Issue 48

T. Febra et alii, Frattura ed Integrità Strutturale, 48 (2019) 242-248; DOI: 10.3221/IGF-ESIS.48.25 244 Low-velocity impact tests were performed using a drop weight-testing machine Instron–Ceast 9340. An impactor with a diameter of 10 mm and mass of 3.4 kg was also used. The tests were performed with the impactor stroke at the centre of centrally supporting the 100x100 mm specimens. Two types of tests were carried out: single impact tests for different impact energies and multi-impacts tests in which the specimens were subjected to successive impacts with increasing energy. For each condition, two/three specimens were tested at room temperature. Figure 1 : View of the insert fibre mat placed in mould. R ESULTS AND DISCUSSION Single impact tests ig. 2a) shows typical energy versus time curves, while Fig. 2b) presents the dynamic load against the displacement, both for the three different insert fibre mats samples. All these tests were performed with an impact energy of 6 J. Fig. 2a) also shows that maximum energy was achieved quickly in the Kevlar mat composite, due to its higher dynamic stiffness, as demonstrated in Fig. 3b). For this type of impact energy multiaxial glass fibre mesh has the lower recovered energy, which is quite similar for the other two insert mats. Figure 2 : Influence of the insert material on the impact response for 6 J impact energy: a) Energy versus time; b) Load versus displacement. Fig. 3a) presents the average values of three tests for each condition of the recovered energy versus impact energy, showing that biaxial glass fiber netting insert promotes the highest values of recovered energy, contrary to what happens with multiaxial glass fiber mesh insert which was observed as having a lower perforation energy. Fig. 3b) presents the dynamic impact stiffness (calculated as the ratio between the maximum load and the displacement at maximum load) against the displacement, showing a slow decrease for the three insert fibers only for impact energies higher than 10 J. Kevlar composites exhibit dynamic stiffness more than 25% higher than both glass fiber composites. F