Issue 47

F. Cucinotta et alii, Frattura ed Integrità Strutturale, 47 (2019) 367-382; DOI: 10.3221/IGF-ESIS.47.27 373 (a) (b) Figure 5 : Microscope pictures of the external skins of A sandwich (a) and along the thickness of B sandwich (b) (zoom factor to 32x). Tab. 8 shows the mechanical properties of the basic materials of the B sandwich. The basic properties of carbon and resin are the same of the A sandwich, while the core is lighter. The percentage of weight and volume of carbon fibres with respect to the total are the same of the A sandwich (see Tab. 4) and consequently also the mechanical properties of the undirectional laminas. Basic materials σ R [N/mm 2 ] E [N/mm 2 ] G [N/mm 2 ] ν ρ [kg/mm 3 ] Carbon 4070 248000 103330 0.20 1.80E-06 Core M100 2.11 110 40 0.33 1.07E-07 Resin 110 3400 1310 0.30 1.20E-06 Table 8 : Mechanical properties of the basic materials. In this case, only the cross-ply laminate of Carbon [0/90] (see Fig. 4 – (e)) differs from the previous ones, since the Carbon [-45/45] is equivalent to that of the A sandwich. Tab. 9 shows the mechanical properties of each laminate in the B sandwich. Cross-ply laminate σ R11 [N/mm 2 ] σ R22 [N/mm 2 ] E1 [N/mm 2 ] E2 [N/mm 2 ] G12[N/mm 2 ] ν 12 Carbon [-45/45] 801.2 801.2 9400 9400 31700 0.68 Carbon [0/90] 1049 1048 65040 65040 2530 0.03 Table 9 : Mechanical properties for each cross-ply laminate in B sandwich. Experimental set up Two different experimental test campaigns have been conducted for each type of sandwich. The four-point bending test has been conducted with an ITALSIGMA machine, having a maximum load capacity of 20 kN. The boundary conditions of this test are shown in Fig. 6. The diameter of the rollers was 20 mm and the lowering speed was set to 0.4 mm/s. A minimum of three bending tests was conducted for each specimen. The experimental set up for both the specimen types is shown in Fig. 7.