Ammunition and explosives – Blasting – Mat or deflector
Patent
1990-07-12
1993-07-27
Nelson, Peter A.
Ammunition and explosives
Blasting
Mat or deflector
102307, 102323, 102325, F42D 500
Patent
active
052312453
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a method of using explosive charges and to apparatus for practising the said method.
It is well known in the art that when an explosive charge is detonated the detonation produces two major effects on its immediate surroundings;
(1) shock waves, which travel outwardly in all directions from the detonated charge, and
(2) a high pressure, generated by the gases produced by the detonating charge, the above effects are utilized directly to affect a target.
When an explosive charge is used to break rock, masonry or the like masses the explosive is generally confined to a borehole where, on detonation, the shock wave travels outwardly through the surrounding mass having little effect thereon whilst the high pressure developed by the detonated charge produces such compression forces in the surrounding mass as to effect fracture along natural planes of weakness.
For convenience hereinafter the effects of the high pressure on its surroundings shall be referred to as a "pressure pulse".
When a so called "plaster" charge is applied to one surface of a metal sheet or plate part of the shock wave travels through the metal target to blow a so called "spall" from that surface of the metal target remote from the detonated charge. The spall is formed exclusively by the shock wave. The pressure pulse also effects the target and can deform the metal surface which was in contact with the detonated charge such that, if the plaster charge is sufficiently large, the target material between the explosive charge and the spall cavity can be deformed, being bent inwardly to the spall cavity, and in some cases so deformed as to break the metal target. Thus, with this method the shock wave displaces a spall from that surface of the metal target remote from the detonated charge and the pressure pulse can produce deformation of the metal target, including a breakthrough into the spall cavity.
In a more recent use of explosives for cutting targets, such as metal sheets or plates, the explosive mass is arranged to direct two shock wave fronts simultaneously into the target to effect a break of the target along the line of collision of the two shock wave fronts. Thus, in this mode of operation, the target is affected essentially by the shock wave front and the pressure pulse has little effect upon the target.
In the well known "shaped" charge arrangement a solids element is spaced from a target surface and an explosive mass is detonated on that surface or surfaces of the solids element remote from the target. With this arrangement the shock wave front passing through the solids element has little effect thereon but the pressure pulse deforms the solids element and drives that element, in blade-like form, at very high velocity against the target to effect at least an indentation of the target. Thus, with this mode of operation, the useful energy of the explosive mass is directed to the deformation and acceleration of the solids element and has little effect on the target but it is essential for all prior art methods for using shaped charges that the explosive mass be applied directly to the solids element to ensure that the high pressure pulse has the desired effect on the solids element and the solids element must be spaced from the target only by a vacuum, or less preferably a gaseous medium, as any other medium will adversely affect the shape and velocity of the deformed solids element.
There are well known difficulties in utilizing all the aforesaid methods of using explosives in underwater situations. Boreholes are difficult to drill accurately and the difficulties in drilling and charging boreholes increases as the depth of the water increases. Plaster charges have little effect on underwater rock and masonry structures. Two shock wave cutting requires only small amounts of explosive but is relatively ineffective on rock and masonry structures. Shaped charges, requiring as they do a complete absence of liquid medium between the solids element and the target, are complex and expensive to produce, difficult to
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patent: 3172361 (1965-03-01), Thouzeau
patent: 3806025 (1974-04-01), Marshall
patent: 4151798 (1979-05-01), Ridgeway
patent: 4498391 (1985-02-01), Gergo
patent: 4736796 (1988-04-01), Arnall et al.
patent: 4836079 (1989-06-01), Barrett
patent: 4905601 (1990-03-01), Gabriel et al.
Drucker William A.
Explosive Developments Limited
Nelson Peter A.
LandOfFree
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