Kevlar® ropes

The most spectacular application example to date is perhaps the Aberfeldy footbridge over the river Tay in Scotland (see Fig. 11.4). This bridge is 113-m long, has a deck width of 2.2 m, and a main span of 113 m [4]. The entire deck structure, hand rails, and A-frame towers are pultruded composites, and the cable stays are Kevlar ropes. The deck structure is assembled from a modular system of pultruded 6-m long, hollow components, which consist of 70 percent by weight of E glass and 30 percent pigmented isophtalic polyester resin. 

A failure in 1983 when aramid fibres began to be used illustrates the problems that can arise. A ship. Ocean Builder, was to be used to erect an oil rig in the Gulf of Mexico. Five weeks before, 12 buoys were secured to anchors by Kevlar ropes. When the Ocean Builder arrived and the mooring lines were picked up, four ropes broke reportedly at 20% of break load. The up-and-down movement of the buoys had led to axial compression fatigue of the Kevlar fibres. 

Fig. 19. Axial compression failures, from Hearle el al. (1998, chapter. 19). (a) Broken and unbroken yarn segments in a Kevlar rope, (b) Buckling and break of a fibre in a Twaron rope.

Figure 8.7 Applying an epoxy to secure plastic buoyancy spacers to a Kevlar rope on a marine seismic cable...

Kevlar fibers are supplied by DuPont as Kevlar-29 and 49. The former is characterized by high tensile strength and the latter by high initial modulus(4). Some Kevlar-29 end uses are in ropes and cables, which are as strong as steel at one-fifth the weight, and in ballistic vests. Some Kevlar-49 end uses are in reinforcing resins and composites for aerospace structures, boat hulls, and sport equipments. 

Kevlar fibers are available in four forms Kevlar, Kevlar 29, Kevlar 49 and the recently developed Kevlar 149. Kevlar is designed specifically for reinforcements of elastomers (e.g. tires and belts), while Kevlar 29 is used primarily for tensile members sueh as ropes, cables, webbings and ballistic cloth. Kevlar 49 and 149 are designed for reinforcement of high performance PMCs. Kevlar 149 offers a 40%... 

A third interesting aspect of this story is that Du Pont s aramide fiber was not specifically the result of market-driven research. When this fiber was patented in 1971 there was no commercial application in view. However, within ten years, three varieties of Kevlar fiber were commercialized by Du Pont for dozens of reinforced plastic applications in radial passenger tires, belts, in protective clothing, such as gloves or ballistic and flak vests, in ropes and cables in racing kayaks and canoes, and in commercial aircraft. Thus the Kevlar fiber by no means resulted from the functional, bottom-up, approach which is sometimes considered as a major characteristic of materials science. The aramide fiber resulted from the traditional style of industrial research which was successful in the plastic era and confirms the leadership of chemistry in materials technologies. 

Ropes, cables, coated fabrics for inflatables, architectural fabrics, and for ballistic protection fabrics. Ship to shore mooring lines are made of aramid fibers because of its resistance to saltwater corrosion. Vests made of Kevlar 29 are used by law enforcement agencies in many countries. Later we discuss this application in some detail. 

The proposed end applications of Kevlar (Yang, 1989) and related fibers include ballistic and fire protective apparel, hard armors, reinforced tires and rubber goods, various forms of composites, filament wound pressure vessels, marine ropes, optical cables and industrial gloves. Almost all of them utilize the high tensile properties and high heat-resistance. 

LCP fibres are used for making heavy-duty ropes and belts and also as the reinforcing fibres of composite materials. An important application of Kevlar is in the fabrication of bullet-proof clothing. The easy mouldability, good mould filling and low thermal expansion of thermotropic LCPs, combined with their resistance to solvents and their stability at temperatures up to 120 °C or higher make them suitable for precision mouldings for use in a variety of components such as electrical connectors. 

Yarns are available in a variety of deniers and merge types that vary in the balance of tensile properties. Special finishes can be applied to increase lubricity, improve fatigue in wet applications, or provide better UV resistance. Ropes using Kevlar or Twaron are particularly useful for static applications or where maximum modulus is required. Technora-based ropes are suited for dynamic applications where resistance to fatigue is important. 

Take, for example, the two major commercialized advanced composite fibers, Kevlar and carbon fiber. When Kevlar was first developed, DuPont believed it would be used as a replacement for fiberglass in ropes, tire cords, and many... 

There is also an opportunity to use fibre ropes as tension textiles in buildings. An example is a bus station in Cambridge, UK (Fig. 13.25), erected in 1991. The structure was designed with four masts, each with a pair of forestays and back stays to support the 7-metre cantilevered roof. The stays are made of Parafil ropes with a Kevlar core their function is primarily to resist snow loading, but they are permanently stressed to... 

I i/i. 12.. Slirfiice abrasion, (a) Kevlar pulled lo-and-fro over a pin. (b) Wool again.sl a rotating pin. (c) Nylon against a rotating pin. (d) Yarn-on-yarn abrasion of polyester, (e) From wet nylon rope after tension eyeling. (I. g) From worn nylon Hovercraft rope. For further explanation, see Fig. I. 

Yarn buckling tests were carried out in the FIBRE TETHERS 2000 (1994, 1995) Joint industry project. Failure due to axial compression fatigue was also studied in fibres from fatigued ropes in the study. As discussed below, the constraints on fibres within the yarns, especially if they were re.strained in a shrink-tube in the laboratory te.st or within ropes, causes very sharp fibre kinks to form. Kevlar, Vectran and Dyneema all showed kink-bands within fibres and breaks over short lengths. 

Three types of Kevlar aramid fibers are available a high-tensile-strength, high-modulus type for reinforcement of plastic a similar fiber for use in ropes, cables, coated fabrics, and protective clothing and a third type designed to reinforce rubber products such as tires, belts, and hoses. 

The melting temperature of copolymer is reduced by introducing kinked structural unit i.e isophthalic acid in place of terephthalic acid and obtained melt spun filaments that displayed high tensile properties. The product was commercialized under the name "Ekonol" in 1985. The properties of Ekonol fibers are impressive and comparable with that of Kevlar 49 fibers as shown in Table 8.2 [75]. Ekonol fibers may be used for ropes, cables, composite, and protective apparel. 

Dyneema, the strongest commercially available fabric, is an oriented polyethylene polymer with a molecular weight 100 times greater than that of high-density polyethylene. It is lighter than Kevlar and at least 40% stronger. A rope made of Dyneema can lift almost... 

Recently, high-performance fibres have been developed based on aromatic polyamides, also known as aramids. These are tough enough to be used in rope and cable manufacture, or in protective clothing or body armour. An example of an aromatic polyamide used to make high-strength fibres is poly(p-phenylene terephthalamide), the trade name of which is Kevlar or Twaron ... 

The exceptional properties of Kevlar have led to its use in making bullet-proof vests, ropes, fire-protective clothing (as used by Formula 1 racing drivers) and modern leathers worn by motorcycle riders. It is also used to reinforce other materials, such as the rubber in tyres. 

Kevlar fiber can also be used to make fabric or woven into rope or twine. In fabric form the high tensile shength of the individual fibers results in a fabric that is exceptionally resistant to tearing or puncture. Fabric made from Kevlar fiber is often used to manufacture gloves, sleeves, jackets, chaps, and other clothing designed to protect... 

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