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采用圆柱形拉伸试样，在不同预剪应变状态和低温条件下，研究了２０钢破坏过程的宏观力学行为和细观机理。揭示了材料的断裂韧度参数一临界空穴扩张比宏观参数ＶＧＣ及其细观参数Ｒｃ／Ｒｏ随预剪应变或低温的变化规律；提出了一种确定空穴扩张比（ＶＧ）破坏理论适用范围的方法。文中还基于扫描电镜（ＳＥＭ）观察分析，讨论了由温度和预剪应变引起的两类韧脆转变过程的细观机制。
The macroscopic mechanical behavior and meso-mechanism of 20 steel failure process were studied under different pre-shear strain and low temperature conditions by using cylindrical tensile specimens. The variation law of fracture toughness parameters critical brittleness expansion ratio (VGC) and its mesoscopic parameters (Rc / Ro) with pre-shearing strain or low-temperature is revealed. A method to determine the valence of void growth (VG) The scope of the method. Based on the observation and analysis of SEM, the meso-mechanism of two types of ductile-brittle transitions caused by temperature and pre-shear strain is also discussed.