PSI - Issue 33

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

687

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that release gas inside semi-solids and supplied in a great variety of shapes, sizes, densities and types of aluminum alloy; specifically, these foams are made by inserting the extruded bars, before expansion, between two aluminum alloy sheets which undergo a hot lamination to form a sandwich with thin walls of aluminum alloy and a core made of alloy aluminum and foaming agent. For metal-composite sandwich panels, two Alulight panels are used (Dim. 620 × 620 × 20 mm and 620 × 620 × 30 mm), as shown in Figure 1a. The selected matrix is a two-component low viscosity epoxy resin called EC147 with hardener W147, produced by ELANTAS Italia S.r.l. of Collecchio (PR) and frequently used in nautical field. As reinforcement, the 100 g/m2 PLAIN balanced 50/50 and the 160 g/m 2 TWILL 50/50 balanced fiberglass are the selected fabrics for lamination process of AFS panels. As reported in Table 1, an almost-isotropic symmetrical lamination sequence is chosen for both sample series of the two panels and two layers of balanced fabric (0/ 90 and ±45°) that offers good uniformity in terms of stiffness and good resistance to crack propagation [Jones (1999)]. a b c

Fig. 1. (a) Sections of Alulight panels 20 mm thick (above) and 30 mm (below), (b) vacuum bag of the panel at the end of the process; (c) AFS 30 specimens.

Table 1. Properties of the constituent materials of the sandwich panels.

Sample batch

N.° Of samples

Dim. [mm 3 ]

Alulight Foam thickness [mm]

Foam Density [kg/m 3 ]

Glass fabric

Fabric density [g/m 2 ]

Layout

AFS-20

9

200 × 110 × 20 200 × 110 × 30

20

382.00

PLAIN

100

[0° / 90° / +45°/-45°] [0° / 90° / +45°/-45°]

AFS-30

9

30

630.00

TWILL

160

The suitable configuration for the AFS elements could consist of the lowest possible weight of the final samples, that increases according to the foam thickness; in fact, this type of interface offers an improvement performance in terms of adhesion and mechanical properties without excessively modifying the weight to m 2 ratio of the final product [Zhang et al. (2003)]. The hand lay-up is the employed lamination process with a subsequent vacuum bag to remove the air incorporated and the resin excess during the layout process, as shown in Fig. 1b, applying a uniform pressure between the GFRP skins and the aluminum foam skins. A preliminary preparation of the metal surface is fundamental for good adhesion with the FRP laminate. As shown Fig. 1c, the manufactured sandwich panels are subsequently cut to obtain a batch of specimens to be tested, nine specimens denotated AFS-20 and nine samples AFS-30. 2.2. Experimental procedures The MTS 810 model with a maximum load capacity of ± 100 kN is the testing machine system employed for the simulation of impact damage on AFS samples. The impactor consists of a 23 mm diameter stainless steel sphere, as