Multifunctional Reactive Composite Structures Fabricated From Reactive Composite Materials |
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申请号 | US11425663 | 申请日 | 2006-06-21 | 公开(公告)号 | US20080093418A1 | 公开(公告)日 | 2008-04-24 |
申请人 | Timothy P. Weihs; David M. Lunking; Ellen M. Heian; Yuwei Xun; Richard Bowman; Gary Catig; David van Heerden; Somasundaram Valliappan; Omar Knio; Joseph Grzyb; | 发明人 | Timothy P. Weihs; David M. Lunking; Ellen M. Heian; Yuwei Xun; Richard Bowman; Gary Catig; David van Heerden; Somasundaram Valliappan; Omar Knio; Joseph Grzyb; | ||||
摘要 | A reactive composite structure having selected energetic and mechanical properties, and methods of making reactive composite structures enabling the construction of complex parts and components by machining and forming of reactive composite materials without compromising the energetic or mechanical properties of the resulting reactive composite structure. | ||||||
权利要求 | |||||||
说明书全文 | The present application is related to, and claims priority from, U.S. Provisional Application No. 60/692,857 filed on Jun. 22, 2005, which is herein incorporated by reference. The present application is further related to, and claims priority from, U.S. Provisional Application No. 60/692,822 filed on Jun. 22, 2005, which is herein incorporated by reference. The present application further is related to, and claims priority from, U.S. Provisional Application No. 60/740,115 filed on Nov. 28, 2005, which is herein incorporated by reference. The United States Government has certain rights in this invention pursuant to Award 70NANB3H3045 supported by NIST through its Advanced Technology Program. This invention relates to energetic materials. In particular, it concerns methods for fabricating useful assemblies and components from reactive composite materials comprising metals. These components provide energetic output and possess sufficient strength, stiffness, and other mechanical properties to serve structural functions. Reactive composite materials (RCMs) are useful in a wide variety of applications requiring the generation of intense, controlled amounts of heat or light quickly or from a localized region. Such composite materials typically comprise two or more phases of materials, spaced in a predictable fashion throughout a composite in uniform layers, non-uniform layers, islands, or particles that, upon appropriate excitation, undergo an exothermic chemical reaction that spreads rapidly through the composite structure generating heat and light. Reactive composite materials (RCMs) and the application of RCMs have been discussed in the above-mentioned patent applications, each of which is herein incorporated by reference. Reactive composite materials may be used to join bodies together, as by welding, soldering or brazing; to initiate other reactions; or as heaters, light sources, interrupters of electrical or other signal paths, propellants, security devices, separators and splitters, sensors, and energetic structural materials—structural components with energetic capabilities. Energetic structural materials are multifunctional materials that provide structural integrity, mechanical properties (such as strength, ductility, fracture toughness and elastic modulus) similar to those found in metals, and controllable energy release in the same material. An energetic structural material can perform several functions, and can offer several advantages over materials that serve either a purely structural or purely energetic purpose. Energetic structural materials may also provide new functionality and properties not previously seen in either structural materials or energetic materials. There are a wide variety of applications that can benefit from the inclusion of energetic structural materials to either augment or replace current structural materials or current energetic materials. For example, design and fabrication of explosive bolts, clamps, or other mechanical fasteners that release other components when activated can be simplified if the material utilized provides both mechanical strength and energy release. A rupture membrane in a MEMS device that provides strength against fluid or gas pressure, yet ruptures upon ignition is another example. A linchpin or other one-time release mechanism that can be electrically activated remotely without need for either mechanical action or the presence of an explosive is another possibility, as is a membrane dividing two chemicals in a tank, where the membrane can be ignited and ruptured to allow rapid mixing of the chemicals. In mining, utilizing an energetic structural material as the liner of a shape charge or penetrator designed to fracture and penetrate rock can provide additional energy for rock fracture and potentially reduce the amount of explosive required to penetrate to a given depth. Security applications, such as the destruction of electronic devices, can be enabled when components such as enclosures for printed circuit boards or hard drive platens are fabricated from a material that can quickly release sufficient energy to disrupt the operation of the device, such as by breaking a circuit board or melting a hard drive. Finally, applications within military devices are also possible. In particular, structural components such as the housing for electronics, the skin of a missile, fragments launched by a warhead, or casings for munitions can be manufactured from an energetic structural material instead of an inert, purely structural material. Other useful structures can be envisioned for the military as well, such as a bridge that can be easily destroyed after being used to traverse a river or other obstacle. Thus, applications for energetic structural materials range from small MEMS devices to large military devices. Current structural materials typically possess limited energy release properties. Common structural materials such as steels, aluminum, or composites provide only mechanical strength and stiffness, and do not provide any significant energy release if stimulated with a pulse of thermal or kinetic energy. In fact, these materials may absorb energy and degrade the energetic properties of devices such as munitions and shaped charges. On the other hand, the low cost and ease of formability of these materials, as well as their good mechanical properties, make them difficult to replace. Conversely, current energetic materials typically have limitations regarding their mechanical properties or their ability to be formed into strong and stiff structural elements. Hydrocarbon-based and nitrogen-based energetic materials, such as many explosives, display low strength and stiffness compared to structural materials such as metals. The formability of many explosives is also limited to casting and extrusion since the sensitivity of the majority of explosives prohibits machining or other standard means of shaping. The mass density of polymer-based energetic materials is significantly less than that of steels (<2 g/cc vs. 7.87 g/cc for steel), a fact that may hinder or prohibit their use as structural members in certain applications such as penetrators, where high mass density is preferred. Currently, the dangers inherent in energetic materials limit their manufacture and restrict their utilization in applications as structural members or components. To date, two different classes of materials have shown promise as potential energetic structural materials. Powder compacts or powder mixtures in binders such as epoxy are one class of materials. The other class includes reactive composite materials (RCMs), as discussed herein. Powder-based energetic structural materials consist of micro- or nanometer-scale powders that are well mixed before processing. These powder mixtures are usually either pressed into powder compacts or dispersed into a binder such as an epoxy. However, both powder compacts and powders dispersed in a binder typically display poor mechanical properties. Many powder compacts are brittle or friable and difficult to machine due to their nature as particle agglomerations and their inherent porosity. Powders dispersed in a binder display properties similar to the pure epoxy matrix, with low density, strength, and stiffness as compared to structural materials such as steel, aluminum and titanium. Also of concern are the health and safety hazards associated with toxic or flammable powders. However, the raw materials for powders are low cost and easy to obtain, and are useful in different applications. Reactive composite materials, in contrast, include energetic materials with significant mechanical properties. In RCMs, two or more different materials that mix and react exothermically, such as aluminum and nickel or titanium and boron carbide, are placed in intimate contact over micro- or nanometer scales. These composite materials are currently fabricated either by vapor deposition or by mechanical formation. The processing method determines to a large extent their mechanical properties. Vapor-deposited RCMs, described in detail in U.S. Pat. No. 6,736,942 to Weihs, et al., possess high strength and stiffness, but generally have low ductility or formability, limiting the shapes and forms into which they can be manufactured. Vapor-deposited RCMs are also technically challenging and expensive to fabricate in large or thick sections, and have to date been available only as thin foils. This is appropriate for many energetic applications, particularly in microelectronics, as shapes can be fabricated by punching and by patterning and lift-off techniques incorporated into the deposition process. Also, vapor-deposited foils are appropriate for applications of planar heat generation, such as joining. Available material geometries and properties impose limitations on the applications of vapor-deposited material on a larger scale, e.g. in macroscopic structural applications requiring large volumes of material, energetic applications requiring high heat per unit volume, or applications requiring the energetic component to have a complex geometry. Reactive composite materials can also be formed mechanically as foils or sheets via cold-rolling, described in detail in U.S. Provisional Application No. 60/692,822. These mechanically-formed foils or sheets demonstrate better overall ductility and machinability than similar vapor-deposited materials, as well as readily tunable energetic properties, such as reaction velocity, ignition threshold and heat of reaction. Mechanical formation permits flexibility in the ignition sensitivity and reactivity of RCMs over a very large range. Materials and microstructures can be produced that allow for safe handling and processing at ambient temperature without triggering a self-propagating reaction in the entire structure. For instance, Al/Ni based RCM will not self-propagate at room temperature when the bilayer thickness is on the order of 2 μm or larger. However, heating the sample to near the melting point of aluminum will enable the reaction to occur. If the sample is heated locally, any reaction will be localized and will not propagate into the rest of the structure. The entire sample must be heated above the auto-ignition temperature for the reaction to propagate. This ability to tune the energetic properties through control of the microstructure enables the use of processing previously not possible in energetic materials, such as conventional machining, electro-discharge machining, soldering, brazing, or even welding pieces of RCM together into larger structures. Another advantage of mechanical formation is that RCM sheets fabricated by cold rolling and wires or rods made by wire forming (e.g. drawing, swaging, or rolling) have a highly oriented microstructure, exhibiting large variations in mechanical properties depending on the orientation of the sample tested. This anisotropy, or texture, may be exploited to produce a wide variety of structural forms, similar to the way the texture of wood may be used. Constructing useful components or parts from reactive composite structures (RCSs) comprising reactive composite materials (RCMs) requires some particular understanding of the interaction between the energetic properties and the mechanical properties of the RCM utilized within the RCS. The present invention sets forth both RCMs and fabrication techniques that permit the unique mechanical and energetic properties of reactive composite structures (RCSs) to be incorporated into components, parts, and devices. Briefly stated, the present invention provides an energetic material, methods of making the same, and fabrication methods that permit the construction of complex parts and components from the energetic material, without compromising either the material's energetic or mechanical properties. The present invention covers the application of RCMs as formable and machinable energetic materials, and the joining and forming necessary to fabricate complex and useful components from bulk energetic materials without igniting the materials. The present invention sets forth methods for joining RCMs. Selection of the joining method, together with the properties and proportions of the RCM and any joining medium, permits control of both the mechanical properties and the energetic properties of the material. Mechanical properties that can be controlled include but are not limited to yield strength, tensile strength, hardness, fracture toughness, and ductility. The resulting structures exhibit mechanical properties similar to common structural materials such as aluminum and steel and retain the energetic properties of RCMs. Energetic properties so controlled include but are not limited to ignition threshold, auto-ignition temperature, reaction velocity, energy release rate, energy density, gas release, and reaction temperature. Utilizing methods of the present invention, RCMs and combinations thereof can be formed into useful, complex shapes by conventional machining and forming techniques while remaining safe to handle and process. The materials may be formed into two-dimensional shapes such as simple or complex cutouts from sheet and plate, or into three-dimensional shapes such as beams, shells, trusses, and other useful forms. Utilizing RCMs as energetic components is simplified by joining two or more pieces of RCM together into a single structure. Current fabrication methods restrict individual pieces of RCM to small sizes and thin gauges, but these limitations can be overcome by methods of the present invention for joining several RCM pieces together along the edges, by laminating thin sheets together to form a thicker bulk material, or by some combination of these two methods. Pieces of RCM may be joined together by one of a variety of joining technologies (such as epoxy, solder, brazing, and welding) to form a thick, large area material with improved strength and stiffness and/or increased energy output. The foregoing features and advantages of the invention as well as presently preferred embodiments thereof will become more apparent from the reading of the following description in connection with the accompanying drawings. In the accompanying drawings which form part of the specification: Corresponding reference numerals indicate corresponding parts throughout the several figures of the drawings. It is to be understood that the drawings are for illustrating the concepts of the invention and are not to scale. The following detailed description illustrates the invention by way of example and not by way of limitation. The description enables one skilled in the art to make and use the invention, and describes several embodiments, adaptations, variations, alternatives, and uses of the invention, including what is presently believed to be the best mode of carrying out the invention. The present invention sets forth different methods for making reactive composite structures (RCS) having components or bodies which consist of reactive composite materials (RCM), via various assembly, joining, and shaping methods. The reactive composite materials in the reactive composite structure can then be ignited at a subsequent point in time to carry out an intended function of the reactive composite structure. The invention additionally sets forth characteristics of the RCM required to make these methods feasible. Fundamental to the fabrication methods discussed below is the tunability of RCM properties. One embodiment sets forth an RCM that can be manufactured to be ignition-insensitive at ambient temperature. By varying the type and amount of processing, such as the amount of mechanical deformation, the scale of the microstructure and thus the auto-ignition temperature of the RCM may be precisely controlled. An RCM 101 may be created in which the reaction is self-propagating at a given temperature if a large pulse of energy 102 (thermal or kinetic) is applied locally 103 as shown in Another embodiment includes control of the mechanical properties of an RCM through control of mechanical deformation. For instance, as mechanical processing increases, the tensile strength of Al/Ni RCM foil increases and then decreases. Another embodiment of the invention includes control of the reaction properties of an RCM through control of mechanical deformation. For example, in In another embodiment, a sheet or foil RCM 300, which may be flat, curved, bent, or otherwise formed, is joined at the edges to produce three-dimensional structures, including but not limited to I-, L-, and box-beams, trusses, and shells. A few examples are shown in In another embodiment of the present invention, a laminated structure consisting of two or more pieces of RCM 401 can be fabricated by stacking pieces of RCM 401 into a single RCS 400 with a joining medium 402, such as an epoxy or solder, between the RCM pieces 401. This enables fabrication of structures and geometries that might otherwise be difficult or costly to manufacture by another means. One approach to joining two or more pieces of RCM 401 is by a joining material 402 such as an epoxy or glue. In this embodiment, a thick laminated plate 400 composed of sheets of RCM 401 can be joined under pressure with the joining material 402, such as EPON 826 resin with EPON 3223 hardener, manufactured by Miller-Stephenson, as shown in In a related embodiment, the properties or the thickness of the joining medium 402, for instance epoxy, may be varied to produce different mechanical or energetic properties in an RCS. The properties and thickness of the joining medium 402 may also be varied from layer to layer within one RCS 400 to provide more insulation or less between layers of RCM 401, or to vary the energy density, reactivity, or other properties across the thickness of the reactive composite structure 400. In another embodiment of this invention, shown in For example, 21 squares of Al/Ni based RCM 601, each with a bilayer thickness of approximately 20 μm and an overall thickness of 500 μm, were alternately layered with 50 μm sheets of a CerroTru foil joining medium 602. This resulting stack was dipped into a bath of Kester 715 flux and reflowed under clamping pressure in an oven at 450° F. for one hour. This process yielded a laminated structure 600 of RCM pieces as shown in In an alternate embodiment, a thick plate RCS may be fabricated by welding or hot pressing two or more RCM sheets together. Similarly, RCM pieces could be welded at the edges to create three-dimensional shapes. As discussed above, the RCM can be designed with a coarse microstructure that is not self-propagating, allowing the material to be locally welded without changing the structural or energetic properties of the overall components. This selection enables a variety of welding options, such as but not limited to, TIG welding, gas flame welding, ultrasonic welding, friction stir welding, etc. In a related embodiment, the RCM pieces may be actively cooled to prevent the pieces from becoming hot enough to ignite or anneal during a welding procedure. This cooling may be effected by clamping the RCM between pieces of metal to conduct heat away, or by holding the RCM in a bath of chilled water or liquid nitrogen, or by other means. Because RCMs typically possess high thermal conductivities, excess heat near a weld may be readily drawn away without igniting the entire structure. In another embodiment, shown in In an alternate embodiment, shown in In yet another embodiment, shown in In another embodiment of the invention, shown in In another embodiment of this invention, shown in In another embodiment of this invention, one or more layers of material 1201 that are not an RCM but which could be a metal, ceramic, polymer, or combination, may be joined to one or more pieces of an RCM 1202 to alter various properties, including but not limited to reaction stability, mechanical strength and ductility, energy output, emissivity, gas output, and density. The non-RCM layers 1201 may be added to one or both surfaces of a planar RCM 1202, as a laminated layer 1201 between layers of RCM 1202, or some combination of the two, such as are illustrated in Added to the outside surface of an RCS 1202, a non-RCM layer 1201 can tune both the mechanical and reactive properties of the RCS. A layer of non-reactive material 1201 on the surface will help to stabilize the RCS, increasing the threshold needed for ignition. A thick outer layer of ductile non-RCM material 1201 over a brittle RCM 1202 will also prevent breakage of the component during manufacture, handling, or use. Alternatively, a hard outer layer of non-RCM material 1201 will increase the surface hardness of the material. Energetic properties may also be tailored by addition of an outer non-RCM layer 1201. Cladding an RCM 1202 with a material 1201 that burns in air, such as, but not limited to, titanium, aluminum, magnesium, epoxy, or a hydrocarbon, can increase the amount of heat generated by the RCS after the RCM 1202 is ignited. Cladding an RCM 1202 with a material 1201 with a low melting point, for instance indium, and/or a high heat of fusion, will alter the peak temperature reached at the surface and the overall energy density. Other cladding materials 1201 may be selected to alter properties such as electromagnetic emissivity, gas output (with a layer of solid hydrocarbon, for instance), thermal conductivity, RF radiation sensitivity, electrostatic discharge sensitivity, electrical resistivity, and magnetic susceptibility. For example, 30 μm of Al/Ni RCM vapor-deposited on a 0.005″ thick sheet of polyethylene may be wrapped around a cylinder of flexible solid rocket propellant. The reactive multilayer is then used to ignite the propellant, but before this occurs, the polymer backing offers considerable structural support to the cylinder, preventing it from bending during the rest of the assembly process. Added to the interior of an RCS, a non-RCM layer 1201 can readily tune the mechanical properties of the RCS. Joined by any of the means above, a mechanically strong or ductile interior layer helps overcome some limitations of RCMs, such as the low ductility of vapor-deposited RCM 1202. Likewise, other properties, such as but not limited to strength, stiffness, density, thermal conductivity, electrical resistivity, ESD sensitivity, and magnetic properties, can be tailored by addition of a non-RCM layer 1201 to the interior of the RCS. Simultaneously adding non-RCM layers 1201 to both the interior and exterior of an RCS enables independent control of many of the above listed properties. The energetic properties of RCSs may be varied across a component 1200 by using layers of RCM with different ignition thresholds, reaction velocities, or heats of reaction. For instance, a laminated RCS 1200 formed from individual layers of RCM may have its reaction properties vary across its thickness, while a complex shell or truss may have structural or energetic properties that vary from one end of the RCS 1200 to the other, such as shown in For example, two pieces 1301 of Al/Pd RCM 50 μm thick, with an average bilayer thickness of 200 nm, were clad onto the surfaces of an Al/Ni-based RCM 1302 which was 300 μm thick, with an average bilayer thickness greater than 500 nm (and thus not self-propagating at room temperature). The resulting structure 1300, as illustrated in In a variation shown in In another embodiment of the present invention, illustrated in In another embodiment, an RCM 1601 formed as a wire may be woven into mesh or cloth, as shown in Another embodiment of the present invention is a method for igniting very stable RCSs 1702 by propelling them into a solid object 1701 at very high velocities, as shown schematically in As various changes could be made in the above constructions without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense. |