1、Designation: D7361 07 (Reapproved 2018)Standard Test Method forAccelerated Compressive Creep of Geosynthetic MaterialsBased on Time-Temperature Superposition Using theStepped Isothermal Method1This standard is issued under the fixed designation D7361; the number immediately following the designation
2、 indicates the year oforiginal adoption or, in the case of revision, the 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 accelerated t
3、esting for compres-sive creep properties using the stepped isothermal method(SIM).1.2 The test method is focused on geosynthetic drainagematerials such as HDPE geonet specimens.1.3 The SIM tests are laterally unconfined tests based ontime-temperature superposition procedures.1.4 Ramp and hold (R+H)
4、tests may be completed inconjunction with SIM tests. They are designed to provideadditional estimates of the initial rapid compressive creepstrain levels appropriate for the SIM results.1.5 This method can be used to establish the sustained loadcompressive creep characteristics of a geosynthetic tha
5、t dem-onstrates a relationship between time-dependent behavior andtemperature. Results of this method are to be used to augmentresults of compressive creep tests performed at 20 6 1 C andmay not be used as the sole basis for determination oflong-term compressive creep behavior of geosynthetic mate-r
6、ial.1.6 The values stated in SI units are to be regarded as thestandard. The values given in parentheses are for informationonly.1.7 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
7、 appro-priate safety, health, and environmental practices and deter-mine the applicability of regulatory limitations prior to use.1.8 This international standard was developed in accor-dance with internationally recognized principles on standard-ization established in the Decision on Principles for
8、theDevelopment of International Standards, Guides and Recom-mendations issued by the World Trade Organization TechnicalBarriers to Trade (TBT) Committee.2. Referenced Documents2.1 ASTM Standards:2D1621 Test Method for Compressive Properties of RigidCellular PlasticsD2990 Test Methods for Tensile, Co
9、mpressive, and FlexuralCreep and Creep-Rupture of PlasticsD4439 Terminology for GeosyntheticsD5262 Test Method for Evaluating the Unconfined TensionCreep and Creep Rupture Behavior of GeosyntheticsD6364 Test Method for Determining Short-Term Compres-sion Behavior of Geosynthetics3. Terminology3.1 De
10、finitions:3.1.1 For definitions related to geosynthetics, see Terminol-ogy D4439.3.1.2 For definitions related to creep, see Test MethodsD2990 and D5262 and Terminology D4439.3.2 Definitions of Terms Specific to This Standard:3.2.1 compressive creeptime-dependent deformation thatoccurs when a specim
11、en is subjected to a constant compressiveload.3.2.2 compressive creep modulusin SIM analysis, the loaddivided by the percent compressive strain at any given point intime.3.2.3 dwell timetime during which conditions (particularload) are held constant between temperature steps.3.2.4 mean test temperat
12、urethe arithmetic average of alltemperature readings of the atmosphere surrounding the testspecimen for a particular temperature step, starting at a timenot later than established temperature ramp time, and finishingat a time just prior to the subsequent temperature reset.1This test method is under
13、the jurisdiction of ASTM Committee D35 onGeosynthetics and is the direct responsibility of Subcommittee D35.02 on Endur-ance Properties.Current edition approved Feb. 1, 2018. Published February 2018. Originallyapproved in 2007. Last previous edition approved in 2012 as D7361 07 (2012).DOI: 10.1520/D
14、7361-07R18.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.Copyright ASTM International, 100 Barr Harbor Driv
15、e, PO Box C700, West Conshohocken, PA 19428-2959. United StatesThis international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recommendations iss
16、ued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.13.2.5 offset modulus method or pointingdata analysismethod used to normalize any prestrain in the samples byshifting the origin of a stress-versus-strain curve to an axisorigin of coordinates, that is, to coordinates (0
17、,0).3.2.6 ramp and hold (R+H) testa creep test of very shortduration, for example, 100 to 1000 s.3.2.7 shift factorthe displacement along the log time axisby which a section of the creep or creep modulus curve ismoved to create the master curve at the reference temperature.Shift factors are denoted
18、by the symbol when the displace-ments are generally to shorter times (attenuation) or the symbolaTwhen the displacements are generally to longer times(acceleration).3.2.8 stepped isothermal method (SIM)a method of expo-sure that uses temperature steps and dwell times to acceleratecreep response of a
19、 material being tested under load.3.2.9 time-temperature superpositionthe practice of shift-ing viscoelastic response curves obtained at different tempera-tures along a horizontal log time axis so as to achieve a mastercurve covering an extended range of time.3.2.10 viscoelastic responserefers to po
20、lymeric creep,strain, stress relaxation, or a combination thereof.4. Summary of Test Method4.1 SIMA procedure whereby specified temperature stepsand dwell times are used to accelerate viscoelastic creepcharacteristics during which strain and load are monitored as afunction of time.4.1.1 Compressive
21、CreepConstant compressive load inconjunction with specified temperature steps and dwell timesare used to accelerate compressive creep strain response.4.2 R+HTest specimens are ramp loaded at a predeter-mined loading rate to a predetermined load and held underconstant load (short-term creep test).5.
22、Significance and Use5.1 Use of the SIM decreases the time required for creep tooccur and the obtaining of the associated data.5.2 The statements set forth in 1.5 are very important in thecontext of significance and use, as well as scope of thestandard.5.3 Creep test data are used to calculate the cr
23、eep modulusof materials as a function of time. These data are then used topredict the long-term creep deformation expected of geosyn-thetics used in drainage applications.NOTE 1Currently, SIM testing has focused mainly on geonets madefrom high-density polyethylene. Additional testing on other materi
24、als isongoing.5.4 R+H testing is done to establish the range of creepstrains experienced in the brief period of very rapid responsefollowing the peak of the load ramp.6. Apparatus6.1 Loading PlatensLoading platens for SIM and R+Htests should conform to Test Method D6364, Standard TestMethod for Dete
25、rmining the Short-Term Compression Behav-ior of Geosynthetics.6.2 Testing MachineA universal testing machine or adead-weight loading system with the following capabilities andaccessories shall be used for testing:6.2.1 Load measurement and control,6.2.2 Strain measurement,6.2.3 Time measurement,6.2.
26、4 Environmental temperature chamber to facilitate con-trol of test conditions,6.2.4.1 Temperature measurement and control facilities,6.2.5 Other environmental measurement and control, and6.2.6 Computer data acquisition and control.7. Sampling7.1 The specimens used for R+H and SIM tests should all be
27、taken from the same sample.7.2 Remove one (1) test specimen from the sample for eachSIM test.7.3 Remove one (1) test specimen from the sample for eachR+H test.8. Test Specimens8.1 Specimens should be at least 120 by 120 mm (4.7 by4.7 in.).8.2 Number of Tests:8.2.1 A single specimen is usually suffic
28、ient to define amaster creep or relaxation curve using the SIM. However, ifonly a single SIM test is to be performed, the location of theonset of creep strain or modulus curve should be confirmedusing at least two R+H tests.9. Conditioning9.1 Compression testing via Test Method D6364 and SIMtesting
29、shall be conducted using 20 6 1 C as the reference ortemperature standard. If the laboratory is not within this range,perform tests in a suitable environmental chamber capable ofcontrolled cooling and heating. The environmental chambershould have a programmable or set-point controller so as tomainta
30、in temperature to 20 6 1 C. When agreed to, areference temperature other than 20 C can be utilized. Also,when agreed to, the results of testing under this standard can beshifted from one reference temperature to another.9.2 Allow the specimen adequate time to come to tempera-ture equilibrium in the
31、laboratory or environmental chamber.Generally, this can be accomplished within a few hours (seeNote 2).9.3 Record the relative humidity in the laboratory or envi-ronmental chamber for all tests.10. Selection of Test Conditions10.1 The standard environment for testing is dry, since theeffect of eleva
32、ted temperature is to reduce the humidity ofambient air without special controls.10.2 The standard reference temperature is 20 C unlessotherwise agreed to. The individual reference temperature foreach SIM test is the average achieved temperature of the firstdwell time.D7361 07 (2018)210.3 Testing te
33、mperatures are to be within 62 C of thetarget test temperatures. It is critically important that the testspecimen has equilibrated throughout its thickness so as toavoid nonisothermal conditions. Initial trials are necessary toestablish this minimum equilibrium time.NOTE 2Laboratory experience has s
34、uggested that the use of calibratedthermocouples located near, affixed to, or embedded within the testspecimen may facilitate a successful temperature compliance test for thespecimen material. It is suggested that the laboratory perform the plannedSIM temperature steps using an unloaded sacrificial
35、test specimen and,with the use of these thermocouples, measure the temperature change ofthe specimen at its thickest or most mass-dense region. The time requiredfor the specimen to reach the target temperature is recorded and used asthe minimum dwell time. The upper limit of the temperature ramp tim
36、e isnot known. Successful tests with some materials have been run withtemperature ramp times of up to 4 min.10.4 Testing temperatures are to be maintained within61.0 C of the mean achieved temperature.10.4.1 Temperature steps and dwell times must be such thatthe steady-state creep rate at the beginn
37、ing of a new step is notso different from that of the previous that it cannot beestablished within the identified ramp time.11. Procedure11.1 The same or similar load or strain control shall beapplied to the load ramp portion of R+H and SIM tests. Theload rate control (in units of kN per min) that i
38、s applied shallachieve a narrow range of strain rates expressed in percent perminute, as agreed upon. Generally, 10 % of the nominalthickness of the test specimen per minute or 1.0 6 0.1 mm/min(0.04 6 0.004 in./min), whichever is greater, will be satisfac-tory.NOTE 3A linear ramp of load versus time
39、 will not generally result ina linear-strain-versus-time relationship because stress-versus-strain curvesare not linear for most geosynthetic materials.11.2 Achieve the test loads for R+H and SIM tests within62 % of the target loads, and maintain any achieved loadwithin 60.5 % of its values for the
40、duration of the test. A briefovershoot of the target load that is within 62 % of the targetload and limited toa1to2-stime duration is acceptable forload control systems.11.3 Replicate test loads for R+H and SIM tests should bewithin 60.5 % of the average of the achieved loads for a testset.11.4 Insp
41、ect the specimen installation to be sure the materialis properly aligned with the platens and with the loading axis.11.5 Ensure that the load cell used is calibrated properlysuch that it will accurately measure the range of compressiveloads anticipated.11.6 Ensure that the extensometer used (if any)
42、 is calibratedproperly such that it will accurately measure the range ofcompressive strains anticipated.11.7 Time, load, and deformation data shall be collected ata minimum rate of two readings per second during the initialloading ramp portions of tests and a minimum rate of tworeadings per minute d
43、uring constant load portions of tests. Ifload is applied by means of dead weights, with or without alever, regular measurement of load after the ramp is notnecessary.11.8 The environmental chamber and temperature coolershall be capable of maintaining the specimen temperaturewithin 61 C in range of 0
44、 to 100 C, and of changing thespecimen temperature by up to 15 C, within the identifiedramp time (see Note 2).11.9 Unless otherwise agreed upon, the temperature stepsfor polyolefin geosynthetics shall not exceed 7 C.NOTE 4Examples that have been successful are a 7 C step with a10 000-s dwell time fo
45、r HDPE.11.10 Unless otherwise agreed upon, the dwell time for allSIM tests shall not be less than 10 000 s. Unless otherwiseagreed upon, the total time for SIM tests not terminated inrupture shall not be less than 60 000 s.11.11 The temperature data acquisition rate during SIMshall be a minimum of o
46、nce per minute.11.12 If desired, accelerated compressive property tests canbe conducted in liquid, vapor, or gaseous mixtures to simulateunique environmental exposures.12. Calculation12.1 Ramp and Hold (R+H) Results:12.1.1 Plot stress and secant (creep) modulus versus strain,and strain and secant (c
47、reep) modulus versus linear and logtime. Use the offset modulus method to point the curves asdescribed in 12.1.2.12.1.2 Identify the elastic strains at the ramp peaks and theinitial rapid creep strain levels for comparison to the ramp andinitial creep portions of the SIM results.12.2 SIM Test Result
48、s (See Appendix X1 for Examples):12.2.1 Compute and plot stress and secant (compressivecreep) modulus versus strain for each specimen, using theoffset modulus method to point the curve. Then plot compres-sive creep strain, compressive creep modulus, stress, andtemperature as a function of linear tim
49、e. Inspect these plots toidentify that the test objectives were achieved.12.2.2 Plot compressive creep modulus (or compressivestrain) versus log time after rescaling the elevated temperaturesegments to achieve slope matching as follows: the semi-logarithmic slopes of a modulus (or compressive strain) curveat the beginning of a higher temperature step should beadjusted to match the slope of the end of the preceding lowertemperature by subtracting a time “t” from each of the dwelltimes of higher temperature steps.12.2.3 Re-plot the compressiv
