The behaviors which are shown by a textile material when it is subjected to a torsional force is called torsional property.
1. Torsional rigidity
2. Breaking twist
3. Shear modulus
1.Torsional rigidity: Torsional rigidity can be defined as the torque required against twisting is done for which torque is termed as torsional rigidity.
Mathematically, torsional rigidity = ηET2/ρ
Where, η = shape factor, E = specific shear modulus (N/tex)
Specific torsional rigidity: Specific torsional rigidity can be defined as the torsional rigidity of a fiber of unit linear density.
Mathematically, specific torsional rigidity = ηE/ρ
Unit: N-m2 /Tex
2.Breaking twist: The twist for breaking of a yarn is called breaking twist. It also can be defined as the number of twists required to break a yarn. Breaking twist depends on the diameter of fiber and it is inversely proportional to its diameter.
That is, Tb ∞ 1/d
Where, Tb = Breaking twist, d = diameter of fiber
Breaking twist angle: This is the angle through which outer layer of fiber are sheared at breaking.
Mathematically, α = tan-1(πdTb)
Where, α = breaking twist angle, d = diameter of fiber, Tb = breaking twist per unit length
Breaking twist angle of different fibers:
Fiber |
Breaking twist angle (α) |
Cotton |
35* |
Viscose |
33* |
Polyester |
50* |
Wool |
40* |
Silk |
39* |
Glass |
4* |
3.Shear modulus: Shear modulus is defined as the ratio of shear stress & shear strain. Shear modulus is measured in radians.