Rate-dependent Mechanical Behaviors And Constitutive Relationships Of Five Main-body Materials Of Hybrid Ⅲ Dummy

As an important tool for the collision safety research of vehicles,the crash dummy can be used to simulate the damage suffered by human in collision accidents,and accurate material parameters of the dummy will determine the credibility and accuracy of the mechanical response of the dummy during the collision.Crash dummy（especially Hybrid Ⅲ dummy）have been gradually applied in high-speed train collision simulation analysis.However,research of the influence of material strain rate effect on the dynamic response of dummies structure in train collision condition is rare in the existing studies.At present,researches on mechanical properties of materials mostly focused on quasi-static and high strain rate,while little attention has been paid to medium strain rate range,but train structure collision process is mostly in medium strain rate deformation range.Therefore,the dynamic mechanical behavior and constitutive equation of five main-body materials of Hybrid Ⅲ dummy（6061-T6 aluminum alloy,30Cr Mn Si A alloy steel,polyethylene,styrene-butadiene rubber and polyurethane foam）under medium strain rate were studied in this thesis by adopting an experiment-based method which combines finite element simulation and theoretical analysis.The main research process and results are as follows:（1）The tensile mechanical properties experiment of 6061-T6 aluminum alloy at five strain rates(0.001 s^-1,0.1 s^-1,1 s^-1,10 s^-1,100 s^-1)was carried out,the effects of strain rate on its flow stress and fracture morphology were discussed,and the dynamic tensile constitutive relationship was established.Combined with the tensile test and numerical simulation of the notched sample,the influence of the stress triaxiality on its fracture strain was found and the Johnson-Cook failure model parameters were obtained.The results show that the fracture surface of 6061-T6 aluminum alloy specimens shows obvious dimple characteristics at different strain rates,and the fracture mechanism is ductile fracture.Its yield strength,flow stress and plastic deformation capacity increase when the strain rate increase,while the fracture strain decrease when the stress triaxiality increase.（2）The data of tensile stress-strain response relationship of 30Cr Mn Si A alloy steel under different strain rates was obtained.The strain hardening behavior and strain rate strengthening effect of the material were analyzed,and the rate-dependent dynamic constitutive model was established.And based on the uniaxial tensile finite element analysis under multiple working conditions,the influence of the sample geometry and boundary conditions（clamping state）on the tensile test results was discussed.The results show that both polyethylene and styrene-butadiene rubber exhibit obvious hyperelasticity characteristics,and their compressive stress and elastic modulus increase with the increase of strain rate.（3）The hyperelastic properties of polyethylene and styrene butadiene rubber under static and dynamic compression were analyzed,and the influence of strain rate on key parameters such as compression stress and elastic modulus of the two materials was discussed.And the rate-dependent hyper-viscoelastic constitutive model which took the hyperelastic and viscoelastic mechanical properties of materials into account was established.The results show that both polyethylene and styrene-butadiene rubber exhibit obvious hyperelasticity characteristics,and their compressive stress and elastic modulus increase with the increase of strain rate.（4）Based on the test results of dynamic compression mechanical properties of polyurethane foam under different strain rates,the three-stage characteristics of its stress-strain response relationship were analyzed,and the influence of strain rate on its compressive stress,densification strain and energy absorption performance was further revealed.And the rate-dependent constitutive relationship of polyurethane foam which took the three-stage stress-strain response characteristics into consideration was established.The results show that within the strain rate range studied in this thesis,the stress-strain response of the polyurethane foam shows obvious three-stage deformation characteristics,and with the increase of strain rate,the compression stress and maximum ideal energy absorption efficiency of polyurethane foam increase,while the compaction strain and maximum energy absorption efficiency decrease.In this thesis,an experimental study on the static and dynamic mechanical properties of five main-body materials of Hybrid Ⅲ dummy was carried out,the stress-strain response relationship of the material under different strain rates was obtained,and the mechanical response characteristics and rate correlation of material were discussed,and the dynamic constitutive relations of five main materials were established,which can provide real and reliable material parameters for the research and development of crash physical dummy and the establishment of its finite element model,which has important academic and engineering value.