ASTM_D_7811_-_13.pdf

Designation:D781113Standard Test Method forBow and Skew Using a Measuring Tool1This standard is issued under the fixed designation D7811;the number immediately following the designation indicates the year oforiginal adoption or,in the case of revision,the year of last revision.A number in parentheses indicates the year of last reapproval.Asuperscript epsilon()indicates an editorial change since the last revision or reapproval.1.Scope1.1 This test method is used to determine the bow and skewof woven and knitted fabrics over a fixed distance,using ameasuring tool.1.2 This test method is useful when a small specimen or cutparts need to be evaluated for bow and skew,provided a warpor fill,or both,reference line is available,to aid in aligning thetool.1.3 Test Method D3882 may be used when measuring bowand skew in fabric in rolls.However,results obtained withD3882 may not be comparable with results obtained by this testmethod.1.4 There is no known ISO equivalent standard.1.5 The values stated in SI units are to be regarded asstandard.No other units of measurement are included in thisstandard.1.6 This standard does not purport to address all of thesafety concerns,if any,associated with its use.It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2.Referenced Documents2.1 ASTM Standards:2D123 Terminology Relating to TextilesD1776 Practice for Conditioning and Testing TextilesD3882 Test Method for Bow and Skew in Woven andKnitted FabricsD3990 Terminology Relating to Fabric DefectsE177 Practice for Use of the Terms Precision and Bias inASTM Test MethodsE691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test Method3.Terminology3.1 For all terminology related to fabric defect terms,referto Terminology D3990.3.1.1 The following terms are relevant to this standard:bow,double bow,double hooked bow,double reverse bow,hookedbow,knitted fabric,skew,standard atmosphere for testingtextiles.3.2 For all other terminology related to textiles,refer toTerminology D123.4.Summary of Test Method4.1 A straightedge is placed across the fabric between twopoints at which a marked filling yarn,knitted course,desig-nated printed line,or designated design meets the two selvagesor edges.The greatest distance between the straightedge andthe marked filling line,knitted course,designated printed line,or designated design is measured parallel to the selvage.5.Significance and Use5.1 This test method provides a standard procedure forobtaining data for research and development,quality control,acceptance and rejection under specifications,and for specialpurposes.5.2 The data obtained by this test method is applicable to thematerial under the conditions of this particular test and is notnecessarily the same as obtained under other environments inuse.5.3 This test method is considered satisfactory for accep-tance testing of commercial shipments.5.4 If there are differences of practical significance betweenreported test results for two laboratories(or more),compara-tive tests should be performed to determine if there is astatistical bias between them,using competent statistical assis-tance.As a minimum,the test samples to be used are ashomogeneous as possible,are drawn from the material fromwhich the disparate test results were obtained,and are ran-domly assigned in equal numbers to each laboratory for testing.Other fabrics with established test values may be used for thispurpose.The test results from the two laboratories should becompared using a statistical test for unpaired data,at aprobability level chosen prior to the testing series.If a bias is1This test method is under the jurisdiction ofASTM Committee D13 on Textilesand is the direct responsibility of Subcommittee D13.60 on Fabric Test Methods,Specific.Current edition approved July 1,2013.Published August 2013.DOI:10.1520/D7811-13.2For referenced ASTM standards,visit the ASTM website,www.astm.org,orcontact ASTM Customer Service at serviceastm.org.For Annual Book of ASTMStandards volume information,refer to the standards Document Summary page onthe ASTM website.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 found,either its cause must be found and corrected,or futuretest results must be adjusted in consideration of the knownbias.5.5 Boworskewcanbeinducedduringfabricmanufacturing,dyeing,tentering,finishing,or other operationswhere a potential exists for uneven distribution of tensionsacross the fabric width.Bow and skew are more visuallydispleasing in colored,patterned fabrics such as plaids andhorizontal stripes rather than in solid colors because thecontrast makes the distortion more prominent.These defectsmay cause sewing problems in such fabrics and drapingproblems in finished products.Wavy or sharp breaks in the bowline are more detrimental to the appearance of small spec