Assessment of NDT interferometric techniques for impact damage detection in composite laminates

In this paper, the feasibility of using optical methods to detect impact damage in thin laminates is investigated and discussed. Specimens impacted with different energy levels were analysed by a holographic procedure and by an electronic speckle pattern interferometry technique; the results obtained with the two techniques were compared with those acquired by a pulse-echo full-volume ultrasonic technique. The investigation showed that both optical methods were able to identify the presence of impact damage, with an efficiency dependent on the through-thickness location of the delaminations produced by impact. The adoptation of the ESPI technique allowed significant reductionn in inspectioon times, but quantitative estimates of impact damage were drastically impaired by the high level of speckle noise typical of the technique