Explosively Formed Projectile (EFP)
Explosive-Formed Penetrating (EFP) Warhead
Explosively Formed Penetrator (EFP) Warhead
Explosively Forged Penetrator (EFP) Warhead
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.
The concept of using explosive energy to deform a metal plate into a coherent penetrator while simultaneously accelerating it to extremely high velocities offers a unique method of employing a kinetic energy penetrator without the use of a large gun. A typical explosively formed projectile (EFP) is comprised of a metallic liner, a case, an explosive section, and an initiation train. Very often there is also a retaining ring to position and hold the liner-explosive subassembly in place. EFP warheads are normally designed to produce a single massive, high velocity penetrator. After detonation, the explosive products create enormous pressures that accelerate the liner while simultaneously reshaping it into a rod or some other desired shape. The EFP then hits the target at a high speed, delivering a significantly high mechanical power.
An EFP warhead configuration may be comprised of a steel case, a high-explosive charge, and a metallic liner. Explosively formed penetrator (EFP) warheads have been designed to project a single massive high velocity penetrator to attack the top of armored vehicles. Such armor perforation capability needs further improvement to counter new generations of harder armored vehicles, without resorting to a larger caliber weapon system. In developing a warhead configuration that meets system constraints and also meets performance requirements, several parameters in the warhead configuration must be redesigned to achieve an optimum configuration. Several warhead configurations have been developed to accommodate varying system constraints.
Explosively Formed Penetrator warheads can defeat the target at very long standoffs. EFP warheads consist of an explosive billet and a metal liner. When the explosive is detonated, the detonation wave forms the liner into a high-speed long rod penetrator and propels the penetrator towards the target at speeds greater that Mach 6.
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.
Current anti-armor ordnance employ explosively formed elongated penetrators for piercing armored vehicles and equipment. Such penetrators are generally one of two types: rearward folding or forward folding. In forward folding types a warhead containing an explosive charge drives the periphery of a metal plate, referred to as a liner, forward with an axial velocity greater than the axial velocity of the central portion causing the periphery to fold over and converge forward of the central portion and form an elongated penetrator. In rearward folding the explosive charge drives the periphery of the liner forward with an axial velocity less than the axial velocity of the central portion causing the periphery to fold over and converge rearward of the central portion to form the elongated penetrator.
In these approaches, then, the axial velocity component is critical in determining the final desired shape of the penetrator and this is a well accepted technique. However, in certain applications, for example, where the explosively formed penetrator is delivered from the warhead assembly of a missile or projectile, the explosively formed penetrator encounters the skin of the missile or projectile during the critical earlier stages when the liner is being formed into the penetrator shape by the folding action of the periphery over the center. The engagement of the liner with the skin radically alters the axial velocities of the periphery thereby disrupting the folding. This disruption of the forming process causes the penetrator to fragment or otherwise lose its effectiveness as a penetrator. To avoid this, provision is made to remove the impeding portion of the skin using clearing charges or skin just prior to the liner folding action cutting devices which significantly increase the cost and complexity of the systems.
In consequence of the development that has taken place on the protection side through the introduction of composite armor, active armor, etc., the importance of improving the penetrability of the warhead has, however, increased. Developments have therefore led to increasingly longer and heavier hollow charges. In certain cases this can be accepted, typically for all-target shells etc., but for severely weight-optimized designs, with limited space etc., this method is inappropriate. With state-of-the-art technique, therefore, limit has been reached in practice as regards the length and weight of the charges.
In order to increase the penetrability, hollow charges differing from conventional hollow charges have also been developed in recent times. These charges can, for instance, comprise an auxiliary body disposed in front of or integrated with the metal cone of the charge so that upon initiation of the charge it generates a slug which follows behind the actual penetration jet and penetrates and enlarges the hole made by the penetration jet. Alternatively, the hollow charge may have a warhead with two complete hollow charges, so-called tandem hollow charges, which after the projectile is fired accompany each other as an integral unit during the greater part of the travel towards the target, only to separate at a predetermined distance from this and to continue towards the target at mutually slightly different velocities along largely the same trajectory and thereafter to hit the target with a sufficient interval of time to enable the charge which reaches the target first to detonate the explosive in any active armour before the second charge reaches the target, so that this latter charge penetration jet is able to work without disturbance and also is assisted by the penetration work already performed by the first charge which has already detonated within the same confined area of the charge.
In order to function in the intended manner each of the two hollow charges in such a tandem hollow charge must have its own ignition system with associated safety device. To separate the two hollow charges, it is also necessary to have a smaller parting charge, e.g. a powder charge, between the two charges in order to impart to each of these its own velocity change.
It is realized that the penetrating ability against active armor can be increased significantly through two such interacting charges. It is also realized, however, that the warhead of the projectile will be significantly more expensive with two complete hollow charges, each including its own ignition system and a parting charge.
A tandem-projectile can be adapted in particular for compartmentalized targets (multi-layer armor). Two armor-penetrating devices are incorporated in the shell body of a tandem shell. These armor-penetrating devices distinguish each other with respect to their moment of impact; the rear one of the two devices encompasses a shaped hollow explosive charge arrangement. Such a device has two coaxial shaped hollow explosive charges arranged one behind the other. When the device impacts on a target the rear shaped hollow explosive charge is the one that first becomes operative. From a lining forming part of the rear charge a pointed spike is formed; this spike is adapted to be ejected through the forward hollow charge by passing through an opening disposed in the apex of the forward charge and produces a channel in the armor plate of the target. The forward shaped hollow explosive charge is thus ignited with delay relative to ignition of the rear shaped hollow explosive charge. The pointed spike formed by the forward shaped hollow explosive charge thus follows the said channel produced by the rear shaped hollow explosive charge and becomes operative at a preselected position.
It has been observed that difficulties occur when the compartmentalized reinforced target is impacted obliquely by the afore-described known projectile. The difficulties can be attributed to the strongly reduced cross section of the penetrating channel produced by the spike of the first shaped hollow explosive charge as compared to the cross section of such a channel when a perpendicular impacting of the shell and the target occurs. Consequently, only a relatively small surface area is damaged which is a drawback. A further drawback resides in the behavior of such a known shell relative to an active armor. What is meant here by an active armor is an arrangement of explosive charges in the region of the outer armor, by the activation of which the spike formed by the shaped hollow explosive charge is disturbed and is made ineffective with respect to the main armor.
Advanced armor techniques employ a small armor explosive charge that can deform the explosive cone of a shaped charge or deflect the armor piercing subcaliber round normally used in destroying armor such as on a tank. Therefore, there is a need for a multi-warhead that has the capability of defeating armor that is protected with an outer explosive charge arrangement that is designed to defeat a round that has a single blow effect. Therefore, it is an object of this invention to provide a multi-warhead that has a multiplicity of subcaliber warheads that are designed to strike the target and destroy the small protective explosive charges around the armor and then deliver the main warhead to the armor proper for piercing the armor in an effective manner.
Two major applications have evolved for explosively formed projectiles or warheads, namely, long-standoff sensor-fuzed submunitions and medium standoff, close-overflight missiles. The former application, which is the more traditional one, requires the formation of a single-piece EFP capable of flying in a stable fashion to the target. This refinement has led to the flared EFP rod and, more recently, to the finned EFP rod designs.
For the medium or short-standoff applications, a new type of EFP was developed. The need for an aerodynamic shape is not necessary for these applications because of the short distance the EFP must travel, hence, the length of the rod was increased and the flared tail was eliminated from the design. In fact, some of these rods are purposely stretched beyond their breaking point and fracture into several pieces resulting in greater total length.
Prior art devices have tried to solve this problem of selectable effects through the use of different or multiple initiation points for the shape charge munition. The complex shape of the detonation wave produced was intended to interact with the liner causing it to break up into a number of individual fragments. The problem with this approach is that it requires a relatively complex initiation scheme.
|Join the GlobalSecurity.org mailing list|