高应变率下GH4720Li合金热压缩性能研究

Study on hot compression properties of GH4720Li alloy at a high strain rate

为了研究镍基高温合金GH4720Li在高应变率下的动态力学性能,利用分离式霍普金森压杆(SHPB)对材料进行了温度范围为20~1000℃,应变率为10~5000 s^(-1)的单轴热压缩试验,获得了不同温度不同应变率下材料的应力应变曲线。结果表明:在相同的试验温度条件下,GH4720Li合金在高、低2种应变率条件下表现出了不同的动态力学性能。在低应变率(10 s^(-1))条件下,GH4720Li合金的应力值随着温度的升高而降低;在高应变率(1000 s^(-1),5000 s^(-1))条件下,GH4720Li合金的应力值在特定温度(400~800℃)随着温度的升高而升高。结合已获得的试验数据,通过数值拟合的方法对原始Johnson-Cook(J-C)本构方程进行了修正,以满足GH4720Li合金在高应变率下应力的变化规律。通过线性相关系数和平均误差对修正的J-C本构方程精度进行了验证。结果显示:修正的J-C本构方程与试验数据吻合良好,可以大幅度提高J-C本构方程对GH4720Li合金在大应变率范围下的拟合精度。

In order to study the dynamic mechanical properties of nickel base superalloy GH4720Li at a high strain rate,this paper carries out uniaxial thermal compression tests to the materials with a Split Hopkinson Pressure Bar(SHPB)in a temperature range of 20℃to 1000℃and a strain rate range of 10 s^(-1) to 5000 s^(-1).The stress-strain curves of the materials at different temperatures and different strain rates are obtained.The results show that under the same test temperature,GH4720Li alloy shows different dynamic mechanical properties at a high and a low strain rates.At a low strain rate(10 s^(-1)),the stress value of GH4720Li alloy decreases with the increase of temperature.Under the condition of a high strain rate(1000 s^(-1) or 5000 s^(-1)),the stress value of GH4720Li alloy increases with the increase of temperature in a specific temperature range(400℃to 800℃).Combined with the obtained test data,the original Johnson-Cook(J-C)constitutive equation is modified by the numerical fitting method to meet the stress variation law of GH4720Li alloy at a high strain rate.The accuracy of the modified J-C constitutive equation is verified by linear correlation coefficient and mean error.The results show that the modified J-C constitutive equation is in good agreement with the experimental data,which can greatly improve the fitting accuracy of the J-C constitutive equation to the GH4720Li alloy in a large range of strain rates.