1、Designation: D3768 11Standard 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
2、 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 u
3、nits 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 limit
4、ations prior to use.NOTE 1There is no known ISO equivalent to this standard.2. Referenced Documents2.1 ASTM Standards:2D3040 Practice for Preparing Precision Statements forStandards Related to Rubber and Rubber Testing; Re-placed by D 44833E691 Practice for Conducting an Interlaboratory Study toDete
5、rmine 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 specific
6、ation 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 material specifi-cations, then the def
7、ault conditions apply.NOTE 2This 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, capabl
8、e 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 be1This test method is under the jurisdictio
9、n ofASTM 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-
10、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.3Withdrawn. The last approved version of this historical s
11、tandard is referencedon www.astm.org.FIG. 1 Example Fixture for Flexural Recovery Test1*A Summary of Changes section appears at the end of this standard.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.less than 3 mm. The specimen shal
12、l 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 stand
13、ard 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 specime
14、nclamp 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 a
15、s 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 contactwith the b
16、end 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. Sta
17、rt 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. Thediffere
18、nce between these readings and the initial reading is theappropriate flexural recovery value in degrees.8. Calculation8.1 The intercept of the mandrel edge of the specimen onthe protractor scale in degrees = f.8.2 The flexural set after 30 s is given by:Flexural Set (30 s) = f30 s f0 (see Note 3).8.
19、3 The flexural set after 300 s is given by:Flexural Set (300 s) = f300 s f0 (see Note 3).NOTE 3This measurement in the automotive industry is customarilyreferred to as recovery.9. Report9.1 The report shall include the following:9.1.1 Direction of cutting,9.1.2 Conditioning procedures before testing
20、,9.1.3 Flexural set (30 s), average of three,9.1.4 Flexural set (300 s), average of three, and9.1.5 Sample thickness.10. Precision and Bias10.1 Table 1 is based on a round robin4conducted in 1980in accordance with Practice D3040, involving three materialstested by four laboratories. For each materia
21、l, all the sampleswere prepared at one source and the individual specimens werealso prepared at one source. Each test result consisted of oneindividual determination. Each laboratory obtained four testresults for each material. (WarningThe explanation of r(10.2-10.2.2) is only intended to present a
22、meaningful way ofconsidering the approximate precision of these test methods.The data in Table 1 should not be applied to acceptance orrejection of materials, as these data apply only to the materialstested in the round robin and are unlikely to be rigorouslyrepresentative of other lots, formulation
23、s, conditions, materials,or laboratories. Users of this test method should apply theprinciples outlined in Practice E691 to generate data specific totheir materials and laboratory (or between specific laborato-ries). The principles of 10.2-10.2.2 would then be valid forsuch data.)10.2 Concept of r i
24、n Table 1If Srhas been calculated froma large enough body of data, and for test results that wereaverages from testing three specimens for each test result, then:10.2.1 Repeatability: Two test results obtained within onelaboratory shall be judged not equivalent if they differ by morethan the r value
25、 of that material. r is the interval representingthe critical difference between two test results for the samematerial, obtained by the same operator using the sameequipment on the same day in the same laboratory.4Supporting data have been filed at ASTM International Headquarters and maybe obtained
26、by requesting Research Report RR:D20-1191.FIG. 2 Specimen Mounted in Fixture FIG. 3 Specimen Being Bent Around MandrelD3768 11210.2.2 Any judgment in accordance with 10.2.1 would havean approximate 95 % (0.95) probability of being correct.10.3 There are no recognized standards by which to esti-mate
27、bias of this test method.11. Keywords11.1 flexural; microcellular; recovery; urethaneSUMMARY OF CHANGESCommittee D20 has identified the location of selected changes to this standard since the last issue, D3768 - 06,that may impact the use of this standard. (December 1, 2011)(1) Changed the wording i
28、n Note 1 to conform to ASTMD4968, Annex 2.(2) Increased the relative humidity tolerance range and theoverall conditioning time in 6.1.(3) Added 6.2 for Test Conditions.ASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin t
29、his standard. Users of this standard are expressly advised that determination of the validity of any such patent rights, and the riskof infringement of such rights, are entirely their own responsibility.This standard is subject to revision at any time by the responsible technical committee and must
30、be reviewed every five years andif not revised, either reapproved or withdrawn. Your comments are invited either for revision of this standard or for additional standardsand should be addressed to ASTM International Headquarters. Your comments will receive careful consideration at a meeting of there
31、sponsible technical committee, which you may attend. If you feel that your comments have not received a fair hearing you shouldmake your views known to the ASTM Committee on Standards, at the address shown below.This standard is copyrighted by ASTM International, 100 Barr Harbor Drive, PO Box C700,
32、West Conshohocken, PA 19428-2959,United States. Individual reprints (single or multiple copies) of this standard may be obtained by contacting ASTM at the aboveaddress or at 610-832-9585 (phone), 610-832-9555 (fax), or serviceastm.org (e-mail); or through the ASTM website(www.astm.org). Permission r
33、ights to photocopy the standard may also be secured from the ASTM website (www.astm.org/COPYRIGHT/).TABLE 1 Precision for Flexural Recovery TestAProperty MaterialFlexural Modulus,MPa (psi)Average SrBrCFlexural set Urethane A 700 (100 000) 14.22 0.751 2.10(30 s) Urethane B 350 (50 000) 13.77 0.812 2.
34、27Urethane C 175 (25 000) 10.32 1.488 4.17Flexural set Urethane A 700 (100 000) 9.08 0.849 2.38(300 s) Urethane B 350 (50 000) 8.38 0.660 1.85Urethane C 175 (25 000) 5.69 0.785 2.20AValues expressed in units of degrees.BSr= within-laboratory standard deviation for the indicated material. It is obtained by pooling the within-laboratory standard deviations of the test results from all of theparticipating laboratories:Sr5 s1!21s2!2 1sn!2#/nCr = within-laboratory critical interval between two test results = 2.8 3 Sr.D3768 113
