1、Designation: D2731 15Standard Test Method forElastic Properties of Elastomeric Yarns (CRE Type TensileTesting Machines)1This standard is issued under the fixed designation D2731; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the
2、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. Scope1.1 This test method covers the determination of elasticproperties of “as produced” elastomeric yarns made fromrub
3、ber, spandex or other elastomers. Elastic properties includeforce at specified elongations, permanent deformation andstress decay. Other hysteresis related properties can be calcu-lated.NOTE 1For a method designed specifically for testing rubber threads,refer to Test Method D2433.1.2 This test metho
4、d is not applicable to covered, wrapped,or core-spun yarns or yarns spun from elastomeric staple.1.3 This test method is applicable to elastomeric yarnshaving a range of 40 to 3200 dtex (36 to 2900 denier).1.4 The values stated in either SI units or U.S. Customaryunits are to be regarded separately
5、as standard. Within the text,the U.S. Customary units are in parentheses. The values statedin each system are not exact equivalents; therefore, eachsystem shall be used independently of the other.1.5 This standard does not purport to address all of thesafety concerns, if any, associated with its use
6、. 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.2. Referenced Documents2.1 ASTM Standards:2D76 Specification for Tensile Testing Machines for TextilesD123 Terminology
7、Relating to TextilesD1776 Practice for Conditioning and Testing TextilesD2258 Practice for Sampling Yarn for TestingD2433 Test Methods for Rubber Thread (Withdrawn 2012)3D2591 Test Method for Linear Density of Elastomeric Yarns(Short Length Specimens)D2653 Test Method for Tensile Properties of Elast
8、omericYarns (CRE Type Tensile Testing Machines)D4848 Terminology Related to Force, Deformation andRelated Properties of TextilesD4849 Terminology Related to Yarns and FibersD6717 Test Method for Linear Density of Elastomeric Yarns(Skein Specimens)3. Terminology3.1 For all terminology relating to D13
9、.58, Yarns andFibers, refer to Terminology D4849.3.1.1 The following terms are relevant to this standard:deformation, elastomeric yarn, elongation, force at specifiedelongation, linear density, permanent deformation, stress, stressdecay.3.2 For definitions of other terms related to force anddeformat
10、ion, refer to Terminology D4848. For all other termsrelated to textiles, refer to Terminology D123.4. Summary of Test Method4.1 A specimen, mounted in a CRE-type tensile machine, isinitially subjected to a series of five loading/unloading cyclesin which the specimen is extended and relaxed between z
11、eroand 75 % of the elongation at first filament break (FFB).During the fifth cycle, the specimen is held at the maximumextension point for 30 s, then unloaded to allow a return to itsoriginal gage length position. The specimen is then subjectedto a sixth load/unload cycle.4.2 Force at specified elon
12、gations are calculated from theforce-elongation curve for the first and fifth loadings and forthe fifth unloading. Stress decay is calculated on the fifth cycle.Extension at a specified force is determined on the sixthloading and is used to calculate the permanent deformation.5. Significance and Use
13、5.1 This test method is considered satisfactory for accep-tance testing of commercial shipments since current estimates1This test method is under the jurisdiction of ASTM Committee D13 on Textilesand is the direct responsibility of Subcommittee D13.58 on Yarns and Fibers.Current edition approved Feb
14、. 1, 2015. Published March 2015. Originallyapproved in 1968. Last previous edition approved in 2012 as D273107(2012).DOI: 10.1520/D2731-15.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume
15、 information, refer to the standards Document Summary page onthe ASTM website.3The last approved version of this historical standard is referenced onwww.astm.org.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1of between-laboratory pr
16、ecision are acceptable and the methodis used extensively in the trade for acceptance testing.5.1.1 If there are differences of practical significance be-tween reported test results for two laboratories (or more),comparative tests should be performed to determine if there isa statistical bias between
17、 them, using competent statisticalassistance. As a minimum, use samples for such comparativetests that are as homogeneous as possible, drawn from the samelot of material as the samples that resulted in disparate resultsduring initial testing, and randomly assigned in equal numbersto each laboratory.
18、 The test results from the laboratoriesinvolved should be compared using a statistical test forunpaired data, at a probability level chosen prior to the testingseries. If bias is found, either its cause must be found andcorrected, or future test results for that material must beadjusted in considera
19、tion of the known bias.5.2 Force at Specified Elongation (FASE) is a measure ofthe tensile force required to extend a textile material withinspecified limits. This characteristic of elastomeric yarn indi-cates the resistance that will have to be overcome by the wearerwhile putting on a garment made
20、of the material and is also anindication of the garments resistance to deformation caused bynormal body movements during wear. The elongations used forthese measurements are typically 100 %, 200 % and 300 %.5.3 Permanent Deformation (set) is a measure of the in-crease in length of an elastomeric yar
21、n resulting from cyclicstretching and relaxation. The characteristic is a visible indi-cation of the realignment of intermolecular bonds within theelastic material. As with stress decay, the amount of setincreases with yarn extension; however, for any particularextension, little or no additional set
22、 takes place after five cyclesof exercising. Generally, the characteristic set of the yarn isdeveloped during fabric preparation and the fabric itself showsa negligible amount of set.5.4 Stress decay increases with yarn extension, but at anyspecified extension the stress decay takes place in the fir
23、st 30s with insignificant decay after 5 min. This characteristic iscaused by the gradual realignment of intermolecular bondswithin the elastic material, and helps to explain the changes inyarn properties that accompany cyclic stretching and relaxing.The realignment of the bonds is a reversible effec
24、t. Followingcomplete relaxation of the yarn, the molecules tend to assumetheir original configuration with just about complete elimina-tion of the previously observed strain.5.5 This test method was developed using elastomeric yarnsin the “as-produced” condition, but may be used for treatedelastomer
25、ic yarns provided the treatment is specified. Themethod does not cover the removal of finish for the determi-nation of elastic properties of “finish-free” elastomeric yarns.6. Apparatus6.1 Specimen Boards, with short pile or plush surfaces ofblack or contrasting color, for storing specimens during c
26、on-ditioning.6.2 Tensile Testing Machine, CRE-type, conforming toSpecification D76 with respect to force indication, workingrange, capacity and verification of recorded elongation, capableof cycling, and designed for operation at a pulling speed of 500mm/min (20 in./min).6.3 Clamping Assembly, pneum
27、atically operated, with jawsas described in Test Method D2653.6.4 Computer or Microprocessor, interfaced, with automaticdata gathering system, optional.6.5 Tensioning Weights, with various masses from 10 mg to3 g to pretension the specimen to 30 to 50 mN/tex (0.3 to 0.5mgf/d) before testing.6.6 Air
28、Supply, capable of providing 415 kPa (60 psi) to thepneumatic clamps.7. Sampling, Test Specimens, and Test Units7.1 Lot SampleAs a lot sample for acceptance testing, takea random number of shipping units directed in an applicablematerial specification or other agreement between the pur-chaser and th
29、e supplier, such as an agreement to use PracticeD2258. Consider shipping cases or other shipping units to bethe primary sampling units.NOTE 2An adequate specification or other agreement between thepurchaser and the supplier requires taking into account the variabilitybetween shipping units, between
30、packages or ends within a shipping unit,and between specimens from a single package to provide a sampling witha meaningful producers risk, consumers risk, acceptable quality leveland limiting quality level.7.2 Laboratory SampleAs a laboratory sample for accep-tance testing, take at random from each
31、shipping unit in the lotsample the number of packages directed in an applicablematerial specification or other agreement between the pur-chaser and the supplier, such as an agreement to use PracticeD2258. Preferably, take the same number of packages fromeach of the shipping units selected. If differ
32、ing numbers ofpackages are to be taken from the shipping units, determine atrandom which shipping units are to have each number ofpackages for testing.7.3 Test SpecimensFrom each package or end in thelaboratory sample, take six specimens as directed in 7.3.1.7.3.1 Remove the outer layer of yarn from
33、 the package.Avoid any damaged areas in selecting segments for testing.Carefully unwind yarn from the package with as low as tensionas possible to avoid stretching. As test specimens, cut approxi-mately 125 mm (5 in.) long segments of yarn from eachpackage, taking them at intervals of at least1m(1yd
34、). Threeof the six specimens are used as spare to allow for unacceptablebreaks, such as caused by slippage or breaking in the clamps.7.4 Determine the tex (denier) of the yarn for each labora-tory sample using Test Method D2591 or Test Method D6717.7.5 Determine the elongation at first filament brea
35、d (FFB)for each laboratory sample as directed in Test Method D2653.8. Preparation of Apparatus and Calibration8.1 Prepare and verify the calibration of the tensile testingmachine as directed in the manufacturers instructions.8.2 Set up and adjust the CRE-type tensile testing machineas follows:D2731
36、1528.2.1 Examine the acrylic clamp jaw face for wear andreplace as needed. Position the jaw faces horizontally in theclamps.8.2.2 Set the distance between the jaw faces (gage length) to50 6 1mm(26 0.05 in.).NOTE 3A convenient technique for checking the gage length is toplace a piece of carbon paper
37、and white paper in the clamps and close theclamps. The distance between the marks made on the white paper by thecarbon paper represents the set gage length.8.2.3 Use a force measuring system such that the cyclingforce will be between 30 and 80 % of full scale capacity.8.2.4 Set the Cycling Limits as
38、 follows:8.2.4.1 Set Minimum Extension to nominal gage length(zero extension).8.2.4.2 Set Maximum Extension equivalent to 75 % of theelongation at first filament break of the elastomeric yarn (see10.2) or 300 % of gauge length.8.2.5 Set the crosshead speed to 500 mm/min (20 in./min) or1000 % extensi
39、on per min.8.2.6 Set the extension measuring system as follows:8.2.6.1 When using a chart recorder, set the chart speed to500 mm/min (20 in./min).8.2.6.2 When using an interfaced computer ormicroprocessor, set parameters to obtain selected propertiesusing suppliers directions and Specification D76.8
40、.2.7 Set the air pressure for pneumatic clamps to 415 kPa(60 psi). At this pressure, the clamping force is approximately450 N (100 lb).9. Conditioning9.1 Condition the specimens relaxed on specimen boards inthe standard atmosphere for testing as directed in PracticeD1776.10. Procedure10.1 Test the r
41、elaxed specimens in the standard atmospherefor testing textiles.NOTE 4The force measuring system should be zeroed prior to runningany specimens and periodically during the course of the test, particularlyif drift is observed in the zero value of the force measuring system.10.2 Select the appropriate
42、 pretensioning weight based onthe linear density of the yarn that will provide a 30 to 50mN/tex (0.3 to 0.5 mgf/d) tension to the yarn.10.3 Attach the selected tensioning weight (10.2)tothespecimen such that when the specimen is placed in the lowerclamp, the tensioning weight will hang freely.10.4 P
43、osition a specimen centrally between the top clampfaces and close the clamp. Ensure that the tension weight ishanging freely below the bottom clamp.10.5 Close the lower clamp and remove the tensioningweight.10.6 Start the test apparatus and cycle the specimen fivetimes between the limits established
44、 in 8.2.4.NOTE 5If using a chart recorder, only the first loading cycle andcomplete fifth cycle need be recorded on the chart.10.7 On the fifth cycle, stop the crosshead at the maximumextension limit and hold for 30 s. At the end of holding at themaximum extension limit, return the crosshead to gage
45、 length.10.8 Immediately, start the crosshead and record the loadingportion of a sixth cycle.10.9 Return the crosshead to the zero position, remove thespectrum and continue testing until all specimens have beentested for each laboratory sampling unit and for the lot.11. Calculation or Interpretation
46、 of Results11.1 Force at Specified Elongation (FASE)Determine theFASE as follows:11.1.1 From the tensile hysteresis chart for each specimen,read and record the force at 100, 200 and 300 % elongation onthe first loading cycle, the force at 300 % elongation on thefifth loading cycle, prior to holding
47、for 30 s, and the force at100 and 200 % elongation of the fifth unloading cycle to thenearest cN (0.1 gf).11.1.2 Calculate the average FASE for each of the elonga-tions and applicable cycles determined in 11.1.1 for eachlaboratory sampling unit and for the lot to the nearest cN (0.1gf).11.2 Stress D
48、ecayDetermine the percent stress decay asfollows:11.2.1 From the chart and on the fifth loading cycle, readand record the force at maximum extension and the force afterholding at maximum extension for 30-s for each specimen.11.2.2 Calculate the average percent stress decay for eachspecimen to the ne
49、arest 0.1 %, using Eq 1D 5FL,52 FU,5!FL,5 100 (1)where:D = stress decay, %,FL,5= loading force at maximum extension on fifth cycle,cN (gf), andFU,5= unloading force after 30 s hold on fifth cycle (start ofunload cycle), cN (gf).NOTE 6Stress in yarns is expressed as force per unit area or force perlinear density. However, the units of force are used in Eq 1 because thearea or linear density in units of stress effectively cancel one another in theequation.11.2.3 Calculate the average percent stress decay for eachlaboratory sampling unit and for the lot.11.3 Permanent
