Kevlar/epoxy composites

In a unidirectional Kevlar/epoxy composite the modular ratio is 20 and the epoxy occupies 60% of the volume. Calculate the modulus of the composite and the stresses in the fibres and the matrix when a stress of 50 MN/m is applied to the composite. The modulus of the epoxy is 6 GN(m. ... 

Davidovitz, M, Mittelman. A., Roman. I. and Marom. G. (1984). Failure modes and fracture mechanisms in flexure of Kevlar-epoxy composites. J. Mater. Sci. 19, 311-294. 

V.V. Nesarikar, V.K. Jain, S.K. Choudhury Travelling wire electrochemical spark machining of thick sheets of Kevlar-epoxy composites. Proceedings of the Sixteenth AIMTDR Conference (1994), pp. 672-677. 

The aL of Kevlar 49 (obtained by them) gave excellent agreement with measured values for unidirectional Kevlar/epoxy composites in terms of the Schapery model, which is an improvement over the reported axial aL of Kevlar fiber and those of Kevlar epoxy composites reported by Strife and Prewo [90]. 

Fig. 12. Photon-emission from the Kevlar/epoxy composite.

As described by DuPont researchers, significant weight saving and low flammability are the primary driving forces behind the adoption of Kevlar by the aircraft industry. Kevlar-epoxy composites are 25-50% lighter than those from glass and aluminum and have better tensile properties. Because thermotropic LCPs offer a low viscosity for the impregnation of carbon fibers and excellent chemical resistance, LCP-carbon fiber composite has been developed as a secondary composite for the aerospace industry [6]. 

Imieh nska K, Castaings M, Wojtyra R, Haras J, Le Clezio E and Hosten B (2004) Ait-coupled ultrasonic C-scan technique in impact response testing of carbon fibre and hybrid glass, carbon and Kevlar/epoxy composites, J Mater Process Technol 157-158 513-522. 

Originally developed for tyre cords, Kevlar-type materials have also become widely used in composites. Uses include filament-wound rocket motors and pressure vessels, metal-lined Kevlar-overwrapped vessels in the space shuttle, boat and kayak hulls, Kevlar-epoxy helmets for the US military, and as one of the reinforcements in composite lorry cabs. 

Example 3.7 A thin unidirectional Kevlar fibre/epoxy composite has the properties listed below. If the fibres are aligned at 6 to the x-axis, show how... 

Example 3.19 A single ply Kevlar 49/epoxy composite has the following properties. 

Penn, L.S., Tesoro, G.C. and Zhou, H.X. (1988). Some effects of surface-controlled reaction of Kevlar 29 on the interface in epoxy composites. Polym. Composites 9, 184-191. 

Fig. 6.12. Toughness maps depicting contours of predicted fracture toughness (solid lines in kJ/m ) for (a) glass-epoxy composites as a function of fiber strength, Uf, and frictional shear stress, tf and (b) Kevlar-cpoxy composites as a function of at and clastic modulus of fiber, Ef. The dashed line and arrows in (a) indicate a change in dominant failure mechanisms from post-debonding friction, Rif, to interfacial debonding, Sj, and the effect of moisture on the changes of Of and Tf, respectively. Bundle debond length...

Penn L.S., Bystry F A. and Marchionni H.3. (1983). Relation of interfacial adhesion in Kevlar/epoxy systems to surface characterisation and composite performance. Polym. Composites 4, 26. 

Duvis, T., Papaspyrides, C.D. and Skourlis, T. (1993). Polyamide coating on carbon fibers and potential application in carbon/Kevlar/epoxy hybrid composites. Composites Sci. Technol. 48, 127-133. 

Sohn, M.S. and Hu, X.Z. (1994). Mode II delamination toughness of carbon fiber/epoxy composites with chopped Kevlar fiber reinforced composites. Composites Set. Techno . 52, 439-448. 

Fig. 10. Stress-strain diagram of a unidirectional epoxy composite with Kevlar 49, tested under tension and compression 80)...

Like other composite properties, the wear resistance is influenced by the orientation of reinforcing fibres. Sung and Suh found that with biaxially-oriented glass fibre and molybdenum disulphide in a PTFE matrix (Duroid 5813), the wear resistance was greatest when the highest proportion of fibre was normal to the sliding surface. The same effect was found with a graphite fibre/epoxy composite and a Kevlar fibre/epoxy composite. 

Very significant improvement in interlaminar shear strength was observed for the Kevlar/epoxy and Zylon/epoxy composites with fibers treated with hyperbranch AD-102. 

S Y Lo, H T Hahn and T T Chaio, Swelling of Kevlar 49/epoxy and S2-glass/ epoxy composites . Progress in Science and Engineering of Composites, ICCMIV, Tokyo 1982, pp 987-1000. 

Fanucci, J.P. (1987) Thermal response of radiantly heated kevlar and graphite/epoxy composites. /. Compos. Mater., 21 (2), 129-139. 

Now many composite materials are used in aircrafts (Fig. 18). Graphite/epoxy and graph te/Kevlar are commonly used. For these materials, polysulfides (120) have been used as sealants. To provide airframe integrity, everything has to be sealed, preferably with flexible sealants that allow joint movement, fuel and weather resistance, and corrosion prevention. Today airframes are guaranteed to have a service life of 20 years without any corrosion damage. For this reason, the inhibited polysulfides are used to prevent corrosion between aluminum and graphite/epoxy composite parts. 

Initially, Kevlar was used in car tires as reinforcement for the elastomeric matrix (rubber) however, nowadays the most widely known appHcation of Kevlar/epoxy is in body armor [27]. Other uses include fireproof suits for firefighters, gloves, and helmets [28]. Their high strength-to-weight ratio makes them more suitable for use as reinforcement, for example, in composite materials primarily where flexure properties are important, such as aircraft wings [29]. 

In addition to giving a measure of the deformation within fibres, the strain-induced band shifts in Raman spectra have been used to follow the micromechanics of fibre reinforcement in model polydiacetylene/epoxy composites (13). The critical length has been measured directly (13) and the effect of resin shrinkage has been examined in detail (14,15). It has also been demonstrated that the technique can be employed to measure fibre strain optically in a high voliine fraction Kevlar 49/epoxy composite (16). In this present paper we demonstrate that Raman microscopy can also be used to measure fibre strain in carbon fibre reinforced PEEK composites (17) and to give a direct measure of residual thermal shrinkage stresses in PEEK matrix composites. 

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