Aging condition identification of viscoelastic sandwich structure based on empirical wavelet transform and Hilbert envelope demodulation

Viscoelastic sandwich structures (VSSs) have been widely used in mechanical equipment. The aging condition monitoring of VSSs is essential for fault prevention of mechanical equipment. However, the ageing condition identification of VSS is still a challenging task since the change of structural response caused by the ageing of viscoelastic sandwich structure (VSS) is very puny. Therefore, a novel identification method based on empirical wavelet transform (EWT) and Hilbert envelope demodulation is proposed for the ageing condition identification of VSS. First, EWT is constructed to decompose the vibration response signals of VSS into a set of sub-band signals, so that the aging condition feature components are allocated in a certain frequency band. Second, the sub-band signals that contain rich aging condition information are selected and used to reconstruct a new signal. Thirdly, the reconstructed signal is analyzed with Hilbert envelope demodulation to obtain an envelope spectrum. Finally, the low band energy of envelope spectrum is calculated as detection index to identify the aging condition of VSS. The proposed method is verified with a well-designed VSS in which the viscoelastic core subjected to accelerated ageing in a thermal-oxygen ambient. The results show the outstanding performance of the proposed method.