Table 6: Modal frequencies identified by PP, FDD, and SSI (, ) methods from experimental specimens under random excitation.

— — 1st bending 2nd bending 1st bending/torsion 3rd bending   PP (Hz) 31.60 68.88 84.66 165.95 Undamaged FDD (Hz) 31.77 68.03 83.04 166.08   SSI (Hz) 31.61 67.62 82.60 166.37   PP (Hz) 26.69 51.00 — 92.07 22.2% delaminated FDD (Hz) 27.01 50.77 — 91.79   SSI (Hz) 26.83 50.67 — 91.74   PP (Hz) 27.60 55.94 — 96.79 51.9% delaminated FDD (Hz) 27.51 54.53 — 96.80   SSI (Hz) 27.56 55.52 — 96.94   PP (Hz) 24.41 44.69 — 84.38 74.1% delaminated FDD (Hz) 24.01 44.77 — 84.54   SSI (Hz) 24.31 44.37 — 84.63