Local bispectral characteristics of nonlinear vibro-acoustic modulations for structural damage detection

Higher order spectral analysis is used for structural damage detection based on nonlinear vibroacoustic modulations. A combined low-frequency vibration and high-frequency ultrasonic excitation is used, leading to nonlinear vibro-acoustic modulated responses in the presence of structural damage. The response data are analysed using a modulation signal bispectrum and bicoherence. The analysis of local amplitude and phase of these characteristics is proposed for structural damage detection. The method is illustrated using numerical simulations and experimental data. The latter involves impact damage detection in composite plates. The results show that - in contrast to the classical higher order spectral analysis - the method identifies all nonlinear damage-related coupled components correctly, distinguishes these components from undesired non-damage related modulations, and therefore shows a potential for reliable structural damage detection.