Vibration modal analysis of defects in composite T-stiffened panels

This paper presents a numerical and experimental investigation into the detection of defects in composite T-stiffened panels using vibration modal analysis. The analysis was performed on carbon fibre/epoxy laminate panels containing a delamination crack or porosity. Experimental testing revealed that vibrational excitation of the defective panels altered the vibration mode response, which was measured using scanning laser vibrometry. Testing showed that changes to the mode shape curvature of the lower order vibrational wave modes was the most reliable indicator of damage within the stiffened panel whereas high order modes were less sensitive to the presence of damage. This was confirmed with vibrational analysis of T-stiffened panels using finite element modelling. Modelling also revealed that damage detection using vibration mode shape curvature analysis was dependent on defect location with the technique less likely to find damage in regions of high damping such as the web.