Abstract:
A seal-healing material that is used to form fuel tanks and other fuel containing items uses a pair of reagents disposed within multiple individual cells on either side of a polymer film with other polymer films forming the outer boundaries of each set of cells. The reagents, when mixed, chemically react to form a sealant. An elastomeric sheet is bound to each polymer film such that a fibrous material is disposed between each polymeric film and elastomeric film.

Description:
This application claims the benefit of U.S. provisional patent application, No. 61/891,491, filed on Oct. 16, 2013, which provisional patent application is incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a self-sealing system that is used to form a fuel container such as a vehicle fuel tank or a fuel storage tank, wherein the system automatically self-seals immediately upon penetration damage to the system. 
     2. Background of the Invention 
     The construction of a fuel tank depends on the type of vehicle and/or structure onto which the tank is installed, and the vehicle or structure&#39;s usage or mission. Fuel tanks and systems in general are constructed of materials that do not react chemically with any fuels. For vehicles, some fuel tanks are an integral part of the structure while others rely on a fuel bladder that fits into a pre-designed fuel storage cavity. For those tanks that are integral to the structure, the structure has to be appropriately sealed to prevent leakage of fuel. Other aspects of tank design include access panels for inspection and repair, sumps and drains to collect water and sediments, and a fuel distribution system to transport the fuel between tanks and the propulsion system. Although these other features are critical to the fuel tank design, they do not affect the critical feature that effect the ability of the tank to contain the fuel and tolerate any damage, especially from penetrating events. 
     To address penetration damage in current fuel system design, there is a reliance on the fuel to activate the sealing mechanism. In a self-sealing fuel tank, the penetrator, such as a projectile or shrapnel, passes through the fuel tank wall into the fuel. After perforation by the penetrator, the elastic materials in the fuel tank wall spring back to yield a small entrance and exit hole. Once this has occurred, the leaking fuel contacts the inner layer of fuel tank wall which is composed of a sealant material, typically un-vulcanized rubber or gum rubber. Upon contact, the sealant material swells and completes the seal of the hole created by the penetrator, preventing further leakage of fuel. With this approach, the sealing process relies on swelling of the sealant material as it absorbs the liquid hydrocarbon fuel and the subsequent cohesion of the perforated sealant material that happens to spring back into contact with itself. 
     A typical self-sealing fuel tank is composed of various elements, which elements contribute to the self-sealing characteristic of the fuel containment system. These elements consist of four primary layers of materials. These layers are the inner liner, the nylon fuel barrier, the sealant, and the retainer. The vast majority of self-sealing fuel tanks currently in service contain these four primary layers of materials. If additional plies are used in the construction of the fuel tank, the additional plies will be related to one of these primary plies. 
     The inner liner material is constructed of Buna N synthetic rubber and its function is to prevent fuel from coming in contact with the sealant, thereby mitigating the potential for premature swelling or deterioration of the sealant. Buna rubber is an artificial substitute for crude or natural rubber which is produced from butadiene and sodium. Buna rubber is made in two types, which are Buna S and Buna N, with Buna S being the most common type of synthetic rubber. The Buna S, however, is unsuitable for use as an inner liner material since the petroleum hydrocarbons causes it to swell and eventually dissolve. Not being affected by petroleum hydrocarbons, Buna N is ideal for this application; however, due to its porous nature, a nylon barrier is necessary to prevent the fuel from contacting the sealant. 
     The second material in the system is an unbroken film of nylon designed to prevent fuel from diffusing into the fuel tank wall. This layer is typically brushed, swabbed, or sprayed in three or four hot coats to the outer surface of the inner liner during the construction process. The sealant material, which is made from a natural gum rubber, is the next material used in the fuel tank and it remains dormant until the tank is ruptured or penetrated by an object, such as a projectile. The sealing action occurs due to a chemical reaction that occurs between the sealant and the petroleum hydrocarbon based fuel. This reaction occurs as soon as vapors contact the material which causes it to extend or swell to several times its normal size. This process effectively closes the rupture and prevents the fuel from escaping. 
     The final material is the retainer which serves the purpose to provide strength and support for the tank while increasing the efficiency of the mechanical action by returning the fuel tank wall to its original shape when punctured. This layer is typically fabricated from cotton or nylon cord fabric impregnated with Buna N rubber. 
     Although self-sealing bladder type fuel tanks can differ in the types of materials used and their sequencing, the basic construction process remains the same. The use of elastomeric material on the inner and outer surface of the bladder act to minimize the hole size and the sealant material is activated by contact with the fuel and/or vapors causing it to swell thereby effectively sealing the puncture. 
     Other techniques exist to provide self-sealing capability to integral fuel tanks; however, these techniques tend to rely largely on the use of visco-elastic materials that can be applied to the interior of the fuel containment area. Upon penetration, the elasticity of the material minimizes the hole size and pressure from the fuel forces the material into the hole providing a seal. Unfortunately this approach, though it has similar features to the previously described self-sealing fuel tanks, is not as effective as that used in self-sealing fuel bladders. 
     Emphasis on reduced system and subsystem weight has pushed the application of these current self-sealing material technologies to marginal levels of performance. Recent testing of current state-of-the-art fuel tanks has demonstrated marginal levels of self-sealing performance for the required protection levels. The need to reduce weight while maintaining ballistic and crashworthy performance remain. Achieving weight reduction while maintaining desired protection levels, is not possible using fielded conventional fuel tanks materials and designs. In addition, initiatives in fuel development that emphasize the need for improved fuel efficiency, lower emissions, and alternative fuels, have resulted in efforts to reformulate fuels. The fundamental performance of the self-sealing technologies has been brought into question as changes in fuel compositions effect the absorption of fuel into the sealant material. Consequently, current wound sealing techniques can no longer be the sole methodology in designing self-sealing systems. Future fuel formulations require new approaches to self-sealing fuel tanks designs. 
     SUMMARY OF THE INVENTION 
     The fuel containment autonomous self-sealing system of the present invention offers a solution to the aforementioned needs in the art. The fuel containment autonomous self-sealing system is an autonomous self-sealing system that seals a perforation independently of contact with the fuel. The sealing process is activated solely by the penetration event. In addition, the fuel containment autonomous self-sealing system can be custom designed to fit various forms and functions, thereby possessing greater versatility than traditional self-sealing technology. The fuel containment autonomous self-sealing system can be customized to address various sizes of damage, integrated into a bladder design, and applied to integral fuel containment applications. 
     The fuel containment autonomous self-sealing system of the present invention is comprised a polymeric structure that a first outer surface and a second outer surface, each formed from an elastomeric layer. A first reagent is disposed within a series of first cells within the polymeric structure while a second reagent is disposed within a series of second cells within the polymeric structure such that the first cells and the second cells are separated from one another. When the first reagent and the second reagent mix due to a perforation through some of the first cells and some of the second cells allowing the first reagent and the second reagent to mix, the first reagent and the second reagent chemically react forming a sealant. The series of first cells are kept separate from the series of second cells by a polymeric sheet that is frangible. The first reagent may have a foaming agent that causes expansion of the combined first reagent and the second reagent whenever the first reagent and the second reagent are mixed. A first elastomeric layer is bound to the first outer surface of the polymeric structure such that a first fibrous material is disposed between the first elastomeric layer and the polymeric structure while a second elastomeric layer bound to the second outer surface of the polymeric structure such that a second fibrous material is disposed between the second elastomeric layer and the polymeric structure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a sectioned perspective view of a portion of the fuel containment autonomous self-sealing system of the present invention. 
         FIG. 2  is an exploded perspective view of the portion of the fuel containment autonomous self-sealing system of  FIG. 1 . 
         FIG. 3  is a sectioned perspective view of a portion of the flow restriction and damage bridging subsystem of the fuel containment autonomous self-sealing system. 
         FIG. 4  is an exploded perspective view of the portion of the flow restriction and damage bridging subsystem of  FIG. 3 . 
         FIG. 5  is an exploded perspective view of a portion of the reagent sealing subsystem of the fuel containment autonomous self-sealing system in a two layer configuration. 
         FIG. 6  is an exploded perspective view of a portion of the reagent sealing subsystem of the fuel containment autonomous self-sealing system in a multi-layer configuration with the polymer film layers removed for brevity and clarity. 
         FIG. 7  is a perspective of a portion of the fuel containment autonomous self-sealing system, exploded, with a penetration through a portion of the system. 
     
    
    
     Similar reference numerals refer to similar parts throughout the several views of the drawings. 
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to the drawings, it is seen that the fuel containment autonomous self-sealing system of the present invention, generally denoted by reference numeral  10 , is comprised of a pair of subsystems, namely the flow restriction and damage bridging subsystem  12  and the reagent sealing subsystem  14  such that the reagent sealing subsystem  14  is bounded on either side by the flow restriction and damage bridging subsystem  12 . 
     Each flow restriction and damage bridging subsystem  12  is a dual layer member that has a highly elastic elastomeric material layer  16  that is bound to a bridging material layer  18 . The bridging material layer  18  is comprised of inert fibrous elements that are compatible with the sealing reagents used within the system  10  and fluids held in the fuel storage container. Typically these fibers are fiberglass, but are modified as required depending on the fluids and sealant reagents used. The bridging material  18  is loosely contained between the elastomeric material layer  16  and the polymer film  20 , described below. The bridging material  18  is retained by the seal developed around the edge of the various layers that form a cell. This mechanical capturing of the material permits its free expansion when penetrated, allowing it to better fill the void created by a penetrating act and perform its fluid flow restriction function. To facilitate assembly, a tack adhesive may be used to fix the bridging material&#39;s position, but this is done sparingly and does not affect the integrity of the system. 
     The reagent sealing subsystem  14  is comprised of a pair of polymer film layers  20  that form the outer skins of the reagent sealing subsystem  14 . Located between the polymer film layers  20  are two or more reagent layers  22   a  and  22   b . A second reagent layer  22   b  is separated from the first reagent layer  22   a  by another polymer film material separator layer  24 . As seen, each reagent layer  22   a  and  22   b  is formed into multiple individual cells  26 , which includes the illustrated polygon cells of any desired geometry, channels, voids, etc., such that the reagent  22   a  and  22   b  in each cell  26  is separated from the reagent  22   a  and  22   b  in adjoining cells  26 , the polymer film  20  forming the individual cells  26  against the separator layer  24 , the polymer film  20  also minimizing air permeability between individual cells  26 . The cells  26  holding the first reagent  22   a  and the cells  26  holding the second reagent  22   b  may be, but need not necessarily be of the same size, and may, but need not necessarily correspond in position (the cells overlay each other) with one another. The various layers  20 ,  22   a ,  22   b , and  24  are bound to their respective adjoining layers in appropriate fashion. The method of joining varies based on the system application, and involves the use of adhesives and/or thermal sealing of the layers  20 ,  22   a ,  22   b , and  24  to one another along the perimeter of the abutting layers  20 ,  22   a ,  22   b , and  24 . The key element is to attach the layers  20 ,  22   a ,  22   b , and  24  without impeding their functionality or that of the contained reagents  22   a  and  22   b . As seen in  FIG. 5 , the reagent sealing subsystem  14  can be constructed as a two layer reagent layer  22   a  and  22   b  configuration, or as seen in  FIG. 6 , the reagent sealing subsystem  14  can be constructed as a multi-layer reagent layer configuration such that each first reagent layer  22   a  is adjacent to one or more second reagent layers  22   b  and vice versa with each reagent layer  22   a  separated from any adjoining reagent layers  22   b , by a polymer film separator material layer  24 , the number of reagent layers  22   a  and  22   b  used depending on the application including the perceived threats that may be encountered. The reagent layers  22   a  and  22   b  are selected for the specific type of containment system based on compatibility with the fluid being stored, environmental conditions, basic system parameters such as weight, and degree or size of perforation to be considered and may include polyurethane reagent system where one reagent is a polyol and the other, an isocyanate or epoxy reagent system where one reagent is a polyepoxide prepolymer (or resin) and the other, a catalytic hardener, among others. The materials of the two layers  22   a  and  22   b  are quick reacting with one another and have a viscosity that provides a balance in flow properties to support mixing, leading to activation without escaping from the containment cell  26 . The outer reagent layers  22   a  or  22   b  may have a higher viscosity relative to any inner layers to permit faster mixing. 
     The fuel containment autonomous self-sealing system  10  is constructed by having a pair of flow restriction and damage bridging subsystems  12  form the outer skin and inner skin of the fuel containment autonomous self-sealing system  10  with a reagent sealing subsystem  14  sandwiched between this pair of flow restriction and damage bridging subsystems  12 . The elastomeric material layer  16  of each flow restriction and damage bridging subsystem  12  faces outwardly with the elastomeric material layer  16  of the other flow restriction and damage bridging subsystem forming the inside of the fuel container facing inwardly (not illustrated). The bridging material layer  18  is attached to the outer surface of its respective polymer film layer  20  in appropriate fashion. The bridging material layer  18  is loosely contained between the elastomeric material layer  16  and the elastic polymer film layer  20 . It is retained by the seal developed around the edge of the elastomeric material layer  16  and the polymer film layer  20 , the bridging material layer  18  captured therebetween. This mechanical capturing of the material permits its free expansion when penetrated allowing it to better fill the void created and to perform its fluid flow restriction function. To facilitate assembly, a tack adhesive may be used to fix its position, but this is done sparingly and does not affect the integrity of the system. 
     When perforation of the fuel containment autonomous self-sealing system  10  occurs, the projectile P (bullet, shrapnel, etc.), initially penetrates the elastomeric layer  16  of the outer flow restriction and damage bridging subsystem  12 . As this elastomeric layer  16  is highly elastic, this elastomeric layer  16 , upon being penetrated, quickly expands and snaps back, which helps minimize the penetration hole H. Thereafter, the projectile P travels through the bridging material layer  18  of this flow restriction and damage bridging subsystem  12 , the bridging material layer  18  further helping in the development of a seal from the penetration. The bridging material layer  18  serves two basic function which are to restrict fluid movement from the storage container into the sealing reagents  22   a  and  22   b  and from the sealing reagents  22   a  and  22   b  to either the contained fluid and/or exterior of the system  10 , and to act as a nucleating site to support the formation of the seal. In the case of restricting fluid flow, the fibrous material acts as a loose barrier to retard this movement. It is designed to provide adequate time for the reagents  22   a  and  22   b  to react with one another, thereby forming the seal. Second, the bridging material layer  18  acts a site for the reactants  22   a  and  22   b  to attach to as the reagents chemically react with one another during the sealing process, and provide a reinforcing feature for bridging the hole H. Essentially, the reacted reagents  22   a  and  22   b  only need to bridge the fibers in the bridging material layer  18  and not the entire expanse of the hole H during the initial sealing stages. Thereafter, the projectile P penetrates the outer elastic polymer film layer  20  of the reagent sealing subsystem  14 . The elastic nature of the elastic polymer film layer  20  helps minimize the penetration hole H on this layer. Thereafter, the projectile P penetrates one or more cells  26  of the first reagent layer  22   a , Thereafter, the projectile P penetrates the polymer film separator material layer  24  and thereafter penetrates one or more cells  26  of the second reagent layer  22   b , thereby causing the reagent  22   b  within the penetrated cell  26  or cells  26  of this reagent layer  22   b  to mix with the previously penetrated cell  26  or cells  26  of the first reagent layer  22   a , causing the two reagents  22   a  and  22   b  to mix, resulting in a chemical reaction between the reagents. This reaction provides a bonding mechanism that fuses the perforated layers together. For a system design that accommodates large perforations due to the removal of the elastomeric layer by the perforating event, resulting in a gaping hole, selected reagents  22   a  and  22   b  include those with a foaming component, that upon activation, possess an expansion agent resulting in a volumetric increase in the material which fills the void of the missing material thereby facilitating a seal, further sealing the penetration hole H therethrough. The polymer film separator material layer  24 , by being frangible, maximizes the hole of penetration through this polymeric film separator material layer  24 , in order to facilitate the interaction of the functioning reagents  22   a  and  22   b  (the reagents  22   a  and  22   b  of the cells  26  that have been penetrated) between the adjoining reagent layers  22   a  and  22   b , which helps quickly seal the penetration hole H. Thereafter, the projectile P penetrates the inner elastic polymer film layer  20  of the reagent sealing subsystem  14 . Again, the elastic nature of the elastic polymer film layer  20  helps minimize the penetration hole on this layer (if the penetration of the fuel containment autonomous self-sealing system  10  is a multi-layer reagent layer  22   a  and  22   b  configuration, the projectile P penetrates the next polymeric film separator material layer  24  and then the next first reagent layer  22   a  and thereafter the next polymeric film separator material layer  24  and thereafter the next second reagent layer  22   b  and continues in this fashion until encountering the inner elastic polymer film layer  20 ). It is not necessary for the innermost reagent layer to be a second reagent layer  22   b , for if the innermost reagent layer is a first reagent layer  22   a , then this layer  22   a  simply mixes with the second reagent layer  22   b  that had been penetrated just prior to the penetration of the innermost layer, going through the polymeric film separator material layer  24  that separates the two reagent layers  22   b  and  22   a . Thereafter, the projectile P travels through the bridging material layer  18  of the inner flow restriction and damage bridging subsystem  12 , the bridging material layer  18  further helping in the development of a seal from the penetration. Finally, the projectile P penetrates the elastomeric layer  16  of the inner flow restriction and damage bridging subsystem  12 . Again, as this elastomeric layer  16  is highly elastic, this elastomeric layer  16 , upon being penetrated yields and quickly snaps back to shape which helps minimize the penetration hole. 
     The use of multiple cells  26  within each reagent layer  22   a  and  22   b  allows for the capability to seal multiple perforations. Each cell  26  is sized to provide sufficient reagent material for a given penetration without overwhelming the damage site, thereby wasting reagent material  22   a  and  22   b.    
     While the invention has been particularly shown and described with reference to an embodiment thereof, it will be appreciated by those skilled in the art that various changes in form and detail may be made without departing from the spirit and scope of the invention.