Continuous filament random mats

Fibrous Composites. These composites consist of fibers in a matrix. The fibers may be short or discontinuous and randomly arranged continuous filaments arranged parallel to each other in the form of woven rovings (coUections of bundles of continuous filaments) or braided (8). In the case of chopped strand mat the random arrangement is planar. In whisker (needle-shaped crystals or filaments of carbon and ceramics) reinforced materials the arrangement is usually three-dimensional and the resulting composites are macroscopically homogeneous. 

Continuous Filament Mat (CFM)—A non-woven material similar to chopped strand mat except that the fibres are swirled at random and are continuous. 

Mat—A fibrous material consisting of randomly orientated chopped or swirled continuous filaments loosely held together with a binder. 

The reinforcement used is generally a combination of uni directional roving and random mat (continuous filament mat). This combination provides a reasonably optimised set of properties in the longitudinal and the transverse directions respectively. Other reinforcement types may be used, including woven roving, chopped strand mat (nonsoluble binder), needled mat and multi-axial non-woven. 

To cater for the variety of composite fabrication techniques, fibres may be formed into woven rovings, knitted preforms or continuous random mats (CRM) or chopped into lengths of >20 mm to <5 mm for use in moulding compounds or assembling into chopped strand mat (CSM). For these textile processes, the polymeric component of the size is required to maintain strand integrity and filament strength. The random continuous and chopped strand mats require additional polymeric binders. 

The above fibre reinforcements are available in several forms that include almost parallel bundles of continuous filaments, either untwisted (rovings) or twisted (yarns), and short fibres (chopped) with a length of 3 mm to 50 mm (Keller, 2003). For use in pultrusion, fibre reinforcements can be worked to obtain textile products with several reinforcing directions. There are, therefore, several products available, either with randomly oriented fibres, which can be short (chopped strand mat) or continuous (continuous strand mat), or with oriented reinforcements (such as woven and non-woven fabrics, stitched fabrics, grids and meshes), which can be biaxial (0°/90° or -i-45°/-45°) or triaxial (0°/-i-45°/ 5°), the latter being considerably more expensive and less widely used in pultrusion. All these forms can be further combined to make complex textile products with continuous oriented fibres, together with randomly oriented short or continuous fibres. Figure 9.1 shows examples of forms of fibre reinforcement. 

Air Force (AFHL) and, later, U.S. Navy (NSSC), was commercialized by Union Carbide in 1974, when a random mat fiber was produced, and in 1975, when a continuous filament yarn ("Thomel P-55") was produced. 

Thermoplastic resins are generally reinforced with short fibres (for use with injection moulding and not considered in this book), with long fibres (thermoplastic sheet compound, Chapter 5) or with glass mat (i.e. glass mat thermoplastics or GMT). Polypropylene is the resin most used as the matrix for GMT and the reinforcement is usually a random mat, primarily chopped strand but it may be continuous filament or needled mat. 

Fibrous reinforcement in popular usage is almost synonymous with fibreglass, although other fibrous materials (carbon, boron, metals, aramid polymers) are also used. Glass fiber is supplied as mats of randomly oriented microfibrils, as woven cloth, and as continuous or discontinuous filaments. Hand lay-up is a versatile method employed in the construction of large structures such as tanks, pools, and boat hulls. 

This is made from continuous swirls of fibre strands and has some advantage over chopped mats in that there is continuity of fibres, which are interlocked albeit still in a random array. The overall nature is still similar to chopped fibre mats, continous filament mats but are more open and springy and their structural use is again limited. They are however used in pultrusions in combination with rovings and fabrics. 

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