ASTM D6992-03(2015)
(Test Method)Standard Test Method for Accelerated Tensile Creep and Creep-Rupture of Geosynthetic Materials Based on Time-Temperature Superposition Using the Stepped Isothermal Method
Standard Test Method for Accelerated Tensile Creep and Creep-Rupture of Geosynthetic Materials Based on Time-Temperature Superposition Using the Stepped Isothermal Method
SIGNIFICANCE AND USE
5.1 Use of the Stepped Isothermal Method decreases the time required for creep to occur and the obtaining of the associated data.
5.2 The statements set forth in 1.6 are very important in the context of significance and use, as well as scope of the standard.
5.3 Creep test data are used to calculate the creep modulus of materials as a function of time. These data are then used to predict the long-term creep deformation expected of geosynthetics used in reinforcement applications.
Note 1: Currently, SIM testing has focused mainly on woven and knitted geogrids and woven geotextiles made from polyester, aramid, polyaramid, poly-vinyl alcohol (PVA) and polypropylene yarns and narrow strips. Additional correlation studies on other materials are needed.
5.4 Creep rupture test data are used to develop a regression line relating creep stress to rupture time. These results predict the long term rupture strength expected for geosynthetics in reinforcement applications.
5.5 Tensile testing is used to establish the ultimate tensile strength (TULT) of a material and to determine elastic stress, strain and variations thereof for SIM tests.
5.6 Ramp and Hold (R+H) testing is done to establish the range of creep strains experienced in the brief period of very rapid response following the peak of the load ramp.
SCOPE
1.1 This test method covers accelerated testing for tensile creep, and tensile creep-rupture properties using the Stepped Isothermal Method (SIM).
1.2 The test method is focused on geosynthetic reinforcement materials such as yarns, ribs of geogrids, or narrow geotextile specimens.
1.3 The SIM tests are laterally unconfined tests based on time-temperature superposition procedures.
1.4 Tensile tests are to be completed before SIM tests and the results are used to determine the stress levels for subsequent SIM tests defined in terms of the percentage of Ultimate Tensile Strength (TULT). Additionally, the tensile test can be designed to provide estimates of the initial elastic strain distributions appropriate for the SIM results.
1.5 Ramp and Hold (R+H) tests may be completed in conjunction with SIM tests. They are designed to provide additional estimates of the initial elastic and initial rapid creep strain levels appropriate for the SIM results.
1.6 This method can be used to establish the sustained load creep and creep-rupture characteristics of a geosynthetic. Results of this method are to be used to augment results of Test Method D5262 and may not be used as the sole basis for determination of long term creep and creep-rupture behavior of geosynthetic material.
1.7 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.8 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: D6992 − 03(Reapproved 2015)
Standard Test Method for
Accelerated Tensile Creep and Creep-Rupture of
Geosynthetic Materials Based on Time-Temperature
Superposition Using the Stepped Isothermal Method
This standard is issued under the fixed designation D6992; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope priate safety and health practices and determine the applica-
bility of regulatory limitations prior to use.
1.1 This test method covers accelerated testing for tensile
creep, and tensile creep-rupture properties using the Stepped
2. Referenced Documents
Isothermal Method (SIM).
2.1 ASTM Standards:
1.2 The test method is focused on geosynthetic reinforce-
D2990Test Methods forTensile, Compressive, and Flexural
ment materials such as yarns, ribs of geogrids, or narrow
Creep and Creep-Rupture of Plastics
geotextile specimens.
D4439Terminology for Geosynthetics
1.3 The SIM tests are laterally unconfined tests based on D4595Test Method for Tensile Properties of Geotextiles by
time-temperature superposition procedures. the Wide-Width Strip Method
D5262Test Method for Evaluating the Unconfined Tension
1.4 Tensile tests are to be completed before SIM tests and
Creep and Creep Rupture Behavior of Geosynthetics
the results are used to determine the stress levels for subse-
quent SIM tests defined in terms of the percentage of Ultimate
3. Terminology
Tensile Strength (T ). Additionally, the tensile test can be
ULT
3.1 FordefinitionsrelatedtogeosyntheticsseeTerminology
designed to provide estimates of the initial elastic strain
D4439.
distributions appropriate for the SIM results.
3.2 FordefinitionsrelatedtocreepseeTestMethodsD2990
1.5 Ramp and Hold (R+H) tests may be completed in
and D5262.
conjunction with SIM tests. They are designed to provide
additional estimates of the initial elastic and initial rapid creep
3.3 Definitions of Terms Specific to This Standard:
strain levels appropriate for the SIM results.
3.3.1 creep modulus—in SIM analysis, the load divided by
the percent strain at any given point in time.
1.6 This method can be used to establish the sustained load
3.3.2 dwell time—time during which conditions (particular
creep and creep-rupture characteristics of a geosynthetic.
load) are held constant between temperature steps.
ResultsofthismethodaretobeusedtoaugmentresultsofTest
Method D5262 and may not be used as the sole basis for
3.3.3 mean test temperature—the arithmetic average of all
determinationoflongtermcreepandcreep-rupturebehaviorof
temperature readings of the atmosphere surrounding the test
geosynthetic material.
specimen for a particular temperature step, starting at a time
not later than established temperature ramp time, and finishing
1.7 The values stated in SI units are to be regarded as
at a time just prior to the subsequent temperature reset.
standard. No other units of measurement are included in this
standard.
3.3.4 offset modulus method or pointing—data analysis
method used to normalize any prestrain in the samples by
1.8 This standard does not purport to address all of the
shifting the origin of a stress versus strain curve to an axis
safety concerns, if any, associated with its use. It is the
origin of coordinates; that is, to coordinates (0,0).
responsibility of the user of this standard to establish appro-
3.3.5 ramp and hold (R+H) test—a creep test of very short
duration; for example, 100 to 1000 s.
This test method is under the jurisdiction of ASTM Committee D35 on
Geosynthetics and is the direct responsibility of Subcommittee D35.02 on Endur-
ance Properties. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved May 1, 2015. Published June 2015. Originally contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
approved in 2003. Last previous edition approved in 2009 as D6992 – 03(2009). Standards volume information, refer to the standard’s Document Summary page on
DOI: 10.1520/D6992-03R15. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D6992 − 03 (2015)
3.3.6 shift factor—the displacement along the log time axis predict the long-term creep deformation expected of geosyn-
by which a section of the creep or creep modulus curve is thetics used in reinforcement applications.
NOTE 1—Currently, SIM testing has focused mainly on woven and
moved to create the master curve at the reference temperature.
knitted geogrids and woven geotextiles made from polyester, aramid,
Shift factors are denoted by the symbolAT when the displace-
polyaramid, poly-vinyl alcohol (PVA) and polypropylene yarns and
mentsaregenerallytoshortertimes(attenuation)orthesymbol
narrowstrips.Additionalcorrelationstudiesonothermaterialsareneeded.
AT when the displacements are generally to longer times
5.4 Creep rupture test data are used to develop a regression
(acceleration).
line relating creep stress to rupture time. These results predict
3.3.7 stepped isothermal method (SIM)—a method of expo-
the long term rupture strength expected for geosynthetics in
sure that uses temperature steps and dwell times to accelerate
reinforcement applications.
creep response of a material being tested under load.
5.5 Tensile testing is used to establish the ultimate tensile
3.3.8 tensile creep—time-dependent deformation that oc-
strength (T ) of a material and to determine elastic stress,
ULT
curs when a specimen is subjected to a constant tensile load.
strain and variations thereof for SIM tests.
3.3.9 tensile creep-rupture—time dependent rupture that
5.6 Ramp and Hold (R+H) testing is done to establish the
terminates a creep test at high stress levels.
range of creep strains experienced in the brief period of very
3.3.10 time-temperature superposition—the practice of
rapid response following the peak of the load ramp.
shifting viscoelastic response curves obtained at different
temperatures along a horizontal log time axis so as to achieve
6. Apparatus
a master curve covering an extended range of time.
6.1 Grips—GripsforSIMandR+Htestsshouldbethesame
3.3.11 ultimate tensile strength (T )—short term strength
ULT
as the grips for ultimate strength tensile tests. Neither slippage
value used to normalize creep rupture strengths.
nor excessive stress causing premature rupture should be
3.3.12 viscoelastic response—refers to polymeric creep, allowed to occur.
strain, stress relaxation or a combination thereof.
6.2 Testing Machine—A universal testing machine or a
dead-weightloadingsystemwiththefollowingcapabilitiesand
4. Summary of Test Method
accessories shall be used for testing.
4.1 SIM—Aprocedure whereby specified temperature steps
6.2.1 Load measurement and control,
and dwell times are used to accelerate viscoelastic creep
6.2.2 Strain measurement and control,
characteristics during which strain and load are monitored as a
6.2.3 Time measurement,
function of time.
6.2.4 Environmental temperature chamber to facilitate con-
4.1.1 Tensile Creep—Constant tensile load in conjunction
trol of test conditions,
with specified temperature steps and dwell times are used to
6.2.4.1 Temperature measurement and control facilities,
accelerate creep strain response.
6.2.5 Other environmental measurement and control, and
4.1.2 Tensile Creep-Rupture—A tensile creep test where
6.2.6 Computer data acquisition and control.
high stress levels are used during testing to ensure rupture,
while specified temperature steps and dwell times are used to
7. Sampling
accelerate creep strain response characteristics. Strain is moni-
7.1 The specimens used for tensile, R+H and SIM tests
tored as a function of time.
should all be taken from the same sample.
4.2 Tensile Tests—Test specimens are rapidly loaded over a
7.2 Remove sufficient test specimens for tensile testing in
short period to achieve rupture. The selection of a suitable
accordance with the selected tensile testing procedure (see
tensile test is dependent upon the type of material tested (see
Section 8).
Section 8). Tensile tests to support creep and creep-rupture
tests are performed under the same control of loading or strain
7.3 Remove one (1) test specimen from the sample for each
rateasusedtoloadorstrainthetestspecimensduringcreepor
SIM test.
creep rupture tests.
7.4 Remove one (1) test specimen from the sample for each
4.3 R+H—Test specimens are ramp loaded at a predeter-
R+H test.
mined loading rate to a predetermined load and held under
constant load (short term creep test). 8. Test Specimens
8.1 Geogrid specimens should be single ribs, unless other-
5. Significance and Use
wise agreed upon.
5.1 Use of the Stepped Isothermal Method decreases the
8.2 Yarn specimens of geogrids or geotextiles should be
time required for creep to occur and the obtaining of the
single ply or multiple ply strands, unless otherwise agreed
associated data.
upon.
5.2 The statements set forth in 1.6 are very important in the
8.3 Geotextile specimens should be 50 mm wide strips,
context of significance and use, as well as scope of the
unless otherwise agreed upon.
standard.
NOTE 2—Single geogrid ribs and narrow strip specimens are preferred
5.3 Creep test data are used to calculate the creep modulus
todeterminetheeffectofappliedloadonthetensilecreeppropertiesofthe
of materials as a function of time. These data are then used to material separate from the effect of sample width on the tensile properties
D6992 − 03 (2015)
of the material. However, correlation between narrow geotextile strips or not known. Successful tests with some materials have been run with
single geogrid ribs to wider representative specimens should be estab- temperature ramp times of up to four minutes.
lished.
10.4 Test temperatures are to be maintained within 61.0°C
8.4 The length of the test specimen is determined by the
of the mean achieved temperature.
type of grip used. Refer to specific tensile test procedure for
10.4.1 Temperature steps and dwell times must be such that
guidance.
the steady state creep rate at the beginning of a new step is not
so different from that of the previous that it cannot be
8.5 Number of Tests:
established within the identified ramp time.
8.5.1 A single specimen is usually sufficient to define a
master creep or relaxation curve using the SIM. However, if
11. Procedures
only a single SIM test is to be performed, the location of the
11.1 The same or similar load or strain control shall be
onset of creep strain or modulus curve should be confirmed
applied to the tensile tests and the load ramp portion of R+H
using at least two short term creep (R+H) tests.
and SIM (creep and creep-rupture) tests. The load rate control
8.5.2 Generally 12 to 18 specimens are needed to define a
(in units of kN per min) that is applied shall achieve a narrow
stress-rupturecurverepresentingmultiplerupturetimes.Fewer
rangeofstrainratesexpressedinpercentperminute,asagreed
specimens would be needed to define a specific region of the
upon. Generally 10 6 3% per min (or 20 6 3% per min for
curve, for example the percent T at1×10 h (= 110 year)
ULT
European practice) will be satisfactory.
rupture life.
NOTE 4—Alinear ramp of load versus time will not generally result in
a linear strain versus time relationship because stress versus strain curves
9. Conditioning
are not linear for most geosynthetic materials.
9.1 Tensile and SIM testing shall be conducted using 20 6
11.2 Achieve the test loads for R+H and SIM tests within
1°C as the reference or temperature standard. If the laboratory
62% of the target loads, and maintain any achieved load
is not within this range, perform tensile tests in a suitable
within 60.5% of its values for the duration of the test.Abrief
environmental chamber capable of controlled cooling and
overshoot of the target load that is within 62% of the target
heating. The environmental chamber should have a program-
load and limited toa1to2s time duration is acceptable for
mable or set-point controller so as to maintain temperature to
load control systems.
20 6 1°C.When agreed to, a reference temperature other than
11.3 Replicate test loads for R+H and SIM tests should be
20°C can be utilized. Also, when agreed to, the results of
within 60.5% of the average of the achieved loads for a test
testing under this standard can be shifted from one reference
set.
temperature to another.
11.4 Pretensioning up in accordance with the governing
9.2 Allow the specimen adequate time to come to tempera-
tensiletestisacceptable.Themethodusedtodefinezerostrain
ture equilibrium in the laboratory or environmental chamber.
is to be identified and reported.
Generally this can be accomplished within a few hours (see
11.5 The same or similar grips shall be used for tensile,
Note 3).
R+H and SIM tests. Care should be taken to use grips that do
9.3 Record the relative humidity in the laboratory or envi-
not initiate failure or incur slippage at stress levels which may
ronmental chamber for all tests.
produce specimen rupture (for example, at loads greater than
55% of T for polyester).
ULT
10. Selection of Test Conditions
11.6 Inspect grips to insure loading surfaces are clean and
10.1 The standard environment for testing is dry, since the
that padding, if used, is free of defects and is secured properly.
effect of elevated temperature is to reduce the humidity of
11.7 Inspectthespecimeninstallationtobesurethematerial
ambient air without special controls.
is properly aligned with the grips and with the loading axis.
10.2 The standard reference temperature is 20°C unless
11.8 Insurethattheloadcellusediscalibratedproperlysuch
otherwise agreed to. The individual reference temperature for
that it will accurately measure the range of tensile loads
each SIM test is the average achieved temperature of the first
anticipated.
isothermal dwell.
11.9 Insure that the extensometer used (if any) is calibrated
10.3 Testing temperatures are to be within 62°C of the
properly such that it will accurately measure the range of
target test temperatures. It is critically important that the test
tensile strains anticipated. If rupture is anticipated, take pre-
specimen has equilibrated throughout its thickness so as to
cautions to insure that the rupture event will not damage the
avoid nonisothermal conditions. Initial trials are necessary to
extensometer or create a hazard for the machine operator.
establish this minimum equilibrium time.
NOTE3—Laboratoryexperiencehassuggestedthattheuseofcalibrated
11.10 Unles
...
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: D6992 − 03 (Reapproved 2009) D6992 − 03 (Reapproved 2015)
Standard Test Method for
Accelerated Tensile Creep and Creep-Rupture of
Geosynthetic Materials Based on Time-Temperature
Superposition Using the Stepped Isothermal Method
This standard is issued under the fixed designation D6992; 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 accelerated testing for tensile creep, and tensile creep-rupture properties using the Stepped
Isothermal Method (SIM).
1.2 The test method is focused on geosynthetic reinforcement materials such as yarns, ribs of geogrids, or narrow geotextile
specimens.
1.3 The SIM tests are laterally unconfined tests based on time-temperature superposition procedures.
1.4 Tensile tests are to be completed before SIM tests and the results are used to determine the stress levels for subsequent SIM
tests defined in terms of the percentage of Ultimate Tensile Strength (T ). Additionally, the tensile test can be designed to provide
ULT
estimates of the initial elastic strain distributions appropriate for the SIM results.
1.5 Ramp and Hold (R+H) tests may be completed in conjunction with SIM tests. They are designed to provide additional
estimates of the initial elastic and initial rapid creep strain levels appropriate for the SIM results.
1.6 This method can be used to establish the sustained load creep and creep-rupture characteristics of a geosynthetic. Results
of this method are to be used to augment results of Test Method D5262 and may not be used as the sole basis for determination
of long term creep and creep-rupture behavior of geosynthetic material.
1.7 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.8 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.
2. Referenced Documents
2.1 ASTM Standards:
D2990 Test Methods for Tensile, Compressive, and Flexural Creep and Creep-Rupture of Plastics
D4439 Terminology for Geosynthetics
D4595 Test Method for Tensile Properties of Geotextiles by the Wide-Width Strip Method
D5262 Test Method for Evaluating the Unconfined Tension Creep and Creep Rupture Behavior of Geosynthetics
3. Terminology
3.1 For definitions related to geosynthetics see Terminology D4439.
3.2 For definitions related to creep see Test Methods D2990 and D5262.
3.3 Definitions of Terms Specific to This Standard:
3.3.1 creep modulus—in SIM analysis, the load divided by the percent strain at any given point in time.
3.3.2 dwell time—time during which conditions (particular load) are held constant between temperature steps.
This test method is under the jurisdiction of ASTM Committee D35 on Geosynthetics and is the direct responsibility of Subcommittee D35.02 on Endurance Properties.
Current edition approved June 1, 2009May 1, 2015. Published July 2009June 2015. Originally approved in 2003. Last previous edition approved in 20032009 as D6992
– 03.03(2009). DOI: 10.1520/D6992-03R09.10.1520/D6992-03R15.
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.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D6992 − 03 (2015)
3.3.3 viscoelastic response—mean test temperature—refers to polymeric creep, strain, stress relaxation or a combination
thereof.the arithmetic average of all temperature readings of the atmosphere surrounding the test specimen for a particular
temperature step, starting at a time not later than established temperature ramp time, and finishing at a time just prior to the
subsequent temperature reset.
3.3.4 tensile creep—offset modulus method or pointing—time-dependent deformation that occurs when a specimen is subjected
to a constant tensile load.data analysis method used to normalize any prestrain in the samples by shifting the origin of a stress
versus strain curve to an axis origin of coordinates; that is, to coordinates (0,0).
3.3.5 tensile creep-rupture—ramp and hold (R+H) test—time dependent rupture that terminates a creep test at high stress
levels.of very short duration; for example, 100 to 1000 s.
3.3.4 time-temperature superposition—the practice of shifting viscoelastic response curves obtained at different temperatures
along a horizontal log time axis so as to achieve a master curve covering an extended range of time.
3.3.6 shift factor—the displacement along the log time axis by which a section of the creep or creep modulus curve is moved
to create the master curve at the reference temperature. Shift factors are denoted by the symbol AT when the displacements are
generally to shorter times (attenuation) or the symbol AT when the displacements are generally to longer times (acceleration).
3.3.7 stepped isothermal method (SIM)—a method of exposure that uses temperature steps and dwell times to accelerate creep
response of a material being tested under load.
3.3.8 tensile creep—time-dependent deformation that occurs when a specimen is subjected to a constant tensile load.
3.3.9 tensile creep-rupture—time dependent rupture that terminates a creep test at high stress levels.
3.3.10 mean test temperature—time-temperature superposition—the arithmetic average of all temperature readings of the
atmosphere surrounding the test specimen for a particular temperature step, starting at a time not later than established temperature
ramp time, and finishing at a time just prior to the subsequent temperature reset.practice of shifting viscoelastic response curves
obtained at different temperatures along a horizontal log time axis so as to achieve a master curve covering an extended range of
time.
3.3.11 ultimate tensile strength (T )—short term strength value used to normalize creep rupture strengths.
ULT
3.3.12 offset modulus method or pointing—viscoelastic response—data analysis method used to normalize any prestrain in the
samples by shifting the origin of a stress versus strain curve to an axis origin of coordinates; that is, to coordinates (0,0).refers to
polymeric creep, strain, stress relaxation or a combination thereof.
3.3.10 ramp and hold (R+H) test—a creep test of very short duration; for example, 100 to 1000 s.
3.3.11 dwell time—time during which conditions (particular load) are held constant between temperature steps.
3.3.12 creep modulus—in SIM analysis, the load divided by the percent strain at any given point in time.
4. Summary of Test Method
4.1 SIM—A procedure whereby specified temperature steps and dwell times are used to accelerate viscoelastic creep
characteristics during which strain and load are monitored as a function of time.
4.1.1 Tensile Creep—Constant tensile load in conjunction with specified temperature steps and dwell times are used to
accelerate creep strain response.
4.1.2 Tensile Creep-Rupture—A tensile creep test where high stress levels are used during testing to ensure rupture, while
specified temperature steps and dwell times are used to accelerate creep strain response characteristics. Strain is monitored as a
function of time.
4.2 Tensile Tests—Test specimens are rapidly loaded over a short period to achieve rupture. The selection of a suitable tensile
test is dependent upon the type of material tested (see Section 8). Tensile tests to support creep and creep-rupture tests are
performed under the same control of loading or strain rate as used to load or strain the test specimens during creep or creep rupture
tests.
4.3 R+H—Test specimens are ramp loaded at a predetermined loading rate to a predetermined load and held under constant load
(short term creep test).
5. Significance and Use
5.1 Use of the Stepped Isothermal Method decreases the time required for creep to occur and the obtaining of the associated
data.
5.2 The statements set forth in 1.6 are very important in the context of significance and use, as well as scope of the standard.
5.3 Creep test data are used to calculate the creep modulus of materials as a function of time. These data are then used to predict
the long-term creep deformation expected of geosynthetics used in reinforcement applications.
NOTE 1—Currently, SIM testing has focused mainly on woven and knitted geogrids and woven geotextiles made from polyester, aramid, polyaramid,
poly-vinyl alcohol (PVA) and polypropylene yarns and narrow strips. Additional correlation studies on other materials are needed.
D6992 − 03 (2015)
5.4 Creep rupture test data are used to develop a regression line relating creep stress to rupture time. These results predict the
long term rupture strength expected for geosynthetics in reinforcement applications.
5.5 Tensile testing is used to establish the ultimate tensile strength (T ) of a material and to determine elastic stress, strain
ULT
and variations thereof for SIM tests.
5.6 Ramp and Hold (R+H) testing is done to establish the range of creep strains experienced in the brief period of very rapid
response following the peak of the load ramp.
6. Apparatus
6.1 Grips—Grips for SIM and R+H tests should be the same as the grips for ultimate strength tensile tests. Neither slippage nor
excessive stress causing premature rupture should be allowed to occur.
6.2 Testing Machine—A universal testing machine or a dead-weight loading system with the following capabilities and
accessories shall be used for testing.
6.2.1 Load measurement and control,
6.2.2 Strain measurement and control,
6.2.3 Time measurement,
6.2.4 Environmental temperature chamber to facilitate control of test conditions,
6.2.4.1 Temperature measurement and control facilities,
6.2.5 Other environmental measurement and control, and
6.2.6 Computer data acquisition and control.
7. Sampling
7.1 The specimens used for tensile, R+H and SIM tests should all be taken from the same sample.
7.2 Remove sufficient test specimens for tensile testing in accordance with the selected tensile testing procedure (see Section
8).
7.3 Remove one (1) test specimen from the sample for each SIM test.
7.4 Remove one (1) test specimen from the sample for each R+H test.
8. Test Specimens
8.1 Geogrid specimens should be single ribs, unless otherwise agreed upon.
8.2 Yarn specimens of geogrids or geotextiles should be single ply or multiple ply strands, unless otherwise agreed upon.
8.3 Geotextile specimens should be 50 mm wide strips, unless otherwise agreed upon.
NOTE 2—Single geogrid ribs and narrow strip specimens are preferred to determine the effect of applied load on the tensile creep properties of the
material separate from the effect of sample width on the tensile properties of the material. However, correlation between narrow geotextile strips or single
geogrid ribs to wider representative specimens should be established.
8.4 The length of the test specimen is determined by the type of grip used. Refer to specific tensile test procedure for guidance.
8.5 Number of Tests:
8.5.1 A single specimen is usually sufficient to define a master creep or relaxation curve using the SIM. However, if only a single
SIM test is to be performed, the location of the onset of creep strain or modulus curve should be confirmed using at least two short
term creep (R+H) tests.
8.5.2 Generally 12 to 18 specimens are needed to define a stress-rupture curve representing multiple rupture times. Fewer
specimens would be needed to define a specific region of the curve, for example the percent T at 1 × 10 h (= 110 year) rupture
ULT
life.
9. Conditioning
9.1 Tensile and SIM testing shall be conducted using 20 6 1°C as the reference or temperature standard. If the laboratory is
not within this range, perform tensile tests in a suitable environmental chamber capable of controlled cooling and heating. The
environmental chamber should have a programmable or set-point controller so as to maintain temperature to 20 6 1°C. When
agreed to, a reference temperature other than 20°C can be utilized. Also, when agreed to, the results of testing under this standard
can be shifted from one reference temperature to another.
9.2 Allow the specimen adequate time to come to temperature equilibrium in the laboratory or environmental chamber.
Generally this can be accomplished within a few hours (see Note 3).
9.3 Record the relative humidity in the laboratory or environmental chamber for all tests.
D6992 − 03 (2015)
10. Selection of Test Conditions
10.1 The standard environment for testing is dry, since the effect of elevated temperature is to reduce the humidity of ambient
air without special controls.
10.2 The standard reference temperature is 20°C unless otherwise agreed to. The individual reference temperature for each SIM
test is the average achieved temperature of the first isothermal dwell.
10.3 Testing temperatures are to be within 6 2°C 62°C of the target test temperatures. It is critically important that the test
specimen has equilibrated throughout its thickness so as to avoid nonisothermal conditions. Initial trials are necessary to establish
this minimum equilibrium time.
NOTE 3—Laboratory experience has suggested that the use of calibrated thermocouples located near, affixed to or embedded within the test specimen
may facilitate a successful temperature compliance test for the specimen material. It is suggested that the laboratory perform the planned SIM temperature
steps using an unloaded sacrificial test specimen and, with the use of these thermocouples, measure the temperature change of the specimen at its thickest
or most mass-dense region. The time required for the specimen to reach the target temperature is recorded and used as the minimum dwell time. The upper
limit of the temperature ramp time is not known. Successful tests with some materials have been run with temperature ramp times of up to four minutes.
10.4 Test temperatures are
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