carbon fiber reinforcement and architecture-woven 3D fabrics

A problem encountered with C/C composites prepared from 2D fabrics is that cleavage can subsequently occur between layers, leading to premature failure of the composite. This is a problem that does not occur with 3D structures due to the lack of laminae.

Hill and co-workers have described the use of woven integrated structures for engineering preforms.

Soden and Hill have described the fabrication of a diverse range of flat and shaped preforms using conventional weaving, undertaken on an electronically controlled Jacquard power loom with a CAD design package developed at Ulster University.

The yarns within a cross-section can be classified depending on their interlinking characteristics:

1. Inplane interlacers always remaining in their layer of origin and following a designated interlacing weave pattern.
2. Inplane stuffers that are straight uncrimped yarns lying in their layer of origin and not partaking in any interlacing.
3. Through the thickness interlinking yarns, which do contribute to the Z-axis proportion by forming connections to other layers that penetrate a proportion of, or total, fabric thickness.

The diverse range of 3D weave architectures can be categorized as:

1. Integrated structures—tend to be based on plain, twill and satin weaves with through thickness interlinks.
2. Warp binding or orthogonal type architecture—have uncrimped yarn paths bound together by yarns penetrating the total thickness from surface to surface, interspersed with groups of stuffer warps. This type has poor drapeability.
3. Shaped preforms—a preform can be produced by weaving a shaped reinforcement in a flat form and then opening or folding after removal from the loom to give the required shape. Folding a preform can form gaps, which will give resin rich areas in the composite, but these can be eliminated by careful initial design. In multilayer architecture, twill and satin weaves are preferred, since plain weaves exhibit high crimp levels.

Proprietary 3D weaving processes: magnaweave was an early 3D structure and described by Ko with details of mechanical composite properties.

Autoweave was a process developed by Brochier in France and licenced exclusively to Avco/Textron in the USA. The radial reinforcement in Autoweave is a screw-like reinforced phenolic resin rod, which is produced as a continuous stock, cut to length and inserted by computer control into an expendable low cost phenolic foam mandrel. The axial and circumferential reinforcements, which can be either dry fiber or a prepreg, are then positioned precisely in the radial corridors to produce a 3D preform.

A 3D sandwich structure, sometimes referred to as Parabeam, consists of two bi-directional woven fabrics mechanically connected with vertical woven plies. The fabric has a preset space between the two surface decks and this hollow core can be filled with materials such as foam. This structure was developed at the Universities of Leuven and Zaragoza, where two layers of 3D fabrics were connected by orthogonal threads using velvet weaving technology and since a 3D fabric was required, the pile threads were intentionally not cut. However, the pile threads were erroneously cut, producing two pieces of velvet fabric, which were jokingly dubbed 2.5D and this terminology appears to have been universally adopted. These so called 2.5D fabrics are stated to overcome the problem of delamination in composites.

Knitted 3D fabrics: Weft flat knitting machines, in conjunction with computer control, can produce a variety of 3D structures from one yarn including boxes, cones and spheres. In warp knitting, it is normal to use an adapted Raschel machine fitted with two needle bars and several guide bars. Each needle bar produces a flat fabric, with the two flat fabrics simultaneously connected forming a sandwich, which can be readily impregnated with resin.