PSI - Issue 2_A

F. Cucinotta et al. / Procedia Structural Integrity 2 (2016) 3660–3667 Author name / Structural Integrity Procedia 00 (2016) 000–000

3665

6

Figure 9 – Damage Degree vs Energy (a) - Volume vs Energy (b)

3.2. Repeated impact tests Repeated impact stage has been conducted at constant impact energy level until the upper skin. A specific clamping system has been designed by the writers in order to ensure the repeated impacts in the same point. More specimens have been tested for each impact level in order to verify the results repeatability. Figure 10 (a) shows the average value of Peak Forces versus the repeated impact number. Standard deviations and relative regression curves (e.g. linear, polynomial or exponential) has been showed. It is possible to note that the matching regression curve is well done for all plots. The value of the slope at the origin of the force-displacement curve is the stiffness (Figure 10 b). The stiffness is not significantly influenced by the impact energy. In the first impact, Peak Force is constant for each energy level (Figure 10 a).

Stiffness [N/mm]

Peak Forces [N]

0 1000 2000 3000 4000 5000 6000 7000

2500

y = ‐20,119x 2 + 63,101x + 5394,8 R² = 0,9719

2000

13J

15.5J

18J

1500

1000

y = 1628,4x ‐0,866 R² = 0,9858

y = ‐82,039x 2 + 24,03x + 5898,7 R² = 0,9833

y = ‐42,33x 2 + 86,54x + 5686,2 R² = 0,9936

y = 2183,8x ‐1,095 R² = 0,9304

500

y = 1477,5x ‐1,01

13J 15.5J 18J

R² = 0,994 0

0

5

10

15

0

5

10

15

Impact number

Impact number

Figure 10 – Peak Forces vs Impact number (a) – Stiffness vs Impact number (b)

The low standard deviation is a good estimation of repeatability of the tests. The Impress Volumes, detected by the 3D scan, grow in a linear way with the number of impacts. Although, there is a medium standard deviation.