WO2017178357A1

WO2017178357A1 - Reinforcement fabric

Info

Publication number: WO2017178357A1
Application number: PCT/EP2017/058350
Authority: WO
Inventors: Thomas James
Original assignee: Hexcel Reinforcements Uk Limited
Priority date: 2016-04-12
Filing date: 2017-04-07
Publication date: 2017-10-19
Also published as: GB2551104A; DE112017001983T5

Abstract

A reinforcement material which comprises layers of fibrous reinforcement material each layer comprising multiple fiber tows extending parallel to one another. The reinforcement material further comprises stitching which contrasts with the fiber tows.

Description

REINFORCEMENT FABRIC

The present invention relates to mouding materials and in particular to reinforcement materials or reinforcement fabrics. More particularly, the present invention relates to fabrics useful as reinforcement in composite structures and the resulting structures. A known method of forming reinforced plastics articles and composites is to lay a mat of a non-woven or woven glass fiber or other reinforcement material and wet the mat of material with a synthetic resin material, to cure the resin, and to remove the moulded article from the mould. When a greater thickness of reinforced composites material is required in the moulded article, then further mats of reinforcing material are laid upon the first, wetted, and cured. Textile fabric materials useful as reinforcement in such composite structures typically are either woven or stitch-bonded fabrics, using yarns of fibers such as fiberglass, carbon, or aramid (Kevlar) fibers. To form a useful article, each layer of the textile material must be fully wetted by the synthetic resin material before curing to avoid the creation of voids in the article, reducing its strength and integrity. The advantage of a woven fabric in composite structure is that the fabric is very pliable. This characteristic is advantageous when laying the fabric inside of an open or closed mold, where the resin is either applied or injected. The disadvantage of woven fabric in a composite structure is that a weave creates weak places in the yarn. This is due to how the yarns must go up-and-down in a weave forming crimps. These crimps create weak locations, in the finished composite structure.

For a non-woven fabric, or stitch-bonded fabric, the yarns are non-crimped, i.e., there is no repeated up-and-down orientation of the yarn as in a woven fabric. The yarns in a non-woven, stitch-bonded fabric can be laid-out in a fabric machine direction (warp of 0 degrees), perpendicular to the machine direction (weft or filling of 90 degrees), or at a +45/-45 degree angle to the machine direction. The yarns in this type of fabric are non-crimped.

Non-crimped fabrics have a wide range of applications and they may be pre-impregnated with a resin matrix containing one or more resin components and one or more curative components or they may be infused with a resin following their lay-up in a mould by means of conventional infusion techniques such as resin transfer moulding (RTM) and vacuum assisted resin transfer moulding (VARTM).

As non-crimp reinforcement fabrics contain a large number of fiber plies, it is important that these fabrics are laid up correctly in the mould and that they are not distorted in any way during subsequent moulding process steps which include lay-up, compression, evacuation, resin infusion and curing because distortions in the fiber orientation of the final cured composite part affect the mechanical performance of the part. Also distortions are aesthetically not please and give rise to undulations, dents and other imperfections such as pin holes and poor surface quality.

The present invention aims to address this problem and/or to provide improvements generally.

According to the invention there is provided a reinforcement material, a use, a method and a part as defined in any one of the accompanying claims.

In an embodiment of the invention there is provided a reinforcement material comprising a layer of fibrous reinforcement material comprising multiple fiber tows extending parallel to one another and stitching, wherein the stitching contrasts with the fiber tows.

The stitching preferably retains the orientation of the fiber tows in the layer.

In a preferred embodiment the reinforcement material contains multiple layers of fibrous reinforcement materials. The stitching bonds the multiple layers in relation to one another. In a further embodiment, the reinforcement material is non-woven. Preferably the reinforcement material is a non-crimp non-woven fabric comprising multiple layers.

The multiple layers may be maintained in their relative orientation by stitching. The stitching is formed by a yarn. The yarn has a colour which contrasts with the colour of the fiber tows of the layers. The fiber tows may comprise glass fiber, hemp, aramid, Kevlar^tm or carbon fiber and/or a mixture thereof. Preferably, the fiber tows comprise carbon fiber.

In a preferred embodiment the stitching comprises a contrasting colour which is selected such that in International Commission on Illumination (CIE) 1931 XYZ color space the colour of the stitching is selected in relation to the fiber tows so that at least one of the values X, Y, Z for the stitching differs from the corresponding parameter for the fiber tow by at least 10 to 100%, preferably from 15 to 80%, more preferably from 15 to 60%, and most preferably from 20 to 50% . This ensures that the stitching contrasts with the fiber tows.

In a further embodiment, two parameters selected from X, Y and Z differ from the corresponding parameters for the fiber tow by a percentage which ranges from 10 to 100%, preferably from 15 to 80%, more preferably from 15 to 60%, and most preferably from 20 to 50%.

In another embodiment, the parameters X, Y, and Z differ from the corresponding parameters for the fiber tow by a percentage which ranges from 10 to 100%, preferably from 15 to 80%, more preferably from 15 to 60%, and most preferably from 20 to 50%.

The colour and the relevant parameters CIE 1931 X, Y and Z are measured using a Hunterlab Labscan XE with UV in accordance with CIE No.15:2004.

In a preferred embodiment, the stitching comprises a yarn, the yarn being selected from the colours blue, yellow, green or red and/or combinations of the aforesaid colours. In another embodiment, the stitching may comprise multiple yarns, each having a different colour.

The stitching may be in the form of a tricot stitch, a pillar stitch or combinations of the aforesaid stitch patterns. The direction of the stitching is defined in this application as the direction in which the centre line of the stitching extends. This direction is selected to secure the layers in relation to one another and to also secure the fiber tows in each layer in their relative orientation.

The direction of the stitching may be defined by an offset angle β in relation to the direction of the tows of each layer, with β being the smallest angle between the tow direction and the direction of the stitching and 0° < β <90°, preferably 1 ° < β <89°, more preferably 2° < β <45°, and even more preferably 3° < β <85° and/or combinations of one or more of the aforesaid ranges.

In a further embodiment there is provided a method of manufacturing a composite part comprising the steps of a. providing one or more layers of a reinforcement material as herein before described in a mould to form a moulding assembly; b. applying a vacuum envelope to the moulding assembly; c. infusing the assembly with a flowable resin matrix; d. curing the resin matrix by increasing the temperature of the assembly; and e. removing the cured moulding assembly from the mould. The vacuum envelope is transparent so that the stitching can be viewed and any distortions in the reinforcement material can be spotted and remedied.

The invention will now be illustrated by way of example only with reference to the following Example 1 . Example 1

A multi-axial carbon fiber non crimp fabric of a weight of 407 gram per m² (gsm) comprises 4 layers of parallel carbon fiber tows of AS4 carbon fiber as supplied by Hexcel in different orientations as follows:

Layer 1 : 0° Layer 2 : - -45°

Layer 3 : 90°

Layer 4 : +45°

Each layer has a fiber areal weight of 100 grams per m² (100 gsm). The fibers are stitched together by a texture polyester yarn of 78 dtex using a ½ pillar tricot stitch having a stitch gauge of 6.0 gg, a stitch length of 2.5 mm at a stitch weight of 7 gsm.

The fabric is supplied on a roll at a width of 1270 mm.

The stich yarn is selected in the colour red to provide a contrasting colour with the carbon fiber tows.

In use, a layer of this material is laid up in a mould to form a moulding assembly. Using the standard VARTM process, the assembly is covered in a transparent vacuum envelope and vacuum is applied to the assembly. The assembly is infused with RTM 6 resin as supplied by Hexcel at room temperature conditions (21 °C). Following infusion, the temperature of the assembly is raised to 80 °C for 4 hours to cure the resin matrix. Finally, the cured moulding assembly is removed from the mould. The contrasting stitching enables visual inspection for any distortions in the reinforcement material during the various process steps for producing the cured moulding assembly or composite part. To facilitate visual inspection, the vacuum envelope is transparent so that the stitching remains visible. There is thus provided a multi-axial non crimp fabric which enables detection of distortions by comprising contrasting stitching include a method of moulding and manufacturing composite parts including parts made from the aforesaid fabric.

Claims

1 . A reinforcement material comprising a layer of fibrous reinforcement material comprising multiple fiber tows extending parallel to one another and stitching, wherein the stitching contrasts with the fiber tows.

2. A material according to claim 1 , wherein the material comprises multiple layers of fibrous reinforcement material each layer having tows which extend in a direction which differs from the direction of the tows of the layers in contact with this layer.

3. A material according to claim 1 or 2, wherein the tows are flat.

4. A material according to any of the preceding claims, wherein the stitching is perpendicular to the tows of at least one layer.

5. A material according to any of the preceding claims, wherein the stitching is offset at an angle β in relation to the direction of the tows of each layer, with angle β being the smallest angle between the direction of the tow and the stitching and with Oo < β <90o, preferably 1 o < β <89o, more preferably 2o < β <45o, and even more preferably 3o < β <85o and/or combinations of one or more of the aforesaid ranges.

6. A material according to any of the preceding claims, wherein the stitching comprises a stitch yarn comprising a colour which contrasts with the fiber tows.

7. A material according to any of the preceding claims, wherein he stitching comprises a contrasting colour which is selected such that the colour of the stitching is selected in relation to the fiber tows so that at least one of the values X, Y, Z of CIE 1931 XYZ color space for the stitching differs from the corresponding parameter for the fiber tow by at least 10 to 100%, preferably from 15 to 80%, more preferably from 15 to 60%, and most preferably from 20 to 50% .

8. A material according to any of the preceding claims, wherein the stitching runs in parallel spaced lines or directions when the material is directly supplied off a roll or spool, the lines being perpendicular to the axial direction of the roll or spool.

9. A material according to any of the preceding claims, wherein the stitching runs in the warp direction.

10. A material according to any of the preceding claims, wherein the stitching runs in the weft direction.

1 1 . A material according to any of the preceding claims, wherein the colour is selected from red, blue, green, yellow, or orange and/or a combination of one or more of the aforesaid colours.

12. An infused moulding comprising a material according to any of the preceding claims wherein the resin matrix is a solid at room temperature (21 °C).

13. A moulding according to claim 12 wherein the resin matrix is transparent.

14. A mouding according to any of claims 12 or 13, wherein the stitching is visible in the matrix.

15. A moulding according to any of claims 12 to 14, wherein the stitching runs in lines or directions which are parallel to one another.

16. A method of manufacturing a composite part comprising the steps of a. providing one or more layers of a material according to any of claims 1 to 1 1 in a mould to form a moulding assembly; b. applying a vacuum envelope to the moulding assembly; c. infusing the assembly with a flowable resin matrix; d. curing the resin matrix by increasing the temperature of the assembly; and e. removing the cured moulding assembly from the mould.

17. The method of claim 16 wherein the layers are provided in the mould such that the stitching remains parallel.

18. The method of claims 16 or 17 wherein the stitching is parallel prior to laying up of the material.

19. The method of claim 16 or 17 or 18 wherein the stitiching is parallel following step b and/or following step d.

20. The method of claims 16 to 19, wherein the vacuum envelope is transparent.

21 . Use of stitching to show distortions in a reinforcement material comprising a layer of fibrous reinforcement material comprising multiple fiber tows extending parallel to one another and stitching, wherein the stitching contrasts with the fiber tows.

22. Use according to claim 21 , wherein the reinforcement material comprises the features of any of claims 2 to 1 1 .

23. A composite part comprising a material as defined in any of claims 1 to 1 1 and/or produced by means of a method as defined in any of claims 16 to 20.

24. A composite part according to claim 23 wherein the part is a vehicle part, particularly but not exclusive a roof panel or roof.