Rocket motors containing fiber-reinforced polymer composite structures and their electromagnetic induction manufacturing methods.

Abstract

The present invention relates to a resin composition, a fiber-reinforced polymer structure, and an electromagnetic induction manufacturing method thereof. The magnetic induction manufacturing method is a pulse manufacturing method that can be optionally combined with a cooling step between pulses. The fiber-reinforced polymer structure can take the form of, but is not limited to, pipes, pressure vessels such as rocket motor cases and fire extinguishers, golf club shafts, tennis and badminton rackets, skis, snowboards, ice hockey sticks, fishing rods, bicycle frames, boat masts, oars, paddles, baseball bats, and softball bats. Such fiber-reinforced polymer structures may be supplemented with other materials, such as rocket propellants, to form articles such as rocket motors.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to U.S. Provisional Patent Application No. 62 / 940,830, filed November 26, 2019, the entire contents of which are incorporated herein by reference as if fully set forth. Government Rights This invention was made with government support from the United States Air Force. The United States Government has the right to practice or have practiced this invention in any country.

[0002] FIELD OF THE INVENTION The present invention relates to polymer composites, fiber-reinforced polymer composite structures, and electromagnetic induction processes for their manufacture, and to their use in cases such as pressure vessels, rocket motor cases, athletic equipment, pipes, and other lightweight structural components. [Background technology]

[0003] Background of the Invention Fiber-reinforced polymer structures are manufactured by processes that typically require oven curing of an adhesive polymer resin system that comprises the structure. The use of high-temperature resin systems is desirable because they can impart high-temperature strength to the resulting fiber-reinforced polymer structure. Unfortunately, when high-temperature resins are used, the process is limited to articles that do not contain heat-sensitive materials, such as rocket propellants. This is because high oven temperatures are required to cure the resin, and such high temperatures impart excessive thermal energy to the heat-sensitive materials. Excessive thermal energy can lead to decomposition of the heat-sensitive materials and, in the case of rocket propellants in particular, can even lead to spontaneous ignition, creating conditions that create explosive hazards. Summary of the Invention

[0004] Applicant has recognized that the problem lies not only in the amount of thermal energy provided by the curing oven, but more importantly, in the rate at which such thermal energy is provided. In short, Applicant has recognized that the true cause of the problem lies in the lack of thermal control applied in conventional resin curing methods. Applicant has discovered that the electromagnetic induction process, which is a pulsed process that can optionally couple cooling steps between pulses, can achieve adequate thermal curing of resin systems having a wide range of cure temperatures without applying excessive thermal energy to heat-sensitive materials.

[0005] Accordingly, applicants disclose electromagnetic induction manufacturing, which is a pulsed manufacturing process with any combination of cooling steps between pulses, and fiber reinforced polymer structural cases manufactured by such processes, articles including such cases, and methods of using such cases and articles. [Means for solving the problem]

[0006] Summary of the Invention The present invention relates to resin compositions, fiber-reinforced polymer structures, and electromagnetic induction processes for producing them. Such electromagnetic induction processes may be pulse processes, with or without cooling steps between pulses. The fiber-reinforced polymer structures described above may take the form of pipes, pressure vessels such as rocket motor cases and fire extinguishers, golf club shafts, tennis and badminton rackets, skis, snowboards, ice hockey sticks, fishing rods, bicycle frames, boat masts, oars and paddles, baseball bats, and softball bats. Such fiber-reinforced polymer structures may also be supplemented with other materials, such as rocket propellants, to form articles such as rocket motors.

[0007] Additional objects, advantages, and novel features of the present invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following, or may be learned by practice of the invention. The objects and advantages of the present invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims. [Brief explanation of the drawings]

[0008] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the present invention and, together with the general description of the invention given above and the detailed description of the embodiments given below, serve to explain the principles of the invention.

[0009] FIG. 1 is a schematic diagram of the basic components of an induction heating system.

[0010] Figure 2 is a schematic diagram of the principle of magnetic induction heating of a fiber-reinforced polymer composite case.

[0011] FIG. 3 is a schematic diagram of a continuous solenoid coil fitted into the dome region of a fiber reinforced polymer composite case so that the spacing between the coil and the case is constant.

[0012] FIG. 4 shows a three-turn solenoid coil linearly translated across the cylindrical region of a fiber-reinforced polymer composite case.

[0013] FIG. 5 shows a single-lobed axial coil placed on a fiber reinforced case.

[0014] 6A and 6B show a single lobe axial coil disposed on a fiber reinforced polymer case and tilted at an angle α to be parallel to the direction of the fiber tows in the helical and / or polar layers.

[0015] FIG. 7 shows a single lobe axial coil placed on a fiber reinforced polymer case with both ends shaped to match the curved outer surface of the dome section.

[0016] FIG. 8 shows a multi-lobal axial coil disposed on a cylindrical region of a fiber reinforced polymer case.

[0017] FIG. 9 shows a hybrid coil having both solenoidal and axial coil elements in series.

[0018] FIG. 10 is a cross-sectional view of a fiber reinforced polymer rocket motor case with insulation.

[0019] 11A-11F show non-limiting structures of thermosetting resin monomers and catalysts suitable for electromagnetic induction heat treatment of fiber reinforced polymer casings.

[0020] 12A-12C show non-limiting structures of cyanate ester resin and curing catalyst systems that have been found to be effective in pulsed electromagnetic induction curing processes.

[0021] Figure 13 shows a fiber-reinforced polymer composite paddle containing resin surrounded by a coil that can be energized to cure the resin.

[0022] FIG. 14 is a graph showing the effect of cyanate ester resin composition and catalyst type on the interlaminar shear strength of carbon fiber reinforced polymer composites at a test temperature of 200° C.

[0023] It should be understood that the accompanying drawings are not necessarily to scale and represent somewhat simplified representations of various features illustrating the underlying principles of the present invention. Particular design features of the implementation procedures disclosed herein are determined in part by the particular intended application and use environment. Such design features include, for example, the particular dimensions, orientation, location, and shape of the various specific components shown. Certain features of the illustrated embodiments may be enlarged or curved relative to other features, for example, to facilitate visualization and clear understanding. In particular, features of thin sections may be made thicker, for example, for clarity or illustration. DETAILED DESCRIPTION OF THE INVENTION

[0024] Detailed Description of the Invention definition "Fiber reinforced polymer composite structure," as used herein, refers to pipes, pressure vessels such as rocket motor cases and fire extinguishers, golf club shafts, tennis and badminton rackets, skis, snowboards, ice hockey sticks, fishing rods, bicycle frames, boat masts, oars and paddles, baseball bats, softball bats, and the like.

[0025] The articles "a," "an," and "the," as used herein, mean "at least one," unless otherwise specified.

[0026] The word "including" as used herein means without limitation.

[0027] All ingredient or composition levels, unless otherwise stated, refer to the active portion of that ingredient or composition and exclude impurities such as residual solvents or by-products that may be present in commercially available versions of such ingredients or compositions.

[0028] All percentages and ratios are calculated by weight unless otherwise specified. All percentages and ratios are calculated based on the total composition unless otherwise specified.

[0029] The recitation of every maximum numerical limitation throughout this specification should be understood to include every lower numerical limitation, as if such lower numerical limitations were expressly written herein. The recitation of every minimum numerical limitation throughout this specification should be understood to include every higher numerical limitation, as if such higher numerical limitations were expressly written herein. The recitation of every numerical range throughout this specification should be understood to include every lower numerical range that is included in such broader numerical range, as if such narrower numerical range were expressly written herein. resin composition

[0030] The applicant discloses a resin composition containing any one of the following a) to i): a) Bismaleimide (BMI), preferably the bismaleimide (BMI) is oligomerized from 4,4'-bismaleimide diphenylmethane, bismaleimide BMI-1,3-tolyl and o,o'-diallylbisphenol A, catalyzed by about 1% to about 5%, preferably about 2%, of dicumyl peroxide or cumene hydroperoxide by weight of the total composition. b) Bisphenol A dicyanate ester, the bisphenol A dicyanate ester being catalyzed with nonylphenol and a metal ion, the nonylphenol being from about 0.5 phr to about 1.99 phr of nonylphenol, preferably from about 0.75 phr to about 1.9 phr of nonylphenol, more preferably from about 1 phr to about 1.8 phr of nonylphenol, even more preferably from about 1.25 phr to about 1.7 phr of nonylphenol, and most preferably from about 1.5 phr to about 1.6 phr of nonylphenol, the metal ion being derived from a metal carboxylate or metal chelate, the metal carboxylate or metal chelate being zinc(II) naphthenate (from about 60 ppm to about 150 ppm of Zn 2+ ), zinc(II) acetylacetonate (approximately 60 ppm of Zn 2+ ), copper(II) acetylacetonate (about 100 ppm to about 500 ppm Cu 2+ ), copper(II) naphthenate (approximately 200 ppm Cu 2+ ), cobalt(II) acetylacetonate (about 170 ppm to about 370 ppm Co 2+ ), or cobalt(III) acetylacetonate (about 120 ppm to about 360 ppm Co 3+ ), wherein the metal chelate is preferably selected from the group consisting of copper(II) acetylacetonate, cobalt(III) acetylacetonate, and combinations thereof. c) bisphenol E dicyanate ester, the bisphenol E dicyanate ester being catalyzed with nonylphenol and a metal ion, the nonylphenol being from about 0.5 phr to about 1.99 phr of nonylphenol, preferably from about 0.75 phr to about 1.9 phr of nonylphenol, more preferably from about 1 phr to about 1.8 phr of nonylphenol, even more preferably from about 1.25 phr to about 1.7 phr of nonylphenol, and most preferably from about 1.5 phr to about 1.6 phr of nonylphenol, and the metal ion being from about 50 ppm to about 360 ppm total Cu. 2+ or Co 3+ and is obtained from a metal chelate, preferably selected from the group consisting of copper(II) acetylacetonate, cobalt(III) acetylacetonate, and combinations thereof. d) bisphenol A dicyanate ester, the bisphenol A dicyanate ester being catalyzed by m-cresol and a metal ion, the m-cresol concentration being from about 0.75 phr to about 6 phr, and the metal ion being from about 50 ppm to about 360 ppm Cu. 2+ or Co 3+ and is obtained from a metal chelate, preferably selected from the group consisting of copper(II) acetylacetonate, cobalt(III) acetylacetonate, and combinations thereof. e) bisphenol E dicyanate ester, the bisphenol E dicyanate ester being catalyzed by m-cresol and a metal ion, the m-cresol concentration being from about 0.75 phr to about 6 phr, and the metal ion being from about 50 ppm to about 360 ppm Cu. 2+ or Co 3+and is obtained from a metal chelate, preferably selected from the group consisting of copper(II) acetylacetonate, cobalt(III) acetylacetonate, and combinations thereof. f) a bisphenol A dicyanate ester, a novolac cyanate ester, nonylphenol, and a metal ion, wherein the bisphenol A dicyanate ester and the novolac cyanate ester are present in a mass fraction of about 0.7:0.3 to about 1:1, the nonylphenol being about 0.5 phr to about 1.99 phr of nonylphenol, preferably about 0.75 phr to about 1.9 phr of nonylphenol, more preferably about 1 phr to about 1.8 phr of nonylphenol, even more preferably about 1.25 phr to about 1.7 phr of nonylphenol, and most preferably about 1.5 phr to about 1.6 phr of nonylphenol, and the metal ion is present in a total of about 50 ppm to about 360 ppm of Cu; 2+ or Co 3+ and the bisphenol A dicyanate ester, the novolac cyanate ester, the nonylphenol, and the metal ion, wherein the metal chelate is preferably selected from the group consisting of copper(II) acetylacetonate, cobalt(III) acetylacetonate, and combinations thereof. g) a bisphenol E dicyanate ester, a novolac cyanate ester, nonylphenol, and a metal ion, wherein the bisphenol E dicyanate ester and the novolac cyanate ester are present in a mass fraction of about 0.7:0.3 to about 1:1, the nonylphenol being about 0.5 phr to about 1.99 phr of nonylphenol, preferably about 0.75 phr to about 1.9 phr of nonylphenol, more preferably about 1 phr to about 1.8 phr of nonylphenol, even more preferably about 1.25 phr to about 1.7 phr of nonylphenol, and most preferably about 1.5 phr to about 1.6 phr of nonylphenol, and the metal ion is present in a total of about 50 ppm to about 360 ppm of Cu; 2+ or Co 3+ and the bisphenol E dicyanate ester, the novolac cyanate ester, the nonylphenol, and the metal ion, wherein the metal chelate is preferably selected from the group consisting of copper(II) acetylacetonate, cobalt(III) acetylacetonate, and combinations thereof. h) a bisphenol A dicyanate ester and a novolac cyanate ester, the bisphenol A dicyanate ester and the novolac cyanate ester being present in a mass fraction of about 0.7:0.3 to about 1:1, catalyzed by m-cresol and a metal ion, the m-cresol concentration being about 0.75 phr to about 6 phr, and the metal ion being about 50 ppm to about 360 ppm Cu; 2+ or Co 3+ and the bisphenol A dicyanate ester and the novolac cyanate ester are obtained from a metal chelate, preferably selected from the group consisting of copper(II) acetylacetonate, cobalt(III) acetylacetonate, and combinations thereof. i) a bisphenol E dicyanate ester and a novolac cyanate ester, the bisphenol E dicyanate ester and the novolac cyanate ester being present in a mass fraction of about 0.7:0.3 to about 1:1, catalyzed by m-cresol and a metal ion, the m-cresol concentration being about 0.75 phr to about 6 phr, and the metal ion being about 50 ppm to about 360 ppm Cu; 2+ or Co 3+ and the bisphenol E dicyanate ester and the novolac cyanate ester are obtained from a metal chelate, preferably selected from the group consisting of copper(II) acetylacetonate, cobalt(III) acetylacetonate, and combinations thereof.

[0031] Resin systems a) through i) in paragraph 0030 are listed in order of preferred, more preferred, and most preferred, with i) being the most preferred. Such resin systems improve the mechanical properties of composites produced from the resin systems under high temperature and stress conditions. Nonylphenol is a proton donor catalyst traditionally utilized in the catalysis of cyanate esters due to its high boiling point. However, nonylphenol is a nine-carbon aliphatic chain that often functions as a residual plasticizer in cured polycyanate systems, degrading resin properties and resulting mechanical properties at high temperatures. The inventors have discovered that when a molecularly aromatic, small-sized proton donor alcohol is used in place of nonylphenol, a smaller amount of m-cresol, for example, can be used to solubilize a given amount of metal chelate, and the combination of the smaller amount and smaller size significantly improves resin properties and resulting composite mechanical properties at high temperatures. The inventors have also discovered that blending dicyanate esters (Types A or E) with novolac-type cyanate esters can further improve the mechanical properties of resins and composites at high temperatures. The novolac-type cyanate esters increase the crosslink density of the cured resin, thereby increasing the resin's softening temperature and therefore its mechanical properties. The higher the proportion of novolac-type cyanate ester used, the greater the resulting high-temperature properties, at the expense of resin toughness. Figure 14 is a graph showing the effect of cyanate ester resin composition and catalyst type on the interlaminar shear strength of carbon fiber-reinforced polymer composites at a test temperature of 200°C.

[0032] Bisphenol E dicyanate ester, bisphenol A dicyanate ester, and novolac cyanate ester are available from Lonza, Inc. (412 Mt. Kemble Ave., Morristown, NJ 07960) and Huntsman Advanced Materials (10003 Woodloch Forest Drive, The Woodlands, TX 77380). Nonylphenol, m-cresol, and suitable metal chelates are available from Sigma Aldrich (2033 Westport Center Dr., St. Louis, MO 63146). Bismaleimide is available from Solvay Composite Materials (4300 Jackson St., Greenville, TX 75401).

[0033] Non-limiting structures of thermosetting resin monomers and catalysts suitable for electromagnetic induction heat treatment of fiber reinforced polymer casings include those shown in Figures 11A-11F.

[0034] Non-limiting structures of cyanate ester resin and curing catalyst systems found to be effective in pulsed electromagnetic induction curing processes include those shown in Figures 12A-12C. Cases of fiber-reinforced polymer composite construction and articles containing such cases

[0035] High-performance items include pipes, pressure vessels such as rocket motor cases and fire extinguishers, golf club shafts, tennis and badminton rackets, skis, snowboards, ice hockey sticks, fishing rods, bicycle frames, boat masts, oars, paddles, baseball bats, and softball bats. Rockets, especially those fueled by solid propellants, are often characterized by structural components such as cases made from fiber-reinforced polymer (FRP) composites. These reinforcing fibers are designed to support operational loads, while adhesive resins maintain the fiber structure and transmit associated stresses. The implementation of FRP in rockets was most recently advanced in the 1990s. This advancement occurred with the application of graphite epoxy motors (GEMs) to the Titan IV's strap-on solid booster, known as the Solid Rocket Motor Upgrade (SRMU). This resulted in a 25% increase in payload capability to orbit. GEM and most other FRP composite rocket cases in production utilize resin systems with softening (glass transition) temperatures below 200°C, with most below 100°C. During operation, rocket components are subject to significant aerodynamic heating due to friction with the air and internal heating due to fuel and oxidizer combustion. Despite their high strength-to-weight ratio, FRP composites, by themselves, may not be able to replace steel in the design phase of rocket components because applications that subject these components to significant thermal loads would require high levels of protective insulation, resulting in volume and propellant mass penalties.

[0036] FRP structural cases, such as those used in the manufacture of solid-fuel rockets, are typically manufactured by the filament winding technique, in which continuous fiber rovings impregnated with an adhesive polymer resin are wound around an insulated, disposable mandrel. After winding, the adhesive resin is typically cured using a convection oven. The mandrel is then withdrawn, and the finished case product is filled with propellant using a slurry casting process and fitted with a nozzle and igniter. However, this traditional manufacturing method limits the complexity of rocket designs because it is difficult to incorporate propellant grain features, thrust-switching hardware, and other features that enhance rocket performance beyond what can be poured into the cylinder. Therefore, in some cases, it is advantageous to manufacture certain articles, such as rockets, from the inside out. For solid-fuel rockets, this involves first manufacturing the propellant grain and associated propellant burn management devices, followed by depositing a structural case onto a propellant grain mandrel, and finally curing the case. When filament winding is used to manufacture the case, the process is called case-on-propellant (CoP) or direct filament winding (DFW). To ensure safety and maintain the functionality of rocket motor components during DFW, low-temperature curing resins are used because the resin must cure without damaging the propellant and, in the worst case scenario, without causing a catalytic reaction that could ignite. Low-temperature resins result in lower-performance cases that require additional structural mass for thermal reinforcement.

[0037] High temperature resins are typically avoided because high oven temperatures are required to cure them, and such high temperatures impart excessive thermal energy to heat-sensitive materials. Applicant has recognized that the source of the problem lies not only in the amount of thermal energy provided by the curing oven, but more importantly, in the rate at which such thermal energy is delivered. In short, Applicant has recognized that the true source of the problem lies in the lack of thermal control available with conventional resin curing methods.

[0038] Electromagnetic induction heating is a process in which an article (workpiece), typically steel, is exposed to an alternating magnetic field generated by alternating current (AC) flowing through a coil (inductor). The workpiece is coupled to the inductor, generating a current in the workpiece. This current is typically concentrated near the workpiece surface near the coil, and the current depth can be adjusted by modulating the AC frequency. Heat is generated due to the inherent resistance of the workpiece to the current, a phenomenon known as resistive heating. This process is typically used for melting, sintering, or heat treating steels containing a certain concentration of iron atoms because such steels are magnetically polarizable and suitable for current generation through hysteresis. This process is applicable to any workpiece material that is inherently electrically conductive and somewhat magnetic. A unique advantage of electromagnetic induction processing is that the heating in the workpiece is instantaneous and can be clearly switched on and off.

[0039] Applicant has recognized that electromagnetic induction processing offers advantages in the heat curing of FRP articles, such as rocket parts, particularly those with filament-wound construction. Applicant has recognized that because graphite (carbon) fibers are reasonably good conductors of electrical current and have inherent resistance, when electrical current can be passed through such fibers, they are expected to generate heat and can therefore be used to cure adhesive resin systems. In contrast to oven curing, which relies on much slower transfer by conduction and convection, the instantaneous nature of induction heating processing, and the ability to specifically regulate the heat source, facilitates precise heat transfer control to underlying components, particularly heat-sensitive components. Applicant has discovered that electromagnetic induction processing can achieve precisely controlled heat curing of resin systems with a wide range of cure temperatures without imparting excessive thermal energy to heat-sensitive materials. Pulsing, optionally combined with cooling steps between pulses, allows for an increased level of control, and measurement devices such as infrared cameras and thermocouples can monitor temperatures at various locations within the workpiece and integrate them into a feedback loop for the induction system's power supply.

[0040] The applicant discloses a fiber-reinforced polymer composite structure, the case of which comprises the following a) and b): a) at least one type of fiber, the fiber having a density of about 1×10 -2 Ωcm to approximately 1×10 -4 It has an electrical resistivity of Ωcm and forms a continuous circuit within the fiber reinforced polymer composite structure. b) at least one resin having a glass transition temperature greater than 200° C., preferably from about 200° C. to about 300° C., and most preferably from about 300° C. to about 400° C. The resin may optionally contain a catalyst to increase the degree of crosslinking of the resin. The fiber reinforced polymer composite structure is a filament wound or fiber placed fiber reinforced polymer composite structural case. Suitable fibers, such as carbon fiber, are available from Cytec Engineered Materials, Inc., Tempe, Arizona, USA; Hexcel, Inc., Stamford, Connecticut, USA; Mitsubishi Chemical America, Inc., New York, USA; Nippon Graphite Fiber Co., Ltd., Cypress, California, USA; Toho Tenax Co., Ltd., Chiyoda-ku, Tokyo, Japan; Toray Industries, Inc., Chuo-ku, Tokyo, Japan; Toray Carbon Fibers America, Inc., Decatur, Alabama, USA; and Zoltek, Inc., St. Louis, Missouri, USA. Preferred resin systems fall into two general categories: thermosets and thermoplastics. General sub-categories of thermosets are (in order of increasing temperature capability) epoxies, benzoxazines, bismaleimides, phthalonitriles, cyanate esters, and polyimides. Epoxies, benzoxazines, bismaleimides, cyanate esters, and combinations thereof are preferred due to their greater responsiveness to pulse curing. The preferred resin systems discussed above are those that cure by addition or homopolymerization, have relatively low viscosities prior to the cure reaction, and can be catalyzed to significantly increase the rate of the cure reaction. In one embodiment, the following resin and catalyst combinations can be used: homopolymerizable bisphenol E-type cyanate esters catalyzed by the addition of 2-6 phr of nonylphenol and 100-400 ppm of copper from copper(II) acetylacetonate, and addition-type bismaleimides (BMIs) catalyzed by peroxides such as dicumyl peroxide. Suitable resins are available from Cytec Engineered Materials, Inc., Tempe, Arizona (e.g., for bismaleimides), Huntsman, The Woodlands, Texas (e.g., for epoxies, benzoxazines, and cyanate esters), and Lonza (now Arxarda), Basel, Switzerland (e.g., for cyanate esters). The resin-catalyst combination may be an epoxy cured using a curing agent. The curing agents may be, in increasing order of activity, phenols, anhydrides, aromatic amines, cycloaliphatic amines, aliphatic amines, thiols, or combinations thereof. The curing of the epoxy with the curing agent may be catalyzed or accelerated using tertiary amines, carboxylic acids, and alcohols (especially phenols). The resin-catalyst combination may also be a bismaleimide curable by peroxide catalysis. The resin-catalyst combination may also be a cyanate ester curable by alcohol catalysis. The alcohol may have a high boiling point (200-300°C), such as m-cresol (boiling point 203°C) or nonylphenol (293°C). The cyanate ester may also be catalyzed by organometallic compounds. The organometallic compounds include zinc(2+) acetylacetonate, zinc(2+) naphthenate, copper(2+) acetylacetonate, copper(2+) naphthenate, cobalt(2+) acetylacetonate, and cobalt(3+) acetylacetonate.

[0041] 10. The fiber reinforced polymer composite structure of claim 0040, wherein the fiber reinforced polymer composite structure comprises filament wound fibers as described above, wherein the filament wound fibers are selected from the group consisting of polar fibers, helical fibers, hoop fibers, unidirectional zero degree fibers, and combinations thereof, preferably when the fiber reinforced polymer composite structure is a pressure vessel, the vessel comprises hoop fibers, and when axial stiffness is desired, the fiber reinforced polymer composite structure comprises polar fibers, helical fibers, unidirectional zero degree fibers, and / or combinations thereof.

[0042] 2. The fiber reinforced polymer composite structure according to paragraph 40 or 41, wherein the resin is selected from the group consisting of epoxy, benzoxazine, phthalonitrile, cyanate ester, bismaleimide, and polyimide; preferably, the resin is selected from the group consisting of epoxy, benzoxazine, cyanate ester, bismaleimide, and combinations thereof; more preferably, the resin is selected from the group consisting of benzoxazine, cyanate ester, bismaleimide, and combinations thereof; even more preferably, the resin is selected from the group consisting of bismaleimide, cyanate ester, and combinations thereof; most preferably, the resin comprises at least one cyanate ester.

[0043] The fiber-reinforced polymer composite structure according to any one of paragraphs 0040 to 0042, further comprising a mandrel containing rocket propellant. The mandrel has at least two ends and at least two counter electrode openings. The ends and counter electrode openings are located at opposite ends of the fiber-reinforced polymer composite structure case. In this case, the at least one type of fiber and the at least one type of resin form a case that encases the mandrel, except for the counter electrode openings.

[0044] In the case of a fiber reinforced polymer composite structure as described in paragraph 0043, the rocket propellant is a solid propellant or a hybrid propellant or a liquid propellant.

[0045] The fiber reinforced polymer composite structure of paragraph 43 or 44 further comprises an insulating material disposed between the casing and the mandrel. Preferably, the insulating material comprises rubber. In one embodiment, the rubber comprises fibers and / or particulates. In one embodiment, the fibers are Kevlar and / or carbon fibers. In one embodiment, the particulates are silica.

[0046] The fiber reinforced polymer composite structure of any of paragraphs

[0043] to

[0045] , comprising at least one igniter and at least one nozzle, the at least one igniter and the at least one nozzle being positioned in at least one of the counter electrode openings so as to be opposite each other.

[0047] Examples of fiber-reinforced polymer composite structures are shown in Figures 10 and 13. Figure 10 shows a cross-sectional view of an insulated fiber-reinforced polymer rocket motor case. The fiber-reinforced polymer rocket motor case includes a fiber-reinforced polymer composite case 13, inner insulation 14, solid propellant 15 (heat-sensitive mandrel), and a metal shaft 16. During electromagnetic induction processing, current generation is concentrated in the outer layers, and the insulation provides some protection for the solid propellant. The heat-sensitive mandrel may be further protected by current pulses combined with cooling steps between cycles. Figure 13 shows a fiber-reinforced polymer paddle 21 containing resin. The paddle is surrounded by a coil 22. The resin can be cured by passing current through the coil. Fiber-reinforced polymer composite structural case and method of manufacturing an article including such a case

[0048] Articles such as high performance solid rocket motor cases have fiber reinforced polymer (FRP) because FRP has a higher strength-to-weight ratio than steel. A standard solid rocket motor with an FRP case is typically manufactured in the following manner: (1) Fabricate a metal mandrel or washout mandrel. (2) Apply internal insulation to the mandrel surface. (3) Apply FRP to the insulated mandrel by filament winding, hand layup, or tow / tape application. (4) Cure the FRP in a convection oven. (5) Remove the mandrel (for items other than rocket motor cases, the method typically ends here). (6) Install propellant casting machinery. This machinery has a bore former (core). Typically, this tool has a star pattern to control surface area during the early stages of the burn cycle to tailor the motor's thrust profile. (7) Cast the propellant slurry into the case. (8) Cure the propellant in a convection oven, typically at 60°C. (9) Remove the center bore former. (10) Install the nozzle and ignition system.

[0049] Another method for manufacturing articles such as high-performance solid rocket motor cases comprising fiber-reinforced polymer (FRP) is as follows: The solid propellant grain is first fabricated, along with the associated propellant burn management devices. The structural case material (fiber and resin) is then placed over the propellant grain mandrel. The resin is then cured. To ensure safety and maintain functionality of the rocket motor components during resin curing, low-temperature curing resins are used because the resin must cure without damaging the propellant and, in the worst case scenario, causing a pyrocatalytic reaction. Low-temperature resins result in lower-performance cases that require additional structural mass for thermal reinforcement and protection.

[0050] Applicants disclose an improved manufacturing method for producing a FRP composite structural case or an article comprising such a case. This method uses an electromagnetic induction heating system that passes an alternating current (AC) current through a hollow metal conductive coil at a frequency in the kilohertz range. The conductive coil can be fabricated from hollow copper tubing. While a voltage is applied to the copper coil, water can be passed through the copper coil. This removes heat generated by the inherent electrical resistance of copper. The coil can have a variety of structural shapes, including solenoid, pancake, and various configurations that match the surface curvature of the CFRP cylindrical or dome-shaped case of a typical rocket motor. In a solenoid coil, the motor case is located within the inner diameter of the coil, while in a pancake coil, the coil is planar and located near the surface of the CFRP. The magnetic fields generated by both types of coils are different. The magnetic field generated by a pancake coil is located close to the coil and decreases rapidly in strength with distance from the coil surface. In a solenoid coil, the magnetic field is generated over a much larger area within the coil, but to a lesser extent outside. The strength of the magnetic field can be adjusted by the number of turns in the solenoid coil. The more turns, the stronger the resulting magnetic field. The coil may be formed by filling it with a medium such as sand to prevent the internal channel from shrinking during winding. The CFRP is placed on a mandrel that does not couple to the magnetic field (does not generate heat). The magnetically uncoupled mandrel can be constructed from aluminum, rubber, glass-reinforced composites, solid rocket propellants, etc. The CFRP is applied to the cylindrical mandrel by filament winding, hand layup, and / or tow / tape application. Once the CFRP is fully applied to the mandrel, the target induction coil structure is placed near the CFRP structure. This can be accomplished in several ways. In one method, a solenoid coil is placed around the cylindrical portion of the motor case, and the solenoid can be tapered to fit closely to the dome area of ​​the case. In another method, the raised surface of a pancake coil can be placed near the surface of the CFRP. If the size of the CFRP structure being processed or the power limitations of the induction heating system do not allow for complete coverage of the CFRP, the coil and induction work head can be mounted on a filament winding machine, tow / tape application machine, or lathe, and a coil of smaller dimensions compared to the CFRP structure can be translated back and forth across the CFRP to facilitate heating. This technique can provide a consistent temperature across a cylindrical CFRP piece of large length or diameter. It has also been shown to be extremely useful when power limitations on induction heating systems are encountered, at the expense of time to heat to a given temperature. Specifically, in one example, a three-turn solenoid coil, 3 inches long and 6 inches inside diameter, was used in this manner to process a cylindrical CFRP piece 30 inches long, 5.75 inches inside diameter, and 0.060 inches thick (6 hoop layers). Following a slow temperature increase to 149°C, that temperature was consistently maintained for 12 hours by translating the coil back and forth across the CFRP. By applying current to the coil in a controlled manner, complex curing cycles of adhesive resins on the CFRP can be achieved. Both temperature increases and constant temperature maintenance can be achieved if the carbon fiber response can be adequately expressed as a function of power input. An infrared camera is used during processing to monitor the CFRP surface temperature for regulation and quality control purposes.In the manufacturing process for propellant upper cases, pulse hardening has been found to be effective in controlling heat transfer to the internal insulating interface with the solid propellant grains. For example, if the desired CFRP hardening temperature is 250°C and the solid propellant grain interface cannot exceed 60°C, a pulse is generated to rapidly bring the CFRP to 250°C and the pulse is maintained until the solid propellant interface reaches 60°C, as measured by an embedded thermocouple (preferably a metal thermocouple, such as an E-type, that is not magnetically coupled) placed at the interface. At that point, the pulse is turned off, and convective cooling gas can be flowed over the CFRP to efficiently remove heat from the solid propellant interface. The cooling gas can be generated by evaporating liquid nitrogen from a cryogenic source, or it can be compressed air or an inert gas. Once the temperature at the solid propellant interface has dropped to a lower temperature, the next pulse can begin. This process can be repeated any number of cycles until the desired total CFRP hardening time has elapsed, and can be controlled via an established communication feedback loop between the thermocouple, IR camera, induction heating system, and cooling system. If the mandrel case is temperature-insensitive, the temperature at the CFRP can be maintained constant until full cure is achieved. CFRP resin systems can be tailored to cure quickly with the assistance of a catalyst or selected to cure in response to pulse types. The efficiency of carbon fiber heating is a function of the induction heater power, current frequency, and layup structure. Increasing power and frequency (especially the latter) improves the carbon fiber response. However, because the coil automatically tunes to a specific frequency, this is usually not an easily adjustable variable and depends on the coil structure. CFRP configured at a 90-degree angle to the mandrel axis is most efficient at heating in the presence of a conventional solenoid coil (the coil is oriented in the same direction as the wound fiber), but heat generation has also been observed in layups with smaller angles.

[0051] Induction heating systems capable of generating the appropriate coil frequency typically use a resonant circuit. This resonant circuit includes a generator (power supply), a capacitor, and an inductor. The generator, capacitor, and inductor may be connected in parallel or series. A radio frequency (RF) power supply can be used to achieve the desired frequency range. Suitable types of RF power supplies include vacuum tube and solid-state types. The former provide frequencies in the 200-450 kHz range, while the latter provide frequencies in the 50-450 kHz range. Solid-state power supplies are particularly suitable because they typically provide the highest frequency range. Such power supplies may be powered by metal-oxide semiconductor field-effect transistor (MOSFET) output devices.

[0052] Suitable commercially available induction heating systems include the EASYHEAT (1-10 kW) and EKOHEAT (10 kW-500 kW) system products from Ambrell, Rochester, New York, USA; power supplies and induction heating systems from UltraFlex Power Technologies, Ronkonkoma, New York, USA; and generators and heating heads from CEIA USA, Twinsburg, Ohio, USA.

[0053] Applicant discloses a method for making a fiber reinforced polymer composite structure. The fiber reinforced polymer composite structure includes a mandrel. Preferably, the mandrel comprises a material selected from the group consisting of aluminum, rubber, glass reinforced composites, rocket propellants, and combinations thereof. The mandrel is wrapped with at least one resin and at least one fiber via a filament winding and / or fiber placement process, whereby the fibers form a continuous circuit. The fibers are about 1×10 -2 Ωcm to approximately 1×10 -4The fiber reinforced polymer composite structure has an electrical resistivity of Ωcm. The method includes applying a magnetic field, generated by an alternating current having a frequency in the kilohertz range, to the fiber reinforced polymer composite structure in a continuous or pulsed manner until the at least one resin cures. The kilohertz range is preferably in the range of 50 kHz or higher, more preferably in the range of about 50 kHz to about 450 kHz. Optionally, between pulses, the fiber reinforced polymer composite structure may be cooled by passing a cooling fluid over the fiber reinforced polymer composite structure. Preferably, the cooling fluid is a gas, more preferably the gas is an inert gas, and most preferably the gas comprises nitrogen. Specifications for fluids suitable for cooling induction coils typically include a minimum pressure differential of 30 psi, a maximum inlet temperature of 95°F, a pH of 7.0-9.0, chloride content less than 20 ppm, nitrate content less than 10 ppm, sulfate content less than 100 ppm, calcium carbonate content less than 250 ppm, total dissolved solids content less than 250 ppm, no solids that precipitate at temperatures below 135°F, resistivity greater than 2500 Ω-cm at 77°F, containing a magnetite eliminator and corrosion inhibitor, and containing a maximum concentration of 50% antifreeze in the form of unrestricted ethylene glycol. Preferably, the cooling fluid is ion-free or essentially ion-free. Where I is the current and R is the resistivity of the coil, I 2 The required flow rate of cooling fluid flowing through the coil is determined from the calculation of R and the allowable temperature of the coil itself.

[0054] The Applicant discloses a method according to paragraph 0053, in which the magnetic field is generated by passing the alternating current, the frequency of which belongs to the kilohertz range, through a coil, the coil including an internal passage through which a cooling fluid can pass. The coil preferably has a magnetic field of at least 4.5 x 10 7 S / m, and more preferably about 4.5×10 7 S / m to approximately 5.8 × 10 7 S / m, and most preferably about 5.8×107 S / m to approximately 6 × 10 7 S / m, as measured by ASTM E1004 (Standard Test Methods for Determining Electrical Conductivity Using Electromagnetic (Eddy Current) Methods) at 20° C. In this case, preferably, the coil is formed of copper, silver, gold, or a combination thereof.

[0055] The applicant discloses a manufacturing method according to paragraphs 0053-0054. In this regard, the manufacturing method uses at least one coil selected from the group consisting of a solenoid coil, an axial coil, a helical coil, and a multi-axial coil. Typically, if the coil is a solenoid coil, the solenoid coil is aligned so as to be perpendicular to the longitudinal axis of the fiber reinforced polymer composite structure. If the coil is an axial coil, the axial coil is aligned so as to be parallel to the longitudinal axis of the fiber reinforced polymer composite structure. If the coil is a helical coil, the helical coil is aligned so as to be oriented at an angle of 0 to 90 degrees relative to the longitudinal axis of the fiber reinforced polymer composite structure. If the coil is a multi-axial coil, the orientation of the multi-axial coil is aligned so as to be oriented at an angle of 0 to 90 degrees relative to the longitudinal axis of the fiber reinforced polymer composite structure.

[0056] The applicant discloses a manufacturing method according to paragraphs 0053-0055, in which the coil is translated across the surface of the fiber reinforced polymer composite structure. As the coil power increases, the coil's ability to accommodate higher AC frequencies decreases. By translating the coil, the tradeoff between the coil's available frequency and coil power is significantly reduced. As a result, by translating the coil, a smaller magnetic induction system can be used to cure larger fiber reinforced polymer composite structures.

[0057] The applicant discloses a manufacturing method according to paragraphs 0053 to 0056, in which the fibers of the filament wound structure are selected from the group consisting of polar fibers, helical fibers, hoop fibers, unidirectional zero-degree fibers, braided sleeves, and combinations thereof. Preferably, when the fiber reinforced polymer composite structure is a pressure vessel, the fiber reinforced polymer composite structure comprises hoop fibers, and when axial stiffness is desired, the fiber reinforced polymer composite structure comprises polar fibers, helical fibers, unidirectional zero-degree fibers, braided sleeves, and / or combinations thereof.

[0058] The applicant discloses a process according to paragraphs 0053 to 0057, in which the at least one resin has a glass transition temperature greater than 80°C, preferably greater than 200°C, more preferably from about 250°C to about 400°C, and most preferably from about 300°C to 400°C.

[0059] The applicant discloses a manufacturing method according to paragraphs 0053 to 0058. In this regard, the resin is the following a) or b): a) The resin is cured by a continuous magnetic field. The resin is selected from the group consisting of epoxy, benzoxazine, phthalonitrile, cyanate ester, bismaleimide, and polyimide. Preferably, the resin is selected from the group consisting of epoxy, benzoxazine, cyanate ester, bismaleimide, and combinations thereof. More preferably, the resin is selected from the group consisting of benzoxazine, cyanate ester, bismaleimide, and combinations thereof. Even more preferably, the resin is selected from the group consisting of bismaleimide, cyanate ester, and combinations thereof. Most preferably, the resin comprises at least one cyanate ester. b) The resin is cured by a continuous magnetic field. The resin is selected from the group consisting of epoxies, benzoxazines, bismaleimides, cyanate esters, and combinations thereof. Preferably, the resin is selected from the group consisting of benzoxazines, bismaleimides, cyanate esters, and combinations thereof. More preferably, the resin is selected from the group consisting of bismaleimides, cyanate esters, and combinations thereof. Most preferably, the resin comprises at least one cyanate ester.

[0060] The applicant discloses a method for fabricating a fiber-reinforced polymer composite structural case according to paragraphs 0053-0059. In this regard, the fiber-reinforced polymer composite structural case further includes a mandrel containing rocket propellant. The mandrel has at least two end portions and at least two counter electrode openings. These end portions and counter electrode openings are located at opposite ends of the fiber-reinforced polymer composite structural case. The at least one type of fiber and the at least one type of resin form a casing that encases the mandrel, excluding the counter electrode opening. Preferably, the surface temperature of the rocket propellant is prevented from reaching 60°C. It is generally believed that solid propellant grains should not be exposed to temperatures higher than 60°C during manufacturing to avoid premature aging, which can degrade the grain's mechanical properties, change its burn rate, activate the migration of freely mobile plasticizers in the propellant to the grain interface, affecting interfacial adhesion or other key properties, and promote delamination between the case and the grain, potentially leading to motor failure during operation. The worst case scenario is that the propellant may ignite as a result of exposure to high temperatures.

[0061] The applicant discloses a method for manufacturing a fiber reinforced polymer composite structural case according to paragraph 0060. In this regard, the rocket propellant is a solid propellant, a hybrid propellant, or a liquid propellant.

[0062] Applicant discloses a method for making a fiber reinforced polymer composite structural casing according to paragraphs 0060-0061. In this regard, the fiber reinforced polymer composite structural casing includes an insulator disposed between the casing and the mandrel. Preferably, the insulator includes rubber. In one embodiment, the rubber includes fibers and / or particulates. In one embodiment, the fibers are Kevlar and / or carbon fibers. In one embodiment, the particulates are silica.

[0063] The applicant discloses a method for fabricating a fiber-reinforced polymer composite structural case according to paragraphs 0060-0062, wherein the fiber-reinforced polymer composite structural case includes at least one igniter and at least one nozzle, the at least one igniter and the at least one nozzle being positioned in at least one of the counter electrode openings so as to be opposite each other.

[0064] Applicant discloses a method for making a fiber reinforced polymer composite structural casing in accordance with paragraphs 0053-0063, wherein the method comprises pulse curing said at least one resin.

[0065] The applicant discloses a method of making a fiber reinforced polymer composite structural case according to paragraphs 0053 to 0064, in which the fiber reinforced polymer composite structural case is actively or passively cooled in the intervals between the pulses.

[0066] Additional process details are shown in Figures 1-9. Figure 1 is a schematic diagram of the basic components of an induction heating system. The induction heating system includes a power supply (inverter) 1, a tank circuit (work head) 2, a coil 3, a water cooling system 4, a temperature controller 5, a thermocouple 6, an infrared camera 7, and a workpiece 8. Figure 2 is a schematic diagram illustrating the principle of magnetic induction heating of a fiber-reinforced polymer composite case. The fiber-reinforced polymer composite case has a polar or helical layer of fiber-reinforced polymer composite material and a hoop layer of fiber-reinforced polymer composite material. The polar or helical layer forms a dome 9 and extends in a direction parallel to the axis of the case, while the hoop layer is oriented perpendicular to the axis of the case. Using the coil configuration shown, current is induced primarily in this layer and in the mandrel base, which is made of a heat-sensitive material. A solenoid coil 12, through which an alternating current I and a cooling fluid flow rate Qdot are flowing, generates a magnetic field. The strength of this magnetic field, determined by the current amperage and the number of coil turns, generates eddy currents in the hoop layer. The electrical resistivity of the fiber generates heat, which can cure the polymer adhesive resin. Figure 3 is a schematic diagram of a continuous solenoid coil. This continuous solenoid coil is fitted to the dome region of the fiber-reinforced polymer composite case so that the spacing between the coil and the case is constant. Here, eddy currents are generated in the workpiece in the opposite direction to the current flowing through the coil. The fiber resistivity is low in the hoop layer because the fiber orientation is aligned for current generation and therefore less obstructed. The dome region has higher electrical resistivity because the current must jump between fibers. Therefore, heating is less effective in these regions. Figure 4 shows a three-turn solenoid coil. This solenoid coil is linearly translated across the cylindrical region of the fiber-reinforced polymer composite case. This technique allows a short coil to heat a long section of the case. The coil is effective when the power capacity of the electromagnetic induction equipment is limited. The translation technique facilitates heating of items much larger than the coil, at the expense of the time it takes for the workpiece to reach the target temperature.Figure 5 shows a single-lobe axial coil placed on a fiber-reinforced casing. In this configuration, the magnetic field is generated very close to the coil, generating current most efficiently in the polar or helical layers of the casing. If the fibers are continuous, current flows through the fibers, generating heat on the opposite side of the casing where the coil is not present. This technique allows for uniform heating in the dome portion by rotating the casing while the coil is energized. Figures 6A and 6B show a single-lobe axial coil placed on a fiber-reinforced polymer casing. The lobe axial coil is tilted at an angle α to be parallel to the fiber tow direction in the helical and / or polar layers. Manipulating the coil angle can affect the rate and magnitude of heat generation in the fibers. Figure 7 shows a single-lobe axial coil placed on a fiber-reinforced polymer casing. Both ends of the lobe axial coil are shaped to match the outer surface of the dome portion. This coil allows for more efficient and sizable heating in the dome portion of the casing. Figure 8 shows a multi-lobe axial coil placed over a cylindrical region of a fiber-reinforced polymer case. This coil covers a larger area on the case, thereby increasing the rate and magnitude of heat generation. Uniform heating can be achieved throughout the case, with the rate and magnitude being proportional to the number of coil lobes. During heating, the case can be rotated to improve temperature uniformity. Finally, Figure 9 shows a hybrid coil with both solenoidal and axial coil elements in series. Example

[0067] The following examples illustrate some specific features and advantages of embodiments of the present invention. They are examples of the implementation of the present invention and are intended to confirm the validity of the principles described for the present invention, but should not be construed as limiting the scope of the present invention.

[0068] Example 1 The solid rocket motor case mandrel assembly is placed on a cylindrical metal shaft. This mandrel assembly serves as a base for fabricating a fiber-reinforced polymer structural case, comprised of any number of individual solid propellant grains. Metal counterbore pieces (bosses) are attached to the forward and aft ends of the propellant grain subassemblies. These counterbore pieces facilitate the attachment of the igniter and nozzle after the solid rocket structural case is fabricated. The individual solid propellant grains may be cast and cured within a preformed rubber-based internal insulation. Alternatively, the insulation may be applied to the solid propellant grains after they are placed on the shaft. Any components associated with the vectoring and attitude control system may also be incorporated into the propellant grain subassembly. Once fully assembled, the case mandrel is inserted into the vise chuck of a filament winding machine. Carbon fiber tows are then wound onto the mandrel using a filament winding process to form polar, helical, and hoop layers in any desired sequence. The carbon fiber tow is pre-impregnated with a cyanate ester resin and a cure-accelerating catalyst. Hand layup of unidirectional zero-degree layers and / or braided sleeves may be performed. Once the filament winding process is complete, a coil is placed over the filament-wound rocket motor case (workpiece) in close proximity (within 5 mm) to the surface of the rocket motor case. The coil consists of a hollow copper tube formed in a conventional solenoid configuration. The coil is connected to an induction heater with a work head and power supply. The induction heater is configured based on predetermined parameters to achieve a specific amperage and time cycle known to avoid excessive heat transfer to the propellant grains. Alternatively, a thermocouple is placed at a strategic location at the boundary between the propellant grains and the internal insulation, and a lead from the mandrel assembly is connected to the induction heater's control software to facilitate a feedback loop for pulse power control. The induction coil is energized with an alternating current at the natural frequency of the coil and work head circuit.For effective processing, the frequency should be greater than 50 kHz. When energized, the induction coil generates a magnetic field whose strength is determined by the current amperage, coil diameter, and number of coil turns. This magnetic field then induces current through any conductors in the workpiece, with the current strongest in the vicinity of the coil. Therefore, the strongest current is generated within the conductive carbon fibers. Due to the inherent electrical resistivity of the fibers, current flows most efficiently through continuous carbon fibers, generating heat. Due to the orientation of the solenoid coil, current is most efficiently generated in the hoop layers (those oriented perpendicular to the shaft axis). These layers therefore generate the most heat. The heat generated within the carbon fibers is transferred to the cyanate ester resin, accelerating its curing reaction. The cyanate ester is optimally cured by maintaining it at 150°C for one hour, followed by at least one hour at 220°C. However, prolonged temperatures above 60°C must be avoided at the interface between the propellant grains and the internal insulation. The electromagnetic pulse is terminated when the interface temperature reaches 60°C. The carbon fiber reinforced polymer (CFRP) structure is then cooled either passively or actively. In active cooling, a stream of gaseous nitrogen is passed over the CFRP surface until the interface cools to 30°C before the next electromagnetic pulse is initiated. The length of the next heating pulse is extended depending on the depth of the pulse cooling. Cycles of electromagnetic pulse heating and cooling are performed until the target degree of cure of the CFRP resin is achieved.

[0069] Example 2 The manufacturing method according to Example 1 is carried out, but in this Example 2, the coil is configured to have multiple axial lobes. These axial lobes are parallel to the axis of the filament-wound CFRP laminate. This type of coil generates more heat in the polar and helical layers that form the dome. The coil can also be configured and implemented to have both solenoid and axial elements.

[0070] Example 3 The manufacturing method according to Example 1 is carried out, but in this Example 3, a thermoplastic resin such as poly(ether-ether-ketone) is used as the CFRP adhesive resin. A shrink tape or film, or other pressure-intensifying medium such as silicone rubber, is placed on the CFRP laminate. During induction heating of the CFRP, the generated heat is transferred to the pressure-intensifying medium, thereby applying a compressive force to the CFRP laminate. This strengthens the thermoplastic matrix.

[0071] Example 4 In another embodiment, the mandrel for filament winding is constructed of metal. The mandrel has a monolithic structure. Ideally, the selected metal will bond weakly to magnetic fields (e.g., aluminum is a good candidate) so that the adhesive resin used in the filament winding process is not degraded by excessive heat exposure during processing. The filament-wound composite material is placed on the mandrel and cured, after which the mandrel can be left in place or removed. This process can be used to manufacture composite pipes, rods, poles, braids, etc.

[0072] Example 5 In this example, the process shown in Example 4 is carried out, but instead of processing separate objects in a batch process, the process is used continuously. Long, continuous sections of filament-wound composite material are processed through separate sections of the induction coil, which allows the resin in the composite material to harden. After passing through the induction coil elements, the processed continuous article may be cut into separate sections for faster mass production of specific parts.

[0073] Example 6 In this example, the manufacturing method described in Example 4 is carried out, but in this application, the mandrel is a metal puzzle type, composed of plaster, or composed of a water-soluble work material (e.g., a mandrel composed of particulates bound with sodium silicate, polyvinyl alcohol, or polyvinylpyrrilidone, or a water-soluble salt). The filament-wound composite on this type of mandrel is induction-cured, and then the mandrel is withdrawn. In the case of a metal puzzle mandrel, the mandrel is broken up through the counter electrode opening and withdrawn piece by piece. In the case of plaster, the mandrel is crushed and the resulting pieces are withdrawn. In the case of a water-soluble work, the mandrel is washed away. Using this type of mandrel, more complex shapes such as turbine blades and crankshafts can be manufactured.

[0074] Example 7 Boat Mast: A preform with the desired internal structure is fabricated. Flat panels with predetermined dimensions are then cut from the carbon fiber unidirectional mat prepreg on a two-dimensional routing table. Multiple flat panels are manually placed on the preform. After a prepreg layer is placed, plastic tape is attached to the prepreg surface under tension, compressing, reducing, and eliminating wrinkles. Before the next prepreg layer is placed, the plastic tape is removed unless it is the last layer. The last layer is left as is. After all the prepregs are attached to the preform, a breather cloth is placed on the plastic film. Typically, the entire boat mast assembly is processed under vacuum and pressure in an autoclave to cure the prepreg resin. However, to avoid this time-consuming and costly process, magnetic induction curing is used. To do this, once the breathable fabric is attached, the assembly is placed in a bag as in autoclaving, but a silicone rubber sheet of pressure-enhancing medium is attached to the surface of the breathable fabric, and then glass fiber is wrapped around the silicone surface under high tension. The subassembly is then placed in a magnetic induction coil to allow the resin to cure.

[0075] Example 8 Piping / Tubing: Carbon fiber composite tubes and piping are first fabricated by cutting unidirectional and / or woven prepreg patterns using a computer numerically controlled device. These flat patterns are then wrapped around a mandrel to form a tubular shape. Once all prepreg layers are in place, a plastic layer film is wrapped around the exterior of the prepreg under tension or compression tape. The tension or compression tape serves to firmly bind the materials together during resin curing. The piping / tubing assembly is then inserted into a magnetic induction coil for more precise and faster curing compared to oven curing, thereby increasing the throughput of the unit. After curing, the tape is removed and the mandrel is removed to produce the finished product.

[0076] Example 9 Automotive Drive Shaft: In the fabrication of a carbon fiber composite automotive driveshaft, an adhesive resin for carbon fiber filaments is first mixed with particulate additives that provide additional reinforcement. A continuous tow of carbon fiber is then drawn through a solution containing the resin mixture and stacked at a predetermined angle onto a mandrel by wet filament winding. The mandrel has the dimensions of the shaft's inner diameter. Once this winding is complete, compression tape is attached to the surface of the composite under tension, providing compression during resin curing. The driveshaft assembly is cured more precisely and quickly than oven curing by placing a magnetic induction coil around the assembly while it is still on the filament winding machine. The part is rotated by a chuck on the winding machine during resin curing. This process step eliminates the need for an oven. Once the adhesive resin has cured, the compression tape is removed and the mandrel is withdrawn. Metal end members are then bonded to the driveshaft ends to provide a durable connection during installation in the vehicle.

[0077] Example 10 Adhesive Resin and Fiber Impregnation: A preferred resin system is comprised of bisphenol E dicyanate ester and novolac-type cyanate ester. The resin system is catalyzed by a combination of nonylphenol and a metal chelate, such as copper(II) acetylacetonate. The resin system is a 70:30 combination of bisphenol E dicyanate ester and novolac cyanate ester. The resin system is combined with 2 phr of nonylphenol and 360 ppm of Cu. 2+The following is prepared: 700 grams of liquid bisphenol E dicyanate ester is added to a glass container. Then, 300 grams of liquid novolac-type cyanate ester is added to the same container. Using a hot plate, immersion bath, and jacketed container, the two cyanate ester components are heated to 80°C and stirred until the mixture is homogenous and no distinct phases are discernible. Mixing is accomplished with a large magnetic stir bar or overhead mechanical stirrer. Homogenization typically takes up to three hours, and once complete, the mixture is cooled to room temperature. To a separate glass container, most preferably a glass scintillation vial, 30 grams of liquid nonylphenol is added. Also, 0.022 grams of copper(II) acetylacetonate is added in the form of a blue powder. The magnetic stir bar is immersed in the liquid in the vial. The vial is then placed on a hot plate, and the mixture is heated to 60-100°C. The mixture is then stirred until homogenization is complete, as evidenced by the disappearance of particulate copper(II) acetylacetonate. This process typically takes up to 12 hours, with the processing time decreasing as the temperature increases. Once this process is complete, the catalyst mixture is allowed to cool. Finally, 20.015 grams of the catalyst mixture is added to the cyanate ester mixture at room temperature and stirred manually or mechanically. The resulting cyanate ester and catalyst mixture is then used to manufacture carbon fiber reinforced polymer towpregs. Carbon fiber tows are impregnated with the resin using a suitable continuous impregnation machine. This continuous impregnation machine includes at least a resin reservoir, a resin deposition system, an impregnation die, a fiber take-up system, and a fiber tensioning device. The resin is continuously deposited onto the continuous carbon fiber tow, pulled through the impregnation die, and the resulting towpreg is then wound.

[0078] The present invention has been illustrated by the description of one or more embodiments thereof, and those embodiments have been described in considerable detail. However, it is not intended that the appended claims be restricted or in any way limited to such details. Additional advantages and modifications will be readily apparent to those skilled in the art. Accordingly, the invention in its broader aspects is not limited to the specific details, representative apparatus and methods, and illustrative examples described and shown. Accordingly, departures may be made from such details without departing from the scope of the general inventive concept.

Claims

1. 1. A rocket motor including a fiber reinforced polymer composite structure, comprising: a) at least one type of fiber, the fiber being 1×10 －２ Ωcm to 1×10 －４ Ω cm and form a continuous circuit within the fiber reinforced polymer composite structure; b) at least one resin, the resin constituting the fiber reinforced polymer composite structure having a glass transition temperature greater than 200° C., preferably between 200° C. and 300° C., most preferably between 300° C. and 400° C., the resin optionally containing a catalyst to increase the degree of crosslinking of the resin; The fiber-reinforced polymer composite structure is a filament-wound or fiber-layed fiber-reinforced polymer composite structure, The rocket motor comprises a mandrel encased by the at least one fiber and the at least one resin, the mandrel containing a rocket propellant.

2. 2. The rocket motor of claim 1, wherein the fiber reinforced polymer composite structure has fibers in a filament wound structure selected from the group consisting of polar fibers, helical fibers, hoop fibers, and combinations thereof, preferably when the fiber reinforced polymer composite structure is a pressure vessel, the vessel has hoop fibers, and when axial stiffness is desired, the fiber reinforced polymer composite structure has polar fibers, helical fibers, and / or combinations thereof.

3. 3. The rocket motor according to claim 1 or 2, wherein the resin is selected from the group consisting of epoxy, benzoxazine, phthalonitrile, cyanate ester, bismaleimide, and polyimide, preferably the resin is selected from the group consisting of epoxy, benzoxazine, cyanate ester, bismaleimide, and combinations thereof, more preferably the resin is selected from the group consisting of benzoxazine, cyanate ester, bismaleimide, and combinations thereof, even more preferably the resin is selected from the group consisting of bismaleimide, cyanate ester, and combinations thereof, and most preferably the resin comprises at least one cyanate ester.

4. The rocket motor comprises a fiber reinforced polymer composite case as the fiber reinforced polymer composite structure formed by the at least one type of fiber and the at least one type of resin, and the mandrel; The rocket motor according to any one of claims 1 to 3, wherein the mandrel has two counter electrode openings formed at two ends of the mandrel, the two counter electrode openings are located at both ends of the fiber reinforced polymer composite case, and the at least one type of fiber and the at least one type of resin form the fiber reinforced polymer composite case that encases the mandrel except for the counter electrode openings.

5. 5. The rocket motor of claim 4, wherein the rocket propellant is a solid propellant or a hybrid propellant.

6. A rocket motor as described in claim 4 or 5, wherein the rocket motor comprises an insulator disposed between the fiber reinforced polymer composite case and the mandrel, preferably the insulator comprising rubber.

7. A rocket motor as described in any one of claims 4 to 6, comprising at least one ignition device and at least one nozzle, the at least one ignition device and the at least one nozzle being positioned in at least one of the counter electrode openings so as to be positioned opposite each other.

8. 1. A method of manufacturing a rocket motor including a fiber reinforced polymer composite structure, comprising: The rocket motor includes a mandrel containing a rocket propellant, the mandrel being wrapped by a filament winding process and / or a fiber placement process with at least one resin and at least one fiber to form a continuous circuit from the fibers, the fibers being 1×10 -２ Ωcm to 1×10 -４ It has an electrical resistivity of Ω cm, The method includes a step of curing the resin encasing the mandrel containing the rocket propellant by repeatedly applying at intervals current pulses of alternating current having a frequency in the kilohertz range and a magnetic field generated by the current pulses to the fiber reinforced polymer composite structure until the at least one resin is cured; The kilohertz range is preferably in the range of 50 kHz and above, more preferably in the range of 50 kHz to 450 kHz; Optionally, between pulses, the fiber reinforced polymer composite structure is cooled by passing a cooling fluid over the fiber reinforced polymer composite structure, preferably the cooling fluid is a gas, more preferably the gas is an inert gas, and most preferably the gas comprises nitrogen.

9. the magnetic field is generated by passing the alternating current, at a frequency in the kilohertz range, through a coil, the coil including an internal passage through which a cooling fluid can pass; The coil preferably has a capacitance of at least 4.5×10 ７ S / m, more preferably 4.5×10 ７ S / m to 5.8 x 10 ７ S / m, and most preferably 5.8×10 ７ S / m to 6 x 10 ７ 9. The process of claim 8, wherein the conductive material has a conductivity of 0.1 S / m.

10. The method of claim 9, wherein the current pulse is passed through at least one coil selected from the group consisting of a solenoid coil, an axial coil, a helical coil, and a multi-axial coil.

11. 11. The method of claim 9 or 10, wherein the coil is translated across a surface of the fiber reinforced polymer composite structure.

12. The fibers of the filament wound construction are selected from the group consisting of polar fibers, helical fibers, hoop fibers, braided sleeves, and combinations thereof; Preferably, when the fiber reinforced polymer composite structure is a pressure vessel, the fiber reinforced polymer composite structure comprises hoop fibers, and when axial stiffness is desired, the fiber reinforced polymer composite structure comprises polar fibers, helical fibers, braided sleeves, and / or combinations thereof.

13. 13. The process according to any one of claims 8 to 12, wherein the at least one resin has a glass transition temperature higher than 80°C, preferably higher than 200°C, more preferably between 250°C and 400°C, and most preferably between 300°C and 400°C.

14. a) the resin is cured by a continuous magnetic field, the resin being selected from the group consisting of epoxies, benzoxazines, phthalonitriles, cyanate esters, bismaleimides, and polyimides, preferably the resin is selected from the group consisting of epoxies, benzoxazines, cyanate esters, bismaleimides, and combinations thereof, more preferably the resin is selected from the group consisting of benzoxazines, cyanate esters, bismaleimides, and combinations thereof, even more preferably the resin is selected from the group consisting of bismaleimides, cyanate esters, and combinations thereof, most preferably the resin comprises at least one cyanate ester; or b) the resin is cured by a continuous magnetic field, the resin being selected from the group consisting of epoxies, benzoxazines, bismaleimides, cyanate esters, and combinations thereof, preferably the resin is selected from the group consisting of benzoxazines, bismaleimides, cyanate esters, and combinations thereof, more preferably the resin is selected from the group consisting of bismaleimides, cyanate esters, and combinations thereof, most preferably the resin comprises at least one cyanate ester; The method according to any one of claims 8 to 13.

15. The rocket motor includes a fiber reinforced polymer composite case as the fiber reinforced polymer composite structure formed by the fiber and the resin, and the mandrel; The method according to any one of claims 8 to 14, wherein the mandrel has two counter electrode openings formed at two ends of the mandrel, the two counter electrode openings being located at opposite ends of the fiber reinforced polymer composite case, and the at least one type of fiber and the at least one type of resin form the fiber reinforced polymer composite case surrounding the mandrel except for the counter electrode openings, preferably such that a surface temperature of the rocket propellant does not reach 60°C.

16. 16. The method of claim 15, wherein the rocket propellant is a solid propellant or a hybrid propellant.

17. 17. The method of claim 15 or 16, wherein the rocket motor comprises insulation disposed between the case and the mandrel, preferably the insulation comprises rubber.

18. The method of any one of claims 15 to 17, wherein the rocket motor includes at least one igniter and at least one nozzle, the at least one igniter and the at least one nozzle being located in at least one of the counter electrode openings so as to be located opposite each other.

19. A method according to any one of claims 8 to 18, wherein the fibre reinforced polymer composite structure is actively or passively cooled in the intervals between the current pulses.

Images