PSI - Issue 37

P. Santos et al. / Procedia Structural Integrity 37 (2022) 833–840 P. Santos et al. / Structural Integrity Procedia 00 (2019) 000 – 000

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(Fernandes et al., 2014; Oliveira et al., 2014). On the other hand, the lower restored energy promoted by the cork layer is a consequence of the cork's intrinsic capacity to absorb energy. Figure 3 shows the damages caused by an impact energy of 3 J, for both materials, in terms of front and back sides of the samples.

Front

Back

a)

Back

Front

b)

Fig. 3. Damages caused by an impact energy of 3 J, for. a) Laminates; b) Sandwich laminates.

It is possible to observe that for laminates, the damage is much more severe because the indentation on the front side of the impact is much deeper than in the sandwich laminate, and on the back side the delamination occurred in the last layer crosses the entire width of the specimen. Regarding sandwich laminates, it is noticeable that on the back side the damage is much more concentrated/localized than in laminates and, in this case, delamination is not as extensive as that which occurred in laminates. According to (Aktaş et al., 2009) it is possible to obtain some impact properties, such as pure elastic limit, penetration, and perforation thresholds, using the ‘‘ Energy Profile Diagram (EPD)’’, in which the relationship between E i and E a is expressed. For this purpose, Fig. 4 shows the energy profile diagram of the materials considered in this study. The data are close, but they are all below the equal energy line. In this context, the absorbed energy is never equal to the impact energy, which means that the penetration threshold has not been reached. However, for laminates and an impact energy of 3 J, the pair of values is much closer to the equal energy line than that of the sandwich laminates (L+cork), showing that this energy value (3 J) is very close to the perforation threshold as shown in Table 1. The data plotted in Fig. 4 can be fitted, for each material by the equation  =  02 +  0 +  , where  is the absorbed energy, 0 is the impact energy and  ,  ,  constants presented in Table 2.