高应变率条件下38CrMoAl钢的动态力学行为及失效模型

38CrMoAl钢是飞机某频繁经受冲击载荷结构的主要材料，为了获得该钢在冲击载荷下的力学行为和失效参数，本文对38CrMoAl钢开展了准静态试验、应变率从650 s^-1至5 500 s^-1的动态力学试验以及应力三轴度试验，对材料的金相组织和断口形貌进行了微观观察分析，最后基于试验结果确定了材料的修正强度模型和失效模型参数。试验结果表明，38CrMoAl钢具有较强的应变率敏感性，材料屈服强度随着应变率的增加具有正应变率强化效应，应变率在10^-3~5 500 s^-1的范围变化时，屈服应力从450 MPa上升到了1 085 MPa，应变率为5 500 s^-1时材料的屈服应力达到了准静态条件下的2.41倍。对材料组织的微观观察分析发现材料主要由呈现颗粒状的回火索氏体组成，材料在高应变速率加载下其塑性发生了下降，断口由韧窝型塑性断口向局部解理断面发生转变，韧窝尺寸也随着应变率的升高而变小。对Johnson-Cook（J-C）强度模型中的应变率强化项进行了修正，使修正后的本构模型可以更有效地描述38CrMoAl钢的动态力学行为，最后结合数值模拟方法确定了材料的J-C失效准则参数。

Dynamic mechanical behavior and failure model of 38CrMoAl steel under high strain rate

38CrMoAl steel is the main material of an aircraft structure frequently subjected to impact loads. To obtain the mechanical behavior and failure parameters of the steel under impact loads, a quasi-static test, a dynamic mechanical test of strain rates from 650 s^-1 to 5 500 s^-1 and a stress triaxiality test were conducted on 38CrMoAl steel. The microstructure and fracture morphology of the material were microscopically observed and analyzed. Finally, the modified strength model and failure model parameters of the material were determined based on the test results. The test results show that 38CrMoAl steel has strong strain rate sensitivity. The yield strength of the material has a positive strain rate strengthening effect as the strain rate increases. When the strain rate changes from 10^-3 s^-1 to 5 500 s^-1, the yield stress rises from 450 MPa to 1 085 MPa. When the strain rate is 5 500 s^-1, the yield stress of the material reaches 2.41 times that under quasi-static conditions. The microscopic observation and analysis of the material structure disclosed that the material is mainly composed of grained tempered sorbite, the plasticity of the material decreases under high strain rate loading, and the fracture is transformed from a plastic dimple-type fracture to a local cleavage one. The litter size also decreases with the increasing strain rate. The strain rate strengthening term in the Johnson-Cook (J-C) strength model was modified to enable the modified constitutive model to more effectively describe the dynamic mechanical behavior of 38CrMoAl steel. Finally the J-C failure criterion parameters of the material were determined.