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"Bar Armour effectivness." Topic


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468 hits since 21 Sep 2018
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Comments or corrections?

UshCha21 Sep 2018 12:52 p.m. PST

OK so bar armour ideal to stop RPG 7 type warheads ,presumably some effect on other Light and Medium weapons? What about guided missiles, does it have any effect or is it too light weight to have much effect?

bsrlee21 Sep 2018 2:15 p.m. PST

It is intended to physically break a conventional HEAT or HESH warhead, which is very light metal in most cases. Once the warhead is distorted it is going to be a lot less effective. It would be less effective against the 'auto-forging' type of HEAT warhead, where the liner is the projectile rather than the gas jet – think 40mm steel slug at 27,000 (27K) fps.

Thresher0121 Sep 2018 2:47 p.m. PST

Also makes it/them detonate from too far away from optimal detonation distance, which further degrades the effectiveness of the weapons, if they go off at all.

Depending upon where it hits, and the angle, it could even make the cone of molten metal totally miss the target, or spray across it at an undesirable angle.

Lion in the Stars21 Sep 2018 8:57 p.m. PST

Exactly.

Slat armor is intended to break up or cause premature detonation of HEAT rounds regardless of source. HEAT rounds are very sensitive to detonation distance (standoff), too close and they won't reach max penetration, and penetration drops rapidly beyond optimum standoff.

It may (should, actually) work against HESH/HEP, but most infantry AT weapons are HEAT. Actually, most AT weapons in general are HEAT, whether infantry-carried or vehicle-mounted.

For that matter, even chain-link fence is enough to mess up RPG warheads, but the slat armor on, say, Strykers is significantly stronger. There were some great pictures in Afghanistan of a Stryker with slat armor driving through a mud brick wall.

shirleys painting21 Sep 2018 11:09 p.m. PST

The Russian BTR70 and BTR80 vehicles have now been fitted with slat armor, which is said to be quite strong. The new "trend" seems to be making the slats and their connections heavier and stronger to make sure the bigger ATGM's can be defeated.

Andy ONeill22 Sep 2018 4:19 a.m. PST

Isn't the main purpose to avoid the contact fuse hitting anything?

That isn't guaranteed, obviously, but then the other effects like stand off, worse angle etc etc are still hopefully going to increase your chance of survival.

Personal logo Extra Crispy Sponsoring Member of TMP22 Sep 2018 7:05 a.m. PST

Chain link fence was commonly used in Vietnam to defeat RPGs…

emckinney22 Sep 2018 3:09 p.m. PST

"It would be less effective against the 'auto-forging' type of HEAT warhead, where the liner is the projectile rather than the gas jet"

Second things first, slat armor is generally ineffective against Explosively Formed Projectiles (self-forging projectiles) because their effective detonation range is in the 10-50 meter range, so there's no need for them to get close enough to contact the bar armor. Because the space between the bars is generally much larger than the the diameter of the slug projected by the EFP, the slug will usually miss the slats, making them irrelevant. If the slug does stike a slat, cutting it apart will be somewhat effective (reducing the mass of the projectile), but the most severe effect occurs if the slat casuses the slug to tumble. That puts less mass per surface area behind the strike, which vastly reduces its penetration.

The penetrator in a HEAT warhead is the copper liner, not any "gas jet." Copper is used for its ductility and moderate density. Gold is a much more effective liner because it is even more ductile and vastly more dense than copper, but obviously it's far too expensive to be practical.

While the gas jet has a small ability to damage armor, it could only penetrate the thinnest armor, and is really only effective against common steel (or common aluminum). Contrary to rumor, there is no "plasma" jet for the simple reason that the explosives in a HEAT warhead don't have enough energy to convert the liner to plasma (and certainly not the gasses of the explosion product) through any combination of temperature and pressure. The combustion temperature is far, far too low.

"Depending upon where it hits, and the angle, it could even make the cone of molten metal totally miss the target, or spray across it at an undesirable angle."

The jet is solid, not molten. This was proved experimentally by section HEAT warheads into disks, clamping them very, very tightly, and the detonating them to fire into water tanks. If the copper was molten, the sections of the the liner would have welded/melted together. The detonations were normal and the jets formed normally, but they simply fell to the bottom of the water tank, sectioned corresponding exactly to the pre-detonation cuts. You can also do some simple calculations of the energy outputs of the explosive, account for 50% loss to the part of the explosion directed outward (equal and opposite reaction), the amount of energy needednyo accelerate the liner to its maximum velocity, and approximation of percentage of the explosive energy going onto the "squeeze," and the energy needed to melt that much copper. The math just doesn't work out!

Please note that the term "jet" was an unfortunate xhoice and is very misleading. It implies that the copper liner is liquid or even gaseous, but it isn't. "Jet" was used because its formation occurs under fluid dynamics: the pressure is so high that the ductile copper flows like a liquid, so you can use fluid dynamics equations to model and predict jet formation with different cone geometries.

The slats can't cause the jet change direction because it simply slices the warhead lengthwise, preventing simultaneous detonation of all of the explosive in the warhead and changing the geometry and dynamics of the detonation, which prevents the jet from forming.

Jet formation depends on symmetrical and carefully timed detonation of the charge to drive the liner forward while also compressing it from the cylinder in. This inverts the liner, with the tip of the cone (at the rear of the warhead) forming the tip of the jet. If the warhead is sliced anywhere along its length and separated slightly, the pressure becomes completely unbalanced and the line escapes through the separations on either side. The result is completely ineffective.

"Also makes it/them detonate from too far away from optimal detonation distance, which further degrades the effectiveness of the weapons, if they go off at all." Fuses on HEAT warheads are very small, so the chance of hitting a bar is tiny. Not a significant part of the defense. You do this with solid spaced armor, if you this is what you're trying for.

"Isn't the main purpose to avoid the contact fuse hitting anohysica+"

No. The bar armor will not bring a HEAT warhead or missile to a stop. The expectation is that the fuse will still trigger, but that the explosive will not form a jet. Some fuses will detonate early due to the shock of the projectile hitting the slats, but that's unreliable.

*That isn't guaranteed, obviously, but then the other effects like stand off, worse angle etc etc are still hopefully going to increase your chance of survival."

Again, bar armor works by disrupting jet formation.

Andy ONeill23 Sep 2018 7:53 a.m. PST

My understanding was that the slats stopped the round going off because the fuse doesn't fire.
It seems that's not quite right.

link

". Bar armor works by exploiting a design feature in the RPG, namely that causing the inner and outer ogives (the hollow conical forward members of the RPG warhead) to become electrically connected causes the piezoelectric nose element to become short circuited, thus denying electrical power to the initiating element at the rear of the RPG. When an RPG passes between the bars of bar armor at high speed without the forward nose element hitting a bar, the outer ogive is crushed into the inner ogive, a short circuit is established, and the RPG is dudded. "

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