nape guard ballistic study - defence research...

Nape Guard Ballistic StudyPerformance of Narrow and Overlapping Soft Armour

E. Fournier

Prepared By:

Biokinetics and Associates Ltd. 2470 Don Reid Drive Ottawa, Ontario, K1H 1E1

Biokinetics Report No.: R09-09bProject Leader: Ed Fournier, (613) 736-0384 Contract Number: W7701-85408 Contract Scientific Authority: Kevin Williams (418-844-4000 ext. 4238)

Defence R&D Canada – ValcartierContract Report

DRDC Valcartier CR 2009-148September 2009

The scientific or technical validity of this Contract Report is entirely the responsibility of the contractor and thecontents do not necessarily have the approval or endorsement of Defence R&D Canada.

Nape Guard Ballistic Study Performance of Narrow and Overlapping Soft Armour

Ed Fournier Biokinetics and Associates Ltd. Prepared By: Biokinetics and Associates Ltd. 2470 Don Reid Drive Ottawa, Ontario K1H 1E1 Biokinetics' Report No. R09-09b Contract Project Manager: Ed Fournier, (613) 736-0384 CSA: Kevin Williams, (418) 844-4000 x 4238 The scientific or technical validity of this Contract Report is entirely the responsibility of the Contractor and the contents do not necessarily have the approval or endorsement of Defence R&D Canada.

Defence R&D Canada – Valcartier Contract Report DRDC Valcartier CR 2009-148 September 2009

Principal Author

Original signed by Ed Fournier

Ed Fournier

Senior Engineer, Biokinetics and Associates Ltd.

Approved by

Original signed by Kevin Williams, PhD

Kevin Williams, PhD

Contract Scientific Authority, Defence R&D Canada Valcartier

Approved for release by

Original signed by Dennis Nandlall, PhD

Dennis Nandlall, PhD

Section Head, Weapons Effects and Protection Section Defence R&D Canada Valcartier

© Her Majesty the Queen in Right of Canada, as represented by the Minister of National Defence, 2009

© Sa Majesté la Reine (en droit du Canada), telle que représentée par le ministre de la Défense nationale, 2009

DRDC Valcartier CR 2009-148 i

Abstract ……..

The Advanced Modular Multi-threat Protective Headwear System (AMMPHS) development program was initiated to address the evolving head protection needs of Canadian soldiers in today’s battlefield. The nape is one area of the head in which additional protection is sought from ballistic threats. AMMPHS nape guard designs have been proposed that comprise short curtains of ballistic fabrics suspended from the rear edge of a helmet. It is not know how these designs will perform under ballistic impact, particularly as the strike location approaches the free edge of the nape guard panels. A series of ballistic tests were conducted with 17 grain FSPs and 96 grain steel spheres where the shot placement was varied from the centre of the test sample to the edge. The effect of overlapping fabric edges was also evaluated to determine the minimum amount of overlap required to maintain uniform ballistic protection. Generally, the results confirm the ability of a fabric ballistic nape guard concept but raise a concern regarding blunt impact trauma to the neck resulting from backface deformation of non-penetrating ballistic strikes.

Résumé ….....

Le programme de développement du système de protection modulaire multi menaces (AMMPHS) a été mis sur pied afin d’adresser les besoins de protection à la tête des soldats canadiens contre les menaces rencontrées sur le champ de bataille. Dans ce cas ci, une protection balistique additionnelle est recherchée au niveau de la nuque. Des concepts de protecteur de nuque AMMPHS ont été proposé. Ces concepts consistent en de courtes toiles de tissu balistique suspendues au rebord arrière du casque. La performance balistique de ces concepts est encore inconnue, en particulier lorsque le point d’impact s’approche de l’extrémité du protecteur qui n’est pas attaché au casque. Une série de tests balistiques a été effectué avec des FSP de 17 grains et des sphères de 96 grains où les points d’impacts variaient du centre vers les extrémités des échantillons. L’effet de chevauchement des tissus a aussi été évalué afin de déterminer le minimum de chevauchement requis pour maintenir une protection balistique uniforme. En général, les résultats confirment la capacité d’un protecteur de nuque souple mais lèvent le doute au sujet des traumatismes contondants au cou reliés aux effets arrières lors d’impacts non pénétrants.

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DRDC Valcartier CR 2009-148 iii

Executive summary

Nape Guard Ballistic Study: Performance of Narrow and Overlapping Soft Armour

Ed Fournier; DRDC Valcartier CR 2009-148; Defence R&D Canada – Valcartier; September 2009.

The Advanced Modular Multi-threat Protective Headwear System (AMMPHS) development program was initiated to address the evolving ballistic, blast and blunt impact head protection needs of Canadian soldiers in today’s battlefield. The nape is one area of the head in which additional ballistic protection is being sought to span the gap in protection offered by the ballistic helmet and the ballistic vest worn by the soldiers.

Prototype nape guard designs have been proposed that incorporate curtains of soft ballistic fabric that drape downwards from the rear of a helmet. To increase the extent of coverage while maintaining head mobility and range of movement, single and two overlapping fabric curtains have been considered.

The proposed nape guard designs were tested to assess their ballistic performance. The testing investigated performance of single panels, dual overlapping panels and shot placement in close proximity to the panels' edge. The materials, which included Artec, Spectra Shield and Kevlar fibre based soft armour, were evaluated against 17 grain FSP and 96 grain steel sphere threats. The areal density, shape, size and stitch pattern were defined by Defence R&D Canada - Valcartier. The results of the testing and their implications on the design of a nape guard are summarized below.

• Against the 17 grain FSP, the single panels of Artec and the Spectra Shield performed the best.

• With the 96 grain sphere the Artec performed the best.

• Pencilling of the ballistic fabric was observed for all fabrics which raises concern of blunt impact trauma to the neck.

• 17 grain FSP tests on overlapping panels determined the minimum overlap needed to maintain the same V50 performance across the height of a dual panel system is approximately 2 cm. If less than 2 cm was employed, the rear panel moved out of the way during the ballistic impact and did not contribute to the stopping ability of the dual panel system, decreasing the effective ballistic limit.

• Vproof testing determined that the proximity to an edge at which penetration would occur varied with material but was between 0.5 cm and 1 cm from an edge.

• Sewing the edge of the panels may reduce the capability of the ballistic panels particularly at impact sites that are closer to an edge. Stitching of the ballistic fabrics should therefore be avoided.

iv DRDC Valcartier CR 2009-148

Sommaire .....


Ed Fournier; DRDC Valcartier CR 2009-148; R & D pour la défense Canada – Valcartier; Septembre 2009.

Le programme de développement du système de protection modulaire multi menaces (AMMPHS) a été mis sur pied afin d’adresser les besoins de protection à la tête des soldats canadiens contre les menaces rencontrées sur le champ de bataille. Le casque ne doit plus protéger uniquement contre la pénétration de projectiles. Il doit aussi prévenir les traumatismes reliés aux effets arrières, les traumatismes contondants ainsi que ceux causés par les effets de souffle. Dans ce cas ci, une protection balistique additionnelle est recherchée au niveau de la nuque pour étendre la protection offerte par le casque de combat et la veste pare-éclat portés par les soldats.

Des prototypes de protecteur de nuque ont été proposé. Ces prototypes consistent en de courtes toiles de tissu balistique qui couvrent la nuque en tout étant suspendues au rebord arrière du casque. Des concepts souples de toiles individuelle et double avec chevauchement ont été considérés pour augmenter la zone de protection tout en maintenant la mobilité et la latitude de déplacement.

Ces concepts de protecteur de nuque ont été testé afin d’évaluer leurs performances balistiques. Le programme d’essai avait pour but d’évaluer la performance des toiles individuelle et double avec chevauchement ainsi que l’effet du point d’impact lorsque que celui-ci se rapproche du rebord. Les matériaux balistiques incluant, Artec, Spectra Shield et Kevlar ont été évalués avec des FSP de 17 grains et des sphères de 96 grains. La densité surfacique, forme, grandeur et le patron de couture ont été définis par le centre de Recherche et Développement pour la Défense Canada de Valcartier. Les résultats des tests et leurs implications sur le concept de protecteur de nuque sont résumés ci-dessous.

• Contre le FSP de 17 grains, les toiles individuelles d'Artec et Spectra Shield se sont avérées les meilleures.

• L'Artec a offert la meilleure performance contre la sphère de 96 grains.

• Des déformations arrières très localisées (pencilling) des tissus balistiques ont été observé pour tous les matériaux ce qui lèvent le doute quant à la protection contre les traumatismes contondants au cou reliés aux effets arrières lors d’impacts non pénétrants.

• Pour maintenir la même performance V50 contre le FSP 17 gr sur toute l’étendue du protecteur, un chevauchement de 2 cm est nécessaire pour le concept de double toile. Lorsqu’il y avait un chevauchement de moins de 2 cm, la toile arrière se déplaçait vers l’extérieur durant l’impact balistique et ne contribuait pas à arrêter le projectile.

DRDC Valcartier CR 2009-148 v

• Les tests Vproof ont déterminé que la distance entre le point d’impact et le rebord à laquelle la pénétration va se produire se situe entre 0.5 cm et 1 cm. Cette distance variait aussi en fonction du matériel balistique utilisé.

• La présence de couture sur les rebords des toiles peut réduire la performance balistique, particulièrement lorsque les points d’impact sont près d’un rebord. Les points de couture devraient donc être évités.

vi DRDC Valcartier CR 2009-148


DRDC Valcartier CR 2009-148 vii

Table of contents

Abstract …….. .............................................................................................................................i

Résumé …....................................................................................................................................i Executive summary ................................................................................................................... iii Sommaire ..... .............................................................................................................................iv

Table of contents.......................................................................................................................vii List of figures...........................................................................................................................viii List of tables ..............................................................................................................................ix

Acknowledgements .....................................................................................................................x 1 Introduction ..........................................................................................................................1

2 Nape Guard Sample Construction .........................................................................................2 3 Test Set-up ...........................................................................................................................3

3.1 Single Panel V50.........................................................................................................3 3.2 V50 of Panel Overlap ..................................................................................................4 3.3 Edge Effects on Ballistic Performance........................................................................5 3.4 Test Matrix ................................................................................................................6

4 Results and Discussions ........................................................................................................7 4.1 Results of Single Panel Test .......................................................................................7 4.2 Results of Overlap Panel Testing..............................................................................10 4.3 Results of Shooting Close to the Edge of Single Panels ............................................13

5 Behind Armour Blunt Trauma to the Neck ..........................................................................17 6 Summary ............................................................................................................................19

References ................................................................................................................................21 List of symbols/abbreviations/acronyms/initialisms ...................................................................23

viii DRDC Valcartier CR 2009-148

List of figures

Figure 1: Nape guard prototype. ..................................................................................................1

Figure 2: Nape shroud panel dimensions and assembly. ...............................................................2

Figure 3: Test set-up for single panel and dual panel nape guard designs......................................3

Figure 4: Test region for determining panels V50..........................................................................4

Figure 5: Test configuration showing increasing overlap (side view). ..........................................5

Figure 6: Shot placement progressively closer to panel's edge. .....................................................6

Figure 7: V50 results for single panel nape guard. .........................................................................7

Figure 8: Pencilling of the nape guard fabric................................................................................8

Figure 9: Nape guard material pushed into the Minicel® backing. ...............................................8

Figure 10: Typical ballistic impact to nape guard test sample. ......................................................9

Figure 11: 17 grain FSP V50 for 3 cm overlapping panels...........................................................10

Figure 12: 17 grain FSP V50 for 2 cm overlapping panels...........................................................11

Figure 13: Typical ballistic impact to dual panel configuration. .................................................12

Figure 14: Ballistic impact 2 cm from the panel's edge...............................................................15

DRDC Valcartier CR 2009-148 ix

List of tables

Table 1: Materials used in nape shroud panel construction. ..........................................................2

Table 2: Test Matrix for both 17 grain FSP and 96 grain sphere threats........................................6

Table 3: Results 17 grain FSP tests close to the edge of a panel. ................................................13

Table 4: Results 96 grain sphere tests close to the edge of a panel. .............................................14

Table 5: Results 17 grain FSP tests close to a stitched edge of a panel........................................14

x DRDC Valcartier CR 2009-148

Acknowledgements

The author would like to acknowledge the substantial contribution to the work reported herein by Doug Baines and Michael Pees for their efforts in conducting the testing of the nape guard components.

DRDC Valcartier CR 2009-148 1

1 Introduction

The Advanced Modular Multi-threat Protective Headwear System (AMMPHS) development program was initiated to address the evolving ballistic, blast and blunt impact head protection needs of Canadian soldiers in today’s battlefield. The nape is one area of the head in which additional ballistic protection is being sought to span the gap in protection offered by the ballistic helmet and the ballistic vest already worn by soldiers. It is anticipated that the AMMPHS design will incorporate a nape guard that extends downward from the back of the helmet, to increase the area of ballistic protection afforded at the rear and sides of the neck. Nape guard design concepts being considered comprise single panels or two overlapping panels of soft ballistic fabric that would extend coverage without limiting head mobility. A prototype nape guard design is shown in Figure 1 below.

Figure 1: Nape guard prototype.

Although current nape guard designs are still in their conceptual phase of development and more work is required to confirm soldier system compatibility, there are questions pertaining to the ballistic performance of short curtains of ballistic fabric that must be answered to gain an understanding of potential nape guard performance. Ballistic tests were performed to:

• Determine the effect of edge proximity on the ballistic resistance of soft armour panels.

• Determine the additive ballistic performance of overlapping panels.

• Determine the effect of behind armour blunt trauma to the neck.

2 DRDC Valcartier CR 2009-148

2 Nape Guard Sample Construction

Proposed designs for the nape guard comprise one panel or two overlapping and articulating soft ballistic panels. The nape shroud panels for testing were fabricated from three different materials as summarized in Table 1 below. The number of fabric layers used for each material was as specified by Defence R&D Canada - Valcartier. A nominal target V50 of 500 m/s was selected for the purposes of this study with the respective areal densities based on 16” x 16” (40.6 cm x 40.6 cm) panel test results.

Table 1: Materials used in nape shroud panel construction.

Material Grade Specification Number of Layers Areal Density (kg/m2)

Artec 3125 ("Soft Steel") 20 2.500

Kevlar KM2 400 30 2.940

Spectra Shield SA-3118 18 3.186

In the final product, the height and width of the panels would vary depending on the size of the helmet and neck length of the soldier however, for the purpose of testing the nape shroud panels were cut to a nominal dimension of 35 cm long and 8 cm high. The multiple fabric layers of each panel were tack sewn together at three locations along the top edge with 19 mm to 25 mm long stitching as shown in Figure 2.

Figure 2: Nape shroud panel dimensions and assembly.


3 Test Set-up

In the proposed nape guard concepts the ballistic panels would be inserted into a fabric carrier which might be attached to the rear of the helmet shell via short lengths of webbing, as shown previously in Figure 1. For the purposes of testing the nape guard ballistic panels were suspended directly by short lengths of webbing attached to the test fixture. For ease of installation, spring clips connected the webbing to the nape guard panels. The test set-up for both single panel and dual panel nape guard configurations are shown in Figure 3.

Figure 3: Test set-up for single panel and dual panel nape guard designs.

The ballistic performance of the nape guard panels were evaluated for both the 17 grain Fragment Simulating Projectile (FSP) and the 96 grain steel sphere. The ballistic evaluation of the nape guard samples comprised three different test configurations as described in the following sections.

Representative tests were filmed at 6000 frames per second using high-speed video to aid in visualizing the behaviour of fabric curtains under ballistic loading.

3.1 Single Panel V50

The first test configuration assessed the ballistic resistance of the three different soft armour materials in a single panel as described in Table 1. Shot placement was limited to the centre region of the panel to minimize edge effects (see Figure 4). The impact sites were nominally spaced 75 mm apart to minimize the influence on subsequent shots and they were at least 50 mm from the ends of the fabric strips. The test samples were smoothed out after each test to remove fabric layer displacement resulting from the impact.

The panels were suspended against a Minicel® backing block and they were held in place at three locations along their top edge as described previously. There was some discussion on the boundary conditions to use, in particular the placement of the panels in contact with the Minicel® backing as this does not capture the offset of the nape guard with the helmet. The decision was made to focus on a set-up that produced repeatable results at this stage of the design study. The final nape guard design will have to be tested with a full set of realistic boundary conditions including offset to a neck surrogate and appropriate lower edge boundary conditions representing the interface with the fragmentation vest collar.


Depending on the amount of damage to the test samples each panel sustained either 3 or 4 ballistic strikes. Therefore, 3 to 4 samples were required for the determination of a single, 10 shot V50. The V50 was determined three times for each sample construction.

Figure 4: Test region for determining panels V50.

3.2 V50 of Panel Overlap

The second test configuration assessed the ballistic performance of the overlap region of two soft armour panels that are representative of a segmented nape guard design. The same test configuration used in the single panel testing was employed with the addition of a second panel suspended with straps that can provide a varying amount overlap, as shown in Figure 5. The straps were affixed to the attachment points on the first panel thus allowing for vertical movement of the second panel. Shot placement was along the centreline of the soft panel overlap. Similarly to the single panel tests the impact sites were nominally spaced 75 mm apart and at least 50 mm from the ends of the fabric strips. The test samples were smoothed out after each test to remove fabric layer displacement resulting from the impact.

The V50 was calculated for increasing overlap of the two panels until the V50 of the single panel was achieved.


Figure 5: Test configuration showing increasing overlap (side view).

3.3 Edge Effects on Ballistic Performance

The third stage of testing evaluated the edge effects on the ballistic resistance of a soft amour panel. As with the previous two test configurations, the test specimens were supported against a Minicel® backing. Using a constant projectile velocity (Vproof), the test samples were shot at impact locations progressively closer to the edges of the test panel, to determine the proximity to the sample edge at which penetration would occur (see Figure 6). Along the length of the test samples, the impact sites were nominally spaced 75 mm apart and at least 50 mm from the ends of the fabric strips. The test samples were smoothed out after each test to remove fabric layer displacement resulting from the impact.


Figure 6: Shot placement progressively closer to panel's edge.

3.4 Test Matrix

The proposed ballistic evaluations of the nape guard soft armour panels are summarized in Table 2 below. The same test matrix applies for both the 17 grain FSP and the 96 grain sphere testing.

Table 2: Test Matrix for both 17 grain FSP and 96 grain sphere threats.

Description Shots per Panel

Shots per V50

# of Panels per V50

# of Repeats

Total # of Panels

Centre Panel – 1 3 10 4 3 12

Centre Panel – 2 3 10 4 3 12

Centre Panel – 3 3 10 4 3 12

Overlapping Panels – 1 3 10 8 3 24



Edge of Panel - 1 4 na na 3 3

Edge of Panel – 2 4 na na 3 3

Edge of Panel – 3 4 na na 3 3


4 Results and Discussions

The results of the ballistic testing of potential nape guard materials are discussed in the following sections.

4.1 Results of Single Panel Test

The average V50 results for single panel nape guards are presented in Figure 7 below. The approximate V50 for larger 16" x 16" (40 cm x 40 cm) test panel of the same material and areal density is also shown. The error bars shown in the figure represent the minimum and maximum V50 obtained for the given nape guard configuration. Results are included for both the 17 grain FSP and the 96 grain sphere.

V50 of Single Panel Nape Guard

550 549 536497 479

413

500 508451 482

411

511

0

100

200

300

400

500

600

700

Artec SpectraShield

Kevlar KM2400

Artec SpectraShield

Kevlar KM2400

Vel

oci

ty (

m/s

)

V50 of Nape Guard Panels Approximate V50 of 16" x 16" Test Samples

17 grain FSP 96 grain Sphere

Figure 7: V50 results for single panel nape guard.

The results presented in Figure 7 show that the Artec and the Spectra Shield nape guards perform similarly against the 17 grain threat when shot along the mid line of the test samples with a V50 of 550 m/s and 549 m/s respectively. The average Kevlar V50 was only 2.5% lower with a V50 of 536 m/s. Note that the areal densities for the three materials were selected to give similar ballistic limit performance of approximately 500m/s based on large panel test data. The performance of all three materials was below that required by the AMMPHS specification indicating more material layers would be required.

Against the 96 grain sphere, the Artec produced the highest average V50 at 497 m/s while the Kevlar had the lowest V50 at 413 m/s or approximately 17% lower. At 479 m/s the Spectra Shield V50 was only 3.6% lower than that for the Soft Steel.


When considering the performance of a nape guard design the amount of backface deformation must be considered. In all the testing, but particularly with the 96 grain sphere, the nape guard fabrics "pencilled" and pushed material into the Minicel® backing to some degree. Examples of "pencilling" and of how the materials pushed into the backing are shown in Figure 8 and Figure 9.

Figure 8: Pencilling of the nape guard fabric.

Figure 9: Nape guard material pushed into the Minicel® backing.

Referring back to Figure 8 and comparing the performance of the thin strips of fabric (8 cm x 35 cm) comprising the nape guard panels to the standard test sized panels (40 cm x 40 cm) it can be seen that the thin strips demonstrate improved performance against the 17 grain FSP for all three materials tested. A 10% improvement in performance is seen with the Artec and Spectra Shield whereas a 6 % improvement was seen with the Kevlar. This finding is inline with research by Cork and Foster [2] that suggests that narrow fabric strips absorb more energy than wider fabric panels. Similarly, improved performance for the 96 grain sphere was observed for the Artec. Interestingly, there was no difference in performance with the Spectra Shield or the Kevlar for the larger fragment.


To help visualize the impact event a few frames from the high speed video are presented in Figure 10 below for impact to the centre of a single panel.

Figure 10: Typical ballistic impact to nape guard test sample.


4.2 Results of Overlap Panel Testing

The results of the 17 grain FSP V50 ballistic testing of overlapping panel configurations are shown in Figure 11 and Figure 12 for 3 cm and 2 cm panel overlap, respectively. Tests were conducted with 1 cm overlap but it was not possible to obtain a V50 as penetration continued to occur with projectile velocities as low 442 m/s, 453 m/s and 464 m/s for the three materials before testing was stopped. In all cases with 1 cm overlap only the outer layers of the top panel were involved in stopping the projectile. After penetrating the first few layers the projectile slipped out from between layers and missed the second panel altogether.

V50 of Dual Panel Nape Guard with 3 cm Overlap

671 665 655

550 549 536

0

100

200

300

400

500

600

700

800

Artec Spectra Shield Kevlar KM2 400

Vel

oci

ty (

m/s

)

V50 Dual Panel 3 cm Overlap V50 Single Panel

Figure 11: 17 grain FSP V50 for 3 cm overlapping panels.


V50 of Dual Panel Nape Guard with 2 cm Overlap

616 588629

550 549 536

0

100

200

300

400

500

600

700

800

Artec Spectra Shield Kevlar KM2 400

Vel

oci

ty (

m/s

)

V50 Dual Panel 2 cm Overlap V50 Single Panel

Figure 12: 17 grain FSP V50 for 2 cm overlapping panels.

Attempts to assess the V50 with the 96 grains were made with each nape guard material using a 3 cm overlap of the panels. This overlap implies that the shot placement is 1.5 cm from the individual panel edges. In this configuration the deflection of the front panel pushes the rear panel out of the way such that the rear panel no longer contributed to stopping the projectile. Testing with less overlap was not attempted.

To help visualize the impact event a few frames from the high speed video are presented in Figure 13 below for impacts to the dual panel configuration.


Figure 13: Typical ballistic impact to dual panel configuration.


4.3 Results of Shooting Close to the Edge of Single Panels

As described in Section 3.3 single panels of the nape guard materials were shot at Vproof velocities at increasing proximity to the panels' edge until penetration occurred. The Vproof for each material was established as 80% of the V50 measured during the single panel V50 testing. The results of the tests with shot placement closer to the edge are presented in Table 3 for the 17 grain FSP and Table 4 for the 96 grain sphere. Tests were also conducted with the 17 grain FSP where the full length of the panels' edges was stitched together as opposed to having loose layers. These results are shown in Table 5.

Table 3: Results 17 grain FSP tests close to the edge of a panel.

Material Distance From Edge (cm)

Strike Velocity (m/s)1

Penetration (Yes/No)

3 443 No

2 448 No

1 443 No

Artec

0.5 405 Yes

3 443 No

2 443 No

1 460 No

Spectra Shield

0.5 401 Yes

3 440 No

2 439 No

1 439 Yes

Kevlar KM2 400

0.5 424 Yes

1 The fastest recorded strike velocity is shown for non penetrating strikes and the slowest recorded strike velocity is shown for penetrating strikes.


Table 4: Results 96 grain sphere tests close to the edge of a panel.




3 406 No

2 399 No

Soft Steel Sewn Edge

1 411 No

3 392 No

2 386 No

Spectra Shield Sewn Edge

1 363 Yes

3 344 No

2 362 No

Kevlar KM2 400

Sewn Edge 1 330 Yes

Table 5: Results 17 grain FSP tests close to a stitched edge of a panel.




3 462 No

2 464 No

1 450 No

Soft Steel Sewn Edge

0.5 430 Yes

3 465 No

2 444 No

1 398 Yes

Spectra Shield Sewn Edge

0.5 439 Yes

3 436 No

2 448 No

1 437 Yes

Kevlar KM2 400

Sewn Edge

0.5 384 Yes

From the results presented in Table 3 Artec and the Spectra Shield single panels would remain effective up to 1 cm from the panels' edge. At less than 1 cm from the edge the panels were displaced sufficiently that the only the top layers were engaged in stopping the projectile. The Kevlar however, only remained effective to 2 cm from the edge after which the significant fraying of the fabric edge and penetration began to occur.

2 The fastest recorded strike velocity is shown for non penetrating strikes and the slowest recorded strike velocity is shown for penetrating strikes.


To help visualize the impact event a few frames from the high speed video are presented in Figure 14 below for impacts that are 2 cm from the panel's edge.

Figure 14: Ballistic impact 2 cm from the panel's edge.

A comparison of the results presented in Table 3 to Table 5 revealed that stitching of the panel's edge did not appear to have any effect on the Artec. This may be due to the already tight weave of this fabric. In the case of the Spectra Shield the stitched edge samples resulted in the occurrence of penetration at 1 cm whereas penetration did not occur at this distance from the edge in the unstitched panels. The stitching may have prevented the Spectra fibres from deforming or elongating. With the Kevlar panels, penetration of the stitched samples still occurred at a 1 cm shot spacing from the edge even though the velocity achieved for those test were less than the targeted Vproof. The stitching also had the effect of reducing the amount of fraying that occurred.


Shot placement with the 96 grain sphere was problematic and could deviate from the targeted point by as much as 1 full diameter of the sphere (~ 11.5 mm). Nevertheless, with sufficient testing the results in Table 4 were obtained. Penetration was not observed with the Artec at 1 cm from the panels. Shots closer to the edge were not achieved. For both the Spectra Shield and the Kevlar penetration did not occur at a 2 cm shot spacing from the edge but in both materials penetration was observed at the 1 cm shot placement from the panel's edge.


5 Behind Armour Blunt Trauma to the Neck

A significant investment has been made in developing appropriate behind armour blunt trauma (BABT) criteria for ballistic impacts to the head, thorax and extremities however, a test methodology does not exist for the neck/nape. The contact force sensor technologies developed for these other body regions could be adapted to assess nape guards but the development of a test methodology depends on an injury criteria and a validated injury tolerance level.

A brief literature review of scientific literature was conducted in an effort to define tolerance levels related to injury severity resulting from direct neck contact from a non penetrating ballistic strike to the nape guard. Although, protecting against projectile penetration is the primary objective of a nape guard, preventing the potential for injury resulting from the associated behind armour blunt trauma is of equal importance.

The literature review was unsuccessful as no information was found pertaining to an injury criterion for blunt impact to the cervical spine neither was any information identified that related impact loads to cervical fracture. Most of the published injury research related to the cervical spine deals with cervical extension, flexion, tensile, compressive and torsion injuries.

Considering the lack of information regarding direct loading of the cervical spine a research paper and a test standard, which consider the tolerance of the lumbar and thoracic spine to direct loading, are discussed below as an initial approach in establishing an injury threshold for the neck.

Bass et al [3] performed impact drop tests onto four cadaveric porcine subjects to assess spinal injury resulting from direct impact. The specimens were placed in a prone position with the thorax and abdomen supported on a rigid reaction plate. The impacts sites were distributed at 10 cm intervals along the spine starting at the level of the mid-sternum and proceeding towards the lumbar spine. An impactor with a mass of either 28 kg or 19.1 kg was dropped from 1 m to vertically impact the spine. The impact energy ranged from 157 J to 252 J. The strike face was cylindrical with a radius of 12.7 mm and length of 80 mm.

The measured reaction forces from the porcine drop tests were scaled to human values using anthropometric parameters. Using the scaled data an injury risk curve was developed where a peak force of 10,200±3900 N represented a 50% risk of injury. The proposed risk curve however, applies to the thoracic and lumbar regions of the spine and not the neck. Furthermore, the load distribution in the porcine tests is much larger than that which would be expected in the behind armour impacts of the nape guard considering the penciling that was observed during the nape guard tests. Additionally, it should be noted that there is a large physiological difference between the cervical and thoracic spine in terms and size, geometry and consequently the likely fracture tolerances.

A personnel protection equipment standard [4] (CSA Z617-05) was identified that incorporated a fracture tolerance level for the thoracic spine. In this standard a 2 kN pass/fail criterion for a 75 J impact from an 90° edged or spherical (49 mm radius) threat was established. According to Bass' injury curve, this 2 kN load would be representative of a less than 5% risk of injury. As noted previously, the physiological differences between the cervical and thoracic spine must not be


neglected in considering this criteria and as with the porcine testing, the impact threats in this standard are likely not representative of the loading conditions of a non penetrating ballistic strike to the nape guard.

Since no other tolerance value could be found for the cervical spine and given the low injury risk to the thoracic spine associated with the CSA fracture threshold , the 2 kN fracture load could be considered as an initial tolerance in assessing the performance of ballistic nape guards until such time when more pertinent data becomes available.


6 Summary

Ballistic tests were performed on individual panels and overlapping panels of three ballistic fabrics to assess their performance in a configuration representative of prototype nape guard designs being considered in the AMMPHS project being led by Defence R&D Canada – Valcartier. The materials, which included Artec, Spectra Shield and Kevlar, were evaluated against 17 grain FSP and 96 grain steel sphere threats.

Against the 17 grain FSP the single panels of Artec and the Spectra Shield performed similarly with V50 of 550 m/s and 549 m/s respectively with the Kevlar results being approximately 2.5% lower.

With the 96 grain sphere the Artec performed the best followed by the Spectra Shield and then the Kevlar.

Against both threats the three materials pencilled during the ballistic strike, a result that would undoubtedly result in contact with the wearer's neck. This finding highlights the need for a backface specification requirement for the AMMPHS nape guard and the need for an injury tolerance for the cervical spine under focal contact loading. A review of scientific literature was unsuccessful at identifying tolerance levels of the neck to contact loading.

Ballistic tests were conducted on overlapping panels to determine the minimum overlap required to maintain the same V50 performance of a single panel across the height of a dual panel system. For all materials configurations it was determined that a minimum of 2 cm overlap is needed. If less than 2 cm was employed the rear panel moved out of the way during the ballistic strike and did not contribute to the stopping ability of the dual panel system.

Tests were conducted at Vproof velocities to determine proximity to the edge at which penetration occurred. For the Soft Steel and the Spectra Shield penetration of the 17 grain FSP projectile only occurred at 0.5 cm from the edge whereas with the Kevlar penetration began to occur at 1 cm from the edge. Similar testing was conducted with test samples having sewn edges and it was found the stitching reduced the effectiveness of the both the Kevlar and the Spectra Shield but had no effect on the Soft Steel.

Penetration of the 96 grain sphere was also observed for both the Spectra Shield and the Kevlar at 1 cm from the edge however, no penetration was recorded for the Soft Steel.

The relevance of these finding to a nape guard design are:

• If a multi panel design is considered a minimum of 2 cm overlap between panels is required.

• A dual panel design is not as effective as a single panel when protecting against a 96 grain sphere.

• The design of the nape guard must consider the pencilling effect of the ballistic fabric.

• Stitching of the ballistic fabrics should be avoided as this may reduce the ballistic performance of the nape guard ballistic particularly as the shot placement approaches the edge of the panels.


It is important to note that these results have broader implications than just the nape guard design which supported the study reported here. Soft armour overlap and small components are characteristic of a range of modular armour systems. The increased performance possible with narrow ballistic components has implications for optimization of areal density. The results for minimum overlap and the drop off in ballistic performance at the edges of soft armour panels should also be considered in armour design, in particular modular armour systems with articulated components (e.g. the interface between shoulder caps/brassards and the fragmentation vest).


References .....

[1] Bayne, T., Fournier, E., Anctil, B., Shewchenko, N., "AMMPHS Specification Review - Head Protection", Biokinetics and Associates Ltd. contract report for Defence Research Canada Valcartier, Biokinetics Report No. R08-09, October 2008.

[2] Cork, C. R., Foster, P. W., "The Ballistic Performance of Narrow Fabrics", International Journal of Impact Engineering, Page 495 to 508, 2007.

[3] Bass. C. R., Rafaels, K. A., Salzar, R. S., Carboni, M., Kent, R. W., Lloyd, M. D., Lucas, S., Meyerhoff, K., Planchak, C., Damon, A., Bass, G. T., "Thoracic and Lumbar Spinal Impact Tolerance", Accident Analysis and Prevention 40 (2008), pages 487 to 495.

[4] "Personal Protective Equipment (PPE) for Blunt Impact", Canadian Standards Association, Standard Number Z617-06, March 2006.


List of symbols/abbreviations/acronyms/initialisms

AMMPHS Advanced Modular Multi-threat Protective Headwear System

BABT Behind armour blunt trauma

DND Department of National Defence

DRDC Defence Research & Development Canada

DRDKIM Director Research and Development Knowledge and Information Management

FSP Fragment Simulating Projectile

R&D Research & Development

V50 Velocity at which 50% of ballistic impacts penetrate

Vproof No penetration expected: 0.8 x V50

DOCUMENT CONTROL DATA (Security classification of title, body of abstract and indexing annotation must be entered when the overall document is classified)

1. ORIGINATOR (The name and address of the organization preparing the document. Organizations for whom the document was prepared, e.g. Centre sponsoring a contractor's report, or tasking agency, are entered in section 8.)

Biokinetics and Associates Ltd. 2470 Don Reid Drive Ottawa, Ontario K1H 1E1

2. SECURITY CLASSIFICATION (Overall security classification of the document including special warning terms if applicable.)

UNCLASSIFIED

3. TITLE (The complete document title as indicated on the title page. Its classification should be indicated by the appropriate abbreviation (S, C or U) in parentheses after the title.)


4. AUTHORS (last name, followed by initials – ranks, titles, etc. not to be used)

Fournier, E.

5. DATE OF PUBLICATION (Month and year of publication of document.)

September 2009

6a. NO. OF PAGES (Total containing information, including Annexes, Appendices, etc.)

40

6b. NO. OF REFS (Total cited in document.)

4

7. DESCRIPTIVE NOTES (The category of the document, e.g. technical report, technical note or memorandum. If appropriate, enter the type of report, e.g. interim, progress, summary, annual or final. Give the inclusive dates when a specific reporting period is covered.)

Contract Report

8. SPONSORING ACTIVITY (The name of the department project office or laboratory sponsoring the research and development – include address.)

Defence R&D Canada – Valcartier 2459 Pie-XI Blvd North Quebec (Quebec) G3J 1X5 Canada

9a. PROJECT OR GRANT NO. (If appropriate, the applicable research and development project or grant number under which the document was written. Please specify whether project or grant.)

12RR08

9b. CONTRACT NO. (If appropriate, the applicable number under which the document was written.)

W7701-85408

10a. ORIGINATOR'S DOCUMENT NUMBER (The official document number by which the document is identified by the originating activity. This number must be unique to this document.)

R09-09b

10b. OTHER DOCUMENT NO(s). (Any other numbers which may be assigned this document either by the originator or by the sponsor.)

DRDC Valcartier CR 2009-148

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Unlimited

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Unlimited

13. ABSTRACT (A brief and factual summary of the document. It may also appear elsewhere in the body of the document itself. It is highly desirable that the abstract of classified documents be unclassified. Each paragraph of the abstract shall begin with an indication of the security classification of the information in the paragraph (unless the document itself is unclassified) represented as (S), (C), (R), or (U). It is not necessary to include here abstracts in both official languages unless the text is bilingual.)

The Advanced Modular Multi-threat Protective Headwear System (AMMPHS) development program was initiated to address the evolving head protection needs of Canadian soldiers in today’s battlefield. The nape is one area of the head in which additional protection is sought from ballistic threats. AMMPHS nape guard designs have been proposed that comprise short curtains of ballistic fabrics suspended from the rear edge of a helmet. It is not know how these designs will perform under ballistic impact, particularly as the strike location approaches the free edge of the nape guard panels. A series of ballistic tests were conducted with 17 grain FSPs and 96 grain steel spheres where the shot placement was varied from the centre of the test sample to the edge. The effect of overlapping fabric edges was also evaluated to determine the minimum amount of overlap required to maintain uniform ballistic protection. Generally, the results confirm the ability of a fabric ballistic nape guard concept but raise a concern regarding blunt impact trauma to the neck resulting from backface deformation of non-penetrating ballistic strikes.

Le programme de développement du système de protection modulaire multi menaces (AMMPHS) a été mis sur pied afin d’adresser les besoins de protection à la tête des soldats canadiens contre les menaces rencontrées sur le champ de bataille. Dans ce cas ci, une protection balistique additionnelle est recherchée au niveau de la nuque. Des concepts de protecteur de nuque AMMPHS ont été proposé. Ces concepts consistent en de courtes toiles de tissu balistique suspendues au rebord arrière du casque. La performance balistique de ces concepts est encore inconnue, en particulier lorsque le point d’impact s’approche de l’extrémité du protecteur qui n’est pas attaché au casque. Une série de tests balistiques a été effectué avec des FSP de 17 grains et des sphères de 96 grains où les points d’impacts variaient du centre vers les extrémités des échantillons. L’effet de chevauchement des tissus a aussi été évalué afin de déterminer le minimum de chevauchement requis pour maintenir une protection balistique uniforme. En général, les résultats confirment la capacité d’un protecteur de nuque souple mais lèvent le doute au sujet des traumatismes contondants au cou reliés aux effets arrières lors d’impacts non pénétrants.

14. KEYWORDS, DESCRIPTORS or IDENTIFIERS (Technically meaningful terms or short phrases that characterize a document and could be helpful in cataloguing the document. They should be selected so that no security classification is required. Identifiers, such as equipment model designation, trade name, military project code name, geographic location may also be included. If possible keywords should be selected from a published thesaurus, e.g. Thesaurus of Engineering and Scientific Terms (TEST) and that thesaurus identified. If it is not possible to select indexing terms which are Unclassified, the classification of each should be indicated as with the title.)

Nape guard; ballistic neck protection; thin strips ballistic performance; suspended ballistic fabric; ballistic performance fabric overlap

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