Determination of the Worst Case for the Ballistic Test of the Soft Armour System Using the 9mm FMJ Bullets Differing in the Structure

Ballistics tests were carried out for two types of textile material samples with dimensions of at least 400 x 400mm: Barrday Barflex U590 (Barrday, USA; surface density: 249 ± 1 g/m², thickness: 0.23 ± 0.02 mm) and Dyneema® SB51 (DSM, The Netherlands;surface density: 256±1g/m2,thickness:0,29 ±0,02mm).

The system tested, Barrday Barflex U590, consisted in 14 layers of the ballistic materials, whereas the Dyneema® SB51 system had 12 layers. The areal density of the soft ballistic applications were as follow:

designed from Barrday Barflex U590 – 3486 g/m²;

For the ballistics tests two 9 × 19 mm FMJ bullets of different manufacturer origins were applied (Figure 1): –

9 mm FMJ/RN/SC (steel jacket), m = 8.0 g ± 0,1 g, type: DM41; manufacturer: RUAG;

Fig. 1.

When developing a new design of ballistic materials, it is necessary to determine their ballistic resistance as described in the selected research methodology specified in available normative documents,such as the speed range V50 at which the probability of penetration of the shield is 50% and is defined for a specific material against a given threat (projectile type).

The bullet hit the test sample at an angle of incidence of 0°, the tolerance of which did not exceed the nominal value by more than ± 5°. Tests were conducted at ambient temperature (20 ± 3) °C, with relative air humidity (50 ± 20) %, within not more than 30 minutes from the moment of removal of the sample from the room where it was thermostated (>16 h).

The following devices were used for testing: –

bullet velocity measurement station (type: infrared photoelectric gate type: BP-02/speed meter VT-08; manufacturer: Institute of Mechanics and Construction Technical University of Warsaw/Poland);

Plasticine was stored for at least 16 hours at a constant temperature (± 2 °C) to ensure a substrate plasticity of 20.0 ± 2.0 mm. To test the plasticity of the plasticine, a steel weight was used, dropping it from a height of 2000 ± 5 mm at least 5 times.

2.2.1.

V50 ballistic protection limit

A ballistic protection limit test was performed using of two types of 9 × 19 mm FMJ ammunition in a selected sequence of shots, max. 8 shots per sample. The dimensions of the samples were 400 × 400 mm. The sequence of shots was chosen to minimize the impact of previous shots on the result of subsequent shots (Figure 2).

Fig. 2.

If no V50 result was obtained for the first sample, the same procedure was continued for subsequent samples until an acceptable speed was obtained within the dispersion according to the methodology.

Calculation methodologies were used in accordance with the following: –

NATO STANAG 2920 Ed.2; [15]

–

NATOSTANAG 2920 Ed.3 – AEP 2920 Edition A, Version 1; [16]

–

NIJ Standard 0101.04 (Ballistic Limit); [17]

–

VPAM Ballistic Standard APR 2006. [18]

V50 tests for the model soft ballistic applications developed were performed to confirm the requirements for the V50 ballistic protection limit of the ballistic insert developed and to preliminary determine the effect of the bullet manufacture.

The V50 results for the Barrday Barflex U590 and Dyneema® SB51 systems using a 9 mm DM41 projectile are presented in Tables 3–4, and for a 9 mm FMJ WINCHESTER projectile - Tables 5–6.

The main conclusion of the abovementioned tests confirm that for the Barrday Barflex U590 ballistic system using the two types of bullets, the V50 parameter achieved a significantly higher value when the 9 mm FMJ WINCHESTER projectile was used in ballistic test (Tables 3 and 5).

With the 9 mm DM41 projectile, the V50 obtained for this system differed by about 20 m/s in tests where the 9 mm FMJ WINCHESTER projectile was used, regardless of the research methodology used. This difference was slightly lower only when applying the methodology from VPAM APR 2006.

A similar phenomenon was found when testing the Dyneema® SB51 ballistic system (Tables 4-6). The V50 level was even higher by about 30 m/s in tests where the 9 mm FMJ WINCHESTER projectile was used, which significantly confirms the impact of the source of missile acquisition on the V50 parameter regardless of the type of ballistic system tested.

The value of the backing material deformation depth (BFD) is one of the parameters determining the bullet resistance of ballistic inserts. According to PN-V-87000:2011, the depth of the deformation cannot be higher than 40 mm. Based on the calculated value of V50, it was assumed that the bullet resistance tests of the above-mentioned materials in accordance with PN-V-87000:2011 methodology should meet the requirements for 9 × 19 mm DM41 and 9 × 19 mm WINCHESTER ammunition (special class 400 ± 15 m/s).

Results of the bulletproof test for Dyneema SB51 and Barrday Barrflex U590 soft ballistic systems using 9x19 FMJ DM41 ammunition are presented in Table 7.

A bulletproof test summary for the Dyneema SB51 and Barrday Barrflex U590 soft ballistic systems using 9 × 19 FMJ WINCHESTER ammunition is presented in Table 8.

The Barrday Barrflex U590 ballistic system obtained a higher value of the BFD when the 9 mm FMJ DM41 projectile was used in the ballistic test (30.9 ±1.8 mm), comparable with the test using the 9 mm FMJ WINCHESTER projectile (27.1 ± 1.5 mm). For the 9 mm FMJ WINCHESTER projectile, the number of shot layers for the Barrday Barrflex U590 are fewer than for the 9 mm FMJ DM41 projectile.

In the ballistic system designed with the Dyneema SB51, a similar phenomenon was found: for the 9 mm FMJ DM41 projectile test; the BFD achieved 28.6 ± 1.8 mm, which was significantly higher than for the test in which the 9 mm FMJ WINCHESTER projectile (26.0 ± 1.1 mm) was used. Moreover, it was also confirmed that the number of penetrated layers in the ballistic system was significantly higher when using the 9 mm FMJ DM41 projectile (4.5 ± 0.5) in comparison to the tests where the 9 mm FMJ WINCHESTER projectile (2.8 ± 0.7) was used.

The BFD and p-BFS (Pdp, Vdp) values for the two soft ballistic systems and using the two types of ammunition:: 9 × 19 FMJ DM41 and 9 × 19 FMJ WINCHESTER are shown in Tables 9–10.

The average value of the deformation volume (Vdps) increased when the 9 mm FMJ DM41 projectile was used in the ballistic test, whereas in the case of Vdpw, this parameter maintained a comparable value for both projectiles for the Barrday Barrflex U590 ballistic system. A comparable phenomenon occurs for Dyneema SB51 ballistic system. Higher values of the average area deformation (both Pdpe and Pdps) were found when the 9 mm FMJ DM41 projectile was applied for the ballistic verification of Barrday Barrflex U590 and Dyneema SB51 soft ballistic systems.

Not all deformations have a simple, spherical geometry, and the sharpness of the deformation shape cannot be easily assessed. Taking the above into account, Pdps/Vdpw deformation was calculated to quantify the effect of the strain shape on injury. However, the correlation is difficult to interpret when it is analyzed over the entire range of the depth of deformation, because this ratio decreases with the increasing size of the deformations (Pdps, Vdpw) regardless of their shape. Nevertheless, deformations with a sharper shape carry the risk of piercing more layers of material, which increases the risk of injury.

The average value of the residual energy was significantly higher for the tests where the 9 mm FMJ DM41 projectile was implemented (Barrday Barrflex - 19.57 ± 2.97 J; Dyneema SB51 - 18.48 ± 2.56 J), confirming the results obtained for the BFD and numbers of shot layers of the ballistic system. For the 9 mm FMJ WINCHESTER projectile, lower average BFD values were obtained than for the 9 mm FMJ DM41 projectile. The fact is that these bullets have a different jacket structure [Figure 4].

Fig. 4.

The average BFD values of the tested ballistic cartridges for the 9 mm FMJ DM41 projectile were in the range of 28.6-30.9 mm, and for the 9 mm FMJ WINCHESTER projectile 26.0– 27.1 mm. It can be seen that lower values were obtained for the 9 mm FMJ WINCHESTER projectile. Deformation as it occurs in the backing material after non-penetrating shooting affects the risk of injury. Using only depth measurement in the area of contact with the body will not provide us with full information about the BABT effect. Deformation as it occurs in a plastic substrate after nonpenetrating fire affects the risk of injury. For this reason, the study was carried out together with measurement of the surface area (Pdp) and volume (Vdp) of deformation, which were performed for both soft ballistic systems under study.

For the same values of deformation depth (Hdp), different surface areas (Pdp) and deformation volumes (Vdp) can be obtained. It can be assumed that the shape of the deformation (Hdp, Pdp and Vdp) can affect the magnitude of the injury. The research also shows that the correlation between the depth of deformation and the surface and volume of substrate deformation for given material systems, such as depth and shape, can be used for a more thorough assessment of ballistic material, taking into account the BABT aspect. There is empirical evidence that deeper deformations are more likely to cause injury, but for similar depths, deformations of greater volume will be more harmful [14].

After analyzing the data on Hdp, Pdp and Vdp in Tables 7-10, it is clear that the 9 mm FMJ WINCHESTER projectile shell carries less energy than the 9 mm FMJ DM41 projectile. This was confirmed not only by the higher values of V50 and the smaller number of pierced layers of material, but also by the residual energy that was transferred to the plastic substrate.