Structural damage detection based on nonlinear vibro-acoustic modulations observed in shear horizontal wave propagation

Recent years have brought more attention to new damage detection approaches based on nonlinear phenomena associated with Shear Horizontal (SH) waves. Many nonlinear effects - previously observed in ultrasonic wave propagation - have been considered for structural damage detection. The major effort has been put on classical nonlinear effects, such as higher harmonic generation. More recently, nonlinear vibro-acoustic modulation and modulation transfer mechanisms have been also observed in SH wave propagation. However, these phenomena have not been used for structural damage detection. The paper attempts to fulfill this gap. The proposed method involves two excitation waves. The low-frequency pumping wave is used for damage perturbation. In addition, high-frequency SH wave is used as a probing wave. The probing wave is modulated by the pumping wave in the presence of structural damage. The method is used in the paper for fatigue crack detection in metallic structural components. The results demonstrate that the proposed approach has a potential for structural damage detection. Previous research work demonstrates that classical nonlinear effects (e.g., higher harmonic generation) observed in SH waves offer better sensitivity to material microdefects than similar effects observed in longitudinal wave propagation. Therefore, it is anticipated that non-classical nonlinear affects associated with SH wave propagation will show similar potential. However, more research work is needed to confirm this assumption.