Tensile modulus fibre orientation

Generally it is found that PPT fibres are highly oriented and that those variants with the lowest values of orientation angle exhibit the highest tensile modulus. Indeed the average crystallite orientations derived from azimuthal peak widths at half maximum intensities of the 200 reflections in Kevlar 49 and Kevlar 29 are found to be nine and eleven degrees respectively. 

The properties of NR eomposites are eontrolled by natural fibre eontent, natural fibre orientation and adhesion between green fibre and NR matrix." The mechanieal property of the polymer eomposite increased. The modulus and hardness and oil resistanee of the resulting NR increased with inereasing tea leave waste but the tensile strength and elongation at break of the NR compound decreased as a function of tea leave waste. In addition, the NR compound with tea leave and carbon black exhibits excellenee in thermal properties. The polymer composite possesses the best properties at 30 phr of modified tea leave with MMA and 30 phr of carbon black. 

Using the Cox model for a fibre composite, already discussed [12], and neglecting the very small contribution E" V" arising from the tensile modulus of the comphant matrix, the extensional modulus E of the highly oriented polymer becomes... 

Another very important idea is that drawing involves the stretching of a polymer network in which the junction points of the network are formed by physical entanglements. Even if crystallisation occurs, the deformation of the polymer network determines the overall constraints on the macroscopic deformation, which can occur during the fibre or film extrusion process and in subsequent tensile drawing or die drawing processes. The development of molecular orientation is a major factor in the development of physical properties such as tensile modulus and tensile strength and hence relates to the deformation of the molecular network. 

Figure 1.6(a) The effect of fibre orientation on composite tensile modulus. Calculated for a 60 v/o, unidirectional laminate. The angle refers to that between the fibres and the load axis. 

The function N(0)=p(0)sin0 is proportional to the total number of domains in the fibre at an angle 0 with the fibre axis. The determination of the modulus using sonic frequencies will yield a higher value of g than the method by which the modulus is derived from the initial slope of the tensile curve. For random orientation of the chains in a fibre (sin20),=O.5 and the modulus of an isotropic fibre is given by Eiso 4g. 

For a polymer fibre with a single orientation angle the modulus, E, or the slope at each point of the tensile curve, is a function of the tensile stress and given by... 

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