PSI - Issue 18

Costanzo Bellini et al. / Procedia Structural Integrity 18 (2019) 373–378 Author name / Structural Integrity Procedia 00 (2019) 000–000

377

5

Finally, the statistical examination carried out on the results is presented in Table 3. The ANOVA (Analysis of Variance), accomplished to find out whether a significant factor effect exists, determined that the contribution value of the number of sheets factor was very low, instead that one of the adhesive presence was very high; therefore, it can be concluded that the former factor was unaffecting, while the latter one was influencing. The contribution relevant to the interaction between factors was too low and so it was not reported in that table. Also, the p-value was determined for each factor, in order to gain a more reliable outcome: whether the p-value of a factor is higher than 5%, the generally employed threshold, the relevant data mean cannot be deemed differing and so it is reputed to be unaffecting. In this case, the p-value analysis confirmed what asserted previously, since it was higher than 5% for the number of sheets factor, while it was lower than the threshold value for the adhesive presence factor; consequently, the latter factor can be reputed influencing for the ILSS value of FMLs, while the former one cannot be.

Table 3. ANOVA analysis of results obtained for ILSS experimental tests. Source Seq SS Contribution F-value

p-value 12.9%

n. sheet adhesive

5.993

4.85% 75.84% 19.31% 100.00%

2.79

93.744 23.864 123.602

35.35

0.0%

error total

4. Conclusion This article presents a research activity carried out on CARALL, a special kind of FML based on aluminium sheets and carbon fibre composite material. A critical characteristic of this material is the interface between metal and composite, that must be as strong as possible for the laminate reliability. Therefore, this work deals with the estimation of the effect of both the number of metal sheets with a constant aluminium/CFRP volume ratio, and consequently the layer thickness, and the type of metal/composite interface, if based on structural adhesive or the prepreg resin alone. Different laminates with these characteristics were produced and tested, following the standard for three-point bending on short beam and so determining the ILSS, a mechanical property largely dependent on metal/composite interface quality for this kind of laminates. The ILSS tests determined that the laminate having the best interface was that one with a single aluminium sheet bonded with adhesive, instead of the similar one without adhesive that was the worst one. Indeed, the laminate with two metal sheets bonded with the prepreg resin resulted in very low shear strength and was not considered in this study. Moreover, a statistical analysis was carried out with the aim of determining which factor was the most influential, finding that the effect of the number of metal sheets on ILSS was very low, instead the bonding characteristic between metal and composite conditioned significantly the material shear strength. As future development, a micrographic analysis can be executed on the fracture surface in order to define the damage mode occurred in the specimens during the short beam three-point bending test. References Bellini, C., Di Cocco, V., Iacoviello, F., Sorrentino, L., 2019. Performance evaluation of CFRP/Al fibre metal laminates with different structural characteristics. Composite Structures 225, 111117. doi: 10.1016/j.compstruct.2019.111117. Bellini, C., Di Cocco, V., Iacoviello, F., Sorrentino, L., 2019. Experimental Analysis of Aluminium Carbon/Epoxy Hybrid Laminates under Flexural Load. Frattura ed Integrità Strutturale, 49, 739. doi: 10.3221/IGF-ESIS.49.66. Bellini, C., Parodo, G., Polini, W., Sorrentino, L., 2018. Influence of Hydrothermal Ageing on Single Lap Bonded CFRP Joints. Frattura ed Integrità Strutturale 45, 173. doi: 10.3221/IGF-ESIS.45.15. Botelho, E.C., Pardini, L.C., Rezende, M.C., 2007. Evaluation of hygrothermal effects on the shear properties of Carall composites. Materials Science and Engineering A 452-453, 292. doi: 10.1016/j.msea.2006.10.127. Botelho, E.C., Silva, R.A., Pardini, L.C., Rezende, M.C., 2004. Evaluation of Adhesion of Continuous Fiber-Epoxy Composite/Aluminum Laminates. Journal of Adhesion Science and Technology 18, 1799. doi:10.1163/1568561042708377. Cortés, P., Cantwell, W.J., 2005. The Fracture Properties of a Fibre-Metal Laminate Based on Magnesium Alloy. Composites Part B: Engineering 37, 163. doi:10.1016/j.compositesb.2005.06.002.