We analyze the kinetic features and micromechanism of propagation of fatigue cracks in pseudoelastic nitinol alloy with shape-memory effect under the conditions of constant-amplitude cyclic loading with stress ratios R = 0.2 and 0.5. It is established that, independently of the parameter R, fatigue cracks grow by the quasicleavage mechanism, which is explained by the austenite-martensite deformation transformation at the crack tip. This also explains the fact that the maximal value of the stress intensity factor in a loading cycle (but not its range) is responsible for the kinetics of fracture observed as the stress ratio R changes.

中文翻译：

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伪弹性NiTi形状记忆合金中疲劳裂纹扩展的微观机制

我们在应力比为R = 0.2和0.5的恒定振幅循环载荷条件下，以形状记忆效应分析了拟弹性镍钛合金中疲劳裂纹扩展的动力学特征和微观机制。可以确定的是，与参数R无关的是，疲劳裂纹通过准断裂机理而扩展，这可以通过裂纹尖端的奥氏体-马氏体变形转变来解释。这也解释了这样一个事实，即在加载周期中应力强度因子的最大值（而不是其范围）是随应力比R变化而观察到的断裂动力学的原因。