1、Designation: D 3768 06Standard Test Method forMicrocellular UrethanesFlexural Recovery1This standard is issued under the fixed designation D 3768; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A number
2、in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) 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 S
3、I 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 li
4、mitations prior to use.NOTE 1There is no known ISO equivalent to this test method.2. Referenced Documents2.1 ASTM Standards:2D 3040 Practice for Preparing Precision Statements forStandards Related to Rubber and Rubber Testing3E 691 Practice for Conducting an Interlaboratory Study toDetermine the Pre
5、cision 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-mm0.5-in. diameter mandrel at room temperature.3.2 Before proceeding with this test method, referenceshould be made to the specification of the ma
6、terial 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 default conditions
7、 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, capable of indicating
8、 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 in1This test method is under the jurisdiction ofASTM Committee D20 on Plasticsand is the direct responsibility of Sub
9、committee D20.22 on Cellular MaterialsPlastics and Elastomers.Current edition approved March 15, 2006. Published April 2006. Originallyapproved in 1979. Last previous edition approved in 2000 as D 3768 - 96 (2000).2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM C
10、ustomer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Withdrawn.FIG. 1 Example Fixture for Flexural Recovery Test1*A Summary of Changes section appears at the end of this standard.Copyright ASTM Inter
11、national, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.thickness, 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 Unless otherwise specified, condition the speci
12、mens andfixtures a minimum of1hat236 2C and 50 6 5 % relativehumidity before testing.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 en
13、d 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
14、 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 bend mandrel) intercepts th
15、e 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 upo
16、nrelease. 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 a
17、nd 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).8.3 The flexural set after 300
18、 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,9.1.3 Flexural set (30 s),
19、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 D 3040, involving three materialstested by four laboratories. For each material, all the sampleswere prep
20、ared 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 meaningful way ofconsiderin
21、g 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, formulations, conditions, materials,or
22、 laboratories. Users of this test method should apply theprinciples outlined in Practice E 691 to generate data specificto their materials and laboratory (or between specific labora-tories). The principles of 10.2-10.2.2 would then be valid forsuch data.)10.2 Concept of r in Table 1If Srhas been cal
23、culated 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 of that material. r is th
24、e 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.10.2.2 Any judgment in accordance with 10.2.1 would havean approximate 95 % (0.95) probability of being correct.1
25、0.3 There are no recognized standards by which to esti-mate bias of this test method.4Supporting data have been filed at ASTM International Headquarters and maybe obtained by requesting Research Report RR: D20-1191.FIG. 2 Specimen Mounted in Fixture FIG. 3 Specimen Being Bent Around MandrelD37680621
26、1. Keywords11.1 flexural; microcellular; recovery; urethaneSUMMARY OF CHANGESCommittee D20 has identified the location of selected changes to this standard since the last issue, D 3768 - 96(2000), that may impact the use of this standard. (March 15, 2006)(1) Revised Note 2 to remove permissive langu
27、age.(2) Revised 4.1 to give a more detailed description.(3) Revised 4.3 and 7.2 to correct an error in an earlier revisionwhen units were converted from English to SI.(4) Revised 5.1 to remove permissive language.(5) Replaced Fig. 1 with a more representative drawing.(6) Added Fig. 2 and Fig. 3 to i
28、llustrate the proper specimenmounting and bending.ASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this standard. Users of this standard are expressly advised that determination of the validity of any such patent right
29、s, 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 be reviewed every five years andif not revised, either reapproved or withdrawn. Your comments are invited either for r
30、evision of this standard or for additional standardsand should be addressed to ASTM International Headquarters. Your comments will receive careful consideration at a meeting of theresponsible technical committee, which you may attend. If you feel that your comments have not received a fair hearing y
31、ou 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, West Conshohocken, PA 19428-2959,United States. Individual reprints (single or multiple copies) of this standard may b
32、e 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).TABLE 1 Precision for Flexural Recovery TestAProperty MaterialFlexural Modulus,MPa (psi)Average SrBrCFlexural set Urethane A 700 (1
33、00 000) 14.22 0.751 2.10(30 s) Urethane B 350 (50 000) 13.77 0.812 2.27Urethane 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.D3768063
