### Torsional Properties of Fiber | Torsional Properties of Textile Materials

Torsional Properties of Fiber:
It is the property of fiber or material when a Torsional force is applied on it. Here Torsional force is a twisting force that is applied on the two ends of the material in two opposite direction. The behaviors which are shown by a textile material when it is subjected to a torsional force is called torsional property. Torsional properties are..
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

3. Shear modulus:
Shear modulus or modulus of rigidity, denoted by G, or sometimes S or μ, is defined as the ratio of shear stress to the shear strain. Shear modulus' derived SI unit is the pascal (Pa), although it is usually expressed in gigapascals (GPa) or in thousands of pounds per square inch (ksi). Its dimensional form is M1L−1T−2.

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