Interface debonding detection of grouted connection based on Lamb wave energy leakage

Grouted connections (GCs) are transitional elements that have been extensively employed in offshore wind turbine support structure to transfer loads from superstructure to foundation. However, interface debonding defects between steel tube and grout layer have an adverse effect on the durability and fatigue resistance of the GC. An effective interface debonding defects detection approach for GC is necessary. In this study, interface debonding defects detection approach based on Lamb wave energy leakage was proposed and validated numerically and experimentally. Numerical studies on Lamb wave energy leakage models and the GC models were performed to study mechanism of detection approach. Lamb wave is excited on the surface, and stress wave fields and time-history response of models were extracted and compared. Experimental investigations were carried out to verify the applicability of the proposed approach in practice. A scaled GC specimen was constructed and Lamb wave was excited by the PZT patches mounted on the surface of GC specimen. The output voltage of surface-mounted PZT sensors under different axial loads were compared. Both numerical and experimental results show that the proposed approach is effective to the detection of interface debonding defects. The damage evolution index (DEI) based on wavelet packet energy is defined and it can be adopted to qualitatively determine the initiation and evolution of the damage.