Oxeon's Product Manager Materials, Fredrik Ohlsson, presented the paper titled Continuous-length Spread Tow +α/-β Fabrics on the Composites UK annual conference held 5-6 of May in Manchester, United Kingdom. The paper is written by Fredrik Ohlsson and Dr. Nandan Khokar and covers the principles of Oxeon's groundbreaking innovation with +α/-β variants of TeXtreme® Spread Tow Fabrics.

1. 1/7
CONTINUOUS-LENGTH SPREAD TOW +α /-β FABRICS
Fredrik Ohlsson, Product Manager - Materials
Dr. Nandan Khokar, R&D Manager
Oxeon AB, Borås, Sweden
ABSTRACT
Fabrics with +α/-β orientation of spread tows is a recent development. They are
composed of two sets of Spread Tow Tapes arranged at an angle, either equal or
unequal, relative to the fabric’s length direction, such as +45/-45, +30/-60, +50/-25 etc.
These +α/-β fabrics are advantageously produced in continuous-lengths and are
innovative solutions for effectively complementing the existing 0/90 Spread Tow woven
Fabrics to realize easily and quickly an optimized multidirectional lightweight
reinforcement by plying them directly.
This paper explains how the indicated +α/-β fabrics directly help replace the conventional
cross-plied UD structures with the added advantages of improved delamination resistance
and inclusion of virtually crimp-less fibers oriented in two angular directions. As a
consequence, production of lightweight multidirectional reinforcements becomes at once
labour-time-cost saving and efficient while according the benefits of obtaining relatively
high performance, thin, easy-to-handle and well draping reinforcement material. With
use of continuous-length +α/-β fabrics the thickness variation associated with
overlapping joints/splices is eliminated besides wastage of material reduced.
Key words: Spread Tow Fabrics (STF), +α/-β STF, Lightweight carbon reinforcements
INTRODUCTION
Carbon fiber Spread Tow Fabric (STF) in 0/90 fiber angles has rapidly grown in popularity
among composite producers with high demand on weight savings, improved mechanical
performance and surface smoothness. Its usage has spread throughout a variety of
application areas for example within sports and leisure industries. Products such as ice
hockey sticks, golf shafts, rowing boats, wind and kite surfing boards, skis and
snowboards, as also Formula 1 cars, luxury yachts and ultralight aircraft are some
products where STF is being used currently. At the same time STF materials are being
Doc.No: MARFO07 v1.2 Template v.1.2
Oxeon AB | Norrby Långgata 45, SE-504 35, Borås, Sweden | Phone: +46 33 20 59 70 | Fax: +46 33 20 59 79 | contact@oxeon.se | www.oxeon.se

2. 2/7
evaluated in other industries such as aeronautical/aerospace, automotive and
engineering industries.
The reason for STF’s success originates from its unique woven structure resulting by
interlacing 20-50 mm wide stabilized Spread Tow Tapes (STT) as warp and weft in plain
and twill weave patterns. Use of STT brings a number of advantages which are discussed
below.
With a view to further improve composite materials, use of plied materials has been
considered for long to obtain certain mechanical properties in different orientations.
However, to ply a conventional woven material in different orientations requires cutting
relatively smaller pieces from a larger sheet and placing them in relatively different
orientations. This approach evidently creates discontinuities in the fiber structure, which
reduces the reliability of the final composite material, besides creating uneven thickness
due to overlapping.
Therefore, as a natural step to complement the existing range of 0/90 Spread Tow
Reinforcements, continuous-length Spread Tow +α/-β Fabrics with variable fiber angles
such as +45/-45, +30/-60, +50/-25 etc. have been developed recently. This paper
explains how the indicated +α/-β STF directly helps replace the conventional cross-plied
UD and other plied fabric structures. As a first step to evaluate the +α/-β STF, the
+45/-45 variant has been produced.
+α/-β FABRIC FEATURES
The need for including fibers in relatively different orientations has so far been realized
by plying either UD sheets or woven fabric sheets. Whereas use of UD sheets ensures
fiber continuity without any structural integrity, the use of woven fabric sheets, though
having structural integrity, creates fiber discontinuity because they have to be cut
angularly from a larger sheet and laid. Such ‘patches’ of woven material have to be laid
carefully to match with the edges of the previously laid ‘patches’. Often times the woven
material patches are laid in certain sequences with some overlapping, which causes the
problem of thickness variation at the joints. These fiber discontinuities and thickness
variations adversely affect the performance of composite materials. In addition to the
indicated performance related problems, use of woven patches also has an adverse
impact on the economics of production relating to cutting, plying and wastage of
material.
Doc.No: MARFO07 v1.2 Template v.1.2
Oxeon AB | Norrby Långgata 45, SE-504 35, Borås, Sweden | Phone: +46 33 20 59 70 | Fax: +46 33 20 59 79 | contact@oxeon.se | www.oxeon.se

3. 3/7
An approach to overcome some of the discussed problems has been through use of
Non-Crimp-Fabrics (NCF) materials. However, use of NCF materials has certain
drawbacks such as their non-symmetrical arrangement of UD plies, relatively higher
thickness and areal weight of material, in-plane delamination, use of epoxy incompatible
polyester stitching yarns with its corresponding knock-down factor due to stitching crimp.
In an attempt to overcome the problems associated with the use of UDs, NCFs and
conventional woven materials, the +α/-β STF has been developed. In Figure 1 are shown
three different +α/-β constructions. As can be inferred, they represent the constituent
STT arranged in (a) obtuse angle, (b) right angle and (c) acute angle. These
constructions of course have the STT oriented in equal but opposite angles. Should there
be a need for having an +α/-β construction wherein the STTs are incorporated unequally,
then such an +α/-β STF can be also produced as shown in Figure 1(d).
The fiber angle flexibility in the material provides, for example, the possibility to tailor
produce an +α/-β STF with STT in about +55/-55 degrees to uniquely enable direct
production of pressure vessels. Such a fabric could be wound over itself to as many
layers as needed to meet the required performance demand.
Figure 1. Different variants of +α/-β STF constructions: (a) obtuse angled, (b) right angled and (c) acute
angled. While these variants have the STT in equal and opposite orientations, the variant (d) has unequal
orientations of the STT.
Doc.No: MARFO07 v1.2 Template v.1.2
Oxeon AB | Norrby Långgata 45, SE-504 35, Borås, Sweden | Phone: +46 33 20 59 70 | Fax: +46 33 20 59 79 | contact@oxeon.se | www.oxeon.se

4. 4/7
At present +α/-β STF can be produced using STT of different width from high strength
(HS), Intermediate modulus (IM) and high modulus (HM) carbon fiber yarns of high tow
count (12k and above) in fabric areal weights starting at 80 gsm, 76 gsm and 130 gsm
respectively. STTs of lower areal weight will most likely be available shortly hence, the
areal weight of +α/-β STF can also be reduced.
All these variants of +α/-β STF constructions are producible in continuous lengths, which
benefits in eliminating cutting, laying and splicing. Further, such a continuous +α/-β STF
material can be directly preimpregnated as the tapes are well integrated to resist fabric
deformation in both length and width directions. An example of +α/-β STF produced in
+45/-45 STT orientation is shown in Figure 2.
Figure 2. An +α/-β STF with +45/-45 STT orientation
Doc.No: MARFO07 v1.2 Template v.1.2
Oxeon AB | Norrby Långgata 45, SE-504 35, Borås, Sweden | Phone: +46 33 20 59 70 | Fax: +46 33 20 59 79 | contact@oxeon.se | www.oxeon.se

5. 5/7
MECHANICAL PERFORMANCE
Given the arrangement of STT, a composite made from an +α/-β STF is not optimal to
take loads in its longitudinal and lateral directions without getting deformed just as a
composite made from 0/90 STF will shear when loaded angularly. Notwithstanding this
aspect, +α/-β STF is designed to be used along with conventional 0/90 STFs to meet the
required laminate performance demands. Needless to state, individually +α/-β STFs is
considered beneficial for torsional applications.
The mechanical performance of +α/-β STF comes from virtually no in and out of plane
fiber crimp (i.e. crimp angle), fewer interlacing points (i.e. crimp frequency) and
relatively higher fiber volume fraction (i.e. cover factor). Further, because STT has its
fibers well distributed, its wetting by the matrix can be achieved easily and quickly to
ensure improved load transfer in a composite material.
Because the constituent STT are integrated throughout the +α/-β STF the in-plane
delamination risk is substantially reduced. In principle this implies that each +α/-β STF
sheet comprising fibers in two equally opposite angles is symmetrically balanced.
Therefore, use of such +α/-β STF enables to obtain a symmetrically balanced plied
construction directly using relatively fewer sheets. Tables 1 and 2 below together with
Figure 3 and Figure 4 illustrate how symmetrical quasi- and bi-directional balanced
constructions are obtained using relatively fewer STF sheets compared to the existing
NCFs and UDs.
Table 1. Symmetrical Quasi-Isotropic construction
Material Ply sequence No. of fiber layers to achieve
symmetry
UD [0/90/+45/-45/-45/+45/90/0] 8
NCF [NCF(0/90/+45/-45)/NCF(-45/+45/90/0)] 8
STF [STF(0/90)/STF(+45/-45)/STF(0/90)] 6
Doc.No: MARFO07 v1.2 Template v.1.2
Oxeon AB | Norrby Långgata 45, SE-504 35, Borås, Sweden | Phone: +46 33 20 59 70 | Fax: +46 33 20 59 79 | contact@oxeon.se | www.oxeon.se

6. 6/7
Figure 3. Symmetrical Quasi-Isotropic construction of UD/NCF (left) and +α/-β STF (right)
Table 2. Symmetrical bi-directional construction
Material Ply sequence No. of fiber layers to achieve
symmetry
UD [+45/-45/-45/+45] 4
NCF [NCF(+45/-45)/NCF(-45/+45)] 4
STF [STF(+45/-45)] 2
Figure 4. Symmetrical bi-directional construction of UD/NCF (left) and +α/-β STF (right)
Doc.No: MARFO07 v1.2 Template v.1.2
Oxeon AB | Norrby Långgata 45, SE-504 35, Borås, Sweden | Phone: +46 33 20 59 70 | Fax: +46 33 20 59 79 | contact@oxeon.se | www.oxeon.se

7. 7/7
METHOD OF PRODUCTION
The method of producing +α/-β STF is completely new in that it is unlike the principles of
weaving and braiding. The production is virtually endless as there are no STTs oriented in
the fabric length direction. Accordingly, the fabric can be produced in any desired length
that may be required. The angles of STT can be varied as desired on the same machine.
CONCLUSIONS
The new +α/-β STF offers new opportunities in composite material production both in
terms of performance and economics. It can be produced using STT of different widths,
areal weights and fiber types (HS, IM and HM). Its lowest areal weight at present is 76
gsm. The availability of +α/-β STF in different angular variants allows to ply them directly
for obtaining multidirectional fiber orientations. The availability of such fabric in continues
length enables waste reduction and splicing/joints whereby a composite of uniform
thickness can be obtained.
ACKNOWLEDGEMENTS
Sincere thanks are expressed to Mr. Henrik Blycker, CEO, Oxeon AB, Sweden, for his
encouragement and support at all times.
Doc.No: MARFO07 v1.2 Template v.1.2
Oxeon AB | Norrby Långgata 45, SE-504 35, Borås, Sweden | Phone: +46 33 20 59 70 | Fax: +46 33 20 59 79 | contact@oxeon.se | www.oxeon.se