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Message 1 in thread
From: Gary (bb7525241@ntuvax.ntu.ac.sg)
Subject: HESH warheads
Newsgroups: sci.military.moderated
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Date: 1997/03/13
From Gary <bb7525241@ntuvax.ntu.ac.sg>

Doesn anyone here know about HESH(High Explosive Squash Head) warheads? 
I've read that they function by causing a spalling effect. Can someone 
verify this and provide info. on the construction of the warhead itself?


Regards,
Gary
Message 2 in thread
From: madrabit@metronet.com (madrabit@metronet.com)
Subject: Re: HESH warheads
Newsgroups: sci.military.moderated
View this article only
Date: 1997/03/14
From madrabit@metronet.com

Gary <bb7525241@ntuvax.ntu.ac.sg> wrote:


>From Gary <bb7525241@ntuvax.ntu.ac.sg> 
>Doesn anyone here know about HESH(High Explosive Squash Head) warheads? 
>I've read that they function by causing a spalling effect. Can someone 
>verify this and provide info. on the construction of the warhead itself?

HESH (called HEP-High Explosive, Plastic - in the US is a thin walled
shell loaded with explosive (usually plastique, I think) and a base
fuse.  When it hits the target it spreads out in a pancake against the
armor, and detonation causes a shock wave that propagates through  the
target and spalls off the inner wall in a hail of missles.  It is
devistatingly effective against concrete, and does not degrade when
fired from a rifled barrel as HEAT can.

Thr Brits use it instead of HEAT.  Nowadays, I think the only HEP in
US service is the 162mm on the combat engineer vehicle.


Bob Lyle
Message 3 in thread
From: Robb McLeod (antispam@uvic.ca)
Subject: Re: HESH warheads
Newsgroups: sci.military.moderated
View this article only
Date: 1997/03/14
From antispam@uvic.ca (Robb McLeod)

In article <E6zsBy.Bw4@ranger.daytonoh.ncr.com>,
   Gary <bb7525241@ntuvax.ntu.ac.sg> wrote:
>Doesn anyone here know about HESH(High Explosive Squash Head) warheads? 
>I've read that they function by causing a spalling effect. Can someone 
>verify this and provide info. on the construction of the warhead itself?

A HESH round consists of a plastic explosive warhead. with a detonator at the 
rear of the warhead.  Because of the velocity involved, the plastic explosive 
spreads itself over the target "like butter" when it hits.  The detonator 
impacts after this happens, blowing up this nice layer of explosive. 

The unique explosion effects create a stress wave in the armor.  When the 
stress wave reaches the other side, bits of the armor break off as pieces of 
spalling and bounce around inside the tank.

The problem with HESH is that it can't handle spaced armor.  Instead of the 
spalling bouncing around inside the tank, it bounces against the secondary 
plate, and thus, does nothing.

Robb McLeod
rmcleod@uvic.ca
(Please replace the "antispam" with "rmcleod" if replying via email)
Message 4 in thread
From: Gary (bb7525241@ntuvax.ntu.ac.sg)
Subject: Re: HESH warheads
Newsgroups: sci.military.moderated
View this article only
Date: 1997/03/14
From Gary <bb7525241@ntuvax.ntu.ac.sg>

> A HESH round consists of a plastic explosive warhead. with a detonator at the 
> rear of the warhead.  Because of the velocity involved, the plastic explosive 
> spreads itself over the target "like butter" when it hits.  The detonator 
> impacts after this happens, blowing up this nice layer of explosive. 
> The unique explosion effects create a stress wave in the armor.  When the 
> stress wave reaches the other side, bits of the armor break off as pieces of 
> spalling and bounce around inside the tank.

Doesn't this mean that no peneteration of the armour actually occurs? If 
that is the case, then spall liners would certainly ruin the effect, 
won't it?


Gary
Message 5 in thread
From: Robb McLeod (antispam@uvic.ca)
Subject: Re: HESH warheads
Newsgroups: sci.military.moderated
View this article only
Date: 1997/03/17
From antispam@uvic.ca (Robb McLeod)

In article <E71qD0.4Iw@ranger.daytonoh.ncr.com>,
   Gary <bb7525241@ntuvax.ntu.ac.sg> wrote:
>> A HESH round consists of a plastic explosive warhead. with a detonator at 
>>the rear of the warhead.  Because of the velocity involved, the plastic 
>>explosive spreads itself over the target "like butter" when it hits.  The 
>>detonator impacts after this happens, blowing up this nice layer of 
>>explosive. The unique explosion effects create a stress wave in the armor.  
>>When the stress wave reaches the other side, bits of the armor break off as 
>>pieces of spalling and bounce around inside the tank.
>
>Doesn't this mean that no peneteration of the armour actually occurs? If 
>that is the case, then spall liners would certainly ruin the effect, 
>won't it?

Well, yes, but spaced armor will work better.

I suspect you are suggesting that a spall lining will protect against side and 
top HESH hits?  It will help, of course.  Spall linings are a good idea in any 
case.

Against thin armor, like an APC, HESH should blow a large plug of armor into 
the inside of the vehicle, so a spall liner won't help very much in this case.



Robb McLeod
rmcleod@uvic.ca
(Please replace the "antispam" with "rmcleod" if replying via email)
Message 6 in thread
From: Christopher Tomlin (C.Tomlin@lancaster.ac.uk)
Subject: Re: HESH warheads
Newsgroups: sci.military.moderated
View this article only
Date: 1997/03/17
From C.Tomlin@lancaster.ac.uk (Christopher Tomlin)

Gary wrote:
<snip>
> Doesn't this mean that no peneteration of the armour actually occurs? If
> that is the case, then spall liners would certainly ruin the effect,
> won't it?
> 
> Gary

  Well, to resist HESH, you have to both have a spall liner and it must
be able to hold together when the shockwave from the warhead passes
through it. Many old tanks don't have spall liners, and I kinda doubt
that lots of IFV have them either. Real heavy 1st-line MBTs are probably
near immune to this round. Still, HESH has its uses - it won't pass
clean _through_ a lightly armoured target (like APFSDS) and it makes
quite a bang!
chris
Message 7 in thread
From: Mark Pruett (mpruett@relinc.com)
Subject: Re: HESH warheads
Newsgroups: sci.military.moderated
View this article only
Date: 1997/03/18
From mpruett@relinc.com (Mark Pruett)

On Fri, 14 Mar 1997 18:36:36 GMT, Gary <bb7525241@ntuvax.ntu.ac.sg>
wrote:

>
>From Gary <bb7525241@ntuvax.ntu.ac.sg>
>
>> A HESH round consists of a plastic explosive warhead. with a detonator at the 
>> rear of the warhead.  Because of the velocity involved, the plastic explosive 
>> spreads itself over the target "like butter" when it hits.  The detonator 
>> impacts after this happens, blowing up this nice layer of explosive. 
>> The unique explosion effects create a stress wave in the armor.  When the 
>> stress wave reaches the other side, bits of the armor break off as pieces of 
>> spalling and bounce around inside the tank.
>
>Doesn't this mean that no peneteration of the armour actually occurs? If 
>that is the case, then spall liners would certainly ruin the effect, 
>won't it?
>
>
>Gary
>

   What happens is that parts of the inner armor facing break off and
fly around, as well as all the fittings and stuff on that side of the
turret fly off and bounce around.  Spall liners would probably help
some, but I imagine that we're talking too much stuff going too fast
for spall liners to completely defend against.
Message 8 in thread
From: aufsj@IMAP2.ASU.EDU (aufsj@IMAP2.ASU.EDU)
Subject: Re: HESH warheads
Newsgroups: sci.military.moderated
View this article only
Date: 1997/03/17
From aufsj@IMAP2.ASU.EDU

: > A HESH round consists of a plastic explosive warhead. with a detonator at the 
: > rear of the warhead.  Because of the velocity involved, the plastic explosive 
: > spreads itself over the target "like butter" when it hits.  The detonator 
: > impacts after this happens, blowing up this nice layer of explosive. 
: > The unique explosion effects create a stress wave in the armor.  When the 
: > stress wave reaches the other side, bits of the armor break off as pieces of 
: > spalling and bounce around inside the tank. 
: Doesn't this mean that no peneteration of the armour actually occurs? If 
: that is the case, then spall liners would certainly ruin the effect, 
: won't it?

	Most spall liners provide only marginal protection.  The effect 
of a flat plate of kilos of HE going off creates a pretty impressive 
shockwave.  The chunks flying off on the opposite side will typically 
have more than enough energy to tear through typical liners, unlike the 
shards (or 'dust', especially aluminum) created by more conventional AP 
rounds or even the focused blast of a HEAT warhead. 
	The effect depends greatly on the properties of the target. As 
stated, concrete is especially vulnerable and HESH is very nasty against 
fortifications using it. Many modern armors can take a significant HESH 
blast without spalling, but even then the concussion transmitted to the 
occupants inside the vehicle can be downright nasty given the right 
parameters (in older tanks, I've read that AP bouncing off the turret 
sounded like a huge sledgehammer. HESH on the turret "didn't sound like 
anything, at least for a couple of weeks").  As someone else has posted, 
spaced armor is a very effective countermeasure.
	One early argument for HESH is that it is more effective against 
more lightly armored vehicles than typical kinetic rounds.  An anti-tank 
sabot round, for example, might just punch a 2-inch hole in an AFV that 
then just zips behind cover.  The HESH explosion, however, was much more 
likely to kill such a vehicle with one shot.  Against a more heavily 
armored tank, on the other hand, the equation went the other way. The 
HESH round also had a marginal anti-infantry capability, at least more 
than a solid anti-tank round.  HESH, IIRC, also tended to be cheaper and 
easier to manufacture than HEAT 'back then' when it was more common.  But 
another drawback is that the explosive effect of HESH was greatest when it 
hit a flat surface at a 90 degree angle.  This doesn't happen a lot, and 
therefore the impact of the round is not optimal.
	For these and other reasons, it seems that HESH is slowly falling 
out of favor and being replaced by other rounds. 

regards,

------------------------------------------------------------------------
Steven J Forsberg  at  aufsj@imap2.asu.edu                Wizard 87-01
Message 9 in thread
From: Paul J. Adam (paul@jrwlynch.demon.co.uk)
Subject: Re: HESH warheads
Newsgroups: sci.military.moderated
View this article only
Date: 1997/03/17
From "Paul J. Adam" <paul@jrwlynch.demon.co.uk>

In article <E6zsBy.Bw4@ranger.daytonoh.ncr.com>, Gary
<bb7525241@ntuvax.ntu.ac.sg> writes
>Doesn anyone here know about HESH(High Explosive Squash Head) warheads? 
>I've read that they function by causing a spalling effect. Can someone 
>verify this and provide info. on the construction of the warhead itself?

HESH or HEP (High Explosive Plastic) rounds are thin-walled shells whose
nose section is made of a fairly plastic explosive or of a plastic,
inert material. They are almost invariably base fused.

On hitting armour, the nose and its contents deform, forming an
explosive cow pat on the metal :) The base fuse detonates this, causing
a massive shockwave to pass through the armour material.

Rolled steel armour contains numerous imperfections which have been
rolled out flat along the plate, and the shockwave of the detonation
causes a large, razor-edged 'scab' of steel to crack off the inner face
of the armour at high velocity. This has a bad effect on the vehicle and
its occupants.

Composite and/or spaced armour is less affected, but the shockwave and
concussion still have considerable effect on fire control systems,
turret drives, crew, drivetrain, et cetera. 

HESH also has excellent properties as a "secondary" round, since its
large explosive payload gives it excellent blast and fragmentation
effects. 

-- 
There are four kinds of homicide: felonious, excusable, justifiable and
praiseworthy...             

Paul J. Adam                                  paul@jrwlynch.demon.co.uk   


Message 10 in thread
From: Carey Sublette (dovesub@primenet.com)
Subject: Re: HESH warheads
Newsgroups: sci.military.moderated
View this article only
Date: 1997/03/24
From dovesub@primenet.com (Carey Sublette)

In article <E777y4.HM3@ranger.daytonoh.ncr.com>, "Paul J. Adam"
<paul@jrwlynch.demon.co.uk> wrote:


> Rolled steel armour contains numerous imperfections which have been
> rolled out flat along the plate, and the shockwave of the detonation
> causes a large, razor-edged 'scab' of steel to crack off the inner face
> of the armour at high velocity. This has a bad effect on the vehicle and
> its occupants.
> 

For your edification - here is a (reasonaby) precise explanation of why
the spalling effect occurs.

A characteristic of shock waves produced by high explosive detonation is
that the pressure behind the shock front is not constant but drops off
very quickly (after all, the high pressure gases of the explosion expand
rapidly, causing the pressure to quickly drop back to atmospheric). This
zone where the pressure drops to (effectively) zero is called the "Taylor
wave" (see pressure diagram below):

          Taylor Wave
         |-----------| *
                     * *
                   *   *
                 *     * -> Shock front motion
               *       *
             *         *
           *           *
**********             **********

Another characteristic of strong shocks travelling through solids is that
roughly equal amounts of energy are deposited in a given (small) volume of
material in the form of kinetic energy, and in compression. This means
that as the shock front passes by, the material is accelerated forward to
some velocity V, and compressed at the same time. When it eventually
decompresses the energy released will add another velocity increment of
magnitude equal to V to the material.

When the shock front reaches the opposite side of the plate the pressure
suddenly drops to zero. The metal decompresses, and the compression energy
causes "velocity doubling", with the plate surface now travelling at 2V.

But, if the plate thickness is equal to the thickness of the Taylor wave
(several millimeters typically), then the outer surface of the plate has

Read the rest of this message... (23 more lines)


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