Patent Description:
Wind turbine generators are used to produce electrical energy using a renewable resource and without combusting a fossil fuel. A wind turbine generator converts kinetic energy from the wind into electrical energy, and includes a tower, a nacelle mounted atop the tower, a rotor hub rotatably supported by the nacelle, and a plurality of rotor blades attached to the hub. The hub is coupled to a generator housed inside the nacelle. Consequently, as wind forces the blades to rotate, electrical energy is produced by the generator. In recent years, wind power has become a more attractive alternative energy source and the number of wind turbines, wind farms, etc. has significantly increased, both on land and offshore. Additionally, the size of wind turbines has also significantly increased, with modern wind turbine blades extending between <NUM> to <NUM> meters or more in length, and the length of wind turbine blades is expected to further increase in the future.

Modern wind turbine blades have a construction that typically includes an outer shell and a spar structure located inside the outer shell. The outer shell provides the aerodynamic aspect of the blade and includes a profile configured to generate lift from the oncoming wind that ultimately causes the blades to rotate. The outer shell typically has a laminate composite construction of a plurality of fiber layers, one or more core materials embedded within the fiber layers, and a resin matrix, and includes a windward half shell and a leeward half shell bonded together at leading and trailing edges of the blade. The spar structure on the inside of the blade provides the load-bearing aspects of the blade. In one known arrangement, the spar structure includes a pair of spar caps and one or more shear webs extending therebetween. The spar caps may be arranged in opposing relation across the height of the blade, with one spar cap being associated with the windward shell half and the other spar cap being associated with the leeward shell half. The spar caps may be integrated into the outer shell such that the spar caps form a portion of the outer shell. Alternatively, the spar caps may be adhesively bonded to an inner surface of the outer shell. The spar caps extend longitudinally along the majority of the length of the wind turbine blade, and in one arrangement may be formed from a stack of pultruded strips of carbon-fiber reinforced plastic.

The shear web is connected between the spar caps and includes an intermediate web and first and second flanges provided at respective first and second ends of the intermediate web. As such, the shear web is substantially I-shaped in cross section and bridges the gap between the windward and leeward sides of the outer shell. The flanges are oriented transversely to the intermediate web when viewed in cross section and provide a means for mounting the shear web between the opposed spar caps. In this regard, the flanges are configured to be bonded to the spar caps by means of adhesive. In one known arrangement, the first and second flanges may be formed from a T-shaped pultrusion of carbon-fiber reinforced plastic and include a foot and an upstand, where the foot forms the flange and the upstand facilitates a connection of the foot to the intermediate web. The intermediate web typically has a laminate composite construction of a plurality of fiber layers, one or more core materials embedded within the fiber layers, and a resin matrix. Depending on the size of the blade and expected loads, the spar structure may include more than one shear web extending between the opposed spar caps.

The outer shell is typically made through a moulding process using a windward mould half and a leeward mould half. In this regard, the fiber layers, such as glass and/or carbon fiber layers, and the core material, such as various foam and/or wood cores, may be laid in the moulds (along with the spar caps when such spar caps are integrated into the outer shell) and resin is admitted into the moulds in a vacuum-assisted resin transfer moulding process (VARTM). The shell halves are then cured within the respective mould halves. The shear web, and more particularly at least the intermediate web thereof, is also typically made through a moulding process using a separate mould tool. In a similar manner, fiber layers, core material, and the T-shaped pultrusions may be laid in the mould tool and resin is admitted into the mould in a vacuum-assisted resin transfer moulding process. The shear web is then cured within the mould. To form the blade, the shear web may be positioned within one of the blade mould halves and one of the flanges of the shear web adhesively bonded to the spar cap associated with the respective shell half. The other shell half (not having the shear web) may then be juxtapositioned relative to the mould half including the shear web. The outer shell may be adhesively bonded along the leading and trailing edges of the blade and the other flange of the shear web may be adhesively bonded to the spar cap associated with the other shell half.

While the wind turbine blade described above and the method of manufacturing the wind turbine blade has proven successful, wind turbine blade manufacturers continually seek improved designs and manufacturing methods, especially as the size of wind turbine blades is expected to increase. In this regard, current manufacturing processes have inherent limitations to design improvements for wind turbine blades. For example, current moulding processes primarily rely on laminate composite constructions (e.g., fiber layers, core material, and resin) for making the outer shell and shear webs of wind turbine blades. Thus, the manufacturing process itself results in certain design constraints that limit a manufacturer's ability to improve wind turbine blade performance.

Additionally, current moulding processes for wind turbine blades lack adaptability that further limits wind turbine blade design. As one can appreciate from a scale perspective, the time and capital investment for producing windward and leeward mould halves and the associated fixtures and equipment for handling the mould halves (e.g., to overturn one mould half relative to the other mold half) are prohibitive. This slow time scale and large capital investment inherent in mould-making not only increases the overall cost of the product offering (e.g., a wind turbine or wind turbine blade) but also limits the ability of a manufacturer to make changes to a blade design during the product life cycle (i.e., cast moulds cannot be easily or cost-effectively altered to accommodate design changes). Thus, a manufacturer has to be fully committed to a certain blade design for an extended period of time in order to obtain a reasonable return on that investment. Inherent aspects of the moulding process and the inability to make changes during the product life cycle often require that the blade be over constrained in its design. More particularly, instead of a detailed, localized design configuration of, for example, the outer shell or the shear web, based on (expected) localized load conditions on the blade, more global design configurations are used that satisfy worst-case load constraints for critical areas of the blade. Thus, much of the blade includes a design configuration that is over constrained for the loads expected in those sections of the blade. This not only represents an unnecessary increase in materials costs (e.g., fiber, resin and core material), but may also represent an unnecessary increase in the overall weight of the shear web and blade.

Furthermore, the loads imposed on the outer shell of the wind turbine blade during use are ultimately transferred to the root end of the blade via the internal spar structure. However, much of that load transfer between the outer shell and the spar structure occurs over a relatively small area of the flanges centered about the shear web (e.g., an I-shaped shear web) and the outer portions of the flanges away from the shear web carry only a small fraction of the load. This results in poor load distribution and high peak loads in the adhesive bond between the flanges of the shear web and the spar caps.

US <NUM>/<NUM> A1 discloses a wind turbine rotor blade with shear web that includes a lattice structure.

In view of the above, manufacturers seek an improved method for making a wind turbine blade, including a method of making a shear web for a wind turbine blade, that overcomes the limitations of current moulding processes. Manufacturers also seek an improved wind turbine blade component, including a relatively strong and light weight shear web, that provides detailed, localized design configurations based on expected load conditions and improved load distributions in the bond region between the shear web and the spar caps.

A shear web for a wind turbine blade that addresses the above deficiencies is disclosed. The shear web includes a lower flange, an upper flange, and a web structure extending between the lower and upper flange. At least one of the lower flange, upper flange, and the web structure includes an open lattice structure having a plurality of elongate fibrous composite spindles intersecting each other at multiple nodes of the open lattice structure. The open lattice structure associated with the shear web may be formed by a continuous fiber-reinforced additive manufacturing process. The open lattice structure provides wind turbine blade components having significantly improved strength-to-weight performance and generally cannot be formed using conventional moulding techniques used in wind turbine blade manufacturing. Moreover, the additive manufacturing process for the blade component provides greater design flexibility and adaptability in blade design not otherwise attainable in current manufacturing processes.

The web structure includes a three-dimensional open lattice structure extending between the lower and upper flanges, wherein the plurality of elongate fibrous composite spindles extends in three dimensions. The arrangement of the fibrous composite spindles may be unstructured, having no observable pattern or ordered building block that forms the open lattice structure. Alternatively, the arrangement of the spindles may be structured, having an identifiable pattern or building block that forms the open lattice structure. For example, in one embodiment, the spindles may be organized into a plurality of panels (i.e., a panel is a building block of the open lattice structure). The web structure includes a plurality of first open lattice panels and a plurality of second open lattice panels, wherein the plurality of first panels intersects the plurality of second panels at multiple nodes to define the three-dimensional open lattice structure. In an exemplary embodiment, the plurality of first and second panels may be arranged to be substantially perpendicular to each other.

In one embodiment, each of the plurality of first panels defines a first extension direction and may include a plurality of spindles that are arranged generally non-perpendicular to the first extension direction in criss-cross fashion (e.g., cross spindles). Additionally, each of the plurality of first panels may include spindles that are generally arranged perpendicular to the first extension direction (e.g., normal spindles). A distribution of spindles may be non-uniform in the first extension direction and be based on a load condition of the shear web. For example, both distributions of normal spindles and cross spindles may be non-uniform in the first extension direction and may be based on a load condition of the shear web. More specifically, in the first extension direction, a density of spindles (e.g., cross spindles and/or normal spindles) in high load regions of the shear web may be greater than the density of spindles in low load regions of the shear web.

Further to this embodiment, each of the plurality of second panels defines a second extension direction and includes a plurality of spindles that are arranged generally non-perpendicular to the second extension direction in criss-cross fashion (e.g., cross spindles). Additionally, each of the plurality of second panels may also include a plurality of spindles that are arranged generally perpendicular to the second extension direction (e.g., normal spindles). A distribution of spindles in each of the plurality of second panels may be substantially uniform in the second extension direction and may be based on providing a more uniform load across the shear web, for example. More specifically, in the second extension direction a density of spindles may be substantially uniform.

In one embodiment, the plurality of second panels may be non-uniformly distributed in the first extension direction and may be based on a load condition of the shear web, for example. More specifically, in the first extension direction, a density of second panels in high load regions of the shear web may be greater than the density of second panels in low load regions of the shear web.

In another embodiment, at least one of the lower and upper flanges includes an open lattice panel oriented to extend in the first extension direction. In this embodiment, the open lattice panel forming the at least one of the lower and upper flanges includes a plurality of spindles (e.g., cross spindles and/or normal spindles) arranged relative to the first extension direction. A distribution of spindles in the panels may be non-uniform in the first extension direction and be based on a load condition of the shear web. More specifically, in the first extension direction, a density of spindles in high load regions of the shear web may be greater than the density of spindles in low load regions of the shear web.

In another embodiment, an end of the lower and upper flanges of the shear web which is configured to be located adjacent a root end of the wind turbine blade may include an extension tab. In one embodiment, the extension tab may include a widened portion configured to increase a bonding surface area of the shear web. Moreover, at a transition region adjacent the end of the shear web, the spindles extending from the lower and upper flanges may have a swept or scalloped configuration. These features in the end of the shear web at the root end of the blade are configured to reduce peel loads between the shear web and the outer shell of the wind turbine blade.

In a further aspect of the invention, the shear web may have a hybrid construction with some aspects of the shear web having a conventional construction and other aspects of the shear web having an open lattice construction formed by a continuous fiber-reinforced additive manufacturing process. By way of example, in one embodiment, the web structure may have a laminate composite construction, the lower and upper flanges may have a laminate composite construction or pultruded construction, and the open lattice structure may be formed on at least one surface of the lower flange, upper flange, and the web structure. In an exemplary embodiment, the web structure may include first and second opposed surfaces, and the open lattice structure may be formed on each surface of the web structure. In another embodiment, each of the lower and upper flanges may include an outer surface, and the open lattice structure may be formed on the outer surface of each of the lower and upper flanges.

In a further embodiment, a wind turbine blade having a shear web as described above is disclosed. In one embodiment, the wind turbine blade may have a sectional blade design and include a first blade section and a second blade section configured to be joined at a connection interface. The first and second blade sections include a first shear web portion and a second shear web portion, respectively, wherein at least the web structure of the first shear web portion and the web structure of the second shear web portion are configured to connect with each other in a nesting relationship when the first and second blade sections are joined together. The arrangement of the fibrous composite spindles in the web structure of the first shear web portion and the arrangement of the spindles in the web structure of the second shear web portion are such that spindles of the shear web are substantially aligned across the connection interface when the blade sections are joined. This arrangement provides continuous lines of force between the lower and upper flanges across the connection joint. A wind turbine having a wind turbine blade as described above is also disclosed.

In yet another embodiment, a method of making a shear web for a wind turbine blade is disclosed. The method includes providing a lower flange; providing an upper flange; providing a web structure configured to extend between the lower and upper flanges; forming at least one of the lower flange, upper flange, and web structure web structure with an open lattice structure having a plurality of elongate fibrous composite spindles intersecting each other at multiple nodes of the open lattice structure; connecting the lower flange to a lower end of the web structure; and connecting the upper flange to an upper end of the web structure. The open lattice structure is formed by a continuous fiber-reinforced additive manufacturing process.

According to the invention, the forming step further includes forming the web structure as a three-dimensional open lattice structure having a plurality of fibrous elongate composite spindles extending in three dimensions. For example, in an exemplary embodiment, forming the web structure as a three-dimensional open lattice structure further includes forming a plurality of first open lattice panels; forming a plurality of second open lattice panels; orienting the plurality of first open lattice panels; and orienting the plurality of second open lattice panels such the plurality of first panels intersects the plurality of second panels at multiple nodes to define the three-dimensional open lattice structure.

In one embodiment, forming the plurality of first panels may further include, for each of the plurality of first panels, forming a plurality of spindles arranged generally non-perpendicular to the first extension direction in criss-cross fashion (e.g., cross spindles). The method may also include, for each of the plurality of first panels, forming a plurality of spindles arranged generally perpendicular to the first extension direction (e.g., normal spindles). In an exemplary embodiment, the method may include non-uniformly distributing the spindles in the first extension direction based on a load condition of the shear web, for example. More specifically, the method may include, in the first extension direction, providing a density of spindles in high load regions of the shear web greater than the density of the spindles in low load regions of the shear web.

In a further embodiment, forming the plurality of second panels may further include, for each of the second plurality of panels, forming a plurality of spindles arranged generally non-perpendicular to the second extension direction in cross-cross fashion (e.g., cross spindles). The method may also include, for each of the plurality of second panels, forming a plurality of spindles arranged generally perpendicular to the first extension direction (e.g., normal spindles). In an exemplary embodiment, the method may include substantially uniformly distributing the spindles in the second extension direction to more uniformly distribute forces across the shear web, for example. More specifically, the method may include in the second extension direction, providing a density of spindles in high load regions of the shear web greater than the density of spindles in low load regions of the shear web.

In another embodiment, the method may include substantially uniformly distributing the plurality of first panels in the second extension direction. More specifically, the method may include, in the second extension direction, providing a substantially uniform density of the plurality of first panels.

In a further embodiment, providing the lower flange and the upper flange may further include, for each flange, forming an open lattice panel and orienting the panel in the first extension direction, wherein the open lattice panels that form the lower and upper flanges are formed by a continuous fiber-reinforced additive manufacturing process.

In one embodiment, forming the panels for the lower and upper flanges may further include, for each of the panels, forming a plurality of spindles relative to the first extension direction (e.g., cross spindles and/or normal spindles). In one embodiment, the method includes non-uniformly distributing the spindles in the first extension direction based on a load condition of the shear web, for example. More specifically, the method may include, in the first extension direction, providing a density of spindles in high load regions of the shear web greater than the density of the spindles in low load regions of the shear web.

In a further embodiment, providing the lower and upper flanges further includes forming an extension tab on each of the lower and upper flanges. In one embodiment, forming the extension tab includes forming the extension tab with a widened portion to increase the bonding surface area. In a further embodiment, the method may include arranging the spindles extending from the lower and upper flanges in a scalloped configuration adjacent the end of the lower and upper flanges including the extension tab.

In still a further embodiment, the method may include forming the lower and upper flanges from a laminate composite construction or a pultruded construction; forming the web structure from a laminate composite construction; and forming the open lattice structure on at least one surface of the lower flange, upper flange, and the web structure.

For example, in one embodiment, the method may include forming the open lattice structure on opposed first and second surfaces of the web structure. Additionally or alternatively, the method may include forming the open lattice structure on an outer surface of each of the lower and upper flanges.

In yet another embodiment, a method of making a wind turbine blade includes forming a first blade half; forming a second blade half; forming a shear web according to the method described above; connecting the shear web to the first blade half; connecting the second blade half to the first blade half; and connecting the shear web to the second blade half. The connection of the shear web to the first and second blade halves and the connection of the first and second blade halves to each other may be done simultaneously or in multiple steps.

In one embodiment, the first and second blade halves may further include moulding each of the first and second blade halves. Additionally, the method may include forming the wind turbine blade as a first blade section and a second blade section configured to be joined at a connection interface. The first and second blade sections include a first shear web portion and a second shear web portion, respectively, and at least the web structure of the first shear web portion and the web structure of the second shear web portion are configured to connect with each other in a nesting relationship. The method further includes connecting the first blade section and the second blade section together at the connecting interface such that the arrangement of the spindles in the web structure of the first shear web portion and the arrangement of the spindles in the web structure of the second shear web portion are substantially aligned across the connecting interface.

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

With reference to <FIG>, a wind turbine <NUM> includes a tower <NUM>, a nacelle <NUM> disposed at the apex of the tower <NUM>, and a rotor <NUM> operatively coupled to a generator (not shown) housed inside the nacelle <NUM>. In addition to the generator, the nacelle <NUM> houses miscellaneous components required for converting wind energy into electrical energy and various components needed to operate, control, and optimize the performance of the wind turbine <NUM>. The tower <NUM> supports the load presented by the nacelle <NUM>, the rotor <NUM>, and other components of the wind turbine <NUM> that are housed inside the nacelle <NUM> and also operates to elevate the nacelle <NUM> and rotor <NUM> to a height above ground level or sea level, as may be the case, at which faster moving air currents of lower turbulence are typically found.

The rotor <NUM> of the wind turbine <NUM>, which is represented as a horizontal-axis wind turbine, serves as the prime mover for the electromechanical system. Wind exceeding a minimum level will activate the rotor <NUM> and cause rotation in a plane substantially perpendicular to the wind direction. The rotor <NUM> of wind turbine <NUM> includes a central hub <NUM> and at least one blade <NUM> that projects outwardly from the central hub <NUM> at locations circumferentially distributed thereabout. In the representative embodiment, the rotor <NUM> includes three blades <NUM>, but the number may vary. The blades <NUM> are configured to interact with the passing air flow to produce lift that causes the central hub <NUM> to spin about a longitudinal axis.

The wind turbine <NUM> may be included among a collection of similar wind turbines belonging to a wind farm or wind park that serves as a power generating plant connected by transmission lines with a power grid, such as a three-phase alternating current (AC) power grid. The power grid generally consists of a network of power stations, transmission circuits, and substations coupled by a network of transmission lines that transmit the power to loads in the form of end users and other customers of electrical utilities. Under normal circumstances, the electrical power is supplied from the generator to the power grid as known to a person having ordinary skill in the art.

The wind turbine blade <NUM> may generally be of an improved design, and in an exemplary embodiment be configured as an elongate structure having an outer airfoil shell <NUM> disposed about an inner support element or spar structure <NUM> disposed inside the outer shell <NUM>. The outer shell <NUM> may be optimally shaped to give the blade <NUM> the desired aerodynamic properties to generate lift, while the spar structure <NUM> is configured to provide the structural aspects (e.g., strength, stiffness, etc.) to blade <NUM>. The elongate blade <NUM> includes a root end <NUM> which is configured to be coupled to the central hub <NUM> when mounted to rotor <NUM>, and a tip end <NUM> longitudinally opposite to root end <NUM>. In the orientation shown in <FIG>, the outer shell <NUM> may include a windward shell half <NUM> that defines the lower side of the blade <NUM>, and a leeward shell half <NUM> that defines the upper side of the blade <NUM>. The windward and leeward shell halves <NUM>, <NUM> are coupled together along a leading edge <NUM> and a trailing edge <NUM> located opposite one another across a chord of the blade <NUM>.

As best illustrated in <FIG>, to increase strength and rigidity, the blade <NUM> may include a spar structure <NUM> that extends longitudinally along at least a portion of the length of the blade <NUM> between the root end <NUM> and the tip end <NUM>. The spar structure <NUM> may extend, for example, a majority of the length of the wind turbine blade <NUM> between the root end <NUM> and the tip end <NUM> (e.g., greater than <NUM>% or <NUM>% of the length of the blade <NUM>). In an exemplary embodiment, the spar structure <NUM> includes a pair of spar caps <NUM>, <NUM> associated with respective windward and leeward shell halves <NUM>, <NUM> and a shear web <NUM> that extends between the opposed spar caps <NUM>, <NUM>. The spar caps <NUM>, <NUM> are generally designed to carry bending loads on the blade <NUM> and the shear web <NUM> is designed to generally carry the shear loads on the blade <NUM>. In one embodiment, the spar caps <NUM>, <NUM> may be integrated within the windward and leeward shell halves <NUM>, <NUM> such that the spar caps <NUM>, <NUM> form part of the outer airfoil shell <NUM>. Such an arrangement is illustrated in <FIG>, for example. In an alternative embodiment (not shown), however, the spar caps <NUM>, <NUM> may be separate elements adhesively bonded to an inner surface of the outer shell <NUM>. In one embodiment, the spar caps <NUM>, <NUM> may be formed from a stack of pultruded fiber-reinforced composite strips. In an alternative embodiment, however, the spar caps <NUM>, <NUM> may have a laminate composite construction of a plurality of fiber layers, resin, and possibly core material.

The shear web <NUM> extends across the height of the blade <NUM> from the windward shell half <NUM> to the leeward shell half <NUM> and between the spar caps <NUM>, <NUM>. In an exemplary embodiment, the shear web <NUM> includes a lower flange <NUM>, an upper flange <NUM>, and an intermediate web structure <NUM> extending between the lower and upper flanges <NUM>, <NUM>. As illustrated in <FIG>, the lower and upper flanges <NUM>, <NUM> of the shear web <NUM> are configured to be adhesively bonded to the inner surfaces of the spar caps <NUM>, <NUM>, respectively. In the embodiment illustrated in <FIG>, for example, the lower and upper flanges <NUM>, <NUM> may have a laminate composite construction of a plurality of fiber layers, resin, and possibly core material which are, in turn, adhesively bonded to the web structure <NUM>. As described in more detail below, aspects of the invention are primarily directed to details of the intermediate web structure <NUM> of the shear web <NUM>. Other aspects of the invention are directed to details of the flanges <NUM>, <NUM> of the shear web <NUM>. Each will be described in detail below.

In this regard, aspects of the invention are directed to the intermediate web structure having a three-dimensional open lattice construction of fibrous composite material. The three-dimensional open lattice construction includes a plurality of elongate structural members made of fibrous composite material extending in three dimensions and intersecting each other to form a web-like network of interconnected, rod-like spindles that collectively form the web structure. Thus, for a given volume of the web structure (e.g., <NUM><NUM>), some fraction of the volume will be occupied by fibrous composite material and the remaining fraction of the volume will be void. Accordingly, the web structure in accordance with aspects of the invention does not have a solid-body construction, like moulded web structures of conventional shear webs, but includes a lattice arrangement with void space. The concept embodied in the three-dimensional open lattice construction is that the load-bearing capacity of the web structure may be significantly increased, such as by arrangement of the spindles in three dimensions, while minimizing the overall weight of the web structure by having considerable void space. In other words, the three-dimensional open lattice construction of the web structure provides a strength-to-weight ratio that exceeds, and in many cases far exceeds, the strength-to-weight ratio of solid composite web structures produced by conventional moulding processes, as described above. This is important as the size of the wind turbine blades continue to grow.

The three-dimensional open lattice construction of the web structure not only provides for increased strength at lower weights, but also provides increased design flexibility through localized arrangements of the spindles based on estimated local load conditions on the web structure (and wind turbine blade). Thus, through the arrangement of the spindles (i.e., elongate members made of fibrous composite material), the web structure may be configured to have high strength in localized regions subjected to high load conditions and reduced strength in localized regions subjected to lower load conditions. In general, this approach dispenses with the less refined, more global approach of conventional moulding operations, and instead provides for a more tailored, detailed approach for providing material and weight where strength is needed and reducing material and weight where strength is not needed. In other words, in expected regions of high load, the web structure may include a greater number of spindles per unit volume (and therefore mass per unit volume), and in expected regions of low load, the web structure may include fewer spindles per unit volume. The spindle distribution (and therefore the strength distribution) of the web structure may be characterized through the concept of density, i.e., the amount of mass of fibrous composite material of the spindles per unit volume of the web structure.

In addition to the above, the three-dimensional open lattice construction of the web structure allows the shear web to be designed in a manner that provides for a more uniform load distribution across the flanges of the shear web and across the bond area between the flanges and the spar caps. Moreover, due to the more uniform load distribution, the peak loads across the flanges and bond area are reduced, thereby reducing the likelihood of a failure in the bonded joint. The ability to strengthen the bond area and decrease the peak loads is also important as the size of the wind turbine blades continue to grow.

To achieve the three-dimensional open lattice construction of the web structure, and the benefits it provides to wind turbine blade manufacturing, the conventional moulding process is partially or wholly abandoned for a more adaptive additive manufacturing (AM) process, such as <NUM>-D printing technologies. In many industrial applications, additive manufacturing processes using polymer-based resins were used to produce prototype parts in the early stages of product development rather than functional parts. This limitation was based primarily on the fact that parts formed from polymer-based resins lacked the necessary mechanical properties required by functional parts during field conditions. More recently, to improve the mechanical properties of parts made by additive manufacturing, fiber strands (e.g., short fibers) have been introduced into the resin matrix within or just outside of the print head of the <NUM>-D printer and then printed together to form a part. While the introduction of short fibers into the matrix increases the strength of the <NUM>-D printed part, it is believed that the strength of such composite parts is less than the traditional mould-based fiber-reinforced composites. Thus, to further increase the mechanical properties of <NUM>-D printed parts, continuous fiber-reinforced additive manufacturing methods have been developed.

Continuous fiber-reinforced additive manufacturing methods integrate a continuous fiber with a resin matrix in the <NUM>-D printing process and may take several forms, including in-situ impregnation, co-extrusion with towpreg, towpreg extrusion, in-situ consolidation, inline impregnation, and possibly others. The essence of these methods is that a continuous fiber or continuous group of fibers is mixed with a resin matrix within a print head or just outside of a print head of a <NUM>-D printer and the fiber(s) and matrix dispensed from the print head to form a part. The inclusion of the continuous fiber within the resin matrix increases the mechanical properties (e.g., strength) of the composite part such that the <NUM>-D printed part may now operate as a functional part during use. Systems that provide continuous fiber-reinforced additive manufacturing are commercially available. By way of example and without limitation, Continuous Composites of Coeur d'Alene, Idaho; Electroimpact of Mukilteo, Washington; Ingersoll Machine Tools of Rockford Illinois; Markforged of Watertown, Massachusetts; moi composites of Milan, Italy; and Orbital Composites of San Jose, California provide commercially available continuous fiber additive manufacturing services.

Continuous fiber-reinforced additive manufacturing provides free-form geometry generation capable of complex and specifically tailored designs based on various design criteria, such as strength, material and weight considerations, to optimize performance. Additionally, such additive manufacturing processes provide the ability to change design configurations without the need to modify or replace tooling. Thus, the use of <NUM>-D additive manufacturing processes to produce functional composite structures releases wind turbine designers and manufacturers from the constraints of conventional moulding processes. This vastly increases the design options for making wind turbine components, including shear webs for wind turbine blades, having improved performance and features. Continuous fiber-reinforced additive manufacturing methods are known and commercially available. Accordingly, a detailed discussion of such devices and processes will not be described in detail herein. Aspects of the invention are directed more to the use of these additive manufacturing processes in the production of wind turbine blade components, such as a shear web for a wind turbine blade.

One embodiment of the invention is directed to the shear web, and more particularly to the intermediate web structure thereof having a three-dimensional open lattice construction formed by fibrous composite spindles extending in three dimensions. The three-dimensional nature of the spindles may be unstructured, having seemingly random orientations of the spindles to form the three-dimensional lattice construction. Alternatively, the three-dimensional nature of the spindles may be structured, wherein there is an identifiable arrangement of spindles that form, for example, a latticed building block. The intermediate web structure may then be formed by an arrangement of multiple latticed building blocks connected to each other to provide the three-dimensional open lattice construction. By way of example, and without limitation, the latticed building block may include various polyhedrons or other three-dimensional geometrical shapes.

As will be discussed in more detail below, in an exemplary embodiment, the three-dimensional open lattice construction may be formed by an arrangement of panels formed from fibrous composite spindles. In other words, a panel is a building block formed by spindles, and the intermediate web structure may be formed by an arrangement of multiple panels to form the three-dimensional open lattice structure (e.g., consider two nonparallel panels intersecting each other at an angle to form the three-dimensional open lattice structure). In an exemplary embodiment, a panel may be box shaped or plate like (e.g., a rectangular prism) that generally defines a primary plane in a first dimension and a second dimension, and has a reduced extent in a third dimension to provide the plate-like configuration of the panel. One can easily imagine, for example, a panel having a length and height (that defines an infinitesimally thin plane) and a width that is significantly less than the length and height to define the plate-like panel. The fibrous composite spindles that form the panel extend within the primary plane of the panel but also have an inherent "width" (e.g., the diameter of the spindles) that generally defines the reduced third dimension of the panel. Thus, the spindles are contained within the volume of the rectangular prism of the panel. The panel is substantially two dimensional but does include a small third dimension due the spindles having a "width" to them. In any event, the concept of a panel being planar or defining a plane accounts for there be an inherent width to the spindles that form the panel. The spindles may extend in various directions within the primary plane and intersect with each other at nodes to form the latticed panels.

In an exemplary embodiment, the three-dimensional open lattice construction of, for example, the intermediate web structure, may be formed by a plurality of the panels arranged in intersecting fashion. In this regard, select pairs of panels of the three-dimensional open lattice structure may intersect each other in a wide range of angles. For example, in one embodiment, pairs of panels may be arranged to be substantially perpendicular to each other. In another embodiment, however, pairs of panels may intersect each other at an angle greater to or less than about ninety degrees, and all of the panels may or may not intersect each other at the same angle. Thus, it should be understood that a plurality of panels may be arranged in a wide range of configurations to form the three-dimensional open lattice construction of the intermediate web structure and should not be limited to that shown and described herein.

<FIG> illustrates a shear web <NUM> in accordance with an exemplary embodiment of the invention. The shear web <NUM> includes lower and upper flanges <NUM>, <NUM> and an intermediate web structure <NUM> produced by a continuous fiber-reinforced additive manufacturing process. Notably, the intermediate web structure <NUM> has a three-dimensional open lattice construction formed by fibrous composite spindles extending in three dimensions. Such a construction cannot be achieved by conventional manufacturing techniques, including conventional moulding processes. More particularly, the web structure <NUM> includes a plurality of first open lattice panels <NUM> and a plurality of second open lattice panels <NUM> that intersect each other to form the three-dimensional construction. Each of the open lattice panels <NUM>, <NUM> may be formed by fibrous composite spindles which extend in various directions within the primary plane defined by the panels. In one embodiment, and as shown in <FIG>, the plurality of first panels <NUM> and the plurality of second panels <NUM> may be arranged substantially perpendicular to each other (e.g., intersect at <NUM> +/- <NUM> degrees) to give the web structure <NUM> a box-like configuration. It should be understood, however, that the open lattice panels <NUM>, <NUM> may intersect each other at other angles and remain within the scope of the present invention.

As illustrated in <FIG> and <FIG>, wind turbine blade <NUM> may be described as having a spanwise direction x generally defined by, i.e. extending between, the root end <NUM> and tip end <NUM> of the blade <NUM>; a chordwise direction y generally defined by, i.e. extending between, the leading edge <NUM> and trailing edge <NUM>, and a thickness wise direction z generally defined by, i.e. extending between, the windward shell half <NUM> and the leeward shell half <NUM>. The lower and upper flanges <NUM>, <NUM> have a plate-like configuration and generally include a primary plane extending in the spanwise direction x and the chordwise direction y, and a significantly smaller extent in the thickness wise direction z. Though being plate-like in configuration, the lower and upper flanges <NUM>, <NUM> are generally thought of as extending along the length of the blade <NUM> in the spanwise direction (referred to as the extension direction for the flanges <NUM>, <NUM>).

The open lattice panels <NUM>, <NUM> of the intermediate web structure <NUM> may be arranged relative to the spanwise, chordwise, and thickness wise directions of the wind turbine blade <NUM>. For example, in an exemplary embodiment, the first panels <NUM> may be arranged such that the primary plane of the panels extends in the spanwise direction and the thickness wise direction, and the significantly smaller extent of the panels <NUM> extends in the chordwise direction (e.g., see <FIG> and <FIG>). Accordingly, these open lattice panels <NUM> may be referred to herein as spanwise panels and may be thought of as generally extending along the length of the blade <NUM> in the spanwise direction (the extension direction of panels <NUM>). Moreover, in this exemplary embodiment, the second panels <NUM> may be arranged such that the primary plane of the panels extends in the chordwise direction and the thickness wise direction, and the significantly smaller extent of the panels <NUM> extends in the spanwise direction (e.g., see <FIG> and <FIG>). Accordingly, these open-lattice panels <NUM> may be referred to herein as chordwise panels and may be thought of as generally extending along the width of the blade <NUM> in the chordwise direction (the extension direction of panels <NUM>). It should be recognized, however, that the three-dimensional arrangement of the web structure <NUM> is not limited to this orientation or arrangement of the open lattice panels <NUM>, <NUM> relative to the spanwise, chordwise, and thickness wise directions of the blade <NUM>. Moreover, while the web structure <NUM> is illustrated as having two spanwise panels <NUM>, this is merely illustrative as the web structure <NUM> may have more than two spanwise panels <NUM> extending along the length of the blade <NUM>, as will be discussed in more detail below. Furthermore, the number of chordwise panels <NUM> and their respective positions along the length of the blade <NUM> may also vary, as will also be discussed in more detail below.

Each of the spanwise panels <NUM> includes a plurality of fibrous composite spindles in different orientations that intersect with each other at multiple nodes within the primary plane generally defined by the spanwise panels <NUM>. In an exemplary embodiment, however, the spindles in the spanwise panels <NUM> may be arranged relative to the spanwise direction of the panels <NUM> (i.e., the extension direction of the panels). For example, the fibrous composite spindles of the spanwise panels <NUM> may include normal spindles <NUM> and cross spindles <NUM> relative to the spanwise direction of the spanwise panels <NUM>. In an exemplary embodiment, the normal spindles <NUM> may be substantially perpendicular to the spanwise direction and the cross spindles <NUM> may be arranged at +/- <NUM> degrees relative to the spanwise direction of the spanwise panels <NUM> in a criss-cross fashion. However, other uniform and/or non-uniform angles of the cross spindles <NUM> may also be possible in alternative embodiments. In one embodiment, the spanwise panels <NUM> may include only or primarily cross spindles <NUM>. In an alternative embodiment, however, the spanwise panels <NUM> may include a combination of cross spindles <NUM> and normal spindles <NUM>. In one embodiment, the distribution of the normal spindles <NUM> in the spanwise direction of the spanwise panels <NUM> may vary depending on various factors, including an expected localized load condition on the blade <NUM>, and more specifically the shear web <NUM>. By way of example, the position of the normal spindles <NUM> in the spanwise direction of the spanwise panels <NUM> may be determined based on the brazier loading of the shear web <NUM>.

<FIG> is a schematic illustration of a characteristic load condition on the shear web <NUM> in the spanwise direction during use of the wind turbine blade <NUM>. In this figure, the x coordinate represents the spanwise direction of the shear web <NUM>; L is the length of the shear web <NUM>; S is the localized load on the shear web <NUM> as a function of distance x in the spanwise direction; x* is a normalized x coordinate based on the length of the shear web <NUM> (i.e., x*=x/L); and S* is a normalized load based on the maximum load experienced by the shear web <NUM> in the spanwise direction (i.e., S*=S(x)/Smax). As illustrated in <FIG>, the location of maximum load <MAT> in the shear web <NUM> generally occurs in the outer half of the shear web <NUM>, i.e., <MAT>. More particularly, and by way of example, the location of maximum load may be between <MAT> depending on the particular wind turbine blade <NUM>. The trend illustrated by <FIG> is that the load is relatively low at the root end <NUM> (and may even change directions adjacent the root end <NUM>), increases toward the mid-blade region, and continues to increase until the maximum load is reached in the outer region of the blade <NUM>. From the point of maximum load, the load then decreases in the direction of the tip end <NUM> of the blade <NUM>.

In general, and in accordance with an aspect of the invention, there will be more normal spindles <NUM> in high load regions of the shear web <NUM> and fewer normal spindles <NUM> in lower load regions of the shear web <NUM>. Thus, adjacent normal spindles <NUM> will be more closely spaced from each other in high load regions of the shear web <NUM> and further spaced from each other in lower load regions of the shear web <NUM>. <FIG> is a schematic illustration of a spanwise panel <NUM> of the shear web <NUM> extending along the length Lb of the wind turbine blade <NUM>. As illustrated in this figure, the spacing between adjacent normal spindles <NUM> adjacent the root end <NUM> of the blade <NUM> may be relatively high. However, the relative spacing between adjacent normal spindles <NUM> starts decreasing in the spanwise direction toward the location of maximum load. Thereafter, the spacing between adjacent normal spindles <NUM> in the spanwise direction starts increasing again toward the tip end <NUM> of the blade <NUM>.

<FIG> is a schematic illustration of a characteristic density distribution of normal spindles <NUM> in the spanwise direction of the shear web <NUM> in accordance with an aspect of the invention. In this figure, ρns is the localized density, i.e., the mass of fibrous composite material that forms the normal spindles <NUM> per unit volume of the spanwise panel <NUM> as a function of distance x in the spanwise direction of the shear web <NUM>; and <MAT> is a normalized density based on the maximum density value along the spanwise panel <NUM> (i.e., <MAT>). As demonstrated in <FIG>, in an exemplary embodiment, the distribution of normal spindles <NUM> in the spanwise direction of the shear web <NUM> may be such that the normalized density distribution of normal spindles <NUM> is a substantially stochastic distribution about the location of maximum load in the shear web <NUM> (i.e., with the maximum of the density distribution at <MAT>). The distribution of normal spindles <NUM> in the spanwise panel <NUM> according to that illustrated in <FIG> is but one possible distribution based on the expected load conditions of the wind turbine blade <NUM>, and shear web <NUM> more particularly. Accordingly, it should be recognized that other distributions that accommodate strength requirements based on expected load conditions are possible and remain within the scope of the present invention.

In one embodiment, the distribution of the cross spindles <NUM> in the spanwise direction of the spanwise panel <NUM> may also vary depending on an expected localized load condition on the shear web <NUM>. By way of example, the position of the cross spindles <NUM> may be determined based on the shear loading of the shear web <NUM>. For a characteristic load distribution on the shear web <NUM> as illustrated in <FIG>, and in accordance with an aspect of the invention, adjacent cross spindles <NUM> will be more closely spaced from each other in high load regions of the shear web <NUM> and further spaced from each other in lower load regions of the shear web <NUM>. Turning to <FIG> illustrating a spanwise panel <NUM> of the shear web <NUM> extending along the length Lb of the wind turbine blade <NUM>, the spacing between adjacent cross spindles <NUM> may be relatively high adjacent the root end <NUM> of the blade <NUM>. However, the relative spacing between adjacent cross spindles <NUM> starts decreasing in a direction toward the location of maximum load. Thereafter, the spacing between adjacent cross spindles <NUM> starts increasing again toward the tip end <NUM> of the blade <NUM>.

<FIG> is a schematic illustration of a characteristic density distribution of cross spindles <NUM> along the length of the shear web <NUM> in accordance with an aspect of the invention. In this figure, ρcs is the localized density, i.e., the mass of composite material that forms the cross spindles <NUM> per unit volume of the spanwise panel <NUM> as a function of distance x in the spanwise direction of the shear web <NUM>; and <MAT> is a normalized density based on the maximum density value along the spanwise panel <NUM> (i.e., <MAT> ρcs/ρMax,cs). As demonstrated in <FIG>, in an exemplary embodiment, the distribution of cross spindles <NUM> in the spanwise direction of the shear web <NUM> may be such that the normalized density distribution of cross spindles <NUM> may be a substantially stochastic distribution about the location of maximum shear load in the blade <NUM> (i.e., with the maximum of the distribution at <MAT>). The distribution of cross spindles <NUM> in the spanwise panel <NUM> according to that illustrated in <FIG> is but one possible distribution based on the expected load conditions of the wind turbine blade <NUM> and the shear web <NUM> more particularly. Accordingly, it should be recognized that other distributions that accommodate strength requirements based on expected load conditions are possible and remain within the scope of the present invention.

Turning now to the chordwise panels <NUM>, in a similar manner and in its broadest scope, each of these panels includes a plurality of fibrous composite spindles in different orientations that intersect with each other at multiple nodes within the primary plane generally defined by the chordwise panels <NUM>. In an exemplary embodiment, the spindles in the chordwise panels <NUM> may be arranged relative to the chordwise direction of the panels <NUM>. For example, the fibrous composite spindles of the chordwise panels <NUM> may include cross spindles <NUM> relative to the chordwise direction of the panels <NUM> (i.e., the extension direction of panels <NUM>). In one embodiment, the cross spindles <NUM> may be arranged at +/- <NUM> degrees relative to the chordwise direction of the panels <NUM>. However, other uniform and/or non-uniform angles of the cross spindles <NUM> are also possible in alternative embodiments. The chordwise panels <NUM> may also include normal spindles <NUM> that are substantially perpendicular to the chordwise direction, depending on, for example, the extent of the chordwise panels <NUM> in the chordwise direction. In one embodiment, the normal spindles <NUM> of the spanwise panels <NUM> may also serve as the normal spindles <NUM> of the chordwise panels <NUM> (see <FIG>). Aspects of the invention, however, are not so limited as the chordwise panels <NUM> may include normal spindles <NUM> that do not correspond to a normal spindle <NUM> in a spanwise panel <NUM>. For example, <FIG> illustrates a chordwise panel <NUM> having a normal spindle <NUM> (shown in phantom) that does not correspond to a normal spindle <NUM> in a spanwise panel <NUM>. In one embodiment, the chordwise panels <NUM> may include only or primarily cross spindles <NUM>. In an alternative embodiment, however, the chordwise panels <NUM> may include a combination of cross spindles <NUM> and normal spindles <NUM>. In one embodiment, the distribution of the spindles <NUM>, <NUM> along the extent of the chordwise panel <NUM> may be based on several factors, including providing a more uniform load distribution across the width of the shear web <NUM> and bond region between the flanges <NUM>, <NUM> and respective spar caps <NUM>, <NUM>.

<FIG> is a schematic illustration of a characteristic load condition on the shear web <NUM> in the chordwise direction during use of the wind turbine blade <NUM>. In this figure, the y coordinate represents the chordwise direction of the wind turbine blade <NUM>; W is the width of the shear web <NUM> in the chordwise direction; T is the localized load on the shear web <NUM> in the chordwise direction of the blade <NUM>; y* is a normalized y coordinate based on the width of the blade <NUM> (i.e., y*=y/W); and T* is a normalized load based on the maximum load experienced by the shear web <NUM> in the chordwise direction (i.e., T*=T(y)/Tmax). Dashed curve A in <FIG> represents a schematic characteristic load condition on a conventional shear web having an I-shaped profile. As discussed above, the characteristic load condition has a maximum shear load near the central portion of the shear web (i.e., <MAT>), where the intermediate web is located, and the vast majority of the load is carried at a relatively small portion of the width of the shear web in the immediate vicinity of the intermediate web.

Curve B in <FIG> represents a schematic characteristic load condition in the shear web <NUM> as illustrated in <FIG>, for example. As illustrated in <FIG>, the location of maximum shear load in the shear web <NUM> generally occurs at the location of the spanwise panels <NUM>, of which there are two in <FIG>, i.e., at the leading-edge side and trailing-edge side of the web structure <NUM>. The presence of the chordwise panels <NUM> facilitates the distribution of the loads at the spanwise panels <NUM> in the chordwise direction to provide a more uniform load distribution in the chordwise direction. Moreover, in an exemplary embodiment, the spanwise panels <NUM> of the web structure <NUM> are preferably located adjacent the edges of the flanges <NUM>, <NUM> of the shear web <NUM> such that the web structure <NUM> extends across a majority of the width of the flanges <NUM>, <NUM>. For example, the web structure <NUM> may have a width greater than <NUM>%, preferably greater than <NUM>%, and even more preferably greater than about <NUM>% of the width of the flanges <NUM>, <NUM>. The lower and upper flanges <NUM>, <NUM> may, in turn, extend the majority of the width of the spar caps <NUM>, <NUM>, such as extending greater than <NUM>%, preferably greater than <NUM>%, and even more preferably greater than <NUM>% of the width of the spar caps <NUM>, <NUM>. This arrangement not only increases the bond area between the spar caps <NUM>, <NUM> and the flanges <NUM>, <NUM> of the shear web <NUM> but also provides for for a more uniform distribution of the loads acting on the bond region.

The trend illustrated by <FIG> is that the shear load is relatively higher at the leading-edge and trailing-edge sides of the shear web <NUM> (due to the location of the spanwise panels <NUM>) and decreases toward the mid-region of the shear web <NUM>. Due to the chordwise panels <NUM>, however, the amount of decrease in load away from the spanwise panels <NUM> is not significant and a portion of the load is distributed to and carried by those chordwise panels <NUM>. As compared to the I-shaped shear web depicted in curve A, the peak load has been significantly reduced and the area over which the load is being distributed is significantly increased.

In one embodiment, the distribution of cross spindles <NUM> in a chordwise panels <NUM> may be held relatively constant in that direction. <FIG> is a schematic illustration of a characteristic density distribution of cross spindles <NUM> in the chordwise direction y of a chordwise panel <NUM>. In this figure, ρcs is the localized density, i.e., the mass of composite material that forms the cross spindles <NUM> per unit volume of the chordwise panel <NUM> as a function of distance y in the chordwise direction; and <MAT> is a normalized density based on the maximum density value along the chordwise panel <NUM> (i.e., <MAT> ρcs/ρMax,cs). Curve A in <FIG> illustrates the embodiment where the cross spindles <NUM> are substantially uniform across the chordwise panel <NUM>.

In an alternative embodiment, however, the distribution of cross spindles <NUM> in the chordwise panels <NUM> may vary depending on an expected localized load condition on the shear web <NUM>. For a load distribution on the shear web <NUM> as illustrated as curve B in <FIG>, there may be more cross spindles <NUM> in high load regions of the shear web <NUM> and fewer cross spindles <NUM> in lower load regions of the shear web <NUM>. In other words, adjacent cross spindles <NUM> may be more closely spaced from each other in high load regions of the shear web <NUM> and further spaced from each other in lower load regions of the shear web <NUM>. Thus, for example, the spacing between adjacent cross spindles <NUM> adjacent the leading-edge side and trailing-edge side of the chordwise panel <NUM> may be relatively lower. However, the spacing between adjacent cross spindles <NUM> may increase in a direction toward the mid-region of the shear web <NUM>.

Curve B in <FIG> is a schematic illustration of a characteristic density distribution of cross spindles <NUM> in the chordwise direction of the web structure <NUM> in such an alternative embodiment. As demonstrated by this curve, in an exemplary embodiment, the distribution of cross spindles <NUM> in the chordwise panel <NUM> may be such that the normalized density distribution of cross spindles <NUM> is a maximum at the leading and trailing edge sides and decreases to a relatively constant level toward the mid-region. The distribution of cross spindles <NUM> in the chordwise panel <NUM> according to that illustrated in curves A and B of <FIG> are but two possible distributions. Thus, it should be recognized that other distributions based on uniformity in load, expected load conditions, etc. are possible and remain within the scope of the present invention.

As noted above, although the chordwise panels <NUM> illustrated in <FIG> include normal spindles <NUM> only at the leading and trailing edge sides of the web structure <NUM>, additional normal spindles <NUM> may be distributed along the chordwise direction of the chordwise panels <NUM> of the web structure <NUM>. Similar to the above, this distribution may be constant in the chordwise direction or may vary in the chordwise direction, depending on an expected localized load condition on the shear web <NUM>, such as that illustrated in <FIG>, for example. Accordingly, the density distribution of the normal spindles <NUM> in the chordwise panel <NUM> may be as illustrated in <FIG>, with curve A illustrating a uniform density distrubtion of normal spindles <NUM> and curve B illustrating a varying density distribution of normal spindles <NUM>. In this latter embodiment, for example, more normal spindles <NUM> may be positioned adjacent the leading edge and trailing edge sides of the panel <NUM> (with smaller spacing between adjacent spindles <NUM>), and fewer normal spindles <NUM> may be positioned in the mid-region of the panel <NUM> (with greater spacing between adjacent spindles <NUM>). The distributions of normal spindles <NUM> in the chordwise panel <NUM> according to that illustrated in <FIG> are but two possible distributions. Thus, it should be recognized that other distributions of normal spindles <NUM> in the chordwise panel <NUM> that accommodate uniformity, expected load conditions, etc. are possible and remain within the scope of the present invention.

In one embodiment (not shown), the chordwise panels <NUM> may be uniformly distributed along the spanwise direction of the shear web <NUM>. In another embodiment, however, the distribution of the chordwise panels <NUM> along the spanwise direction of the shear web <NUM> may vary depending on the expected localized load conditions on the shear web <NUM>. Recall that <FIG> illustrates a characteristic load condition on the shear web <NUM> in the spanwise direction during operation. Thus, in general and in accordance with an aspect of the invention, there will be more chordwise panels <NUM> in high load regions of the shear web <NUM> and fewer chordwise panels <NUM> in lower load regions of the shear web <NUM>. This concept may perhaps be best visualized with reference to <FIG>. In this regard, imagine that each normal spindle <NUM> illustrated in that figure is associated with a chordwise panel <NUM> that extends into the paper and thus not visible from the perspective in that figure.

<FIG> is a schematic illustration of a characteristic density distribution of chordwise panels <NUM> in the spanwise direction of the shear web <NUM>. In this figure, ρcp is the localized density of chordwise panels, i.e., the mass of composite material that forms the chordwise panels <NUM> per unit volume of the web structure <NUM> in the spanwise direction of the shear web <NUM>; and <MAT> is a normalized density based on the maximum density value in the spanwise direction of the web structure <NUM> (i.e., <MAT>). As demonstrated in <FIG>, in an exemplary embodiment, distribution of chordwise panels <NUM> in the spanwise direction of the web structure <NUM> may be such that the normalized density distribution of chordwise panels <NUM> is a substantially stochastic distribution about the location of maximum load in the web structure <NUM> (i.e., with the maximum of the distribution at <MAT>). The distribution of chordwise panels <NUM> in the spanwise direction according to that illustrated in <FIG> is but one possible distribution based on an expected load condition of the wind turbine blade <NUM> and shear web <NUM>. Thus, it should be recognized that other distributions that accommodate strength requirements based on expected load conditions are possible and remain within the scope of the present invention.

The discussion above generally described the possible distribution of cross spindles <NUM> and possibly normal spindles <NUM> in the chordwise direction for a chordwise panel <NUM>. Consideration, however, should also be given to variations in the chordwise panels <NUM> as a function of their position in the spanwise direction of the web structure <NUM>. In one embodiment, for example, the chordwise panels <NUM> may all be the same no matter where they are located along the spanwise direction of the web structure <NUM>. That is, each chordwise panel <NUM> has the same cross spindle <NUM> (and perhaps normal spindle <NUM>) distribution. In an alternative embodiment, however, the chordwise panels <NUM> may vary depending on where the panels <NUM> are located along the spanwise direction of the web structure <NUM>. This variation may depend, for example, on an expected localized load condition on the web structure <NUM>.

By way of example and without limitation, based on the characteristic load distribution shown in <FIG>, the density of the cross spindles <NUM> in a chordwise panel <NUM> located in a low load region, such as adjacent the root end <NUM> of the blade <NUM>, may be less than the density of the cross spindles <NUM> in a chordwise panel <NUM> located in a high load region, such as in the outer portion of the blade (e.g., <MAT>). This general relationship is schematically reflected in <FIG>. More particularly, <FIG> illustrates a chordwise panel <NUM> having cross spindles <NUM> with a relatively low density that might be more appropriately positioned adjacent the root end <NUM> of the blade <NUM> where lower loads are expected. <FIG>, on the other hand, illustrates a chordwise panel <NUM> having cross spindles <NUM> with a relatively high density that might be more appropriately positioned in the outer region of the blade <NUM> where higher loads are expected.

Thus, the density of the cross spindles <NUM> in the chordwise panels <NUM> vary as a function of spanwise position. This variation may be illustrated in an exemplary embodiment by that shown in <FIG>. As demonstrated in this figure, the density of cross spindles <NUM> in the chordwise panels <NUM> may be such that the normalized density distribution is a substantially stochastic distribution about the location of maximum load in the web panel <NUM> (i.e., with the maximum of the distribution at <MAT>). The distribution according to that illustrated in <FIG> is but one possible distribution based on expected load conditions of the wind turbine blade <NUM> and web structure <NUM>. Thus, it should be recognized that other distributions that accommodate strength requirements based on expected load conditions are possible and remain within the scope of the present invention. Should the chordwise panels <NUM> also include a distribution of normal spindles <NUM>, the density of normal spindles <NUM> in the panels <NUM> may likewise vary based on position in the spanwise direction of the web structure <NUM>. Thus, a chordwise panel <NUM> in a low load region would include fewer normal spindles than a chordwise panel <NUM> in a high load region. The density of normal spindles <NUM> in the chordwise panels <NUM> may similarly have a substantially stochastic distribution about the location of maximum load in the web structure <NUM>.

As noted above, although the web structure <NUM> illustrated in <FIG> and <FIG> includes only two spanwise panels <NUM> at the leading edge side and trailing edge side of the web structure <NUM>, there may be additional spanwise panels <NUM> distributed in the chordwise direction of the web structure <NUM>. <FIG>, for example, illustrates a web structure <NUM> having more than two spanwise panels <NUM> (e.g., <NUM> spanwise panels <NUM>) distributed in the chordwise direction of the web structure <NUM>. This concept may perhaps be best visualized by imagining that each normal spindle illustrated in that figure is associated with a spanwise panel <NUM> that extends into the paper and thus not visible from the perspective in that figure. In an exemplary embodiment, the spanwise panels <NUM> may be uniformly distributed in the chordwise direction of the web structure <NUM>, as illustrated in <FIG>. <FIG> is a schematic illustration of a characteristic load condition on the shear web <NUM> in the chordwise direction of the web structure <NUM> similar to that shown in <FIG>. Similar to the above, the maximum in the shear load is located at the spanwise panels <NUM> and decreases slightly between the spanwise panels <NUM>. However, the addition of more spanwise panels <NUM> has further reduced the peak shear load and more uniformly distributed the load across the shear web <NUM> in the chordwise direction. The distribution of spanwise panels <NUM> in the chordwise direction according to that illustrated in <FIG> and <FIG> is but one possible distribution. Thus, it should be recognized that other distributions that accommodate load uniformity, expected load conditions, etc. are possible and remain within the scope of the present invention.

The discussion above generally described the possible distributions of normal spindles <NUM> and cross spindles <NUM> in the spanwise direction for a spanwise panel <NUM> (e.g., see <FIG>). Consideration, however, should also be given to variations in the spanwise panels <NUM> as a function of their position in the chordwise direction of the web structure <NUM>. In an exemplary embodiment, for example, the spanwise panels <NUM> may all be the same no matter where they are located along the chordwise direction of the web structure <NUM>. That is, each spanwise panel <NUM> has the same normal spindle <NUM> and/or cross spindle <NUM> distributions. In an alternative embodiment, however, the spanwise panels <NUM> may differ depending on where the panels <NUM> are located along the chordwise direction of the web structure <NUM>.

Based on the above, the design of the three-dimensional open lattice construction of the web structure <NUM> provides multiple ways to vary the strength depending on the expected load conditions on the shear web <NUM>. The general concept is that the web structure <NUM> may include more fibrous composite spindles in higher load regions of the web structure <NUM> and less fibrous composite spindles in lower load regions of the web structure <NUM>. The three-dimensional arrangement of the web structure <NUM> may be attained by providing a plurality of first open lattice panels <NUM> that intersect with a plurality of second open lattice panels <NUM>. The plurality of first panels <NUM> may be spanwise panels generally extending in the spanwise direction and the plurality of second panels <NUM> may be chordwise panels generally extending in the chordwise direction. Each panel <NUM>, <NUM> includes a plurality of fibrous composite spindles extending within the primary plane defined by the panels <NUM>, <NUM>. The spanwise panels <NUM>, for example, may include cross spindles <NUM> and possibly normal spindles <NUM> that have an orientation relative to the spanwise direction of the spanwise panels <NUM>. Similarly, the chordwise panels <NUM> may include cross spindles <NUM> and possibly normal spindles <NUM> that have an orientation relative to the chordwise direction of the chordwise panels <NUM>.

The strength of the web structure <NUM> may be enhanced in high load regions in different ways. For example, for high load regions in a spanwise direction, the local strength of the web structure <NUM> may be increased by one or more of: i) increasing the number of chordwise panels <NUM>; ii) increasing the normal and/or cross spindle density in the chordwise panels <NUM>; and iii) increasing the normal and/or cross spindle density in the spanwise panels <NUM>. Moreover, in a chordwise direction, uniformity of load or local variation in strength of the web structure <NUM> may be accommodated by: i) increasing the number of spanwise panels <NUM> distributed in the chordwise direction; and ii) increasing the normal and/or cross spindle density in the chordwise panels <NUM>. Accordingly, it should be appreciated that designers have multiple options for providing variations in the strength of the web structure <NUM> to accommodate the expected load conditions on the wind turbine blade <NUM> and shear web <NUM> during operation of the wind turbine <NUM> and multiple options for providing a more uniform distribution of loads across the shear web <NUM> and bond region between the flanges <NUM>, <NUM> and spar caps <NUM>, <NUM>.

In this regard, it should be understood that designers may use any combination of the above options to vary the strength response of the web structure <NUM>. By providing a web structure <NUM> having a three-dimensional open lattice construction formed by fibrous composite spindles, not only can strength be more specifically tailored to expected load conditions but the weight of the web structure <NUM> may also be reduced compared to conventional moulded web structures. Thus, through greater design flexibility, shear webs having very high strength-to-weight ratios may be provided to wind turbine blade constructions. This improvement will, in turn, allow further increases in the length of wind turbine blades (and the associated energy capture) at a reduced weight and a reduced cost while also maintaining the structural integrity of the blade.

As discussed above, one drawback of current shear web designs is that the forces along the bond region between the flanges of the shear web and the spar caps are concentrated along a central region of the flanges. Thus, a significant portion of the forces transferred from the outer shell to the spar structure occur in a relatively small width of the bond region. The open lattice construction of the shear web <NUM> also allows the shear load in the shear web <NUM> to be more uniformly distributed over a greater portion of the spar caps <NUM>, <NUM> and flanges <NUM>, <NUM>. This reduces the peak shear load in the bond region between the flanges <NUM>, <NUM> and the spar caps <NUM>, <NUM>. This improvement in load distribution prevents strength limitations in the bond region from inhibiting further increases in blade length.

In the above, the flanges <NUM>, <NUM> of the shear web <NUM> were described as being conventional with a laminate composite construction while the web structure <NUM> had a three-dimensional open lattice construction. In another embodiment, the flanges <NUM>, <NUM> may have an open lattice construction while the web structure has a conventional laminate composite construction. In still a further embodiment, the flanges <NUM>, <NUM> and the web structure <NUM> (i.e., essentially the entirety of the shear web <NUM>) may have a multi-dimensional open lattice construction similar to that described above.

In this regard, <FIG> illustrates a shear web <NUM> having a lower flange <NUM>, an upper flange <NUM> and an intermediate web structure <NUM> (shown schematically) extending between the lower and upper flanges <NUM>, <NUM>. In this embodiment, the upper and lower flanges <NUM>, <NUM> have an open lattice construction of fibrous composite material similar to the panels <NUM>, <NUM> described above. The open lattice construction includes a plurality of elongate structural members of fibrous composite material intersecting each other to form a web-like network of interconnected spindles that collectively form the flanges <NUM>, <NUM>. Accordingly, the flanges <NUM>, <NUM> in accordance with aspects of the invention do not have a solid-body construction like moulded or pultruded flange structures of conventional shear webs but include a lattice arrangement with selectively positioned spindles and void space. The concept embodied in the open lattice construction is that the load-bearing capacity of the flanges <NUM>, <NUM> may be significantly increased, such as by arrangement of the spindles, while minimizing the overall weight of the flanges <NUM>, <NUM> by having significant void space.

Similar to the above, the open lattice construction of the flanges <NUM>, <NUM> not only provides for increased strength at lower weight, but also provides increased design flexibility through localized arrangements of the spindles based on estimated local load conditions. Thus, through the arrangement of the fibrous composite spindles, the flanges <NUM>, <NUM> may be configured to have high strength in localized regions subjected to high load conditions and reduced strength in localized regions subjected to lower load conditions. In other words, in expected regions of high load, the flanges <NUM>, <NUM> may include a greater number of spindles per unit volume, and in expected regions of low load, the flanges <NUM>, <NUM> may include fewer spindles per unit volume. The latticed configuration of the flanges <NUM>, <NUM> of the shear web <NUM> in this embodiment may also be formed through continuous fiber-reinforced additive manufacturing methods as described above.

The open lattice construction of the flanges <NUM>, <NUM> may include panels <NUM> similar to the panels <NUM>, <NUM> described above but having an orientation that has the faces of the panels <NUM> directed toward the windward and leeward sides of the blade <NUM> instead of toward the leading and trailing edges <NUM>, <NUM> of the blade <NUM>. More particularly, the panels <NUM> may be arranged such that the primary plane of the panels extends in the spanwise direction x and the chordwise direction y, and the significantly smaller extent of the panels <NUM> extends in the thickness wise direction z. The flanges <NUM>, <NUM>, and thus the panels <NUM>, may be thought of as generally extending along the length of the blade <NUM> in the spanwise direction (i.e., the extension direction for panels <NUM>). Each of the panels <NUM> that define flanges <NUM>, <NUM> includes a plurality of fibrous composite spindles in different orientations that intersect with each other at multiple nodes within the primary plane generally defined by the panels <NUM>. In an exemplary embodiment, however, the spindles in the panels <NUM> may be arranged relative to the spanwise direction of the panels <NUM>. For example, the fibrous composite spindles of the panels <NUM> may include normal spindles <NUM> and cross spindles <NUM> relative to the spanwise direction of the panels <NUM>. In an exemplary embodiment, the normal spindles are substantially perpendicular to the spanwise direction and the cross spindles <NUM> may be arranged at +/- <NUM> degrees relative to the spanwise direction of the panels <NUM> in criss-cross fashion. However, other uniform and/or non-uniform angles of the cross spindles <NUM> are also possible. The panels <NUM> that define flanges <NUM>, <NUM> may also include edge spindles <NUM> positioned at the leading-edge side and trailing-edge side of the flanges <NUM>, <NUM>. Edge spindles may, however, be omitted from the flanges <NUM>, <NUM>. In one embodiment, the panels <NUM> may include only or primarily cross spindles <NUM>. In an alternative embodiment, however, the panels <NUM> may include a combination of cross spindles <NUM> and normal spindles <NUM>.

Similar to the above, the distribution of the normal and cross spindles <NUM>, <NUM> in the spanwise direction of the flanges <NUM>, <NUM> may vary depending on the expected localized load conditions on the shear web <NUM>, and the flanges <NUM>, <NUM> more particularly. Thus, the density of normal spindles <NUM> in the spanwise direction of the flanges <NUM>, <NUM> may vary, with a higher density in high load regions and lower density in lower load regions. Additionally or alternatively, the density of the cross spindles <NUM> in the spanwise direction of the flanges <NUM>, <NUM> may vary, with a higher density in high load regions and lower density in lower load regions. Accordingly, manufacturers also have multiple options when designing the flanges <NUM>, <NUM> of the shear web <NUM> based on an expected load condition. By providing flanges having an open lattice construction formed by fibrous composite spindles <NUM>, <NUM>, <NUM>, not only can strength be more specifically tailored to expected load conditions but the weight of the flanges <NUM>, <NUM> may be reduced compared to conventional moulded web structures. Thus, flanges <NUM>, <NUM> of shear web <NUM> having very high strength-to-weight ratios may be provided to wind turbine blade constructions.

In addition, providing the flanges <NUM>, <NUM> as open lattice constructions may also improve the connection of the shear web <NUM> to the spar caps <NUM>, <NUM> of the spar structure <NUM>. As illustrated in <FIG>, when the flanges <NUM>, <NUM> are bonded to the spar caps <NUM>, <NUM>, sufficient pressure may be applied such that the flanges <NUM>, <NUM> become immersed or embedded within the adhesive used to form the bond. Thus, the bond interface becomes three dimensional. This is in contrast to solid planar flanges in conventional shear webs where the bond interface is two-dimensional (i.e., the bond forms between the adhesive and the generally planar surface of the flange). Furthermore, although the flanges <NUM>, <NUM> in this embodiment are not solid, but of a lattice construction, because the adhesive comes into contact with most or all of the surface of the spindles <NUM>, <NUM>, <NUM> of the flanges <NUM>, <NUM>, the total bonding surface area between the adhesive and the flange may be increased. In any event, it is believed that for one or both of these reasons, the bond between the shear web <NUM> and the spar caps <NUM>, <NUM> will be improved by configuring the flanges <NUM>, <NUM> as open lattice structures.

As discussed above, various embodiments employ a hybrid type of approach to shear web design, where some portion of the shear web includes, for example, a 3D printed lattice structure that complements other portions of the shear web <NUM> formed through more conventional processes. By way of example, an embodiment where the flanges <NUM>, <NUM> of the shear web <NUM> have a conventional construction but the web structure <NUM> is of a three-dimensional open lattice design was discussed in detail above. Another embodiment where the flanges <NUM>, <NUM> of the shear web <NUM> have an open lattice design but the web structure has a conventional construction was also described above. <FIG> is a cross sectional view of another hybrid type of shear web <NUM> having conventional portions and an open lattice structure formed by a continuous fiber-reinforced additive manufacturing process in accordance with aspects of the invention.

In this regard, the shear web <NUM> includes a lower flange <NUM>, an upper flange <NUM>, and an intermediate web structure <NUM> extending between the lower and upper flanges <NUM>, <NUM>. The intermediate web structure <NUM> may have a conventional construction of fiber layers, core material, and resin. The upper and lower flanges <NUM>, <NUM> may be conventional and have a laminate composite construction. Alternatively, the upper and lower flanges may be formed through a pultrusion process. The shear web <NUM> may be formed through conventional moulding processes, for example.

The (thus far) conventionally-made shear web <NUM> includes a web structure <NUM> having a first face <NUM> that generally confronts the leading edge <NUM> of the blade <NUM> and a second face <NUM> that generally confronts the trailing edge <NUM> of the blade <NUM> when the shear web <NUM> is in an operational position within the blade <NUM>. In this embodiment, an open lattice structure <NUM> may be formed on at least one and preferably both of the first and second faces <NUM>, <NUM> of the web structure <NUM>. The addition of the open lattice structure <NUM> to the at least one face <NUM>, <NUM> of the web structure <NUM> may be through continuous fiber-reinforced additive manufacturing methods. In this regard, the at least one face <NUM>, <NUM> may confront the print head of the <NUM>-D printer and the open lattice structure <NUM> printed directly on the at least one face <NUM>, <NUM> of the web structure <NUM>. The open lattice structure <NUM> may be constructed in a manner similar to the spanwise panels <NUM> of the web structure <NUM> described above and include a plurality of normal (e.g., vertical) spindles <NUM> and cross spindles <NUM> that intersect with each other at multiple nodes within the primary plane that defines the panel.

Similar to the discussion above, the density of the normal spindles <NUM> and/or the density of the cross spindles <NUM> may vary in the spanwise direction depending on the local load conditions on the web structure <NUM>. Thus, the density of normal spindles <NUM> in the spanwise direction of the web structure <NUM> may vary, with a higher density in high load regions and lower density in lower load regions. Additionally or alternatively, the density of the cross spindles <NUM> in the spanwise direction of the web structure <NUM> may vary, with a higher density in high load regions and lower density in lower load regions. Accordingly, manufacturers also have multiple options when designing the web structure <NUM> of the shear web <NUM> based on an expected load condition. While the inclusion of the open lattice structure <NUM> to at least one face <NUM>, <NUM> of the web structure <NUM> increases weight, the overall strength of the shear web <NUM> is increased. Thus, a single shear web in accordance with the present design may replace spar structures having multiple shear webs (i.e., the spar structure has fewer shear webs). Accordingly, the overall weight of the spar structure may be reduced.

In an alternative embodiment, in addition to the open lattice structure <NUM> formed on at least one of the faces <NUM>, <NUM> of the web structure <NUM>, an open lattice structure <NUM> similar to structure <NUM> may also be formed on the flanges <NUM>, <NUM> of the shear web <NUM>, such as on an outer face <NUM> of the flanges <NUM>, <NUM>. These open lattice structures <NUM> provide increased strength to the flanges <NUM>, <NUM> and may improve the bonding of the flanges <NUM>, <NUM> to the spar caps <NUM>, <NUM> of the spar structure <NUM>. The overall extent of the flanges <NUM>, <NUM> in the thickness wise direction may also be reduced due to the load carrying capability of the open lattice structures <NUM>. In still a further embodiment, the open lattice structures <NUM> may be formed on the flanges <NUM>, <NUM> with the web structure being of a conventional design with no open lattice structure <NUM> formed thereon. Thus, in at least some of the hybrid embodiments, open lattice structures <NUM>, <NUM> may be selectively added to various portions of a conventionally made shear web <NUM>, including along at least some portion of the web structure <NUM> and/or flanges <NUM>, <NUM> to increase strength.

The design freedom afforded to the shear web as a result of continuous fiber-reinforced additive manufacturing may provide other advantages and address other issues related to shear web design for wind turbine blades. One issue, for example, is that the shear web is typically subjected to relatively high peel loads near the root end of the wind turbine blade. Due to the design flexibility afforded by aspects of the present invention, peel loads in the root end of the blade may be reduced by providing a force path that extends predominantly in the spanwise direction of the shear web. In an exemplary embodiment, this may be achieved by two means. First, as illustrated in <FIG>, the shear web <NUM> may include at the root end <NUM> of the blade <NUM> a portion of the flanges <NUM>, <NUM> that extends beyond the intermediate web structure <NUM> in the spanwise direction (i.e., there is no corresponding web structure between the two opposed flanges). This portion of the flanges <NUM>, <NUM> is referred to herein as the flange extension tab <NUM>.

Second, and as also demonstrated in <FIG>, in a transition region <NUM> of the intermediate web structure <NUM> adjacent the root end <NUM> of the blade <NUM>, the composite spindles <NUM>, <NUM>, <NUM>, <NUM>, either in the spanwise panels <NUM> or the chordwise panels <NUM> extending away from the flanges <NUM>, <NUM> become locally curved or bent (i.e., swept) in a smooth manner so as to intersect the flanges <NUM>, <NUM> at a reduced angle θ. The angle θ preferably becomes progressively smaller in a direction toward the end of the web structure <NUM> (adjacent the root end <NUM> of the blade <NUM>) in the spanwise direction. The localized and progressive curving of the spindles <NUM>, <NUM>, <NUM>, <NUM> of the web structure <NUM> extending from the flanges <NUM>, <NUM> in the transition region <NUM> of the shear web <NUM> adjacent the root end <NUM> of the blade <NUM>, which is referred to herein as a scallop configuration, provides a force path that is more tangential to the plane defined by the flanges <NUM>, <NUM>. Accordingly, the forces are directed more along the spanwise direction of the flanges <NUM>, <NUM> as opposed to a more transverse or perpendicular direction. This local redirection of the forces in the transition region <NUM> reduces the peel forces on the flanges <NUM>, <NUM> of the shear web <NUM> adjacent the root end <NUM> of the blade <NUM>.

The extension tab <NUM> of the flanges <NUM>, <NUM> not only facilitates the scalloped configuration of the spindles of the web structure <NUM> adjacent the root end <NUM> of the blade <NUM> but also provides a more convenient region for providing addition securement of the shear web <NUM> to the inner surface of the blade root. By way of example, <FIG> illustrates an embodiment where the extension tab <NUM> is used in an overlamination process utilizing one or more fiber layers <NUM> and resin to further secure the shear web <NUM> to the outer shell <NUM> at the root end <NUM> of the blade <NUM>. <FIG> illustrates another embodiment where the extension tab <NUM> has a widened portion <NUM> (i.e., an increased width as compared to the flange widths where portions of the web structure exist) moving toward the end of the flanges <NUM>, <NUM> for at least a portion of the length of the extension tab <NUM> (e.g., over <NUM>% and preferably over <NUM>% of the length of the extension tab <NUM>). This configuration, referred to herein as a flipper configuration, provides for an increased area for adhesively bonding the shear web <NUM> to the outer shell <NUM> at the root end <NUM> of the blade <NUM>. An overlamination process may also be used to provide additional securement of the shear web <NUM> at the root end <NUM> of the blade <NUM> (not shown). It should be understood that the above configuration of the extension tab <NUM> of the flanges <NUM>, <NUM> applies to conventionally manufactured flanges through, for example, a moulding process, or flanges <NUM>, <NUM> configured as open lattice structures manufactured through, for example, continuous fiber-reinforced additive manufacturing processes as described above.

As the length of wind turbine blades continue to increase, the logistics of manufacturing and transporting such elongate structures has become increasingly complex. The continued scaling of wind turbine blades and their manufacturing equipment has inherent and practical limitations. To address these limitations, sectional wind turbine blades have been developed that divide the blade into a plurality of sections which are joined end-to-end to form the wind turbine blade. <FIG>, for example, illustrates the wind turbine blade <NUM> being formed by a plurality of blade sections <NUM> that are joined to each other at a connection interface <NUM>. The connection interfaces <NUM> between adjacent blade sections <NUM> may present a point of weakness in the structural integrity of the wind turbine blade <NUM> and are often reinforced to account for the application and transfer of loads on the blade <NUM> in the region about the connecting interface <NUM>.

In this regard, the shear web <NUM> in the respective blade sections <NUM> may be configured to overlap or nest in some manner to provide strength at the connection joint <NUM> between the sections <NUM>. <FIG> illustrate a sectional wind turbine blade <NUM> wherein the web structure 50a from one blade section 116a and the web structure 50b from the adjacent blade section 116b having an overlapping or nesting relationship. In this regard, the web structure 50a includes a recess <NUM> and the web structure 50b includes an extension <NUM> and the extension <NUM> is configured to be received in the recess <NUM> when the blade sections 116a, 116b are connected to each other at the connection interface <NUM>.

In this embodiment, the configuration of the web structure 50a in the first blade section 116a and the web structure 50b in the second blade section 116b are configured to match such that the spindles that form the web structures 50a, 50b are aligned with each other when the extension <NUM> is received in the recess <NUM>. <FIG>, for example, schematically illustrates how the cross spindles <NUM> in a spanwise panel <NUM> of the web structure 50a align with the cross spindles <NUM> in the corresponding spanwise panel <NUM> of the web structure 50b. By aligning the spindles of the web structures between the first and second blade sections 116a, 116b, the force path between the lower and upper flanges <NUM>, <NUM> remains continuous across the connection joint <NUM>. This makes for a stronger connection between the blade segments 116a, 116b.

Claim 1:
A shear web (<NUM>) for a wind turbine blade (<NUM>), comprising:
a lower flange (<NUM>);
an upper flange (<NUM>); and
a web structure (<NUM>) extending between the lower and upper flanges (<NUM>, <NUM>),
wherein at least one of the lower flange (<NUM>), upper flange (<NUM>), and the web structure (<NUM>) includes an open lattice structure (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>) having a plurality of elongate fibrous composite spindles (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) intersecting each other at multiple nodes of the open lattice structure, the web structure (<NUM>) includes a three-dimensional open lattice structure (<NUM>, <NUM>), and wherein the plurality of elongate fibrous composite spindles (<NUM>, <NUM>, <NUM>, <NUM>) extends in three dimensions, characterized in that the web structure (<NUM>) comprises:
a plurality of first open lattice panels (<NUM>), each of the plurality of first panels (<NUM>) including a plurality of spindles (<NUM>, <NUM>) extending within a plane defined by the panels; and
a second plurality of open lattice panels (<NUM>), each of the plurality of second panels (<NUM>) including a plurality of spindles (<NUM>, <NUM>) extending within a plane defined by the panels,
wherein the plurality of first panels (<NUM>) intersects the plurality of second panels (<NUM>) at multiple nodes to define the three-dimensional open lattice structure.