ANALYTICAL METHODS FOR TEXTILE COMPOSITES
[0
nK
/ ±θ
mK
] Y% Axial
where n is the size of the axial yarns in thousands of fibers (K), m is the size of the bias (or
braider) yarns, and Y is the percentage of axial yarns in the preform. For example,
[0
30K
/ ±70
6K
] 46% Axial
indicates a braid with 30K axial yarns and 6K bias yarns, with 46% of the total fiber
volume in the axial yarns, and a braid angle of 70°. While this notation does not convey
many details of the fabric geometry, it suffices for estimates of properties based on
modified 2D laminate theory.
2.3.1.6 3D Interlock Weaves
A 3D weave contains multiple planes of nominally straight warp and weft yarns that
are connected together by warp weavers to form an integral structure. The most common
classes are shown in Fig. 2-14. Within each class, there are several parameters that can be
varied.
Angle interlock weaves can be categorized by the number of layers that the warp
weavers penetrate. Figure 2-14(a) shows a through-the-thickness interlock fabric, in which
the warp weavers pass though the entire thickness. Figures 2-14(b) and (c) show layer-to-
layer interlock patterns, where a given weaver connects only two planes of weft yarns, but
the weavers collectively bind the entire thickness. Various intermediate combinations can be
fabricated, with the weavers penetrating a specified number of layers.
In orthogonal interlock weaves, the warp weavers pass through the thickness
orthogonal to both in-plane directions, as shown in Fig. 2-14(d).
Interlock weaves are sometimes manufactured without straight warp yarns
(stuffers) to produce a composite reinforced predominantly in one direction. They may also
be fabricated with weft rather than warp yarns used for interlock.
A major limitation of 3D weaves is the difficulty of introducing bias direction yarns
to achieve in-plane isotropy. One solution is to stitch additional 2D fabric plies oriented at
±45° onto the woven preform.
