Dynamic Constitutive And Fracture Failure Model Of 6008-T6 Material

Passive safety of trains is more and more valued.In order to provide more accurate material parameters and improve the accuracy of the collision simulation of trains,the dynamic mechanical properties tests under different strain rates and the dynamic fracture tests under different stress states was studied.The dynamic constitutive model and the fracture failure model of the 6008-T6 material suitable for engineering simulation were studied.Firstly,according to the dynamic mechanical property test method and the theory of strain field measurement technology,the test devices were selected and the dynamic tensile specimens were designed.The stress state of the specimen was described by triaxiality,and the fracture specimens with uniform stress distribution were designed,the dynamic mechanical properties and fracture test scheme were given,and the finite element models of 6008-T6 specimens were established according to the test boundary conditions,which was ready for the subsequent researchs.Then,the dynamic mechanical properties of 6008-T6 were studied,and the Johnson-cook and Cowper-Symonds dynamic constitutive models were established.Based on the analysis of the limitations of the classical dynamic constitutive models,a tabular interpolation method was proposed to describe the dynamic mechanical properties of 6008-T6 material,and the influence of strain rate effect of 6008-T6 material on the energy absorption characteristics of energy-absorbing structure on rail vehicles was studied.The results showed that 6008-T6 material has strain rate strengthening effect.The classic Johnson-cook and Cowper-Symonds models lose lots of dynamic test data,and the fitting accuracy is low.The tabular interpolation method can accurately describe the dynamic mechanical properties of 6008-T6 material.With the increase of impact velocity,the strain rate strengthening effect enlarges the impact force and energy absorption of the structure,the shock resistance of the structure is increased,the load history of the expansion energy absorption structure remains unchanged.The induced energy absorption structure can significantly reduce the initial peak force and make the deformation more stable and orderly.With the increase of impact velocity,the strain rate strengthening effect of 6008-T6 material is conducive to improving the energy absorption characteristics of the induced structure,and the influence of strain rate effect should be considered comprehensively in the design of energy-absorbing structure.Finally,the fracture tests under different strain rates and stress states of 6008-T6 material were carried out,and the GISSMO failure model of 6008-T6 material was established.The effect of strain rate on the fracture behavior of 6008-T6 material was studied.The results showed that the fracture behavior of 6008-T6 is different under different stress states,and the influence of stress states should be considered.It was verified by 0° shear test that the GISSMO failure model can accurately describe the fracture behavior of 6008-T6 material under various stress states.The fracture strain of 6008-T6 material decreases with the increase of strain rate.The sensitivity of fracture strain to strain rate is the highest under 0° shear stress.The sensitivity of fracture strain to strain rate decreases with the increase of strain rate.GISSMO failure model can reflect the dynamic failure characteristics of 6008-T6 material to a certain extent,but the influence of different stress states on dynamic fracture strain has not been considered comprehensively.Based on the research of the above two aspects,the mechanical behavior of 6008-T6 material in elastic-plastic stage and fracture failure stage under different strain rates was described,and the dynamic constitutive model and fracture failure model suitable for engineering simulation application were obtained.It can provide more accurate material parameters for the collision simulation calculation of the train and further improve the simulation accuracy of the train collision,which has guiding significance for the design of the train crashworthiness.