Patent Application
20190351624
The present disclosure relates generally to fiber-reinforced polymer structures. More specifically, aspects of this disclosure relate to systems, devices and processes for repairing multidimensional thermoplastic or thermoset polymer composite panels.
Composite materials are used for manufacturing a vast array of modern products. Many current-production automobiles, watercraft, and aircraft, for example, are assembled with load-bearing body panels, aesthetic trim panels, support frame members, as well as various other components that are manufactured, in whole or in part, from composite materials. Fiber-reinforced plastic (FRP) is an example composite material that is used in mass-production manufacturing applications, favored for its high strength-to-weight ratio, increased elasticity, corrosion resistance, and light weight properties. FRP's are typically formed by suspending a high-tensile-strength fibrous material, such as glass, carbon, aramid, or basalt fibers, within a solidified polymer, such as a thermoset epoxy-resin matrix or a thermoplastic polyester or nylon.
As with any product, FRP components are subject to damage during manufacture, while being packaged and shipped to a retailer or customer, or when in service. In automotive applications, for example, an FRP body panel, engine hood, or trunk lid may be disfigured or fractured through forces generated by encounters with rough roads or severe weather during otherwise normal vehicle operation, or as a result of a collision event with another vehicle or a stationary object. These same FRP components may be fabricated with dents, cracks or other defects that result from variations in raw materials, incongruences in processing conditions, and tolerance deviations during manufacturing. Any such damaged components have to be either replaced by new parts or professionally repaired. While both of these options are costly and time consuming, part replacement concomitantly results in unwanted scrap material. Component repair—although typically less expensive with reduced part scrap—may not produce a perfectly repaired part absent perceptible structural imperfections.
Disclosed herein are repair systems and apparatuses for fixing polymer composite structures, methods for making and methods for using such repair systems, and repair techniques for fixing surface damage/defects of multidimensional thermoset or thermoplastic FRP panel structures. By way of example, and not limitation, there is presented a thermoelectric repair system for generating a wrinkle-free repair of damage to a contoured fiber-reinforced thermoplastic (FRT) composite panel. The repair system uses an integrated electrical heating sheet that is designed to generate uniform heat across the repair surface of the FRT part. Prior to heating, a repair patch or repair filler material may be placed in or across the area of repair. An elastic silicon rubber sheet with high thermal stability is placed on top of the damaged area and the immediate surrounding area of the FRT panel. A resin-impregnated carbon-fiber mat (“prepreg”) is then placed across the silicon rubber sheet. This prepreg may be cured, e.g., in situ on the FRT part during repair or offline on an undamaged part prior to repair, to form an interface that matches an undamaged part surface geometry. The heating sheet is laid across the FRT panel/rubber sheet/prepreg stackup; uniform heat is applied to melt the repair material and/or the base material in the repair region. Pressure may be applied, e.g., via vacuum bagging or other suitable procedure, to help ensure uniform contact between the FRT part surface and the rubber sheet/prepreg/heating sheet stackup. Optionally, or alternatively, a die plate that is topographically mapped to an undamaged part geometry may be pressed against the heating element to ensure uniform surface heating, e.g., for panels with recessed surface channels or other intricate geometries.
Attendant benefits for at least some of the disclosed concepts include a defect-free repaired surface, i.e., without perceptible structural or superficial imperfections, for a complex-geometry FRP composite part. Disclosed FRP composite part repair techniques help to improve part serviceability, which in turns helps to decrease plant part scrap rates, warranty costs, and labor costs. Another foreseeable advantage is the ability to repair an FRP component in situ, e.g., after installation on a vehicle or assembly on a final product, without the need for extensive disassembly. Other attendant benefits may include increased part strength, decreased part mass, lower part cost, reduced production costs, and improved fuel economy, e.g., for motor vehicle applications, when compared to conventional counterpart FRP structures.
Aspects of the present disclosure are directed to systems and attendant techniques for repairing filler/fiber-reinforced polymer structures. In an example, a thermoelectric repair system for fixing a contoured surface of an FRP structure is presented. The thermoelectric repair system includes a flexible contact sheet that is fabricated with a thermally stable polymer, and has a textured contact surface that seats on the contoured surface of the FRP structure and overlays the damaged area. A rigid cover sheet, which may be fabricated from a metal material, a polymeric material, a fibrous material impregnated with a thermally conductive resin, and/or a thermally conductive fibrous material impregnated with a resin), has a complementary surface that conforms to the contoured surface of the FRP structure and covers the flexible contact sheet. The thermoelectric repair system also includes an electric heating element that lays against the rigid cover sheet, sandwiching the flexible contact sheet and rigid cover sheet between the FRP structure and the heating element. This heating element applies a substantially uniform heating profile to the contoured surface sufficient to soften and/or melt added filler material and/or base material bordering the damaged area. In one or more alternative configurations, the functional attributes of a first one of the above-described layers may be incorporated into a second one of the layers such that the first layer may be eliminated from the system architecture.
For any of the disclosed systems, methods and devices, the thermally stable polymer of the flexible contact sheet may include a silicone rubber that exhibits negligible deterioration and negligible loss of thermal conductivity at temperatures of at least about 200-250 degrees Celsius (° C.). In addition, the thermally stable polymer may include one or more filler materials interspersed throughout the silicone rubber, e.g., to improve its thermal conductivity and mechanical integrity. This filler material may take on any suitable form, including carbon black, calcium carbonate, boron nitride, alumina, or any combination thereof. For some applications, the flexible contact sheet has a total thickness of about 1 millimeter (mm) or less, and the silicone rubber has a thermal conductivity of at least about 0.1-1.9 watts per meter-kelvin (W/(m·K)).
For any of the disclosed systems, methods and devices, the fibrous material of the rigid cover sheet includes carbon fibers, glass fibers, aramid fibers, basalt fibers, or any combination thereof. In a specific instance, the fibrous material is a carbon-fiber mat or sheet with unidirectional or multidirectional carbon fibers. The thermally conductive resin of the rigid cover sheet may include a thermoset polymer or a thermoplastic polymer; in either instance, the rigid cover sheet resin is different from the resin used in the FRP structure under repair. The rigid cover sheet material may include metals, plastics and composites; and the composite rigid cover may include a fibrous composite.
For any of the disclosed systems, methods and devices, the electric heating element includes an integrated electrical heating sheet. For at least some implementations, the heating sheet includes a pair of polymeric sheet layers with a resistance heating coil sandwiched between these polymeric layers. In a specific instance, these polymeric sheet layers each includes a silicone rubber material or a polyimide material, and the integrated electrical heating sheet has a total thickness of about 0.1 mm to 5.0 mm or, in some embodiments, 1.0 mm or less. The heating element may also be equipped with a thermal couple that is mounted to the integrated electrical heating sheet and operable to communicate with a system controller.
For any of the disclosed systems, methods and devices, the thermoelectric repair system may employ a repair material or patch that is composed of a resin polymer that nests within and/or presses against the damaged area; the repair material/patch is designed to fuse to the FRP structure in response to heat applied by the electric heating element. The thermoelectric repair system may employ a vacuum bag that covers the electric heating element, rigid cover sheet, and flexible contact sheet, and selectively applies a predetermined vacuum pressure to the contoured surface of the FRP structure. As yet another option, the repair system may employ a backing die with a forming surface that is contoured to seat against and conform to a second (underside) contoured surface of the FRP structure that is opposite the contoured surface of the FRP structure.
Additional aspects of this disclosure are directed to methods for assembling and methods for operating any of the disclosed repair systems. In an example, a method is presented for repairing a damaged area of a contoured surface of a fiber-reinforced polymer structure. This representative method includes, in any order and in any combination with any of the above or below disclosed features and options: placing a flexible contact sheet on the FRP structure such that a textured contact surface of the flexible contact sheet seats against the contoured surface and overlays the damaged area of the FRP structure, the flexible contact sheet including a thermally stable polymer; placing a rigid cover sheet on the FRP structure such that a complementary contoured surface of the rigid cover sheet conforms to the FRP structure's contoured surface and covers the flexible contact sheet, the rigid cover sheet including a fibrous material impregnated with a thermally conductive resin; placing an electric heating element against the rigid cover sheet; and applying, via the electric heating element to the FRP structure through the rigid cover sheet and flexible contact sheet, a substantially uniform heating profile. The applied heat is sufficient to soften and/or melt at least a bordering area of the FRP structure's contoured surface neighboring the damaged area.
The above summary is not intended to represent every embodiment or every aspect of the present disclosure. Rather, the foregoing summary merely provides an exemplification of some of the novel concepts and features set forth herein. The above features and advantages, and other features and attendant advantages of this disclosure, will be readily apparent from the following detailed description of illustrated examples and representative modes for carrying out the present disclosure when taken in connection with the accompanying drawings and the appended claims. Moreover, this disclosure expressly includes any and all combinations and subcombinations of the elements and features presented above and below.
The present disclosure is amenable to various modifications and alternative forms, and some representative embodiments have been shown by way of example in the drawings and will be described in detail herein. It should be understood, however, that the novel aspects of this disclosure are not limited to the particular forms illustrated in the above-enumerated drawing. Rather, the disclosure is to cover all modifications, equivalents, combinations, subcombinations, permutations, groupings, and alternatives falling within the scope of this disclosure as encompassed by the appended claims.
This disclosure is susceptible of embodiment in many different forms. There are shown in the drawings and will herein be described in detail representative embodiments of the disclosure with the understanding that these illustrated examples are provided as an exemplification of the disclosed principles, not limitations of the broad aspects of the disclosure. To that extent, elements and limitations that are described, for example, in the Abstract, Introduction, Summary, and Detailed Description sections, but not explicitly set forth in the claims, should not be incorporated into the claims, singly or collectively, by implication, inference or otherwise. For purposes of the present detailed description, unless specifically disclaimed: the singular includes the plural and vice versa; the words “and” and “or” shall be both conjunctive and disjunctive; the words “any” and “all” shall both mean “any and all”; and the words “including” and “comprising” and “having” shall each mean “including without limitation.” Moreover, words of approximation, such as “about,” “almost,” “substantially,” “approximately,” and the like, may be used herein in the sense of “at, near, or nearly at,” or “within 0-5% of,” or “within acceptable manufacturing tolerances,” or any logical combination thereof, for example.
Referring now to the drawings, wherein like reference numbers refer to like features throughout the several views, there is shown in
Thermoelectric repair system 10 is designed to fix and restore the damaged area 16 to a substantially defect-free complex-geometry surface (i.e., one without perceptible structural or superficial imperfections). Seated on top of the contoured surface 14 is a flexible contact sheet 18 that overlays and, in some implementations, directly contacts the damaged area 16 of the FRP structure 12. This flexible contact sheet 18 is fabricated from an elastic, thermally stable polymer. For at least some implementations, the thermally stable polymer of the flexible contact sheet 18 includes (or consist essentially of) a silicone rubber that may exhibit superior thermal stability, high thermal conductivity, tactile compressibility and, if so desired, general resistance to chemicals, oils, debris and dirt. For example, it may be desirable that the silicone rubber exhibit negligible mass deterioration and negligible loss of thermal conductivity at temperatures of at least about 200° C. or, for some applications, at temperatures of at least 250° C. In addition, the silicone rubber may exhibit a thermal conductivity of at least about 0.1 to 1.9 watts per meter-kelvin (W/(m·K)).
Thermal stability and conductivity, as well as tear and tensile strengths of the flexible contact sheet 18, may be selectively modified by adding one or more filler materials to the silicone rubber matrix. By way of non-limiting example, the filler material may comprise, in any combination, carbon black, calcium carbonate, boron nitride, silica, clay, graphite, alumina and/or other filler suitable for the intended application. In a specific example, mixed-particle-size boron nitride powder interspersed in a controlled weight ratio improves thermal conductivity and coefficient of thermal expansion for silicone rubber composites. For at least some embodiments, the flexible contact sheet 18 has a total thickness T1 of about 0.1-1.5 millimeters (mm) or less, which may be substantially uniform over the length and width thereof. Desired stretchability and compressibility may be achieved with a polymer Shore A durometer hardness of about 80 or less or, in at least some embodiments, about 20-40 Shore A.
With continuing reference to
To prevent deformation of the contoured panel when it is heated to softening during the repair process, to prevent the surface texture of the heating element from being imprinted onto the panel surface, and to facilitate uniform surface heating with improved in-plane thermal conductivity that will help to preclude formation of localized hot or cold spots, the thermoelectric repair system 10 employs a rigid cover sheet 22 that is placed over the damaged area 16, seated against the FRP structure's contoured surface 14. With this arrangement, the flexible contact sheet 18 is sandwiched between the rigid cover sheet 22 and FRP structure 12. According to the representative architecture of
Rigid cover sheet 22 is fabricated with a complementary (lower) surface 24 that is shaped and sized to conform to the contoured exterior surface 14 of the FRP structure 12; when properly positioned, the cover sheet 22 of
Draped across the rigid cover sheet 22 of
The thermoelectric repair system 12 may employ a variety of different heating devices; the electric heating element 26 of
For applications in which damage has resulted in a loss of or a gap in material, such as where the part suffers a puncture, deep gouge, or sizeable cavity, repair material may be introduced to the damage zone prior to initiating the repair process. In accord with the representative arrangement presented in
Turning next to
Many polymer composite parts, such as cargo bed panels for pickup trucks and industrial vehicles, are formed with elongated channels and other recessed structural features. These recessed features my cause bridging and gaps between the heating element 26 and the contoured surface 114, an example of which is designated generally at 101 in
To complete a repair of a damaged/defective contoured surface of a polymer composite structure, such as the FRP structure 12 of
Aspects of the present disclosure have been described in detail with reference to the illustrated embodiments; those skilled in the art will recognize, however, that many modifications may be made thereto without departing from the scope of the present disclosure. The present disclosure is not limited to the precise construction and compositions disclosed herein; any and all modifications, changes, and variations apparent from the foregoing descriptions are within the scope of the disclosure as defined by the appended claims. Moreover, the present concepts expressly include any and all combinations and subcombinations of the preceding elements and features.
