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Shaped charges can be divided into two types, those producing relatively slow moving projectiles, the so- called"explosively formed penetrator or projectile" (EFP) and those producing fast moving stretching jets,"jetting shaped charges". These two types can be distinguished by fundamental differences.
The liner of an EFP is a shallow dish with the depth of the dish typically being less than 0.25 of its diameter whereas the liner of a jetting shaped charge is typically a cone or hemisphere in which the depth of the liner cavity is greater than 0.4 of its diameter.
The shape most commonly used for the jetting liner is a cone, with an internal apex angle of 40 to 90 degrees. Other widely used shapes include hemispheres, tulips, trumpets, ellipses, and bi-conics; the various shapes yield jets with different velocity and mass distributions.
The chief advantage of the EFP over a conventional (e.g., conical) shaped charge is its effectiveness at very great standoffs
Wide angle cones and other liner shapes such as plates or dishes do not jet, but give instead an explosively formed projectile or EFP. The projectile forms by dynamic plastic flow and has a velocity of 1-3 kms-l . Target penetration is much less than that of a jet, but the hole diameter is larger with more armour backspall.
An EFP must be aerodynamically stable so as to strike the target within a small miss distance and a small angle of obliquity. In the U.S., extensive work has focused on forming EFPs with canted fins, to induce spin-up. By forming canted fins on an EFP, improvements in aerodynamic stability can be realized.
There exist near a dozen patented methods of creating fins and canted fins.
For example by placing some pieces of metal where you want to slow down the accelerarion and cause a bent shape in the liner.
The need for an aerodynamic shape is not necessary for the medium or short-standoff.
An EFP is designed to produce a non-stretching projectile moving at a velocity in the range from about 1.5 to about 3 km/s whereas a jetting shaped charge produces a stretching jet with a tip velocity in the range from about 3 to 10 km/s and a rear end velocity less than the tip velocity such that there is a velocity gradient along the jet which causes the jet to stretch.
EFP liners are typically thicker than jetting shaped charge liners of a similar diameter.
The EFP projectile velocity depends on the liner to explosives layer thickness ratio.
Because EFPs are not intended to produce very fast moving jets, they require less explosive. Jetting shaped charges in the prior art are therefore typically longer than EFPs of a similar diameter.
If the EFP perforates the armour, extensive behind armour effects BAE will occur. The BAE is mainly caused by the hot armour and slug fragments being injected into and bouncing inside the interior space and the overpressure (blast) caused by this debris.
Aluminium and composite armour limits the BAE caused from fragments.
Which limits the harm to those hit directly by the EFP projectile itself.
But the resistance can fire multiple EFPs at the same vehicle to make sure that noone survives.
What happends if you are hit from an EFP ?
The picture below is for comparison and shows what happens if you are hit from US fine calibre munition and splinter.
If you are hit by an EFP the same thing will happen as if you are hit from a cannon.
Someone hit from a 25mm calibre automatic cannon (. . .accurate up to 2.5 km . . .)
Anyone hit by an EFP and surviving will never go back to work again. The limb is off, and can't be repaired.
Everyone surviving will cost a million dollar in medical aid, while a dead soldier cost 50 dollar for a coffin. The resistance win more on mutilating the enemy instead of killing.
A clue :
When you read about wounded enemy troops after an EFP attack then it's not as harmless as it used to be.
Designing Explosively Formed Projectiles
Explosively formed projectiles (EFP) have been used to defeat armored vehicles for more than 30 years. The EFP warhead was derived from the Misznay-Schardin device, which consists of a right circular cylinder of explosive, with a shallow cavity in one end that is fitted with a thin metallic liner. Upon detonation, the liner dynamically transforms into an aerodynamic projectile traveling at high velocity (typically 1500-2000 m/s). Figure 1 shows the formation process for a tactical EFP warhead from its initial predetonation state to the fully formed profile.
1 The shape of the liner.
The geometry of the liner's bottom surface primarily affects the velocity of the liner as a function of radius early in the EFP formation process. Making this surface too concave will cause the liner material to be driven inward more than desired. Making this surface too flat will result in a broad, flat projectile.
Two different types of EFP projectiles.
2 The thickness of the liner as a function of radius.
Altering the geometry of the top surface of the liner (defined by a second-degree polynomial) relative to the bottom surface changes the thickness of the liner as a function of radius. This changes the mass distribution and strength of the liner across its radius. These effects determine the shape of the liner late in the EFP formation process. While the explosive charge accelerates the liner, the center begins to move with a greater velocity than the outer edge. During EFP formation, the material near the outside edge of the liner slows the material near the center of the liner. This process produces a tremendous amount of strain in the liner. If the liner is made too thick towards its outer edge, localized strain will cause the metal to fail, resulting in metal chunks instead of an EFP. Making the liner too thin will cause the same problem. A correctly designed liner balances the competing effects.
3 The explosives / liner thickness ratio.
The thickness ratio between the explosives layer and the liner determines the projectiles velocity.
And also affects the strain during the EFP formation process.
It also depends on type of explosives used.
4 Shaping the detonation wave propagation
The arrows in the picture below show the delay time between when the detonation wave reaches the center and when it reaches the outer edge of the liner, for three different flat liner locations.
The delay time (arrow lengths) and arrow directions also represents strain that can break the liner apart.
Some types of shaped charges have elongated explosives layer or use explosive lenses combining two layers of different types of explosives. Or other smart solutions for shaping the detonation wave.
But since most EFP designs works well without that I think you can save your time.
Also remember that big air bubbles in the explosives can destroy the shape of the detonation wave.
(The blue thing in this picture is the blasting cap.)
5 Creating fins
At longer distance do you need fins to stabilize the projectile.
But this is not necessary for roadside bombs at distances of perhaps 20 meters.
At distances of more than 100 meters the projectiles drift off in "banana" bent paths becomes visible, which you can cancel by adding "canted" fins that makes the projectile spin like a rifle bullet. (Turn the fins a degree.) (Not necessary if the target is big like a house.)
You can create the fins by shaping the detonation wave with obstacles or slow down the acceleration at specific points of the liner by adding mass (weight, pieces of metal chunks) . See the picture below.
(Also see patent : 5365852 at the bottom of this page, about creating fins.)
Note the metal fragments on the picture to the left side. Textron EFP
Also note that the liner looks like being cone shaped instead of dish shaped.
Accuracy as function of spin rate.
EFP liners can be made of circular plates or made of steel bars. And the main difference is that the circular liners creates conetailed aerostable projectiles while steel bars creates unstable projectiles.
An aerostable projectile will always hit the target perpendicular with its nose first. And a perpendicular hit always gives maximum penetration in the target.
The projectiles penetration cabability is proportional to the projectiles lenght in the direction of the movement.
The penetration depth depends on the impact angle. And the maximum penetration is at a perpendicular impact.
An aerodynamically stable projectile will adjust itself. While simpler EFPs made of a bent steelbar perhaps will rotate like a boomerang.
Some extremely long stretched circular EFP designs have no cone tail and is also broken up into multiple fragments, and have no aerostability, and can only be used at short to medium distance.
A simpler EFP made of a steel bar is easier to build, and the aerodynamic instability will not affect the impact angle at short roadside bomb distance.
Multiple_EFP is an EFP with a special liner with many small dishes.
It launches many small projectiles from the same blast.
Useful against light armoured targets.
Is an easy homebuilt EFP built from a flat steel plate with plastic explosives attached to one side.
The disadvantage is that this weapon will give a broad short projetile that is more optimized for demolition of buildings instead of armour penetration.
If the projectile isn't aerodynamically stable then this is a short to medium distance weapon.
The countermeasures against RPG does not work against EFP.
RPG Rocket Propelled Grenade is no big threat says the U.S. military even if it can punch a hole through 30 cm armour steel, because the countermeasure is too easy.
But they worry about the EFPs because it makes their road transports vulnerable and is a big threat to the entire occupation.
The U.S. and British military are hanging empty metal boxes and "slat_armour" (metal bars) and chicken wire on their vehicles, to predetonate the RPG-7 grenades.
RPG-7 is a jetting weapon and is neutralized by predetonating at a relatively short distance from the real armour.
It's not possible to neutralize EFPs that easy because EFP is a projectile, not a jet.
Slat armour on a stryker, protecting against RPGs.( a jet weapon)
But it does not protect against EFPs
EFP from the newsIED Blows Up British Army's Main Battle Tank;
Advanced roadside bombs
23 April 2007 BBC NEWS
A British Challenger 2 tank has been penetrated by a roadside bomb in Iraq, leaving the driver seriously injured, the Ministry of Defence has confirmed.
NBC News Dec. 8, 2006
BAGHDAD, Iraq - Of the many dangers lying in wait for American soldiers in Iraq, the U.S. military increasingly fears one thing: the new, advanced roadside bombs planted by insurgents.
"There are very few things we fear," says Col. Douglass Heckman. "When a simple roadside bomb goes off, it's not going to kill us most of the time. A sniper can't penetrate -- we keep the gunners down -- small arms can't penetrate. ... In fact, a vehicle-borne suicide bomber typically isn't going to hurt us. The thing that scares us is the advanced roadside bombs."
Heckman's teams of military trainers embedded with the 9th Iraqi Army Division have reason to be wary.
In their sector of Baghdad east of the Tigris River, at least five U.S. military advisors have been killed by roadside bombs in the last two weeks -- among them the first full colonel killed in combat in the war and two lieutenant colonels who died in the same vehicle.
Unlike regular roadside bombs, EFP's -- explosive-formed penetrators -- remain intact as they explode. The steel tubes with curved metal seals form a kind of super bullet that can go directly through a tank's armor.
The new, more lethal shaped charges are behind most of the attacks that often kill several servicemembers with one blast. Eleven U.S. troops were killed on Wednesday, making it the deadliest day this year. Five of those servicemembers died in a single roadside bomb attack near Tikrit, the military said.
Homemade EFP liners and an EFP found in Iraq.
It's obvious that these are not factory made in Iran, but simple sewage pipes or lamp-posts cut in a garage in Iraq.
Only a small fraction of the roadside bombs used in Iraq are explosively formed penetrators. But the device produces more casualties per attack than other types of roadside bombs, the paper noted.
NYTimes August 8, 2007
The devices, known as explosively formed penetrators, were used to carry out 99 attacks last month according to American military officials.
Of the 69 members of the American-led forces killed in action in July, the lowest toll in months, 23 died as a result of attacks with the devices, according to data supplied by General Odierno?128;™s command. Of the 614 allied troops who were wounded that month, 89 were hit in penetrator attacks.
Though explosively formed penetrators account for a small fraction of roadside bomb attacks in Iraq, they cause a disproportionately large number of casualties.
Many of the penetrators faced by American forces are difficult to counter. Because they fire from the side of the road, the militants do not need to dig a hole to plant them, making them well suited for urban use. Because they are set off by a passive infrared sensor, they cannot be thwarted by electronic jamming.
1200 roadsidebombs each month but only 99 of them are EFP's
The EFP's Killing efficiency :
99 attacks with EFP in July 2007 kills 23 and wounds 89.
Means 23 % killing efficiency.
Compare to the other types of roadsidebombs which have less than 4% killing efficiency.
Patents on EFP
Drawing from patent : 5033387 Typical EFP shape
Patent : 5365852 How to create an EFP with fins.
A thin cross shaped foil between the liner and explosives.
The patent does not tell what the foil is made of, but it says about 25% of the liners thickness.
You can also create fins by placing pieces of metal in front of the liner to slow down the acceleration. Textron EFP with a cone shaped liner instead of a dish shaped.
Patent : 4649828 The liner is cut to create Multiple EFPs.
Clothes-pin shaped projectiles.
Not usable by the resistance because it's too complicated, but it gives a clue about an easier way to build EFPs.
Patent : 6606951 EFP antiarmour mine
http://www.freepatentsonline.com download the pdf-files
A possible easier way to build EFPs
The resistance consist of amateurs which most of them are unskilled in using tools or shaping EFP liners. Which means that if a a weapon need to much work then noone will build it.
And they will rather waste 1000 kg of explosives on a big bomb for the ears and eyes that won't kill anything.
What you need is a simplified EFP construction and it's the liner that must be simplified.
You can't find circular dish shaped liners ready to use anywhere, you can't buy them.
But you can find steel bars everywhere.
The clothes-pin shaped EFP from patent 4649828 tells us that there might be an easier way to build EFPs.
Clothes-pin EFP from patent 4649828
Simplified Improvised Multiple EFP SIM-EFP
At shorter roadside bomb distance there is no need for any aerostable cone tailed projectiles, which means that the liner can be simplified.
A SIM-EFP is built of simple cut and bent steel bars.
A SIM-EFP is a construction that fits in between the linear cutting charge and the platter charge.
And the main difference is how much the rectangular liner plate is bent. See picture below.
A simplified EFP has a thicker liner and thicker explosives layer.
If there is any trouble with breaking up in fragments then try a thicker liner plate or a rounded back.
The penetration in armor steel is the same as the projectile length.
Which is half the length of the steel bar.
No trouble with timing differences anymore
If using multiple ordinary EFPs in parallel, then it's necessary to use a single blasting cap and equal length explosives filled tubing to cancel the timing differences that can destroy or aim some EFPs in the wrong direction. But SIM-EFP doesn't need any explosives filled tubing, because the entire construction is collected together in the same unit. This is timesaving when planting the EFPs.
The SIM-EFP is by it's construction optimized for killing armored vehicles.
Because it launches a swarm of projectiles that are perfectly spread out for killing vehicles, and also projectiles that are optimized for armor penetration. See picture below.
A perfect spread out swarm of armor penetrating projectiles.
Everyone inside are hit, and noone will survive.
Longer timing error allowed.
Easier to kill fast moving vehicles.
The SIM-EFP is a weapon that are easier to build, which means improved production. Easier to plant and more effective and timesaving at killing armored vehicles.
When the production of EFPs becomes too easy, then it will become the standard weapon instead of a rarely used special weapon. And that will improve the resistance's striking power and killing efficiency and force the enemy to abandon the roads.EFPs are 6 times more effective than the big bombs at killing the enemy.
You have to do some experiments about the optimal shape of the liner and explosives layer.
Make sure that the liner doesn't fold forward or get any other bad projectile shapes.
Try different constructions against a concrete wall and use the construction with the best penetration capability.
Try evaluate the design below, because it is so powerful that it will change the battlefield if it works.
Heavy tank killer ?
A simple bent steelbar with explosives attached.
Maybe a rounded backside profile to prevent the breaking up in fragments ?
Or a round profile ?
It's flat design also makes it easier to hide in the terrain.
See the picture below that shows a circular and a flat EFP side by side.
Which one do you think is the easiest to hide in the terrain ?
If you have to dig it down ?
It's easier to create a long rod projectile from a flat EFP design compared to a circular EFP design.
Because it's easier to cut and bend a steel bar than it is to build a one meter diameter dish liner.
And perhaps the steel bar doesn't have to be bent at all (compare to a platter charge) which makes it a lot easier.
With this design you are not limited to attacking the heaviest tanks from the top or bottom anymore. You can kill them from a side attack.
Circular EFPs of that size are difficult to build. Which means that if you want a homebuilt heavy tank penetrator then you must abandon circular EFPs and try a flat EFP design.
Ask any expert in the workshop and they will agree.
If you got nothing else then take a railroad track. Send it like a projectile through the enemy's tanks.
Flat EFPs are only useful at short and medium roadside bomb distance because they are not aerostable.
Try weld the steelbar together with an aerodynamic shaped tail. Do your own experiments.
The flat EFP design is also an argument for redesigning nuclear powerplants because it's easy to build at home a weapon launching a projectile straight through a nuclear powerplant.
If you haven't learnt anything from Tjernobyl or the WTC already then there is no hope for you.
The reactor itself should be placed underground 10 to 20 meters below the surface in a safe nuclear powerplant design. That will also protect against airplane attacks. Another lesson from Tjernobyl is that they had to dig the reactor down after the disaster, so why not save some time and have it dug down before any disaster.
Very big homebuilt efp
Some home built EFPs found in Iraq.
The EFPs made the US lose the war on the ground, and they were forced to abandon the roads and begin bombing an invisible enemy from above. Which explain the increase in aerial bombings of what they call suspected insurgents, which means innocent peasants, women and children. And later they had to recruit puppet troops to do the dirt work on the ground in order to survive and improve the US statistics of killed troops.
The EFPs were abandoned by the Mahdi resistance because their leader the chicken Mr Al-Sadr stabbed the resistance in the back and told them to lay down their weapons and not to fight the enemy. And he prolonged the US occupation with many years. What a hero.
Demining machines and weapons.
What they all got in common is that they are all useless against EFP because the EFP strikes from a side attack.
Most of the resistance's big bombs are too easily neutralized with the tools below.
So much work and money lost.
And they must start using EFPs if they want to kill the enemy.
This machine below whips the ground with chains with heavy force and detonates the mines.
But it's useless against EFP.
The mine roller blows up the bombs, and only the roller is damaged instead of the entire vehicle.
But it's useless against EFP.
The mine plow digs up the mines and creates a safe passage for tanks and troops.
And it's useless against EFP.
Ground penetrating radar and a computer memory is used to save a record of what the road looks like for many miles. If anything has changed since last then there is a bomb.
And it's useless against EFP.
The robot arm and the remote controlled tiny machine in the picture below is used to undig bombs at safe distance away from
And it's useless against EFP.
The MCLC and other similar antimine weapons.
A 100 meter long hose filled with explosives is laid out with the help of a rocket.
It will blow a 100 meter long and a few meters wide passage through a mine field.
And it's useless against EFP.
The main disadvantage of EFPs is that they must be remote controlled.
Or else you must try build a dual microphone electronic device that listens to the sound of the vehicles in the air or in the ground, and then detonates the EFP. Or try build an extremely low power IR tripwire.
The difference between a point weapon and line weapon
The big bombs are a point weapon, which means that the enemy is safe as long as he keeps himself away from the killing point. And the enemy can stop their vehicles at a safe distance and send in the remote controlled robots to check for bombs. And try to disarm the bomb.
EFPs on the other hand is a line weapon, a cannon. And there is no safe distance from a cannon.
More advantages of line weapons :
If you intend to block the enemy's traffic on a hundreds of meters wide battlefield. The the EFP is more economic and also harder to neutralize.
A single EFP can cover a width of hundreds of meters.
If you instead use ordinary antitank mines, then must you plant hundreds of mines side by side to do the same job, which becomes more expensive.
It's easy to create a safe passage through an ordinary minefield. Typically with an explosives filled tube that predetonates the mines, or with a mineplow. You can't neutralize an EFP with the same simple methods because the EFP is not located where you intend to drive.
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تاريخ التسجيل : 10/01/2011
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