Aramid fibre mechanical properties

Aramid fibres have high specific mechanical properties and are used for their attractive characteristics such as ... 

In all cases, carbon fibres lead to the highest mechanical performances compared to glass and aramid fibres. Nevertheless, their impact behaviour and price restrict their consumption. Glass fibres yield the cheapest composites but performances are more limited. Table 6.10 compares the properties of the main fibre types and shows some examples of properties for a nylon matrix reinforced with short fibres of the three types. 

Figures 9.19 and 9.20 present a survey of the mechanical properties of some (unidirectional) composites, in comparison with some other materials. In Figure 9.19 the values of modulus and strength are plotted as such, while in Figure 9.20 these values have been divided by the specific mass. From Figure 9.20 the enormous advantage of composites with respect to stiffness and strength per unit weight, in comparison to metals, is clearly visible. The modem carbon and aramide composites are superior to those based on glass fibres, for the specific stiffness even by a factor between 4 and 5.

The mechanical properties of paracrystalline aramides and other high-performance polymeric fibres are shown in Table 19.11. In comparison some other fibres are mentioned in this table (see also Sect. 13.6). Aramide fibres display a very high refractivity (refractive index and strong birefringence // 2.2, n 1.6). 

In this respect, (thermoset) plastics composites with discontinuous fibre products are already mostly used in the car body applications, where polyester/E-glass is predominating (mostly because of polyesters, economy, ease of processability and reasonable mechanical properties provided), followed by use of phenolics (when fire retardance is required, in friction linings and engine compartments), and epoxies. Replacement by carbon or aramid fibre reinforcements can reduce body mass by 40% (compared to steel) and with more added strength, but the cost is unfavourable at the moment, as mentioned previously [12, 13]. 

Superior mechanical properties, including impact strength and resistance to delamination, are claimed for reinforced plastics made from three-dimensional fabrics [1], Other reinforcement forms include continuous swirl mat, designed to have a minimum of fibre ends, and hybrid fabrics containing two different reinforcing fibres, for example, glass and aramid. There are many different ways in which two different fibres can be combined together. 

Carbon and aramid fibres are anisotropic with different values of mechanical and thermal properties in the main directions, whereas glass fibres are isotropic (Eckold 1994). 

Natural polymeric fibres, mostly cellulosics, have been used since ancient times for reinforcement. Mechanical properties of these are inferior to glass, carbon or aramid fibres. Cellulosics are usually used as a laminating material, in the woven form. Processing... 

Other types of fibre having potential use in ballistic protection include PBO (Zylon), which has superb mechanical properties, but its tensile strength has been found to be susceptible to degradation under certain extreme temperature and humidity conditions. The M5 fibre is claimed to be stronger and lighter than aramids and UHMWPE as well as most current armour materials in personal armour systems, but is found to have similar problems to PBO. 

Zhong L X, Fu S H, Zhou X S and Zhan H Y (2011), Effect of surface microfibrillation of sisal fibre on the mechanical properties of sisal/aramid fiber hybrid composites . 

Table 9.4 presents typical ranges of variation for several physical and mechanical properties of FRP bars made of glass (GFRP), carbon (CFRP) and aramid (AFRP) reinforcement. For the typical fibre content, all FRP reinforcing bars present low density, about one-sixth to one-quarter that of steel bars (again, the main competitor), which facilitates transport and... 

The APC materials typically nsed for on-site rehabilitation of timber and concrete are composed of glass, carbon or aramid fibres and a polyester, epoxy or polynrethane polymeric matrix. Glass fibres are the most frequently used due to their moderate cost and good mechanical properties when compared to carbon fibres. They are used normally in the form of pultruded profiles or strips, fabrics (tissues) or mats. Carbon fibres are mainly used in the form of pultruded profiles of solid, open or hollow cross-sectional shapes. While in timber applications both thermoplastic and thermosetting matrix types are used, in concrete applications only the latter type is used. 

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