Chamfered strip and beam for a spar cap of a wind turbine blade

The invention is directed at a strip for a spar cap of a wind turbine blade, wherein the strip is made from a composite ma terial. Further, the invention is directed at a beam for the spar cap having two or more of these strips. Also, the inven tion is directed at a spar cap having two or more of these beams and a wind turbine blade having one or more of these spar caps.

Wind turbine blades must be able to efficiently convert wind into a spinning movement of the wind turbine blades, so that the energy of the wind can be converted into rotary mechani cal movement of a rotor to which the wind turbine blades are attached. Dimensions of wind turbines and wind blades are ev er increasing, and consequently are increasing the challenges to overcome during the manufacturing processes of such wind turbine rotor blades.

It is preferable, to use materials having a high specific modulus (elastic modulus per mass density of a material), al so known as stiffness to weight ratio, in wind turbine blades to deal with the square-cube law governing the scaling of wind turbine blades. Therefore, composite materials such as carbon fiber-reinforced plastic having a high specific modu lus are commonly used in wind turbine blades.

Generally, strips made from composite material, such as car bon, may be applied in the manufacturing of a pre-casted spar cap so as to form a rectangular parallelepiped geometry. The strips are typically chamfered at both ends during manufac ture to ensure a smooth thickness reduction and also a smooth stiffness transition to interfaces, which for example may be made from unidirectional glass plies and be provided at the end of beam. Without chamfering the strips at these loca- tions, a significant shear stress transfer between different layers of strips in the spar cap may create cracks and delam ination in-between the layers of strips and in between the strips and the interfaces, and eventually lead to a failure of the wind turbine blade.

FIG. 3 shows a perspective view on a portion of a spar cap 31 according to the prior art. The upper illustration in FIG. 3 shows an exploded view of two beams 40.1, 40.2 joined on top of each other so as to form the spar cap 31 seen in the bot tom illustration of FIG. 3.

An upper beam 40.1 of the two beams 40.1, 40.2 has three strips 50.1, 50.2, 50.3 made from a composite material and joined with each other along their longitudinal extension. Each of the strips 50.1, 50.2, 50.3 has a chamfered end re gion 51.1, 51.2, 51.3. These end regions 51.1, 51.2, 51.3 are located at free ends of the strips 50.1, 50.2, 50.3. The chamfer in these end regions 51.1, 51.2, 51.3 is provided along its thickness. A lower beam 40.2 of the two beams 40.1, 40.2 has the same chamfer design as the top beam 40.1.

The direction of the chamfer of the chamfered end regions 51.1...51.6 of the strips 50.1...50.6 is unified in the longitu dinal direction of the spar cap 31. The chamfered end regions 51.1...51.6 of adjacent strips 50.1...50.6 start and end at re spectively the same length position of the strips 50.1...50.6.

The design of the spar cap in the state of the art can only be changed in a very limited way to further improve the above-mentioned shear stress transfer and further optimize other areas for improvement, such as areas relating to design and mass of the spar cap, for example.

Thus, there is still a need for a design of a spar cap and components thereof, in particular strips and beams, which provides improved stress distribution and design options at little manufacturing costs. This problem is solved by the subject-matter of the claims. Therefore, this object is solved by a strip for a spar cap of a wind turbine blade according to claim 1, a beam according to claim 7, a spar cap according to claim 13, a wind turbine blade according to claim 14 and a method for machining a strip according to claim 15. Further details of the invention unfold from the other claims as well as the description and the drawings. Thereby, the features and details described in connection with the strip of the invention apply in connec tion with the beam according to the invention, the spar cap of the invention, the wind turbine blade of the invention and the method of the invention as well as the other way around, so that regarding the disclosure of the individual aspects of the invention it is or can be referred to one another.

According to a first aspect of the invention, the problem is solved by a strip for a spar cap of a wind turbine blade. The strip is made from a composite material comprising a matrix and a reinforcement. The strip comprises a first end region and a second end region connected to one another in a longi tudinal direction of the strip by an intermediate region. The intermediate region comprises two mutually opposed longitudi nally extending and parallelly disposed intermediate surfac es. A thickness of the strip is determinable perpendicular to the two intermediate surfaces. A width of the strip is deter minable perpendicular to the longitudinal direction of the strip and perpendicular to the thickness of the strip. At least one of the first and the second end regions is a cham fered end region, wherein the at least one chamfered end re gion starting from the intermediate region and extending in the longitudinal direction is simultaneously chamfered along the width and the thickness of the strip. The at least one chamfered end region has a first edge at the intermediate re gion and a second edge at its free end, wherein the first edge and the second edge are substantially parallel to one another. In the invention, the strip is chamfered or, in other words, tapered along its thickness and its width. Thereby, the strip according to the first aspect of the invention provides for particularly good shear stress transfer in the spar cap and provides advantageous design possibilities due to the chamfer of the strip along the width and the thickness of the strip.

Due to the substantially parallel edges in the at least one chamfered end region, the strip with chamfer in the thickness and width directions of the strip may be manufactured very cost-effective. The wording that the edges are substantially parallel to each other includes that the edges are parallel to each other as well as tolerances from an exact parallel ism. A single cutting step may be used in order to cut the strip such that the edges located at the end of the strip are parallel with each other and the chamfer is provided in the width and thickness direction. Thereby, cost-intensive ma chining of geometrically complex end regions of the strip may be avoided. The advantageous method for manufacturing the strip of the first aspect of the invention will be described later on in more detail.

The chamfer of the strip in the chamfered end region along the width means that the first edge and the second edge run transverse to the direction or extension of width of the strip. Thereby, when the first edge and the second edge run perpendicular to the longitudinal extension or together with the direction or extension of width of the strip, there is no chamfer of the strip along the width. Accordingly, the cham fer along the width of the strip may be seen when viewing the first edge and the second edge.

A width chamfer angle of the chamfer of the at least one chamfered end region is determinable or measurable between the first edge and the longitudinal direction or length of the strip. The width chamfer angle may be within the range of 10° to 80 °, in particular within the range of 20° to 70° and more particularly within the range of 30° to 60°. The width chamfer angle is an angle of less than 90° because the cham fered end region is chamfered in width direction of the strip. Because the second edge is substantially parallel to the first edge, the second edge has substantially the same width chamfer angle as the first edge determinable between the second edge and the longitudinal direction of the strip.

A thickness chamfer angle of the chamfering of the at least one chamfered end region is determinable or measurable be tween a bottom intermediate surface of the intermediate sur faces and a chamfered surface of the chamfered edge region. The thickness chamfer angle may be in the range of 0.2° to 5°, in particular in the range of 0.4° to 3° and moreover in particular in the range of 0.6° to 2°. The chamfered surface is the top surface having the chamfer or tapering along the thickness of the strip. The bottom intermediate surface is the one of the two intermediate surfaces which is opposite to the chamfered surface because the chamfered end region is chamfered at the top but not at the bottom. The chamfered surface on the other hand is adjacent to the top intermediate surface opposite to the bottom intermediate surface. The chamfered surface and the top intermediate surface share the first edge with each other or, in other words, are separated from one another by the first edge.

The reinforcement of the composite material may comprise uni directional fibers arranged in the longitudinal direction of the beam. In particular, the reinforcement of the composite material may be a plurality of unidirectional fibers.

The composite material may be a fiber-reinforced plastic, in particular a carbon fiber-reinforced plastic. Fiber- reinforced plastics, in particular carbon fiber-reinforced plastics, have a particularly high stiffness-to-weight ratio and are therefore preferably used where high loads are ap plied to the strip and thereby to the spar cap in which they are used. Further or alternative fiber-reinforced plastics for use in the strip may be glass fiber-reinforced plastic and aramid fiber-reinforced plastic, for example. In a carbon fiber-reinforced plastic, carbon fibers are the reinforcement and a polymer resin, such as epoxy, is the matrix. A carbon fiber-reinforced plastic may comprise further fibers such as glass fibers or aramid fibers as reinforcement. However, it is preferable that the carbon fiber-reinforced plastic com prises predominantly carbon fibers as reinforcement. Alterna tively, as the composite material of the strip, composite wood, ceramic matrix composite or a metal matrix composite may be used.

The strip may be a pultruded part or profile. Such pultruded strips may be employed in a particularly cost-efficient man ner in the manufacturing of the spar caps for the wind tur bine blades. It has been found that the machining of pultrud ed strips for the manufacture of spar caps including the above-mentioned single step of cutting may be implemented in a very cost-efficient manner.

According to a second aspect of the invention, the above- mentioned problem is solved by a beam for a spar cap of a wind turbine blade. The beam comprises at least two strips according to the first aspect of the invention. The strips are joined to each other such that they extend in parallel along a common longitudinal direction of the strips and the beam.

The joining of the strips with each other such that they ex tend in parallel along a common longitudinal direction of the strips and the beam may be done by adhesion. For example, the joint of the strips may be established by means of resin molding. The joined strips may be arranged adjacent to one another. The strips may be located in a common plane of the beam. The advantageous chamfered end regions provide for sev eral design possibilities with respect to arrangement of the strips in the beam. Different numbers of strips may be employed in the beam. For example, two, three, four, five or more strips may be used. The width of the intermediate regions of the individual strips in the beam may vary or be the same for all of the strips in the beam. The length and thickness of the interme diate regions of the strips is preferably the same for all of the strips in the beam.

The at least two strips may be located at outer longitudinal sides of the beam. Their chamfered end regions may be cham fered towards each other along their width and in the common longitudinal direction. In other words, the first edges and second edges of the chamfered end regions of the at least two strips may be extending towards each other in the common lon gitudinal direction. Such a design may also be referred to as a double side chamfer design. The design is particularly ad vantageous with respect to mitigating the risk of failure of the beam due to fatigue. This is achieved by the width cham fering of the chamfered end regions, whereby transverse wrin kles in the beam are avoided.

The double side chamfering design enables variation of the width of the beam and thereby the spar cap in the longitudi nal direction or, speaking in terms of the wind turbine blade, the spanwise direction of the wind turbine blade. Ac cordingly, the width of the beam may decrease in the longitu dinal direction towards its free end. Accordingly, the beam may be positioned as close to the tip of the wind turbine blade as possible. Further, the overall blade mass and mass moment may be lowered and consequently the costs of the wind turbine blade may be decreased.

At least two of the chamfered end regions of the strips in the beam may be different from one another. In particular, the chamfered end regions being different from one another may have different width chamfer angles and/or starting posi tions of the chamfer along the length of the strips or, in other words, have their first edges provided at different length positions of the strips. Accordingly, the chamfered end regions of the strips are thereby distributed asymmetri cally with respect to a center line of the beam extending in the longitudinal direction. Such asymmetric design may be used to improve the load characteristics of the wind turbine blade at the trailing edge or leading edge, for example, by accordingly distributing the overall chamfer towards the trailing edge or leading edge.

The first edges of the strips may be connected to each other forming a common first edge and the second edges of the strips may be connected to each other forming a common second edge. Thereby, an integral design of the beam is provided without having any possibly detrimental design aspects. The first edges and second edges may be aligned in a straight line with each other or connected together as such that a corner is formed between the edges.

At least one further strip may be disposed in between the at least two strips according to the first aspect of the inven tion, wherein that further strip is not chamfered along its width. Accordingly, the further strip may only be chamfered along its length. The thickness chamfer angle of the further strip may be the same as the one of the two strips according to the first aspect of the invention.

According to a third aspect of the invention, the invention is solved by means of a spar cap for a wind turbine blade, the spar cap having at least two beams according to the sec- ond aspect of the invention stacked on top of one another as layers of the spar cap.

The different beams or layers of the spar cap may be adhe sively joined to each other. For example, resin molding may be used for joining them with each other. The number of beams or layers stacked on top of each other may be in the range of 2 to 12, for example. According to a fourth aspect of the invention, the above- mentioned problem is solved by means of a wind turbine blade of a wind turbine, the wind turbine blade comprising a shell and a spar having at least one spar cap according to the third aspect of the invention.

The spar cap according to the third aspect of the invention may be located at different locations of the wind turbine blade. For example, such a spar cap may be located in the main spar but alternatively or additionally may also be lo cated at the trailing edge or at any other spar location of the wind turbine blade.

According to a fifth aspect of the invention, the above- mentioned problem is solved by means of a method for machin ing a strip according to the first aspect of the invention. The method comprises the step of machining the at least one chamfered end region in the strip. The machining is performed by cutting off a portion from the at least one chamfered end region in the strip in a single cutting step such that the at least one chamfered end region is machined.

For the cutting step, any simple cutting tool such as a blade may be used. The cutting tool may be oriented relative to the strip such that the width chamfer angle and the thickness chamfer angle are machined into the strip when the cutting tool is guided through the strip. Because it is sufficient to perform only a single cutting step to machine the chamfered end region having the chamfer along width and thickness, the machining and consecutive layup of the strips for the beam and the spar caps can be done very efficiently. Accordingly, the method provides for an effective yet cost-efficient pro duction of wind turbine blades.

Further advantages, features and details of the invention un fold from the following description, in which by reference to drawings FIGS. 1 to 9 embodiments of the present invention are described in detail. Thereby, the features from the claims as well as the features mentioned in the description can be essential for the invention as taken alone or in an arbitrary combination. In the drawings, there is schematical ly shown:

FIG. 1 a side view on an embodiment of a wind turbine ac cording to the invention,

FIG. 2 a sectional view along a transversal plane of an embodiment of a wind turbine blade according to the invention and of the wind turbine of FIG. 1,

FIG. 3 a side perspective view on a spar cap according to the prior art,

FIG. 4 a side view on a strip for a spar cap of the wind turbine blade of FIG. 2,

FIG. 5 a side perspective view on a portion of the strip of FIG. 4 for use in a spar cap according to FIG. 2,

FIG. 6 a schematic representation of a portion of a spar cap according to a first embodiment of the inven tion,

FIG. 7 a schematic representation of a portion of a spar cap according to a second embodiment of the inven tion,

FIG. 8 a schematic representation of a portion of a spar cap according to a third embodiment of the inven tion, and

FIG. 9 a schematic representation of a portion of a spar cap according to a fourth embodiment of the inven tion. Same objects in FIGS. 1 to 9 are denominated with the same reference number. If there is more than one object of the same kind in one of the figures, the objects are numbered in ascending order with the ascending number of the object being separated from its reference number by a dot.

FIG. 1 is a side view on an embodiment of a wind turbine 1 according to the invention. The wind turbine 1 is provided with three wind turbine blades 10.1, 10.2, 10.3 attached to a hub 4 of the wind turbine 1, which is connected to a nacelle 3 of the wind turbine 1, the nacelle 3 being supported on a mast 2 of the wind turbine 1.

FIG. 2 is a sectional view along the transversal plane of line II-II depicted in Fig. 1 of the wind turbine blade 10.1 of the wind turbine 1 of Fig. 1. The wind turbine blade 10 has a trailing edge 11 and a leading edge 12. The wind tur bine blade 10.1 comprises a shell 20 and a spar 30. The spar

30 comprises three spar caps 31.1, 31.2, 31.3. The two spar caps 31.1, 31.2 face each other and are connected to one an other by means of a spar web 32. The spar caps 31.1, 31.2 form the main spar of the wind turbine blade 10. The spar cap 31.3 is arranged at the trailing edge 11 of the wind turbine blade 10.

The described design of the wind turbine blade 10 is only ex emplary and other designs may benefit from the strips 50 and beams 40 as proposed by this invention. In particular, the spar caps 31 manufactured using the strips 50 and beams 40 as described herein may be located at any suitable location of spar caps 31 in such wind turbine blade 10.

In the exemplary drawing of FIG. 2, the spar cap 31.3 com prises four beams 40.1, 40.2, 40.3, 40.4 stacked on top of one another. However, any number of beams 40 can be provided in any of the spar caps 31.1, 31.2, 31.3. Each of the beams 40 employed in the wind turbine blades

10.1, 10.2, 10.3 may be made up of several strips 50 located adjacent to each other as will be explained with reference to the following drawings. Each one of these strips 50 is made from a composite material. The number of beams 40 and strips 50 provided in the following embodiments of the invention is only chosen according to one example and may be amended to any other suitable number. For example, the number of beams 40 in a spar cap 31 may be 2 to 12 and the number of adjacent strips 50 may be 2 to 8, for example.

FIG. 3 shows a perspective view of a portion of a spar cap 31 according to the prior art. The upper illustration in FIG. 3 shows an exploded view of two beams 40.1, 40.2 joined on top of each other so as to form the spar cap 31 seen in the bot tom illustration of FIG. 3.

A top beam 40.1 of the two beams 40.1, 40.2 has three strips

50.1, 50.2, 50.3 made from a composite material and joined with each other along their longitudinal extension. Each of the strips 50.1, 50.2, 50.3 has a chamfered end region 51.1,

51.2, 51.3. These end regions 51.1, 51.2, 51.3 are located at free ends of the strips 50.1, 50.2, 50.3. The chamfer in these end regions 51.1, 51.2, 51.3 is provided along its thickness. A bottom beam 40.2 of the two beams 40.1, 40.2 has the same chamfer design as the top beam 40.1.

The direction of the chamfer of the chamfered end regions 51.1...51.6 of the strips 50.1...50.6 is unified in the longitu dinal direction of the spar cap 31. The chamfered end regions 51.1...51.6 of adjacent strips 50.1...50.6 start and end at re spectively the same length position of the strips 50.1...50.6.

FIG. 4 is a side view on a strip 50 for one of the spar caps 31 in the wind turbine blade 10 of FIG. 1. This strip 50 is designed according to a possible embodiment of the invention and is further illustrated in FIG. 5. The strip 50 has an intermediate region 53 and two longitudi nally opposed end regions 51, 52 being separated from one an other by means of the intermediate region 53. The end regions 51, 52 are chamfered in a longitudinal direction D (see FIG.

5) measurable along the length L of the strip 50.

The intermediate region 53 has two mutually opposed interme diate surfaces 54, 55. The intermediate surfaces 54, 55 ex tend longitudinally in the longitudinal direction D. The in termediate surfaces 54, 55 are disposed parallel to each oth er. The intermediate surfaces 54, 55 may be generally planar. The term generally planar includes planar and deviations from planar surfaces depending on the material of the intermediate region 53 and/or the manufacturing process by means of which it is manufactured. A thickness T of the strip 50 is determi nable or measurable between the intermediate surfaces 54, 55 and perpendicular to the intermediate surfaces 54, 55.

The end regions 51, 52 are chamfered or, in other words, ta pered in the longitudinal direction D following the length L of the strip 50. Accordingly, the end regions 51, 52 may also be referred to as chamfered or tapered end regions 51, 52. A thickness chamfer angle b of the chamfered end regions 51, 52 in the longitudinal direction (depicted only for the cham fered end region 51 but also applicable to the chamfered end region 52 with the same or a different thickness chamfer an gle b) is determinable or measurable between the bottom in termediate surface 55 and the chamfered surface 59 of the chamfered end region 51. The chamfered surface 59 is the top surface of the chamfered end region 51. The bottom intermedi ate surface 55 is the one of the intermediate surfaces 54, 55 which is opposed to the top intermediate surface 54 of the intermediate surfaces 54, 55 and the chamfered surface 59.

The bottom intermediate surface 55 extends away from the in termediate region 53 towards and with the chamfered end re gions 51, 52 as the strip 50 is not chamfered on the bottom side thereof but only on the top side as seen in FIG. 4. Ac cordingly, the chamfered end regions 51, 52 have the bottom intermediate surface 55 as common, in particular planar, sur face.

In other words, the chamfered end regions 51, 52 are tapered or chamfered such that the thickness T of the end regions 51,

52 decreases along its length L towards free ends 58.1, 58.2 of the end regions 51, 52. The thickness T tapers with the second chamfer angle b.

FIG. 5 shows a side perspective view on a portion of the strip 50 of FIG. 4. The portion of the strip 50 having the chamfered end region 52 is not depicted but may be designed equally with respect to the design and/or dimensions, in par ticular chamfer angles and b, to the chamfered end region 51 seen in FIG. 5.

From FIG. 5 it may be taken that the strip 50 is not only chamfered along its thickness T with the thickness chamfer angle b in its chamfered end region 51 but that the chamfered end region 51 is as well or simultaneously chamfered or ta pered along the width W of the strip 50 with a width chamfer angle a. The width W of the strip 50 is measurable perpendic- ular to the thickness T and perpendicular to the length L or the longitudinal direction D, along which the length L of the strip 50 is measurable.

The width chamfer angle is measurable or determinable be tween a first edge 56 and the longitudinal direction D. The width chamfer angle is different from 90°, in particular less than 90 °, as it provides a chamfer. It may be within the range of 30° to 60°, for example.

The first edge 56 is an edge between the intermediate region

53 and the chamfered end region 51. The chamfer or taper of the chamfered end region 51 starts from the first edge 56.

The chamfered end region 51 ends at a second edge 57 located at one of two free ends 58 of the strip 50. The second edge 57 is substantially parallel to the first edge 56. Due to the edges 56, 57 being substantially parallel to one another, the chamfered end region 51 may be manufactured by one single step of cutting away a piece of the strip 50 at the chamfered end region 51. A complex and expensive machin ing is avoided and such machining of the strip 51 can be em ployed with little effort into consequent manufacturing of the beam 40 and spar cap 31.

FIGS. 6 to 9 show different embodiments of portions of beams

40.1, 40.2 and portions of spar caps 31 according to the in vention, which are manufacturable by using multiples of the strip 50 of FIGS. 4 and 5. The beams 40.1, 40.2 and the spar caps 31 are shown only in portion with one end, whereas the other end may be designed similar in shape and/or dimension.

The FIGS. 6 to 9 employ strips 50 according to FIGS. 4 and 5. However, the illustrations in FIGS. 6 to 9 are a schematic representation of the beams 40.1, 40.2 and the spar caps 31. Due to the small thickness chamfer angles b employed in the chamfer end regions 51, the chamfering may not be particular ly visible from the FIGS. 6 to 9. Accordingly, reference is made to the drawings FIGS. 4 and 5 with regard to the thick ness chamfers, which are exaggerated for illustration purpos es in FIGS. 4 and 5.

In each one of the spar caps 31 of FIGS. 6 to 9, two beams

40.1, 40.2 are employed. However, depending on the thickness T of the strips 50 and the required thickness of the spar cap 31, more or less than two beams 40.1, 40.2 may be used to manufacture the spar cap 31. Also, in FIGS. 6 to 9, three strips 50 are being employed for each one of the beams 40.1,

40.2. However, the number of strips 50 may be amended to two, four or more depending on the width W of the strips 50 and the required width of the spar cap 31.

The beam 40.1 in FIG. 6 makes use of two strips 50.1, 50.2 designed according to FIG. 5. A further strip 60.1 is placed in between the two strips 50.1, 50.2. The two strips 50.1, 50.2 are located at outer longitudinal sides 41, 42 of the beam 40.1 or, in other words, the strips 50.1, 50.2 form the longitudinal sides 41, 42 of the beam 40.1. Further strip

60.1 may be made from the same material as the strips 50.1, 50.2. The strips 50.1, 50.2, 60.2 are joined adjacent to each other along their length.

The chamfered end regions 51.1, 51.2 are simultaneously cham fered in the direction of the width W und the thickness T of the strips 50.1, 50.2. However, the chamfering is provided such that the chamfered end regions 51.1, 51.2 are chamfered towards each other. In other words, the first edges 56.1,

56.2 are extending towards each other along the length L or the common longitudinal direction D of the strips 50.1, 50.2, 60.1.

The further strip 60.1 is an intermediate strip 60.1 not hav ing a chamfer along the width W of that strip 60.1. This may be seen from the first edge 66.1 and second edge 67.1 of that further strip 60.1, which runs perpendicular to the common longitudinal direction D.

The further strip 60.1 has a chamfer along its thickness T. The thickness chamfer angle b of the further strip 60.1 may be the same as the thickness chamfer angles b of the strips 50.1, 50.2. In other words, the chamfer or taper along the thickness T of the strips 50.1, 50.2, 60.1 is the same for all of them.

The first edges 56.1, 66.1, 56.2 are connected to each other so as to form a common first edge of the beam 40.1. Also, the second edges 56.1, 66.2, 56.2 are connected to each other so as to form a common second edge of the beam 40.1.

The beam 40.2 is designed just like the beam 40.1 but has a greater length L extending in the common longitudinal direc tion D. The beam 40.1 is placed on top of the beam 40.2 and thereafter the beams 40.1, 40.2 are joined with each other, for example by means of resin molding. Thereby, the spar cap 31 seen in the lower portion of FIG. 6 is obtained.

Both beams 40.1, 40.2 are tapered at their free ends 44.1,

44.2 due to the width chamfer of the respective strips 50.1,

50.2, 50.3, 50.4 in their chamfered end regions 51.1, 51.2,

51.3, 51.4.

FIG. 7 shows a spar cap 31 similar to the one of FIG. 6 but with a slight amendment with respect to the outer strips

50.1, 50.2 used in the beam 40.1 (and in the beam 40.2 be neath it).

The strip 50.1 has a chamfered end region 51.1 starting at a position of length L of the strip 50.1 before the chamfered end region 51.3 of the strip 50.3 starts. The length differ ence of the positions of length L at which the chamfered end regions 51.1, 51.2 respectively start is indicated by an A.

Also, the width chamfer angle of the strip 50.1 is smaller than the width chamfer angle of the strip 50.2. Such asym metric design of the overall chamfered end regions 51.1,

61.1, 51.2 may be used to provide different characteristics for particular locations of spar caps 31 in the wind turbine blade 10.

FIG. 8 shows a further example of an asymmetric design of a spar cap 31 with respect to the chamfered end regions 51.1,

51.2, 51.3. The first edges 56.1, 56.2, 56.3 are lined up so as to form a common first edge along a straight line. Also, the second edges 57.1, 57.2, 57.3 are lined up so as to form a common second edge along a straight line. To achieve this, the strips 50.1, 50.2, 50.3 are provided with the same width chamfer angle but the chamfered end regions 51.1, 51.2,

51.3 start at different positions of length L of the strips 50.1, 50.2, 50.3 such that the first edges 56.1, 56.2, 56.3 and the second edges 57.1, 57.2, 57.3 are aligned with each other.

FIG. 9 shows a further example of an asymmetric design of a spar cap 31 with respect to the chamfered end regions 51.1, 51.2, 51.3. In this design of the spar cap 31, the beams 40.1, 40.2 are once again designed the same with respect to the chamfered end regions 51.1, 51.2, 51.3 but they have dif ferent lengths L. As in FIG. 8, three strips 50.1, 50.2, 50.3 are designed with chamfer along width W and thickness T. How ever, they are designed to form a common first edge and a common second edge having a V-shape.