Patent Description:
Generally, a wind turbine includes a tower, a nacelle mounted on the tower, and a rotor coupled to the nacelle. The rotor generally includes a rotatable hub and a plurality of rotor blades coupled to and extending outwardly from the hub. Each rotor blade may be spaced about the hub so as to facilitate rotating the rotor to enable kinetic energy to be converted into usable mechanical energy, which may then be transmitted to an electric generator disposed within the nacelle for the production of electrical energy. Typically, the blades are fabricated from composite materials formed in a mold. For instance, carbon fiber composite, glass fiber composite, or fiber reinforced plastic preforms can be laid-up and infused with a resin to bond the layers into final form.

Composite infusions are closed-mold processes for fabricating large fiber-reinforced composite structures. In the simplest form, a laminate fiber preform is installed onto a mold surface and sealed with an outer mold surface. A vacuum is applied to remove entrapped air from the preform and resin is then allowed to infuse into the preform and cure. As typical thermosetting resins have high viscosities, processing techniques have been developed to improve the speed and quality of resin infusion. The flow rate v (m/s) of a resin can be expressed as v = -K•ΔP/µ; where K denotes permeability, an index representing the easiness of impregnation into the reinforcing fiber base material with the resin, P denotes the pressure of the resin, and µ denotes the viscosity of the resin. In this formula, ΔP represents the pressure gradient. As the value of permeability increases, it becomes easier to impregnate the reinforcing fiber base material with the resin. It can be seen that the impregnation distance of the resin is proportional to the permeability of the reinforcing fiber base material used and the pressure of the resin and inversely proportional to the viscosity of the resin.

One processing technique uses a flow medium for a faster injection of resin into a fiber layup structure in order to produce a composite. Specifically, flow media are used in order to distribute resin within a fiber layup structure and to increase the injection speed of the resin into the fiber layup structure. Depending on the geometry and the final size of the produced composite component it is often not possible to inject the necessary amount of resin without the use of a flow medium, because the flow resistance of the resin into the fiber layup structure is too large.

A large number of different flow media are known which are usable for a variety of different processing conditions. However, common for these different flow media is the somewhat labor intensive lay-up of the respective flow medium and even more so, the removal of the respective flow medium after the resin within the composite component has been cured. Furthermore, during use, the flow medium absorbs a relative large amount of resin, which must subsequently be discarded.

<CIT> describes systems, methods, and apparatus for controlling a flow of a material through a vehicle component. The apparatus may include a plurality of baffle, each baffle layer of the plurality of baffle layers having a contour, wherein at least one space between at least some of the plurality of baffle layers defines at least one flow path. The apparatus may also include a first plurality of spacers positioned in the at least one flow path, the first plurality of spacers having one or more hydrodynamic properties determined based on a first plurality of dimensions, the one or more hydrodynamic properties determining, at least in part, a second flow property of the at least one flow path. A first flow path may be defined by a first baffle layer and second baffle layer. Moreover, a second flow path may be formed between the second baffle layer and a third baffle layer. Furthermore, a third flow path may be formed between the third baffle layer and a fourth baffle layer. A flow front may be controlled using one or more flow paths of a flow medium.

In one aspect, a method for producing a composite laminate component for a wind turbine is disclosed as initially assembling a laminated structure having at least two reinforced layers and a plurality of interleaf layers positioned adjacent to one of the at least two reinforced layers. Then placing the laminated structure into a mold where resin is sequentially and independently transferred into each layer of the plurality of interleaf layers. Then curing the transferred resin in the laminated structure to form a composite laminate component having the at least two reinforced layers, the plurality of interleaf layers, and cured resin.

In another aspect, the present subject matter discloses a system. The system includes a wind turbine composite laminate component having at least two reinforced layers and a plurality of interleaf layers positioned adjacent to one of the at least two reinforced layers. The system includes a resin infusion manifold comprising independently controlled outlets to the plurality of interleaf layers. The system is configured to sequentially and independently transfer resin into each layer of the plurality of interleaf layers, and cure the transferred resin in the laminated structure to form a composite laminate component comprising the at least two reinforced layers, the plurality of interleaf layers, and cured resin.

In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope of the invention as defined in the appended claims.

In general, the present subject matter discloses systems and methods for fabricating composite laminates by placing high permeability flow media interleaf layers in the thickness of the laminate stack with a dedicated resin feed line for each flow media interleaf layer. Providing a dedicated feed line for each interleaf layer significantly increases the pressure driving force through-thickness which is at least partially responsible for the fill time reduction. Infusion of resin through the composite thickness is accomplished by sequentially triggering the resin feed lines, which can also prevent defect formation in the composite structure. Also, a separation layer, such as a non-porous peel ply section, can be placed between the resin feed lines to prevent defect formation.

The term "fiber" as used herein means thin filamentous fibers, but may also be rovings (fiber bunches), bands of rovings or mats, which may be felt mats of single-fibers or mats of fiber rovings. Alternatively, fiber in the form of non-woven, melt-spun fiber mat or fabric may be impregnated with a modified polyester matrix resin to form a prepreg for use in a variety of fabrication processes. Chopped or milled fibers may also be used. The fibers used in the present invention are preferably glass fibers or carbon fibers. By the term carbon fiber is meant any of the conventional carbonized or graphitized fibers obtained by known processes from such organic fiber or filament precursors as rayon, polyacrylonitrile (PAN), pitch or the like.

The term "resin" as used herein means a natural or synthetic resin or a suitable polymer. The resin can be a combination of a liquid ethylenically unsaturated monomer and unsaturated polyester to form a polyester resin composition. The resin can also be a polyester, vinyl ester and epoxy resin. However, the resin in the context of the present invention can also be a combined system including other chemicals such as catalysts, hardening agents, accelerator and additives (e.g. thixotropic, pigment, filler, chemical/fire resistance, etc.).

The term "curing" as used herein means that the resin becomes a chemically resistant hard solid. The molecules in the resin will cross-link assisted by catalysts or hardening agents, and the process is a non-reversible chemical reaction.

The term "porous" as used herein is used to describe a material structure filled with voids or pores and relates to a three-dimensional structure allowing flow of a liquid phase in multiple directions of the structure such as a knitted, woven, needled or crocheted, foamed, or filter-like material.

The term "high permeability" is considered intrinsic permeability of a media with values ranging from <NUM> × <NUM>-<NUM> to <NUM> × <NUM>-<NUM> m<NUM>, and "low permeability" is considered values ranging from <NUM> × <NUM>-<NUM> to <NUM> × <NUM>-<NUM> m<NUM>.

Referring now to the drawings, <FIG> illustrates a perspective view of one embodiment of a wind turbine <NUM> of conventional construction. As shown, the wind turbine <NUM> includes a tower <NUM> extending from a support surface <NUM>, a nacelle <NUM> mounted on the tower <NUM>, and a rotor <NUM> coupled to the nacelle <NUM>. The rotor <NUM> includes a rotatable hub <NUM> and at least one rotor blade <NUM> coupled to and extending outwardly from the hub <NUM>. For example, in the illustrated embodiment, the rotor <NUM> includes three rotor blades <NUM>. However, in an alternative embodiment, the rotor <NUM> may include more or less than three rotor blades <NUM>. Each rotor blade <NUM> may be spaced about the hub <NUM> to facilitate rotating the rotor <NUM> to enable kinetic energy to be transferred from the wind into usable mechanical energy, and subsequently, electrical energy. For instance, the hub <NUM> may be rotatably coupled to an electric generator positioned within the nacelle <NUM> to permit electrical energy to be produced.

Referring now to <FIG>, a perspective view of one of the rotor blades <NUM> shown in <FIG> is illustrated. As shown, the rotor blade <NUM> generally includes a blade root <NUM> configured for mounting the rotor blade <NUM> to the hub <NUM> of the wind turbine <NUM> (<FIG>) and a blade tip <NUM> disposed opposite the blade root <NUM>. A body <NUM> of the rotor blade <NUM> may generally be configured to extend between the blade root <NUM> and the blade tip <NUM> and may serve as the outer casing/skin of the blade <NUM>. In several embodiments, the body <NUM> may define a substantially aerodynamic profile, such as by defining a symmetrical or cambered airfoil-shaped cross-section. As such, the body <NUM> may include a pressure side <NUM> and a suction side <NUM> extending between a leading edge <NUM> and a trailing edge <NUM>. Further, the rotor blade <NUM> may have a span <NUM> defining the total length between the blade root <NUM> and the blade tip <NUM> and a chord <NUM> defining the total length between the leading edge <NUM> and the trialing edge <NUM>. As is generally understood, the chord <NUM> may vary in length with respect to the span <NUM> as the rotor blade <NUM> extends from the blade root <NUM> to the blade tip <NUM>.

In several embodiments, the body <NUM> of the rotor blade <NUM> may be formed as a single, unitary component. Alternatively, the body <NUM> may be formed from a plurality of shell components. For example, the body <NUM> may be manufactured from a first shell half generally defining the pressure side <NUM> of the rotor blade <NUM> and a second shell half generally defining the suction side <NUM> of the rotor blade <NUM>, with the shell halves being secured to one another at the leading and trailing edges <NUM>, <NUM> of the blade <NUM>. Additionally, the body <NUM>, the blade root <NUM>, and the blade tip <NUM> may generally be formed from any suitable material. For instance, in one embodiment, the blade root <NUM> may be formed entirely from a laminate composite material, such as a carbon fiber reinforced laminate composite or a glass fiber reinforced laminate composite.

<FIG> and <FIG> depict a portion of thick composite laminated structure <NUM>, such as portion of blade root <NUM>. The laminated structure <NUM> can have at least two reinforced layers <NUM> and a plurality of interleaf layers <NUM> positioned adjacent to one of the at least two reinforced layers <NUM>. To eliminate the risk of premature gelling of infusion resin before the laminated structure <NUM> is filled, and to increase the speed of the resin flow front <NUM> through the laminated structure <NUM> thickness (i.e. eliminate slow infusion), and to reduce the risk of infusion defects, each interleaf layer <NUM> of the thick composite laminated structure <NUM> has a dedicated, isolated, and independent resin feed line <NUM>, <NUM>, <NUM> attached to it. Those resin feed lines <NUM>, <NUM>, <NUM> are sequentially opened during resin infusion, using a predetermined time delay between initiation of resin feed to each subsequent interleaf layer <NUM>, to bring fresh resin into the interleaf layer <NUM> which maximizes the pressure gradient in the resin flow direction as each feed line is sequentially and independently triggered open. As seen in <FIG>, the resin flow front <NUM> can be staggered in the resin flow direction such that the resin flow fronts <NUM> are not in the same vertical plane. Computer simulations and subcomponent field trials have demonstrated about a <NUM>% reduction in resin fill time for a thick composite laminate <NUM>.

For example, at the wind blade root <NUM> section where the thickest laminate is in a blade shell (i.e. root overbuild region), a narrow piece of non-porous (impermeable to resin) peel ply <NUM> can be placed directly underneath an entrance portion of each interleaf layer <NUM> to guide resin flow directly from the dedicated resin feed line <NUM>, <NUM>, <NUM> and avoid potential resin race tracking occurring between the root <NUM> end face of the laminate and the root edge dam surface. The peel ply <NUM> can be in the root overbuild region which can be trimmed off in a secondary operation.

The high permeability interleaf layer <NUM> media can be a continuous fiber mat having an intrinsic permeability in the range of about <NUM> × <NUM>-<NUM> to about <NUM> × <NUM>-<NUM> squared meters. The interleaf layer <NUM> acts as a structural ply and can have its own resin feed line <NUM>, <NUM>, <NUM> that can be triggered individually, independently and sequentially by a resin flow control circuit <NUM>. A resin infusion manifold <NUM> can supply resin <NUM> through control valves <NUM> on each resin feed line <NUM>, <NUM>, <NUM> to sequentially trigger the supply of resin to each resin feed line <NUM>, <NUM>, <NUM>, thereby providing faster resin infusion that is less prone to form infusion defects. The interleaf layer <NUM> structural media can be woven, knitted, open celled foam, sponge-like, mesh-like, filter-like, or combinations thereof. The interleaf layer <NUM> can be an elastic and/or flexible material, which can be inserted in the laminated structure <NUM> not only in a planar but also in a three-dimensionally curved manner, such as corrugated.

As mentioned above, laminated structure <NUM> filling time and the speed of the resin flow front <NUM> for thick laminates is primarily a function of thru-thickness intrinsic permeability (K) and pressure difference driving force, or pressure gradient (ΔP). Pressure gradient (ΔP) decreases as resin flows into the component and movement of flow front <NUM> becomes slower and slower. By independently, individually, and sequentially triggering intermediate resin feed lines <NUM>, <NUM>, <NUM> attached to each high permeability interleaf layer <NUM>, the pressure gradient (ΔP) resets to maximum value and thereby filling the laminate <NUM> faster. High permeability interleaf layers <NUM> assist resin <NUM> flow by quickly transporting resin <NUM> in-plane.

<FIG> is a graph showing a <NUM>st resin feed line (FL) triggered first, then the <NUM>nd, <NUM>rd, and <NUM>th FL's are triggered independently and sequentially by a time delay that can be predetermined in an independent test, for example, by timing the flow front <NUM> to wet the one stack. In the <FIG> embodiment, all stacks of reinforced layers <NUM> are equal thickness and ply. The predetermined time delay for triggering feed line resin flow is graphed as "Percent Total Time" for sequentially transferring the resin into each interleaf layer of this exemplary laminate component. The predetermine time delay between the <NUM>st feed line (FL) and the <NUM>nd FL is about <NUM>% of the total time. The feed line flow predetermined time delay between the <NUM>st interleaf layer <NUM> and the <NUM>rd interleaf layer <NUM> is about <NUM>% of the total time. And the feed line flow predetermined time delay between the <NUM>st interleaf layer <NUM> and the <NUM>th interleaf layer <NUM> is about <NUM>% of the total time.

<FIG> is a table of the laminate component <NUM> fill times, graphed in <FIG>, showing the actual fill time (minutes) being reduced from a baseline actual value of <NUM> minutes to an actual value of <NUM> minutes using independent and sequential resin flow to each interleaf layer <NUM> as disclosed herein. The modeled fill time values closely matched the actual values with a <NUM> minute baseline improved to <NUM> minutes. Both actual and modeled results showed about <NUM>% reduction in fill time for the exemplary component.

The method and system disclosed herein of producing composite laminated structures <NUM> can infuse a curable viscous or liquid resin into the interleaf layers <NUM> with fiber reinforced layers <NUM> layered in the mold. The interleaf layer <NUM> can be a pre-cured solid layer made of a material having a higher intrinsic permeability with respect to the resin than the reinforced layer <NUM>. Although the same material may be used for the interleaf layers <NUM> as is used for the fiber reinforced layers <NUM>, it may be advantageous if a different material is used for forming the interleaf layers <NUM>. This can provide a desired stiffness ratio of the interleaf layers <NUM> to the fiber reinforced layers <NUM> after curing the resin. Additionally, the interleaf layers <NUM> may be corrugated to increase the space available for resin flow.

Claim 1:
A method for producing a composite laminate (<NUM>) component for a wind turbine (<NUM>), comprising;
assembling a laminated structure (<NUM>) comprising at least two reinforced layers (<NUM>) and a plurality of interleaf layers (<NUM>) positioned adjacent to one of the at least two reinforced layers (<NUM>),
placing the laminated structure (<NUM>) into a mold,
sequentially and independently transferring resin (<NUM>) into each layer of the plurality of interleaf layers (<NUM>), and
curing the transferred resin (<NUM>) in the laminated structure (<NUM>) to form a composite laminate component (<NUM>) comprising the at least two reinforced layers (<NUM>), the plurality of interleaf layers (<NUM>), and cured resin (<NUM>).