The values of modulus obtained in
tensile tests range from over 2,500 g-wt/tex for glass and about 1,800 The shape factor becomes greater, and the rigidity
increases, the more distant the material is from the center.
It will be seen that with an asymmetrical shape there may
be a difference according to the
direction of bending: in practice, the fibers will usually twist so as to bend
about the easiest direction. For simple shapes, values may be obtained by integration from a
relation derived For more complicated
shapes, either numerical computation or experiment will be necessary. Table
above gives some typical values.
As the fineness in as a squared
term, and in view of the range of values occurring in practice – from 0.1 tex
for a fine stretched rayon to 1 Tex for a coarse wool and higher for some hair
fibers and man-made monofils – it will be the most important factor in
determining the flexural rigidity. The choice of filament denier is thus
important in deciding flexibility.
It is convenient to introduce a quantity which is independent of the fineness of the specimen. We may call this quantity the SPECIFIC FLEXURAL RIGIDITY, Rf; it is equal to the flexural rigidity of a filament of unit tex. It will be given by:
The values of Rf using values of
the modulus obtained in tensile tests are given in table. They show the great
flexibility of acetate filaments and the stiffness of stretched rayaon and
glass.
It is
convenient to introduce a quantity which is independent of the fineness of the
specimen. We call this quantity the specific flexural rigidity, Rf ; it is
equal to the flexural rigidity of filament of unit tex. It will be given
by:
Rf =
[(1/4 π ) (η E/ r)] x
10-5 g-wt cm2 /
tex2……+
The values of Rf, the specific
flexural rigidity using values of the modulus obtained in tensile tests are
given below:-
Fiber Specific
Flexural Rigidity, Rf (g-wt cm2 / tex x 10-4 )
Viscose 1.94
Fortisan 4.48
Acetate 0.83
Wool 1.99
Silk 1.89
Nylon 1.42
Glass 9.1
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