Online fatigue crack detection and growth modelling through higher harmonic analysis: A baseline-free approach

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 A 1 over the square of the second harmonic frequency A 2 , 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.