Ammunition and explosives – Blasting – Detonation wave modifying
Patent
1992-04-14
1995-01-03
Nelson, Peter A.
Ammunition and explosives
Blasting
Detonation wave modifying
102310, F42B 1032
Patent
active
053775945
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to linear explosive cutting or fracturing charges.
A frequent requirement of demolition work, e.g., when demolishing oil tankers or other large vessels for scrap, is the severing of steel targets by means of explosives.
Among the advantages of explosives over other methods, such as mechanical cutting methods or burning, are safety, since the operator does not need to be close to the target structure at the moment of demolition, speed, and the relative ease of transportation of the means of demolition, since explosive charges are compact in comparison with the equipment required for mechanical cutting or burning.
Explosives may be used for demolition by direct application to the target surface, although attachment is often difficult, the technique inefficient for a given quantity of explosive, and the result almost invariably disorderly and needlessly destructive for the task in hand. Also projected fragments constitute a particular hazard when this method is used.
Much greater explosive efficiency results from the use of shaped charges, such as linear cutting charges wherein a high explosive is caused to act on an angle-section strip of metal in such a way that the two limbs of the angle-section are driven towards each other, thereby generating an elongate jet of extremely fast-moving metal which has great penetrating power, even on steel targets. However, such linear cutting charges are rigid and cannot be conformed to targets which are not flat.
An alternative method of imparting directionality to the energy released by an explosive depends upon the shaping of shock waves generated by the explosive within the target. The shock waves may be caused to fracture targets according to two principle mechanisms. By initiating a mass of explosive in contact with, or close to, the target surface at its two outer extremities with respect to the plane of intending fracture, the two separate detonation wave fronts converge along the centre line, and collide. The first mechanism results from the extreme violence of such a collision which generates a narrow zone of extremely high pressure on the target surface which fractures the target. If, on the other hand, the width of the charge is approximately twice the thickness of the target, and the thickness of explosive sufficient only to give a pressure pulse of sufficiently short duration, then the fracturing mechanism consists of the coincidence of reflected tension waves from the far side of the target surface. These reflected tension waves cause a sudden application of tensile forces across the plane of intended fracture, and the target splits from the distal surface towards the surface on which explosive was placed. In practice, both mechanisms usually occur at the same time, with one of the two mechanisms clearly preponderant.
One explosive cutting charge using such a mechanism is disclosed in European Patent No. 0043215 wherein a series of detonation wave collision charges are arranged in cavities in a continuous rubber matrix. This charge has a small degree of flexibility in the fracture plane but little or no lateral flexibility. Another linear cutting charge is disclosed in U.K. patent application No. 8513325 wherein a prism or lens-section strip of inert material is interposed between a strip of explosive and the target. This has the effect of focusing the explosively generated shock wave along the intended fracture plane within the target. Although this linear cutting charge can be made inherently but weakly magnetic by the use of magnetic rubber for forming the wave-shaping element, it again has the practical disadvantage of only very limited flexibility so that its stiffness coupled with a tendency to elastically recover its initial shape remain limiting factors when the cutting charge is used in practice.
The present invention has as its object to provide a linear explosive cutting or fracturing charge, and an element for use in forming same, which overcomes or mitigates the problem of inflexibility common to known linear cuttin
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