PSI - Issue 33

Costanzo Bellini et al. / Procedia Structural Integrity 33 (2021) 824–831 Author name / Structural Integrity Procedia 00 (2019) 000–000

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For a better numerical model validation, some micrographs were taken on the broken specimens to identify the fracture characteristics. It can be observed that, for the long beam, the specimen failure was due to the breakage of the fibre in the central zone of the specimen, as visible in Fig. 6b, while the interface between the composite material and the aluminium, that was characterized by the presence of the adhesive, remained intact. These results were found by the numerical model too; in fact, as it can be noted in Fig. 6a, the failure was due to the breakage of elements in the central zone of the lower surface, as found by experimental tests.

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Fig. 6. Element failure in long beam specimen: (a) numerical model; (b) real specimen.

A similar comparative analysis was carried out also on the short beam specimens. The micrographs taken on the broken specimens highlighted that the failure was due to delamination of the composite materials; in fact, both intra layer and inter-layer delaminations were observed. An instance of the former is visible in Fig. 7b. Moreover, no failure was observed at the aluminium-adhesive and composite-adhesive interfaces, denoting the effectiveness of the adhesive. The numerical model gave a comparable result; in fact, as can be noted in Fig. 7a, the failure of some composite material elements in the centre of the simulated specimen was comparable to what was found in the experimental tests.

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Fig. 7. Element failure in short beam specimen: (a) numerical model; (b) real specimen.