JEC COMPOSITES MAGAZINE - Issue #71 - March 2012 - 96

fabrics
a) b) c) d) e) f)

Fig. 2: The principle of Oblique Fibre Technology fundamentally differs from weaving and braiding processes

(a) only two mutually angled tape supply sources are required, located at either sides of a bed; (b) a pre-determined length of tape is drawn out and cut from the first source; (c) the cut tape is placed in the preset angle on the bed; (d) as before, a predetermined length of tape is drawn out and cut from the second source; (e) the cut tape is placed in the preset angle over the previously laid tape; and (f) tapes are alternately drawn out, cut and laid in their preset angles on the bed through a certain manipulation to produce a continuous-length integrated bias fabric directly. The OFT process produces a continuous-length integrated bias fabric by continually intersecting and overlapping the two mutually angled tapes. Figure 3 shows a recently developed OFT machine for producing carbon bias fabrics. These bias fabrics, called +α/-β Spread Tow fabric (STF), wherein α-β signify the orientation angles of the constituent tapes, are now commercially available under Oxeon’s brand name TeXtreme®. The OFT process can incorporate all types of tapes in a wide range of mutually angular orientations, and is not limited only to +45/-45 angles. Thus, the mutual angle between the tapes in +α/-β STF can be either (a) an acute angle, (b) a right angle, (c) an obtuse angle, or (d) a mixed angle. Figure 4 exemplifies these four angular variants of +α/-β STF.

For tubular applications, the preferred fibre orientations are in the range +/- 50º to +/- 55º. It is also necessary to have fibres in the longitudinal and radial directions of a tube, as indicated in Figure 5. By combining a suitable +α/-β STF with 0º/90º STF, a multidirectional structure can be directly obtained to obtain the required fibre orientations.

Fig. 4: OFT process incorporates all types of tapes in +α/-β STF, which can be produced in four angular variants. The mutual angles of tapes exemplified in (a), (c) and (d) can be different

Fig. 5: Through combined use of +α/-β STF and 0º/90º STF, multi-directional fibre orientations can be directly obtained for tubular applications

Fig. 3: The first OFT machine producing trial TeXtreme® +α/-β STF

The conventional roll-wrapping process illustrated in Figure 6 can be employed to enable the direct production of circular and non-circular tubular products, such as those exemplified in Figure 1. Two different approaches could be considered: (i) One or more types of +α/-β STF, together with 0º/90º STF, are separately fed and simultaneously roll-wrapped as plies over a suitable mandrel, and (ii) A pre-ply of +α/-β STF and 0º/90º STF is directly fed and roll-wrapped over a mandrel. For producing circular and non-circular tubular items, suitably shaped and constructed mandrels are required, together with suitable means for impregnating the reinforcements and applying heat and pressure on the roll-wrapped STF, to obtain the required final shape and dimensions of the tubular composite product.

96 jec composites magazine / No71 March 2012

JEC COMPOSITES MAGAZINE - Issue #71 - March 2012

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