According to the requirements of GTR 9 and FMVSS208 regulations,the vehicle collision models are analyzed and verified.Secondly,sensitivity analyses of pedestrian lower legform protection and vehicle front impact are proposed.The orthogonal design method is used to determine the sensitivities of bumper system variable parameters on the performance indexes of the crashworthiness and lower legform protection.Then the coupling relationships between the variable parameters and the evaluation indexes are studied.Sensitivity and coupling analyses lay the foundation for the subsequent approximate model and multidisciplinary collaborative optimization design.Finally,aiming at the shortage of traditional multidisciplinary collaborative optimization method,an improved multidisciplinary collaborative optimization method is put forward.The consistency constraint in the whole system is altered to dynamic constraint by introducing dynamic factor.Furthermore,the norm forms of the subsystem objective function and the main-system constraint function are changed to improve the convergence and computational efficiency of the multidisciplinary collaborative optimization method.On this basis,through integrating optimal Latin hypercube design(OLHD),the response surface method(RSM),a novel collaborative optimization of NPR bumper system is constructed,then using two kinds of multi-objective optimization algorithms to search for optimal solutions in the main-system and subsystem.The research of this paper can provide a theoretical basis and technical support for the development and design of the vehicle bumper system.