Page 372 - Engineered Interfaces in Fiber Reinforced Composites
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Chapter 8. Improvement of interlaminar fracture toughness with interface control 353
Balanced lock stitch Unbalanced lock stitch
Needle Needle
thread thread
Bobbin Bobbin
thread thread
Chain stitch
Fig. 8.22. Stitching techniques. After Ogo (1987).
The preforms can be designed for composites subjected to very complex loading
conditions, because of the large extensibility and conformability of the preform. A
weft knitting or a warp knitting process may be used to produce three-dimensional
knitted fabrics. For additional strengthening in the [O'] and [90"] directions, laid-in
yarns are often added inside the knitting loops, as illustrated in Fig. 8.24. The major
advantages of knitted preforms include enhanced through-the-thickness stiffness
and strength with the characteristics of unidirectional laminates (KO et al., 1986).
11 I Needle and needle thread
Bobbin and bobbin thread
Fig. 8.23. Schematic illustration or the lock stitch process. Arm Ogo (1987).
