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Fibre strength measurement - introduction, single fibre strength, Universal tensile tester

Measurement of strength

  • To measure fibre strength, the proper sample should be prepared.
  • During clamped fibre, a specified gauge length is vital, because if the gauge length is longer than specified it will lower the value of strength.
  • The extent of change of strength with gauge length and the number of fibres tested at a time affects the test results.
  • Strength tests on fibre bundles are generally carried out at nominal zero gauge length.
  • However, tests at zero gauge length do not give all the information required about the strength of the fibres in a sample, as the influence of weak spots would not come into play at this test length and, therefore, it would be desirable to carry out the tests at finite gauge lengths. 
  • Therefore the bundle strength measured at 1/8 inch (3mm) gauge length should have a better correlation with yarn strength than the strength values measured at other gauge lengths. 
  • Jaw pressure to hold fibres, number of fibres in the bunch, bundle alignment, calming, and proper combing are necessary to arrange very carefully to achieve the appropriate result.

Single fibre test

Single fibre strength is measured by various instruments among them 2 are more popular. 

One is a Universal tensile tester and another is steal-o-meter
The individual fibre test is time-consuming and required lots of tests to create the appropriate results.

Universal tensile tester

The universal tensile tester is a robust and portable instrument used for measuring the tensile strength of the fibre and some other mechanical properties. 

This instrument is capable of recording the tensile load-elongation curves of a range of samples from single fibres to thick fabric strips, which cover a wide spectrum of mechanical characteristics. 

Universal tensile tester
Universal tensile tester

To measure the strength of fibre, the sample of fibre is clamped between two jaws

This instrument has two jaws vertically. 

The upper jaw is suspended from the ‘load cell’ which is the load-sensing device, while the lower jaw is mounted on the ‘cross-head which can be moved up and down at controlled speeds. 

The crosshead speed, which decides the rate of extension of the specimen, can be varied from 0.05 cm/min to 50 cm/min in 12 steps. 

The choice of the suitable load cell from among the four cells which cover a range from 2 g to 500 kg. is made by the load requirements of the specimen under test. 

In this method, the load cell contains a bonded wire type of strain gauge which consists essentially of a cantilever beam with a resistance wire bonded to the surface. 

The upper jaw carrying the specimen is suspended from the free end of the cantilever beam such that the tension developed in the specimen leads to an infinitesimally 

small bending of the beam. 

As a result, the wire bonded to the beam increases in length and hence in electrical resistance in proportion to the tension in the specimen. 

Since this resistance wire forms one arm of a Wheatstone bridge circuit, which is excited by an oscillator and remains normally balanced, any tension in the specimen would cause a misbalance in the circuit. 

The resulting signal is amplified to operate a recorder pen. Thus when the test specimen is extended, the recorder pen moves across the chart through a distance proportional to the tension in the specimen. 

Since the deflection of the end of the beam is infinitesimally small, the Instron works as a ‘constant rate of extension’ instrument when the crosshead is moved at a steady rate. 

The crosshead and chart are driven synchronously through magnetic clutches and convenient gears to provide a choice of constant and reversible extension speeds. 

The chart movement can be varied to achieve a range of extension magnifications. As a result of the simultaneous movement of the pen and the chart, the former responded to the tension in the specimen, and the latter synchronized to the specimen extension.

The trace on the chart represents the load-elongation curve. 

The Instron is also equipped with an Integrator which is a convenient device for obtaining the area under the load-elongation curve which measures the work of rupture. 

Questions -

  1. How strength is measured?
  2. What is a single fibre test?
  3. What is the universal test?
  4. How universal tensile tester works?


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Elsevier. (2016). Performance testing of textiles (1st ed.). Woodhead Publishing.

Houck, M. M. (2009). Identification of Textile Fibers (M. M. Houck, Ed.; 1st ed.). Woodhead Publishing.

Textile School. (2010, October 27). Fibre Identification - tests to identify a fibre. Textile School

Trivedi, Y. (2020, April 10). Identification of Textile Fibers. Textilesphere.com

(N.d.). from

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