Conclusions

• Experimental analysis of dynamic response of the composite plates with and without delamination has been carried out on composite plates with different ply orientations. Laser Doppler Vibrometer (LDV) is used for capturing the vibration signatures with the aim to detect delamination in composite plates. A standard finite element software package ABAQUS is used to determine modal frequencies for healthy composite plates of different orientations. The results of experimental modal analysis show good agreement with modal frequencies predicted in numerical analysis.
  
  Followings are the major conclusions from the experimental modal analysis:
  
• Presence of delamination causes changes in modal frequencies. A general decrease in modal frequencies is observed for all the laminates. This decrease is more prominent in the cases of delamination present in higher shear zone. Additional local modes are noticed at higher frequencies in all the delaminated composite plates suggesting change in vibration signatures in the presence of delaminations.
  
  
• Modal damping observes a general increase for all the modes in the presence of delamination. Damping is higher for delaminations present closer to the clamped end in comparison to one away from the fixed end. Delaminations present in the middle layer show greater damping characteristics in comparison to one in the outer layers. It has been observed that in some cases though the decrease in modal frequency is nominal, the specimens show good damping behavior. It is suggestive of the fact that damping is a more sensitive indicator of stiffness or loss of it.
  
  
• The present study suggest that use of advanced and precise optical measurement systems such as Laser Doppler Vibrometer in extracting vibration signatures offer a potential on-line and off-line structural health monitoring alternative for the structures. Its advantage lies in it being a non contact type of sensing device in which mass loading of specimen is absent and dynamic responses may be recorded in purest form. LDV also offers good repeatability and reproducibility of the measurements.