Rieter

Fiber elongation

Index

Three concepts must be clearly distinguished:

  • permanent elongation:
    that part of the extension through which the fiber does not return on relaxation;
  • elastic elongation:
    that part of the extension through which the fiber does return on relaxation;
  • breaking elongation:
    the maximum possible extension of the fiber until it breaks, i.e.  the permanent elongation and the elastic elongation together.

Elongation is specified as a percentage of the starting length. The elastic elongation is of decisive importance since textile products without elasticity would hardly be usable. They must be able to deform (e.g. at knee or elbow) in order to withstand high loading (and also during processing), but they must also return to shape. The fiber elongation should therefore be at least 1-2% (glass fibers), and preferably slightly more. The greater crease-resistance of wool compared with cotton arises, for example, from the difference in their elongation:

  • cotton 6-10%;
  • wool 25-45%.

The following scale represents the cotton fiber elongation  [27]:

  • below 5.0% = very low;
  • 5.0-5.8% = low;
  • 5.9-6.7% = average;
  • 6.8-7.6% = high;
  • above 7.6% = very high.

Man-made fibers show higher elongation values from about 15 to 30%. For functional textile goods, still higher elongations are necessary sometimes, but they make processing in the spinning mill more difficult, especially in drafting operations. Higher elongations are needed for sportswear, hoisery, corsetry, and stretch products. If a fiber is subjected to tensile loading, demands are made on both its strength and elongation. Strength and elongation are therefore inseparably connected. This relationship is expressed in the so-called stress/strain diagram. For each type of fiber, there is a typical curve. In blending, it should be ensured that the stressstrain curves of the fibers to be blended are similar in shape. Measurment of elongation is difficult and time consuming.