Issue 47

F. Cucinotta et alii, Frattura ed Integrità Strutturale, 47 (2019) 367-382; DOI: 10.3221/IGF-ESIS.47.27 369 with three different energy levels (20 J, 40 J, 60 J), comparing again the load-displacement curve. A complete description of the considered materials (along with the mechanical properties of each specimen), a full description of the experimental procedure and a step-by-step description of the numerical set-up are reported. M ATERIALS AND METHODS Tested samples wo different types of sandwich were considered, widely used for racing boats manufacturing. The sandwiches under investigation have been produced by two different racing team for the same competition category of the UIM ( Unione Internationale Motonautique ). Firstly, a four-point bending test was performed on both specimen types. Then, in a second campaign, drop impact tests with increasing energy levels were performed. The results of these experimental tests were finally exploited for FE model validation. The two sandwiches have been both manufactured with the hand lay- up technique. The general specimen for the bending test was 800 mm x 100 mm with a total thickness depending on the stacking sequence of the laminates, according to the rule 508.03 of the UIM offshore rules 2017. The general specimen for the impact drop test was 100 mm x 100 mm and total thickness depending on the stacking sequence of the laminates; in this case, since there is not a reference rule, the impact parameters have been chosen according to ASTM D-07136 standard, as in Cucinotta et al. [20]. The two principal directions for defining engineering constants (Orientation of the fibres, Young Modulus, Poisson coefficient and Shear Modulus) were depicted with x (direction 1) and y (direction 2) as shown in Fig. 1. The two types of sandwich have been called, respectively A and B. Figure 1 : Specimen dimensions and reference system used for bending test (left) and for impact test (right). The two materials, called A sandwich and B sandwich, are designed for the same competition class by different builders. However, the main characteristics are a little different, as highlighted in the Tab. 1. A Sandwich B Sandwich Total thickness [mm] 35.9 33.0 Weight area density [kg/m 2 ] 13.2 7.7 Table 1 : General characteristics of Specimen A. The A sandwich is composed by two different exterior laminated skins and central homogeneous core. The general characteristics of each ply inside the sandwich are shown in Tab. 2. The total thickness of the A sandwich is about 35.9 mm. Ply Orientation [°] Wet thickness [mm] Dry mass density E-Glass [0/90] 0.48 4.50E-07 [kg/mm 2 ] Carbon [-45/45] 0.45 4.07E-07 [kg/mm 2 ] Carbon [0/-45/+90/+45] 1.71 8.07E-07 [kg/mm 2 ] Carbon [-45/+45] 0.45 4.07E-07 [kg/mm 2 ] Core Gurit-M130 30.00 1.40E-07 [kg/mm 3 ] Carbon [-45/+45] 0.45 4.07E-07 [kg/mm 2 ] Carbon [0/-45/+90/+45] 1.71 8.07E-07 [kg/mm 2 ] Carbon [-45/+45] 0.45 4.07E-07 [kg/mm 2 ] Kevlar [0/90] 0.26 1.75E-07 [kg/mm 2 ] Table 2 : General characteristics of A sandwich. T