ASTM_D_3768_-_11.pdf

Designation:D376811Standard Test Method forMicrocellular UrethanesFlexural Recovery1This standard is issued under the fixed designation D3768;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.Scope*1.1 This test method covers the procedure and apparatus formeasuring the flexural recovery of microcellular urethanes.1.2 The values stated in SI units are to be regarded asstandard.1.3 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.NOTE1There is no known ISO equivalent to this standard.2.Referenced Documents2.1 ASTM Standards:2D3040 Practice for Preparing Precision Statements for Stan-dards Related to Rubber and Rubber Testing(Withdrawn1987)3E691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test Method3.Significance and Use3.1 This test method is used to indicate the ability of amaterial to recover after a 180 bend around a 12.7-mm(0.5-in.)diameter mandrel at room temperature.3.2 Before proceeding with this test method,referenceshould be made to the specification of the material being tested.Any test specimen preparation,conditioning,or dimensions,orcombination thereof,and testing parameters covered in thematerials specification shall take precedence over those men-tioned in these test methods.If there are no materialspecifications,then the default conditions apply.NOTE2This test method is applicable to solid urethanes.4.Apparatus4.1 Flexural Recovery Test FixtureThe test fixture shallconsist of a 12.7-mm diameter mandrel mounted to a baseequipped with a protractor.A drawing of a typical test fixtureis shown in Fig.1.4.2 Timer,capable of indicating seconds.4.3 Thickness Indicator,accurate to 0.03 mm.5.Test Specimens5.1 The test specimens shall be cut from molded plaques orparts.The recommended standard test specimen is 4 mm inthickness,and the minimum specimen thickness shall not beless than 3 mm.The specimen shall be 25 mm in width by 150mm in length(1 by 6 in.).6.Conditioning6.1 ConditioningCondition the test specimens and the testfixture at 23 6 2C(73.4 6 3.6F)and 50 6 10%relativehumidity for not less than 24 h prior to testing,unlessotherwise specified.6.2 Test ConditionsConduct tests in the standard labora-tory atmosphere of 23 6 2C(73.4 6 3.6F)and 50 6 10%relative humidity,unless otherwise specified.7.Procedure7.1 There shall be at least three recovery measurements.7.2 Measure the thickness of specimen to the nearest 0.03mm.7.3 Insert the test specimen in the lower slot of the specimenclamp and position the end of the specimen flush with the rearface of the bend mandrel.Tighten the clamp while holding thespecimen in a horizontal position.(Do not allow the outer endof the specimen to be in contact with the base of the testfixture.)A spacer of approximately the same thickness as thetest specimen must be used in the upper slot to ensure properclamping in the lower slot.A specimen mounted in a testfixture at the start of a test is shown in Fig.2.7.4 Make an initial reading where the mandrel edge of thespecimen(the surface of the test specimen that is in contact1This test method is under the jurisdiction of ASTM Committee D20 on Plasticsand is the direct responsibility of Subcommittee D20.22 on Cellular Materials-Plastics and Elastomers.Current edition approved Dec.1,2011.Published January 2012.Originallyapproved in 1979.Last previous edition approved in 2006 as D3768-06.DOI:10.1520/D3768-11.2For 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.3The last approved version of this historical standard is referenced onwww.astm.org.*A Summary of Changes section appears at the end of this standardCopyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 with the bend mandrel)intercepts the protractor scale.Make areading to the nearest 1 and record the value.7.5 Apply force approximately 30 mm(1.25 in.)from theclamp and bend the specimen 180 around the mandrel.Holdthe specimen for 5 6 1 s in the bent position,then releaseslowly and allow to recover.Start the timer immediately uponrelease.Do not allow the specimen to drag on the fixture baseduring recovery.Aspecimen that is being bent 180 around themandrel is shown in Fig.3.7.6 Read the intercept of the mandrel edge of the specimenon the protractor scale after 30-s and 300-s recovery.Thedifference between these readings and the initial read