Dynamic Constitutive And Fracture Failure Model Of SUS301L-MT Material

In order to improve the passive safety of trains,the SUS301L-MT material commonly used in trains was studied.Tensile tests with different strain rates and quasi-static fracture failure tests with different stress states were carried out in sequence.The dynamic constitutive model and GISSMO fracture failure model of the material were established to provide relatively accurate material parameters for train collision simulation.The specific research content is:Firstly,according to the strain rate of the end deformation of the train,the strain rate range of the material dynamic tensile tests was determined.Based on this,the suitable test equipment was selected,and the size of the tensile specimen,stress and strain data acquisition method were determined.For the fracture failure tests,according to the concept of stress triaxiality and finite element simulation method,the fracture failure samples with uniform stress state were preliminarily designed,and the parameter identification method was determined according to the characteristics of the failure model,which was ready for subsequent experiments and data processing.Then,the dynamic and static tensile tests of SUS301L-MT material were carried out.The stress and strain of the material were obtained and the dynamic mechanical properties of the material were analyzed.The traditional dynamic constitutive model was established.Through the analysis of the limitations of the traditional constitutive model,the modified C-S constitutive model suitable for the material was proposed.From the theoretical and simulation aspects,the two interpolation methods of the DEFINE TABLE model included in LS-DYNA were deeply analyzed.The comparison of simulation and experimental was used to find the material model with higher simulation accuracy.The results showed that: SUS301L-MT material has obvious strain rate strengthening effect,but the strain rate strengthening effect is different under different plastic strain.As the plastic strain increases,the strengthening effect is weakened.The traditional J-C and C-S constitutive models have the problem of plastic strain selection when fitting parameters.If the plastic strain is different,the fitting parameters and effects are different.And neither model can describe the material properties of strain rate enhancement which decreases with increasing strain.Adding the correction coefficient term of the flow stress amplification factor based on the traditional C-S constitutive model can effectively improve the fitting effect of the traditional constitutive model.The simulation accuracy of the DEFINE TABLE model is higher,but the simulation results of the force-displacement curves with the linear-interpolation and log-linear interpolation are different.The SUS301L-MT material is more suitable for linear interpolation.Finally,the quasi-static fracture tests of SUS301L-MT material under different stress states were carried out.The corresponding fracture strain data were obtained.The characteristics of the GISSMO failure model were analyzed.The GISSMO failure model of the material was established and verified by 45° shear test.The limitations of the model application were analyzed..The results showed that: The fracture morphology and fracture strain of SUS301L-MT material under different stress states are different,and the influence of stress state on the fracture behavior of the material needs to be considered.The GISSMO failure model has high precision in describing the material failure behavior.In this paper,the understanding and setting of the GISSMO failure model are accurate in the simulation.Based on the experimental data,the combination of LS-OPT optimization and manual selection was used to find the parameters of GISSMO model suitable for different stress states.The fracture morphology and force-displacement curves of the finite element simulation results based on this model agree well with the experimental results.The comparison of the fracture morphology and the force-displacement curve of the 45° shear test showed that the GISSMO failure model accurately reflected the fracture failure characteristics of the material.The GISSMO failure model is currently only applicable to finite element models of high mesh mass and small mesh size,and cannot accurately reflect the effect of strain rate effect on fracture failure behavior,which is limited in simulation applications.Through the research of the above two aspects,the dynamic constitutive model and fracture failure model of SUS301L-MT material used in simulation were obtained.The dynamic constitutive model and fracture failure model can be applied simultaneously in structural collision simulation to express the dynamic behavior and failure behavior of the material.The comprehensive consideration of material collision characteristics can improve the accuracy of train collision simulation to some extent.