Issue 30

N. Mortas et alii, Frattura ed Integrità Strutturale, 30 (2014) 403-408; DOI: 10.3221/IGF-ESIS.30.48 405 R ESULTS AND D ISCUSSION mpact tests were carried and Fig. 2 shows the load-time, load-displacement and energy-time curves for sandwiches with pure epoxy resin and epoxy enhanced by nanoclays. These diagrams are representative of all specimens tested and they agree with the literature [2-4, 14-15]. 0 0.5 1 1.5 2 2.5 0 2 4 6 8 10 Load [kN] Time [ms] 0 0.5 1 1.5 2 2.5 0 2 4 6 Load [kN] Displacement [mm] a) b) 0 1 2 3 4 5 6 0 10 20 30 Energy [J] Time [ms] c) Figure 2 : a) Typical load-time curves; b) Typical load-displacement curves; c) Typical energy-time curves. In detail, it is possible to observe that the force increases up to a maximum value (P max ) followed by a drop after the peak load. The impact energy was not high enough to infiltrate full penetration, because the impactor sticks into specimens and rebound always. The beginning of the plateau coincides with the loss of contact between the striker and the specimen, so, this energy coincides with that absorbed by the specimen [3, 4, 16]. The addition of nanoclays promotes major maximum impact loads with values, relatively to the control samples, around 11.9% higher. These results agree with the studies developed by Reis et al . [3] where, for example, the addition of clays promoted maximum loads around 16.1% highest than occurred in Kevlar with pure epoxy resin. For Gustin et al . [17] the differences observed in maximum forces results in the different failure modes, because each sample type has different tensile and shear properties. In terms of displacement, sandwiches manufactured with pure resin presented values about 17.0% higher. This phenomenon is interesting, because the displacement should be controlled, sometimes, in terms of design [3]. Finally, the elastic energy is calculated as the difference between the absorbed energy and the energy at peak I With nanoclays With nanoclays With nanoclays Without nanoclays Without nanoclays Without nanoclays