JEC COMPOSITES MAGAZINE - Issue #79 - March 2013 - 91

performance. 2D woven fabrics are the most commonly used
structures for ballistic fabrics. Plain weave fabrics exhibit the
highest level of intersection density, followed by twill and then
satin. Therefore, the dimensional stability and the control over
yarns in a plain weave fabric is the highest among these three
basic structures. Stempień [13] studied the influence of a woven
fabric structure on the propagation velocity of a tension wave
and found that the propagation velocity depends not only on
the propagation velocity in yarn, but also on the parameters
of the woven fabric structure, such as the weave, and weft and
warp densities. Maximum propagation velocity of the tension
wave occurs in plain woven fabrics. 3D fabrics are constructed
by interlacing yarns in the network-forming fashion while introducing a third dimension other than the planar dimension. The
main advantage of a 3D structure is reinforcement in throughthe-thickness direction; hence the dimensional stability of
3D fabrics is much greater than that of 2D fabrics [14]. A
combined structure was also created to improve the protection
against bullets. Steeghs et al [15] invented a kind of ballistic
vest containing a stack of flexible fabrics and a stack of flexible
unidirectional layers, in which the fabrics contain strong fibres
of a first kind, the unidirectional layers contain strong fibres of a
second kind, and the fibres in a unidirectional layer run essentially parallel and are disposed at an angle to fibres in an adjacent layer. Roylance [16] studied the ballistic impact of textile
structures and found that the vast majority of ballistic energy
was deposited in the orthogonal fibres passing through the
impact point, while the other fibres are essentially ineffective,
which suggests possible improvements in the design of textile
structures intended for dynamic impact applications. Cork and
Foster [17] studied the relationship between fabric width and
ballistic impact performance. In this study, two narrow fabrics
with and without selvages were compared with a full-width
sample of the same structure. The result showed that the narrow
fabric strip without selvages had improved ballistic performance
over larger clamped fabric sheets, or wider strips. The inclusion of a selvedge into the narrow fabric strip further increases
ballistic performance. For a given type of fibre, Sun and Chen
[18] found that the construction of the woven fabric is the main
influencing factor affecting how the waves propagate, which is
directly related to the protective performance of the fabrics.

Ballistic fabric engineering
Fabric penetration modes
In general, high-velocity projectiles may penetrate ballistic
fabrics in three modes, depending on the interaction between
the impacting projectile and the fabric layer. Firstly, the projectile can break the fibre and get through the fabric. This happens
to the first few fabric layers in the body armour panel when the
projectile still carries a high level of impact energy. From this
point of view, the use of fibres with stronger impact strength
would certainly contribute to better protective body armour.
The second mode in which a projectile penetrates a fabric is
that it passes between the adjacent yarns. The use of tight fabric

constructions such as the plain weave in ballistic fabrics certainly helps the yarns resist to the pushing force in the impact
vicinity. Some researchers reported on the use of unidirectional
fabrics for better performance but they had to constrain the
fabric by other means. The third way that a projectile penetrates
a fabric is by pulling the yarns out of the plane of the fabric. This
happens especially when the projectile is about to be stopped in
the fabric assembly. The second and the third forms of penetration both indicate the influence of fabric construction and
between-yarn friction on the ballistic performance of the fabric.
The energy loss is calculated from v0 and v1, which are the
projectile velocities before and after penetrating the fabric target
as follows.
(4)
The energy loss for the projectile or the energy absorption for
the fabric panel is often used as a performance indicator for
single-layer or multi-layer ballistic panels based on penetration
tests.
Fabric balance indicator
Cork and Foster [17] defined the balance indicator for woven
fabric as follows:
(5)
where n1 and n2 are the warp and weft densities and T1 and T2
are the linear densities of the warp and weft yarns, respectively.
Obviously, S=1 indicates that the fabric cover in both warp and
weft directions is the same, and a small value of S tells that the
fabric cover in warp and weft directions is very different. They
were able to show that fabrics with a high balance indicator
cause greater energy loss of the projectile.
Fabric fineness
It was also demonstrated that for the given fabric areal density,
fabric panels made of finer fabrics cause more energy loss than
with coarser fabrics. This suggests that fine ballistic fabrics are
able to provide better ballistic protection than coarse ones.
However, when taking cost into consideration, the use of fine
fabrics for ballistic protection is more expensive than the use of
coarse fabrics.
Yarn gripping
Researches show that inter-yarn friction in a woven fabric
helps improve ballistic performance [3]. In practice, different
measures can be taken to enhance yarn gripping. Researchers
at the University of Manchester devised different methods to
increase yarn gripping in woven fabrics (GRPG-1 and GRPG2) through weaving.
GRPG-1 is a novel 2D woven structure that can be readily manufactured using existing weaving technology with virtually no
No79 March 2013

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JEC COMPOSITES MAGAZINE - Issue #79 - March 2013

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