Dynamic Constitutive Model of Stainless Steel Fe-Cr-Ni Based on Isothermal True Stress-Strain Curves

Abstract

Austenitic stainless steel Fe-Cr-Ni is widely used in aviation, chemistry, energy, due to its excellent properties of high-temperature performance. In this study, the splitting Hopkinson pressure bar with high-temperature system was employed to evaluate the dynamic mechanical properties of stainless steel Fe-Cr-Ni. The true stress-strain curves were obtained under varying conditions, including variable strains, strain rates and temperatures. The true stress increases and levels off as the true strain increases, while increases as the strain rate increases, but decreases sharply as the deformation temperature rises. The deformation temperature is consist of healing temperature and adiabatic temperature. The adiabatic temperature rise related to the specific heat capacity was calculated. The actual deformation temperatures were calculated under different strains by combining the true stress-strain curves. The true stress-strain curve under variable temperature was corrected to the stress-strain curve under isothermal state by using the thermal softening rate, which decoupled the strain and temperature. The Power-Law and Johnson-Cook constitutive models were fitted based on the real stress-strain isothermal curve. The fitting accuracy of Power-Law model was 1.61% for different strain rates at room temperature in average, 3.51% for fixed strain rate at different temperatures. While the fitting accuracy of Johnson-Cook model was 2.94% for different strain rates at room temperature in average, 6.18% for fixed strain rate at different temperatures.奥氏体不锈钢Fe-Cr-Ni因其优异的高温性能而广泛应用于航空、化工、能源等领域。本研究采用高温系统劈裂霍普金森压力棒对不锈钢Fe-Cr-Ni的动态力学性能进行了评价。真实的应力-应变曲线是在不同条件下获得的，包括可变的应变、应变速率和温度。真实应力随着真实应变的增加而增加并趋于平稳，而随着应变速率的增加而增加，但随着变形温度的升高而急剧降低。变形温度由愈合温度和绝热温度组成。计算了与比热容相关的绝热温升。通过结合真实应力-应变曲线计算了不同应变下的实际变形温度。利用热软化速率将变温下的真实应力-应变曲线修正为等温状态下的应力-应变曲线，使应变与温度解耦。基于真实应力-应变等温曲线拟合幂律模型和Johnson-Cook本构模型。幂律模型在室温下对不同应变速率的拟合精度平均为1.61%，对不同温度下的固定应变速率的拟合精度为3.51%。Johnson-Cook模型在室温下不同应变率的拟合精度平均为2.94%，不同温度下固定应变率的拟合精度为6.18%。

Keywords: Split Hopkinson pressure bar, Dynamic mechanical properties, Temperature-dependent specific heat capacity, Adiabatic temperature rise, Isothermal stress-strain curve, Constitutive models