Abstract:
This invention is a novel lightweight blast resistant container. It consists of containers made of a blast resistant fiber reinforced polymer resin matrix composite. The invention employs a novel construction configuration whereby the container is created by the appropriate nesting of composite parts to create a cube, box or multi-faceted geometry. As a result of the nesting, the box like geometry exhibits characteristics that cause the geometry to behave more like a sphere than a box when subjected to internal blast pressures. Such an approach provides an optimized minimum weight solution by fully utilizing the entire material volume, whereby ultimate tensile strength can be simultaneously developed everywhere in the container.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The invention relates to a lightweight multi-sides container capable of resisting an explosive detonation dut to bombs or other explosive devices without rupture. The invention applies to any situation where an explosive device is detonated in a container. The invention is particularly applicable to cargo containers, such as Unit Load Devices used on aircraft, or shipping containers used on ships or trucks.  
         [0002]     One possible scenario for terrorist activity is to place explosive devices in cargo or luggage. Even a small explosive device is adequate to destroy an aircraft. Current practice on wide body aircraft is to put all cargo and luggage into containers called Unit Load Devices (ULD&#39;s). Current ULD&#39;s are constructed of lightweight aluminum, which provides no protection against explosives. Although some ULD&#39;s have been proposed which offer increased blast protection, all proposals to date are too heavy. The U.S. Federal Aviation Administration is actively encouraging the development of effective blast containment in aircraft luggage and cargo holds.  
         [0003]     Similarly other containers such as those used on seagoing ships are vulnerable to explosive detonations. Mailboxes also fall into this category. Most containers for the transport of cargo, mail, and personal goods are constructed of thin metal, which becomes shrapnel during even a small explosion. Thus it is the object of this invention to provide containment of blast overpressure associated with explosive threats without venting or rupture of the containment structure.  
       BRIEF SUMMARY OF THE INVENTION  
       [0004]     The invention is a blast resistant container, constructed entirely or in part of a blast resistant composite material. In the preferred embodiment, the composite material is a fiber reinforcement in a polymer resin matrix.  
         [0005]     In one aspect, the polymer resin matrix is resistant to galvanic corrosion, solvents and chemical agents and exhibits a high specific strength, high specific modulus, high strain to failure, high fracture toughness and is not hygroscopic.  
         [0006]     In another aspect the fiber reinforcement is treated with a special resin compatible sizing which develops a high specific laminate strength, high specific laminate modulus, high laminate strain to failure and a high laminate fracture toughness.  
         [0007]     In another embodiment, the composite material is layered to form a laminate.  
         [0008]     In a further embodiment, the container is constructed of three nested parts, such that circumferential hoop constraint is achieved about three orthogonal axes.  
         [0009]     In another embodiment the container is a Unit Load Device. In one aspect, the Unit Load Device is closed by installing the third part, and in the event of the blast, the expansion of the inner parts against the outer parts serve to develop a self sealing, i.e. gasket, mechanism.  
         [0010]     In another embodiment, the container is a mailbox. In a further embodiment, the container is a cargo container such as used for containerized shipping by sea or truck.  
         [0011]     In another embodiment the container may be used specifically for the safe storage of explosive materials in order to protect the surroundings from an accidental or unanticipated detonation of the explosives stored within the container.  
         [0012]     In a further embodiment, in order to avoid personnel and property damage, the invention may be used by police, firemen or demolition teams as a portable container to safely detonate bombs planted by terrorists.  
         [0013]     In a further embodiment, the invention is a method of constructing a blast resistant container, including providing tools which allow for forming of three nested parts, fabricating and curing the nested parts and, assembling the container from the three nested parts. Circumferential hoop stresses are developed in the winding direction of the broadgoods associated with each part&#39;s geometry. When exposed to an internal blast, each part, within the nested assembly, tends to dilate into a cylindrical shape, reducing the high stresses normally developed at the corners of a rigid box where three edges intersect.  
         [0014]     In a further embodiment of the method, the containers are constructed at least in part using a fiber reinforced, polymer resin matrix, composite. In one aspect, the resin is introduced using a vacuum infusion process. In another aspect, the resin is introduced by pre-impregnating the reinforcement broadgoods.  
         [0015]     One embodiment of the invention involves the construction of a blast resistant container utilizing fiber reinforced polymer composite laminate skins in combination with core materials to form a sandwich type construction. Low density core materials may include opened or closed cell foam, a honeycomb material, nomex, metal foam, or balsa wood. In a further embodiment of the invention, the tool or mandrel for the outer part may be eliminated by using the bonded assembly of the inner parts as the tool or mandrel for fabricating each outer part.  
         [0016]     In another embodiment, a non-circular doorway opening may be cut out from any side wall and an oversized doorway hatch may be inserted inside the container. In further embodiments, the core material may not be included on one side of a container part, an opening may be cut in the outer wall, and a guillotine or sliding door installed in the space left by not including the core. Door stops may be installed to prevent the door from sliding during transit of the container.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]     The detailed description of how to make and use the invention will be facilitated by referring to the accompanying drawings.  
         [0018]      FIG. 1  illustrates the problem solved by the invention where the container is a Unit Load Device  
         [0019]      FIG. 2  shows one of the preferred construction configurations of the invention.  
         [0020]      FIG. 3  shows another construction configuration of the invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0021]     The inventor has produced a completely new concept for blast protection containers, enabled in part by employing very different materials than currently used for container applications. Current container materials such as thin aluminum or steel provide little or no blast protection. Conventional materials exhibit relatively low specific strength and/or specific modulus. Consequently, blast resistant containers constructed using conventional materials do not offer a weight efficient solution. A new class of materials enables a different approach. Such materials are similar to fiberglass in that they utilize a reinforcing fiber architecture, which is infused with a polymer resin matrix. The most effective version of composite construction utilizes materials which exhibit high compressive and tensile specific strengths and high compressive and tensile specific moduli. Specific strength is defined as the ultimate compressive (or tensile) strength of the material divided by its density. Specific modulus is the elastic compression (or tensile) modulus of the material divided by its density. The polymer resin matrix is resistant to galvanic corrosion, solvents and chemical agents. The inventor has developed a particularly suitable version of the material, described in a co-pending application. In this version, the fiber reinforcement is treated with a special resin compatible sizing which develops a high specific laminate strength, high specific laminate modulus, high laminate strain to failure and high laminate fracture toughness. These materials have much higher resistance to blast per unit volume than metals.  
         [0022]     Such materials offer a very different type of blast protection system. Conventional metal ULD containers, which offer little to no resistance to a bomb blast, weigh 150 to 300 pounds. A ULD container made from the preferred composite, exhibiting adequate blast protection to withstand the specified explosive charge weight, would weigh less than 300 pounds, clearly within an acceptable weight range.  
         [0023]     Referring to  FIG. 1 , a container, shown schematically as a ULD  1  contains items such as luggage  2 . If an explosive. device detonates in the container  3 , the blast expands radially outward as a spherical overpressure front. A conventional container, such as an aluminum ULD, will be torn apart (i.e. rupture) by even a small bomb. Since the ULD&#39;s are stored along the bottom of the aircraft fuselage, the blast pattern will likely blow through the fuselage, almost certainly causing the aircraft to fail.  
         [0024]     A blast resistant composite for containers can be produced as follows. A lay-up tool or mandrel in the shape of the container is required. Broadgoods are unrolled from the payout drum and deposited onto the lay-up tool. The width of the reinforcement fiber broadgoods is sufficient to cover the required width dimension of the container. The reinforcement broadgoods are continuously wrapped around the tool (mandrel) in the direction represented by the black rectangles in  8 ,  11  and  16  of  FIG. 3 , until the required laminate thickness is achieved. A Compressor draws a vacuum for ply stack debulking (i.e. consolidation of stacked plies). The Compressor is also used for Resin Infusion if the Tool is stacked with dry Broadgoods rather than prepreg. A Convection Oven is used for Laminate Curing when Prepreg Broadgoods are used. The Oven consists of insulated walls and a heater with a recirculating forced air blower. If Vacuum Infusion Processing is used to fabricate parts then resin drums and infusion lines facilitate the delivery of resin into the vacuum bagged dry stack of Broadgoods.  
         [0025]     The composite may be produced using vacuum assisted resin infusion capability. The vacuum being drawn on the bag sucks air out of the bag while sucking resin into the bag and simultaneously serves to consolidate the layers of reinforcement. The resin contains a catalyst which initiates the curing of the consolidated stack of plies at ambient temperature. Alternatively, the inventor believes a pre-impregnation manufacturing approach is also advantageous. The reinforcing fiber is pre-impregnated (commonly referred to as prepreg) with partially cured (i.e. B-staged) resin while still in broadgoods tape or woven fabric form. A release film is applied to the prepreg broadgoods which is peeled off prior to the stacking of prepreg layers onto the Tool or mold. The prepreg stack is intermittently consolidated (i.e. debulked) by vacuum bagging until the required number of plies are deposited onto the Tool. The ply stack is vacuum bagged and oven cured to net thickness. This approach eliminates the need for using wet resin during the fabrication of the container. The above processes can be repeated over the tool several times to form a multi-layer laminate of the composite  
         [0026]     Because an explosive blast creates a spherical overpressure wave front, blast protection requires three dimensional resistance. A fundamental design principle in the containment of explosive detonations states that the greater the interior container volume (relative to the volume of explosive) the lower the areal density required to prevent container rupture (where areal density is defined as the weight per unit surface area of the container). However, container weight is the product of areal density and container surface area. Consequently, the optimum i.e. lightest container geometry for blast mitigation maximizes container internal volume while simultaneously minimizing container surface area. The geometry which best achieves this characteristic is a sphere. As a spherical shape is not practical for most container applications, the inventor uses a novel construction technique wherein a non-spherical geometry such as a cube, six-sided box or any other multi-faceted container, is made to act like a sphere in the way it reacts to internal pressure. As shown in  FIG. 2 , the container is constructed as three nested parts. Part B at  7  fits inside of Part A at  5 . When put together the two parts may or may not be bonded together with adhesives. The assembly may be mounted to a base  6  for some applications. The third part C at  4  fits over the A/B assembly. C may or may not be bonded. Also, C may or may not contain a doorway cutout. However the door is a weak point. Therefore, in one embodiment of the invention a doorway is cut out in part A and part C, which has no doorway cutout, is only installed after the container is loaded. If a blast occurs the overpressure will cause dilation of A/B into the walls of C. A gasket or other seal can be employed between C and A/B. Thus, in the event of a blast, the three nested parts provide three dimensional circumferential hoop constraint. Each of the three parts A, B and C attempt to deform into a cylindrical shape as each part resists the blast overpressure. Circumferential hoop stresses are developed in the winding direction of the broadgoods associated with each part&#39;s geometry. Such a tendency for each independent part, within the nested assembly, to dilate into a cylindrical shape, reduces the high stresses normally developed at the corners of a rigid box where three edges intersect. Such an approach offers an optimized minimum weight solution whereby the entire volume of material is simultaneously stressed to ultimate strength with no low stressed (i.e. thicker than required) portions of the container.  
         [0027]     For the ULD application, the inventor envisions that C is held by a tool and installed after the cargo or luggage is loaded. Since part C is lightweight it may be raised or lowered manually, pneumatically (i.e. with positive or negative pressure), hydraulically or mechanically.  
         [0028]     ULD containers are shown in the figures by way of example. This is a particularly suitable application of the invention. However any container requiring blast resistance to internal detonations is contemplated by the invention. Other examples include mail boxes and containerized shipping. Also, police, firemen or demolition teams may use the invention as a lightweight portable container to safely detonate abandoned or concealed terrorist bombs. The invention may also be used to safely store explosives where accidental or unanticipated detonation will not damage surrounding personnel or property.  
         [0029]      FIG. 3  shows the construction of a blast resistant container utilizing fiber reinforced polymer composite laminate skins in combination with core materials to form a sandwich type construction. Part  8  is fabricated by winding dry fiber reinforcement broadgoods or pre-preg broadgoods around a tool or mandrel until the required laminate thickness is achieved. The pre-preg stack of broadgoods is then vacuum bagged and oven cured in such a fashion whereby residual process induced compressive membrane stresses are developed in each part after polymerization (i.e. curing) is completed or, in the case of dry broadgoods, resin infused and cured using a catalyst curing agent contained in the resin. Parts  11  and  16  are fabricated in similar fashion as Part  8  but on different sized mandrels.  
         [0030]     The tool or mandrel for part  11  may be eliminated by using the bonded assembly of  8 ,  9  and  10  as the tool or mandrel for fabricating part  11 . Similarly, the tool or mandrel for part  16  may be eliminated by using the bonded assembly of parts  8 ,  9 ,  10 ,  11 ,  12 ,  13 ,  14  and  15  as the tool or mandrel for fabricating part  16 .  
         [0031]     Low density core materials  9  and  10  may be bonded to the top and bottom of Part  8 . Low density core materials may include but not be limited to, opened or closed cell foam, a honeycomb material, nomex, metal foam, balsa wood, etc. The assembly comprising  8 ,  9  and  10  is then inserted and possibly bonded into Part  11 . Low density core materials  12 ,  13 ,  14  and  15  may then be placed on or bonded to the nested assembly comprised by parts  8 ,  9 ,  10  and  11 . The entire assembly made up of  8 ,  9 ,  10 ,  11 ,  12 ,  13 ,  14 , and  15  is inserted and possibly bonded into part  16 . The entire nested assembly made up of parts  8  through and including  16  may be bonded to a base plate  6  shown in  FIG. 2 . In one rendering of the invention the footprint of base plate  6  may be made equal to or greater than the footprint of  16 . A non-circular doorway opening may be cut out from any side wall and an oversized doorway hatch may be inserted inside the container. As long as the doorway opening is not a circle, an internal hatch geometry may be designed to fit through the doorway opening. The surface area of the internal hatch is made to be greater than the surface area of the doorway opening. Such a configuration develops a self-sealing mechanism as the perimeter of the hatch presses against the inside surface of the container side wall when the container is pressurized by explosive detonation.  
         [0032]     In another approach to creating a blast resistant door, one of the core material panels, namely,  12 ,  13 ,  14  or  15  may be eliminated. If  13  or  15  is eliminated then a gap exists between part  11  and part  16 . A doorway opening may be cut out through parts  11  and  16  on the side of the container where the gap was created by the elimination of either  13  or  15 . This gap may be used to insert a guillotine door from above which bottoms out on the base plate  6  by gravity. Similarly, if  12  or  14  is eliminated then a gap exists between part  8  and  16 . A doorway opening may be cut out through parts  8  and  16  on the side of the container where the gap was created by the elimination of either  12  or  14 . This gap may be used to insert a guillotine door from above which bottoms out on the base plate  6  by gravity. To prevent free sliding of the door while the container is in transit, door stops may be incorporated into the container.  
         [0033]     The vertical guillotine door may become a left or right side sliding door by tipping the entire nested assembly on its side before bonding of the base plate  6 . The base plate  6  is then bonded to the side wall of part  16  which rests on the ground. To prevent free sliding of the door while the container is in transit, door stops may be incorporated into the container.