Ammunition and explosives – Blasting – Detonation wave modifying
Reexamination Certificate
1990-01-09
2002-12-17
Jordan, Charles T. (Department: 3644)
Ammunition and explosives
Blasting
Detonation wave modifying
C175S004600
Reexamination Certificate
active
06494139
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a hole boring charge assembly and in particular to an assembly capable of penetrating concrete targets.
2. Discussion of Prior Art
It is known that the attack, disruption, and destruction of fixed targets such as airfield runways, shelters, bunkers, bridges, roadways, railway marshalling yards and dockyards may be effected by first emplacing and then detonating relatively small quantities of high explosive within or under the target. The materials of construction of these targets are typically strong in compression and yet weak in tension, as exemplified by most forms of concrete. Such emplacement exploits both the inherent confining effect of the target material on the charge of emplaced explosive and the tensile weakness of the target material, and furthermore enhances the transmission of energy f rom the detonated explosive into the immediately adjacent confining medium and onwards into the outlying and underlying target structure. Where the target consists of a wall or a roof of a shelter or bunker, the emplaced charge of explosive may be replaced by a more complex blasting and/or fragmenting device which may include hollow charge and/or secondary pyrophoric effects.
One known technique of rapid implantation of explosive charges into fixed targets is to first breach the surface of the target with a hole-boring charge of explosive before driving the blasting (secondary) charge of explosive into or through the hole so formed. This technique has the advantage that it may be used in both the manual demolition of fixed targets, in which the hole boring and secondary charges will usually be brought separately and sequentially to the target, and in the mechanical attack of such structures by remotely delivered munition systems such as bombs, missiles and shells which incorporate both types of charge in the delivered system. Furthermore, this technique of hole boring is also applicable to the rapid provision of access ways through fixed massive structures for personnel and equipment in the event of accident, emergency, or during the course of urban warfare.
The main requirement for a hole boring charge as applied to fixed targets is that it should be capable of producing a breach in the target of sufficient width and depth of penetration to permit subsequent emplacement of the secondary, blasting charge at a position which will cause enhanced damage to the structure once the secondary charge is detonated. The hole may be large enough to permit complete emplacement of the secondary charge within or even under the target. Alternatively, it may only be large enough to cause a remotely delivered secondary charge to lodge partly in the hole, but this at least has the advantage that it prevents ricochet of the secondary charge away from the target before detonation. In a remotely-delivered munition system in particular, the hole-boring charge should also preferably be of relatively small size and weight in comparison with that of the secondary charge because it is for the most part the latter charge which performs the task of destroying the target.
These requirements have in the past been met in part by the use of a hollow explosive charge having a conical concavity in one face lined with a non-explosive liner. When the charge is detonated, the liner collapses upon its axis and is formed into a high velocity jet which upon impact with the target produces a hole. However, such known hollow charges fail to fulfil all the requirements for a variety of reasons. Hollow charges with concavities having acutely-angled apexes generally collapse the liner into long, narrow, high speed jets. These are capable of penetrating both massive structures and armour to considerable depths. However the resulting holes bored in the target material tend to be narrow and tapered and so are not suitable for the subsequent emplacement of a secondary charge therein. The diameter of the hole can be increased by increasing the diameter of the hollow charge, but the corresponding increase in weight of the hollow charge is undesirable and furthermore the increase in target penetration in targets of finite thickness such as concrete walls, roads and runways may cause the secondary charge to be emplaced beyond the depth at which it can cause maximum damage to that target. Wider holes are also produced for the same calibre of charge using shallower angled, lined concavities (ie concavities with large-angled apexes, of apex angles generally greater than 80°, especially greater than 100°) which generally form the liners into projectiles which tend towards lower velocity, non-jet penetrators. However, the shorter lengths and lower kinetic energies of these penetrators result in a significant reduction in performance especially against concrete targets, necessitating an undesirably large charge mass in order to excavate a hole of sufficient volume to permit emplacement of the secondary charge to an optimum depth.
SUMMARY OF THE INVENTION
It is one object of the present invention to provide a hole boring charge assembly which overcomes the disadvantages associated with the use of a hollow explosive charge.
According to the present invention there is provided a hole boring charge assembly for penetrating a target, comprising a detonatable array of at least three hollow charges of explosive supported laterally of one another in a detonatable array, each charge in the array having a recessed forward face and a nonexplosive liner lining the recessed forward face, detonation means for detonating each charge thereby to project a penetrator, derived from the liner, forwards along a line of trajectory, the charges being geometrically arranged in the array such that the lines of trajectory extend toward the target in the same general direction as a fore-and-aft line of target penetration and detonation initiating means for initiating detonation of the charges in the array in a temporal relationship with respect to one another such that the penetrators are projected towards the target concurrently.
The effect of the linearly projected penetrators impacting concurrently on a target has been found to vary depending on whether they penetrate the target separately or as one. However, the present arrangement of hollow charges has in general been found to produce a hole in a target material of a volume which is significantly larger than that which could be produced by a single hollow charge of the same overall mass.
The mode of failure of the concrete and subsequent formation of the borehole is complex but the following which does not in any way limit the scope of the invention provides an explanation of the possible mechanics involved.
The initial effect of three or more hollow charge penetrators impacting separately and concurrently on a target is, as would be expected, to bore a number of narrow, deep holes into the target equal to the number of hollow charges detonated. The collision of the penetrators with the target material produces intense shock waves which radiate outwards from the holes as they are formed. The strength of the shockwaves radiating from each penetrating jet is sufficiently large to cause material immediately adjacent the holes produced to fail in compression. In the case of impact by a single hollow charge jet, shock wave intensity decreases with distance of travel into the target, and damage is limited to the immediate vicinity of the hole. However, when three or more jets impact concurrently on the target, the transmitted shock waves from adjacent jets are reflected upon collision, and in the process of collision subject the target material to intense compression thus extending the region of failure to encompass the material bounded by the holes. This material may be ejected from the surface of the target upon its subsequent relaxation immediately following compression, an effect which may be assisted by gases generated during penetration by the jets, to leave behind a single and relatively wide resultant borehole encompassing the na
Nixon & Vanderhye P.C.
Qinetiq Limited
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