Issue 48

O. A. Mocian et alii, Frattura ed Integrità Strutturale, 48 (2019) 230-241; DOI: 10.3221/IGF-ESIS.48.24 238 upper facesheet, and a small bulge deformation on the bottom facesheet. Same as composite sandwiches, these panels with PS foam core show less damage on the upper facesheet, with no perforation, but a larger bulge deformation on the bottom facesheet. As a consequence, the indentation depth for sandwich panels with PS foam core is larger than those with PUR foam core (Tab. 5). SPA_PUR SPB_PUR SPC_PUR SPAl_PUR TOP BOTTOM a) SPA_PS SPB_PS SPC_PS SPAl_PS TOP BOTTOM b) Figure 5 : Failure of sandwich panels impacted at 3 m/s: a) PUR foam core; b) PS foam core. At an impact velocity of 4 m/s both facesheets of all composite sandwich panels are perforated (Fig. 6a), except for the bottom facesheet of the SPC_PS panel. The damage area on this facesheet reaches the highest value of all, close to 908 mm 2 , that is 4.6 % of the total area of the sandwich panel. In all other cases, the damage areas on the upper and bottom facesheets are almost the same. It must be noticed that upper composite facesheets fail both through thickness shear mode and tension mode. Though, sandwich panels with PUR core fail mostly under shear mode, due to the brittle behavior of the polyurethane foam, while sandwich panels with PS core fail mostly in tension mode. Moreover, the elastic behavior of the PS foam core allows the impactor to push apart the ruptured fibers and hence create a bigger perforation cavity (see Fig. 6b). The upper facesheet of the aluminum sandwich panels with PUR foam core is perforated and damage is concentrated in the impact zone. While for the PS panels there is no perforation of the panel, but the upper facesheet, among local indentation, undergoes plastic deformation due to bending on random directions from the center to the margins of the panel.