High-speed Time Average Digital Holography for Ndt of Curved Sandwich Structures

Detection of debonds at sharply curved edges on sandwich structures is found difficult using conventional nondestructive testing (NDT) techniques. The advantages of digital holography and time average holographic interferometry were utilized to evolve a new approach to detect debonds on curved sandwich structures which is reported in this paper. Software developed for the high-speed recording, generation and storage of time average digital holograms within a fraction of a second per frame, made possible the capture of mode shape for every 1 Hz frequency increment during the frequency sweep. Thus the local resonance of debond region is easily and quickly visualized with zero chance of missing any such signatures and thus defects. The basic theory, procedure, software details and results are reported in this paper.