Comparison of modal frequencies
Very little change in first four modal frequencies is noticed in healthy and Delam Type-I specimen. This trend is totally different from the earlier two cases. It seems that due to sufficient stiffness in both the planer directions, the cross ply laminate shows little drop in frequency. The comparisons of modal frequencies are shown in Table 40.1.
Table 40.1 Summary of modal parameters for [0/90] cross ply laminate
| S.No. |
Property |
Damage Type |
Modal shapes |
B1 |
T1 |
B2 |
B02 |
1 |
Modal frequency, Hz |
Healthy |
27.5 |
63.8 |
143.8 |
278.8 |
Delam type-I |
27.5 |
61.3 |
146.3 |
277.5 |
2 |
Modal
Damping, % |
Healthy |
12.59 |
1.881 |
6.849 |
3.061 |
Delam type-I |
12.31 |
2.350 |
6.413 |
3.037 |
3 |
Displacement, µm |
Healthy |
6.403 |
1.023 |
0.745 |
0.329 |
Delam type-I |
6.362 |
1.354 |
0.753 |
0.351 |
4 |
Velocity, µm/s |
Healthy |
1106.4 |
400.6 |
673.1 |
576.3 |
Delam type-I |
1099.4 |
521.1 |
691.9 |
617.5 |
Comparison of modal damping
The damping values for the representative modes B1, B2, B02 and T1 listed in Table 40.2. There is hardly any change in modal damping in delaminated specimen in comparison to the healthy laminates. The modal damping values are 12.59 per cent and 12.39 per cent for the healthy and the delaminated specimens.
Comparison of displacement and velocity from frequency response plots
Magnitude of displacement and velocity values for the representative modes are obtained from the frequency response plots and are listed in Table 40.2. The displacements and velocity values for healthy and delaminated specimens show very little variation suggesting the modal parameters are marginally affected by these delaminations. The complete summary of changes in modal parameters for cross ply is presented in Table 40.2.
|
