Issue34

M. Scafidi et alii, Frattura ed Integrità Strutturale, 34 (2015) 622-629; DOI: 10.3221/IGF-ESIS.34.68 626 interrupted paths. Therefore, defects cannot be in the bright zones of the section image, while they could be in the dark areas. In Fig. 8, the section image built with the data extracted from the B-scan of Fig. 5 is shown. Figure 6 : Interruption of the LL-wave due to the defect D1 and corresponding effects on the B-scan map. Figure 7 : Interruption of the LL-wave due to the defect D2 and corresponding effects on the B-scan map. Figure 8 : Section image built from the data of the B-scan of Fig. 5. In Fig. 8, some “shadow” and unanalyzed zones are highlighted. In these last areas, no signal was acquired because the extreme parts of the plate have not been scanned. The shadow zones, instead, correspond to low-intensity signals. In general, in these areas the presence of defects cannot be excluded observing only the section image built with the described procedure. The shadow zones with no defects could be removed by performing the inspection also from the other side of the panel. For the purposes of this research, the shadow zones and the unanalyzed zones have not been considered. To extract the information about the size and the position of the defect, a binarized section image has been built from the section image of Fig. 8 by a threshold procedure. To optimize the results, proper threshold values have been chosen depending on the defect characteristics. In particular, at this stage of the research, they have been defined knowing the value of the defect diameter. The best threshold values are, respectively, 40% and 35 % of the maximum intensity for the defect D1 and D2. The binarized section images are shown in Fig. 9.