Large composite structures and a process for fabricating large composite structures

In a process for fabricating large structures, a composite material panel is continuously pultruded in a pultrusion die assembly and cut transversely to the process direction to provide panel sections. The panel sections can be sufficiently long to extend from one end to an opposite end of the structure. The panel sections are assembled with a joint along adjacent edges using steel-to-composite and composite-to-composite joining technology. The joints can be integrated into the panel longitudinal edges, or separate joint assemblies can be fabricated. In this manner, fewer joints are required. A variety of in-plane and out-of-plane joint assemblies are provided.

BACKGROUND OF THE INVENTION

In certain applications, large scale structures such as buildings and ships are fabricated from steel, a traditional structural material. Similarly, a deckhouse on a ship may be fabricated in a shipyard from steel panels. In such structures, a single wall, floor, or ceiling of the building may be formed from a number of steel panels welded together. The entire structure is further welded to the steel deck of the ship.

Compared to steel, composite materials are much lighter in weight and exhibit good corrosion resistance. Composite materials are formed of reinforcing fibers within a resin matrix. Parts fabricated from composite materials can be made strong and stiff and can be used to advantage in structural applications. However, parts fabricated from composite materials are often more costly than steel parts. The higher cost is generally due to the greater cost of the raw materials coupled with greater tooling and labor costs. Also, composite elements are more complex to join than steel plate and frame structures, which are typically joined relatively simply by welding. Thus, the composite materials may not be used to replace steel, even if their benefits would be advantageous in a particular application, due to cost considerations.

The vacuum assisted resin transfer method (VARTM) is a batch process that can be used to form composite materials into complex three-dimensional shapes. This method requires the fabrication of a mold in the final form of the part to the manufactured. The raw material is cut into appropriately sized pieces and laid up in layers in the mold. The distribution media, hoses, vacuum lines and resin lines are set. Then the resin is injected and allowed to cure. The part is then unbagged and demolded. The support materials must then be disposed of and the mold cleaned, and the entire process repeated for the next part. This process is costly due to the higher raw material costs, the hand labor required, single part processing, long cure cycle, and the amount of scrap material generated. Thus, the cost per pound of VARTM composites is high compared to steel fabrication.

Pultrusion is another known fabrication process for forming composite material parts. Pultrusion is generally more suitable for forming two-dimensional shapes. The initial tooling costs can be high, but pultrusion is a continuous process from which many parts can be formed relatively economically with less labor than VARTM. Thus, in certain applications, pultrusion can be more advantageous than VARTM.

Both VARTM and pultrusion are not yet as cost efficient as steel fabrication, however. Thus, a composite material fabrication process that is competitive with steel fabrication for large scale structures would be beneficial.

SUMMARY OF THE INVENTION

The present invention relates to a process for fabricating large structures and to the structures formed by this process. The structures are formed from a plurality of large pultruded structural panels. Composite-to-composite and steel-to-composite joint designs for the edges of the panels are provided for assembling the panels into a structure.

More particularly, a continuous composite material panel is pultruded in a pultrusion die assembly. The continuous panel has opposed longitudinal edges extending in the process direction. After exiting the pultrusion die assembly, the continuous panel is cut transversely to the process direction into panel sections of the desired length for the particular structure. The panel sections are assembled into the desired structure by joining two or more panel sections with a joint along adjacent edges. The joint may be formed by edge details integrated into the panel's longitudinal edges during the pultrusion process and/or by a separate joint assembly that interconnects the adjacent panels along their edges. At least some of the panels may be assembled to extend from one end to an opposite end of the structure. Thus, with the present invention, the number of joints required in the structure as a whole can be minimized.

Thus, the invention provides a cost- and performance-effective alternative to welded steel construction. The steel-to-composite and composite-to-composite joint designs for both in-plane (bulkhead, deck) and out-of-place (deck to bulkhead, bulkhead to bulkhead) panel joints have self-fixturing attributes and high unit load capacities. More structural applications can take advantage of the reduced weight, corrosion resistance and tailored performance benefits of composite materials using the present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1illustrates a multi-level structure, such as a deckhouse for a ship, that can be taken as an example of the present invention. Such a structure10may include perimeter walls12, a bottom floor or deck14, a roof deck16, and intermediate decks or flooring18. The structure may be framed with vertical framing elements20spaced periodically along its length and horizontal or transverse cross beams22at the level of each deck. The structure's outer or perimeter walls may be vertical or tapered somewhat from vertical, as illustrated, depending on the application.

Such a structure may require a variety of in-plane and out-of-plane joint assemblies to attach all of the various panel sections together to arrive at the desired final structure configuration. For example, the perimeter walls of adjacent levels are attached together with in-plane joints. The perimeter walls are attached to the horizontal deck and ceiling panel sections with out-of-plane joints. Interior walls or bulkheads may require a variety of corner joint assembly configurations, depending on the structure's design. Such a structure may also need to be attached to a preexisting foundational surface, such as a steel deck24.

The composite material panels and joint assemblies are formed using a pultrusion process, illustrated schematically inFIG. 2. The pultrusion process generally is known and will not be described in detail herein. Composite materials are typically formed from glass or carbon fibers and polyester, vinyl ester, epoxy, or polyurethane resins, although other materials can be used. The composite material panels can be of any suitable type. They can be sandwich panels with a suitable core material, such as balsa, foam, honeycomb, stitched cores, or fabric-reinforced cores. The panels can be solid laminates without a core, rib-stiffened or blade-stiffed panels, or cellular core panels.

According to the present invention, the pultrusion equipment is preferably located at the site where the structure is to be constructed. On-site fabrication eliminates the need to ship the panels by truck, rail, or barge, which would minimize the size of the panels. For example, panels transported by truck can generally be no longer than 53 feet, and panels transported by rail can generally be no longer than 80 feet. Barged panels can be somewhat longer, but the panel length is still constrained by the barge's capacity. When the pultrusion equipment is located at the construction site, the length of a pultruded panel is essentially unlimited. Portions of a pultruded panels can be cut off to form a panel section of any desired length. Preferably, the panel sections are at least four feet in width and the length in the process direction is at least twice as long as the width. The panels can readily be formed with greater widths, such as eight feet, ten feet, or more. The length of the panel exiting the pultrusion die assembly is essentially unlimited. The panel is cut across the length to form the panel sections of any desired length, such as twenty feet, forty feet, one hundred feet, or more. Panel sections can be several hundred feet long.

The panel sections are assembled into a structure with a joint along adjacent longitudinal edges of the panel sections. The panel can be continuously pultruded with each longitudinal edge in the process direction having joint details integrated therein. Alternatively, a separate joint assembly can be fabricated and used to join two panel sections along adjacent longitudinal edges. The separate joint assembly may be fabricated as a continuous pultrusion that is, like the panel, cut to any desired length. A number of joint details are described with more particularity below. Preferably, at least a portion of the panel sections are assembled to extend from one end to an opposite end of the structure. See, for example, panel sections12inFIG. 1. In this manner, the number of joints in the structure can be minimized.

One embodiment of an assembly process for a structure is illustrated inFIGS. 3A-3C. The structure shown has four levels, although any desired number of levels could be provided. Similarly, the structure shown has tapered walls, although the walls could be vertical if desired. Also, in the process shown, the structure is assembled on a foundation surface, such as a steel deck. The structure can be, for example, several hundred feet long.

In the first step, a steel frame30outlining the perimeter of the enclosure is welded to the steel deck32. The steel frame includes a joint assembly between the horizontal steel deck and the vertical composite perimeter panels, described further below. In step2, wall, floor, and ceiling frame members34, either composite or steel, are attached to the deck plate frame. Next, a first level of long pultruded composite perimeter panel sections36are attached in any suitable manner, such as with mechanical fasteners or adhesive bonding or both, to the vertical frame members. Then, long pultruded joint assemblies38are attached to the upper edges of the long perimeter panel sections. Alternatively, the longitudinal lengths of the panel sections can be pultruded with the joint details integrated therein, eliminating the need for a separate joint assembly. The joint between two wall panel sections and a deck panel section is illustrated with more particularity inFIGS. 5A and 5B. In this example, the joint assembly is cut out to accommodate the vertical framing elements.

In step5, a long pultruded deck panel section40is slid onto the deck beams34. A plurality of long deck panel sections can be used, placed with the long edges adjacent, if the width of the floor is greater than the width of a pultruded deck panel section. Next, a second level of long pultruded composite perimeter panel sections42are attached to the joint assembly along the upper edge of the first level of perimeter panel sections, as by adhesive bonding, mechanical fastening, or both. Then, long joint assemblies44are attached to the upper edges of the long perimeter panel sections of the second level. In step8, a long pultruded deck panel section (or panel sections)46is slid into place.

In step9, a third level of continuous long pultruded composite perimeter panel sections48are attached to the joint assembles44along the upper edges of the second level of perimeter panel sections42. Next, long joint assemblies50are attached to the upper edges of the third level of perimeter panel sections. The next deck panel section (or panel sections)52is slid into place. The final perimeter panel sections54are attached to the upper edges of the third level perimeter panel sections, and a final panel edge connector56is installed on the joint assembly along the top edge of the perimeter panel sections. The upper level deck panel section is then slid into place. End walls60are added at each end.

In another variation of the assembly process, illustrated inFIGS. 4A-4B, a base frame is welded to the steel deck and vertical frame members are installed as above. However, only the lowest level of transverse deck beams are installed in step2. After installation of the first level of perimeter panel sections, a deck panel section can be dropped in vertically along the continuous length without interference from the pre-installed transverse deck beams for the upper level decks. The transverse deck beams are then installed following the installation of the deck panel sections for the level immediately below. This process avoids the need to slide the deck panel sections into place.

In a further alternative assembly process, the structure is assembled upside down, illustrated inFIGS. 6A-6D. In this process, the upper perimeter corner joint pieces are laid out. The top deck panel section is laid down. As above, several deck panel sections can be laid down with a longitudinal panel to panel joint therebetween if necessary. Then, transverse beams or joists are laid out. The vertical frame elements are assembled with appropriate fixturing. Top interior deck space bulkheads are assembled in their desired positions. In step6, top deck panel sections are laid onto bulkhead edges and frame tabs. It will be appreciated that the interior bulkheads can be formed from pultruded panel sections and using the joint technology of the present invention.

Top deck space perimeter panel sections or bulkheads are attached to the upper perimeter joint pieces. Interdeck joints are attached to the edges of the perimeter panel sections in step7. Top deck supporting cross members or joists and then third deck space bulkheads are added. Next, a third deck is added. In step11, third deck perimeter panel sections or bulkheads and interdeck joints are added. Third deck supporting frame cross members are added. Second deck space interior bulkheads are placed in their desired locations, and a second deck is added. In step15, second deck perimeter panels or bulkheads are added. Then, second deck supporting frame cross members are placed. In step17, first deck space interior bulkheads are added. Next, the first deck perimeter panels and bulkheads are placed and the main deck joint piece added. Then, the entire assembled structure is turned over in place and fixed to the supporting deck.

A variety of joint assemblies suitable for use in structures such as described above are illustrated inFIGS. 7-27. The joint assemblies are illustrated as pieces separate from the panel sections. However, it will be appreciated that the joint details of these joint assemblies can be readily integrated into the longitudinal, or process direction, edges of the continuous panel during the pultrusion process. For ease of description, the joint details are described in conjunction with separate joint assemblies.

In the assembly of the structure, the elements of the joint assembly and the panel sections are fastened in any suitable manner, such as with a suitable bonding agent, such as epoxy, mechanical fasteners, or a combination of joining methods. Mechanical fasteners can suitably be used to provide integrity while the bonding agent is curing. Mechanical fastening can include fasteners such as bolts or screws, or can include devices that snap together or other interlocking elements integrally formed on corresponding portions of the joint to prevent removal once fitted together. By integrating interlocking elements into the joints, the joints can be self-fixturing.

A panel-to-panel-to-deck joint assembly80is illustrated inFIG. 7. This joint assembly joins two linearly aligned panel or plate-like structures82,84with a third panel or plate-like structure86, such as a deck, at an angle. In the embodiment illustrated, the joint assembly is formed in two pieces, a joint member88and an angle member90. The joint member includes a lineal piece92and a ledge or flange94. The lineal piece includes two recesses96,98to receive the two panels82,84that are linearly aligned. The angle member90sandwiches the edge of the third panel86, such as a deck element, against the joint ledge or flange94. The joint member and angle member are preferably pultruded to any length desired. In assembly, the deck panel is laid against the flange and the angle member placed against the deck panel. The colinear panels are inserted into the recesses. All the elements are suitably fastened. The joint assembly could be formed as one unitary piece with the angle piece integral with the joint member if desired. In this case, the deck panel is slid or otherwise inserted into the recess between the flange and the angle piece.

The three panel structures can be formed of a composite material or a metal such as steel. The joint assembly is particularly suitable for joining composite material panels to a steel deck or composite panel. In the embodiment illustrated, the panels82,84are a sandwich type having a core102and face skins104. The long edges106are tapered, and the face skins wrap around and cover the long edges. The tapered edge improves load transfer across the joint and can be readily formed in a composite material fabrication process. The deck element86is illustrated with a rectangular edge, although its edge could be tapered as well.

FIG. 8illustrates a joint assembly110in which the lineal piece112is disposed at other than a right angle with respect to the flange114, which is suitable for use with perimeter walls angled from vertical, as shown above inFIG. 1.FIG. 9illustrates a joint assembly120in which the colinear panels have been recessed along their long edges122so that the lineal piece124of the joint assembly lies flush with the outer surface of the panels.FIG. 10illustrates a joint assembly130in which the deck panel132has been recessed to receive the angle member134.

A joint assembly140for joining four panels at right angles is illustrated inFIG. 11. This joint assembly is suitable, for example, as an internal bulkhead corner joint. This joint assembly includes four flanges144extending from a central hub146. Each flange has a recess for receiving a panel structure148. The joint assembly can be suitably formed by pultrusion using suitable insert dies150,151(shown in phantom) to form the recesses and each corner. A number of rods152can be placed in the central hub for strengthening in the joint assembly.FIG. 12illustrates a joint assembly160in which the recesses162in the flanges164are tapered to receive panels166having tapered cores168that fit into the recesses and face sheets170that extend over the flanges of the joint assembly.FIG. 13illustrates a joint assembly180in which the panel edges182can be recessed and the flanges184can be configured to lap the recessed edge. As will be apparent, a combination of flange designs can be used. Additionally, less than four flanges may be provided if desired. For example,FIG. 14illustrates a joint assembly190having two flanges for joining two panels at a corner.

A further joint assembly200for joining two panels at a corner is illustrated inFIG. 15. This joint assembly includes two flanges202integrally joined to form a corner204of any desired angle, such as a right angle as shown, and a beam member206configured to fit against the panel members208within the corner. Although a right angle joint is illustrated, it will be appreciated that any desired angle can be provided. In this embodiment, the flanges are tapered, and the panel edges are recessed to fit over the tapered flanges. The recessed edges may be formed during the pultrusion process, or recesses may be machined into the edges subsequently. The panels and the joint assembly are fastened in any suitable manner, such as described above. In an alternative embodiment of a joint assembly210illustrated inFIG. 16, the flanges212can be formed separately and fastened together, such as with a mortise and tenon joint214.

A further corner joint assembly220is illustrated inFIG. 17. This joint assembly includes an outer corner member222and an inner corner member224. The outer corner member is fastened to the outer corner formed by two panels226,228butted together. The inner corner member is fastened to the inner corner formed by the two panels. The inner corner member may include additional reinforcing material for strengthening if desired.

FIG. 18illustrates a joint assembly230in which four inner corner members232are arranged to fasten three panels together to form four corners. Two panels234,236are butted against a third panel238along an interior portion thereof.

Still further embodiments of joint assemblies are illustrated inFIGS. 19-25.FIG. 23illustrates a joint assembly that is formed from the parts illustrated inFIGS. 19 and 20.FIG. 24illustrates a joint assembly that is formed from the parts illustrated inFIGS. 20 and 21.FIG. 25illustrates a joint assembly that is formed from the parts illustrated inFIGS. 20 and 22. Thus, in these cases, a common right angle part is used to close each joint. It will be appreciated that other joint configurations are possible, and the particular joint configuration will be selected based on the configuration and strength requirements of the structure.

FIG. 26illustrates an embodiment of a joint assembly240in which the joint details are integrally formed into the longitudinal edges242,244of the panels246,248during pultrusion. One edge244includes a male portion and the opposite edge242includes a female portion. A tab250and mating recess252are also included to provide interlocking of the two portions.

A joint assembly260that is particularly suitable for joining a composite panel262to a steel deck264is illustrated inFIG. 27. This joint assembly includes two recesses266,268extending in a direction of elongation. The recesses are preferably tapered. A steel coaming structure270is welded, brazed, riveted, or attached in any other suitable manner to the steel deck264. If the steel deck is curved, the lower edge of the steel coaming structure can be curved to mate with the steel deck. The upper edge272of the coaming structure is straight and tapered to form a wedge274that fits within the correspondingly tapered lower recess266of the joint assembly. A lower edge276of a composite panel fits within the upper recess. In this way, a composite panel having a straight lower edge can be fitted to a curved or irregular steel deck. The coaming structure extends a sufficient distance above the deck so that it may be readily inspected and so that debris or moisture cannot collect. In an alternative, the lower edge of the composite panel can be formed with a lower recess to receive the upper edge of the coaming structure.

Another method for accommodating the complex curvatures of a foundational surface such as a ship's deck is illustrated inFIGS. 28-30. A panel is continuously pultruded with a constant cross section. The pultruded panel is cut into sections290having the desired lengths for the structure. Each panel is trimmed to mate the edge to the existing curvature, as illustrated inFIG. 29. The joints between the structure and the foundational surface can be formed using a vacuum assisted resin transfer method. In this case, panels are fixed into position (seeFIG. 30), fabric materials to form the joint are positioned in the joint area, the joint area is bagged, and resin is infused along the joint length. This results in a joint that is able to accommodate any local irregularities.

The joint assemblies of the present invention can also be fabricated to provide good electromagnetic interference (EMI) shielding. The panels and the joint assembly can be pultruded with their outermost ply or plies including conductive fibrous or metallic layers and/or conductivity-enhancing particulate fillers. Referring, for example, toFIG. 7, by tapering the recesses in the lineal piece, the joint assembly's outermost plies can extend beyond the joint edge, thereby covering the seam between the joint assembly and the panels. Suitable conductivity-enhancing layered materials include, for example, fabrics and felts made with electrically conductive metal fiber, solid or perforated thin metal foils, and fabric and felts made with metal-coated glass or carbon fiber. Layers of conductive fiber or felt can also provide some mechanical strength and stiffness.

Conductivity-enhancing particulate fillers include, for example, carbon black and various forms of particulate graphite, metal coated particles or metal flakes, or carbon nanotubes and nanofibers. The fillers contribute to overall EMI shielding effectiveness by virtue of the inherent electrical conductivity, and by providing additional conductive paths between the reinforcing fabrics, felts or perforated sheets. Carbon nanotubes and nanofibers can provide electrical conductivity enhancement at relatively low particulate loadings. Carbon black is an excellent UV inhibitor and produces a gray color, reducing the need for painting.

Locating the EMI shielding layer as the outermost ply reduces the risk associated with delamination of the laminate due to lightning strikes. Metallic fabric or felt surfaces also provide a continuous membrane for EMI shielding and good surface area at joints for grounding composite structures to steel hull structures. Also, repeated cyclic loading can lead to the development of microcracks, which create discontinuities in the EMI shield, leading to leaks. Metallic fabrics or felts can provide additional grounding paths across areas of microcracking.

It will be appreciated that the present invention is applicable to a variety of large-scale structures in addition to buildings and ships, such as rail cars, building facades, tunnel liners, bridges, or piers. At least a portion of a ship's hull can be formed according to the invention. The invention is not to be limited by what has been particularly shown and described, except as indicated by the appended claims.