Research On Dynamic Constitutive Relationship Of Q355B Steel Based On Johnson-cook Model

At present,the dynamic response of structures subjected to impact and blast loadings is usually examined by numerical methods as well as experiments.The validity of the numerical simulation relies on the accuracy of the dynamic constitutive model and the corresponding parameters.To obtain the mechanical response of the structure under action of impact more accurately,besides the character of the strain hardening,the influences of the high strain rate,high temperature,large strain,changes of stress state,and load history should be taken into account appropriately.Based on the specification of “High strength low alloy structural steels”(GB/ T1591-2018),Q345 steel is replaced by Q355 steel.It is expected that Q355 steel would be widely exploited in buildings from February 2019;however,the dynamic constitutive relationship of the Q355 steel has been rarely explored.In this paper,the parameters of the Q355 B steel are going to be tested by using the Johnson-Cook(J-C)model,the commonly employed model for impact and blast loading.It is found that the behavior of the temperature softening of the Q355 B steel cannot be appropriately predicted by the J-C model,and thereby,the modified J-C(MJ-C)model is proposed.The validity of the newly proposed model is then successfully checked by Taylor impact tests as well as numerical simulations,which provided a foundation for research works on shock-resistance of building structures.The research contents of this paper are organized as follows:1.Conducting tests for calibration of the J-C model pertinent to the Q355 B steelIn order to calibrate the parameters of the J-C model,experimental tests are performed to capture properties of the material.The stress-strain curve,yield strength,and fracture strain of the Q355 B steel under different temperatures,stress triaxiality conditions,and strain rates are extracted by conducting tensile tests,torsional tests,and Split-Hopkinson Pressure Bar(SHPB)tests.2.Calibration and modification of the J-C model parameters for the Q355 B steelThe constitutive J-C model as well as the parameters of the failure criterion are calibrated based on the test data and the numerical simulation.It is revealed that the relationship between the strength,fracture strain,and temperature of the Q355 B steel cannot be described properly by the common J-C model.To conquer this problem,the temperature item of the J-C model is modified.To this end,the corrected J-C model,namely MJ-C model,is proposed and its corresponding twelve parameters are obtained.3.Verification of the MJ-C model for the Q355 B steel according to Taylor impact testTaylor impact tests are conducted to investigate the fracture behavior of the rigid Q355 B plates under the impact of bullets.Subsequently,a numerical model of the Taylor impact test is developed on the basis of the MJ-C model.The accuracy of the MJ-C model is also verified by comparing the predicted projectile's deformation as well as the fracture behavior of the MJ-C model and those of tests.