This paper presents a novel baseline-free online method for fatigue crack detection and growth modelling of aluminium plates based on the relative second harmonic parameter β′ˆ, which is defined as the ratio of the amplitude of the fundamental frequency A1 over the square of the second harmonic frequency A2, obtained from the response under cyclic fatigue loading. Results reveal that β′ˆ is an effective parameter for online detecting the crack length less than 2 mm and estimating the remaining life, without requiring a baseline signal obtained from the pristine condition. Subsequently, the quantitative relationship between Fatigue crack growth (FCG) and the parameter β′ˆ is developed based on the quadratic polynomial fitting. The reliability of the method is assessed with the Root Mean Square Error (RMSE) and 95% confidence interval. Finally, the robustness of the proposed approach is evaluated by testing specimens with different sensor locations, thereby mitigating the potential sources of uncertainty arising from sensor locations. Results from this research provide a new strategy for online crack detection and growth modelling under fluctuations in loading and boundary conditions.

中文翻译：

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通过高次谐波分析进行在线疲劳裂纹检测和增长建模：一种无基线的方法


本文提出了一种基于相对二次谐波参数 β′ˆ 的铝板疲劳裂纹检测和增长建模的新型无基线在线方法，该参数定义为基频 A1 的振幅与二次谐波频率 A2 的平方之比，从循环疲劳载荷下的响应获得。结果表明，β′ˆ 是在线检测小于 2 mm 的裂纹长度并估计剩余寿命的有效参数，而无需从原始条件获得基线信号。随后，基于二次多项式拟合建立了疲劳裂纹扩展 （FCG） 与参数 β′ˆ 之间的定量关系。该方法的可靠性通过均方根误差 （RMSE） 和 95% 置信区间进行评估。最后，通过测试具有不同传感器位置的样品来评估所提出的方法的鲁棒性，从而减轻传感器位置引起的潜在不确定性来源。这项研究的结果为载荷和边界条件波动下的在线裂纹检测和增长建模提供了一种新策略。