PSI - Issue 53
A. Neto et al. / Procedia Structural Integrity 53 (2024) 338–351 Alexandre de Oliveira Neto / Structural Integrity Procedia 00 (2019) 000–000
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It can be said straightaway, as it is the same for every energy tier, that the Total Energy-Time graphical representation illustrates the variations in energy over time for various impact energy levels. The initial offset is due to different impact velocities. The major factor that helps to understand such graphs is that following the peak energy point, a plateau becomes apparent, denoting the cessation of contact between the impactor and the specimen. The discrepancy between the maximum energy level and the energy corresponding to the plateau defines the elastic energy – the energy conserved by the impactor for the subsequent rebound. A system with lower elastic energy may be more vulnerable to damage or deformation during dynamic events. It has a limited capacity to absorb and release energy, which can lead to structural failure. This property will be presented as a percentage of the impact energy applied. This means that for Tier 1, L1 and its impact energy of 3,4 J, the elastic energy is about 26 % and for L2 30 %, which is in line with the literature, where mostly less impact energy represents a higher percentage of elastic energy.
3.2. Tier 2: Intermediate damage
0 0,5 1 1,5 2 2,5 3 3,5 4 4,5
4,01
L1 L2
1,91
Force [kN]
3,06
1,77
0
0,5
1
1,5
2
2,5
3
3,5
4
4,5
Displacement [mm]
Fig. 8. L1 and L2 F-D graph with intermediate damage
Thanks to increasingly dissimilar impact energies supported by the layups for each categorization of damage, the different behaviour between L1 and L2 is ever clearer. L1 suffers more than double of the impact energy but it doesn’t translate to twice as much plastic deformation. L1 curve’s behaviour near maximum displacement can be explained due to energy dissipation through the tube during heavy impact. It is noteworthy that L1 gave in considerably more during the first phase of the impact, noted by the less accentuated slope up until near 0,5 mm of displacement.
Fig. 9. Tier 2:(a) L1 before permanent damage; (b) L1 at its highest deformation; (c) L1 after impact
In Fig. 9 the effect of higher impact energy is apparent. The permanent deformation, like what was seen in Fig. 5 is relatively centralized and occurs up to the 6 th layer, from the most inboard one. The layer inflicted damage remains the same between the highest deformation moment and after the impact.
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