Issue 47

F. Cucinotta et alii, Frattura ed Integrità Strutturale, 47 (2019) 367-382; DOI: 10.3221/IGF-ESIS.47.27 380 A good correspondence between the linear regions (before damage initiation) can be depicted in all the performed simulations. Moreover, the simulations of the A sandwich provided reliable results also concerning the damage initiation, the specimen stiffness after damage and, also, the maximum elongation before spring-back. On the other hand, the simulations of the B sandwich shown less reliable estimation of the material behaviour after damage. This is maybe due to the lower strength of the material of the B sandwich, which experience a higher damage level which is hardly reproducible through numerical modelling. In order to compare the two specimens, considering also the respectively weights, the specific quantities have been calculated. This quantities are obtained as the ratio between the generic quantity and the weight of the specimen. A comparison of the behaviour of the two sandwich typologies has been showed in Tab. 13 by means of the ratios of each quantity between the two materials (the impact values refer to the tests at 60 J). Test Ratio A/B Weight 1.71 Maximum load before failure 4-point bending 1.87 Specific maximum load 4-point bending 1.09 Deflection to maximum load 4-point bending 1.05 Specific deflection 4-point bending 0.61 Stiffness 4-point bending 1.76 Specific stiffness 4-point bending 1.03 Stiffness Impact (60 J) 1.44 Specific stiffness Impact (60 J) 0.84 Peak Force Impact (60 J) 1.18 Specific peak force Impact (60 J) 0.69 Maximum displacement Impact (60 J) 0.51 Specific maximum displacement Impact (60 J) 0.30 Table 13 : Comparison between A and B sandwich values. It is possible to observe that the maximum load before failure for the A sandwich is almost twice than for the B sandwich. However, the specific maximum load is very similar. Conversely, the peak force derived from impact tests is very similar for both sandwiches and, consequently, the ratio between specific values is lower than one. Moreover, the specific bending stiffness of the two sandwiches is almost the same, while the B sandwich has a higher specific impact stiffness. Finally, the absolute values of the maximum displacement are very similar in bending test, while a ratio of two was found in the impact test. The comparison shows that the bending and impact behaviours of the specimens are not directly connected. This highlights the importance of a reliable FE model: a simple experimental campaign can be conducted to tune and validate the model, while many different testing conditions can be numerically simulated, thus drastically reducing testing time and costs. Finally, it was possible to conclude that the B sandwich (lighter material), has similar specific bending performances but better specific impact behaviour with respect to A sandwich. This result is interesting in order to well balance weight and safety, to obtain the best performances, that is crucial in the world of competition sports. C ONCLUSIONS n this paper, two different kinds of sandwiches for UIM powerboats application were considered, belonging to the same competition class. These materials are very performing and innovative and they are yet very poorly studied. Firstly, an experimental campaign was conducted to assess both quasi-static and dynamic behaviour of the materials. The I