JEC COMPOSITES MAGAZINE - Issue #79 - March 2013 - 93

Energy loss
Equation (4) describes the calculation of the impacting projectile’s energy loss due to the fabric it goes through. This is an
indicator of fabric effectiveness in absorbing and dissipating the
impact energy carried by the projectile.

Fig. 3: Fabric types and their normalised projectile energy loss

Ballistic fabrics with different structural features were tested for
projectile energy loss. Besides GRPG-1, the GRPG-2 fabric,
with more rigorous gripping, was also tested along with the
broad plain woven fabric. The comparison also involved a type
of 3D fabric which has potential application in female body
armour, denoted as 3D4LXX where XX is the weft density
of the fabric. As illustrated in Figure 3, GRPG-2 caused the
highest energy loss from the projectile, followed by GRPG-1.
This is attributed to the enhanced yarn gripping in both fabrics.
The 3D fabric for female body armour compared less favourably among these fabrics. This is because the 3D4LXX fabric
contains free yarns which are under the lowest level of yarn
gripping. The broad plain woven fabric BFPlain ranked third in
this exercise. Figure 4 shows the effectiveness of yarn gripping
for a wider range of methods. A similar tendency is displayed
for the wider choices of yarn gripping methods in plain woven
fabrics.

Study on making up 3D ballistic panels
Angle-laid panels
The construction of ballistic panels is also technologically
challenging. Upon impact from a projectile, the stress and strain
are distributed in each fabric layer and also among the layers.
Woven fabrics are formed by interlacing warp and weft yarns
and therefore they are highly orthotropic. When a woven fabric
is impacted, the strain mainly appears in the directly hit warp
and weft yarn, which are termed primary or principal yarns. In
most ballistic panels for body armour, fabrics are layered up in
the same orientation. This makes the panel orthotropic too. In
an ideal situation, an isotropic ballistic panel would maximise
energy absorption, as illustrated in Figure 5. In a research study
at the University of Manchester, experimental and FE analyses
were carried out to create a panel with angled layering of the
constituent fabrics, because layering offers the opportunity to
change the panel structure.

Fig. 5: Comparison of deformation area for orthotropic and isotropic panels

In the present study, four groups of fabric panels (2, 3, 4 and 8
plies) were selected to study the influence of the layering angle
on energy absorption during high strain rate impact. The plans
for all 4 panels are shown in Figure 6.
A detailed finite element analysis
(FEA) using ABAQUS was
carried out to study the transverse impact of a projectile onto
various woven fabric panels.
The fabric model is modelled at
a yarn-level resolution. Typical
values of 2.67 mm for yarn-crimp
wavelength, 1440 kg/m3 for
yarn volumetric density, and
0.345 mm for fabric thickness are
assumed. The yarn cross section
was meshed using 10 elements
and yarn wavelength using twelve
elements. The projectile was
modelled as a rigid body. Simple
Coulomb friction was introduced

Fig. 4: Energy absorption by fabrics with wider choices of different yarn gripping methods

No79 March 2013

/ jec composites magazine 93

JEC COMPOSITES MAGAZINE - Issue #79 - March 2013

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