Issue 30

N. Mortas et alii, Frattura ed Integrità Strutturale, 30 (2014) 403-408; DOI: 10.3221/IGF-ESIS.30.48 407 mm length promoted a decreasing about 48.2% and 41.5% of the energy dissipated, respectively, for sandwiches with pure resin and resin nano-enhanced. These results were expected, because the matrix enhanced by clays present higher stiffness and, consequently, its ductile behavior decreases [3, 4, 18]. Therefore, the failure occurs along the matrix cracking promoted by the impact load [2]. Sandwiches P mx [kN] SD [kN] Displacement [mm] SD [mm] Energy Dissipated [%] SD [mm] CS without nanoclays 2.35 0.06 4.75 0.24 34.99 2.68 CS with nanoclays 2.63 0.05 4.06 0.11 43.98 1.51  0 = 20 mm without nanoclays 1.66 0.19 5.84 0.44 18.13 8.63  0 = 20 mm with nanoclays 1.99 0.15 4.96 0.31 25.72 0.52 Table 1 : Effect of the gap on the different impact parameters. C ONCLUSIONS he present work studied the benefits of resins nano-enhanced, and the discontinuities of the cores (gap between cores), on the impact response of sandwich composites made by fibre glass/epoxy skins and balsa wood core. Nanoclay Cloisite 30B, specially modified for better dispersion and interface adhesion matrix/clay, were dispersed in 3% of resin weight. The maximum impact loads were obtained with resin enhanced by nanoclays. The opposite tendency was observed for the displacement at peak load, where the lower values were found for nanoclays filled sandwiches. Finally, sandwich composites manufactured with epoxy resin enhanced by 3 wt.% of nanoclays presents the best performance in terms of elastic recuperation. In terms of core's discontinuity, the absence of material decreases the impact strength, but the resin enhanced by nanoclays promotes significant benefits in this context. R EFERENCES [1] Atas, C., Sevim, C., On the impact response of sandwich composites with cores of balsa wood and PVC foam, Compos. Struct., 93 (2010) 40-48. [2] Reis, P.N.B., Santos, P., Ferreira, J.A.M., Richardson, M.O.W., Impact response of sandwich composites with nano- enhanced epoxy resin, J. Reinf. Plast. Comp., 32 (2013) 898-906. [3] Reis, P.N.B., Ferreira, J.A.M., Santos, P., Richardson, M.O.W., Santos, J.B., Impact Response of Kevlar composites with filled epoxy matrix, Compos. Struct., 94 (2012) 3520-3528. [4] Reis. P.N.B., Ferreira, J.A.M., Zhang, Z.Y., Benameur, T., Richardson, M.O.W., Impact Response of Kevlar Composites with Nanoclay Enhanced Epoxy Matrix, Compos. Part B-Eng., 46 (2013) 7-14. [5] Luo, J.-J., Daniel, I.M., Characterization and modeling of mechanical behaviour of polymer/clay nanocomposites, Compos. Sci. Technol., 63 (2003) 1607-1616. [6] Giannelis, E.P., Polymer Layered Silicate Nanocomposites, Adv. Mater., 8 (1996) 29-35. [7] Saber-Samandari, S., Khatibi, A.A., Basic, D., An experimental study on clay/epoxy nanocomposites produced in a centrifuge, Compos. Part B-Eng., 38 (2007) 102-107. [8] Shi, H.Z., Lan, T., Pinnavaia, T.J., Interfacial effects on the reinforcement properties of polymer-organoclay nanocomposites, Chem. Mater., 8 (1996) 1584-1587. [9] Hosur, M.V., Mohammed, A.A., Zainuddin, S., Jeelani S., Impact performance of nanophased foam core sandwich composites, Mater Sci Eng A, 498 (2008) 100-109. [10] Hosur, M.V., Mohammed, A.A., Zainuddin, S., Jeelani, S., Processing of nanoclay filled sandwich composites and their response to low velocity impact loading, Compos. Struct., 82 (2008) 101-116. T