Test results

As mentioned previously, the aim of this dynamic test campaign is to quantify the transmitted pressure attenuation of the brittle mineral foam on a rigid and immovable high mass structure. The samples used for this study were 80x80 square cross section specimens, divided by one-layered (60mm), two-layer (120mm) and confined (60mm) specimens. To ensure consistency of results, three tests for each type of sample were conducted. Unfortunately some of the results obtained during the test campaign reached values of saturation from the measure equipment making these unreadable.

The results on Graph 3.7 show the reflected pressure from the plate measured at the end of the EDST and the force transmitted to the high mass structure. The latter shows oscillation in values, this is due to the vibration caused by the impact of the blast wave on the structure and the returning to equilibrium from the system since the structure was not fixed to the ground level. For this reason, to better understand the results obtained, a moving average was used to identify a peak of force from the blast wave and the stabilization of the structure right after. These results can be observed with the example from Graph 3.7.

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Graph 3.7: Reflected pressure measured at end of the EDST and the transmitted force to the high mass structure for the one-layer samples

As it was referred in Chapter 1, the base of a sacrificial cladding philosophy is that the pressure transmitted to a structure with the solution applied will show a decrease in pressure when compared to the reflected pressure. The pressure transmitted to the structure is approximately the value of the plateau stress of the brittle mineral foam [34].

By analysing Graph 3.8 to Graph 3.10, and taking into account the sacrificial cladding philosophy, it is possible to notice that the brittle mineral foam brings advantages when used for the attenuation of loading by a shock wave. However, it is important to note that the estimated reflected pressure measured at the end of the EDST is overestimated which will lead to a big dispersion of values.

Even though, by continuing to use the moving average as reference to avoid the vibrations created by the impact, it is possible to observe that the transmitted pressure as peak regarding the impact of the front plate at the end of EDST but it tends to the plateau stress measured in Sub-Chapter 3.1 for a 80mmx80mmx60mm parallepiped sample (𝜎?1=207,4 kPa).

-1 0 1 2 3 4 5

0 0,25 0,5 0,75 1 1,25 1,5 1,75 2 2,25 2,5

Pressure [MPa]

Time [ms]

Reflected Pressure - Test 1 Reflected Pressure - Test 3

-6 -4 -2 0 2 4 6 8

0 1 2 3 4 5 6 7 8 9 10 11 12

Force [kN]

Time [ms]

Test 1: Transmitted Force Test 3: Transmitted Force

Test 1: Transmitted Force - Moving Average Test 3: Transmitted Force - Moving Average

43 Graph 3.8: Sacrificial cladding philosophy applied to the One-layer Test 1 sample

Graph 3.9: One-layered results for Test 3

The two-layer solution showed some different results from the one-layer solution, with a decrease of the first peak and the transmitted value (𝜎?1=165,7 kPa), but what was verified was that there is not a large influence. This may have happened because one of the layers was not crushed or as damaged as the other (lower layer), one of the layers was not “requested” as the applied load ended up being absorbed by one of the layers or the split by the two. This phenomenon is presented in Figure 3.14.

-1 0 1 2 3 4 5

0 0,25 0,5 0,75 1 1,25 1,5 1,75 2 2,25 2,5

Pressure [MPa]

Time [ms]

One-layered Sample - Test 3

Refleted Pressure Transmitted Pressure

Transmitted Pressure - Moving Average

44

Graph 3.10: Two-layered samples results

Figure 3.14: Brittle mineral foam samples after loading: (a) One-layered sample, (b) Two-layered sample where only the top layer absorbed the loading, (c) Two-layered sample where the loading

attenuation was divided by the two layers

-1 0 1 2 3 4 5

0 0,25 0,5 0,75 1 1,25 1,5 1,75 2 2,25 2,5

Pressure [MPa]

Time [ms]

Two-layered Sample - Test 2

Reflected Pressure Transmitted Pressure

Transmitted Pressure - Moving Average

-1 0 1 2 3 4 5

0 0,25 0,5 0,75 1 1,25 1,5 1,75 2 2,25 2,5

Pressure [MPa]

Time [ms]

Two-layered Sample - Test 3

Reflected Pressure Transmitted Pressure

Transmitted Pressure - Moving Average

(a) (b) (c)

45 In the case of a confined solution the peak of pressure was smaller when compared to the non-confined sample. However, the values of transmitted pressure tend to smaller values, corresponding to the plateau stress for the confined solution (𝜎_?1=253,1 kPa). What was also observed is that this solution presents a behaviour similar to the two-layered sample. However, the value of plateau stress is higher, this could mean that, as the plateau stress is not yet reached, this solution has a better attenuation capability. In addition, it is possible to guarantee the presence of more base material without resorting to the need to increase thickness, which means an advantage when the space of application of this solution with this foam is limited.

Graph 3.11: One-layered confined samples results

-1 0 1 2 3 4 5

0 0,25 0,5 0,75 1 1,25 1,5 1,75 2 2,25 2,5

Pressure[MPa]

Time [ms]

One-layered confined Sample - Test 1

Reflected Pressure Transmitted Pressure

Transmitted Pressure - Moving Average

-1 0 1 2 3 4 5

0 0,25 0,5 0,75 1 1,25 1,5 1,75 2 2,25 2,5

Pressure [MPa]

Time [ms]

One-layered confined Sample - Test 3

Reflected Pressure Transmitted Pressure

Transmitted Pressure - Moving Average

46

Moreover, to be possible to have a base of comparison with other solutions, there were conducted tests for Polyurethane (PU) foam, similar to the ones used in [21]. The samples tested were one-layered and two layered samples. The result comparison is in Table 3.4.

Figure 3.15: Brittle mineral foam (up) and Polyurethane foam (down) Table 3.4: Brittle mineral foam and PU foam raw results

It is clear that, by Table 3.4, the PU foam has a clear advantage to the Mineral foam, but this raw results compare the peak of reflected pressure with first peak of transmitted pressure, which is a consequence of the EDST loading and vibration of the structure. When appliyng the moving average, as it was in the previous results, the values of Table 3.5 shows an advantage when using the mineral foam. The values for two-layered solution with both foams are similar, but when comparing the one-layered samples this show an improved attenuation capacity. An other important aspect to refer it that, since the PU foam has 30mm thickness, the results for a two-layered (60mm) sample are still not as good as a mineral foam one-layer sample, which presents the same thickness.

h=60mm

h=30mm

Foam Test Pressure peak [MPa]

Transmitted pressure [MPa]

1 4,51 1,25 72,22

3 5,00 0,93 81,34

1 4,44 0,91 79,44

3 3,78 0,87 77,02

2 6,96 1,28 81,53

3 5,39 0,96 82,21

Pressure Difference [%]

Mineral

PU

≃

≃ 76,78

81,87

≃78,23 Mineral

Confined

ONE LAYER

Foam Test Pressure peak [MPa]

Transmitted pressure [MPa]

2 3,87 0,88 77,18

3 4,08 0,94 77,04

2 4,68 0,78 83,40

3 4,58 0,79 82,74

Pressure Difference [%]

Mineral ≃77,11

PU ≃83,07

TWO LAYERS

47 Table 3.5: Brittle mineral foam and PU foam results with the moving average applied

Foam Test Pressure peak [MPa]

Transmitted pressure

1 4,51 0,59 86,93

3 5,00 0,35 93,05

1 4,44 0,42 90,53

3 3,78 0,44 88,29

2 6,96 0,90 87,01

3 5,39 0,54 90,04

≃89,99 Mineral

Confined ≃89,41

ONE LAYER

PU ≃88,53

Pressure Difference [%]

Mineral

Foam Test Pressure peak [MPa]

Transmitted pressure

2 3,87 0,46 88,21

3 4,08 0,41 90,04

2 4,68 0,52 88,83

3 4,58 0,49 89,35

PU ≃89,09

TWO LAYERS

Pressure Difference [%]

Mineral ≃89,13

48

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