Understanding the ballistic event: methodology and initial observations
Understanding the ballistic event: methodology and initial observations
Adam Healey 0 1
John Cotton 1
Stuart Maclachlan 1
Paul Smith 0
Julie Yeomans 0
0 University of Surrey , Stag Hill Campus, Guildford, Surrey GU2 7XH , UK
1 Lucideon Limited , Queens Road, Penkhull, Stoke-on-Trent, Staffordshire ST4 7LQ , UK
The purpose of the study is to accelerate the development of ceramic materials for armour applications by substantially increasing the information obtained from a high-energy projectile impact event. This has been achieved by modifying an existing test configuration to incorporate a block of ballistic gel, attached to the strike face of a ceramic armour system, to capture fragments generated during the ballistic event such that their final positions are maintained. Three different materials, representative of the major classes of ceramics for armour applications, alumina, silicon carbide, and boron carbide, have been tested using this system. Ring-on-ring biaxial disc testing has also been carried out on the same materials. Qualitative analysis of the fracture surfaces using scanning electron microscopy and surface roughness quantification, via stereo imaging, has shown that the fracture surfaces of biaxial fragments and ballistic fragments recovered from the edges of the tile are indistinguishable. Although the alumina and boron carbide fragments generated from areas closer to the point of impact were also similar, the silicon carbide fragments showed an increase in porosity with respect to the fragments from further away and from biaxial testing. This porosity was found to result from the loss of a boron-rich second phase, which was widespread elsewhere in the material, although the relevance of this to ballistic performance needs further investigation. The technique developed in this work will help facilitate such studies.
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Ceramic armour material systems have been in use
for over one hundred years and since the Vietnam
War they have provided protection from
high-velocity projectiles to vehicles, aircraft, and personnel
on the battlefield. The key property for an armour
system is the ability to resist high-energy projectile
impacts, which is referred to as ballistic performance.
If this can be combined with a low weight (by using
low density materials), this offers the prospect of
increased fuel economy and/or manoeuvrability.
Ideally, these properties will be delivered at a low
cost.
Common ceramic materials used for armour
systems are aluminium oxide (Al2O3), known as
alumina, silicon carbide (SiC), and boron carbide (B4C).
Of these, the most widely used is alumina, due to its
comparatively low cost of manufacture and
effectiveness in protecting against common battlefield
threats. Silicon carbide is of lower density and able to
resist higher energy impacts but is more expensive.
Finally, boron carbide has very low density and high
impact resistance, but the high cost often restricts it to
applications where weight-saving is critical, such as
in aircraft [1]. New ceramic materials are currently in
development to improve on these baseline materials.
A significant obstacle in armour development is an
incomplete understanding of the phenomena that
occur when a high-velocity projectile strikes an
armour target. Upon penetration, the bullet and the
ceramic strike face undergo a number of processes,
such as fragmentation, to dissipate the kinetic energy
of the projectile to the extent that what remains is
completely stopped by the composite backing of the
armour system. The high speed nature (strain rates of
approximately 108 s-1) and resulting damage to
samples inflicted during this interaction, known as
the ballistic event, make it difficult to identify the
individual mechanisms that dissipate the kinetic
energy of an incoming projectile [2, 3]. Further, it is
very problematic to systematically alter one property
of a ceramic, such as grain size, to gauge its effect on
ballistic performance, without inadvertently altering
other microstructural parameters. Some properties of
ceramics, such as compressive strength, are also
known to be strain-rate dependent, causing changes
in the material behaviour between test regimes and
affecting the nature of brittle fragmentation [4].
Furthermore, the ballistic event is sensitive to changes in
strike face and backing material combinations, as
well as projectile type, speed, and other variables.
Thus, predicting the outcome is challenging [5, 6].
Consequently, the only widely accepted method of
assessing how effective a new system or material is at
resisting impact is to subject it to ballistic testing. Due
to the statistical nature of the mechanical properties
of ceramics this is a very expensive process; a robust
test requires a minimum of 25 armour samples [7],
and over 100 are required for a full understanding of
the statistics of the material. This high cost is a
significant barrier in the development of new armour
materials.
A new test (or suite of (...truncated)