Issue34

M. Scafidi et alii, Frattura ed Integrità Strutturale, 34 (2015) 622-629; DOI: 10.3221/IGF-ESIS.34.68 628 defect shape and position are unknown, the lengths of the two parts of the path cannot be determined separately. Under these conditions, all the points for which the sum of the distance from two fixed point (generation and receiver point) is L L ( x G ) could be reflection points. In particular, all the points on the semi-ellipse with generation and receiver points as foci and with the sum of the distances from them equal to L L ( x G ) could be reflection points. Since the generation and receiver points are on the x -axis (fig. 4), the generic equation of the ellipse having the possible reflection points is:   2 2 2 2 1 c x x y a b    (4) where a and b are, respectively, the major and minor semi-axes of the ellipse, whose values, for the analyzed case, are:   2 L G L x a  (5)   2 2 2 2 L G L x D b               (6) and x c is the abscissa of the center of the ellipse (central point between the two foci at D distance ), that is linked to the generation point by the following relationship: 2 c G D x x   (7) Finally, for each scan step, knowing x G and calculating L L ( x G ), the ellipse passing through the reflecting point of the defect can be drawn. The envelope of all the ellipses determines the shape of the defect. Fig. 11 shows, for the defect D1, the envelope of the ellipses superimposed to the circular profile of the drilled hole. A very good agreement is found in the matching of the experimental and real data. Figure 11 : Envelope of the ellipses (blue lines) drawn for the defect D1 and defect contour (black circle). The envelope of the ellipses shown in Fig. 8 determines only one half of the defect profile. The other part of the profile can be determined by applying the same algorithm to the experimental data coming from an inspection performed in the opposite side of the panel. C ONCLUSIONS A new procedure of analysis of the B-scan image obtained by laser UT for NDE has been presented in this paper. It has been shown that, using an appropriate lay-out optimized to detect the longitudinal wave reflected by the opposite side of the panel, it is possible to define the main characteristics of the defects. In particular, the size, the position and the shape of the defect can be determined. The main dimensions and the position of the defect can be defined analyzing some section images built from the B-scan maps. These section images, if suitably filtered, allow to calculate the coordinates of the defect center.