Comparison of the modal frequencies

A general decrease in modal frequencies is seen due to the presence of delaminations. Healthy ply has first modal frequency at 32.5 Hz. It decreases to 30.0 Hz for Delam Type-I and 27.5 Hz for Delam Type-II composite laminates. Similar decrease is observed in other three modal frequencies. These changes are shown in Figure 38.3 (a), (b) and (c) .

Figure 38.3 (a) Shift in natural frequencies corresponding to B1 and T1 modes due to delamination in 0^o plies

Figure 38.3 (b) Shift in natural frequencies corresponding to the B2 mode due to delamination in 0^o plies

Figure 38.3 (c) Shift in natural frequencies corresponding to the B22 mode due to delamination in 0^o plies

Four additional local modes are present in the Delam Type-I case at 887.5 Hz, 912.5 Hz, 992.5 Hz and 1325 Hz. These local modes seem to have been generated due to delamination as they are not seen in the healthy laminate. Similarly, six additional local modes are observed in Delam Type-II case at 976.3 Hz, 1442.5 Hz, 1577.5 Hz, 1592.5 Hz, 1806 Hz and 1892.5 Hz respectively.