Abstract:
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.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This nonprovisional utility application claim the benefits of Provisional Patent Application No. 60/926,190 with a filing date of Apr. 26, 2007. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     This invention was made under federally sponsored research and development and entitles the federal government to royalty free rights. 
    
    
     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. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
       The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention, and together with the description, serve to explain the principles of the invention. 
         FIG. 1  is a top view of one side of the primary embodiment of the present invention. 
         FIG. 2  is a top view of the geometric shapes set forth in  FIG. 1 . 
         FIG. 3  is a top view of one side of the primary embodiment of the present invention. 
         FIG. 4  is a cross-section view of  FIG. 3  along section  4 - 4 . 
         FIG. 5  is an exploded top view of the primary embodiment set forth in  FIG. 4 . 
         FIG. 6  is a top view of one side of the secondary embodiment of the present invention. 
         FIG. 7  is a top view of one side of the secondary embodiment of the present invention. 
         FIG. 8  is a cross-section view of  FIG. 7  along section  8 - 8 . 
         FIG. 9  is an exploded top view of the secondary embodiment set forth in  FIG. 7 . 
         FIG. 10  is a separate embodiment of the cross section view of  FIG. 8 . 
     
    
    
     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 to  FIGS. 1 and 2  of the first embodiment of this invention, the explosive sheet material  100  is in the projected shape of two flat geometric diamond shapes  200  that have been laid over one another in a geometric plane and rotated 90 degrees about their centroid with respect to one another. The Diamond Charge  200  to 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 apexes  202  at the short axis of the diamond that is parallel to the long axis of the pipe when the long axis of the diamond with apexes  204  is wrapped around the pipe. The long axis of the diamond charge is equal to the circumference of the pipe to be cut. 
     Referring to  FIG. 1 , the explosive charge  100  has four apexes  204  that are equidistant from the centriod of the area of the explosive sheet material. When the four apexes  204  are simultaneously initiated, the four colliding shock wave fronts induce tensile fractures in the shape of a cruciform in a target material. The explosive charge  100  can be selected by one skilled in the art based upon the amount of force desired by the user of the device. Preferably, the explosive charges  100  will 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 charges  100  are 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 to  FIGS. 3 and 4 , the explosive charge  100  is wrapped around flat block  300  having two sets of parallel sides, a top  302  and bottom  303 , of square pieces of flexible sheet material filled with additional laminas  304  of 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 point  400  atop parallel side  302 . As part of this form, four pieces of mitered half-round wooden molding  306  surrounds 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, block  300  will be marked with pre-printed positioning guide-lines that are not shown on its top surface of sheet material  302  to assure that the four apexes  204  are wrapped around said block with their apexes meeting at the center of top square of flexible sheet material  302 . This will also assure that the block is not assembled up-side-down, because the internal laminas  304  in block  300  may not be of the same material in the immediate vicinity of the bottom lamina of flexible magnetic material as the top lamina  302  of flexible magnetic material. Changing a lamina next to the bottom lamina  303  from 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 lamina  302  from a lower density to a higher density. Therefore, block  300  may 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 block  300  may be used against two different target thicknesses that depend on the up and down orientation of tamper block  300 . When the assembly  300  and explosive charge  100  are 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 to  FIGS. 4 and 5 , the invention includes a smoothing layer of flexible magnetic material  500  that attenuates the shock effect between explosive charge  100  and the target  502  to prevent spall and fragmentation. The thickness of this layer may be adjusted in combination with the additional adjustment of the mass of tamper layers  304  of block  300  to effectively produce a near fragment-free aperture in target  502 . Changing tamper layers  304  from low density cardboard to high density flexible magnetic material in the immediate vicinity of bottom tamper layer  303  has 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 charge  100  facing the target. The smoothing layer  500  is shown as a square piece of material, but other geometric shapes are possible. The smoothing layer  500  sits directly atop the target  502 . The assembly  300 , explosive charge  100 , and smoothing layer  500  may 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 target  502  without the use of adhesives or tape. 
     Referring to  FIGS. 1 and 5 , a booster charge  504  of explosive sheet material in the shape of a disc is centrally placed atop the four apexes  204  of explosive charge  100  to assure the four apexes  204  initiate simultaneously when wrapped around tamper block  300 . When the initiating means  506  is activated, booster charge  504  that is part of the explosive train subsequently initiates explosive charge  100  to create a meeting of shock waves that will fault or fracture said target  502  after passing through smoothing layer  500 . The subsequent blast of explosive charge  100  will 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 means  506  may comprise any type of explosive initiator that will reliably initiate the type of explosive material used as booster charge  504 . Preferably, the initiating means will be located approximately in the center  505  of booster charge  504 . One preferred initiating means comprises an electric blasting cap because such a device is standard equipment in a bomb disposal technician&#39;s kit. The invention may also include a blasting cap holder means  508  of thin steel and approximately 2.25 inches long and 0.30 inch in diameter. The holder consists of a C-shaped trough  510  and three supporting legs  512 . The legs  512  are bendable to assure the center of trough  510  will align the output end  514  of blasting cap  506  centrally with the top of booster charge  504 . Blasting cap holding means  508  is standard equipment of a bomb disposal technician&#39;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 in  FIG. 2  between apexes  204  of 5.60 inches and virtual apexes  202  of 3.11 inches, when wrapped around a block  300  with 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 apexes  204  of 5.60 inches is slightly greater than the perimeter of the minimal cross sectional area of block  300  that passes through the centroid of the block and normal to parallel sides  302  and  303 . A MK II MOD 0 blasting cap  506  and booster charge  504  of 0.083 inch thickness and ¾ inch diameter are used to initiate explosive sheet  100 . A 3 inch square piece of said flexible material is used as the smoothing layer  500 . 
     Referring to  FIG. 6 , yet a second embodiment of the invention is presented. This embodiment of the invention is shown primarily in  FIG. 6 , an explosive sheet  600  in the shape of an isosceles triangle with apexes  602 . When the three apexes are simultaneously initiated, expanding shock waves  604 ,  606 , and  608  will be produced. Shock waves  604 ,  606 , and  608  will meet on lines  610 ,  612 , and  614  in 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 sheet  600  vice explosive sheet  100  as shown in  FIG. 1  are that the shock waves generated from the three disparate apexes  602  meet head-on at midpoints  616  along the sides of said sheet and meet at greater head-on angles than the four apex configuration of explosive sheet  100 . 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 to  FIGS. 7 and 8 , a flat block  700  in the shape of an isosceles triangle has two sets of parallel sides, a top  702  and bottom  703 , of triangular pieces of flexible sheet material filled with additional laminas  704  of triangular pieces of: flexible sheet material, cardboard, other low density material, or a combination thereof. The tamper block  700  is constructed of identical materials to that used to construct tamper block  300  as shown in  FIG. 4 . 
     Referring to  FIGS. 4 ,  7 ,  8 , and  9 , the  FIG. 8  cross-section of block  700  along section  8 - 8  shows laminas  702 ,  703 , and  704  that correspond to the  FIG. 4  laminas  302 ,  303 , and  304  of block  300 . 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 sheet  600  that faces the target  502 . The block also serves as a form to hold the explosive sheet material  600  in the correct position to effect simultaneous ignition of the three apexes as shown in  FIG. 9 . As part of this form, three pieces of mitered half-round wooden molding  706  surround 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, block  700  will be provided with pre-printed positioning guide-lines  708  on its top surface of flexible sheet material  702  to assure that the three apexes  602  as shown in  FIG. 6  are wrapped around said block with their apexes meeting at the center of the top side of flexible sheet material  702 . For field assembly, block  700  may also be marked with pre-printed position guide-lines (not shown) on its bottom surface of sheet material  703  as previously taught to adjust the cutting ability when said block is turned upside down. When the assembly  700  and explosive charge  600  are 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 to  FIG. 9 , isosceles triangular shaped sheet explosive  600  is shown wrapped around tamper block  700 . The length of a side of sheet explosive  600  will be approximately 1.5 times the length of the side of laminas  702 ,  703 , or  704  that are all isosceles triangles with identical side lengths. A smoothing layer  900  with 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 charge  600  facing the target. The smoothing layer  900  is shown as an isosceles shaped piece of material, but other geometric shapes are possible. The smoothing layer  900  material is identical in thickness and composition to smoothing layer  500 . The assembly  700 , explosive charge  600 , and smoothing layer  900  will 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 target  502  without the use of additional adhesive or tape. Again, initiating means consisting of blasting cap  506  that is held in place by the trough  510  of blasting cap holder  508  with bendable legs  512  to align centrally the output end  514  of said blasting cap against the center  505  of booster charge  504  will effect the detonation of explosive sheet  600  via simultaneous detonation of its three disparate apexes. Upon detonation of explosive sheet  600  that is wrapped around tamper block  700 , the meeting of generated shock waves in explosive sheet  600  will result in a cutting through smoothing layer  900  to fault and fracture target plate  502  in a “y” configuration as taught in  FIG. 6 . The additional blast and shock from said explosive sheet will be attenuated by smoothing layer  900  to create a plurality of petals cantilevered from the target material as in a blooming flower to form a near fragment-free opening in target  502  along the fault and fracture lines in target plate  502 . 
     Referring to  FIG. 10 , a separate embodiment is shown of the cross-section view of  FIG. 8 . A tamper block  1000  is comprised of laminas  1002 ,  1003 , and  1004  that correspond to  FIG. 8  laminas  702 ,  703 , and  704  that are all isosceles triangles in shape. These laminas  1002 ,  1003 , and  1004  are of the same materials and thickness as laminas  702 ,  703 , and  704 , but have adjusted areas to approximate the outer curved periphery of wooden moldings  706  of  FIG. 7 . Elimination of wooden moldings  706  will simplify field assembly of block  700  because there are fewer components. Again, block  1000  will be provided with pre-printed positioning guide-lines  708  on its top  1002  and/or bottom  1003  surfaces of flexible magnetic material for field assembly. An adhesive to keep laminas  702 ,  703 , and  704  in 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.