High-Performance Composites for Underwater Applications

Abstract

The underwater structure includes a half-cylinder with ribs arranged on an interior surface thereof, the half-cylinder and the ribs being of semi-monocoque construction including a fiber reinforced thermoplastic composite material.

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to U.S. Patent Application No. 63 / 133,521, filed January 4, 2021, which is incorporated by reference in its entirety. [Background technology]

[0002] The present disclosure relates to materials for underwater applications, and more particularly to high performance composite materials for underwater applications.

[0003] Materials used to construct undersea encapsulation systems, such as those for drones and missiles, must meet a variety of criteria. They must be resilient to high pressure, moisture penetration / ingress, and harsh underwater environments for extended periods of time. They must also be highly reliable and require little to no maintenance. Additionally, materials used to form undersea encapsulation systems must accommodate a wide variety of payloads and low-risk launch modes. Summary of the Invention

[0004] An underwater structure and a method for manufacturing the same are disclosed. According to one or more embodiments of the present disclosure, the underwater structure includes a half cylinder with ribs arranged on an inner surface. The half cylinder and the ribs are of semi-monocoque construction with a fiber reinforced thermoplastic composite material.

[0005] According to another embodiment of the present disclosure, an underwater structure includes a cylinder that is a monocoque structure with a fiber reinforced thermoplastic composite material.

[0006] Furthermore, according to another embodiment of the present disclosure, a method of manufacturing an underwater structure includes heating and applying a fiber reinforced thermoplastic composite material under pressure to a mold such that the fibers extend continuously around or along the length of the underwater structure to form a semi-monocoque or monocoque underwater structure.

[0007] Additional features and advantages are realized through the techniques of the present disclosure. Other embodiments and aspects of the present disclosure are described in detail herein and are considered a part of the claimed disclosure. For a better understanding of the present disclosure, together with its advantages and features, reference is made to the description and drawings.

[0008] For a more complete understanding of this disclosure, reference is now made to the following brief description in conjunction with the accompanying drawings and detailed description, in which like reference numerals represent like parts, and in which: [Brief description of the drawings]

[0009] [Figure 1A] FIG. 1 is a perspective view of a half-cylinder formed from a fiber-reinforced thermoplastic composite material according to an embodiment of the present disclosure.

[0010] [Figure 1B] FIG. 1B is a perspective view of a rib (stiffener) of the semi-cylinder of FIG. 1A according to an embodiment of the present disclosure.

[0011] [Diagram 2] FIG. 2 is an exploded perspective view of an underwear capsule formed from two half-cylinders according to an embodiment of the present disclosure.

[0012] [Diagram 3] FIG. 1 is a flow diagram for manufacturing a semi-monocoque component from a fiber reinforced thermoplastic composite material according to an embodiment of the present disclosure.

[0013] [Figure 4] FIG. 1 is a schematic diagram of a process flow for forming ribs / stiffeners from a fiber reinforced thermoplastic composite according to an embodiment of the present disclosure.

[0014] [Diagram 5] FIG. 1 is a perspective view of a monocoque cylinder formed from a fiber reinforced thermoplastic composite material according to an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Current materials used to construct undersea capsule systems, such as for drones and missiles, include metals such as aluminum, corrosion-resistant steel (CRES), titanium, and epoxy composites. The metals are formed as half-cylinders that are later fastened, bonded, or welded together to form the final capsule. However, such metals have drawbacks. The materials are heavy, susceptible to corrosion, and very labor intensive. Additionally, forming capsules using such metals presents manufacturing challenges. For example, the half-cylinders must be effectively sealed together by fastening, which requires reliance on an upstream supply chain for fasteners and / or materials. The epoxy composites used to form the undersea capsules also present various challenges. For example, epoxy composites are not hermetic to water penetration. Additionally, the mechanical properties of epoxy composites can degrade when wet.

[0016] For subsea applications, materials must be highly resilient to high pressures and harsh environments, require little to no maintenance, and the materials used to create the subsea systems must accommodate a wide variety of payloads and low-risk launch modes.

[0017] Described herein are subsea systems and methods of manufacture formed from fiber reinforced thermoplastic composites. Subsea systems include structures that are submerged for extended periods of time, such as in the sea / ocean, such as pressure vessels, underwater hulls, and underwater capsules. Thermoplastic composites include polyetheretherketones (PEEK), in some embodiments, reinforced across the structure with continuous fibers, such as graphite fibers. A method for forming the subsea structures is the in-situ consolidation (ISC) process, which creates a unitary reinforced structure without the need for secondary bonding or fastening of the reinforcement to a skin, as the entire reinforced structure is formed in a single processing step forming a monocoque or semi-monocoque structure.

[0018] Fiber reinforced thermoplastic composites provide subsea structures that resist water penetration (e.g., 0.25% absorption vs. 1% absorption for epoxy composites over 2 years at 1020 meters depth) and superior (2-5 times greater) damage resistance (e.g., fracture toughness) compared to epoxy composites. Composites also provide higher continuous use resin temperatures compared to epoxy resins (e.g., 300°F-500°F vs. 225°F-350°F for epoxy). This can minimize or eliminate the need for insulation (cost, weight) when used in close proximity to or in contact with other system components or structures that may be hot. Monocoque composites also offer the potential for other benefits such as approximately 56% weight reduction, approximately 10% increase in interior volume, and 3-year water tightness in certain applications.

[0019] 1A is a perspective view of a half-cylinder 100 formed from a fiber-reinforced thermoplastic composite material according to an embodiment of the present disclosure. The half-cylinder 100 includes a plurality of reinforcing ribs 102 (also referred to as stiffeners) arranged along the interior concave surface of the curved body 104 of the half-cylinder. The reinforcing ribs 102 may be of any shape, size, and / or dimension and serve to structurally reinforce or strengthen the curved body 104. In some embodiments, the ribs 102 extend partially or completely across the circumference or even diameter of the curved body 104 from one side to the other. In other embodiments, the ribs 102 extend partially or completely along the longitudinal length of the curved body 104.

[0020] 1B is a perspective view of a rib 102a (reinforcement) of the half-cylinder 100 of FIG. 1A, which is fused in situ to the curved body 104 in an in situ solidification process, as described in more detail below. The rib 102a includes a first arm 106 adjacent a first surface of the curved body 104 (FIG. 1A) of the reinforced half-cylinder 100, a second arm 108 adjacent a second surface of the curved body 104, and a body 109 (which provides structural reinforcement for the curved body 104 of the half-cylinder 100) extending between the first arm 106 and the second arm 108.

[0021] The half-cylinders described herein including reinforcing ribs / stiffeners are formed from a fiber reinforced thermoplastic composite. According to some embodiments, the thermoplastic of the composite is polyetheretherketone (PEEK). Other non-limiting examples of thermoplastics for the composite include low melting point polyaryletherketone (LMPAEK), polyphenylene sulfide (PPS), polyetherimide (PEI), or any combination thereof.

[0022] Non-limiting examples of fibers in a thermoplastic composite include long continuous carbon fibers (e.g., graphite fibers), fiberglass fibers, para-aramid (KEVLAR®) fibers, or combinations thereof. According to one or more embodiments, the fibers in the thermoplastic composite are graphite fibers. In some embodiments, the fiber reinforced thermoplastic composite is graphite fiber reinforced polyetheretherketone (PEEK). The fibers are not short fibers, but rather long continuous fibers that run along the length, diameter (or any angle in between) of the semi-cylinder section or rib. The fibers are present in the composite in an amount of about 40% to about 60% fiber by volume, according to some embodiments. The fibers in the composite are continuous. Through an in-situ solidification (ISC) process, the fibers are cut to the desired length when applied to the part / mold. This ISC process results in continuous fiber lengths ranging from 4 inches to 30 feet.

[0023] FIG. 2 is an exploded perspective view of an underwater capsule 200 formed from two half-cylinders 100 according to an embodiment of the present disclosure. Once formed separately, the two reinforced half-cylinders 100 are joined together by various methods including mechanical methods such as fasteners, or chemical methods such as adhesives, or thermal methods such as welding or fusion, or any combination thereof. Because the half-cylinders 100 are formed from a thermoplastic composite material, they can self-fuse together by heating the material without the need for additional adhesives. The underwater capsule 200 houses dunnage and other support structures 202 for the encapsulated payload. End caps 204 are arranged on the ends of the two half-cylinders 100 once they are glued / fixed together to form a hollow capsule.

[0024] 3 is a flow diagram for forming a part, such as a reinforced half-cylinder, from a fiber-reinforced thermoplastic composite according to an embodiment of the present disclosure. In box 302, a mold for the part is provided. In some embodiments, the mold includes a half-cylinder with reinforcements, for example as shown in FIG. 1A. The reinforcements are pre-formed and applied (see boxes 304 and 306). The mold allows the entire part, including the curved body of the half-cylinder and multiple internal ribs / reinforcements, to be formed in a single mold.

[0025] Fiber reinforced thermoplastic composite ribs / stiffeners are preformed in box 304. In box 306, the preformed ribs / stiffeners are applied to the mold such that their faying surfaces against the skin to be applied are exposed.

[0026] In box 308, the fiber reinforced thermoplastic composite is applied to the mold containing the ribs / stiffeners to form the skin. In box 310, the fiber reinforced thermoplastic composite applied to the mold forming the skin passes over the mating surface of the ribs / stiffeners, whereby the fiber reinforced thermoplastic composite fuses to the ribs / stiffeners. During this application process, heat (e.g., by a laser) and pressure (by an application roller of an ISC machine) are applied to the fiber reinforced thermoplastic composite to form the part in an in situ solidification process. The skin fibers run continuously along the circumference or length of the part. Because the fibers in the composite are long, they wrap or run continuously throughout the mold, adding strength, rather than containing short fibers dispersed throughout the material. In situ solidification utilizes the ability of the thermoplastic to melt, bond (or fuse) to itself, and cool back down into a solid structure. Continuous fibers can be applied to the mold in any direction as well as within or over complex contoured surfaces.

[0027] If the part is a reinforced half cylinder, the reinforcing ribs conform to the half cylinder shell. In other words, the part is a semi-monocoque structural part. In situ solidification allows the reinforced structure to be formed without the need for secondary bonding or fastening of the reinforcement to the skin. In some embodiments, the temperature used to heat the thermoplastic composite, such as PEEK, is about 350 to about 450°C.

[0028] If the part is a reinforced half-cylinder, two reinforced half-cylinders are bonded together to form the submarine capsule. Optionally, end caps are bonded to the ends of the capsule. The two half-cylinders are bonded together by fusing them together through the application of heat and pressure, applying an adhesive, mechanically fastening, or any combination thereof.

[0029] 4 is a schematic diagram of a process flow for forming ribs or stiffeners from a fiber reinforced thermoplastic composite according to an embodiment of the present disclosure. A fiber reinforced thermoplastic composite 404 is heated and then forced into a cavity of a mold 406 using pressure 408. A compression surface 402 that mirrors the shape of the mold 406 compresses the composite 404 into the mold 406. The heat and pressure are maintained for a period of time to allow the material 404 to conform to the shape of the mold 406 and fully solidify. To demold after the part is formed, the part is cooled from the molding temperature, the compression surface 402 is removed, and the final part formed to the shape of the mold 406 can be lifted out 410.

[0030] The methods described herein may be used to create parts having any shape, size, or dimensions, and the methods are not limited to forming reinforced half cylinders. Figure 5 is a perspective view of a monocoque cylinder 500 formed from a fiber reinforced thermoplastic composite material according to an embodiment of the present disclosure.

[0031] The composite materials and methods described can be used to create affordable, high performance, complex underwater structures in addition to undersea capsules. The materials and methods can also be used in some embodiments for offshore drilling applications.

[0032] Various embodiments of the present disclosure are described herein with reference to the associated drawings. Alternative embodiments may be devised without departing from the scope of the present disclosure. In the following description and drawings, various connections and relationships between elements (e.g., above, below, adjacent, etc.) are described, however, as one skilled in the art will appreciate, many of the relationships described herein are not orientation dependent, provided that the described functionality is maintained even if the orientation is changed. These connections and / or relationships may be direct or indirect, unless otherwise specified, and the present disclosure is not intended to be limiting in this respect. Thus, the coupling of entities may refer to direct or indirect coupling, and the relationship between entities may be a direct or indirect relationship. As an example of an indirect relationship, reference in this description to forming layer "A" above layer "B" includes the situation where one or more intermediate layers (e.g., layer "C") are between layer "A" and layer "B", so long as the relevant properties and functions of layer "A" and layer "B" are not substantially altered by the intermediate layer(s).

[0033] The following definitions and abbreviations should be used in interpreting the claims and the specification. As used herein, the terms "comprises," "comprising," "includes," "including," "has," "having," "contains," or "containing," or any other variation thereof, are intended to cover a non-exclusive inclusion. For example, a composition, mixture, process, method, article, or device that includes a list of elements is not necessarily limited to only those elements but can include other elements not expressly listed or that are inherent to such composition, mixture, process, method, article, or device.

[0034] Moreover, the term "exemplary" is used herein to mean "serving as an example, instance, or illustration." Any embodiment or design described herein as "exemplary" should not necessarily be construed as preferred or advantageous over other embodiments or designs. The terms "at least one" and "one or more" are understood to include any integer number greater than or equal to one, i.e., 1, 2, 3, 4, etc. The term "plurality" is understood to include any integer number greater than or equal to two, i.e., 2, 3, 4, 5, etc. The term "connected" can include indirect and direct "connected."

[0035] References in the specification to "one embodiment," "embodiment," "exemplary embodiment," and the like indicate that the described embodiment may include a particular feature, structure, or characteristic, but every embodiment may or may not include the particular feature, structure, or characteristic. Moreover, such phrases do not necessarily refer to the same embodiment. Moreover, it is submitted that when a particular feature, structure, or characteristic is described in connection with an embodiment, it is within the knowledge of one of ordinary skill in the art to affect such feature, structure, or characteristic in connection with other embodiments, whether or not explicitly described.

[0036] For purposes of the following description, the terms "above," "below," "right," "left," "vertical," "horizontal," "top," "bottom," and their derivatives refer to the structures and methods described as oriented in the drawings. The terms "overlying," "on," "above," "located on," or "located on" mean that a first element, such as a first structure, is on a second element, such as a second structure, and that an intervening element, such as an interface structure, can be between the first and second elements. The term "direct contact" means that a first element, such as a first structure, and a second element, such as a second structure, are connected without any intermediate conductive, insulating, or semiconducting layer at the interface of the two elements.

[0037] The terms "about," "substantially," "approximately," and variations thereof are intended to include the degree of error associated with measurement of a particular quantity based on equipment available at the time of filing. For example, "about" can include a range of ±8% or 5% or 2% of a given value.

[0038] The flow charts and block diagrams in the figures illustrate possible implementations of methods of manufacture and / or operation according to various embodiments of the disclosure. Various functions / operations of the methods are illustrated by blocks in the flow diagrams. In some alternative implementations, the functions noted in the blocks may occur out of the order noted in the figures. For example, two blocks shown in succession may in fact be executed substantially simultaneously, or the blocks may often be executed in the reverse order, depending on the functionality involved.

[0039] Corresponding structures, materials, acts, and equivalents of all means or step-plus-function elements in the following claims are intended to include any structure, material, or act for performing a function in combination with other claimed elements as specifically claimed. The description of the present disclosure has been presented for purposes of illustration and description, but is not intended to be exhaustive or to limit the disclosure to the disclosed form. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the present disclosure. The selection and description of the embodiments have been made in order to best explain the principles and practical application of the present disclosure, and to enable others skilled in the art to understand the present disclosure to various embodiments with various modifications suitable for the particular use intended.

[0040] While preferred embodiments to the present disclosure have been described, it will be understood that those skilled in the art, both now and in the future, may make various improvements and enhancements that fall within the scope of the following claims, which should be interpreted to maintain the appropriate protection for the disclosure originally described.

Claims

1. An underwater structure, comprising: a semi-cylinder having a plurality of ribs arranged on an inner surface thereof, the semi-cylinder and the plurality of ribs being semi-monocoque structures comprising a fiber reinforced thermoplastic composite material, the fiber reinforced thermoplastic composite material comprising continuous fibers extending continuously along a circumference of the semi-cylinder having the plurality of ribs, the fiber reinforced thermoplastic composite material comprising polyetheretherketone (PEEK), and each of the plurality of ribs extending across the curved body of the semi-cylinder from one side of the curved body to the other side of the curved body. Underwater structures.

2. 10. The underwater structure of claim 1, wherein the fiber reinforced thermoplastic composite material comprises carbon fiber, fiberglass fiber, para-aramid fiber, or a combination thereof.

3. 10. The underwater structure of claim 1, wherein the continuous fibers have a length of from 4 inches to 30 feet.

4. The underwater structure of claim 1 , wherein the continuous fibers are present in an amount of about 40% to about 60% by volume.

5. The underwater structure of claim 1 , wherein the fiber reinforced thermoplastic composite material comprises graphite fibers.

6. A method for manufacturing an underwater structure, comprising the steps of: applying a fiber reinforced thermoplastic composite material under pressure and under heating to a mould such that continuous fibres of said fiber reinforced thermoplastic composite material extend continuously around a circumference of said underwater structure to form a semi-monocoque underwater structure comprising said fiber reinforced thermoplastic composite material; The method of claim 1, wherein the underwater structure comprises a semi-cylinder having a plurality of ribs arranged on an inner surface, the fiber reinforced thermoplastic composite material comprises polyetheretherketone (PEEK), and each of the plurality of ribs extends across the curved body of the semi-cylinder from one side of the curved body to the other side of the curved body.

7. The method of claim 6 , wherein the fiber reinforced thermoplastic composite comprises carbon fiber, fiberglass fiber, para-aramid fiber, or a combination thereof.

8. 7. The method of claim 6, wherein the continuous fibers have a length of from 4 inches to 30 feet, and the continuous fibers are present in an amount of from about 40% to about 60% by volume.

9. The method of claim 6 , wherein the fiber reinforced thermoplastic composite material comprises graphite fibers.

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