ASTM D7811-13(2017)

5.1 This test method provides a standard procedure for obtaining data for research and development, quality control, acceptance and rejection under specifications, and for special purposes.

5.2 The data obtained by this test method is applicable to the material under the conditions of this particular test and is not necessarily the same as obtained under other environments in use.

5.3 This test method is considered satisfactory for acceptance testing of commercial shipments.

5.4 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, 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. Other fabrics with established test values may be used for this purpose. The test results 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 must be adjusted in consideration of the known bias.

5.5 Bow or skew can be induced during fabric manufacturing, dyeing, tentering, finishing, or other operations where a potential exists for uneven distribution of tensions across the fabric width. Bow and skew are more visually displeasing in colored, patterned fabrics such as plaids and horizontal stripes rather than in solid colors because the contrast makes the distortion more prominent. These defects may cause sewing problems in such fabrics and draping problems in finished products. Wavy or sharp breaks in the bow line are more detrimental to the appearance of small specimens of a sewn assembly.

1.1 This test method is used to determine the bow and skew of woven and knitted fabrics over a fixed distance, using a measuring tool.

1.2 This test method is useful when a small specimen or cut parts need to be evaluated for bow and skew, provided a warp or fill, or both, reference line is available, to aid in aligning the tool.

1.3 Test Method D3882 may be used when measuring bow and skew in fabric in rolls. However, results obtained with D3882 may not be comparable with results obtained by this test method.

1.4 There is no known ISO equivalent standard.

1.5 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.

1.6 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, health and environmental practices and determine the applicability of regulatory limitations prior to use.

1.7 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.