Apparatus and method for a low fragment explosive access tool using one piece of explosive sheet in the form of a simple geometric shape, a booster charge of explosive sheet in the form of a disk, a blasting cap, and inert materials

Apparatus and method for an explosive access tool using one piece charge of explosive sheet in the form of a simple geometric shape, a disk shaped booster charge, a blasting cap, and inert materials. The one piece charge of explosive sheet, envelopes an inert tamper block with its apexes meeting on the top side of the block facing away from the target. A smoothing layer, preferably in a mostly square shape, is placed between the target and the explosives covering the bottom side of the tamper block. An initiating means is connected to the apexes of the explosive charge so that upon initiation, a series of detonation waves are generated to meet in a manner that result in a plurality of petals cantilevered that are formed in the target material, substantially between the intersections of the meeting shock waves, to define a near fragment-free opening in the target material.

BACKGROUND OF THE INVENTION

The present invention pertains to the field of producing near fragment-free access openings, more particularly to the field of using explosive materials that produce near-fragment free openings in hardened structures such as metal shipping containers and most particularly to the field of using explosive material to produce near-fragment free openings in hardened containers that house agents or substances that must not be overly disturbed.

Bomb squad technicians regularly deal with packages that need to be opened for immediate inspection or remotely in locations where heavy cutting tools may not be assembled or time is of the essence. In order to reduce the risks associated with opening such packages, technicians primarily use either robotic tools or explosive access tools that can be initiated from a distance. For certain types of packages or containers, robotic access tools, which often lack precision, power, and are cumbersome, cannot be employed. For these types of packages, such as sea-land containers, metal drums, or other hardened containers, explosive access tools are the only option.

Various explosive tools have been employed for this purpose. One technique is to employ a linear shaped charge to create an opening in the hardened container. These shaped charges comprise a chevron shaped metallic casing, which is usually copper, aluminum, or lead, that contains a quantity of high explosives. The charge cuts the hardened container by accelerating each side of the chevron shaped wedge into each other, forming a high velocity metal jet. However, this technique, like merely using high explosives to directly cut into hardened targets, produces many fragments, which are capable of overly disturbing the contents within the container.

In order to alleviate this fragmentation problem, a device commonly know as the Magic Cube™ was developed and disclosed in U.S. Pat. No. 6,220,166. This device comprises a sheet explosive that is initiated at four different points and a buffer material, made up of three sheets of stacked, low density material, such as polyethylene foam which is placed between the explosive and the target. Various types of tapes and adhesives are required in order to combine these elements and affix the final device to the target. While the device does alleviate the fragmentation problem discussed above under certain circumstances, it does have several problems associated with its intended use. First, due to the complexity of the device, any particular embodiment is designed to operate on only one range of specific wall thickness. Second, also due to the complexity of the device, it is relatively expensive.

Another device commonly known as the X-Cutter™ was developed, disclosed and claimed in U.S. Pat. No. 6,865,990 to alleviate the fragmentation problem. This device comprises a flexible material, preferably in a mostly square shape, having substantially orthogonal grooves scored into one side. An explosive charge, usually in the form of sheet explosives, is cut to fit the side opposite the grooves, in substantially the same shape as the grooves, without extending beyond the periphery of the flexible material. An initiating means is connected to the explosive charge so that upon initiation, the grooves focus the explosive charge so that a plurality of petals cantilevered from the target plate are formed in the target material, substantially between the ends of the grooves, to define a fragment-free opening in the target material. Again, this device does alleviate the fragmentation problem discussed above under most conditions, but it does not have the simplicity of fabrication of the invention herein presented. The X-Cutter™ needs the grooves to be placed in the flexible material in a machine shop.

Therefore, it is desired to provide an explosive access tool that produces little fragmentation, is inexpensive, simple to fabricate, and can be used on containers made of steel, having various shapes and of varying wall thickness.

BRIEF SUMMARY OF THE INVENTION

The present invention comprises a simplified explosive access tool used by bomb squad technicians and others who require immediate and/or remote access to suspect packages and containers. The invention solves several problems associated with current tools along with the using of explosive materials carried by many bomb squad technicians in the field.

Accordingly, it is an objective of this invention to provide an explosive access tool that creates near fragment-free openings in target materials.

It is a further object of this invention to provide an explosive access tool that can be employed on magnetic targets made of steel without the use of adhesives, tapes, or bonding agents.

A further object of this invention is to provide an explosive access tool that is inexpensive compared to present explosive access tools.

A yet further object of this invention is to provide explosive access tools that can be employed on targets of varying wall thickness with the same amount of explosives.

This invention accomplishes these objectives and other needs related to creating a near fragment-free openings in target materials by providing a device that uses a flexible magnetic sheet material to help form a tamper block in the shape of a simple geometric form, a square, the first embodiment of this invention, or an isosceles triangle, the second embodiment of this invention, and a separate smoothing layer comprised of a single lamina of said flexible material and of said form. An explosive charge, usually in the form of a sheet of explosives, is cut in the projected shape of two flat geometrical diamonds or equilateral quadrilaterals that have been centrally rotated ninety degrees with respect to one another in their geometrical plane for the square tamper block, and an isosceles triangle of sheet explosives for the triangular tamper block. These explosive charges are wrapped around the aforementioned respective tamper blocks to allow their apexes to meet centrally above the top side of the tamper block. A booster charge consisting of a small disc of sheet explosives is placed centrally upon the top of the apexes. This assembly is placed atop a smoothing layer of flexible material in the respective shape of a square or triangle but extending out from the periphery of the tamper block and sheet explosive wrapping. The bottom side of the smoothing layer interfaces with the target. An initiating means is connected proximately centrally to the explosive booster charge that produces a plurality of shock waves that are simultaneously formed at the apexes of the square or triangular formed sheet explosives. These shock waves meet along straight lines that centrally meet on the bottom side of the tamper block. The meeting of the shock waves fault or fracture the steel target below in a pattern that allows the shock and blast that is attenuated through the smoothing layer to open a plurality of petals cantilevered from the target material and define a near fragment-free opening in the target material. When more energy is imparted into these petals from the explosive sheet by those skilled in the knowledge of the invention described herein with regard to the mass of the tamper block and thickness of the smoothing layer, the petals may be made to tear further back into the target material and open further beyond the initial fault or fracture lines without fragmenting or breaking off, and without changing the quantity of explosive sheet.

Finally, the invention also comprises a method of using the device described herein to create an opening in a target material.

DETAILED DESCRIPTION OF THE INVENTION

The invention, as embodied herein, comprises an explosive access tool used to create near fragment free openings in target materials, often the walls of packages or containers that need to be opened for immediate inspection or remotely in locations where heavy cutting tools may not be assembled. The elements of the tool are made up of one piece of explosive sheet in the form of a simple geometric shape, a booster charge of explosive sheet in the form of a disc, a blasting cap, and inert materials. The inert materials comprise a tamper block assembly, a smoothing layer, and a blasting cap holder means. The tamper block assembly has two flat parallel surfaces, a top and a bottom, comprised of flexible sheet material and a filler material between the two exterior flat surfaces of flexible sheet material that may consist of additional flexible sheet material, laminas of thin cardboard, or other low density material. This block serves to: 1) position the one piece of explosive sheet in the form of a simple geometric shape to undergo simultaneous detonation of its disparate apexes, and 2) act as a tamper that will enhance the breaching capability of said explosive sheet positioned below the bottom side of the tamper block. Another piece of inert flexible material is placed between one side of the explosive sheet and the target material. This piece of inert flexible material will be referred to as a smoothing layer. This layer prevents spall and fragmentation in the target material. The smoothing layer is larger in area than the explosive sheet that would interface with the target in the absence of the smoothing layer. A booster charge in the shape of a disc of explosive sheet is place centrally on top of the point at which the apexes of the explosive sheet meet on the top side of said tamper block. The booster charge assures simultaneous detonation of the apexes of the explosive sheet. Initiating means are connected proximately central to the booster charge in order to initiate the explosives. A blasting cap holder means aligns the blasting cap central to the booster charge. The arrangement of said explosive sheet, booster charge, and inert materials allows the shock waves generated from the disparate apexes of the explosive sheet to collide in the explosive sheet facing the target in a cruciform configuration for the first embodiment of this invention and a “y” configuration for the second embodiment of this invention. The result in a faulting or fracture of the target in such a manner to allow petals cantilevered from the target material as in a blooming flower to form and produce an aperture in the target material with minimal fragmentation.

The elements of the tool are made of materials, many of which are already carried by bomb squad technicians that are relatively inexpensive and light weight. In general, the invention comprises a flexible material that is used as both a smoothing layer and tamper with regards to the explosive charge. The term flexible, as it is used in this application, refers to a non-rigid material, capable of being flexed without the use of outside tools or machinery. Therefore, steel based materials would not be flexible, but materials such as polymeric materials or rubber materials would be flexible. An example of such a material is a flexible magnetic sheet material that is a magnetic powder material placed into a thermoplastic base material manufactured by Magnum Magnetics Corporation. This material provides the necessary mass to act as an excellent tamper. Further, the material acts as an excellent smoothing layer and is very frangible, a property that does not produce large and dangerous fragments. This material is manufactured with a 2 mil layer of vinyl on its top or bottom surface that may be used for graphics and printing as explained later in this specification.

Referring toFIGS. 1 and 2of the first embodiment of this invention, the explosive sheet material100is in the projected shape of two flat geometric diamond shapes200that have been laid over one another in a geometric plane and rotated 90 degrees about their centroid with respect to one another. The Diamond Charge200to those skilled in the art of demolition is used to cut steel pipe by inducing tensile fractures through the interaction of two colliding shock wave fronts from an explosive charge of sheet explosive when simultaneously detonated at opposite ends. The opposite ends that are simultaneously initiated are the apexes202at the short axis of the diamond that is parallel to the long axis of the pipe when the long axis of the diamond with apexes204is wrapped around the pipe. The long axis of the diamond charge is equal to the circumference of the pipe to be cut.

Referring toFIG. 1, the explosive charge100has four apexes204that are equidistant from the centriod of the area of the explosive sheet material. When the four apexes204are simultaneously initiated, the four colliding shock wave fronts induce tensile fractures in the shape of a cruciform in a target material. The explosive charge100can be selected by one skilled in the art based upon the amount of force desired by the user of the device. Preferably, the explosive charges100will be in the form of a sheet explosive that can be cut to a desired size. A preferred type of explosive material comprises pentaerythritol tetranitrate (PETN). Exemplary explosive charges100are 0.043 inch thick and 0.083 inch thick PETN sheet explosives manufactured by E.I. DuPont. This explosive sheet material is also referred to as Detasheet.

Referring toFIGS. 3 and 4, the explosive charge100is wrapped around flat block300having two sets of parallel sides, a top302and bottom303, of square pieces of flexible sheet material filled with additional laminas304of square pieces of: flexible sheet material, cardboard, or other low density material. The mass of this block is important because it acts as a tamper that controls the effectiveness of the energy delivered from the explosive sheet in accordance with the Gurney Equations. Therefore, one skilled in the art may adjust the cutting ability of the explosives without adding additional explosives. The block also serves as a form to hold the explosive sheet material in the correct position to effect simultaneous ignition of the four apexes at centrally located point400atop parallel side302. As part of this form, four pieces of mitered half-round wooden molding306surrounds the four edges of the block. The laminas and molding are held in place by a suitable adhesive that is not shown. If the explosive access tool herein described is not pre-assembled by a manufacturer, but assembled from its inert and explosive sheet components and assemblies in the field, block300will be marked with pre-printed positioning guide-lines that are not shown on its top surface of sheet material302to assure that the four apexes204are wrapped around said block with their apexes meeting at the center of top square of flexible sheet material302. This will also assure that the block is not assembled up-side-down, because the internal laminas304in block300may not be of the same material in the immediate vicinity of the bottom lamina of flexible magnetic material as the top lamina302of flexible magnetic material. Changing a lamina next to the bottom lamina303from a lower density to a higher density has much more effect on the cutting ability of this tool than changing a lamina next to the top lamina302from a lower density to a higher density. Therefore, block300may have different tamper effects if turned upside down. These effects may be used to advantage when this tool is assembled in the field. The same tamper block300may be used against two different target thicknesses that depend on the up and down orientation of tamper block300. When the assembly300and explosive charge100are entirely pre-assembled in a factory, these two parts may be held together by an adhesive or suitable low-fragmenting type packaging that are not shown herein.

Referring toFIGS. 4 and 5, the invention includes a smoothing layer of flexible magnetic material500that attenuates the shock effect between explosive charge100and the target502to prevent spall and fragmentation. The thickness of this layer may be adjusted in combination with the additional adjustment of the mass of tamper layers304of block300to effectively produce a near fragment-free aperture in target502. Changing tamper layers304from low density cardboard to high density flexible magnetic material in the immediate vicinity of bottom tamper layer303has a dramatic effect on the breaching efficiency of this invention in accordance with the teachings of the Gurney Equations. The area of the smoothing layer is greater than the area of the explosive charge that would normally contact the target if the smoothing layer were not in place and is centrally located directly under the explosive charge100facing the target. The smoothing layer500is shown as a square piece of material, but other geometric shapes are possible. The smoothing layer500sits directly atop the target502. The assembly300, explosive charge100, and smoothing layer500may be held together in the field with tape not shown. When the invention is assembled in a factory, an adhesive or packaging material that is not shown may be employed to hold the said assembly and components together. The magnetic properties of the smoothing layer will hold the invention in contact with a steel target502without the use of adhesives or tape.

Referring toFIGS. 1 and 5, a booster charge504of explosive sheet material in the shape of a disc is centrally placed atop the four apexes204of explosive charge100to assure the four apexes204initiate simultaneously when wrapped around tamper block300. When the initiating means506is activated, booster charge504that is part of the explosive train subsequently initiates explosive charge100to create a meeting of shock waves that will fault or fracture said target502after passing through smoothing layer500. The subsequent blast of explosive charge100will open the target material along the fracture or fault lines to create a plurality of petals cantilevered from the target material as in a blooming flower. The initiating means506may comprise any type of explosive initiator that will reliably initiate the type of explosive material used as booster charge504. Preferably, the initiating means will be located approximately in the center505of booster charge504. One preferred initiating means comprises an electric blasting cap because such a device is standard equipment in a bomb disposal technician's kit. The invention may also include a blasting cap holder means508of thin steel and approximately 2.25 inches long and 0.30 inch in diameter. The holder consists of a C-shaped trough510and three supporting legs512. The legs512are bendable to assure the center of trough510will align the output end514of blasting cap506centrally with the top of booster charge504. Blasting cap holding means508is standard equipment of a bomb disposal technician's kit and may be held in place with tape (not shown) when assembled in the field. When the invention is assembled in a factory, an adhesive or packaging material that is not shown may be employed to hold the blasting cap in position. Further, said blasting cap may be replaced by other ignition means, for example, an exploding bridge wire (EBW) detonator that may be shipped as one unit with the explosive components of this invention in place when duly qualified in accordance with hazard classification regulations.

In a preferred embodiment of this invention it was found that an explosive charge of 0.083 inch thick Detasheet with distances that are referred to inFIG. 2between apexes204of 5.60 inches and virtual apexes202of 3.11 inches, when wrapped around a block300with 2 inch square laminas, a top and bottom piece, of 0.060 inch thick flexible magnetic material with a 0.02 inch thick coating of white vinyl facing out and fillers of cardboard laminas between the non vinyl sides of said flexible material, totaling ½ inch in overall thickness that is surrounded by ½ inch round wooden molding, said explosive charge produced an aperture through which an 8 inch diameter volley ball would pass in a section of 2 millimeter thick Cor-ten steel that is used in the construction of sea-land shipping containers. The distance between apexes204of 5.60 inches is slightly greater than the perimeter of the minimal cross sectional area of block300that passes through the centroid of the block and normal to parallel sides302and303. A MK II MOD 0 blasting cap506and booster charge504of 0.083 inch thickness and ¾ inch diameter are used to initiate explosive sheet100. A 3 inch square piece of said flexible material is used as the smoothing layer500.

Referring toFIG. 6, yet a second embodiment of the invention is presented. This embodiment of the invention is shown primarily inFIG. 6, an explosive sheet600in the shape of an isosceles triangle with apexes602. When the three apexes are simultaneously initiated, expanding shock waves604,606, and608will be produced. Shock waves604,606, and608will meet on lines610,612, and614in a “y” configuration that will be employed to produce fault lines or fractures in a metal plate when arranged in accordance to the teachings herein. These fault lines or fractures in a metal plate will permit said plate to form petals cantilevered from the target plate that open as the petals of a blooming flower and produce a near fragment-free opening. Advantages of explosive sheet600vice explosive sheet100as shown inFIG. 1are that the shock waves generated from the three disparate apexes602meet head-on at midpoints616along the sides of said sheet and meet at greater head-on angles than the four apex configuration of explosive sheet100. One skilled in the art of fracturing steel plates in half with colliding shock waves that are produced by sheet explosives, e.g., Detasheet, will design a device to generate shock waves that meet in a more head-on manner within said explosive sheet to produce a better line-of-cut.

Referring toFIGS. 7 and 8, a flat block700in the shape of an isosceles triangle has two sets of parallel sides, a top702and bottom703, of triangular pieces of flexible sheet material filled with additional laminas704of triangular pieces of: flexible sheet material, cardboard, other low density material, or a combination thereof. The tamper block700is constructed of identical materials to that used to construct tamper block300as shown inFIG. 4.

Referring toFIGS. 4,7,8, and9, theFIG. 8cross-section of block700along section8-8shows laminas702,703, and704that correspond to theFIG. 4laminas302,303, and304of block300. In accordance with previous teachings herein, the mass of this block is important because it acts as a tamper that controls the effectiveness of the energy delivered from the explosive sheet in accordance with the Gurney Equations. Therefore, one skilled in the art may adjust the cutting ability of the explosives without adding additional explosives by adjusting its mass, especially the mass immediately adjacent to explosive sheet600that faces the target502. The block also serves as a form to hold the explosive sheet material600in the correct position to effect simultaneous ignition of the three apexes as shown inFIG. 9. As part of this form, three pieces of mitered half-round wooden molding706surround the three edges of the block. These laminas and molding are held in place by a suitable adhesive that is not shown. When the explosive access tool herein described is not pre-assembled by a manufacturer, but assembled from its inert and explosive sheet components and assemblies in the field, block700will be provided with pre-printed positioning guide-lines708on its top surface of flexible sheet material702to assure that the three apexes602as shown inFIG. 6are wrapped around said block with their apexes meeting at the center of the top side of flexible sheet material702. For field assembly, block700may also be marked with pre-printed position guide-lines (not shown) on its bottom surface of sheet material703as previously taught to adjust the cutting ability when said block is turned upside down. When the assembly700and explosive charge600are entirely pre-assembled in a factory, these two parts may be held together by an adhesive or suitable low-fragmenting type packaging that are not shown herein.

Referring toFIG. 9, isosceles triangular shaped sheet explosive600is shown wrapped around tamper block700. The length of a side of sheet explosive600will be approximately 1.5 times the length of the side of laminas702,703, or704that are all isosceles triangles with identical side lengths. A smoothing layer900with an area greater than the area of the explosive charge that would normally contact the target if the smoothing layer were not in place and is centrally located under the explosive charge600facing the target. The smoothing layer900is shown as an isosceles shaped piece of material, but other geometric shapes are possible. The smoothing layer900material is identical in thickness and composition to smoothing layer500. The assembly700, explosive charge600, and smoothing layer900will be held in place with tape (not shown) or other previously stated means (not shown) herein. The magnetic properties of the smoothing layer that is composed of flexible magnetic sheet will hold the invention in contact with a steel target502without the use of additional adhesive or tape. Again, initiating means consisting of blasting cap506that is held in place by the trough510of blasting cap holder508with bendable legs512to align centrally the output end514of said blasting cap against the center505of booster charge504will effect the detonation of explosive sheet600via simultaneous detonation of its three disparate apexes. Upon detonation of explosive sheet600that is wrapped around tamper block700, the meeting of generated shock waves in explosive sheet600will result in a cutting through smoothing layer900to fault and fracture target plate502in a “y” configuration as taught inFIG. 6. The additional blast and shock from said explosive sheet will be attenuated by smoothing layer900to create a plurality of petals cantilevered from the target material as in a blooming flower to form a near fragment-free opening in target502along the fault and fracture lines in target plate502.

Referring toFIG. 10, a separate embodiment is shown of the cross-section view ofFIG. 8. A tamper block1000is comprised of laminas1002,1003, and1004that correspond toFIG. 8laminas702,703, and704that are all isosceles triangles in shape. These laminas1002,1003, and1004are of the same materials and thickness as laminas702,703, and704, but have adjusted areas to approximate the outer curved periphery of wooden moldings706ofFIG. 7. Elimination of wooden moldings706will simplify field assembly of block700because there are fewer components. Again, block1000will be provided with pre-printed positioning guide-lines708on its top1002and/or bottom1003surfaces of flexible magnetic material for field assembly. An adhesive to keep laminas702,703, and704in positions is not shown.

The invention also includes method of creating near fragment free openings in target materials using the above described invention.

What is described are specific examples of many possible variations on the same invention and are not intended in a limiting sense. The claimed invention can be practiced using other variations not specifically described above.