I hereby license SAMPE to publish this paper and to use it for all SAMPE’s current and future

publication uses. Copyright 2010 by Sigmatex. Published by Society for the Advancement of

Material and Process Engineering with permission.

The Manufacture of One Piece Woven 3 Dimensional Carbon Fiber

Nodal Structures.

Christopher McHugh

Sigmatex

Manor Farm Road

Runcorn, Cheshire WA71TE

ABSTRACT

The use of Carbon Fiber 3D structures, whilst relatively new is becoming predominantly popular

in various technical applications. Novel processes can be employed to create various woven

architectures, however by adapting current technology, a wider skill base is available and the

manufacturability of complex structures and near net preforms becomes more attractive. The

purpose of this paper is to demonstrate how by combining current state of the art weaving

technology, 3D structural components can be manufactured. The ability to manufacture Nodal

structures in near net shape will provide repeatable components and reduced layup times with the

possibility to change weave style for improved functionality. Included in the work will be the

design method and manufacturing process resulting in a woven prototype structure.

1. INTRODUCTION

Whilst many methods exist for the manufacture of nodal textile structures, their use in Carbon

composite structures are limited. Textile knitted structures exist containing tubes with multiple

junctions, woven nodal structures have also been created for vascular implants, with the use of

shuttle weaving technology [1]. Both of these methods have their advantages for flexible textile

components, however for the manufacture of Carbon Fiber Nodal structures, the manufacturing

process provides inherent problems. During the course of this paper, the method of designing and

weaving 3D nodal preforms will be demonstrated, using conventional weaving methods. The

design and manufacturing method will focus on a generic node geometry which is currently

being developed as part of the UK Technology Strategy Board funded Advanced Composites

Truss Structure project.

2. METHODS OF MANUFACTURING NODAL SHAPES

Nodal shapes can be created by both Knitting and weaving processes. These methods of fabric

forming provide excellent properties for standard textile applications, where flexibility is

required, for example apparel. However the method by which the structures are manufactured

presents problems for the processing of Carbon fibers. Knitted fabrics are produced by the

creation of interconnected loops to form a material. The limitation of the material in composite

applications stems from the process limitations of the carbon fiber. When carbon fiber is

subjected to bending, the fiber filaments can split causing a reduction in fiber strength. The

combination of loops and acute angles during the knitting process limits the possibilities in

structural carbon fiber applications.

Woven carbon fiber structures are common in the composites Industry, with different weave

constructions offering different properties. During the weaving process the threads are interlaced

without the need to loop, so fiber strength is maintained. Additionally there are different weave

styles with less interlacing and lower crimp to further utilise the performance benefits offered by

Carbon Fiber. The Nodal structures can be created by weaving pockets in a multilayered

structure in various orientations. The nodes manufactured using this pocket method, can be

woven at any angle and can be woven with tapers.

3. 3D WEAVES SUITABLE FOR NODAL APPLICATIONS

3D textile structures are considered to improve inter-laminar shear, damage tolerance and other

through thickness properties [2]. There are various types of weave styles currently used for 3D

materials requiring through thickness reinforcement, each with their own characteristics.

Orthogonal, Angle Interlock, Layer to Layer and Stitched multilayer weaves will all provide Z

direction reinforcement, however they all have different material properties. The requirement for

drapability combined with through thickness reinforcement, will influence the chosen weave

style for this application. The following are some examples of multilayer weave styles which

have binding reinforcement through the thickness, with and without extra binding threads. The

images have been generated using TexGen software currently being developed by The

University of Nottingham [3].

3D Orthogonal weaves are designed with the Z binder going directly though the material as

shown in Figure 1. Orthogonal weaves can be designed to provide a certain amount of

drapability by reducing the sett of the fabric construction or by reducing the amount of Z binder

points. However when compared with Angle Interlock structures, Orthogonal structures with the

same sett will be stiffer, as all the layers within the structure are bound and interply movement is

reduced.

Figure 1 - Orthogonal Weave - X section through weft

Angle Interlock weaves are designed with the Z binder passing through the 3D material at an

angle. By varying the step of the Z binder through the structure, angles of higher and lower

amounts can be achieved. As with the Orthogonal weaves, Angle Interlock weave properties can

be influenced by changing the fabric sett and the amount of Z binding. Another important factor

using Angle Interlock weaves is the number of layers. If we consider two angle interlock fabrics

with the same angle but of double the thicknesses, the number of through thickness interlacing

points will be halved for the thicker structure. An angle Interlock weave is demonstrated which

shows the path of the Z binder passing from one surface to the other in Figure 2.

Figure 2 - Angle Interlock Weave - X section through weft

Layer to Layer weaves also use a Z binder thread which is used to link the layers. Each layer of

stuffer weft threads are stitched by the Z binder. Unlike Orthogonal and Angle Interlock

structures, the layer to layer weave style requires many more binder threads with each stuffer

thread having an adjacent binder thread. The Orthogonal and Angle Interlock weave styles can

use a single binder for each warp stack independent of number of layers, whilst the binders in a

Layer to Layer weave are directly linked to the number of layers. The image in Figure 3 shows

the number of binders for each warp stuffer stack for a Layer to Layer and Angle Interlock

weave style. In the illustration the thick threads are stuffers, with the binder as the thin thread.

This high density of interlacing would prohibit the drape of a 3D structure and will also have

implications on the material density capable of being achieved during the weaving process.

Figure 3 - Layer to Layer Binders compared to Angle Interlock Binder - X section through warp

Orthogonal, Angle Interlock and Layer to Layer weave styles are designed so that the Z binder

is used to bind the multiple layers of Warp and Weft Stuffers, if the Z binder was not used the

stuffer threads would fall apart. The Stitched multilayer shown in Figure 4 is based on 8 layers of

plain woven fabric which has threads stitching through to the next layer. This weave differs from

binder types, in that the stitches are achieved by the warp threads which make up the woven

structure as opposed to separate Z binder threads.

Figure 4 - Stitched Multilayer Weave – X section through weft

The stitched multilayer weave will have good drape by allowing a certain amount of interply

movement and rotation. The plain weave configuration whilst increasing the crimp will also

provide structural integrity during further processing.

4. DESIGN METHOD

The design description will focus on aspects of the weave design only and the process of creating

a finished design from initial CAD geometry. The process flow has already been defined [4],

with the main design requirements being Material Construction Definition, Protocol definition

and Design Creation.

4.1 Material Construction Definition

In the instance of creating the nodal structure, CAD geometry needs to be created demonstrating

angles required and key dimensional information. The actual Weave Design can be created from

a CAD drawing combined with the image or created solely using the weave design software. For

the purpose of this sample the Nodal structure was created using weave design software from

existing CAD geometry which was provided by Oxford Brookes University as part of the ACTS

project. An image of the proposed shape is demonstrated in Figure 5.

Figure 5 - 3D Nodal Design (Image by Alan Bond, Composite Integration Ltd)

With the Nodal shape determined the type of weave structure needs to be created which will

provide the required shape. As already discussed there are various types of 3D weaves available,

however with the complexity of the shapes and the acute angles present the weave type would

need to exhibit excellent drape characteristics. With the high amount of interlacing points, both

the Orthogonal and layer to layer variants would not be suitable. The Angle Interlock structures

are very open by their nature, which would make the material more drapable, however the thread

stability would be an issue and would limit handling and further processing of the finished

material. As the structure would need to be manipulated to form the shapes of the nodes, loose

threads at the node openings would have a tendency to fall away, so a stable material would be

preferred.

To overcome these issues a stitched multilayer weave would be the preferred option, the

structure will maintain some fabric stability during manipulation and will also have better

comparable drape than the other variants. Conformability to complex shapes is also achievable

with the weave style allowing a certain amount of interplay movement and rotation. Due to each

fabric layer being woven in a plain weave configuration, a higher degree of stability during

subsequent processing would be achieved compared to bound weave styles.

4.2 Protocol Definition

The thread density of the material produced by the loom is classified as the sett, or ends and

picks per inch (or cm). The weaving reed and Jacquard capabilities determine the ends per inch,

whilst the picks per inch is determined by the loom take up system. If there is a requirement to

change the pick density during weaving, this will be programmed during the design process.

Once the sett has been determined by knowing the fabric areal weight (FAW) per layer and

number of layers required, the design can be created.

Conventional CAD drawings use dimensional data however the weave CAD software uses pixels

with one pixel relating to 1 warp and weft thread. In order to transfer the dimensional data from

the CAD drawings to useable weave CAD information a simple calculation is used where the

fabric set is multiplied by the dimension required. If crimp is induced into the structure due to

weave style or thread properties this also needs to be built into the calculation. This resultant

number relates to the number of pixels used in the design.

4.3 Design Creation

With material and protocol defined it is possible to create the desired Nodal structure. For the

purpose of this paper the design of a generic node will be demonstrated, from initial CAD data

through to woven part. The image in Figure 6 shows the design that will be designed as a woven

structure.

Figure 6 - Nodal Structure

The weave style that will be used to create the Node has been established as a stitched

multilayer. This weave style will form the basis of the structure, however various weave repeats

will need to be created for the different zones making up the complete part. The nodal areas will

be created by splitting the multilayer structure at the nodal zones, where the fabric layers split to

form woven pockets. There are various methods of achieving a split which can include

interchange weaves to create a cross over at that point or a straight fabric split. For the purpose

of this design a straight split will be used to form the nodal pockets. The fabric will be designed

so that each node will have an equal number of layers on each side of the split. This will ensure

that the amount of fiber on each side of the node is the same. This method of splitting the layers

is demonstrated in the following images. The first image Figure 7 shows how through thickness

binding is achieved using the woven thread from one layer to stitch the 2 layers together.

Figure 7 - Warp thread linking 2 layer structure

Figure 8, demonstrates how each layer of a stitched multilayer material can be produced. As no

actual binders are used in the structure, the linking of the layers is achieved by the stitching

thread as shown in Figure 7 which forms part of each of the woven layers.

Figure 8 - Stitching of 8 layered structure

The split or pocket, which will form each node, is created by missing the link at the centre point

as shown in Figure 9

Figure 9 - Split point of 8 layered structure

4.4 Design Modification

With the style of weave and the method of creating the nodes determined, the nodal structure is

converted from an image to a weavable structure. The protocol definition is used to create a

weave file image where the length unit has been converted into total pixels. Figure 10 shows an

image which has been converted to pixel form with each of the smaller pixels relating to 1 warp

and weft thread.

Figure 10 - Nodal image converted to Pixel image

The zones of the structure are identified by different colours, which signify different weave

structures used in the area. Although there are only 2 weave zones identified in the above image,

in reality the number of different zones possible can be hundreds in the same structure. This is

dependent on the complexity of the design and the number of different weaves required.

If there is a requirement to change the density of the structure by increasing the number of ends

and picks per unit length, then the design would also need to be modified to accommodate this.

5. MANUFACTURING METHOD

Work already carried out has determined the possibilities achievable by using conventional

manufacturing methods [5]. With the advent of improved thread control through shedding

improvements achievable using the Unival 100 Jacquard, additional benefits can be realised.

This nodal structure will be woven using conventional weaving machinery including a Dornier

Rapier loom and a Staubli Unival 100 Jacquard.

5.1 Initial concept generation

Following from the design process, an initial sample was designed and woven to provide an

indication of the conformability of the structure to the required shape. Based on the nodal

structure in Figure 6, a design was generated which would provide a woven structure with 8

layers at a fabric sett of 80 warp and weft threads per inch in total. The fiber used was HTS40

12K Carbon fiber in both warp and weft directions. The image in Figure 11, demonstrates how

the structure conforms around the struts at the split point with minimal effort.

Figure 11 - Conformability of 3D weave

5.2 3D Weaving development

Whilst the use of 3D multilayer weave styles demonstrated the drape and conformability

achievable, further obstacles needed to be overcome. The manufacturing of a Truss with both

horizontal and vertical elements presents its own problems. The following series of images

demonstrates the problem of converting a 2D woven structure with 3D weaves, into a shape that

has both horizontal and vertical elements. In Figure 12, both horizontal and vertical elements are

woven at the same time with the fabric split creating the pocket for the insertion of the strut.

Figure 12 - 2D Structure with 3D weaves

To form an upright element the material in the vertical plane will need to be folded around the

expanded pocket, creating folds in the excess materials as they are formed around the Truss.

Figure 13 - Vertical element folded round to form upright element

In order to overcome this issue a structure would have to be woven where the weaving process

followed a different plane during the weaving of the pocket as shown in Figure 14.

Figure 14 - Preferred 3D Architecture

5.3 New 3D woven structure

The requirement of the change in direction during the weaving process has led to the

development of a novel weaving process where a structure can be woven which provides the

solution to the issues already identified in Figure 13. Although a process of weaving around

corners has been identified [6], the product created by this new method provides a number of

opportunities to manufacture structures that can be used for other structural applications. The

image in Figure 15 demonstrates the woven angled preform with a strut inserted.

Figure 15 - Woven angle with strut inserted

6. DISCUSSIONS AND CONCLUSIONS

By using 3D weave styles which demonstrate improved drape properties, combined with the

method illustrated of designing nodal structures, it is possible to reduce the time taken to

manufacture 3D Truss structures. The image in Figure 16, shows how a nodal shape can be

manufactured using weaving technology. Manufactured using the design and manufacturing

methods already identified, the possibilities offered by this type of woven preform are extensive.

The component illustrated has a weight of 5139 gsm and is woven using the stitched multilayer

weaves. The structure is woven with eight layers of plain woven material stitched to provide

through thickness reinforcement. Further development is being carried out to link the vertical and

horizontal truss sections by further splitting the multilayer structure and creating a Pi shape for

attachment of the upright to the lower horizontal section.

Figure 16 - Woven 3D Nodal Truss

With this method of designing a 3 Dimensional structure, any problems with laying of plies is

eliminated. Since all layers are woven in one process no layup is required and the position of all

aspects of the nodal structure are the same. The design can be woven on loom in multiple widths,

with each design an exact replica of the adjacent one on loom. This is easily achieved by

manipulating the start point of the weave repeats which make up the design or using a jacquard

tie, where the ends of each repeat are linked to the same lifting hook.

One of the areas for further work on this type of structure is the Fabric stability. During trimming

of the structure the carbon threads are very unstable, whilst a tight weave is used to improve the

stability further binding is required. This can be achieved in various ways including the use of

binder material applied to outer surfaces, or alternatively using binding material within the

structure itself at the points where necessary. With the flexibility offered by using a jacquard, it

is possible to weave threads into the structure with binding material already applied. This will

usually require the application of heat to create a bond, which could be an issue, however it is an

option. The weaving of pre-impregnated fiber is also possible, as investigated by the PreCarBi

project [7].

Another important aspect achieved using this type of multilayer weave structure is the improved

drape compared to Solid Z bound 3D weave styles e.g. Orthogonal. Whilst the conformability of

the structure to the tooling is still to be established, using weave styles with improved drape

characteristics will be beneficial in the making up process and tooling process.

Drape can also be influenced by changing the weave styles within the structure. Whilst the

weave demonstrated is made up of 8 layers of stitched plain weave, it is also possible to change

the weave on each layer. It may be beneficial to influence the drape where the conformability to

a less angular shape is desired by having tighter weaves on one surface than the other.

The development of the ability to weave in different planes is also necessary and will provide a

greater opportunity to exploit 3D technology in the future.

7. FURTHER WORK AND POSSIBLE END USES OF OUT OF PLANE 3D

STRUCTURE

The nodal structure designed and manufactured demonstrates the capabilities achievable with the

weaving process using conventional weaving machinery. The methods used to manufacture the

structure can also be employed to manufacture other key feature components where there is a

requirement to create a structure that has improved structural rigidity. Conventional methods of

creating pockets or splitting woven structures result in the overall fabric density on each surface

being equal to the sum of the set on each layer in that direction, warp or weft. If we consider a

split in the weft direction then;

(Weft Sett ends/cm * weft ratio at the split on upper layer )+ (Weft Sett ends/cm* weft ratio in

upper layer = Total sett determined by loom primary take down function.

So for a 40 ends per cm structure with a 50:50 split there would be 20 ends/cm per layer.

Similarly with an 80:20 split, the upper would be 32 ends per cm and the lower would be 8 ends

per cm.

Using the new method of creating split layer woven structures each layer can have a completely

different weft density on each layer without being the sum of the sett determined by the loom

take down. The resulting fabric woven on the loom will result in a loop being formed as

demonstrated in the image in Figure 17.

Figure 17 - Woven loop on loom

By using this method of manufacture shapes can be manufactured which require high density

material in a structure with an uneven split. Since the pocket is woven and is flexible, the fabric

will form any shape that is inserted into it. Some examples are demonstrated below in Figure 18.

Figure 18 - shapes achievable with different densities on each surface

The continuous development of the weaving manufacturing process for composite applications

will enable a greater variety of structures to be manufactured. Ultimately, the market demand for

increased production rates combined with a greater understanding of 3D structures and the

capabilities will result in the adoption of this technology for a diverse range of end uses.

8. REFERENCES

1 Mageba Textilmaschinen Web page. Accessed 20-11-09 http://www.mageba.com/eng/shuttle.htm

2 W.Hufenbach et al. Delamination behaviour of 3D Textile reinforced composites – experimental and numerical

approaches CDCM2006 – Conference on Damage in Composite Materials. Stuttgart. Sept, 2006.

3 Texgen Software V3.3.0 accessed 15-12-09 http://texgen.sourceforge.net/index.php/Main_Page

4 McHugh.C. The Use of Recent Developments in Conventional Weaving Shedding Technology to Create 3D One

Piece Woven Carbon Preforms. SAMPE Journal. 45(6) (2009):33-41.

5 Chen.X. CAD/CAM of 3D woven fabric for conventional looms: The First World Conference on 3D Fabrics and

Their Applications. Manchester.2008.

6 Legrand.X et al. A New Technique of weaving 3D surface application to Carbon/Epoxy corner fitting plies.

Accessed 09-12-09 http://web.univ-

ubs.fr/limatb/EG2M/Disc_Seminaire/ESAFORM_09/data/pdf/paper345zefbx.pdf

7 Mehdi Asareh, Andrew R. Mills and Denis, D.R. Cartié “INVESTIGATION OF PREFORM

MANUFACTURING TECHNIQUES USING NOVEL BINDER COATED CARBON FIBRE TOW”

Accessed 11-12-09.http://extra.ivf.se/eccm13_programme/abstracts/1706.pdf