Optimization Study On Crashworthiness Of Hot Stamping Thin Walled Structure With Functionally Graded Strength

With the continuous deepening of automotive lightweight research,gradient strength performance parts(FGS)has been widely concerned and applied.Nowadays,the hot stamping technology of high strength steel has been wildly used to achieve the production of gradient mechanical properties parts,which can realize the lightweight of the vehicle and improve the passive safety of the vehicle.However,it has not been widely studied that how to design the automobile body parts with functionally gradient strength based on the hot stamping technology.In this paper,thin-walled structure parts with functional gradient strength were manufactured by hot stamping technology.The crashworthiness on gradient strength of hot stamping thin-walled structures based on related parameters,such as the gradient intensity coefficient m,top strength S and collision angle ?,was investigated,And the performance optimization research based on related optimization methods was executed.First of all,based on the high strength hot stamping forming process,the 22MnB5 high strength steel was treated by different processes,and the uniaxial tensile test was carried out to obtain the stress-strain curves.A hat shaped part with two layers of gradient mechanical properties was designed and tested.The comparative analysis of the experimental data and the finite element simulation data show that the change trend of the force displacement curve is similar.And the reliability of the finite element modeling process and the mechanical curves of the thermal gradient thin walled structure with gradient strength were proved.Secondly,the functional design of the graded thermal punching thin wall structure is carried out.By changing the gradient coefficient,the strength of the top and the angle of oblique collision,and so on,the paper studies the crashworthiness performance of the gradient strength hot stamping thin-walled structure in axial and oblique impact.The results show that the peak strength and the maximum energy absorption of the thin-walled structure with gradient strength are better than those of the same intensity homogeneous hot stamping thin-walled structure.In the axial impact,the gradient coefficient and the top strength have a great influence on the peak force and energy absorption.And the gradient coefficient and the top strength also have a great influence on the peak force and the weighted energy absorption,but also have an important influence on the critical buckling load angle.Furthermore,the radial basis function(RBF)fitting is performed based on the simulation data,and the genetic algorithm(NSGA-II)is used to design the multi-objective optimization.The results show that the gradient strength structure designed by this method is better than the uniform strength structure with the same mass.Finally,the mechanical performance gradient design of the front side of a car is analyzed,and the finite element frontal collision analysis is carried out.The simulation results show that the gradient strength of front rail in the collision energy absorption is decreased and the cowl invasion is significantly improved than the original homogeneous strength rail.It also reflects the gradient strength of hot stamping structure design and related technology on the improvement of vehicle collision safety of the value.