Dynamical Compression Experiment And Dynamical Constitutive Law Of High Nitrogen Steel

The dynamical performance of material is one of the most active direction in the mechanical performances researches,and researching the dynamical performances of materials has important means in the mechanical researches.For military and civilian design of new materials,these researches have practical applications of significance and scientific values.The alloy steels are named High Nitrogen Steels(HNS) if the nitrogen element percent in the ferrites is above 0.08%or the nitrogen percent is more than 0.4%in the austenite.The nitrogen element can endow the High Nitrogen alloy Steel many excellent performances by the interactive action with the other elements(Mn,Cr,V,Nb,Ti etc):such as high intensity,good toughness and plasticity,large creep resisting force,good corrosion resistance and so on.These performances make High Nitrogen Steel as a perfect armor and armor-piercing bullet material.Thus,researching the dynamical performances and the dynamical constitutive equations of High Nitrogen Steel will have profound scientific significance.In this paper,practicing the dynamical compression experiments on the High Nitrogen Steel made by two different technology processes by using the method of experimental test associated with theoretical analysis and numerical simulation, and then we could get their dynamical stress-strain relationship.These achievements were basic to research the dynamical performances and dynamical constitutive law of High Nitrogen Steels.Dynamical compression experiments to the High Nitrogen Steel made by two different technologies processes -air-cooling and water-cooling,have been done by the split Hopkinson pressure bar(SHPB) technique.During these experiments, we could get a lot of exact data,then obtained the stress-stain relation curves and the dynamical compress yield strengths in different strain-rates of the both specimens.The results showed that for High Nitrogen Steel made by two different technology processes,the dynamical stress-strain relations had obvious rate-relevance,and the strain-rate effect of dynamical compression yield strengths was weak,but the strain-rate effect of strain hardening was obvious.Described the dynamical mechanical behaviors of the High Nitrogen Steel made by two different technology processes with the Johnson-Cook constitutive models,and determined the parameters in the Johnson-Cook constitutive models by fitting the experimental results.The fitted Johnson-Cook curves were well inosculated with the stress-strain curves obtained from the dynamical compression experiments on High Nitrogen Steel,and the fitting processes were finished by Origin 7.0 software.In this paper,finite element simulations to the two kinds of High Nitrogen Steel materials had been done by using the large general-purpose finite element software:ANSYS/LS-DYNA.The parameters of Johnson-Cook constitutive model were obtained by fitting the experiment data.At the end of the finite element simulation,we got the deformation of the specimens,and also obtained the stress-strain relation curves of the specimens from treating the simulated data by the calculating procedure of the Hopkinson pressure bar.These curves of simulation results showed that they were well inosculated with the curves obtained by the dynamical compression experiments.Compared the ballistic limit velocity V₅₀(simulating the average-target velocity of the fragments or special bullet when the transmission probability was 50%) of the High Nitrogen Steel material with the V₅₀ of the 603 armored steel, and also set up the finite elements models of high-speed projectile penetrating the High Nitrogen Steel target and 603 armored steel target,simulated the armor penetration abilities of the High Nitrogen Steel and 603 armored steel.603 armored steel was widely used at current.Both of the constitutive models of bullet and target were Johnson-Cook constitutive models during the simulation process. The result showed that the V₅₀ and the armor penetration ability of High Nitrogen Steel was better than that of the 603 armored steel.