Flexural
properties
The behaviors shown by
textile materials (fibre, yarn and fabric), when it is subjected to bending, are
known as flexural properties.
a)
Flexural rigidity:
Flexural rigidity is the resistance
of a textile fibre against bending. It can also be defined as the couple
required to bend the fibre to unit curvature. The unit of flexural rigidity is
N-mm2, N-m2 etc.
Mathematically, Flexural rigidity,
Rf = 1 x ηЕT2
4∏ ρ
Where,
η = Shape factor
Е = Specific shear modulus (in N/tex)
T = Linear density (in tex)
ρ = Density (in gram/cm3)
Specific
flexural rigidity:
The specific flexural rigidity is
the flexural rigidity of a textile fibre of unit linear density. Specific
flexural rigidity is usually expressed as N-mm2/tex, N-m2/tex
etc.
Mathematically, Specific flexural
rigidity = 1 x ηЕ(1)2 = 1 x
ηЕ
4∏
ρ 4∏ ρ
b) Bending recovery:
The power of recovery from an
immediate curvature of textile fibre is known as bending recovery. For example,
nylon of 15 denier shows 100% recovery from a small curvature, whereas only 20%
recovery is obtained from a large curvature.
c) Bending modulus:
Bending modulus
can be defined as the ratio between bending stress and bending strain. Here,
bending strain is usually expressed as degree or radian.
So, Bending modulus = Bending stress
Bending strain
Shape factor:
Shape factor is a quantity or
number that indicates the thickness or cross-section of a fibre. Shape factor
is usually expressed by η.
If η =1, then the fibre is round
shaped.
If η >1, then the fibre
thickness is increased.
If η <1, then the fibre
thickness is reduced.
Shape factor of different fibres:
|
Fibre
|
Shape factor
|
Fibre
|
Shape factor
|
|
Viscose
|
0.74
|
Acetate
|
0.67
|
|
Wool
|
0.80
|
Nylon
|
0.91
|
|
Silk
|
0.59
|
Glass
|
1.0 |
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