Standard Test Method for Elastic Properties of Elastomeric Yarns (CRE Type Tensile Testing Machines)

Importancia y uso:

5.1 This test method is considered satisfactory for acceptance testing of commercial shipments since current estimates of between-laboratory precision are acceptable and the method is used extensively in the trade for acceptance testing.

5.1.1 If there are differences of practical significance between reported test results for two laboratories (or more), comparative tests should be performed to determine if there is a statistical bias between them, using competent statistical assistance. As a minimum, use samples for such comparative tests that are as homogeneous as possible, drawn from the same lot of material as the samples that resulted in disparate results during initial testing, and randomly assigned in equal numbers to each laboratory. The test results from the laboratories involved should be compared using a statistical test for unpaired data, at a probability level chosen prior to the testing series. If bias is found, either its cause must be found and corrected, or future test results for that material must be adjusted in consideration of the known bias.

5.2 Force at Specified Elongation (FASE) is a measure of the tensile force occurring while extending a textile material within specified limits. This characteristic of elastomeric yarn indicates the resistance that will have to be overcome by the wearer while putting on a garment made of the material and is also an indication of the garment's resistance to deformation caused by normal body movements during wear. The elongations used for these measurements are typically 100 %, 200 % and 300 %.

5.3 Permanent Deformation (set) is a measure of the increase in length of an elastomeric yarn resulting from cyclic stretching and relaxation. The characteristic is a visible indication of the realignment of intermolecular bonds within the elastic material. As with stress decay, the amount of set increases with yarn extension; however, for any particular extension, little or no additional set takes place after five cycles of exercising. Generally, the characteristic set of the yarn is developed during fabric preparation and the fabric itself shows a negligible amount of set.

5.4 Stress decay increases with yarn extension, but at any specified extension the stress decay takes place in the first 30 s with insignificant decay after 5 min. This characteristic is caused by the gradual realignment of intermolecular bonds within the elastic material, and helps to explain the changes in yarn properties that accompany cyclic stretching and relaxing. The realignment of the bonds is a reversible effect. Following complete relaxation of the yarn, the molecules tend to assume their original configuration with just about complete elimination of the previously observed strain.

5.5 This test method was developed using elastomeric yarns in the “as-produced” condition, but may be used for treated elastomeric yarns provided the treatment is specified. The method does not cover the removal of finish for the determination of elastic properties of “finish-free” elastomeric yarns.

Subcomité:

D13.58

Volúmen:

07.01

Número ICS:

59.080.20 (Yarns)

Palabras clave:

elastic properties; elastomeric yarn; force at specified elongation; permanent deformation; stress decay;