UNIDIRECTIONAL LAID NONWOVEN AND USE THEREOF

Abstract

For the production of components made of fiber-reinforced composites, in particular for the production of rotor blade belts, a unidirectional non-crimp fabric made of glass fiber rovings is provided, the non-crimp fabric having a first stabilizing layer on the underside thereof and a second stabilizing layer on the upper side thereof, which layers are sewn together by pillar stitching.

Claims

1. A unidirectional non-crimp fabric of glass fiber rovings for the production of fiber composites, comprising: a first stabilization layer on an underside thereof and a second stabilization layer on an upper side thereof, wherein the first stabilization layer and second stabilization layer are sewn to each other by pillar stitching.

2. The unidirectional non-crimp fabric according to claim 1, wherein the pillar stitching extends essentially parallel to the glass fiber rovings.

3. The unidirectional non-crimp fabric according to claim 1, wherein the pillar stitching has a stitch density of between 5 stitches per inch (spi) and 12 stitches per inch (spi).

4. The unidirectional non-crimp fabric according to claim 1, wherein at least one stabilizing element is present in parallel to the direction of the non-crimp fabric.

5. The unidirectional non-crimp fabric according to claim 4, wherein the at least one stabilizing element is rod-shaped.

6. The unidirectional non-crimp fabric according to claim 5, wherein the at least one stabilizing element is formed as a pultrudate of glass fiber and resin.

7. The unidirectional non-crimp fabric according to claim 1, wherein the first and/or the second stabilization layer is formed as a weft layer and/or as a fleece and/or as a mat.

8. The unidirectional non-crimp fabric according to claim 7, wherein at least one stabilization layer comprises the weft layer, wherein the weft layer is arranged at an angle in the range of 65 to 110, with respect to the direction of the non-crimp fabric.

9. The unidirectional non-crimp fabric according to claim 8, wherein both stabilization layers comprise the weft layer arranged at essentially the same angle with respect to the direction of the non-crimp fabric.

10. The unidirectional non-crimp fabric according to claim 7, wherein at least one of the first and second stabilization layers comprises the weft layer, wherein the weft layer is made of glass fibers.

11. The unidirectional non-crimp fabric according to claim 10, wherein the weft layer is made of glass fiber rovings having a weight of between 34 tex and 300 tex.

12. The unidirectional non-crimp fabric according to claim 7, wherein both stabilizing layers comprise the weft layer, wherein the weft layers are stitched true to mesh.

13. A method for producing a wind turbine component, comprising: obtaining the unidirectional non-crimp fabric according to claim 1, and producing a component of a wind turbine therewith.

14. The method according to claim 13, wherein rotor blade components are produced.

15. The method according to claim 13, wherein rotor blade belts are produced.

16. The unidirectional non-crimp fabric according to claim 8, wherein the weft layer is arranged at an angle in the range of 80 to 100.

17. The unidirectional non-crimp fabric according to claim 2, wherein the pillar stitching has a stitch density of between 5 stitches per inch (spi) and 12 stitches per inch (spi), and wherein at least one stabilizing element is present in parallel to the direction of the non-crimp fabric.

18. The unidirectional non-crimp fabric according to claim 17, wherein the at least one stabilizing element is rod-shaped, and wherein the at least one stabilizing element is formed as a pultrudate of glass fiber and resin.

19. The unidirectional non-crimp fabric according to claim 18, wherein the first and/or the second stabilization layer is formed as a weft layer and/or as a fleece and/or as a mat, wherein at least one stabilization layer comprises the weft layer, wherein the weft layer is arranged at an angle in the range of 65 to 110, with respect to the direction of the non-crimp fabric, and wherein both stabilization layers comprise the weft layer arranged at essentially the same angle with respect to the direction of the non-crimp fabric.

20. The unidirectional non-crimp fabric according to claim 19, wherein at least one of the first and second stabilization layers comprises the weft layer, wherein the weft layer is made of glass fibers, wherein the weft layer is made of glass fiber rovings having a weight of between 34 tex and 300 tex, and wherein both stabilizing layers comprise the weft layer, wherein the weft layers are stitched true to mesh.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The present invention will be explained in more detail with reference to a preferred exemplary embodiment. In the drawings:

[0024] FIG. 1 schematically shows the structure of a rotor blade of a wind turbine;

[0025] FIG. 2 schematically shows a sectional view of the structure of a rotor blade of a wind turbine;

[0026] FIG. 3 schematically shows the structure of a rotor blade belt;

[0027] FIG. 4 schematically shows the structure of a glass fiber roving;

[0028] FIG. 5 schematically shows the structure of a unidirectional non-crimp fabric comprising two stabilizing layers of a fleece;

[0029] FIG. 6 schematically shows the structure of a unidirectional non-crimp fabric comprising two stabilizing layers formed as mats;

[0030] FIG. 7 schematically shows the structure of a unidirectional non-crimp fabric comprising two stabilizing layers formed as weft layers;

[0031] FIG. 8 schematically shows front and rear views of pillar stitching;

[0032] FIG. 9 schematically shows front and rear views of tricot pillar stitching;

[0033] FIG. 10 schematically shows front and rear views of tricot stitching;

[0034] FIG. 11 schematically shows a plan view of a unidirectional non-crimp fabric comprising tricot pillar stitching;

[0035] FIG. 12 schematically shows a plan view of a unidirectional non-crimp fabric comprising pillar stitching; and

[0036] FIG. 13 schematically shows the structure of a unidirectional non-crimp fabric comprising two stabilizing layers of fleece and stabilizing element in the fabric layer.

DETAILED DESCRIPTION OF THE INVENTION

[0037] Due to their strength characteristics, fiber-reinforced composites made using the unidirectional non-crimp fabrics of glass fiber rovings provided here are particularly suitable for the production of components for wind turbines. FIG. 1 schematically shows the basic construction of a rotor blade 100 of a wind turbine. The rotor blade 100 is fixed to the rotary axle of a wind turbine as an extension of the root section 102. Below the shell 110, on the upper side and the underside, a belt 104 extends across shear webs 106, only one of which is shown in FIG. 1. The belts extend closer to the leading edge 114 than the trailing edge 116. FIG. 2 schematically shows a rotor blade 200 in cross-section, comprising belts 204 and shear webs 202, wherein each of the positions of the trailing edge 208 and the leading edge 206 are shown. The belts 204 extend along the entire rotor blade from the root section to the blade tip.

[0038] The belts 104 receive the main load of the forces acting on the rotor blade 100 when wind is blowing, and transmit them via the axle hub to a nacelle of the wind turbine, to generate electrical energy from the kinetic wind energy. This is why the belts have to have particularly high tensile stiffness in the longitudinal extension of the rotor blade, which is why a fiber-reinforced composite on the basis of a unidirectional non-crimp fabric is particularly suitable. Unidirectional non-crimp fabrics can also be used at the leading and trailing edge areas. Due to the different mechanical requirements, bi-, tri- or multiaxial fabrics can also be used for other rotor blade components, such as the shell 110, the shear web reinforcements 108, the core region 112 or the root section 102.

[0039] FIG. 3 schematically shows the basic construction of a rotor blade belt 300. A plurality of non-crimp fabrics 304 was stacked in accordance with the shape of the belt 300 to be produced, treated with resin 302, and this resin-containing overall structure was cured. This can be done using various methods known to the person skilled in the art: in the RTM method (Resin Transfer Moulding), for example, the resin 302 is injected into a closed mould, in which the non-crimp fabrics 304 have been placed before. In the vacuum infusion method, the non-crimp fabrics 304 are placed into the mould and covered by an air-tight plastic film. The resin 302 is sucked into the fabrics 304 between the mould and the film with the aid of a vacuum. Once the resin 302 is cured, the plastic film is removed and the belt 300 is taken out of the mould. Suitable resins and process parameters are known to the person skilled in the art.

[0040] FIG. 4 schematically shows a glass fiber roving 400 comprising a plurality of glass filaments 402. Usually, glass fiber rovings have a diameter of between about 12 m and about 24 m. For the production of rotor blade belts, in particular, glass fiber rovings 400 having a diameter of between about 17 m and 24 m may be suitable. Typical weights are about 1000 tex to 9600 tex, preferably 2400 to 4800 tex.

[0041] FIGS. 5 to 7 and 13 schematically show the structure of various unidirectional non-crimp fabrics 500, 600, 700, 1300 made of glass fiber rovings 502, 602, 702, 1302 for the production of fiber-reinforced composites comprising a first stabilizing layer 504, 604, 704, 1304 at its underside and a second stabilizing layer 506, 606, 706, 1306 at its upper side, stitched together by a knitting thread 508, 608, 708, 1308. For better identification of the details in the drawings, the unidirectional non-crimp fabrics 500, 600, 700, 1300 shown with reference to the present example are variants that are stitched true to gauge and essentially parallel to the glass fiber rovings 502, 602, 702, 1302. The glass fiber rovings 502, 602, 702, 1302 form an unfixed, freely spread layer, wherein for better understanding, the glass fiber rovings 502, 602, 702, 1302 are shown substantially spaced and slightly spread. In further variants, the stitching can also be not true to gauge and/or parallel to the glass fiber rovings 502, 602, 702, 1302. Both the stitching true to gauge and the parallel stitching result in particularly uniformly structured non-crimp fabrics without fiber damage and with reduced undulation tendency. This has a positive effect on the mechanical properties of the resulting components made of fiber-reinforced composite. Moreover, the spacing of the glass fiber rovings 502, 602, 702, 1302 or, as the case may be, their overlap and their degree of spreading may vary.

[0042] The non-crimp fabrics 500, 600, 700 corresponding to FIGS. 5, 6 and 7 differ in that the stabilizing layers 504, 604, 704, 1304, 506, 606, 706, 1306 each have a different configuration. In the present examples, both stabilizing layers 504, 506, 604, 606, 704, 706 each have the same configuration. In the example shown in FIG. 5, both stabilizing layers 504, 506 are a fleece, in the example shown in FIG. 6, both stabilizing layers 604, 606 are a mat, and in the example shown in FIG. 7, both stabilizing layers 704, 706 are a weft layer. In variants not shown in the drawings, both stabilizing layers can each have a different configuration and can have multiple layers. In the case of the variant having stabilizing layers comprising a weft layer, such as is shown in FIG. 7, the weft layer, or at least one of the two weft layers, can also comprise wefts that are less uniformly arranged which, as the case may be, can be arranged in a fashion that is less parallel.

[0043] It should be noted that in the examples shown here, the non-crimp fabrics 500, 600, 700 have precisely three layers, namely the two stabilizing layers on either side of a glass fiber roving layer. In variants not shown in the drawings, the non-crimp fabrics can also comprise three, four, five or more stabilizing layers and two, three, four or more unidirectional glass fiber roving layers. They can also comprise further, unspecified layers. All of the layers provided can be arranged in an order adapted to the desired application. Advantageously, the two outermost layers are stabilizing layers.

[0044] The unidirectional non-crimp fabric 1300 according to the example shown in FIG. 13, like the fabric shown in FIG. 5, has a fleece as the first and second stabilizing layer 1304, 1306, respectively. It differs from the examples according to FIGS. 5, 6, 7, in particular, in that it comprises at least one stabilizing element 1312 in parallel to the orientation of the non-crimp fabric. In the example shown in FIG. 13, a non-crimp fabric 1300 having four glass fiber rovings 1302 and one stabilizing element 1312 is depicted. In variants, instead of each fifth glass fiber roving 1302, a larger or smaller number of glass fiber rovings 1302 could also be replaced by a stabilizing element 1312. Herein, the stabilizing elements can be arranged at regular or irregular intervals. In the example shown in FIG. 13, the stabilizing element 1312 has a rod shape and is formed as a pultrudate made of glass fiber and resin. In variants, this could also be pultrudates of other fibers than glass fibers, or the resin could be uncured or only partially cured. Preferably, the pultrusion resin is adapted to the matrix resin of the fiber-reinforced composite to be produced.

[0045] In the example shown in FIG. 7, comprising weft layers as stabilizing layers 704, 706, the weft layers are formed of glass fiber rovings having a weight of between 34 tex and 300 tex, preferably between 40 tex and 150 tex, particularly preferably between 40 tex and 80 tex. Herein, both stabilizing layers 704, 706 are arranged at essentially the same angle with respect to the non-crimp fabric orientation, namely about 90. In variants, the weft layer can also be arranged at an angle in the range between 65 and 110, preferably between 80 and 100, with respect to the non-crimp fabric orientation. In the present example, the individual wefts have a spacing of a little more than a width of a roving 702 with respect to each other and are bound together in a manner true to mesh by means of stitching to the glass fiber rovings 702 using knitting threads 708.

[0046] It should be noted that the material of the stabilizing layers as well as the knitting threads for stitching are adapted to the resin used for further processing to produce a fiber-reinforced plastic component. In particular, hybrid fibers can be used. It is also possible to provide the non-crimp fabric with a binder, to fix it in a desired contour or shape as a preform.

[0047] The presence of two stabilizing layers in the proposed unidirectional non-crimp glass roving fabrics allows the three layers, i.e. the first stabilizing layer, the non-crimp fabric layer and the second stabilizing layer to be stitched together by means of pillar stitching. The structure of the pillar stitching is schematically shown in FIG. 8 for a first and a second thread 804, 806 on the front side 800 and the back side 802. For reasons of comparison, FIG. 9 shows the tricot pillar stitch and FIG. 10 the tricot stitch in an analogous fashion, for a first and a second thread 904, 906 and 1004, 1006, respectively, on the front side 900 and 1000, respectively, and the back side 902 and 1002, respectively. In the tricot stitch and the tricot pillar stitch which, unlike the pillar stitch, can also be used in unidirectional non-crimp roving fabrics comprising only one stabilizing layer, the knitting thread is always, or at least partially, routed across the rovings, even if stitching is performed in parallel to the rovings. This has as a result that when the unidirectional non-crimp fabrics are placed in the moulds and they are deformed in the lateral direction, warping may arise, which results in undulations in the non-crimp fabric.

[0048] This is schematically shown in FIG. 11 for a unidirectional non-crimp fabric 1100 made of glass fiber rovings 1102 and knitting threads 1104 stitched by means of tricot pillar stitching. When stitching is performed by means of tricot stitching, the undulation formation is even more pronounced. After the composite has been produced, undulation can lead to weaker strengths and stiffnesses than desired in the resulting component and can be regarded as a production defect. Furthermore, as a result of the tricot pillar stitching, or tricot stitching, drapability of the unidirectional non-crimp fabric in the lateral direction can be reduced, which can lead to creasing and/or wrinkling and consequently to reduced strength when the non-crimp fabric is placed in the mould for further processing. Furthermore, depending on the gauge of the knitting thread, routing the knitting thread 1104 across the rovings 1102 can lead to undesirable thickening of the non-crimp fabric. Moreover, depending on the gauge of the knitting thread and the stitching tension, in particular when the stitching is not true to gauge, material can be displaced at the point of the needle entry, which can lead to undulations and constrictions of the glass rovings 1102. This, in turn, can lead to the formation of defects, or so-called fish eyes, in the cavities at the place of needle entry, at which resin collects when the fabric is infused with resin. Since cured resin is often brittle and, with most resins, the knitting thread only connects with difficulty with the resin matrix, microscopic cracks can arise in the interface region between the knitting thread and the resin matrix under dynamic loading, which can lead to later damage by untimely material fatigue.

[0049] When the knitting threads 1204 are stitched by means of pillar stitching, as schematically shown in FIG. 12, they extend in parallel to the rovings 1202 extending straight as before. The pillar stitching enables much better deformation behaviour in the lateral direction than the tricot stitching or tricot pillar stitching so that wrinkling and creasing can be avoided when the non-crimp fabric is inserted in a mould prior to resin injection. The drapability is thus substantially better with pillar stitching than with tricot stitching or tricot pillar stitching. Moreover, the non-crimp fabrics can be placed in a flatter state without smoothing. In particular, the pillar stitching can be performed in such a manner that the glass fiber rovings are not perforated and no undesired resin islands are formed during further processing. The higher the percentage of knitting threads with respect to the unidirectional non-crimp fabric according to the present invention, the better the impregnating properties. However, if the percentage of the knitting thread is too high, this has a negative impact on drapability, so that the non-crimp fabric becomes stiffer. For the production of the rotor blade belts, in particular, a stitch density of between 5 stitches per inch and 12 stitches per inch has proven suitable in view of good drapability while retaining good impregnating properties. To increase the impregnation speed, thicker knitting threads and/or smaller intervals of the knitting threads can be provided.

[0050] Overall, however, the non-crimp fabric according to the invention comprising pillar stitching while keeping the parameters equal, has better impregnating properties for resin than non-crimp corresponding fabrics comprising other stitching connections, such as tricot stitching or tricot pillar stitching. It should be noted that better drapability can be observed with pillar stitching as compared to other stitching methods, even when the stitching is performed at a different angle than parallel to the rovings.

[0051] Tests have shown that in comparison to unidirectional non-crimp glass fiber roving fabrics having only one stabilizing layer and tricot stitching or tricot pillar stitching while keeping all other conditions and process parameters equal, the unidirectional non-crimp glass roving fabric of the present invention comprising two stabilizing layers and pillar stitching can achieve an increase in the tensile strength in the range of about 25% to 40% in a glass-fiber-reinforced laminated composite.

[0052] If a rotor blade belt is taken for example, which has a maximum thickness of about 100 mm, non-crimp fabrics having a surface weight of 1200 g/m.sup.2 require about 110 to 120 layers of a unidirectional non-crimp glass fiber roving fabric having only one stabilizing layer and a tricot stitch or a tricot pillar stitch, whereas when the unidirectional non-crimp glass fiber roving fabric having two stabilizing layers and pillar stitching is used, only 100 to 110 stacked unidirectional non-crimp fabric layers are needed to produce a rotor blade belt having comparable strength and stiffness. The smaller number of non-crimp fabric layers has the advantage that the production of the belt involves shorter laying times and smaller amounts of resin. The resulting weight savings for the belt and therefore also for the rotor blade can also have the effect that the nacelle and the tower of a wind turbine can also be reduced in weight.

[0053] Among others, tensile tests in accordance with DIN EN ISO 527-5 were carried out on three variants of unidirectional non-crimp fabrics made of glass fiber rovings. All three of the variants taken here as examples were cured laminar composites of epoxy resin, namely the resin system commercially available as HEXION RIMR135/RIMH137 on the basis of two stacked unidirectional non-crimp glass roving fabrics to achieve the minimum thickness required by the standard. Sample 1 had two non-crimp glass roving fabrics of glass fibers available as NEG Hybon 2002 with 2400 tex, or a nominal surface weight of 944 g/m.sup.2, each comprising a first and second stabilizing layer, arranged as weft layers of NEG Hybon 2002 with 68 tex, or a nominal surface weight of 12 g/m.sup.2 and at an angle of about 87 with respect to the basic fabric orientation, and an average of 1.8 stitches per cm. The stitching was carried out with a 76 dtex knitting thread made of polyester in the pillar stitch with respect to the weft layers not true to mesh, with a stitch density of 10 stitches per inch essentially parallel to the glass fiber rovings. Sample 2 differed from sample 1 in that the two non-crimp glass fiber roving fabrics were made of glass fibers available as 3B W2020 with 2400 tex, or a nominal surface weight of 944 g/m.sup.2, thus fibers made out of high-modulus glass. Sample 3 was a reference sample, which differed from sample 1 in that it only comprised one stabilizing layer, otherwise, however, formed in the same way as sample 1 or sample 2, and in that the stitching, unlike the stitching of sample 1 and sample 2, was carried out using a tricot stitch.

[0054] The tensile tests in accordance with DIN EN ISO 527-5 resulted in an average tensile strength of 1166 MPa for sample 1, 1270 MPa for sample 2 and 907 MPa for the reference sample 3. Since for reasons of manufacture, the fiber volume content varied about 532 Vol. %, the actual content was measured for each sample and the measured tensile strengths were linearly converted to a fiber content of 53 Vol. %.

[0055] Measurements on samples having other resin systems, other glass fiber rovings, other stabilizing layers, in particular also with fleeces and mats, but also with other variants of the weft layers, in particular with reference to its weight, spacing or orientation, as well as with stitching true to mesh and/or gauge, and with stitching having other stitch densities also resulted in increases in tensile strength.

LIST OF REFERENCE NUMERALS

[0056] 100 rotor blade [0057] 102 root section [0058] 104 belt [0059] 106 shear web [0060] 108 shear web reinforcement [0061] 110 shell [0062] 112 core area [0063] 114 leading edge [0064] 116 trailing edge [0065] 200 rotor blade [0066] 202 shear web [0067] 204 belt [0068] 206 leading edge [0069] 208 trailing edge [0070] 300 belt [0071] 302 resin [0072] 304 non-crimp fabric [0073] 400 roving [0074] 402 filament [0075] 500 non-crimp fabric [0076] 502 glass fiber roving [0077] 504 first stabilizing layer [0078] 506 second stabilizing layer [0079] 508 knitting thread [0080] 600 non-crimp fabric [0081] 602 glass fiber roving [0082] 604 first stabilizing layer [0083] 606 second stabilizing layer [0084] 608 knitting thread [0085] 700 non-crimp fabric [0086] 702 glass fiber roving [0087] 704 first stabilizing layer [0088] 706 second stabilizing layer [0089] 708 knitting thread [0090] 800 front side [0091] 802 back side [0092] 804 first thread [0093] 806 second thread [0094] 900 front side [0095] 902 back side [0096] 904 first thread [0097] 906 second thread [0098] 1000 front side [0099] 1002 back side [0100] 1004 first thread [0101] 1006 second thread [0102] 1100 non-crimp fabric [0103] 1102 roving [0104] 1104 knitting thread [0105] 1200 non-crimp fabric [0106] 1202 roving [0107] 1204 knitting thread [0108] 1300 non-crimp fabric [0109] 1302 glass fiber roving [0110] 1304 first stabilizing layer [0111] 1306 second stabilizing layer [0112] 1308 knitting thread [0113] 1310 fabric layer [0114] 1312 stabilizing element