ASTM D3768-22

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: D3768 − 16 D3768 − 22
Standard Test Method for
Microcellular Urethanes—Flexural Recovery
This standard is issued under the fixed designation D3768; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope*
1.1 This test method covers the procedure and apparatus for measuring the flexural recovery of microcellular urethanes.
1.2 The values stated in SI units are to be regarded as standard.
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety safety, health, and healthenvironmental practices and determine the
applicability of regulatory limitations prior to use.
NOTE 1—There is no known ISO equivalent to this standard.
1.4 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
D883 Terminology Relating to Plastics
D3040 Practice for Preparing Precision Statements for Standards Related to Rubber and Rubber Testing (Withdrawn 1987)
D3489 Test Methods for Microcellular Urethane Materials
E456 Terminology Relating to Quality and Statistics
E691 Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
E2935 Practice for Evaluating Equivalence of Two Testing Processes
3. Terminology
3.1 For definitions of terms Terms used in this test method standard are defined in accordance with Terminology D883and
associated with plastics issues, refer to terminology contained in , unless otherwise specified. For terms relating to precision and
bias and associated issues, the terms used in this standard are defined in accordance with Terminology D883E456.
3.2 The following definition is from Test Methods D3489:
This test method is under the jurisdiction of ASTM Committee D20 on Plastics and is the direct responsibility of Subcommittee D20.22 on Cellular Materials - Plastics
and Elastomers.
Current edition approved Oct. 1, 2016March 15, 2022. Published October 2016March 2022. Originally approved in 1979. Last previous edition approved in 20112016
as D3768 - 11.D3768 - 16. DOI: 10.1520/D3768-16.10.1520/D3768-22.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
The last approved version of this historical standard is referenced on www.astm.org.
*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
D3768 − 22
FIG. 1 Example Fixture for Flexural Recovery Test
3.2.1 microcellular urethane, n—an elastomeric material made by the interaction of a polyol and an organic isocyanate, having
3 3
cell diameters in the range from 0.0001 to 0.001 mm, with a minimum density of 160 kg/m (10 lb/ft ).
4. Significance and Use
4.1 This test method is used to indicate the ability of a material 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 shall be made to any specification for the material being tested. Any test
specimen preparation, conditioning, or dimensions, or combination thereof, and testing parameters covered in the materials
specification shall take precedence over those mentioned in these test methods. If there are no material specifications, then the
default conditions apply.
NOTE 2—This test method is applicable to solid urethanes.
5. Apparatus
5.1 Flexural Recovery Test Fixture—The test fixture shall consist of a 12.7-mm diameter mandrel mounted to a base equipped with
a protractor. A drawing of a typical test fixture is shown in Fig. 1.
5.2 Timer, capable of indicating seconds.
5.3 Thickness Indicator, accurate to 0.03 mm.
D3768 − 22
FIG. 2 Specimen Mounted in Fixture
6. Test Specimens
6.1 The test specimens shall be cut from molded plaques or parts. The recommended standard test specimen is 4 mm in thickness,
and the minimum specimen thickness shall not be less than 3 mm. The specimen shall be 25 mm in width by 150 mm in length
(1 by 6 in.).
7. Conditioning
7.1 Conditioning—Condition the test specimens and the test fixture at 23 6 2°C (73.4 6 3.6°F) and 50 6 10 % relative humidity
for not less than 24 h prior to testing, unless otherwise specified.
7.2 Test Conditions—Conduct tests in the standard laboratory atmosphere of 23 6 2°C (73.4 6 3.6°F) and 50 6 10 % relative
humidity, unless otherwise specified.
8. Procedure
8.1 There shall be at least three recovery measurements.
8.2 Measure the thickness of specimen to the nearest 0.03 mm.
8.3 Insert the test specimen in the lower slot of the specimen clamp and position the end of the specimen flush with the rear face
of the bend mandrel. Tighten the clamp while holding the specimen in a horizontal position. (Do not allow the outer end of the
specimen to be in contact with the base of the test fixture.) A spacer of approximately the same thickness as the test specimen must
be used in the upper slot to ensure proper clamping in the lower slot. A specimen mounted in a test fixture at the start of a test
is shown in Fig. 2.
8.4 Make an initial reading where the mandrel edge of the specimen (the surface of the test specimen that is in contact with the
bend mandrel) intercepts the protractor scale. Make a reading to the nearest 1° and record the value.
8.5 Apply force approximately 30 mm (1.25 in.) from the clamp and bend the specimen 180° around the mandrel. Hold the
specimen fo
...