ASTM D1445/D1445M-12

This test method is considered satisfactory for acceptance testing when the levels of the laboratories are controlled by the use of the same reference standard cotton samples because the current estimates of between-laboratory precision are acceptable under these conditions. 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, ensure the test samples to be used are as homogeneous as possible, are drawn from the material from which the disparate test results were obtained, and are randomly assigned in equal numbers to each laboratory for testing. The test from the two laboratories should be compared using a statistical test for unpaired data, at a probability level chosen prior to the testing series. If a 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.

This test method is useful in research studies to determine the influence of variety, environment, and processing on fiber strength and elongation; and in studies of the relationships between these fiber properties, processing performance, and quality of end-product.

Values obtained for flat bundle tenacity and elongation show a high correlation with values measured on single fibers and require much less time and skill.

Studies have shown that strength measurements obtained with different types of instruments are highly correlated, but the results are on different levels.

By use of correction factors calculated from tests made on standard calibration samples of known or established test values, the results obtained with different types of instruments at a specified gauge length can be adjusted to comparable levels. Due to the normal variation in cottons, strength test results for one gauge length cannot be reliably estimated from tests made at a different gauge length.

The terms tensile strength and breaking tenacity are sometimes used interchangeably. They are relational but are not equivalent (see 12.1.1 and 12.1.2). Tenacity is commonly expressed as centinewtons per tex (cN/tex), grams-force per denier (gf/den) or pounds-force per denier (lbf/den). Tenacity in centinewtons/tex is numerically equal to tenacity in grams-force/tex times 0.981.

1.1 This test method covers the determination of (1) the tensile strength or breaking tenacity of cotton fibers as a flat bundle using a nominal zero gauge length, or (2) the tensile strength or breaking tenacity and the elongation at the breaking load of cotton fibers as a flat bundle with ¹/₈-in. [3.2-mm] clamp spacing. This test method is applicable to loose ginned cotton fibers of untreated cottons whether taken before processing or obtained from a textile product.

1.2 This test method is designed primarily for use with special fiber bundle clamps and special strength testing instruments but may be used with other tensile strength and elongation testing machines when equipped with appropriate adapters to accommodate the fiber clamps.

Note 1—Other methods for measuring the breaking tenacity of fiber bundles include Test Method D1294, Test for Breaking Strength of Wool Fiber Bundles1 in gauge Length; and D5867, Test Method for Measurement of Physical Properties of Cotton Fibers by High Volume Instruments.

1.3 The values stated in either SI units or inch-pound units are to be regarded separately as standard. The values stated in each system may not be exact equivalents; therefore, each system shall be used independently of the other. Combining values from the two systems may result in non-conformance with the standard.

1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.