In polymeric composite terms, a fabric is defined as a manufactured assembly of long fibres of carbon, aramid or glass, or a combination of these, to produce a flat sheet of one or more layers of fibres. These layers are held together either by mechanical interlocking of the fibres themselves or with a secondary material to bind these fibres together and hold them in place, giving the assembly sufficient integrity to be handled. Fabric types are categorised by the orientation of the fibres used, and by the various construction methods used to hold the fibres together. The four main fibre orientation categories are: Unidirectional, 0/90 (woven, stitched or hybrid), multiaxial, and other/random. Multiaxial fabrics are described in this article.
Other / Random Fabrics
Chopped Strand Mat
Chopped strand mat (CSM) is a non-woven material which, as its name implies, consists of randomly oriented chopped strands of glass which are held together – for marine applications - by a PVA emulsion or a powder binder. Despite the fact that PVA imparts superior draping handling and wetting out characteristics users in a marine environment should be wary of its use as it is affected by moisture and can lead to osmosis like blisters. Today, chopped strand mat is rarely used in high performance composite components as it is impossible to produce a laminate with a high fibre content and, by definition, a high strength-to-weight ratio.
Tissues are made with continuous filaments of fibre spread uniformly but randomly over a flat surface. These are then chemically bound together with organic based binding agents such as PVA, polyester, etc. Having relatively low strength they are not primarily used as reinforcements, but as surfacing layers on laminates in order to provide a smooth finish. Tissues are usually manufactured with area weights of between 5 and 50g/sqm. Glass tissues are commonly used to create a corrosion resistant barrier through resin enrichment at the surface. The same enrichment process can also prevent print-through of highly crimped fabrics in gelcoat surfaces.
Braids are produced by interlacing fibres in a spiral nature to form a tubular fabric. The diameter of the tube is controlled by the number of fibres in the tube’s circumference, the angle of the fibres in the spiral, the number of intersections of fibre per unit length of the tube and the size (tex) of the fibres in the assembly. The interlacing can vary in style (plain, twill, etc.) as with 0/90 woven fabrics. Tube diameter is normally given for a fibre angle of ±45 but the braiding process allows the fibres to move between angles of about 25 and 75, depending on the number and tex of the fibres. The narrow angle gives a small diameter whereas the wider angle gives a large diameter. Therefore along the length of one tube it is possible to change the diameter by variation of the fibre angle - a smaller angle (relative to zero) giving a smaller diameter and vice versa. Braids can be found in such composite components as masts, antennae, drive shafts and other tubular structures that require torsional strength.