Study On Crashworthiness Of Thin-walled Structure Considering Hot Forming History

As an advanced lightweight manufacturing process for fabricating ultra-high-strength automotive body components,the hot forming technology owns the capacity for greatly improving the lightweight level and the safety of automobiles.On the basis of the foundation of metal plastic deformation,the forming process and forming history inevitably induce the variation of following mechanical properties of formed materials,and further affect the crashworthiness of the automotive body-in-white.Hot forming is a complex thermo-mechanical-metallurgical coupled fabrication process.At the same time,hot formed parts have characteristics of high strength and poor toughness,and the fracture failure is easy to occur during collision.All of these factors should result in the effect of the hot forming history on the anti-collision performance is more complicated than the conventional cold forming.In order to achieve a wider application of hot formed structures on automotive bodies,an accurate prediction of its crashworthiness must be conducted.On the basis of the research roadmap of refined crashworthiness simulation coupled the hot forming history for auto-body thin-walled structures,the following experimental and simulated works were conducted:Firstly,the mechanical properties of quenched boron steels with different hardness grades were tested.Series of quenched boron steel samples with multiple hardness levels were fabricated in terms of different hot forming process schemes.The uniaxial tensile test and the hardness test were executed respectively to obtain the stress-strain relationship and the corresponding hardness value,and further accurately establish the hardness-stress-strain relationship of quenched boron steel.Furthermore,a series of quenched top-hat thin-walled structural samples in terms of hot forming process were fabricated,and the crashworthiness performance indexes were obtained as the benchmark of numerical simulation.Subsequently,a damage failure model applied to the quenched boron steel was established to meet the requirement of considering the hot forming history.Based on the GISSMO damage model,four kinds of pre-strain samples were prepared by high temperature uniaxial tensile,and five subsamples with varying stress triaxiality geometry were designed and cut.The failure strain-stress triaxiality relationships of different pre-strained quenched boron steels were measured by means of digital image correlation measurement technology and finite element simulation,and further identified the corresponding damage accumulation parameters and analyzed the mesh dependence,and finally achieved the accurate prediction of the failure process of high strength quenched boron steel.Finally,the modeling procedure of the thin-walled structure crash model considering the hot forming history was effectively constructed and effects of hot forming history parameters on the crashworthiness was investigated.On the basis of the mesh information mapping,component partitioning,material constitutive and failure model considering hot forming history,the crash model of quenched boron steel auto-body thin-walled structure considering all hot forming history parameters was successfully built.The effect of specific hot forming history parameter on numerical results of crashworthiness was further evaluated.The results show that refined crash simulation modeling considering with full hot forming history has the highest prediction accuracy.The actual hot forming hardness distribution can reduce the peak force and improve the energy absorption.The thickness distribution reduces the peak force and the energy absorption,and the residual stress has little effect on crashworthiness performance.The proposed modeling approach of auto-body thin-walled structure coupled hot forming history can effectively simulate the deformation behavior of actual hot forming parts in the automobile body crashing process,which owns theoretical and application value.