1、Designation: D3768 16Standard 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:2D883 Terminology Relating to PlasticsD3040 Practice for Preparing Precision Statements for Stan-dards Related to Rubber and Rubber Testing (Withdrawn1987)3D3489 Test Methods for Mic
5、rocellular Urethane MaterialsE691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test Method3. Terminology3.1 For definitions of terms used in this test method andassociated with plastics issues, refer to terminology containedin Terminology D883.3.2 The following def
6、inition is from Test Methods D3489:3.2.1 microcellular urethane, nan elastomeric materialmade by the interaction of a polyol and an organic isocyanate,having cell diameters in the range from 0.0001 to 0.001 mm,with a minimum density of 160 kg/m3(10 lb/ft3).4. Significance and Use4.1 This test method
7、 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.4.2 Before proceeding with this test method, reference shallbe made to any specification for the material being tested. Anytest specimen preparation, conditioning,
8、 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.NOTE 2This test method is applicable to solid urethanes.5.
9、Apparatus5.1 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. 1.5.2 Timer, capable of indicating seconds.5.3 Thickness Indicator, accurate to 0.03 mm.6. Test Spec
10、imens6.1 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.).7. Conditioning7.1 ConditioningConditi
11、on 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.7.2 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
12、 otherwise specified.8. Procedure8.1 There shall be at least three recovery measurements.8.2 Measure the thickness of specimen to the nearest 0.03mm.1This test method is under the jurisdiction ofASTM Committee D20 on Plasticsand is the direct responsibility of Subcommittee D20.22 on Cellular Materia
13、ls -Plastics and Elastomers.Current edition approved Oct. 1, 2016. Published October 2016. Originallyapproved in 1979. Last previous edition approved in 2011 as D3768 - 11. DOI:10.1520/D3768-16.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at s
14、erviceastm.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 Int
15、ernational, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States18.3 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 horiz
16、ontal 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
17、of a test is shown in Fig. 2.8.4 Make an initial reading where the mandrel edge of thespecimen (the surface of the test specimen that is in contactwith the bend mandrel) intercepts the protractor scale. Make areading to the nearest 1 and record the value.8.5 Apply force approximately 30 mm (1.25 in.
18、) 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 aro
19、und themandrel is shown in Fig. 3.8.6 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 reading is theappropriate flexural recovery value in degrees.9. Calculation9.1 The intercept of the
20、mandrel edge of the specimen onthe protractor scale in degrees = .9.2 The flexural set after 30 s is given by:Flexural Set (30 s) = 30 s 0 (see Note 3).9.3 The flexural set after 300 s is given by:Flexural Set (300 s) = 300 s 0 (see Note 3).NOTE 3This measurement in the automotive industry is custom
21、arilyreferred to as recovery.10. Report10.1 The report shall include the following:10.1.1 Direction of cutting,10.1.2 Conditioning procedures before testing,10.1.3 Flexural set (30 s), average of three,10.1.4 Flexural set (300 s), average of three, and10.1.5 Sample thickness.11. Precision and Bias11
22、.1 Table 1 is based on a round robin4conducted in 1980in accordance with Practice D3040, involving three materialstested by four laboratories. For each material, all the sampleswere prepared at one source and the individual specimens werealso prepared at one source. Each test result consisted of one
23、individual determination. Each laboratory obtained four testresults for each material. (WarningThe explanation of r(11.2 11.2.2) is only intended to present a meaningful way ofconsidering the approximate precision of these test methods.The data in Table 1 shall not be applied to acceptance orrejecti
24、on 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,4Supporting data have been filed at ASTM International Headquarters and maybe obtained by requesting Research Report
25、RR:D20-1191.FIG. 1 Example Fixture for Flexural Recovery TestFIG. 2 Specimen Mounted in FixtureFIG. 3 Specimen Being Bent Around MandrelD3768 162or laboratories. Users of this test method shall apply theprinciples outlined in Practice E691 to generate data specific totheir materials and laboratory (
26、or between specific laborato-ries). The principles of 11.2 11.2.2 would then be valid forsuch data.)11.2 Concept of r in 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:11.2.1 Repeatabilit
27、yTwo test results obtained within onelaboratory shall be judged not equivalent if they differ by morethan the r value 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 sa
28、me day in the same laboratory.11.2.2 Any judgment in accordance with 11.2.1 would havean approximate 95 % (0.95) probability of being correct.11.3 There are no recognized standards by which to estimatebias of this test method.12. Keywords12.1 flexural; microcellular; recovery; urethaneSUMMARY OF CHA
29、NGESCommittee D20 has identified the location of selected changes to this standard since the last issue, D3768 - 11,that may impact the use of this standard. (October 1, 2016)(1) Added referenced documents D883 and D3489 to Section2.(2) Added new Terminology, Section 3, and renumbered sub-sequent se
30、ctions.(3) Removed non-mandatory language from mandatory sec-tions.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
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35、Drive, Danvers, MA 01923, Tel: (978) 646-2600; http:/ 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 2.27Urethane C 175 (25 000) 10.32 1.488 4.17Flexural s
36、et 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:Sr5ffss1d21ss2d21ssnd2g/ngCr = within-laboratory critical interval between two test results = 2.8 Sr.D3768 163
