PSI - Issue 33

R. Nobile et al. / Procedia Structural Integrity 33 (2021) 685–694 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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sector. In AFS-30 specimens, the presence of the higher density GFRP fabric (160 g / m 2 ) results in an order of magnitude difference in impact force greater than 550%. In addition, a non-destructive detection of impactord area is carried out on the batch of impacted specimens; the NDT analysis involves a depth of a couple of tenths of a mm (near the laminate-core interface); therefore, the C scan maps were carried out in an interval between 0-1 mm and short heating times (3s) were used for the thermographic tests. For a better characterization of the damage, the UT-C-scan and thermal maps were exported and manipulated in the MATLAB environment. A routine was developed for the binarizations of the different experimental maps, assigning a threshold value of suitable amplitude selected based on the average values of the intact zones calculated in regions of interest (or ROIs). a b

Fig. 5. (a) Example of simulated impact damage on AFS-20_P5 and (b) AFS-30_P5 specimens.

a

b

Fig. 6. (a) S-scan, (b) C-scan (top) and binarized C-scan (bottom) maps of AFS-20_P5 specimen.

Specifically, the threshold values were taken by averaging the amplitudes detected on the contour of the impact area where the amplitude varies rapidly around the defect. This allowed us to process images where the impact imprint was clearly distinguished from the external zone and the specimen area, as seen in Fig. 6, 7 and 8.

Table 2. Comparative analysis between UT and IRT results.

Impact depth [mm]

C-scan damage area [mm]

C-scan damaged area A UT [mm 2 ]

Thermal damaged area A IRT [mm 2 ]

Sample batch

ID sample

[A UT -A IRT ] / A UT [%]

65.26 46.99 53.48 56.77 -49.30 -17.94

AFS-20

P4-20 P5-20 P6-20 P4-30 P5-30 P6-30

4 4 4 4 4 4

24 × 21.53 39.5 × 33.41

441.55 961.46

153.37 509.68 155.53 260.44 339.48 614.78

20 × 25

334.3

AFS-30

37 × 16.82 25.5 × 22.89 36.5 × 26.85

602.44 227.38 521.25