Issue 49

C. Bellini et alii, Frattura ed Integrità Strutturale, 49 (2019) 739-747; DOI: 10.3221/IGF-ESIS.49.66 741 presented 2 levels for each factor. The analysis was carried out through three-point bending tests on the CARALL specimens with different stacking and dissimilar bonding strategy. Specimen type Number of metal sheet Adhesive Type A 1 yes Type B 1 no Type C 2 yes Type D 2 no Table 1 : Full factorial plan for factor influence analysis. As concerns the stacking sequence, two laminates with CFRP laminate as external layer were considered; in particular, one consisted of two layers of CFRP and one of aluminium, while the other one was formed by two layers of aluminium and three layers of carbon fibre. In order to maintain the laminate thickness and the CFRP/aluminium ratio constant, the aluminium sheet thickness of the former typology was equal to 0.6 mm and one composite laminate was composed by six prepreg plies, for a total of 12 plies, while the latter type presented two 0.3 mm thick aluminium foil and three CFRP layers consisting of four prepreg plies each. In such a manner, the obtained laminate thickness was 5 mm. In order to evaluate the influence of the adhesive interface between the composite material and the aluminium sheet on the mechanical performance of the hybrid laminates, both FMLs with and without adhesive were produced and tested. In particular, for the former ones a structural adhesive, typically used in the aeronautical field, was adopted, while the bonding interface of the latter ones relied on the self-adhesive capacity of the resin being a part of the prepreg material. The different types of FML studied in the present work are reported in Fig. 1. Four specimens were tested for each set of parameters, so 16 flexure tests were carried out in total. a) b) c) d) Figure 1 : Different kinds of FML considered in this work: a) one metal sheet with adhesive, b) one metal sheet without adhesive, c) two metal sheets with adhesive, d) two metal sheets without adhesive. The metal sheets considered for this work were made of aluminium Al 1100, while the composite material was the SE70/RC303T/1270/38%, a prepreg system made of SE70 epoxy resin and a carbon twill style fabric. 2x2 twill is a weaving style that provides a diagonal pattern with one or more warp fibres woven in a regular manner above and below two or more weft fibres; the warp and weft are the sets of threads that together contribute to the creation of the fabric. The resin weight content was 38% and the fabric areal density was 303 g/m 2 . As concerns the bonding agent used in some specimens,