Ductile failure under ultra-low cycle fatigue (ULCF) loading is often the limit service state of a nuclear structure. In the paper, ULCF tests for a C-Mn-Si steel are carried out. It is observed that the fracture displacement decreases as the number of fatigue cycles increases. An energy-based model, which considers the effects of both stress triaxiality and cyclic loading on the critical fracture strain energy, is proposed. Coupled with the new model, finite element analyses of the round notched specimens can predict the equivalent plastic strain and the number of fatigue cycles to fracture within a scatter band of 1.5.

中文翻译：

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基于断裂应变能模型的超低周疲劳破坏研究

在超低周疲劳（ULCF）载荷下的延性失效通常是核结构的极限使用状态。在本文中，对C-Mn-Si钢进行了ULCF测试。观察到，随着疲劳循环次数的增加，断裂位移减小。提出了一种基于能量的模型，该模型考虑了应力三轴性和循环载荷对临界断裂应变能的影响。结合新模型，对圆形缺口样品的有限元分析可以预测等效塑性应变和在1.5的散射带内断裂的疲劳周期数。