The dual Fourier transform spectra (DFTS): a new nonlinear damage indicator for identification of breathing cracks in beam-like structures

Fatigue damage is a common type of structural damage associated with long-term cyclic loading operating on engineering structures. Within the fatigue damage phenomenon, the breathing cracks are basic and widely occurred forms of fatigue damage in structures. Therefore, the identification and assessment of breathing cracks are very crucial. Some damage identification methods to assess the breathing cracks are available, but they have a common limitation is that they focus on detection of the breathing crack, but they cannot characterize its severity. Hence, the characterization of breathing cracks by creating robust nonlinear damage indicators, that can accurately quantify the degree of nonlinearity of breathing cracks, is of great significance. To this end, a robust nonlinear damage factor is developed by effectively utilizing the Fourier transform in a multi-stage manner. The procedure of creating this factor involves two steps of progressive use of fast Fourier transform (FFT): (i) damage detection, where the secondary peaks of the Fourier spectrum indicate the presence of breathing cracks and imply the dynamic inner interactions of them, and (ii) damage quantification, where the FFT of the Fourier spectrum is implemented and the resulted features that can quantitatively depict the degree of nonlinearity of breathing cracks are utilized. The new method is called the dual Fourier transform spectra (DFTS), where the FFT of the Fourier spectrum is defined as a robust nonlinear damage factor for breathing crack assessment in beam-like structures. Various single and multiple damage scenarios are studied numerically and experimentally after considering noisy conditions. The proposed method demonstrates outstanding performance and can be recommended for damage detection and quantification of fatigue-breathing cracks in beam-like structures.

Automated summary

This paper discusses the importance of identifying and assessing breathing cracks in fatigue damage, and proposes a robust nonlinear damage factor using Fourier transform. The method demonstrates outstanding performance through detection and quantification of damage, and is recommended for fatigue-breathing crack assessment in beam-like structures.