ASTM D2731-01
(Test Method)Standard Test Method for Elastic Properties of Elastomeric Yarns (CRE Type Tensile Testing Machines)
Standard Test Method for Elastic Properties of Elastomeric Yarns (CRE Type Tensile Testing Machines)
SCOPE
1.1 This test method covers the determination of elastic properties of "as produced" elastomeric yarns made from rubber, spandex or other elastomers. Elastic properties include force at specified elongations, permanent deformation and stress decay. Other hysteresis related properties can be calculated.
Note 1—For a method designed specifically for testing rubber threads, refer to Test Method D 2433.
1.2 This test method 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 yarns having a range of 40 to 3200 dtex (36 to 2900 denier).
1.4 The values stated in either SI units or U.S. Customary units are to be regarded separately as standard. Within the text, the U.S. Customary units are in parentheses. The values stated in each system are not exact equivalents; therefore, each system shall be used independently of the other.
1.5 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 and health practices and determine the applicability of regulatory limitations prior to use.
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Designation:D2731–01
Standard Test Method for
Elastic Properties of Elastomeric Yarns (CRE Type Tensile
Testing Machines)
This standard is issued under the fixed designation D 2731; 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 (e) indicates an editorial change since the last revision or reapproval.
1. Scope D 4848 Terminology for Force, Deformation and Related
Properties of Textiles
1.1 This test method covers the determination of elastic
D 6717 Test Method for Linear Density of Elastomeric
properties of “as produced” elastomeric yarns made from
Yarns (Skein Specimens)
rubber, spandex or other elastomers. Elastic properties include
force at specified elongations, permanent deformation and
3. Terminology
stress decay. Other hysteresis related properties can be calcu-
3.1 Definitions:
lated.
3.1.1 deformation, n—a change in shape of a material
NOTE 1—For a method designed specifically for testing rubber threads,
caused by forces of compression, shear, tension, or torsion.
refer to Test Method D 2433.
3.1.2 elastomeric yarn, n—a nontextured yarn which can be
1.2 This test method is not applicable to covered, wrapped,
stretched repeatedly at room temperature to at least twice its
or core-spun yarns or yarns spun from elastomeric staple.
originallengthandwhichafterremovalofthetensileforcewill
1.3 This test method is applicable to elastomeric yarns
immediately and forcibly return to approximately its original
having a range of 40 to 3200 dtex (36 to 2900 denier).
length.
1.4 The values stated in either SI units or U.S. Customary
3.1.3 elongation, n—the ratio of the extension of a material
units are to be regarded separately as standard. Within the text,
to the length of the material prior to stretching.
the U.S. Customary units are in parentheses. The values stated
3.1.4 force at specified elongation (FASE), n—the force
in each system are not exact equivalents; therefore, each
associated with a specific elongation on the force-extension or
system shall be used independently of the other.
force-elongation curve.
1.5 This standard does not purport to address all of the
3.1.5 linear density, n—for fiber and yarn,mass per unit
safety concerns, if any, associated with its use. It is the
length.
responsibility of the user of this standard to establish appro-
3.1.6 permanent deformation, n—the net long-term change
priate safety and health practices and determine the applica-
in a dimension of a specimen after deformation and relaxation
bility of regulatory limitations prior to use.
under specified conditions.
3.1.6.1 Discussion—Permanent deformation in elastomeric
2. Referenced Documents
yarns is frequently referred to as “set”. Elastomeric yarns
2.1 ASTM Standards:
which have been deformed will eventually return to, or nearly
D 76 Specification for Tensile Testing Machines for Tex-
to, the original dimension with relaxation.
tiles
3.1.7 stress, n—the resistance to deformation developed
D 123 Terminology Relating to Textiles
within a material subjected to an external force.
D 1776 Practice for Conditioning and Testing Textiles
3.1.8 stress decay, n—in mechanics, the reduction in force
D 2258 Practice for Sampling Yarn for Testing
to hold a material at a fixed deformation over a period of time.
D 2433 Test Methods for Rubber Thread
3.1.9 For definitions of other terms related to force and
D 2591 Test Method for Linear Density of Elastomeric
deformation, refer to Terminology D 4848. For definitions of
Yarns (Short-Length Specimens)
other terms related to textiles used in this standard, refer to
D 2653 Test Method for Tensile Properties of Elastomeric
Terminology D 123.
Yarns (CRE Type Tensile Testing Machines)
4. Summary of Test Method
4.1 Aspecimen, mounted in a CRE-type tensile machine, is
This test method is under the jurisdiction ofASTM Committee D13 onTextiles
initially subjected to a series of five loading/unloading cycles
and is the direct responsibility of Subcommittee D13.58 on Yarns.
in which the specimen is extended and relaxed between zero
Current edition approved Sept. 10, 2001. Published November 2001. Originally
published as D 2731 – 68. Discontinued 1979 and reinstated as D 2731 – 01.
Annual Book of ASTM Standards, Vol 07.01.
3 4
Annual Book of ASTM Standards, Vol 09.02. Annual Book of ASTM Standards, Vol 07.02.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D2731
and 75 % of the elongation at first filament break (FFB). 5.5 This test method was developed using elastomeric yarns
During the fifth cycle, the specimen is held at the maximum in the “as-produced” condition, but may be used for treated
extension point for 30 s, then unloaded to allow a return to its elastomeric yarns provided the treatment is specified. The
original gage length position. The specimen is then subjected method does not cover the removal of finish for the determi-
to a sixth load/unload cycle. nation of elastic properties of “finish-free” elastomeric yarns.
4.2 Force at specified elongations are calculated from the
force-elongation curve for the first and fifth loadings and for 6. Apparatus
the fifth unloading. Stress decay is calculated on the fifth cycle.
6.1 Specimen Boards, with short pile or plush surfaces of
Extension at a specified force is determined on the sixth
black or contrasting color, for storing specimens during con-
loading and is used to calculate the permanent deformation.
ditioning.
6.2 Tensile Testing Machine, CRE-type, conforming to
5. Significance and Use
Specification D 76 with respect to force indication, working
range,capacityandverificationofrecordedelongation,capable
5.1 This test method is considered satisfactory for accep-
of cycling, and designed for operation at a pulling speed of 500
tance testing of commercial shipments since current estimates
mm/min (20 in./min).
of between-laboratory precision are acceptable and the method
6.3 Clamping Assembly, pneumatically operated, with jaws
is used extensively in the trade for acceptance testing.
as described in Test Method D 2653.
5.1.1 If there are differences of practical significance be-
6.4 Computer or Microprocessor, interfaced, with auto-
tween reported test results for two laboratories (or more),
matic data gathering system, optional.
comparative tests should be performed to determine if there is
6.5 Tensioning Weights, with various masses from 10 mg to
a statistical bias between them, using competent statistical
3 g to pretension the specimen to 30 to 50 mN/tex (0.3 to 0.5
assistance. As a minimum, use samples for such comparative
mgf/d) before testing.
teststhatareashomogeneousaspossible,drawnfromthesame
6.6 Air Supply, capable of providing 415 kPa (60 psi) to the
lot of material as the samples that resulted in disparate results
pneumatic clamps.
during initial testing, and randomly assigned in equal numbers
to each laboratory. The test results from the laboratories
7. Sampling, Test Specimens, and Test Units
involved should be compared using a statistical test for
unpaired data, at a probability level chosen prior to the testing
7.1 Lot Sample—As a lot sample for acceptance testing,
series. If bias is found, either its cause must be found and take a random number of shipping units directed in an
corrected, or future test results for that material must be
applicable material specification or other agreement between
adjusted in consideration of the known bias. the purchaser and the supplier, such as an agreement to use
5.2 Force at Specified Elongation (FASE) is a measure of Practice D 2258. Consider shipping cases or other shipping
units to be the primary sampling units.
the tensile force required to extend a textile material within
specified limits. This characteristic of elastomeric yarn indi-
NOTE 2—An adequate specification or other agreement between the
catestheresistancethatwillhavetobeovercomebythewearer
purchaser and the supplier requires taking into account the variability
while putting on a garment made of the material and is also an
between shipping units, between packages or ends within a shipping unit,
indicationofthegarment’sresistancetodeformationcausedby and between specimens from a single package to provide a sampling with
a meaningful producer’s risk, consumer’s risk, acceptable quality level
normalbodymovementsduringwear.Theelongationsusedfor
and limiting quality level.
these measurements are typically 100 %, 200 % and 300 %.
5.3 Permanent Deformation (set) is a measure of the in-
7.2 Laboratory Sample—As a laboratory sample for accep-
crease in length of an elastomeric yarn resulting from cyclic
tance testing, take at random from each shipping unit in the lot
stretching and relaxation. The characteristic is a visible indi-
sample the number of packages directed in an applicable
cation of the realignment of intermolecular bonds within the
material specification or other agreement between the pur-
elastic material. As with stress decay, the amount of set
chaser and the supplier, such as an agreement to use Practice
increases with yarn extension; however, for any particular
D 2258. Preferably, take the same number of packages from
extension,littleornoadditionalsettakesplaceafterfivecycles
each of the shipping units selected. If differing numbers of
of exercising. Generally, the characteristic set of the yarn is
packages are to be taken from the shipping units, determine at
developed during fabric preparation and the fabric itself shows
random which shipping units are to have each number of
a negligible amount of set.
packages for testing.
5.4 Stress decay increases with yarn extension, but at any 7.3 Test Specimens—From each package or end in the
specified extension the stress decay takes place in the first 30 laboratory sample, take six specimens as directed in 7.3.1.
s with insignificant decay after 5 min. This characteristic is 7.3.1 Remove the outer layer of yarn from the package.
caused by the gradual realignment of intermolecular bonds Avoid any damaged areas in selecting segments for testing.
within the elastic material, and helps to explain the changes in Carefully unwind yarn from the package with as low as tension
yarn properties that accompany cyclic stretching and relaxing. as possible to avoid stretching.As test specimens, cut approxi-
The realignment of the bonds is a reversible effect. Following mately 125 mm (5 in.) long segments of yarn from each
complete relaxation of the yarn, the molecules tend to assume package, taking them at intervals of at least1m(1 yd). Three
their original configuration with just about complete elimina- ofthesixspecimensareusedassparetoallowforunacceptable
tion of the previously observed strain. breaks, such as caused by slippage or breaking in the clamps.
D2731
7.4 Determine the tex (denier) of the yarn for each labora- 10.3 Attach the selected tensioning weight (10.2) to the
torysampleusingTestMethodD 2591orTestMethodD 6717. specimen such that when the specimen is placed in the lower
clamp, the tensioning weight will hang freely.
7.5 Determine the elongation at first filament bread (FFB)
for each laboratory sample as directed in Test Method D 2653. 10.4 Position a specimen centrally between the top clamp
faces and close the clamp. Ensure that the tension weight is
hanging freely below the bottom clamp.
8. Preparation of Apparatus and Calibration
10.5 Close the lower clamp and remove the tensioning
8.1 Prepare and verify the calibration of the tensile testing
weight.
machine as directed in the manufacturer’s instructions.
10.6 Start the test apparatus and cycle the specimen five
8.2 Set up and adjust the CRE-type tensile testing machine
times between the limits established in 8.2.4.
as follows:
8.2.1 Examine the acrylic clamp jaw face for wear and
NOTE 5—If using a chart recorder, only the first loading cycle and
complete fifth cycle need be recorded on the chart.
replace as needed. Position the jaw faces horizontally in the
clamps.
10.7 On the fifth cycle, stop the crosshead at the maximum
8.2.2 Setthedistancebetweenthejawfaces(gagelength)to
extension limit and hold for 30 s. At the end of holding at the
50 61mm(2 6 0.05 in.).
maximum extension limit, return the crosshead to gage length.
10.8 Immediately,startthecrossheadandrecordtheloading
NOTE 3—A convenient technique for checking the gage length is to
place a piece of carbon paper and white paper in the clamps and close the portion of a sixth cycle.
clamps. The distance between the marks made on the white paper by the
10.9 Return the crosshead to the zero position, remove the
carbon paper represents the set gage length.
spectrum and continue testing until all specimens have been
tested for each laboratory sampling unit and for the lot.
8.2.3 Use a force measuring system such that the cycling
force will be between 30 and 80 % of full scale capacity.
11. Calculation or Interpretation of Results
8.2.4 Set the Cycling Limits as follows:
8.2.4.1 Set Minimum Extension to nominal gage length
11.1 Force at Specified Elongation (FASE)—Determine the
(zero extension).
FASE as follows:
8.2.4.2 Set Maximum Extension equivalent to 75 % of the
11.1.1 From the tensile hysteresis chart for each specimen,
elongation at first filament break of the elastomeric yarn (see
read and record the force at 100, 200 and 300 % elongation on
10.2) or 300 % of gauge length.
the first loading cycle, the force at 300 % elongation on the
8.2.5 Setthecrossheadspeedto500mm/min(20in./min)or
fifth loading cycle, prior to holding for 30 s, and the force at
1000 % extension per min. 100 and 200 % elongation of the fifth unloading cycle to the
8.2.6 Set the extension measuring system as follows: nearest cN (0.1 gf).
11.1.2 Calculate the average FASE for each of the elonga-
8.2.6.1 When using a chart recorder, set the chart speed to
500 mm/min (20 in./min). tions and applicable cycles determined in 11.1.1 for each
laboratory sampling unit and for the lot to the nearest cN (0.1
8.2.6.2 When using an interfaced computer or microproces-
gf).
sor, set parameters to obtain selected properties using suppli-
11.2 Stress Decay—Determine the percent stress decay as
er’s directions and Specification D 76.
follows:
8.2.7 Set the air pressure for pneumatic clamps to 415 kPa
11.2.1 From the chart and on the fifth loading cycle, read
(60 psi). At this pressure, the clamping force is approximately
and record the force at maximum extension and the force after
450 N (100 lb).
holding at maximum extension for 30-s for each specimen.
11.2.2 Calculate the average percent stress decay for each
9. Condit
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