Constitutive relations fiber composites

Even in the apparently linear range, the response to stress should be considered as viscoelastic rather than elastic. Most polymers that behave in a linear, viscoelastic manner at small strains (< 1 %) behave in a nonlinear fashion at strains of the order of 1 % or more. However, in a fibrous composite, the resin may behave quite differently than it would in bulk. Stress and strain concentrations may exceed the limiting values for linearity in localized regions. Thus the composite may exhibit nonlinearity (Ashton, 1969 Trachte and DiBenedetto, 1968), as is the case with particulate-filled polymers (Section 12.1.2). Although nonlinearity at low strains is characteristic, Halpin and Pagano (1969) have predicted constitutive relations for isotropic linear viscoelastic systems, and verified their prediction using specimens of fiber-reinforced rubbers. 

Carbon fibers constitute the major load-bearing element of carbon fiber reinforced plastics. The ability of these composites to use effectively the strength and stiffness of carbon fibers depends upon the strength of the lnterfaclal zone, which Is closely related to the surface free energies of the carbon fibers and matrix. 

While polymer blends are used for a wide variety of purposes, those related to toughness or impact resistance constitute the largest tonnage. Similar results are seen with composites note the effect of carbon black on rubber, and glass fibers on plastics. However, specific applications depend on physical properties and morphology, treated next. 

In comparison to cotton, wool or silk, the poultry feather biomass is not a lot used relating to the complex the structure of the feathers. However, the secondary and the tertiary structures of the feathers, i.e. the barbs and the barbules have the morphology and properties that make them suitable for use as reinforcement or filler in composites for several applications [1,2]. Because of a very low density, excellent compressibility and resiliency, warmth retention and typical morphology, poultry feather barbs and barbules are preferable in comparison to other natural and synthetic fibers. In addition, poultry feather fibers are cheap, abundantly available and constitute a renewable source for animal fibers. The density of poultry feather is about 0.8 g/cc compared to about 1.3 g/cc for wool and about 1.5 g/cc for cellulose fiber [1-3]. 

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