Issue 49

C. Bellini et alii, Frattura ed Integrità Strutturale, 49 (2019) 739-747; DOI: 10.3221/IGF-ESIS.49.66 744 case it overcame 10%, even if only for a very small amount. It is worth to note that the results found in this experimental campaign are in accordance with other works on this class of material [10, 22, 23]. It can be noted from the experimental results that the highest strength value came from the laminate without the adhesive film and with only a metal sheet, while the lowest value to that one with two aluminium sheets and glued with adhesive. It can be stated that the presence of the adhesive film was detrimental for the material strength, whereas the decrease of metal sheets number was positive. As concerns the former conclusion, it seemed to be in contradiction with past literature; in fact, several researchers [8,24,25] discovered an improvement due to the presence of the adhesive, but it must be underlined that the enhancement was found only for lap shear and interlaminar shear tests, while the in-plane mechanical properties, as the tensile strength, showed a similar behaviour. Only in the work of Li et al. [25] the flexural behaviour was considered, but the same authors acknowledged their results to be highly depending on specimen and test geometry. Run Type A Type B Type C Type D 1 562.75 658.22 497.84 542.37 2 641.86 644.25 468.88 498.45 3 602.50 655.68 534.33 641.38 4 621.18 734.00 553.30 563.26 Mean 607.07 673.04 513.59 561.36 St. dev. 33.64 41.09 37.66 59.79 CV% 5.54% 6.11% 7.33% 10.65% Table 2 : Flexural strength [MPa] for all the tested specimen. Figure 5 : Comparison of flexural strength for the different type of CARALL. The results of the analysis of variance that was implemented on the experimental results are presented in Tab. 3. It can be noted that the number of aluminium sheets was the most influencing factor, since it had a contribution of 53.41%, while the effect of the other factor, that is the presence of the adhesive, was far less important (16.42%). The contribution of the