Dynamic Mechanical Behavior And Constitution Model Of Automotive Body TWIP Steel Under Dynamic Loading

In recent years,advanced high-strength steels have been gradually used in automotive manufacturing driven by energy saving and vehicle light-weighting.Automotive steel needs high strength,high fracture resistance and impact resistance to ensure structural strength and deformation energy absorption.TWIP steels have attracted the attention of researchers and even the automotive industry due to their strong strain rate effect and excellent formability and deformation energy absorption,but most studies have not considered the load-bearing and deformation conditions when TWIP steels are being applied to the vehicle body.To this end,in this paper,the study of quasi-static mechanical behavior,dynamic impact mechanical behavior and deformation mechanism of TWIP steel are carried out by using the electronic universal material testing machine and Hopkinson compression bar device,and the constitutive model are constructed and applied to the crash simulation analysis of automobile front collision beam,as follows:(1)The effects of strain,strain rate,grain size and loading direction on the mechanical behavior of TWIP steels were investigated.The results show that the flow stress and DSA of as-cast TWIP steel exhibit negative strain rate sensitivity under quasistatic conditions,while the flow stress of TWIP steel exhibits positive strain rate sensitivity under dynamic impact conditions.Grain refinement ensures that TWIP steels maintain good elongation while increasing their yield strength.Appropriate predeformation treatment can intensify DSA,which also has a similar effect to fine-grain strengthening,and the loading direction has less influence on flow stress.(2)The effects of strain,strain rate,grain size and loading direction on the evolution of microstructure were investigated.The results show that under quasi-static conditions,the reduction of strain rate and pre-deformation treatment lead to the formation of more deformation twins.Compared with quasi-static conditions,the volume fraction of twins in TWIP steel under dynamic impact conditions is relatively smaller and gradually decreases with decreasing strain rate,and cross-twins of about 60° were observed.As the strain increases,cracks and adiabatic shear bands appear and dynamic recrystallization occurs within the shear bands.Most of the grains in TDoriented TWIP steels are shifted in the(001)and(111)directions,while most of the grains in RD-oriented TWIP steels are oriented in the(101)and(111)directions.More microcracks form in coarse grain size TWIP steels(3)Based on the modeling theory of the existing mechanical constitutive model of materials under impact loading,the mechanical constitutive model of TWIP steel under impact loading was constructed by analyzing the flow stress,deformation temperature rise and grain size.The results show that the R values of the M-JC constitutive model are higher than 99,14%and the AARE values are lower than 3.86%,which can accurately express the mechanical behavior of TWIP steel under different strain rates.(4)Based on the experimental data,the crash simulation of the front collision beam of the car is carried out to analyze the anti-impact performance of the front collision beam of the car under three-point bending,the frontal 100%and 40%rigid wall collision.The results show that the collision simulation process is realistic and effective,TWIP steel has excellent strong plastic product and excellent collision performance.The application of TWIP steel in body collision structure is of significant engineering application value to promote the lightweight of vehicle body and the realization of China’s "double carbon" goal.