Issue 51

C. Bellini et alii, Frattura ed Integrità Strutturale, 51 (2020) 442-448; DOI: 10.3221/IGF-ESIS.51.32 444 with the prepreg was inserted in the autoclave for curing. Six specimens were extracted from each laminate by diamond disk saw cutting, then they were tested according to ASTM D 2344. In Fig. 1 a type of specimen, that one with one metal sheet, is visible. This test method calculated the ILSS of laminate through the three-point bending of a short beam, that is a bending test with a span-to-thickness ratio of four. Considering that the laminate thickness was 5 mm, the span was set to 20 mm, so the length of the specimens was decided to be 25 mm, while the width was 10 mm. The ASTM standard prescribed also a fixed load speed of 1 mm/min. Figure 1: Short beam specimens with a single aluminium sheet. Figure 2: A specimen during the three-point bending test. R ESULTS he results of the experimental tests carried out on short beam specimens are presented in this section. Both the maximum ILSS and the trend of the shear strength were reported and discussed. In particular, a statistical analysis was carried out on the values found for the ILSS in order to establish if the layers thickness and the metal/composite interface affected this structural parameter. Considering a specimen width b and a specimen thickness h, the ILSS due to the load P can be determined through the following relation, as stated in the ASTM D 2344 standard: 3  4   P ILSS b h  (1) The ILSS values obtained from the three-point bending tests carried out on all the specimens produced in this activity are presented in Fig. 3. It can be noted that the highest shear strength was equal to 49.03 MPa and it was reached by the laminate characterised by a single metal sheet and metal/composite bonding assured by structural adhesive, while the lowest value was equal to 39.08 MPa and was obtained by the other laminate with a singular metal sheet, that one without structural adhesive. Considering the average value, this finding was confirmed, in fact the highest strength belonged to the laminate with a single metal sheet bonded with adhesive and the lowest strength to the one bonded with the prepreg resin, while the strength of the remaining laminate reached a value between the former two. Moreover, the experimental values are quite accurate since the CoV (Coefficient of Variation) of the results is low, in fact it ranged between 3.6% and 3.7% for all the T