Use of the Free Vibration Spectrum to Detect Delamination in Thick Composites

Abstract

A free vibration method was evaluated for damage detection in thick composite plates, whereby vibration was initiated by a single external mechanical pulse and was sensed by piezoelectric patches bonded to the surface of the composite plate. The investigation was conducted on unidirectional fiber glass/epoxy plates approximately 0.387 in (==10 mm) thick, containing controlled delaminations. The free vibration method described in this paper was found relatively insensitive for identifying small to medium delaminations in thick plates. Consequently, several frequency computations using a finite element model were performed to determine the influence of delamination size and location for a single delamination.