Holographic inspection of laminated plates containing two fully-overlapping identical debonds

Debonds in laminated plates, particularly those made of glassfiber-reinforced plastics, can be readily detected using double-exposure holography when an incremental vacuum pressure is applied between exposures. With the aid of a model developed in this paper, a method is presented for inspecting a laminated plate containing flaws in the form of two identical circular debonds which are fully overlapped. Two holograms are taken, one on each side of the plate; the anomalous fringe patterns enable not only the detection of the presence of fully-overlapping debonds, but also an estimation of their size and depths. The technique can be applied during the shop testing, i.e., for the detection of defects occurring during the manufacturing of composite laminates, because both sides of the laminate must be inspected. This capability contributes further to realizing the potential of holography in nondestructive testing and evaluation of components.