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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

ADVANTAGES OF ULTRALIGHT WOVEN SPREAD TOW FABRICS

Fredrik Ohlsson, Product Manager Materials

Nandan Khokar, R&D Manager

Oxeon AB, Borås, Sweden ABSTRACT Woven carbon fiber Spread Tow Fabrics (STF) – TeXtreme® - are being used increasingly in the composite materials industry. They provide relatively increased mechanical performance, weight savings, draping ability and flat surface. As a greater number of filaments are exposed in STF they also present correspondingly improved wetting ability. The limitations of traditional woven fabrics, which are produced using tows, are uniquely overcome by STF because it is made using spread tow tapes. Use of spread tows accords high flexibility in fabric construction. For example, using the same fiber and tow count, an STF of different areal weights and thinness can be obtained to suit a given application. The flatness of STF, which comes from near absence of crimp, significantly reduces accumulation of matrix at the interlacing points and thereby the dead weight of the final composite material. This not only reduces the weight of the final composite material product but also eliminates the print-through defects associated with post curing of the undesired matrix accumulation. This paper presents the advantages of STF in reference to certain products. Keywords: Spread Tow Fabrics, Ultralight composites, Carbon reinforcements INTRODUCTION The usage of STF TeXtreme® has rapidly increased since the time it was first introduced in 2004. It is now well received in and recognised by many different industries. Benefits like relatively straighter fibers, lesser crimp and better mechanical performance have been easily understood. With increased usage of STF other advantages such as improved draping, cutting and handling also got established. Alongside other reinforcement materials such as rovings, unidirectional tapes (UD), non crimp fabrics (NCF) and yarn/tow woven structures, STF is now an accepted member of the textile reinforcement family for advanced composites. SPREAD TOW FABRICS (STF) The theory behind TeXtreme® ultralight woven spread tow fabric is relatively simple. By arranging the fibers in the woven structure in the straightest orientation possible, both in the plane and ALSO out of the plane, the fiber properties can be exploited in the most efficient way for carrying tensile and compressive loads. In a way, TeXtreme® performs mechanically similar to a cross-ply construction of UD with the differences that TeXtreme®, being a fabric, exhibits exceedingly high draping ability than that of the cross plied UD and also its integrated nature is not susceptible to delamination. Through a controlled operation fiber tows of usually 12k and heavier count are gently spread to a tape of certain width and stabilized to prevent the tape folding back into the original tow/yarn form. Because of the spreading action the obtained tapes are extremely

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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

thin. These tapes are used as warps and wefts for producing STF. The use of spread fiber tapes in producing TeXtreme® directly results in a woven material with higher fiber volume fraction and fewer interlacing points and thereby correspondingly lower crimp frequency and crimp angle. The main constructional differences between STF and the traditional tow/yarn woven carbon fabrics are shown in Figure 1.

Figure 1. Compared to woven fabrics produced using tows, the STF combines flatness, thinness, improved

performance and smoothness at the same time with good draping ability.

Figure 2 compares fabric cover factor or fabric density of traditional 1k with flat tow and TeXtreme® produced using 12k tows. As can be observed, the traditional fabric and flat tow fabric have air gaps / openings at every interlacing point whereas TeXtreme® is solid.

Figure 2. The traditional 1k fabric (left) and the flat tow fabric (centre) present lower cover factor in comparison

with TeXtreme® STF (right).

The relatively lower mechanical performance of traditional woven reinforcement fabrics is well known and can be attributed to crimp angle and crimp frequency. How both these factors, which adversely affect the performance of a woven material for composites application, are virtually eliminated by weaving spread tow tapes as warps and wefts have earlier been discussed by Ohlsson and Khokar [1].

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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

FLEXIBILITY When using homogeneous materials like steel or aluminium the construction of a product is designed to fit the material’s structural properties. However, when using composites, the material is designed instead according to the engineering needs of the constructional design of the product. Through this, the structure will be more optimized and hence unnecessary weight can be eliminated. However, conventional fabric constructions and areal weights obtainable have until now been strictly connected and limited to the tow sizes being used and therefore complete optimization has not been possible. A simple overview of the strong link between carbon fiber tow counts and fabric areal weight produced in the conventional manner is shown in Table 1. Spread Tow Fabrics do not follow these set rules. Instead, a few tow sizes are enough to create a large areal weight span; even lighter areal weight STF are possible than conventional fabrics produced using 1k fiber.

Table 1. Comparison of approximate areal weights

Fiber Type and Tow Count Traditional Woven Fabrics - gsm Spread Tow Fabrics - gsm

HS - 1k 90 – 120 not applicable

- 3k 200 – 400 not applicable

- 6k 300 – 500 not applicable

- 12k 500 – 600 80 – 400

IM - 6k 200 – 400 not applicable

- 12k 300 – 400 135 – 250

- 18k not available 76 – 300

- 24k not available 80 – 300

HM - 6k 200 – 500 not applicable

- 12k 300 – 500 130 – 245

To explain the Table above in relation to the flexibility in producing STF with a wide range of areal weights, the following may be considered. By spreading one or several Torayca T700SC 12k fiber tows to 20 mm width, four different tape areal weights could be achieved: 40, 80, 120 and 160 gsm as shown in Figure 3

Figure 3. Areal weight variations on a 20 mm wide tape from Torayca T700SC 12k fiber tow.

40 80 120 160

40 80 120 160 200

80 120 160 200 240

120 160 200 240 280

160 200 240 280 320

W E F T

WARP

T700SC

T700SC

40 80 120 160

40 80 120 160 200

80 120 160 200 240

120 160 200 240 280

160 200 240 280 320

W E F T

WARP

T700SC

T700SC

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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

These different areal weight tape constructions can be used as warp and weft in sixteen different fabric areal weight combinations, wherein four constructions will be balanced (the coloured ones in Figure 4).

Figure 4. Sixteen variations of STF from T700SC 12ks, four being balanced (coloured).

To meet the specific application and performance needs, either different carbon fibers types or other fiber types such as aramid, glass, PE, PP and PBO could be as well used in STF fabric constructions. These fibers can themselves be spread to different areal weights and this way the matrix of possible fabric constructions in reference to fiber types and areal weights can be directly enlarged.

Figure 5. The STF fabric flexibility matrix with three ingoing fibers.

Figure 5 illustrates the flexibility in producing different areal weight STF with only three fiber types. If the numbers of fiber types are increased to seven, as shown in Figure 6, the possibilities of engineering different areal weights and fiber combinations increase enormously. The fabric areal weight-fiber type matrix can grow almost infinitely large if more fibers are considered and also if the tape width is not limited to 20 mm but varied.

40 80 120 160

40 80 120 160 200

80 120 160 200 240

120 160 200 240 280

160 200 240 280 320

W E F T

WARP

T700SC

T700SC

40 80 120 160 50 100 150 33 49 65 81 98 114

40 80 120 160 200 90 140 190 73 89 105 121 138 154

80 120 160 200 240 130 180 230 113 129 145 161 177 193

120 160 200 240 280 170 220 270 153 169 185 201 218 234

160 200 240 280 320 210 260 310 193 209 225 241 258 274

50 90 130 170 210 100 150 200 83 99 115 131 148 164

100 140 180 220 260 150 200 250 133 149 165 181 198 214

150 190 230 270 310 200 250 300 183 199 215 231 248 264

33 73 113 153 193 83 133 183 66 82 98 114 131 147

49 89 129 169 209 99 149 199 82 96 114 130 147 163

65 105 145 185 225 115 165 215 98 114 130 146 163 179

81 121 161 201 241 131 181 231 114 130 146 192 179 195

98 138 177 218 258 148 198 248 131 147 163 179 196 212

114 154 193 234 274 164 214 264 147 163 179 195 212 228

W E F T

WARP

T700SC TR50S Zylon HM

T700SC

TR50S

Zylon HM

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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

Figure 6. The number of STF possibilities could be almost infinitely large as the tape width can vary and many more fibers are available. CUSTOMER CASES This section describes a few industrial applications incorporating TeXtreme® Spread Tow Fabrics for reducing weight and/or other important properties. SHARK AERO is a Slovakian designer and manufacturer of high performance ultra- light aircraft. For them weight savings is of great importance in this highly weight limited class of aircraft. To produce a new model, Shark replaced their conventional yarn/tow woven 200 gsm and 90 gsm fabrics with TeXtreme® 160 gsm and 80 gsm STF respectively to reduce the weight of fuselage and wings. This way they could meet the specifications demanding maximum weight of Ultra Light Aircraft to be 300 kg when empty.

Figure 7. Shark Aero’s Ultra Light Aircraft is manufactured with TeXtreme® to reduce weight. Source: [2]

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BAUER HOCKEY is the world’s most recognized designer, manufacturer and marketer of ice hockey equipment. For their top of the line sticks they switched to using TeXtreme® 100 gsm STF. Both the shaft and the blade of their model Bauer Vapor X:60 incorporate TeXtreme® to achieve optimal weight reduction and enhanced performance. The stick has received great feedback from top players in both the North American hockey league NHL, and the Swedish hockey league Elitserien.

Figure 8. Bauer X:60 incorporating 100 gsm TeXtreme® STF in both shaft and blade. Source: [3]

One of the major benefits of TeXtreme® for this application is its straighter 0 and 90 degree orientation fibers jointly contributing to low deformation of the semi-oval cross section of the shaft. BALTIC YACHTS is an internationally recognised luxury yacht manufacturer located in Jakobstad, Finland. Their fully custom yachts in lengths up to 200 feet are built in sandwich construction with carbon fiber skins. Their main objective for using TeXtreme® 160 gsm was to achieve improved surface finish by avoiding the print through effect, which normally occurs with conventional tow/yarn woven fabrics, when subjected to unintentional post cure process. Weight reduction was of course an additional benefit.

Figure 9. Surface smoothness improvements by TeXtreme® in marine applications. Source: [4]

FORMULA 1 is perhaps the most weight and performance sensitive industry in the world. By switching to TeXtreme® teams have been able to reduce the weights of parts by 25 to 30 percent. TeXtreme® STFs of 76 gsm intermediate modulus and 130 gsm high modulus types are being used by most of the teams.

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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

Figure 10. TeXtreme® reduces weight in Formula 1 cars. Source: [5]

BOARDS & MORE is a German producer of water sport equipment under the brands North Kites and Fanatic. They have used an unbalanced TeXtreme® fabric for their extreme performance kite boards to achieve optimized flexibility and weight.

Figure 11. North Kites Select Board built with an unbalanced TeXtreme® fabric. Source: [6]

Conclusions Woven Spread Tow Fabrics (STF) – TeXtreme® - is recognised now as a new member of textile reinforcement family for the advanced composite industry. Their performance has been established through a variety of applications. It is increasingly preferred over traditional tow/yarn woven materials because of its unique advantageous features such as higher fiber content, virtually no fiber crimp, relative thinness, flatness and smoothness besides good draping and handling abilities.

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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

STF presents the unique flexibility for achieving optimal reinforcement design for specific application needs relating to mechanical performance. Fiber tows of different counts and fibers of different types can be uniquely combined to produce endless variations in STF areal weights. Several industrial products, such as ultralight aircraft, sporting goods, racing cars and yachts, have confirmed benefits with use of TeXtreme®. Acknowledgement Sincere thanks are expressed to Mr. Henrik Blycker, CEO, Oxeon AB, Sweden, for his encouragement and support at all times. References [1] Ohlsson, F. and Khokar, N., New Opportunities in Lightweight Spread Tow Fabrics (STF) from Carbon Tows of 12k Counts, IC3, Arcachon, France [2] http://www.shark.aero/ (Accessed on 2010-05-31) [3] http://www.bauer.com/gear/player/sticks (Accessed on 2010-05-31) [4] http://www.balticyachts.com/ (Accessed on 2010-05-31) [5] Oxeon AB [6] http://www.northkites.com/ (Accessed on 2010-05-31)