JEC COMPOSITES MAGAZINE - Issue #76 - October/November 2012 - 77

Thus, it is now possible for the first time to produce non-crimp fabrics with locally-adjusted drapability by varying the stitch type in the direction of production. A change of stitch type can now be done in minutes, because the change of the pattern discs is inapplicable. This is especially an advantage Fig. 10: Non-crimp fabric with a local variation of for research the stitch type institutes, which mostly produce small batches. Furthermore, the integration of a second linear drive to be able to influence the stitch type also lateral to the direction in a certain range is already planned. Outlook Non-crimp fabrics with different stitch types – pillar, tricot

and satin – have been produced with varying stitch lengths. The influence of these parameters on the drapability and mechanical properties are currently being investigated. Drapability will be determined, among others, by means of a picture frame test. In a first step, the drape characteristics of NCF with a constant stitch type and stitch length will be determined. In a second step, the mutual influence of the different stitch types will be considered. Figure 11 shows the results of preliminary tests conducted with biaxial noncrimp fabrics produced by means of the novel electro-mechanically driven guide bar. The biaxial non-crimp fabrics where tested in and lateral to the processing direction. The correlation of stitch type and stitch length and their mutual influence on mechanical properties will also be determined. Thereby, their influence on in-plane and offplane properties will be analyzed.

Multi-step preforming
Multi-step preforming is the conversion of textiles such as multiaxial non-crimp fabrics or woven fabrics, but also the above-mentioned multiaxial warp-knits, into complex shaped preforms in a sequence of automated processing steps. Three-dimensional sub-preforms such as 3D braids or 3D woven structures can also be integrated. As an example for complex FRP structures, Figure 12 shows a rib-stiffened half-shell. The half-shell itself can be plane, uni- or multiaxially curved. Stiffening profiles such as top-hat, T or L profiles can be integrated. Rib-stiffened half-shells can be applied as self-supporting outer skins in lightweight constructions such as aircrafts. The production of complex preforms has certain analogies with modern steel processing (Figure 12). Multiaxial warp-knitted NCF can be compared to tailored blanks while braided structures match tailored tubes. Multi-step preforming corresponds to assembly lines for metal components. Cutting, handling, draping and joining are the main processing steps in the textile assembly line. They are briefly introduced below.

Fig. 11: Characteristic force-path diagram of a biaxial non-crimp fabric

Fig. 12: Anology between steel processing and preforming

No76 October - November 2012

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JEC COMPOSITES MAGAZINE - Issue #76 - October/November 2012

Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #76 - October/November 2012