PSI - Issue 80

Yuhang Pan et al. / Procedia Structural Integrity 80 (2026) 43–52

46

4

YuhangPan / Structural Integrity Procedia 00 (2023) 000–000

Fig. 1: The experimental platform for online fatigue crack monitoring: (a) experimental fatigue setup; (b) specimen geometry and sensor layout; (c) data acquisition hardware; (d) photograph captured with a Canon 5D camera; (e) di ff erent stages of the fatigue test—Stage I: no crack; Stage II: 5.8 mm crack; Stage III: failure.

Fig. 2: The framework of the proposed method in this work.

4.1. Feature extraction

The signal obtained from fatigue loading is analyzed in both the time domain and the frequency domain. A comparative study was performed on pristine and fatigue-cracked specimens to investigate the changes in the time and frequency domains of the responses before and after cracking. The results are summarized in Fig. 3. Fig. 3 presents the variations in the time-domain and frequency-domain responses before and after fatigue crack initiation. As shown in Fig. 3(a), the 1 s time-domain signals reveal an overall reduction in response amplitude following crack initiation. Consistent with the feature selection strategy illustrated in Fig. 2, the RMS value was employed to quantify changes in the time-domain response. The RMS decreased from 7.29 (without crack) to 6.75 (with crack), corresponding to a reduction of approximately 7.4%. In the frequency domain (Fig. 3(b)), the amplitude of the fundamental frequency exhibited a reduction of 7.41% after crack initiation, while the second harmonic amplitude decreased by 26.9%. In contrast, the third harmonic am plitude increased by 8.34%. These observations indicate that fatigue crack not only attenuates the primary response but also induces distinct nonlinear spectral changes, particularly a pronounced reduction in the second harmonic component and an increase in the third harmonic component.