PSI - Issue 26

Costanzo Bellini et al. / Procedia Structural Integrity 26 (2020) 120–128 Bellini et al. / Structural Integrity Procedia 00 (2019) 000 – 000

122

3

mechanical behaviour of an FML is affected by several constituent characteristics, as the type of metal sheet and composite layers, the fibre direction of the composite material, the thickness and the distribution of the layers, the ratio between metal and composite, the interface between metal sheets and composite laminates, and so on. In this work, the influence of both the composite/metal interface and the thickness of the layers was analysed. Therefore, different FMLs made of aluminium and CFRP (Carbon Fibre Reinforced Polymer) were produced varying the thickness and the number of the metal sheets and the grouping of the composite plies; besides, two different adhesion solutions between the constituent materials were tested: in a case, a layer of structural adhesive was interposed at the interface between aluminium and CFRP, while in the other the bonding relied on the resin of the CFRP itself. This work is organized in several steps: first of all, there is the definition of the laminates to be tested, in terms of stacking sequence and the type of interface between the metal and the composite. In fact, the behaviour of such kind of material relies on these characteristics. The effect of the stacking sequence and the layer adhesion has been investigated both separately and combined. As visible in Table 1, the full factorial plan of the experimental activity was composed of 2 levels for each of the above-mentioned factors. As concerns the stacking sequence, two FMLs with CFRP laminate as external layers were considered. One consisted of three layers: two of CFRP and one of aluminium, while the other one was formed by five layers: two of aluminium and three of carbon fibre. In order to maintain the CFRP/aluminium ratio constant, the aluminium sheet thickness of the former typology was equal to 0.6 mm, while it was 0.3 mm for the latter. As regards composite laminates, in the former case each layer was composed of six prepreg plies, while in the latter they were only four. However, in both cases a total of 12 plies of prepreg were present in the whole FML. In such a manner, the obtained laminate thickness was about 5 mm. For assessing the effect of the adhesive interface between the aluminium sheet and the CFRP on the mechanical performance of the hybrid laminates, two solutions were tested: in a case, a structural adhesive typically used in the aeronautical field, that was the AF 163 AF 2k, was considered, while in the other case the bonding interface was guaranteed by the self-adhesive capacity of the resin of the prepreg material. The FML types studied in this research activity are visible in Fig. 1, in which the carbon laminates are in black, the aluminium sheets are in grey and the adhesive is in red. 2. Materials and methods

Fig. 1. The FML types investigated in this work.

Table 1. The experimental plan. Factor

Number of levels

Level value

Prepreg resin Structural adhesive

Adhesive

2

3 (1+2) 5 (2+3)

Number of layers

2