ASTM D3882-08 (2020) pdf free.Standard Test Method for Bow and Skew in Woven and Knitted Fabrics.
In comparing two averages of three deter-minations when using the procedures in this test method, thedifferences should not exceed the single-operator precisionvalues shown in Table 1 for the respective number of tests in 95out of 100 cases when all the observations are taken by thesame well-trained operator using the same piece of equipmentand specimens randomly drawn from the sample of material.Larger differences are likely to occur under all other circumstances.
An interlaboratory testwas run in 1981 in which randomly drawn specimens of threematerials were tested in each of three laboratories for fabricbow and in each of four laboratories for fabric skew.Twooperators in each laboratory each tested two specimens of eachmaterial for bow and skew using Test Method D3882.Theprecision statement is based upon a testing plan described inPractices D2904 and D2906.The three fabrics were: (1) 65 %polyester/35 % cotton plaid approximately 3.9 oz/yd2 (2) 50 %polyester/50 % cotton fancy weave of 3.8 oz/yd2, and (3)100 % cotton denim of approximately 15.2 oz/yd2. Fabric bowranged from 1.7 to 2.6 % for Fabric A,0.6 to 2.3 % for FabricB,and 0.9 to 1.2 % for Fabric C. Skew ranged from 3.6 to8.2 % for Fabric A,8.2 to 12.3 % for Fabric B, and 5.4 to 7.4 %for Fabric C.The components of variance for bow and skew expressed as standard deviations were calculated to be thevalues listed in Table 2.
For the components of variance reported inTable 1, two averages of observed values should be consideredsignificantly different at the 95 % probability level if thedifference equals or exceeds the critical differences listed inTable 1.
The procedure of this test method produces atest value that can be defined only in terms of a test method.There is no independent, referee method by which bias may bedetermined.This test method has no known bias.
Measure the skew in three places spaced as widely aspossible along the length of the fabric or along a minimum of1 m (1 yd). If possible，make no measurement closer to theends of the roll or piece of fabric than 1 m.
Follow a distinctive color yarn or pattern line acrossthe width of the fabric. Trace one filling yarn, knitting course,or printed line across the full width of the fabric using a softpencil or suitable marker (Line AC if righthand skew, Line DCif left-hand skew).
Place a rigid straight edge or t-square across the fabricwidth perpendicular to the selvage or edge such that itcoincides with the lower point on the fabric at which thedistinctive color yarn or pattern line, or marked yarn meets oneof the selvages or edges (Line BC).ASTM D3882 pdf download.