ISO 5079 Textile Fibers - Determination of Breaking Force and Elongation at Break of Individual Fibers

The International Organization for Standardization (ISO) standard, "ISO 5079 Textile fibers - Determination of breaking force and elongation at break of individual fibers", describes a test method and conditions for determining the breaking force and elongation at break of individual fibers in the conditioned or wet state. These determinations of fiber properties do not generally yield the same results when performed on different types of testing equipment. To avoid such discrepancies, this standard is limited to the use of a constant-extension-rate testing machine. It is applicable to all fibers, including crimped fibers, provided that the available fiber length allows the gauge length specified in this standard. For natural fibers (especially wool and cotton), the most frequently performed breaking test is the testing of fiber bundles (ISO 3060 and IWTO 32-82 standards).

For the purposes of this standard, the following terms and definitions apply:

• Fracture strength refers to the maximum force developed when a test specimen is brought to rupture in a tensile test under specified conditions.
• Rupture force refers to the force at the point of rupture of the test specimen during the tensile test.
• Extension refers to the increase in length of a test specimen during tensile testing.
• Elongation is the ratio of the extension of a test specimen to its initial length. Elongation is expressed as a percentage.
• Elongation at break is the extension of a test specimen at the breaking force.
• Elongation at fracture is the extension of a test specimen at fracture force.
• Gage length is the distance between two effective compression points of a testing device. In guide groove or wrap-around post clamps, it is the distance between the effective compression points measured along the path of the specimen.
• Initial length is the length of a test specimen (between two effective compression points) under specified pre-stress at the start of a test.
• Pre-stress is the stress applied to a test specimen at the beginning of a tensile test.
• A constant-extension-rate testing machine (CRE testing machine) is a tensile testing machine equipped with a fixed clamp and another clamp that moves at a constant speed throughout the test. The entire testing system is virtually deflection-free.
• Breaking strength is the ratio of breaking force to linear density.

In principle, the elongation at break is recorded during testing. If breaking strength is to be calculated, the linear density of individual fibers or the average linear density of the laboratory sample is also required. If necessary, the force and elongation at break are recorded.

Preconditioning, conditioning and test atmospheres should be as specified in the ISO 139 standard.

To ensure that the sample is representative of the material and that the test sample taken from the laboratory sample is representative of that sample, sampling must be carried out in accordance with ISO 1130. For staple fibers, the length must be sufficient to allow testing at the selected gauge length. For filaments, cut the sample into short pieces to allow for a 20 mm gauge length. Grasp individual filament sections at one end with pliers and carefully remove the required number of test samples from the sections. The effective portion of the fiber being tested must not be damaged during test sample preparation.

Test samples are conditioned and tests are performed in the standard atmosphere specified above.

The machine is adjusted to extend the test specimen as follows:

• For test specimens with an average elongation at break of less than 8 percent, use a clamping speed of 50 percent gauge length per minute.
• For test specimens with an average elongation at break greater than or equal to 8 percent and less than 50 percent, use a 100 percent gauge length moving clamp speed per minute.
• For test specimens with an average elongation at break equal to or greater than 50 percent, use the moving clamp speed at 200 percent gauge length per minute.

For fibers exhibiting excessively high or low elongation, different elongation rates may be applied by agreement of the parties involved. If the nominal elongation at break is unknown, an approximate value is determined through preliminary testing. In cases where the elongation at break found in the preliminary test is around 8 percent or 50 percent, one of the above test speeds will be agreed upon by the parties involved. If the final results differ slightly from those obtained in the preliminary test, it is not necessary to repeat the test at a different speed. If both linear density and breaking force are required for the same fiber, the linear density of the fiber shall be determined according to ISO 1973 before conducting the tensile test.

The pre-stress used for tensile testing in the conditioned or wet state is specified as follows.

• In conditioned tests on staple fibers, a pre-stress per unit linear density specified in the standard is used. For fibers listed in the table, the pre-stress per unit linear density specified is used. A higher pre-stress may be applied, for example, to eliminate crimp, if agreed upon by the parties involved.
• In conditioned tests of filaments, a pre-stress per unit linear density specified in the standard is used.
• In wet tests of staple fibers and filaments, a pre-stress per unit linear density specified in the standard is used for cellulose synthetic fibers, and a pre-stress half that specified in the conditioned test is used for other fibers. Based on the fiber's nominal linear density, the mass required to achieve the required pre-stress is calculated.

Our organization, which has been supporting businesses across all sectors for years through a wide range of testing, measurement, analysis, and evaluation activities, boasts a strong team of employees who closely follow global developments in science and technology and are constantly improving themselves. In this context, we also provide testing services in accordance with the ISO 5079 Textile Fibers - Determination of Breaking Strength and Elongation at Break of Individual Fibers standard.