Composites- Fibre Architecture Flashcards
What is fibre architecture and what does it influence?
The arrangement of fibres in the composite.
Significantly influences composite properties and manufacturing route
1D, 2D, 2.5D, 3D fibre architecture examples
1D: unidirectional laminae, pultruded cross-sections, 1D aligned short fibre systems.
2D: woven, braided and knitted fabrics (bidirectional and multidirectional), 2D randomly aligned long an short fibre systems.
2.5D: cross-ply and angle-ply laminates made from UD laminae, nom-crimp fabrics.
3D: 3D woven systems, 3D randomly-aligned short fibre systems
Features of 1D fibre architectures
All fibres oriented in the same direction. UD laminae and pultruded products are good examples but both are weaker in the transverse direction
Aligning short fibres for 1D
High shear forces used in injection moulding or extrusion align short fibres along the flow direction. In a wide mould, an outer layer (skin) of aligned fibres forms with a more randomly oriented core (aligned by extensional flow around curved flow front). In a narrow mould, the majority of the fibres will be aligned due to plug flow (flat flow front)
What are mats?
2D fibre architecture. Fibres randomly aligned and have small amount of thermoplastic binder to keep them from separating before composite manufacture. Can be continuous fibre mat (CFM) with long fibres or chopped strand mat (CSM) with short fibres. Uniform properties in plane but generally lower than the aligned equivalent.
What materials and process routes can result in randomly aligned 2D architectures?
Sheet or dough/bulk moulding compounds used in compression moulding or spray lay-up.
How to obtain aligned fibres interlaced into a 2D fabric
Use filament winding.
Or use woven fabrics: either as dry fibres or as pre-preg, hand lay-up or resin transfer mould
Directions in a woven system (2D)
Primary warp direction (associated with load direction).
A secondary weft or fill direction (perpendicular to warp).
Advantages and disadvantages of weaving fibres into fabrics
Advantages: reduce delamination (less separating of laminae), reduce anisotropy (more balanced properties), increased drape (ability to conform to curved surfaces).
Disadvantages: undulation or crimp of the fibres (reduces properties and results in different properties in warp and weft directions)
Different bidirectional weave patterns
Plain weave (every warp fibre has a weft fibre and alternates between going over and under them for every weft fibre).
Basket weave (2 by 2 plain weave).
Twill (basket weave but adjacent warp fibre shifted up one weft fibre for sequence of above and below).
Satin weave (every warp fibre goes under 3 weft fibres then above next one, repeat)
How does weaving pattern affect crimp angle?
High for plain weave
Low for satin weave
Pattern also affects drape and mechanical properties
Another weave pattern in 2D
Tri-axial weaves.
Very complicated but trying to optimise propertiesnin more than one direction
Braiding
Simultaneous interlacing of three or more yarns around one axis. Most suited to tubular or hollow structures. Delamination resistant but fibres are still being crimped
Knitting
Interlooping of yarns. More flexible than woven fabrics (better drape). Delamination resistant but fibres still being crimped
Two options for combining UD fabrics into laminates without having to weave. 2.5D
Avoids crimp issues.
UD fabrics laminated together: cross-ply, angle-ply.
Lightly stitch UD fabrics together as desired: non-crimp fabrics have multiple stitched layers which still allow movement so drape is possible
