Issue 49

C. Bellini et alii, Frattura ed Integrità Strutturale, 49 (2019) 739-747; DOI: 10.3221/IGF-ESIS.49.66 742 it was the AF163-2k film adhesive. It had a thickness of about 0.24 mm and a carrier, made of glass fibres, was present inside it for resistance increment purpose. As regards the manufacturing process of the CARALL specimens, four laminates, one for each FML type considered in this work, were produced by the vacuum bag process. The mould consisted of a 10 mm thick steel plate, whose dimensions were 500 x 400 mm 2 , on which the four laminates were produced simultaneously, since the mould area was enough ample. In fact, it was decided to produce laminates with dimensions equal to 200 x 110 mm 2 , from which extract four specimens with dimensions of 160 x 20 mm 2 . The vacuum bag is a manufacturing process typically adopted in the aeronautical industries for composite material parts production. For the purpose of the present work, the mould surface was treated with Marbocote, a release agent necessary to warrant a safe part removal at the end of the manufacturing process, without part damage or breakage. Then, all the materials required for CARALLs manufacturing, that were the prepreg plies, the aluminium sheets and the adhesive plies, were cut into the right size and stacked as described in Fig. 2. Then, the four stacks were covered with a release film and a breather fabric: the latter was needed for evacuating air and gases out of the bag, while the former was used to separate the breather from the laminates. A caul plate was placed on the top prepreg layer to obtain a smooth surface finish on both laminate sides. Finally, the mould was closed with the vacuum bag, closed with a butyl sealant tape, and the vacuum was applied and maintained until the thermal cycle end. After the mould preparation, the parts were polymerized in an autoclave following the thermal cycle suggested by the prepreg manufacturer, that was suitable for the adhesive cure too. In fact, the cure process is a very important step in polymeric material manufacturing [18,19]. This cycle scheduled a heating ramp with a rate of 2 °C/min and a temperature dwell of 100 min at 100 °C. At the end of the curing process, the laminates were taken from the mould and trimmed by a diamond disk saw, obtaining the desired specimens. The produced specimens for type A FML are visible in Fig. 3. Figure 2 : Prepreg plies and aluminium sheets after the stacking phase. Figure 3 : Specimens cut from the FML plates. The bending tests carried out on the specimens to evaluate the flexural characteristic referred to the ASTM D790. This test method considered a three-point loading system applied to a simply supported beam. In particular, the test involved two cylindrical shape supports on which the rectangular cross-section specimen was laid, loaded by a cylindrical punch, halfway