experimental results on ballistic plates with ......and 709, supplied by teijin aramids and...

Proceedings of the 6th International Conference on Mechanics and Materials in Design,

Editors: J.F. Silva Gomes & S.A. Meguid, P.Delgada/Azores, 26-30 July 2015

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PAPER REF: 5534

EXPERIMENTAL RESULTS ON BALLISTIC PLATES WITH

STRATIFIED ARAMID FABRICS

Catalin Pirvu1(*), Lorena Deleanu

1, Simona Badea

2, Marcel Istrate

3

1Faculty of Engineering, “Dunarea de Jos” University of Galati, Galati, Romania

2Department Scientific Research Center for CBRN Defense and Ecology, Bucharest, Romania

3Stimpex SA Bucharest, Romania

(*)Email: [email protected]

ABSTRACT

This research has as objectives to test stratified composites made of aramid fabrics type SB1

and 709, supplied by Teijin Aramids and intermediate layers of PVB (polyvinyl butyral

Resin), in order to reduce both the specific weight and the deformations caused by the impact

in order to diminish the harm / anti trauma risk.

Light weight packs of 215 g ±5g were obtained with 24 layers for LFT SB1 and 32 layers for

CT 709. They were tested with 9 mm FMJ (full metal jacket) bullet. All tests conditions were

the same for both packs and fires were repeated for each packs.

SEM investigation pointed out a different behavior of the two woven stratified packs. Also,

the bullet failure is different after heating the target-plate.

Keywords: ballistic impact, aramid fabrics, armor plate, PVB binding.

INTRODUCTION

The history of the armor industry and use is a competitive succession in projectile and then

armor performences (Abrate, 2011) (Bhatnagar, 2006). The protective packs been one of the

more efficient protective systems, but its requirements are demanding due to a particular

combination between resistance and mobility in the field. The resistance of a target when it

has been impacted by a projectile is a topic of interest in several important fields of human

activity (military, aerospace, civil and nuclear applications).

Increasing competition within textile composite industry and growth of global market are

incentives enough to prompt identification of the components of flexible textile composites

and the fabrication methods to produced them (Summerscales, 1998).

Ballistic experiments are crucial to further understand the complexity of penetration

mechanics in order to identify key parameters defining the perforation and damage

phenomenon of the armor materials (Hub, 2012), (Nahshon, 2007) (Safta, 2011). The

concurrence between protective plate and projectil intensifies research activities on both

subjects. Even if models and simulation have become closer to the actual facts in ballistic

impacts (Nilakantan, 2012), experimental work is the final step for introducing new materials,

processing methods and improvements in the system response.

Fabrics are introduced in stratified composites able to sustain impact load. At low velocity,

even glass fiber fabrics could have satisfactory results (Rilo, 2008), but for higher velocity

and an increased protection of body and equipment, aramid fabrics exhibit better properties

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(Carrillo, 2012). Recently, nanocomposites reinforced with nanotubes are tested as shields to

protect the soft-tissues during impact (Unnikrishnan, 2013).

The aim of this paper is to point out the differences between two ballistic plates and particular

failure of aramid fibers, based on tests.

In terminal ballistic, the either bullet or armor performance requires complex technics and

experimental will finally characterize the protection system.

In practice, in order to evaluate protection plates and munitions, several civil and military

tests have been considered as reference standards (MIL-STD-376A), the tests results giving

the possibility of including the plates in one of the protection classes. For body armor

protection, standards require not only the absence of perforation, but also a constraint

concerning the print generated in the ballistic clay behind the plate hit by the bullet (44 mm

for NIJ standard – limit that characterizes body vulnerability).

For reasons as fire costs, monitoring equipment access for bullet velocity and shutting

precision, the study has a statistical approach, based on a limited number of fires. As this

study is still at the beginning, the fire is repeated only 6 times for each pack, for close range.

The ballistic protection systems have o wide diversity of solutions taking into account the

nature and structure of the materials and the penetrator characteristics (Carrillo, 2012),

(Bhatnagar, 2013), (Safta, 2011).

This research has as objective to test stratified composites made of aramid fabrics type SB1

and 709, supplied by Teijin Aramids and intermediate layers of PVB, in order to reduce both

the specific weight and the deformations caused by the impact in order to diminish the harm /

anti trauma risk.

TESTING METHODOLOGY

Square samples were cut from the fabrics (200 mm x 200 m). Then, the ballistic package was

made of 24 plies of LFT SB1 fabrics and 32 plies of CT709, the number of plies being

selected in order to keep the mass plate almost equal (approximately 215...220 g).

The plies were bonded with the help of a solution of polyvinyl butyral (PBV) and alcohol.

Then, each pack was compacted at a specific pressure (43 bars), the temperature of the press

plate being heated to a 145 ºC after 10 minutes and this temperature was maintained for other

25 minutes. Then the pressed packs were slowly cooled to the room temperature for 15

minutes.

Tests were done on two types of ballistic packs having 200 mm x 200 mm. Ballistic plates

may be used alone or in combinations with plates made of other materials for improving the

safety factor.

The characteristic of fabrics are given in table 1 and Table 2. CT 709 is a Teijin Aramid

material primary used for body armor, based on unique Twaron microfilament yarns.,having

an excellent ballistic protection combine whit a high level of confort. Particulary used for

body armor vest for women, CT 709 implements a new tipe of ballistic protection based on a

surprising freedom of movement combine whit a high protection. Twaron LFT SB1 is a

flexible material and has a significantly improved bullet resistence compare whit traditional

CT 709 because the weight of the entire pack can be reduce by much as 25 % and achieved

the same level of protection, increasing the confort of the wearer.



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Table 1 - Characteristics of CT 709, plain weave

Linear

Density

[dtexnom]

Warp/

Weft

Twaron-

Type

Warp/

Weft

Set

[per 10 cm]

Set

[per inch]

Areal density

Th

ick

nes

s [m

m]

Minimum

Breaking

Strength

[N/5cm x

1.000]

Minimum

Breaking

Strength

[lb/in x

1.000]

[g/m2] [oz/yd

2]

Warp Weft Warf Weft

War

p

Wef

t

War

p

Wef

t

930f1000 2040 105 105 27 27 200 5.90 0.30 8.0 8.50 0.914 0.971

Table 2 - Characteristics of SB1 coated fabrics

Style Main

Application

Linear

Density

[dtexnom]

Twaron-

Type

Total

weight

[g/m2]

Construction

Bullet

resistant vests

930 f1000

2040 220 2 layers Twaron woven fabric

+ 3 layers thermoplastic film of PE

The first pack was obtained by alternating 24 plies of aramid fabrics SB1

by LDPE foils (0.915–0.925 g/cm3). LDPE has a low melting point (110-

120 ºC) and a good impact resistance. The thickness of this pack was

4.2…4.4 mm (the quantity of LDPE being 15 g for each package). The

second pack was obtained by alternating the same fabrics with PVB

(Polyvinyl Butyral Resin), a resin that have a combination of properties

that make them a key ingredient in a variety of applications: binding

efficiency, adhesion to a large number of surfaces and toughness

combined with flexibility. The ballistic packs were pressed between

metallic plates, at 44 bars, and then heated to 145 ºC and maintain at this

constant temperature for 25 minutes. Then they were cooled to the room

temperature in a period of 10 minutes.

Test were done with the help of a ballistic barrel (velocity of 400 ...410

m/s), using a bullet of 9 mm FMJ (Fig. 1).

After being tested, the packs were cut with the help of a guillotine. Other methods for cutting

the packs were tested, but with no results concerning the cut quality and the influence of

cutting on the zone of interest.

RESULTS AND CONCLUSIONS

The phenomena discussed in this paper improve the understanding of the process of

perforation in particular the effect of the composite material behavior.

The pack LFT SB1+PVB had a better behavior under bullet impact as the print generated in

the ballistic modeling clay has a smaller depth with 2-3 mm as compared to that obtained

when using the pack with plies made of CT 709.

SEM investigation pointed out a different behavior of the two woven stratified packs. Also,

the bullet failure is different after heating the target-plate.

Fig. 1 - 9 mm FMJ

bullet

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a) perforation of the initial plies

(stage I)

b) interlayer deformation (stage II) c) bullet rebond (stage III)

LFT SB1

d) perforation of the initial plies

(stage I)

e) interlayer deformation(stage II) f) bullet rebond (stage III)

CT 709

Fig. 2 - Images during the bullet impact for each pack

(images were obtained by a fast camera, frame rate of 4500/s)

Fig. 1 displays a representative projectile velocity curve during the impact testing of single-

layer clamped fabrics. Taking into account (Nilakantan, 2012), there were identified the three

main stages during the impact of the pack (Fig. 2),

- stage I is dominated deformation and energy dissipation mechanisms; momentum transfer

between the projectile and fabric leads to an increase in the fabric kinetic energy, which is

primarily confined to the pyramidal deformation region or region behind the fronts of the

transverse displacement wave. Simultaneously, the yarns start to decrimp and elongate as

the longitudinal stress wave propagates along the yarn leading to an increase in the yarn

internal or strain energy. If the fabric is partially clamped in a bias orientation, then

frictional yarn reorientation can be a significant energy dissipating mechanism, otherwise

frictional sliding energies remain small in magnitude with respect to the kinetic and

internal energy transformations;

- stage II is dominated by frictional yarn pullout; one or more yarns can be pulled out of

the fabric weave and dissipate significant frictional sliding energy; the rate of projectile

deceleration is usually much lower than in stage I; excessive yarn pullout also promotes

the windowing mechanism, the bullet pushing aside several principal yarns, during its

penetration through the fabric;

- stage III corresponds to the post-impact region where, for non-penetrating impacts, the

projectile may rebound backwards after being arrested by the fabric; depending on the

impact scenario, the projectile velocity history may comprise of only region I or a

combination of two or more regions (Nilakantan, 2012).



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There are other energy dissipating mechanisms, including bullet deformation, acoustic and

heat losses, fabric damping and air drag, filament transverse deformations and inter-filament

(intra-yarn or among fibers) friction.

SEM images were analyzed from three points of view: micro-level for evaluating the fiber

failure, mezo-level for damages of the yarns and macro-level taking into account damages of

plies and the entire pack.

a) b) c)

Fig. 3 - SEM images of the pack made of CT 709

a) b) c)

Fig. 4 - SEM images of the pack made of LSF SB1

Figures 3 and 4 present similar mechanisms of fiber rupture, but the yarns remain denser and

the failed end of the fibers are torn and twist in LSF SB1 pack as compared to more fibers cut

by traction in the pack made of CT 709.

Figure 5 presents details of the end of a broken yarn. Even if the fibbers seem to be similar as

concerning the dimensions, the different weaving style and the structure of the layer (1 layer

for CT 709 and two layers of aramid textile with three thin layer of UDPE, for LASF SB1)

induces different ways of yarn failure. In CT 709 pack, the bullet seems to easier put away

several yarns near those they have been already fractured.

Typical aspects of fibers damage are given in Figures 5 to 8. In the pack made of LSF SB1:

peeling (Fig. 6c) and micro-fibrillation (Fig. 9c) (Fig. 6b, c), shear cut (Fig. 9b); in the pack

made of CT 709: twisting and tailing out of the fibers near the broken end for pack made of

CT 709 (Fig. 5b, c and Fig. 8).

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a) b) c)

Fig. 5 - Aspects of fractured fibers in the pack made of CT 709

a) b) c)

Fig. 6 - Aspects of fractured fibers in the pack made of LSF SB 1

a) b) c)

Fig. 7 - Other SEM images of fractured fibers in the pack made of CT 709

a) b) c)

Fig. 8 - Other SEM images of fractured fibers in the pack made of LSF SB 1

The yarns remain more bundled in LSF SB1 pack as compared to CT 709 pack. The effect of

overlapping the lenticular yarns due to the particular weaving in satin is more effective as



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compared to single woven type with space between yarns, (very probable due to the smaller

curvature radius of the first type).

From Fig. 9, one may notice that polyethylene foils dissipate some amount of impact energy

as the polymer exhibits a damping and bond-retain character.

a) plates cut, the bullet have been extracted. Paper clam was used for

suggesting the initial thickness of the pack

b) frontal view of the pack

Fig. 9 - up: pack of CT 709; down: pack made of LSF SB1

a) view from behind b) front view

Fig. 10 Bullets extracted from the ballistic plates

(left – bullet extracted from SB1, right – bullet extracted from 709)

After tests, the broken plies were numbered for each pack. For instance, packs in Fig. 9 are

characterized as follows: the pack made of CT 709 had 4 broken plies (representing 12.5% of

the hole number of plies - 32) and the pack made of LFT BS1 had 4 plies broken too, but they

represent 16.66% of the total number of plies - 24). The pack with LSF SB1 constrained the

bullet to be more flattened but the bullet arrest in the pack with CT 709 is more gibbous and,

thus, explaining the deeper print in the ballistic clay (Fig.10).

CONCLUSIONS

Packs made of LSF SB1 behave better as concerning the damage of the pack and the final

deformation into the clay support. The gain for LSF SB1 is not very substantial, SEM

investigations supporting this conclusion. Fibers failed in similar ways but yarns and pack

damages are different.

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For each pack type, there were identified the failure stages. All qualitative observations were

in the favor of plates made of LSF SB1. Quantitative evaluation need more tests and a

statistical approach.

ACKNOWLEDGMENTS

The work of CATALIN PIRVU and LORENA DELEANU was supported by Project SOP

HRD /159/1.5/S/ ID 132397 - ExcelDOC.

REFERENCES

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7, no. 1, p. 21-29.

[3]-Nahshon K, G. Michael G, Pontin MG, Evans AG, Hutchinson JW, Zok FW, Dynamic

shear rupture of steel plates, J of Mechanics of Materials and Structures, 2007, vol. 2, no. 10,

p. 2049-2066.

[4]-Bhatnagar A, Lightweight ballistic composites, CRC Press, Boca Raton Boston New York

[5]-Unnikrishnan VU, Unnikrishnan GU, Reddy JN, Rostam-Abadi F., Multiscale analysis of impact

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panel and its staggered improvement with internal-structure model, Int J Mech Mater Des, 2015.

[7]-Rilo NF, Ferreira LMS, Experimental study of low-velocity impacts on glass-epoxy

laminated composite plates, Int J Mech Mater Des, 2008, no. 4, p. 291–300.

[8]-Nilakantan G, Gillespie Jr. J.W, Ballistic impact modeling of woven fabrics considering

yarn strength, friction, projectile impact location, and fabric boundary condition effects,

Composite Structures, 2012, 94, p. 3624–3634.

[9]-Safta I, Contribuţii la studiul teoretic şi experimental al mijloacelor individuale de

protecţie balistică (in Romanian), Military Technical Academy, Bucharest, 2011.

[10]-Carrillo JG, Gamboa RA, Flores-Johnson EA, Gonzalez-Chi PI, Ballistic performance of

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[11]-Summerscales J., Microstructural characterisation of fibre-reinforced composites, CRC

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experimental results on ballistic plates with ......and 709, supplied by teijin aramids and...

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