Increased effort for light-weighting of automotive struc- tures results in replacement of traditional metals to com- posites. Adhesive bonding is the best joining solution for composite components owing to its superior stress dis- tribution and light-weighting. However, adhesive and adhesive-adhered interfaces are the weakest link in the structure. During fatigue crack propagation, joints do not show any significant visual changes. Thus, fatigue dam- age in adhesive bond line is one of the challenging and complex failure mechanisms that requires real-time diag- nostic and prognostic technique to avoid any catastrophic failure. This paper proposes an acoustic technique for real-time fatigue damage diagnosis and prognosis. Based on experimental guided wave modal analysis, symmetric mode at 85 kHz is found to be the most sensitive mode- frequency combination for fatigue monitoring of selected lap-joint specimen. Further, a hybrid data-driven damage propagation model is used to estimate the remaining use- ful life in the bond-line. The developed techniques were successfully implemented and validated on a single lap joint under fatigue loading. Estimated damage levels and remaining useful life are in good agreement with refer- ence measurements. Successful validation is an indicative of potential application of this technology in automotive industries.

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