Issue 47

F. Cucinotta et alii, Frattura ed Integrità Strutturale, 47 (2019) 367-382; DOI: 10.3221/IGF-ESIS.47.27 370 The external plies are respectively in E-Glass and Kevlar, as shown in Fig. 2 (a) and (b), while the internal ones are in Carbon with different orientations. The core material is a structural foam with a Styrene acrylonitrile foam (SAN) polymer base. This type of foam guarantees high toughness and high impact resistance and it has a very good compromise between low weight and high shear strength. (a) (b) Figure 2 : External skins of A sandwich, the E-Glass skin (a) and the Kevlar skin (b) (zoom factor to 32x). Fig. 3 shows two microscope pictures along the thickness of the A sandwich corresponding to the E-Glass side and the Kevlar side (Fig. 3(a) and (b) respectively). (a) (b) Figure 3 : Microscope pictures along the thickness of A sandwich, the E-Glass side (a) and the Kevlar side (b) (zoom factor to 32x). The mechanical properties for the consitutive materials of the A sanwich are reported in Tab. 3, while the weight percentage of the reinforcement materials with respect to the total are reported in Tab. 4. It was then possible to exploit the well known rule of mixtures to calculate the mechanical properties of the undirectional impregnated fiber. The resutls are reported in Tab. 5. Basic materials σ R [N/mm 2 ] E [N/mm 2 ] G [N/mm 2 ] ν ρ [kg/mm 3 ] E-Glass 1500 72400 30170 0.20 2.56E-06 Carbon 4070 248000 103330 0.20 1.80E-06 Core M130 2.85 180 60 0.33 1.40E-07 Kevlar 3620 131000 48520 0.35 1.45E-06 Resin 110 3400 1310 0.30 1.20E-06 Table 3 : Mechanical properties of the basic materials.