Delamination Detection Via Holographic Interferometry Techniques

Abstract

The method of laser holographic interferometry is utilised for the detection of impact induced damage in graphite-epoxy composites. Damaged specimens, having received three different levels of impact energy, as well as virgin ones are used. Real time holography is applied and the straining of the specimens is achieved by heating. It is observed that as the temperature starts rising (ΔT=1–3°C), irregular fringe patterns of closed shape, indicative of deformation anomalies, begin to form at the impacted areas. Further, the more damaged the specimen, the sooner the appearance of these patterns. In contrast, the virgin specimens always produce fringes consisting of a system of almost parallel lines. Comparison of the interferometric images with the C-scans, obtained from an ultrasonic examination of the same specimens, verifies these results.