| The rapid development of the automotive industry has also brought a lot consumption of energy resources and large amounts of carbon dioxide and other gas emissions.How to realize the lightweight design under the premise of security,reduce fuel consumption in order to achieve a more environmentally protection is an inevitable trend in the development of the automotive industry.The use of high-strength steel such as dual phase steel can reduce the weight of car design by reducing the sheet thickness.The mechanical properties of dual phase steel mainly performed: high yield strength and tensile strength,excellent material ductility and work hardening ability and so on.The forming component finished by duplex steel have a good impact of resistance and energy absorption characteristics;it has been widely used such as the absorbing cartridge,bumper beams,and the B-pillar parts in the car body structure.Duplex steel B340-590 DP is selected as the research objectives in this paper,the dynamic mechanical behaviors of this material were researched combined with the methods of experiments,theoretical analysis and numerical simulation,the mainly contents are showed as followed:Firstly,the uni-axial quasi-static and dynamic tensile testing are done respectively with the strain rates:0.003/s,20/s,80/s,180/s and 530/s of the B340-590 DP steel specimens,the true stress-strain curves are finally obtained under different strain rates.According to the obtained true stress-strain curves,mechanical properties such as yield and tensile strength,flow stress and percentage elongation after fracture are analyzed at different strain rates.By metallographic observation showed that there is no third phase produced during stretching,plastic deformation is mainly concentrated in the ferrite,the hardening effect of ferrite is significant with the increase of stress.Secondly,compared with several common basic dynamic mechanical constitutive equations of metallic materials,JC model is selected to characterize B340-590 DP steel constitutive model.The parameter C is expressed as a function of strain rate dependent according to its distribution at different strain rates;the secondary correction is based on the divergence characteristics of the JC constitutive equation,The modified constitutive equation narrowed the deviations greatly from the original experimental curves,This modification improved the fitting precision,and can be able to predict stress-strain relationship under higher strain rate.Finally,based on the finite element analysis software LS-DYNA,the correctness of material constitutive equation in the tensile test was verified through the establishment of uni-axial quasi-static and dynamic tensile models.Through numerical simulation different shapes and different aspect ratio of cross section were considered to the impact of crush buckling mode and strength load bearing of metal pipes.Enter the material constitutive equation curves at different strain rates in the rectangular tube crush model,comparison with experiment deformation mode and force-displacement curve that are fitting very well,the modified constitutive equations are verified available to the engineering practice... |
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