42CrMo钢属于中碳高强度合金钢，作为高速列车车轴等构件的原材料，是负担列车质量的关键部件。在运行中承受冲击和旋转弯曲等多项复杂应力以及恶劣的工作环境。作为列车运行至关重要的部件，车轴材料除了考虑承受正常的设计载荷外，在当前形势下更需要考虑冲击载荷的作用。
本文包括采用RPL100设备完成材料的准静态压缩实验；采用MTS-858微力拉扭试验机完成材料的准静态拉伸实验；采用分离式霍普金森压杆设备（SHPB）完成材料的冲击压缩实验；采用分离式霍普金森拉杆设备（SHTB）完成材料的冲击拉伸实验；采用Zeiss Axio Scope. A1. 光镜完成42CrMo钢不同加载应变率下的微观组织观察实验。实验结果表明，42CrMo钢，作为典型的BCC金属材料，在宽应变率范围内具有典型的高应变率及温度敏感性，同时在冲击加载实验中，出现绝热剪切的变形机制，对材料塑性变形产生重要作用。
针对材料在冲击实验中显示的高应变率相关性，采用位错理论对42CrMo钢变形机理进行解释，并改进了Zerilli-Armstrong模型，引入绝热温升软化项，因为Zerilli-Armstrong模型本身在应变硬化率上的独立性，使得改进后模型，在表征材料应变硬化、温度软化以及应变率效应时可以很好的耦合。为了验证改进的Zerilli-Armstrong模型的合理性和适用性，分别采用不考虑绝热温升的Zerilli-Armstrong模型和引入考虑绝热温升这一不容忽视因素的Zerilli-Armstrong模型，参数优化后获得的理论曲线与冲击实验结果进行比较。得出改进的Zerilli-Armstrong模型，可以很好地描述及预测不同应变率下42CrMo钢的流动应力。
针对42CrMo钢材料显示出的典型BCC金属特性，采用热激活位错理论对材料塑性变形机理进行解释，认为造成准静态到动态力学性能不同的原因在于，不同的滑移系开动条件以及Peierls势垒的高率敏感性。对基于晶体塑性理论的本构模型进行了研究，结合BCC金属塑性变形机理，在剪切变形率演化中引入宏观应变率项，在硬化演化中引入绝热温升软化项。经验证，模型对模拟多晶下准静态实验结果体现出很好适应性，同时，模拟多晶下冲击实验结果也能很好体现应变率效应及热软化效应。
 

42CrMo steel is strong and tough and is mainly used for manufacturing axles and other components of high-speed trains; in addition, after the quenching and tempering process, it has a higher fatigue limit and resistance to repeated impact. Since axles are essential components, in addition to the consideration of normal design loads, the effect of impact loading needs to be considered more specifically. Therefore, studies on the mechanical properties of 42CrMo steel, especially dynamic mechanical properties, are receiving increased attention.
In this study, the quasi-static compression of 42CrMo steel at three different strain rates was studied by RPL100 and the quasi-static tension at three different strain rates was studied by MTS-858. Dynamic compression experiments at three different strain rates are using the split-Hopkinson pressure bar (SHPB) set-up and dynamic tension experiments at three different strain rates are using the split-Hopkinson tension bar (SHTB) set-up. metallographic observation was performed using Zeiss Axio Scope. A1. The results show that, 42CrMo steel, which belongs to typical BCC metal, has high sensitivity of strain rates and temperature under a wide range of strain rates. Particularly, adiabatic shear has been found to be prevalent in high-speed deformation and impact damage.
According to the dynamic experiments, a strain-rate effect is evident in the yield behavior and the strain hardening. The dislocation theory explains the deformation mechanism of 42CrMo steel. Furthermore, a new constitutive model, which includes the thermal softening effect, based on the Zerilli–Armstrong constitutive model, is proposed to describe the dynamic mechanical behavior of 42CrMo steel. The model results are in good agreement with the experimental data, demonstrating that the proposed constitutive model describes the mechanical behavior of 42CrMo steel at various strain rates very well.
Based on the typical properties of BCC metals and the experimental results, the thermal activation theory was used to explain the deformation mechanism of 42CrMo steel. In addition, the high temperature and strain-rate sensitivity of the Peierls stress are the main causes of the strain-rate and softening effects on the macroscopic properties of 42CrMo steel.A modified model based on the crystal plasticity theory is proposed to ac for the macroscopic strain rate of 42CrMo steel and the softening caused by adiabatic temperature rise. We verified that the model describes the quasi-static and dynamic mechanical behavior of 42CrMo steel very well, particularly the effects of strain hardening and thermal softening. The results of this study demonstrate that the new constitutive model can predict the deformation trends of 42CrMo steel well over a wide range of strain rates.
 

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