Disclosure: I was invited by the
Tank Museum at Bovington in 2019. Here you can see the Challenger tank, although
it seems like huge steel beast, its armor also contains ceramics in it. Now, ceramics are
known to be rather hard, but also quite brittle, since often with high hardness comes less
ductility. High hardness can result in the armor breaking and generally reduces also multi-hit
capability. This of course raises the question: why use ceramic armor in the first place?
Well, as so often there are several factors involved, the first and fundamental aspect
here is the disruptor and absorber concept. To put it simply, one wants to disrupt
or blunt the incoming projectile and also absorb the large amounts of energy as
well. So, ideally one combines a material with high-strength that acts as a disruptor:
“The purpose of these high-strength materials is to blunt the incoming projectile or rapidly
erode it. If the projectile is fragmented, a hard material will tend to radially
disperse the fragments, therefore, the kinetic energy of the projectile is
deflected and dispersed in the fragments.” Additionally, to the disruptor, we want
a material that serves as an absorber, so a material, which can sustain large amounts
of plastic deformation before it fails. Examples for absorbers would be rolled homogenous
armor, polymers or fiber-reinforced plastics. In case of World War 2, this concept was realized
to a degree with armor plates that had face hardened armor like the Panzer III. Whereas,
“Homogenous armor has the same hardness all the way through, generally about 220-300 BHN, while
face-hardened armor has a thin layer of 450 to 650 BHN hardness in an otherwise homogenous plate.”
To give you some idea about the effectiveness: 2-pounder armor piercing shell could
penetrate 86 mm of homogenous armor at 0 degree and point-blank range, yet,
only 66 mm if the armor was face hardened. Yet, there is more we need to discuss, because
the ceramics we know from day-to-day life, like those in our bathrooms are a bit different
to the technical ceramics used in armor. Professor Paul Hazell from the University of New South Wales
Canberra will give us a short overview about them: the Ceramics when we the ones that we Deploy
on Armor systems uh generally are well they are always what we call technical Ceramics or
engineering Ceramics which are fully densified structures normally they would comprise of
self-selecting atoms which one of which would be metallic and one would be non-metallic so for
example aluminum oxide so you've got aluminum there and you've got an oxide part of the the
molecule so the what um Ceramics do is that they they offer a really good way of uh providing a
resistance to penetration by simply because they they are hard fully identified structures and what
I mean by that is not to say that they're they're dense per se that they tend to have low density
values compared to other materials but they in in the armor context they tend to have um fairly um
they're strong they're they're resilient they have high harness values and they've been engineered
that way so you know that's why we would choose to use um one of those those materials it's
just a material class that's kind of um provides a good degree of hardness um and low density
The next question to ask, is how ceramic armor could be combined with other armor materials.
As a heads-up for the uninitiated, a HEAT round, is high explosive anti-tank round, also called
hollow or shaped charge, like a Panzerfaust, here is a short visualization about it:
The effect is called the Munroe or Neumann effect. So how does this effect work?
Here you can see the warhead. Such a warhead is generally called a hollow-charge or
a shaped charge, as you can see both make sense because the charge is both hollow and shaped.
So, when the warhead impacts, the impact fuze sets off the booster charge. This then leads
to the detonation of the explosive charge, which focuses the explosion and deforms
the warhead’s conical metal liner into a high-velocity jet. This jet is so fast that
it penetrates the armor. Be aware that it does not burn through. A common misconception
and an error that I made myself in the past. Professor Hazell will give you
now some examples on how ceramic armor could be combined with other armor.
it would depend upon a number of factors we did it would depend upon the type of projectile
that you're you're trying to defeat so for example um a multi-layered where you've got multiple
layers of ceramic might be appropriate for defeating a heat round for various reasons uh
whereas a um for for body armors you know of uh where you would need a ceramic tile um with a
a backing you might choose to use a ceramic and a composite backing which would provide which you
know provide that disruptor absorber concept that I previously mentioned so the Ceramics providing
the hard um outer surface bit like our you know face um hardened example that we discussed with
the Tiger tank and the backing layer provides you know the composite layer provides a kind of an
energy absorbing layer that can absorb the sort of the resulting fragments that are that have formed
so and that's kind of how we we get over that um that that sort of negative aspect I suppose
of of the brittle nature of of ceramics so the composite would be something like kevlar
yes exactly right um you know for for higher um you know for not just for personal
protection but uh if you look at vehicle armor and that type of thing you might
be using a glass fiber reinforced plastic or an ultra high molecular weight
ethylene is another example where um you know those types of of materials are used
you know there's a whole range of of Composites that are used the one composite that shouldn't be
used is actually carbon fiber and the reason for that is carbon tends to have a carbon fibers are
just too brittle and carbon panels tend to have a low trans laminar strength so in other words
they're not very good at dealing with punch forces Now, you probably ask how does a multi-layered
steel-ceramic armor defeat shaped charge jets. Well, glad you asked, since this is described
and shown in professors Hazell’s book: We have a composite armor consisting of 3 layers
of steel and in between are 2 layers of glass. The shaped charge jet penetrates the outer steel
layer, once the jet reaches the interface between the first steel and glass layer shocks
emerge. This does not stop the jet though. Yet, the shock reflects off the steel layer, this
reflected compression wave results in rearward movement of the first steel layer that drives
some parts into the path of the jet. Additionally, at the same time fractured parts of the
glass layer is also pushed into the jet. These movements results in a narrowing of the
penetration cavity and is repeated with the subsequent layers as well. Additionally,
the glass interlayer provides additional resistance to penetration due to spring back:
“When a jet penetrates a glass target, the penetration path opens up to its maximum
diameter within a few microseconds and then closes rapidly after the penetration front
passes. It is thought that the closure of the penetration cavity is caused by rapid
elastic recovery from high pressure near the penetration front.”
Furthermore, shaped charges used against strong ceramics produce narrow
cavities compared to metals. One aspect that makes ceramic suited for
layered armor is that a cone of damage is produced from the point of penetration outward as
you can see here. This means that the energy of projectile load is spread out over a wider
area, which should reduce the load on the absorber layer behind the ceramic armor:
“In the context of a two-component ceramic armour system, it would be expected that
the force of the penetrating projectile would be spread over a larger surface area
implying a better resistance to penetration.” Some properties of ceramic armor make it ideal for
defeating shaped charges, like fragmentation. Yet, these properties are generally less suited
for dealing with kinetic rounds. As such, for me question was, if ceramic armor
can be used against kinetic rounds. with tank armor what you're trying to do is
to maximize process called interface defeat or um or dwell so what you would do there is that
you would design your um your your tank armor so that you can cleverly maintain a compressive force
on the projectile as it's penetrating through it um and uh the way that that's achieved is through
a sort of a clever methodology of confinement um so yeah I'm I'm being deliberately
vague there that's that's all could probably say about in that one that's right
Well, I guess we reached the classified area, so let’s take a short look at some history.
The first wide-scale operational use of ceramic armor was during the Vietnam war, namely for body
armor of US helicopter crews. In 1965 such vest was started to produce, additionally the UH-1 Huey
were also equipped with ceramic armor elements: “[…] in 1965, the UH-I ‘Huey’ was fitted with
‘hard-face composite’ armour kit used in the armoured seats of the pilot and co-pilot. The
seats provided protection against 7.62-mm AP ammunition on the seat bottom, sides and
back using boron-carbide-face fibreglass.” Similar systems were also installed
in the AH-I Cobra as well. Before we summarize this, let us look at
the main advantages and disadvantages of ceramic armor versus metal armor.
The advantages are as follows: Good level of ballistic resistance
relative to the required thickness. Lightweight solution against certain
threats, e.g., shaped charges. Hard material.
Relatively cheap in terms of logistical requirements due to its lightweight and small size
The disadvantages are: Weak multi-hit capability.
Due to its brittleness, it can’t be used for load-bearing
structures, hence it is parasitic in nature. It can easily fracture, which can result in
damage in regular use or even during transport. For high-performing ceramics, the
cost can be relatively expensive. Additionally, the production process
for high-performing ceramics is very complex, which reduces availability.
To summarize, why ceramic armor is used, first, it provides very good resistance
against certain threats like shaped charges, against which regular steel armor
provides very limited resistance. Main drawback of ceramic armor is that it
is far less versatile than steel armor, e.g., you can’t build a tank out of ceramic armor
alone, due to its brittleness it must be combined. Second, due to its high hardness it also works
well as a disruptor against kinetic rounds when combined with a proper absorber material.
Big thank you to Professor Paul Hazell for the interview.
Thank you, the Tank Museum, at Bovington for inviting me.
Thank you for watching and see you next time.
