The fracture properties of a high-strength steel with a body-centered cubic (bcc) crystal structure have been characterized at –196 °C by performing tensile tests with different specimen geometries, three-point bending tests using Charpy specimens, and fracture mechanics tests, covering a broad range of stress states under quasi-static conditions. Both strength and ductility of the bcc steel are significantly increased when the temperature is decreased from room temperature to –196 °C. Enormous plasticity occurs in the material during tensile tests using various specimens at –196 °C, while macroscopic brittle fracture takes place in high triaxiality scenarios. A stress state dependence of ductile to brittle transition properties is observed, as the failure mechanisms at –196 °C change from cleavage fracture to shear failure with decreasing stress triaxiality. A unified stress-state-dependent fracture criterion, which considers the transition of failure mechanisms, is proposed to describe the fracture properties of similar bcc materials at cryogenic temperatures. The threshold triaxiality at which the transition of failure mechanisms takes place is a material property that is determined by the strain hardening capacity and fracture strength. In addition, a probabilistic formulation relying on the extreme value distribution has been incorporated into the model to render the statistical nature of cleavage fracture.

具有体心立方 (bcc) 晶体结构的高强度钢的断裂特性已在 –196 °C 下通过对不同试样几何形状的拉伸试验、使用夏比试样的三点弯曲试验和断裂力学试验进行表征，涵盖准静态条件下的广泛应力状态。当温度从室温降至 –196 °C 时，bcc 钢的强度和延展性均显着提高。在 –196 °C 下使用各种试样进行拉伸试验时，材料会发生巨大的塑性，而宏观脆性断裂则发生在高三轴性情况下。观察到韧性到脆性转变特性的应力状态依赖性，随着应力三轴性的降低，–196 °C 下的失效机制从解理断裂转变为剪切失效。提出了一种统一的应力状态相关断裂准则，该准则考虑了失效机制的转变，以描述类似体心立方材料在低温下的断裂特性。发生失效机制转变的阈值三轴性是由应变硬化能力和断裂强度决定的材料特性。此外，模型中还加入了依赖于极值分布的概率公式，以呈现解理断裂的统计性质。提出来描述类似体心立方材料在低温下的断裂特性。发生失效机制转变的阈值三轴性是由应变硬化能力和断裂强度决定的材料特性。此外，模型中还加入了依赖于极值分布的概率公式，以呈现解理断裂的统计性质。提出来描述类似体心立方材料在低温下的断裂特性。发生失效机制转变的阈值三轴性是由应变硬化能力和断裂强度决定的材料特性。此外，模型中还加入了依赖于极值分布的概率公式，以呈现解理断裂的统计性质。