Issue 49

C. Bellini et alii, Frattura ed Integrità Strutturale, 49 (2019) 739-747; DOI: 10.3221/IGF-ESIS.49.66 743 between the two supports, as visible in Fig. 4. The span between the support was set to 136 mm, while the loading rate to 6 mm/min. The specimens were loaded until the loading nose reached a stroke of 27 mm and then unloaded in order to evaluate the mechanical behaviour of the studied material, even after the maximum load, and so the maximum flexural strength, had been reached. Figure 4 : Three-point bending test for type B specimen. R ESULTS AND DISCUSSION he influence of two factors, such as the number of layers and the presence of the adhesive, on the flexural properties of the CARALL was studied in this work. In particular, the attention was focused not only on the single factor but also on their combination, leading to a more accurate and deeper interpretation of the material behaviour. The three- point bending test results concerned the flexural strength and they were analysed through inferential statistical techniques in order to ascertain the presence or absence of significant differences. For the purposes of the present paper, the assumption of equality of all population means was assumed as the null hypothesis, as commonly done for statistical analysis of data characterized by homoscedasticity, normal population distribution and independency of experimental runs. The observation of the p-value was chosen as criteria for null hypothesis rejection: if its value was below the significance level of 0.05, the generally adopted significance value, then the null hypothesis could be rejected and, consequently, the population means were effectively dissimilar and the influence of the studied factor could not be neglected. The flexural strength of the tested laminates, denoted as σ f , was determined through the following relation, present in ASTM D790 standard and other papers in the literature [10,20,21]: (1) where P represents the load the specimen undergoes, L is the distance between the supports and h and b are the specimen thickness and width, respectively. As it can be noted in Tab. 2 and Fig. 5, the flexural strength ranged between 562.75 MPa and 641.86 MPa for the laminate with one aluminium sheet bonded with adhesive, while it oscillated between 644.25 MPa and 734.00 MPa for the same laminate without the adhesive, in which the composite material bonding on aluminium sheet was assured by the sole prepreg resin. As concerns the CARALL with two metal layers, the flexural strength interval went from 468.88 MPa to 553.30 MPa for the laminate with adhesive and from 498.38 to 641.38 for that one without adhesive. The CoV (Coefficient of Variation) was low for all the CARALL types; in fact, it was equal to about 5-7%, and in only one 2 3   2    f P L b d   T