Study On Optimization Of Crashworthiness Of Front Structure Of A Car Based On Thickness Matching And TRB Structure

With the rapid growth of domestic automobile production and possession,the problems of traffic safety,environmental pollution and energy shortage have become more and more prominent.In the accidents of serious injury or death caused by vehicle crash,frontal crash accidents occupy a large proportion.Improving the frontal crashworthiness of the vehicle structure is extremely important for the safety of the occupants.At the same time,the lightweight of the vehicle structure is of great significance for energy saving and environmental protection of the automobile.Comparing with equal thickness plate and tailor welded blank(TWB),tailor rolled blank(TRB)has the characteristics of varying thickness and the advantages of better crashworthiness and lightweight in body structure applications.In this paper,the key components of the frontal crash structure of a car are studied.The optimization design of the thickness parameters of the front structural components and the optimization of the parameters of front longitudinal beam with TRB structure are used to achieve improvement of the crashworthiness and lightweight design for the front structure.The main research works and results of this paper are as follows:(1)A simplified frontal crash finite element model of the front structure of a car is built,and the low-speed crash simulation of 15km/h is carried out.Through the calculation results,after verifying the validity of the model,the deformation sequence of the front structure,the energy absorption of the structural components and the change of the impact force of the front longitudinal beam are analyzed to evaluate the low-speed crashworthiness of the front structure of the car.The results show that the front structure of the car has good low-speed crashworthiness,but there is still room for improvement.(2)On the basis of the simplified frontal low-speed crash finite element model of the front structure,the thickness parameters of 7 kinds of 13 key structural components,including the front impact beam,the front energy absorbing box,inner and outer plates of the front longitudinal beam and reinforcement parts,and so on,are chosen as the design variables.The Latin hypercube design of experiment is used to collect sample points.The response approximation model constructed by the radial basis function(RBF)with high fitting precision is used to replace the original finite element model.In order to obtain the optimal thickness matching of the front structural components,the multi-objective optimization is solved by using multi-objective genetic algorithm with the mass and total energy absorption of the front structure as objectives,the maximum crash force of the front longitudinal beam as constraint.The optimized front structure has improved crashworthiness under low-speed crash condition and also achieved a weight reduction of 17.6%.(3)For the simplified frontal crash finite element model of the front structure of a car,a high-speed crash simulation of 50km/h is carried out.The front longitudinal beam undergoes large bending deformation,and the crushing deformation is not good,resulting in poor energy absorption of the structure crash.Therefore,based on the optimization of low-speed crash,the TRB structure is applied to the design of inner and outer plates of the front longitudinal beam.According to the stress cloud diagram of the front longitudinal beam in the high-speed collision,each equal thickness zone and transition zone of the inner and outer panels of the front longitudinal beam are determined.In this paper,the thickness of each equal thickness region is taken as the design variable,and the sample points are collected by the Latin hypercube design of experiment.The radial basis neural network method is used to construct the response approximation models about the mass,energy absorption and maximum crash force of the front longitudinal beam under the high-speed collision condition.The design of high-speed crashworthiness of the TRB front longitudinal beam is optimized by using multi-objective genetic algorithm.Compared to the pre-optimization structure,the mass of the final optimized TRB front longitudinal beam was reduced by 1.25%,the energy absorption was increased by 46.83%,the maximum crash force was reduced by 14.95%,and the specific energy absorption was increased by 57.39%.A big improvement is achieved for the crashworthiness without increasing the mass.Finally,the high-speed crash performance and low-speed crash performance of the optimized front structure are verified by simulation.The crash performance meets the requirements,which indicates that the parameters of the optimized TRB front longitudinal beam are reasonable.