Experimental Research On Constitutive Model And Failure Model Of 316LN Stainless Steel

In order to cope with the increasingly severe energy crisis and the pressure of carbon emissions closely related to global climate change,China is actively exploring clean energy to replace traditional fossil fuels.Among them,nuclear energy,as a nearly zero emission clean energy,has become the main object of China’s vigorous development.At present,China’s nuclear energy utilization technology is mainly the third generation pressurized water reactor technology.In the third generation PWR technology,the main material of piping system is 316 LN austenitic stainless steel.The impact resistance of nuclear power system is an important index to evaluate system safety.At present,the response spectrum method is used in the impact analysis of nuclear grade pipeline,and the elastic evaluation method of seismic analysis of nuclear grade pipeline is used for reference.Different from seismic loading,the failure of materials under impact loading is affected by large deformation,strain rate effect,stress state and loading history,which makes the characterization of mechanical properties of materials very complex.Therefore,the primary task of this project is to determine the mechanical properties of 316 LN stainless steel under impact load,obtain its constitutive relationship and failure model,and simulate and predict the deformation behavior of simple stainless steel components under impact load according to the obtained constitutive relationship.(1)The static experiment is designed and implemented.In order to determine the strain hardening effect of 316 LN austenitic stainless steel and the effect of temperature on its constitutive relation,quasi-static uniaxial tensile tests were carried out on round bar specimens at room temperature and high temperature.In the temperature phase experiment,seven temperature gradients were set from 150 ℃ to900 ℃.The experimental results of quasi-static tensile failure of round bar at room temperature and high temperature are applied to failure model fitting.At the same time,in order to determine the effect of stress triaxiality on material failure,tensile test of notched specimen,torsion test of round bar and compression test of cylindrical specimen are designed and implemented.The corresponding load displacement curves are obtained.Finally,the failure strains under different stress states are obtained.(2)A self-developed hydraulic pneumatic device was used to carry out the tensile test of 316 LN at medium strain rate at room temperature.The load displacement curves of 316 LN at strain rates of 10s-1 to 100s-1 were obtained by using force sensor and laser displacement meter.The dynamic mechanical properties of the material at the strain rate of 1000s-1 were obtained by dynamic tensile test with Hopkinson pull rod.The dynamic yield strength and failure strain of the material were obtained by the above medium and high strain rate experiments.(3)Taylor impact test was carried out with a light gas gun.The diameter of the gun barrel is 6 mm and the length diameter ratio of the projectile body is 4:1.In the experiment,it is necessary to change the impact velocity of the bullet hitting the rigid target in order to obtain the different deformation degree of the bullet at low speed and the different failure degree at higher speed.(4)According to the obtained data,the MJC constitutive model of 316 LN austenitic stainless steel was fitted.The fracture strain is obtained by the combination of actual measurement and simulation,and the MJC failure model of the material is fitted.The Taylor impact process was simulated by the obtained material constitutive and failure models.Based on the above experimental study,the following conclusions are obtained:The strain strengthening effect of 316 LN austenitic stainless steel is significant,and the strengthening coefficient n is 0.74;There is strain rate strengthening effect;Before 450 ℃,the yield strength of the material decreases obviously.316LN is a typical ductile material with high failure strain;With the increase of stress triaxiality,the failure strain decreases;The failure strain of the material in shear is smaller than that in uniaxial tension;The strain rate has little effect on the failure strain;Before 750 ℃,the temperature has little effect on the failure strain.When the temperature reaches 900 ℃,the failure strain rises sharply.Due to the significant strain strengthening effect of the material,the deformation area of Taylor impact bar is longer,and the shear strength of the material is lower,and the failure mode of the specimen is close to shear failure.