Damage Localization in a CFRP Beam via Modal Frequency Shifts and Nearest Neighbor Classification

Vibration-Based Structural Health Monitoring (SHM) systems offer significant potential for damage detection due to their non-destructive nature and real-time capabilities, while reducing maintenance costs for aerospace and automotive applications. This study investigates the effect of damage on the modal parameters of a Carbon Fiber Reinforced Polymer (CFRP) fixed-free beam, with the goal of identifying damage location and severity. The lamina material properties of the CFRP were evaluated using composite lamination theory (CLT). By altering the location and depth of the damage, numerical analyses were conducted on the CFRP beam, and discrepancies between the intact and damaged models were examined. Modal frequency shifts were quantified using Relative Natural Frequency Change (RNFC), and RNFC-based mapping surfaces dependent on damage location and severity were generated for first four transverse vibrational modes of the beam. The model was validated through experiments on the intact and damaged CFRP specimens. The beam was excited with an impact hammer near the fixed-end, and responses were collected by piezoelectric sensors placed along the beam and laser vibrometer focused on the free end of the beam. The modal parameters were extracted using Ho-Kalman’s subspace method and experimental RNFC results of damaged samples were calculated. Then Nearest Neighbor search algorithm was successfully employed to estimate the damage location and severity by comparing experimental results to generated RNFC-based mapping surfaces.