Damage detection by piezoelectric patches in a free vibration method

An experimental program was undertaken to evaluate the feasibility of using piezoelectric patches for damage detection in composite materials. The fact that damage development can cause shifts in the natural frequencies of a structural component suggested an impulse-frequency response approach, in which free vibration was initiated by a single external mechanical pulse and was sensed by piezoelectric patches. Patches in both surface-bonded and embedded configurations were tried. The investigation was conducted on unidirectional glass fiber/epoxy laminated plates containing controlled levels of damage, present as interply delaminations. The data obtained from the piezoelectric patches showed the expected decrease in frequency of the natural vibrational modes with increase in damage. The attractiveness of this method lies in its convenience and its potential for use in the field.