Issue 30

N. Mortas et alii, Frattura ed Integrità Strutturale, 30 (2014) 403-408; DOI: 10.3221/IGF-ESIS.30.48 403 Focussed on: Fracture and Structural Integrity related Issues Impact response of balsa core sandwiches Nurdane Mortas Department of Mechatronics Engineering, University of Gaziosman Paşa nurmortas@gmail.com Paulo N.B. Reis Department of Electromechanical Engineering, University of Beira Interior preis@ubi.pt José A.M. Ferreira CEMUC, Department of Mechanical Engineering, University of Coimbra martins.ferreira@dem.uc.pt A BSTRACT . The benefits of resins nano-enhanced on the impact response of sandwich composites made by fiber glass/epoxy skins and balsa wood core were studied. Afterwards, the influence of the core's discontinuity was analyzed in terms of impact strength. For better dispersion and interface adhesion matrix/clay nanoclays were previously subjected to a silane treatment appropriate to the epoxy resin. Resins enhanced by nanoclays promote higher maximum impact loads, lower displacements and the best performance in terms of elastic recuperation. The core's discontinuity decreases the impact strength, but the resin enhanced by nanoclays promotes significant benefits. K EYWORDS . Sandwich composites; Nanoclays; Impact behaviour. I NTRODUCTION tructural sandwich composites have been widely used in many engineering applications as consequence of their superior structural capacity in carrying transverse loads, superior bending stiffness, low weight, excellent thermal insulation and acoustic damping [1, 2]. These materials combine thin skins (to promote high in-plane mechanical properties) with low density cores (to fix the skins and to carry the transverse shear load or to provide other structural/functional duties). For this purpose a large variety of materials can be used. Usually, the skins are made of metal alloy sheet or fiber-reinforced polymer laminates and, in terms of core, metallic honeycomb, polymer foam, syntactic foam, Nomex and balsa wood can be used. For example, balsa is the lightest woods available and it offers salient mechanical and physical properties. However, sandwich composites are very susceptible to the impact loads that occur during the operational or maintenance activities. To improve the impact performance of those materials many researchers propose the addition of low concentrations of nanoparticles into polymers without compromising density, toughness or the manufacturing process [2- 7]. Montmorillonite (MMT) clay is the most popular nanoreinforcement for polymeric nanocomposites as consequence of its relatively high ion exchange capacity, high aspect ratio and economic advantages [8]. S