Flexural properties of textile fibre

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