Mechanical properties of fibers

An important aspect of the mechanical properties of fibers concerns their response to time dependent deformations. Fibers are frequently subjected to conditions of loading and unloading at various frequencies and strains, and it is important to know their response to these dynamic conditions. In this connection the fatigue properties of textile fibers are of particular importance, and have been studied extensively in cycHc tension (23). The results have been interpreted in terms of molecular processes. The mechanical and other properties of fibers have been reviewed extensively (20,24—27). 

Among the basic mechanical properties of fibers are their deformability and tenacity. When an axial stretching force is applied to the fiber, the principal quantitative indices of deformability are the axial elastic modulus (E)... 

The role of the matrix is to protect the filler from corrosive action of the enviroment and to ensure interactions between the fibers by mechanical, physical and chemical effects. The mechanical properties of fiber composites are dependent on the mutual position of the fibers in the monolithic materials. 

Normalized frequency, 11 132 Normalized mechanical properties, of fibers, 11 182... 

Ho, H. and Drzal, L. T., Evaluation of interfacial mechanical properties of fiber reinforced composites using the microindentation method, Composites, A, 27, 961 (1996). 

The mechanical properties of fiber-matrix interfaces 3.2.1. Introduction... 

It is concluded from the above that the mechanical characteristics of CNT composites are not yet well established. In order to have a better insight into the expected performance, idealized upper bounds for various mechanical properties would be useful to have. Although many sophisticated models for predicting the mechanical properties of fiber-reinforced polymers exist, the two most common and simplest ones are the rule of mixtures and the Halpin-Tsai... 

Experimental determination of the properties of any material is very important. This is particularly true in the case of fibrous materials because general insufficient data are available for them. Fibers have one very long dimension and the other two extremely small. This makes determination of their properties, physical and mechanical, far from trivial. In particular determination of their transverse properties, i.e. in the direction of the fiber diameter, can be difiicult. In this chapter we describe experimental techniques to determine some physical and mechanical properties of fibers. 

Mechanical Properties of Fiber. Tenacities and initial moduli were obtained for fiber samples using an Instron tensile tester Model TT-B. The extension rate was 2.54... 

Effects of UV Light on the Chemical and Mechanical Properties of Fiber Forming Polymers... 

Fig. 5.2-1. Mechanical properties of fibers, T = 27°C. a) Stress-strain curves b) Tensile strength and elasticity moduli...

For both designs a microphase separated morphology was found with 20-50 nm peptide domains dispersed in a continuous poly(ethylene glycol) phase. Furthermore, a 100-150 nm superstructure was observed in cast films, which was explained to result from the polydispersity and multiblock character of the polymers. The mechanical properties of fibers and films made from these block copolymers could be modulated by manipulating the length and nature of the constituent blocks. Similar work was reported by Shao et al. [47]. 

Ikble 6.2. Physical and mechanical properties of fibers and coatings. 

The production of the polymer has reached pilot plant scale (batches of 150 kg), and the polymer can be spun and pyrolyzed continuously to long fibers. However, the mechanical properties of fibers made in such large quantities still suffer from too high an oxygen contamination and lag behind by about 20% with respect to tensile strength, as compared to laboratory scale products. 

Linear Polymers Long chains are necessary to confer the mechanical properties of fibers, plastics, and elastomers that make polymers so valuable. Fibers such as cellulose and polyester arc semicrystalline materials in which the same chemical stmeture exists in both rigid microcrystalline and flexible amorphous phases. Plastics may be either semicrystalline, such as poly(ethylene terephthalate) (the same polyester of fibers is also the PET of beverage bottles), or completely amorphous and glassy, such as polystyrene or poly(methyl methacrylate) (PMMA, Plexiglas or Lucite ). Elastomers are completely amorphous and flexible and would flow as a viscous mbbery liquid except that the polymer chains are cross-hnked to prevent macroscopic flow but allow reversible stretching. As an example, poly(dimethylsiloxane)... 

An extensive discussion of all the important aspects and methods of characterization of physical and mechanical properties of fibers is outside the scope of this chapter. Corresponding information can be found in more comprehensive treatises [331,332]. Some typical properties of nylon-6,6, nylon-6, nylon-11, nylon-6,11 and nylon-6,12 are listed in Table 2.5 and Table 2.6. 

Although the most remarkable change by acetalization is the increase in hot-water resistance, the mechanical properties of fibers are also affected. Acetalization has practically no effect on fiber tenacity, but formalization induces brittleness in fibers. For example, a heat-treated fiber shows 70-80% relative knot strength, which drops by formalization to 55-65%. There is a rather large difference of resilience between the formalized and unformalized fibers, as shown in Figure 4.20 [114]. It can be seen that the resilience of the unformalized PVA fibers is rather high, but it drops markedly with an initial formalization of less than 20% the drop in fiber resilience after further formalization is very small. 

In principle, mechanical properties of fibers should be treated as part of the overall physical properties. In most cases, however, they provide the primary motivation for their utilization in industrial and other applications. Consequently, their study constitutes a substantial portion of investigation into the properties of fibers. As such, they merit a separate discussion of their own. 

Table 3 Mechanical properties of fibers processed from biodegradable polymers ...

Mechanical Properties of Fiber- and Polymer-Reinforced Mortars"... 

Hill, R. (1965) Theory of mechanical properties of fiber-strengthened materials - III Self-consistent model. J. Mech. Phys. Solids, 13, 189-198. 

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