Composites aramid/epoxy

In addition to carbon and glass fibers ia composites, aramid and polyimide fibers are also used ia conjunction with epoxy resias. Safety requirements by the U.S. Federal Aeronautics Administration (FAA) have led to the development of flame- and heat-resistant seals and stmctural components ia civiUan aircraft cabias. Wool blend fabrics containing aramids, poly(phenylene sulfide), EDF, and other inherently flame-resistant fibers and fabrics containing only these highly heat- and flame-resistant fibers are the types most frequently used ia these appHcations. 

Garton, A. and Daly, J.H. (1985). Characterization of the aramid-epoxy and carbon-epoxy interphases. Polym. Composites 6, 195-200. 

Janssens, W., Doxsee Jr., L., Verpoest, I. and de Meester, P. (1989). Influence of the fiber-matrix interface on the transverse bending strength of dry and moist aramid-epoxy composites. In Proc. Interfacial Phenomena in Composite Materials 89, (F.R. Jones ed.), Butterworths, London, pp 147-154. 

Verpoest, I. and Springer, G.S. (1988). Moisture characteristics of aramid-epoxy composites. J. Reinf. Plast. Composites 7, 2-22,... 

Bannister, D.J., Andrews, M.C., Cervenka, A.J. and Young, R.J. (1995). Analysis of the single fiber pullout test by means of Raman spectroscopy. Part 11. Micromechanics of deformation for an aramid/ epoxy system. Composites Sci. Technol. 53, 411—421. 

Advanced composites have been used most extensively in helicopters. Sikorsky s S-75 helicopter, for example, is about 25% composite by weight, mostly graphite-epoxy and aramid-epoxy composite materials. Composites are used in rotors, blades, and tail assemblies. Future military helicopters are likely to comprise up to 80% advanced composites by structural weight. Graphite-epoxy composites are likely to be used in the airframe, bulk-heads, tail bones, and vertical fins, while the less stiff glass-epoxy composites will be used in rotor systems. 

J R M D Almeida, Effects of distilled water and saline solntion on the interlaminar shear strength of an aramid/epoxy composite . Composites 1991 22 448-449. 

The adhesion of aramid fiber composites can be improved by a core/shell structure of meta-aramid/epoxy nanofibers [29]. The polymer blends are prepared by electrospinning to enhance the interface adhesion. 

The effect of ultra-high molecular weight poly-(ethylene) (UHMWPE) the on mechanical and solid particle erosive wear behavior of aramid fabric reinforced-epoxy composites has been investigated [64]. A siUca sand of a size of 150-280 fim was used as an erodent. The erosive wear rate of UHMWPE in aramid-epoxy composite exhibits a lower value in comparison to neat composites. A maximum erosion rate was observed at an impingement angle 60 , and the material behaves in a semiductile manner. 

Oh HJ, Kim HY, Kim SS. Effect of the core/ shell structured meta-aramid/epoxy nanofiher on the mechanical and thermal properties in epoxy adhesive composites by electrospinning. J Adhesion 2013. 

The 3p-SBS of untreated aramid composites decreases with increasing V-. The absolute shear strength is much lower than for carbon or glass. This must be caused by the weak aramid-epoxy interface, since the SCF is very low for aramid in epoxy. On the assumption of a weak interface this decrease may also be explained by the rule of mixtures, with the exception of the strong fall at =80 %. This sharp decrease is a good indication that fracture occurs at the interface. 

Fracture surface analysis shows that the transverse crack runs straight through the adhesion treated filaments while it circumvents the untreated filaments. Further improvement in the off-axis strength of aramid-epoxy composites seems unlikely since it is limited by the shear and transverse tensile strength of the aramid fibre itself. 

The measured increase due to the aramid adhesion treatment was different for each test 60 % in bundle pull-out, = 28 % in the 3-point, s 40 % in the 4-point short-beam and, = 60-80 % in transverse bending strength. Further improvement of the off-axis strength of aramid-epoxy composites is limited by the shear and transverse strength of the aramid fibres. In spite of the considerable adhesion improvement aramid-epoxy composites still have a lower shear and transverse strength than glass and carbon fibre composites. However, the corresponding strains are approximately equal because of the lower aramid-epoxy shear and transverse moduli. 

Penn, L., Bystry, F., Karp, W. and Lee, S., Aramid/Epoxy vs. Graphite/Epoxy Origin of the difference in strength at the interface. In Molecular Characterization of Composite Interfaces,ed., H. Ishida and G. Kumar, Plenum Press, New York, 1985, pp. 93-109. 

Andrews M C, Bannister D J and Young R J (1996) The interfacial properties of aramid/epoxy model composites, J Mater Sci 31 3893-3913. 

Roylance M (1982) The effect of moisture on the fatigue resistance of an aramid/epoxy composite, Polym Eng Sci 22 988-993. 

Allred R E and Roylance D K (1983) Transverse moisture sensitivity of aramid/epoxy composites, J Mater Sci 18 652-656. 

MC Andrews, RJ Young, J Mahy. Interfacial failure mechanisms in aramid/epoxy model composites. Composite Interf 2 433-456, 1994. 

Table 4.12 Properties of Unidirectional Aramid/Epoxy Composites (Fiber Volume Fraction, V, = 0.60) (from Ref. 10)...

Humidity does affect composite properties by a small amount carbon/epoxy is the least affected and aramid/epoxy the most. Since the influence is likely to be exaggerated by sample size (with coupons having a large surface area-to-volume), the effect on large components and structures is likely to be less. 

Exposure to water at 88°C has a more drastic effect on glass/epoxy than aramid/epoxy. The greater reduction in shear strength (and hence bond strength) of the glass system and its immediate degradation, compared with a one hour incubation period for the aramid system, indicates that the two fibre composites have differing mechanisms of bond deterioration. 

ARALL laminates, a family of hybrid composites consisting of aramid fibers bonded with epoxy between 0.3 mm thick aircraft ahoy sheets, were introduced in the 1980s (53). The laminates have lower density than even the new Al—Li ahoys and are greatly superior to monolithic aluminum sheet in resisting the growth of fatigue cracks. ARALL laminates have been specified for aircraft stmcture which is subjected to cycHc tension loads (see Laminates). 

Many different thermosetting polymers are used in pultmsion, eg, polyester, vinyl ester, epoxy, and urethane. Reinforcements must be in a continuous form such as rovings, tows, mats, fabrics, and tapes. Glass fibers are the low cost, dominant composition, but aramid and carbon fibers are also used. 

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