Fibres, primary reinforcement

Fibre reinforced cement pastes or mortars are usually applied in thin sheet components, such as cellulose and glass fibre reinforced cements, which are used mainly for cladding. In these applications the fibres act as the primary reinforcement and their content is usually in the range of 5-15% by volume. Special production methods need to be applied for the manufacturing of such composites. 

It should contain a relatively large volume of fibres ( 5% by volume) since this is the primary reinforcement in the thin component. 

The durability of polypropylene FRC has mainly been evaluated in thin sheet components, where the fibres are the primary reinforcement. Polypropylene fibres are known for their high alkali resistivity, and therefore would be expected to... 

Fibre reinforced cements are extensively used in a variety of cladding applications, ranging from small shingles up to large facades units of several metres in size [91-96]. In these applications the composites used are usually thin section components, where the fibres are the primary reinforcement. Glass, polypropylene, carbon and cellulose fibres have been used for these applications. The mechanical and physical properties ofthese composites can be quite different, as demonstrated in Figure 14.21 and Table 14.3 [97]. 

Boron itself has been used for over two decades in filament form in various composites BO3/H2 is reacted at 1300° on the surface of a continuously moving tungsten fibre 12/tm in diameter. US production capacity is about 20 tonnes pa and the price in about 80(. The primary use so far has been in military aircraft and space shuttles, but boron fibre composites are also being studied as reinforcement materials for commercial aircraft. At the domestic level they are finding increasing application in golf shafts, tennis rackets and bicycle frames. 

It is well known that the Young s modulus of a composite can be calculated by the rule of mixtures for long-fibre reinforced material. In the case of whiskers, the rule of mixture is also applied to estimate the change of modulus (conventionally, reinforcements are added to improve the stiffness of a material, though for ceramic matrix composites this is not always the primary concern). 

The traditional TPS for launcher fairings and re-entry capsules consists of an external ablative insulation, fixed or bonded onto a metallic primary structure. Ablative materials are based on thermosets (phenolic and epoxy resins) or elastomers (ethylene-propylene and silicone rubbers) usually filled and reinforced with cork, cotton, glass, silica, quartz, carbon, silicon carbide, nylon and aramid in the form of powders, fibres, fabrics and felt (Table 2). 

Fibre reinforced materials are indeed very versatile. In addition to their use in primary load carrying structures, they have been used as repair materials for structural components made from composites and metals. This chapter highlights several examples which demonstrate the relative ease with which repair to structural components can be achieved with fibre reinforced plastics. It is also pointed out that, as with other materials, the designer of any repair scheme with reinforced plastics must be aware of the effects of the environment on the performance of the materials used. Although fibre reinforced plastics are used in corrosive environments, studies in the Gulf States have shown that severe temperature fluctuations can affect the performance of fibre reinforced plastics in a repair environment. 

Since the row nuclei in the crystallising strained melt act as reinforcing frame structure carrying most of the load in the strained liquid, the not yet crystallised melt inside the frame is able to relax almost completely. It hence either crystallises in conventional manner on the surface of the row nuclei yielding the cylindrites or forms new conventional primary nuclei yielding spherulites as shown by electron microscopy of thick nylon 6 fibres as spun. The coexistence of both structural elements in the fibre as spun with a very small fraction of material in row nuclei explains the poor mechanical properties of such a material and the similarity of fibrous structure obtained after drawing with that obtained from purely spherulitic films. 

Fibre-reinforced composite materials are relatively new and are of interest for primary constructions. These materials are lightweight and may easily be processed into complex forms. In specifically designed primary constructions, the natural forms of organic membranes may have a counterpart in bionic development such as the technical plant stem , which is formed on a model of giant reeds and horsetail (Milwich et al. 2006). 

Reinforcement materials are available in a variety of formats which have been developed with two primary aims, which are not necessarily compatible. These are to achieve the physical properties required by a suitable arrangement of the fibres and at the same time to achieve an acceptable method of manufacture. The forms which are available are ... 

The fibre orientation on the bond surface should be parallel to the primary loading direction. Otherwise it is likely that the Joint will fail due to adherend failure at a relatively low loading level. Owing to a great variety of possible laminate structures and applications, it is unrealistic to require that the fibre orientation on the bond surface and the primary loading direction should be parallel in all connections. This requirement is essential for primary structural connections (see 5.1.1 for definition) and for other connections it is a recommendation. The requirement allows the use of fabrics, woven rovings and uni directional reinforcements on bond surfaces when at least half of the fibres are parallel to the loading direction. In primary structural connections mats are not allowed to be used on bond surfaces. 

Rebars are polymer fibre reinforced-concrete composites, and they are used as primary structures. It is estimated that replacement of steel reinforcing bars by non-corrosive polymer fibres, i.e., by Kevlar or carbon fibres (which gives rise to Kevlar or C-composite bars) for concrete structures produces structures with one-quarter the weight and twice the tensile strength of the steel bar. It is known that, corrosion of steel reinforcement from carbonation or chloride attack can lead to loss of the structural integrity of concrete structures, and such a danger is non-existent for rebars. Thermal expansion coefficient (TEC) values of these fibres are closer to concrete than that of steel, which provides an another advantage and they have the same surface deformation patterns as the steel bars. In addition, they can provide more economy than epoxy-coated steel bars. 

Reinforcements are the primary load carrying constituents and thus determine the strength and rigidity of the resulting pultrudate. The process that requires pulling is only possible because the reinforcement allows the part to be pulled through the die while it cures at the same time. The common reinforcements include glass (E, S or A type), carbon, aramid, boron and several new thermoplastic (polyesters, nylon) fibres. 

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