Patent Application
20070029321
1. Field of the Invention
The present invention relates to blast resistant container assemblies. More particularly, this invention relates to various blast resistant and blast directing container assemblies for receiving explosive articles and preventing or minimizing damage in the event of an explosion. These container assemblies have utility as containment and transport devices for explosive materials.
2. Description of the Related Art
It is well known to employ explosion suppressing structures to minimize the damage caused by fragment and blast forces resulting from the detonation of an explosive device. Many types of explosion suppressing structures are known. For example, U.S. Pat. No. 6,289,816 teaches a water-based apparatus for mitigating the damage from a confined explosion. The water-based apparatus comprises a water-blanket which rests on each explosive to mitigate the gas pressure loading from an inadvertent explosion. U.S. Pat. No. 6,302,026 teaches an explosion-suppressing structure which comprises an explosion-suppressing barrier, such as a wall of liquid-filled tanks or blocks, and rupturable explosion-suppressing roof members, such as hollow rigid bodies containing liquid-filled bags.
In the art of blast containment, blast resistant containers have become particularly desirable for their ability to hold and transport explosives prior to their detonation, while also allowing for explosives to be detonated within the containers, preventing or minimizing damage caused by the explosives. Accordingly, such containers are extremely useful to bomb squads, and are increasingly attractive options for use in airplane cargo containers.
U.S. Pat. No. 3,786,956 teaches a laminated container for explosives that is capable of at least partially absorbing a detonation by delamination of the laminated walls. Explosives placed within the container are spaced from contact with the outer walls of the container by a support structure such as a net, or a material such as plastic foam or foam rubber. U.S. Pat. No. 4,055,247 teaches an explosion containment device including three layers of steel and crushable layers intermediate to the steel layers. U.S. Pat. No. 4,432,285 shows an aircraft explosive storage containment unit that attenuates the effects of a bomb blast and directs the force of the explosion into a specific area.
Many types of blast resistant containers are known. For example, U.S. Pat. No. 4,889,258 teaches a blast-resistant container comprising a high-strength outer housing wherein the housing includes an inner compressible layer of a mixture including vermiculite in a binder effective to space the article from the outer housing, to absorb energy of the blast before transmitted to the outer housing, to distribute the blast forces over a larger surface area of the outer housing, and to impart resistance to the penetration of fragments to the outer housing. U.S. Pat. No. 5,267,665 teaches a container that is designed to suppress shock waves and contain exploding fragments while safely bleeding off or venting high pressure gases. U.S. Pat. No. 6,244,155 teaches a containment structure installed in the wall of a building, the structure having interior and exterior doors for placing suspicious packages inside, a blast deflection chute and a blowout panel to direct over pressure from explosions away from buildings and people. Other blast resistant and/or blast directing containers are described in U.S. Pat. Nos. 4,027,601, 5,170,690, 5,225,622, 5,249,534 and 5,376,426.
Commonly known blast resistant containers have been made with high strength materials including metals such as stainless steel or steel plate. These containers generally are heavy and have a bulky, fixed shape or construction. Improving technology has also introduced blast resistant containers manufactured from high-strength polymeric fibers, which are lighter but as strong as or stronger than metal fibers. For example, U.S. Pat. No. 6,341,708 describes an improved blast resistant container assembly that is composed of high strength fiber materials known as SPECTRA® fibers, commercially available from Honeywell International Inc. This patent describes a blast resistant container assembly comprising at least three bands. A first inner band is nested within a second band which is nested within a third band, with all bands being oriented relative to one another to substantially enclose a volume and to form a container.
This three band box design has several advantages over containers of the prior art, making it extremely attractive in its industry. For example, it eliminates the need for door and panel hinges or door-channel interlock systems, one of the weak points of the prior art containers, since access can be achieved through an open side or sides of the innermost band. Other modifications permit easy access to the container's interior for loading and unloading in spite of limited exterior space constraints. Each of the bands could be collapsed for efficient storage and transported as a set of three or more essentially flat bands for subsequent assembly. Additionally, each band can be manufactured from high strength SPECTRA® fibers. However, the need for further improvements to this three band box design remains.
Particularly, following a contained explosion, a cubical 3-band box tends to experience tensile failure at the corners of the box because the corners “open” following a blast, causing their initial small curvature to expand. Since the fibers of the internal band surface are the first to be loaded in tension, they are continuously loaded more than the fibers of the outer surface of the band. As a result, the layers of material are broken in a sequence from the internal to the external instead of being broken simultaneously at a higher force. This results in a structure that is less stable at the corner areas, rather than exhibiting a uniform stability.
It has now been unexpectedly found that the blast containing performance of three band boxes can be substantially improved by using a special band-winding technique around the corner areas of each band. A sheet of high performance material, e.g. Spectra Shield® brand and the like, is continuously wound around a mandrel having edges, the edges meeting at indented corner areas, to create a multilayered, preferably rectangular band. Comparatively, conventional mandrels have rounded corners that have a small radius of curvature. Under conventional winding procedures, the tension of the wound material forces tight placement of the layers against each other, and the outer layers within the corner area are longer than the inner ones. Thus, upon opening, the inner layers at the corner stretch first. In the method of the present invention, the tension of the wound material at the indented corner areas is less than at the mandrel edges or faces, and the corner layers are free to move out of mutual contact. This winding procedure gives a slack for the inner band layers at the corners that is not provided using the conventional straight winding technique. This slack is reduced during subsequent winds around the mandrel and may eventually disappear for the outermost band layers, with the goal of achieving a uniform tension of the inner and outer band layers upon an explosion. The containers of the invention are particularly useful in aircraft, such as in the cargo holds and passenger cabins of the aircraft, and are particularly useful to bomb squad personnel in combating terrorist and other threats, and for safe munitions transport.
The invention provides a process for forming a blast resistant band comprising:
a) providing a first mandrel having edges, which edges meet at indented corner areas;
b) wrapping at least one sheet comprising a fibrous material around the mandrel edges and indented corner areas in a plurality of layers;
c) securing the plurality of layers of fibrous material together to form a band; and then
d) removing the band from the mandrel.
The invention also provides a process for forming a blast resistant band comprising:
a) providing a first mandrel having edges, which edges meet at indented corner areas;
b) positioning at least one spacer at each of the indented corner areas;
c) wrapping at least one sheet comprising a fibrous material around the mandrel edges and spacers in a plurality of layers;
d) securing the plurality of layers of fibrous material together to form a band; and then
e) removing the band from the mandrel.
The invention further provides a blast resistant container comprising at least one band, each band comprising at least one sheet, said sheet comprising a plurality of layers of a fibrous material, each band having edges that meet at corner areas, each layer of fibrous material having an amount of slack at the corner areas, wherein outwardly successive layers of fibrous material have an amount of slack less than or equal to the amount of slack at the corner areas of underlying layers.
The invention provides blast resistant bands, blast resistant containers and processes for their formation. As used herein, the term “band” is meant to describe a thin, volume-encircling strip. In a process of the invention, at least one blast resistant band is formed around a mandrel 10, as seen in
In the preferred embodiment of the invention, at least one spacer 18 is placed at each of the indented corner areas 14, as seen in
In the preferred embodiment of the invention, the wrapping tension typically is in the range of from about 0.1 to about 50 pounds per linear inch (pli) (about 17.5 N/m to about 8756 N/m), more preferably in the range of from about 2 to about 50 pounds per linear inch (about 350 N/m to about 8756 N/m), most preferably in the range of from about 2 to about 20 pounds per linear inch (about 350 N/m to about 3500 N/m). Prior to wrapping, the sheet of fibrous material 16 is preferably first attached to the mandrel, such as with an adhesive or other conventional technique. As used herein, “sheet” is meant to include a single fiber or a plurality of connected fibers for purposes of this invention.
In another preferred embodiment of the invention, the spacers 18 comprise inflatable tubes. Each of
As discussed above, this additional inner slack at the corners is not provided using conventional straight winding techniques, and has been unexpectedly found to distribute blast forces with greater uniformity than conventional blast resistant articles, resulting in significantly improved blast resistance performance. Referring to
The spacers 18 may alternately, for example, be attached to the mandrel, such as with an adhesive or other means of attachment as may be deemed appropriate by one skilled in the art. The mandrel may also be rotated by conventional means in the art which would be known to one skilled in the art. In
It has been further unexpectedly found that inflatable tube spacers 18 are particularly useful for producing bands having the desired corner shape of the invention, whereby inner band layers have a greater slack, or greater fabric buildup, than outer band layers. In one particularly effective method for forming a band of the invention utilizing inflatable tube spacers, the tubes are substantially inflated at the beginning of the wrapping step, and successively deflated during the wrapping of each additional fabric layer around the mandrel, the tubes preferably being substantially deflated at the culmination of the wrapping of the fabric sheet around the mandrel. This pattern of deflation is particularly effective in providing the inner layers with additional slack, while the overall length of each wrapped layer of fibrous material are generally equal.
Once the wrapping step is complete, the plurality of layers of fibrous material are preferably secured together to form a substantially seamless band, and the band is then preferably removed from the mandrel. To aid in the removal of the band from the mandrel, the mandrel may optionally be covered with release paper or film or be pre-coated with a release coating, such as Teflon® brand. The fabric layers can be secured in a variety of ways, such as by heat and/or pressure bonding, heat shrinking, via adhesives, with staples, by sewing the layers together and other securing means known to those of skill in the art. It is most preferred that the securing step comprises the steps of coating the fiber material with a resin matrix and consolidating the layers of high strength fiber material and the resin matrix either on or off of the mandrel, such as by well known autoclaving techniques. The fiber material can be coated with a resin matrix either before, during or after the wrapping step. By “consolidating” is meant combining the matrix material and the fiber network into a single unitary layer. Depending upon the type of matrix material and how it is applied to the fibers, consolidation can occur via drying, cooling, pressure or a combination thereof, optionally in combination with application of an adhesive. “Consolidating” is also meant to encompass spot consolidation wherein the faces of a band are consolidated but the edges are not. In this fashion, the faces can be made rigid while the edges retain the ability to bend or be bent to permit collapsing or folding of the band.
In the preferred embodiment of the invention, the above process is carried out to produce three individual blast resistant bands which may be united to form a three band container assembly. The cross-section of the volume encircled by a band may vary, although polygonal is preferred to circular, with rectangular being more preferred and square being most preferred. Such cross-sectional shapes are directly determined by the shape of the mandrel around which the sheet of fibrous material is wound. In one method of making the bands of the invention for assembly into a blast resistant container, each individual band is formed around a separate mandrel of a different size, but a similar shape, compared to the mandrel used to form the other bands. For example, as seen in
In another method for making bands for assembly into a multi-band, blast resistant container, each additional band may optionally be formed on a single mandrel by positioning at least one additional spacer on the exterior corner areas of the outermost completed band, and wrapping each additional band around the completed band and additional spacers. In this alternate process, at least three bands are preferably formed in this fashion, followed by removing the bands from the mandrel and uniting the bands to form a container. This method allows formation of all of the bands for a single container at one time.
Many differing container shapes are contemplated by the present invention. For instance, the container assembly can enclose a non-cubic rectangular prism due to the differing rectangular cross-sections of its three bands. It should also be appreciated that substantially more than three bands can readily be utilized in the present invention, even with the basic cube (or rectangular prism) design of the container. Similarly, a basic two band construction can be utilized as well. It is preferred that the outermost band comprises a single continuous band. Furthermore, a large number of coaxial bands can also be coaxially nested one within the other to substitute for any one band in the basic container concept of the invention; the number of bands utilized as an equivalent may depend upon the desired rigidity of the equivalent. It is possible to have several flexible bands which, when nested coaxially, become rigid.
In the preferred embodiment of the invention, each of the bands are aligned with their respective longitudinal axes perpendicular to one another. As a result, each of the six panels forming the faces of container will have a thickness substantially equivalent to the sum of the thicknesses of at least two of the bands where they overlap, and every edge of the container is covered by at least one band of material. Accordingly, a preferred container of the invention comprises a set of at least three nested and mutually reinforcing four-sided continuous bands of blast resistant fibrous material assembled into a cube, wherein all of the corner areas of each band have an outwardly decreasing slack.
In another alternate embodiment of the invention, the desired slack at the corner areas may be achieved by impressing a cogwheel 30 into the sheet of fibrous material 16 at each of said indented corner areas, producing an impression in the sheet at the indented corner areas. This embodiment is illustrated in
When assembled, a three band container of the invention is preferably formed around a load, such as an explosive or airline cargo, by placing the load inside the first band, optionally with a blast mitigating material 26, such as seen in prior art
The container assembly can be a container of the prior art with an access opening on one or more sides thereof, or it can be a container with two bands of the three band concept already discussed and having an access opening on one or more sides thereof. The shape of the band's inner cross-section should conform to the portion of the container that it encircles. A polygonal cross-section is preferred with rectangular being more preferred and square being most preferred. The present container assembly does not require a separate entry door and closure can be achieved without hinges or door channels, avoiding such limitations presented by the prior art. Additional features and designs for the formation of a preferred three band container assembly may be found in U.S. Pat. No. 6,341,708, which is incorporated herein by reference to the extent that it is not inconsistent herewith.
For purposes of this invention, a fibrous layer comprises at least one network of fibers either alone or with a matrix. A fiber denotes an elongated body, the length dimension of which is much greater than the transverse dimensions of width and thickness. Accordingly, the term fiber includes monofilament, multifilament, ribbon, strip, staple and other forms of chopped, cut or discontinuous fiber and the like having regular or irregular cross-sections. The term fiber includes a plurality of any one or combination of the above.
The cross-sections of filaments for use in this invention may vary widely. They may be circular, flat or oblong in cross-section. They also may be of irregular or regular multi-lobal cross-section having one or more regular or irregular lobes projecting from the linear or longitudinal axis of the fibers. It is particularly preferred that the filaments be of substantially circular, flat or oblong cross-section, most preferably the former.
By network is meant a plurality of fibers arranged into a predetermined configuration or a plurality of fibers grouped together to form a twisted or untwisted yarn, which yarns are arranged into a predetermined configuration. For example, the fibers or yarn may be formed as a felt or other non-woven, knitted or woven (plain, basket, satin and crow feet weaves, etc.) into a network, or formed into a network by any conventional techniques. According to a particularly preferred network configuration, the fibers are unidirectionally aligned so that they are substantially parallel to each other along a common fiber direction. Continuous length fibers are most preferred although fibers that are oriented and have a length of from about 3 to about 12 inches (about 7.6 to about 30.4 centimeters) are also acceptable and are deemed “substantially continuous” for purposes of this invention.
It is preferred that within a fibrous layer at least about 50 weight percent of the fibers, more preferably at least about 75 weight percent, be substantially continuous lengths of fiber that encircle the volume enclosed by the container. By encircle the volume is meant in the band or hoop direction, i.e., substantially parallel to or in the direction of the band. By substantially parallel to or in the direction of the band is meant within +/−10°. It is also preferred that the bands of the present invention be substantially seamless. By substantially seamless is meant that the band is seamless across each edge joining adjacent faces for more than at least one full wrap of the fibrous layer and also that at any given point on the band there is at least one wrap/layer that is seamless. With this definition, a band with five faces wherein the first and fifth faces are not joined but overlap would be considered substantially seamless, even though the first and fifth faces are not joined to one another.
The type of fibers used in the blast resistant material may vary widely and can be inorganic or organic fibers. Preferred fibers for use in the practice of this invention, especially for the substantially continuous lengths, are those having a tenacity equal to or greater than about 10 grams/denier (g/d) and a tensile modulus equal to or greater than about 200 g/d (as measured by an Instron Tensile Testing machine). Particularly preferred fibers are those having a tenacity equal to or greater than about 20 g/d and a tensile modulus equal to or greater than about 500 g/d. More preferred are those embodiments in which the tenacity of the fibers is equal to or greater than about 25 g/d and the tensile modulus is equal to or greater than about 1000 g/d. The most preferred fibers have a tenacity equal to or greater than about 30 g/d and a tensile modulus equal to or greater than about 1200 g/d.
Useful high strength fibers suitable for use herein are thoroughly described in commonly owned U.S. Pat. No. 6,341,708, which has been incorporated herein by reference to the extent not inconsistent herewith. The most useful high strength fibers include extended chain polyolefin fibers, particularly extended chain polyethylene (ECPE) fibers, aramid fibers, polybenzoxazole fibers (PBO), polybenzothiazole fibers (PBT), polyvinyl alcohol fibers, polyamide fibers, polyethylene terephthalate fibers, polyethylene naphthalate fibers, polyacrylonitrile fibers, liquid crystal copolyester fibers, glass fibers, carbon fibers, fibers formed from basalt or other minerals, and/or combinations thereof. Particularly preferred are extended chain polyethylene fibers and aramid fibers.
Other suitable fiber types for use in the present invention include fibers comprising pyridobisimidazole-2,6-diyl(2,5-dihydroxy-p-phenylene) moieties, also known as M5® designer fibers. M5® fibers are manufactured by Magellan Systems International of Richmond, Va. and are described, for example, in U.S. Pat. Nos. 5,674,969, 5,939,553, 5,945,537, and 6,040,478, each of which are incorporated herein by reference. If a combination of fibers is used, it is preferred that the fibers be a combination of at least two of polyethylene fibers, aramid fibers, polyamide fibers, carbon fibers, PBO fibers and glass fibers. Specific preferred fibers include M5® fibers, polyethylene Spectra® fibers, poly(p-phenylene terephthalamide) and poly(p-phenylene-2,6-benzobisoxazole) fibers. Most preferably, the fibers comprise high strength, high modulus polyethylene Spectra® fibers.
U.S. Pat. Nos. 4,457,985, 4,623,574 and 4,748,064, which are incorporated herein by reference to the extent that they are not inconsistent herewith, generally discuss such extended chain polyethylene and polypropylene fibers. In the case of polyethylene, suitable fibers are those of weight average molecular weight of at least 150,000, preferably at least one million and more preferably between two million and five million. Such extended chain polyethylene fibers may be grown in solution as described in U.S. Pat. Nos. 4,137,394 and 4,356,138, or may be spun from a solution to form a gel structure, as described in U.S. Pat. Nos. 4,413,110 and 4,551,296, each of which are hereby incorporated by reference.
If a matrix material is employed in the practice of this invention, it may comprise one or more thermosetting resins, or one or more thermoplastic resins, or a blend of such resins. The choice of a matrix material will depend on how the bands are to be formed and used. The desired rigidity of the band and/or ultimate container will greatly influence choice of matrix material. As used herein “thermoplastic resins” are resins which can be heated and softened, cooled and hardened a number of times without undergoing a basic alteration, and “thermosetting resins” are resins which cannot be re-softened and reworked after molding, extruding or casting and which attain new, irreversible properties when once set at a temperature which is critical to each resin.
The tensile modulus of the matrix material in the band(s) may be low (flexible) or high (rigid), depending upon how the band is to be used. The key requirement of the matrix material is that it be flexible enough to process at whatever stage of the band-forming method it is added. In this regard, thermosetting resins which are fully uncured or have been B-staged but not fully cured would probably process acceptably, as would fully cured thermosetting resins which can be plied together with compatible adhesives. Heat added to the process would permit processing of higher modulus thermoplastic materials which are too rigid to process otherwise; the temperature “seen” by the material and duration of exposure must be such that the material softens for processing without adversely affecting the impregnated fibers, if any.
With the foregoing in mind, thermosetting resins useful in the practice of this invention may include, by way of illustration, bismaleimides, alkyds, acrylics, amino resins, urethanes, unsaturated polyesters, silicones, epoxies, vinyl esters and mixtures thereof. Greater detail on useful thermosetting resins may be found in U.S. Pat. No. 5,330,820, incorporated herein by reference. Particularly preferred thermosetting resins are the epoxies, polyesters and vinyl esters, with an epoxy being the thermosetting resin of choice.
Thermoplastic resins for use in the practice of this invention may also vary widely. Illustrative of useful thermoplastic resins are polylactones, polyurethanes, polycarbonates, polysulfones, polyether ether ketones, polyamides, polyesters, poly(arylene oxides), poly(arylene sulfides), vinyl polymers, polyacrylics, polyacrylates, polyolefins, ionomers, polyepichlorohydrins, polyetherimides, liquid crystal resins, and elastomers and copolymers and mixtures thereof. Greater detail on useful thermoplastic resins may be found in U.S. Pat. No. 5,330,820, incorporated herein by reference. Particularly preferred low modulus thermoplastic (elastomeric) resins are described in U.S. Pat. No. 4,820,568, incorporated herein by reference, in columns 6 and 7, especially those produced commercially by Kraton Polymers of Houston, Tex. and described in the bulletin “KRATON Thermoplastic Rubber”, SC-68-81. Particularly preferred thermoplastic resins are the high density, low density, and linear low density polyethylenes, alone or as blends, as described in U.S. Pat. No. 4,820,458. A broad range of elastomers may be used, including natural rubber, styrene-butadiene copolymers, polyisoprene, polychloroprene-butadiene-acrylonitrile copolymers, ER rubbers, EPDM rubbers, and polybutylenes.
In the preferred embodiments of the invention, the matrix comprises a low modulus polymeric matrix selected from the group consisting of a low density polyethylene; a polyurethane; a flexible epoxy; a filled elastomer vulcanizate; a thermoplastic elastomer; and a modified nylon-6. The proportion of matrix to filament in the bands is not critical and may vary widely. In general, the matrix material forms from about 5% to about 50% by volume of the fibers, preferably about 5% to 30%, and most preferably about 5% to 20%. If a matrix resin is used, it may be applied in a variety of ways to the fiber, e.g., encapsulation, impregnation, lamination, extrusion coating, solution coating, solvent coating. Effective techniques for forming coated fibrous layers suitable for use in the present invention are detailed in U.S. Pat. Nos. 4,820,568 and 4,916,000, which are also incorporated herein by reference.
In the preferred embodiment of the invention, it is also desirable that the materials of construction of containers be relatively X-ray transparent in order to be able to X-ray suspicious packages while inside the blast resistant container. Extended chain polyethylene fibers, aramid fibers, and organic matrices are relatively X-ray transparent. In addition these materials will not contribute to shrapnel from an explosion. The preferred blast resistant materials utilized in forming the containers and bands of the present invention are oriented films, fibrous layers, and/or a combination thereof. A resin matrix may optionally be used with the fibrous layers, and a film (oriented or not) may comprise the resin matrix.
There are various methods by which the fibrous sheet 16 of the invention may be fabricated. In one preferred embodiment of the invention, the fibrous sheet material comprises yarn bundles of from about 30 to about 2000 individual filaments of less than about 12 denier, and more preferably of about 100 individual filaments of less than about 7 denier. The yarns are preferably supplied from a creel and are led through guides and a spreader bar into a collimating comb. The collimating comb aligns the filaments in a co-planar, substantially parallel and unidirectional fashion. The filaments are then sandwiched between release papers, one of which is coated with a wet matrix resin. This system is then passed under a series of pressure rolls to impregnate the filaments with the resin. The top release paper is pulled off and rolled up on a take-up reel while the impregnated network of filaments proceeds through a heated tunnel oven to remove resin solvent and then be taken up. Alternatively, a single release paper coated with the wet matrix resin can be used to create the impregnated network of filaments. One such impregnated network is referred to as unidirectional pre-preg, tape or sheet material and is one of the preferred feed materials for making the bands of the invention.
In an alternate embodiment of the invention, two such impregnated networks are continuously cross-plied, preferably by cutting one of the networks into lengths that can be placed successively across the width of the other network in a 0°/90° orientation. This forms a continuous flexible sheet of high strength fiber material. See, for example, U.S. Pat. No. 6,341,708 and U.S. Pat. No. 6,642,159, each of which are incorporated herein by reference in their entireties, for additional description regarding the formation of such fibrous materials. This type of fibrous sheet can then be used to form one or more bands in accordance with the methods of the present invention. This fibrous layer is sufficiently flexible to wrap in accordance with the methods of the present invention, and can also be made substantially rigid, if desired, either by the number of wraps or by the manner in which it is secured.
In another embodiment of the invention, a matrix film material may be simultaneously wound with the fibrous material onto the mandrel, and subsequently consolidated with the fibrous material. The thickness of such a matrix film is preferably at least about 0.1 mil, more preferably from about 0.1 to about 50 mil, and most preferably from about 0.35 to about 10 mil. Generally, the thickness of such a matrix film may be as thick as desired so long as the length is still sufficiently flexible to permit band formation. Matrix films can also be used on the surfaces of the bands for a variety of reasons, e.g., to vary frictional properties, to increase flame retardance, to increase chemical resistance, to increase resistance to radiation degradation, and/or to prevent diffusion of material into the matrix. The matrix film may or may not adhere to the band depending on the choice of film, resin and filament. Heat and/or pressure may cause the desired adherence, or it may be necessary to use an adhesive that is heat or pressure sensitive between the film and the band to cause the desired adherence. Examples of acceptable adhesives include polystyrene-polyisoprene-polystyrene block copolymer, thermoplastic elastomers, thermoplastic and thermosetting polyurethanes, thermoplastic and thermosetting polysulfides, and typical hot melt adhesives.
Films which may be used as matrix materials in the present invention include thermoplastic polyolefinic films, thermoplastic elastomeric films, crosslinked thermoplastic films, crosslinked elastomeric films, polyester films, polyamide films, fluorocarbon films, urethane films, polyvinylidene chloride films, polyvinyl chloride films and multilayer films. Homopolymers or copolymers of these films can be used, and the films may be unoriented, uniaxially oriented or biaxially oriented. The films may include pigments or plasticizers.
Useful thermoplastic polyolefinic films include those of low density polyethylene, high density polyethylene, linear low density polyethylene, polybutylene, and copolymers of ethylene and propylene which are crystalline. Polyester films which may be used include those of polyethylene terephthalate and polybutylene terephthalate. The methods, temperatures and pressures to which the bands of the present invention are exposed to consolidate the fibrous layers of each band, to cure any thermosetting resin, to consolidate fiber networks to each other or to a sheet of a matrix film, vary depending upon the particular system used. Such are described in U.S. Pat. No. 6,341,708 referenced above.
Uniaxially or biaxially oriented blast resistant films may further be adhered to the bands of the invention and can be single layer, bilayer, or multilayer films selected from the group consisting of homopolymers and copolymers of thermoplastic polyolefins, thermoplastic elastomers, crosslinked thermoplastics, crosslinked elastomers, polyesters, polyamides, fluorocarbons, urethanes, epoxies, polyvinylidene chloride, polyvinyl chloride, and blends thereof. Preferred blast resistant films of choice are high density polyethylene, polypropylene, and polyethylene/elastomeric blends. Film thickness preferably ranges from about 0.2 to about 40 mils (about 0.2 μm to about 1016 μm), more preferably from about 0.5 to 20 mils (about 12.7 μm to about 508 μm), most preferably from about 1 to 15 mils (about 25.4 μm to about 381 μm).
In the most preferred embodiments, each fibrous layer has an areal density of from about 0.1 to about 0.15 kg/m2. The “areal density” is the weight of a structure per unit area of the structure in kg/m2. Panel areal density is determined by dividing the weight of the panel by the area of the panel. For a band having a polygonal cross-sectional area, areal density of each face is given by the weight of the face divided by the surface area of the face. In most cases, the areal density of all faces is the same, and one can refer to the areal density of the structure. The areal density per band ranges from about 1 to about 40 kg/m2, preferably from about 2 to 20 kg/m2, and more preferably from about 4 to about 10 kg/m2. In the embodiment where Spectra Shield® composite material forms a fibrous layer, these areal densities correspond to a number of fibrous layers per band ranging from about 10 to about 400, preferably from about 20 to about 200, more preferably from about 40 to about 100. In the three band cube design of the most preferred embodiment of the present invention, each face of the cube comprises two bands of blast resistant material, which effectively doubles the aforesaid ranges for each face of the cube. Where fibers other than high strength extended chain polyethylene, like Spectra® polyethylene fibers, are utilized the number of layers may need to be increased to achieve the high strength and modulus characteristics provided by the preferred embodiments.
Similar to the prior art, a first band of the invention may optionally be filled with a blast mitigating material 26, depicted in prior art
Another technique to achieve a blast mitigating effect is to surround the explosive with heat sink materials. Effective heat sink materials include aqueous foams; aqueous solutions having antifreeze therein such as glycerin, ethylene glycol; hydrated inorganic salts; aqueous gels, preferably reinforced; aqueous mists; wet sponges, preferably elastomeric; wet profiled fibers; wet fabrics; wet felts; and combinations thereof. Aqueous foams are most preferred, especially aqueous foams having a density in the range of from about 0.01 to about 0.10 g/cm3, more preferably from about 0.03 to about 0.08 g/cm3.
In practice, when subjected to explosive forces, a polygonal band or container is capable of transforming into a round, ring-shaped configuration. Ideally, the stress from the explosion is distributed uniformly across the thickness of the fabric layers, meaning that all layers are loaded equally, and resulting in complete transformation of the polygonal shape into the ring shape. In reality, using technology of the prior art, transformation to the desired ring shape is not completed, because the tensile loading of internal band layers starts first and reach failure first, followed by rest of the band layers breaking in sequence. This results in a lower failure strength as compared to the ideal case where all the layers are broken simultaneously.
The following non-limiting examples serve to illustrate the invention.
A three band container consisting of inner, middle, and outer fibrous bands is constructed from sheets of unidirectional, high modulus polyethylene (HMPE) fibers impregnated with Kraton® thermoplastic resin. The HMPE fibers are Spectra® 1000 brand, 1100 denier manufactured by Honeywell International Inc. and have a tenacity of 36 g/denier and a tensile modulus of 1250 g/denier. The Kraton®t resin is a polystyrene-polyisoprene-polystyrene block copolymer commercially available from Kraton Polymers of Houston, Tex.
A 24-inch wide sheet of Spectra Shield® composite material is wrapped onto a four-sided, wooden mandrel. The Spectra Shield® composite material has 75% of its fibers in the hoop direction. The mandrel has dimensions of about 24″×24″×24″, but having carved out corners, and having flexible tubes placed in each of the carved out corners. The sheet is wrapped around the mandrel with increasing tension so that at the last wrap the tube is substantially collapsed (See
Example 1 is repeated using a standard cubic wooden mandrel having dimensions of 24″×24″×24″ with conventional rounded corners. Testing is conducted similar to Example 1. An estimated 42% improvement in box performance is noted with the container of Example 1 compared to the conventional container of this example.
While the present invention has been particularly shown and described with reference to preferred embodiments, it will be readily appreciated by those of ordinary skill in the art that various changes and modifications may be made without departing from the spirit and scope of the invention. It is intended that the claims be interpreted to cover the disclosed embodiment, those alternatives which have been discussed above and all equivalents thereto.
