In aero-engine, blades operate under harsh conditions for extended periods, which makes them highly susceptible to fatigue cracks. The localized and nonlinear structural changes caused by blade crack lead to complex vibration characteristics that are not well understood, posing challenges to the identification of these cracks. This paper proposes an approach for identifying breathing fatigue crack in compressor blade, leveraging the nonlinear features induced by the cracks. Crucial sensitive characteristics are extracted and a crack indicator for accurate crack detection is defined. Initially addressing the typical morphology of fatigue breathing cracks, a dynamic model of blade with cracks is developed to analyze their impact on the natural frequencies. Nonlinear contact forces are introduced to characterize the "breathing" effect of the fatigue crack, allowing for the determination of the harmonic distribution patterns in the blade's vibration response under various excitation conditions. A finite element model is then established considering the crack morphology, by adopting the contact element. Based on that, the nonlinear response characteristics associated with the blade's primary, sub-harmonic, and super-harmonic resonances are explored. A crack-sensitive parameter is defined and extracted from the nonlinear responses, under different crack propagation stages. At last, effectiveness and reliability of the defined parameter for identifying cracks is validated through a vibration fatigue test.

中文翻译：

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一种带呼吸疲劳裂纹的叶片非线性振动特性及损伤检测方法


在航空发动机中，叶片在恶劣条件下长时间运行，这使得它们极易受到疲劳裂纹的影响。叶片裂纹引起的局部非线性结构变化导致复杂的振动特性尚不清楚，对这些裂纹的识别提出了挑战。本文提出了一种利用裂纹引起的非线性特征识别压缩机叶片呼吸疲劳裂纹的方法。提取关键的敏感特性，并定义用于准确检测裂纹的裂纹指示器。首先解决疲劳呼吸裂纹的典型形态，开发了带裂纹的叶片动力学模型来分析它们对固有频率的影响。引入非线性接触力来表征疲劳裂纹的“呼吸”效应，从而可以确定叶片在各种激励条件下振动响应中的谐波分布模式。然后，通过采用接触元件建立考虑裂纹形貌的有限元模型。在此基础上，探讨了与叶片的初级、次谐波和超谐波谐振相关的非线性响应特性。在不同的裂纹扩展阶段，定义并从非线性响应中提取裂纹敏感参数。最后，通过振动疲劳试验验证了用于识别裂纹的定义参数的有效性和可靠性。