1、Designation: D 7361 07Standard Test Method forAccelerated Compressive Creep of Geosynthetic MaterialsBased on Time-Temperature Superposition Using theStepped Isothermal Method1This standard is issued under the fixed designation D 7361; the number immediately following the designation indicates the y
2、ear 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 (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers accelerated testing for comp
3、res-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) tests may be co
4、mpleted 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 that dem-onstrates
5、 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 1C andmay not be used as the sole basis for determination of longterm compressive creep behavior of geosynthetic material.1.6 The value
6、s 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 appro-priate saf
7、ety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D 1621 Test Method for Compressive Properties Of RigidCellular PlasticsD 2990 Test Methods for Tensile, Compressive, and Flex-ural Creep and Creep-Rupture of Pl
8、asticsD 4439 Terminology for GeosyntheticsD 5262 Test Method for Evaluating the Unconfined TensionCreep and Creep Rupture Behavior of GeosyntheticsD 6364 Test Method for Determining Short-Term Compres-sion Behavior of Geosynthetics3. Terminology3.1 Definitions: For definitions related to geosyntheti
9、cs seeTerminology D 4439.3.2 Definitions: For definitions related to creep see TestMethods D 2990 and D 5262.3.3 Definitions of Terms Specific to This Standard:3.3.1 viscoelastic responserefers to polymeric creep,strain, stress relaxation or a combination thereof.3.3.2 compressive creeptime-dependen
10、t deformation thatoccurs when a specimen is subjected to a constant compressiveload.3.3.3 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 rang
11、e of time.3.3.4 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 by the symbol when the displace-ments are generally to shorter times (attenuation) or t
12、he symbolaTwhen the displacements are generally to longer times(acceleration).3.3.5 stepped isothermal method (SIM)a method of expo-sure that uses temperature steps and dwell times to acceleratecreep response of a material being tested under load.3.3.6 mean test temperaturethe arithmetic average of
13、alltemperature readings of the atmosphere surrounding the testspecimen for a particular temperature step, starting at a time1This test method is under the jurisdiction of ASTM Committee D35 onGeosynthetics and is the direct responsibility of Subcommittee D35.02 on Endur-ance Properties.Current editi
14、on approved Dec. 1, 2007. Published March 2008.2For 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.1Copyright AST
15、M International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.not later than established temperature ramp time, and finishingat a time just prior to the subsequent temperature reset.3.3.7 offset modulus method or pointingdata analysismethod used to normalize an
16、y prestrain in the samples byshifting the origin of a stress vs. strain curve to an axis originof coordinates, that is, to coordinates (0,0).3.3.8 ramp and hold (R+H) testa creep test of very shortduration, for example, 1001000 seconds.3.3.9 dwell timetime during which conditions (particularload) ar
17、e held constant between temperature steps.3.3.10 compressive creep modulusin SIM analysis, theload divided by the percent compressive strain at any givenpoint in time.4. Summary of Test Method4.1 SIMA procedure whereby specified temperature stepsand dwell times are used to accelerate viscoelastic cr
18、eepcharacteristics during which strain and load are monitored as afunction of time.4.1.1 compressive 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 predet
19、er-mined loading rate to a predetermined load and held underconstant load (short term creep test).5. 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 Section 1.5 are very impor-tant in the co
20、ntext of significance and use, as well as scope ofthe standard.5.3 Creep test data are used to calculate the creep 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, S
21、IM testing has focused mainly geonets made fromhigh density polyethylene. Additional testing on other materials 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 P
22、latensLoading platens for SIM and R+Htests should conform to Test Method D 6364, Standard TestMethod for Determining 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 shal
23、l be used for testing:6.2.1 load measurement and control,6.2.2 strain measurement,6.2.3 time measurement,6.2.4 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.
24、6 computer data acquisition and control.7. Sampling7.1 The specimens used for R+H and SIM tests should all betaken 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 s
25、hould be at least 120 mm 3 120 mm (4.7 in.3 4.7 in.).8.2 Number of tests8.2.1 A single specimen is usually sufficient 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 c
26、onfirmedusing at least two R+H tests.9. Conditioning9.1 Compression testing via Test Method D 6364 and SIMtesting 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 ofcontroll
27、ed cooling and heating. The environmental chambershould have a programmable- or set-point controller so as tomaintain temperature to 20 6 1C. When agreed to, a referencetemperature other than 20C can be utilized.Also, when agreedto, the results of testing under this standard can be shifted fromone r
28、eference temperature to another.9.2 Allow the specimen adequate time to come to tempera-ture equilibrium in the 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
29、tests.10. Selection of Test Conditions10.1 The standard environment for testing is dry, since theeffect of elevated temperature is to reduce the humidity ofambient air without special controls.10.2 The standard reference temperature is 20C unlessotherwise agreed to. The individual reference temperat
30、ure foreach SIM test is the average achieved temperature of the firstdwell time.10.3 Testing temperatures are to be within 62C of thetarget test temperatures. It is critically important that the testspecimen has equilibrated throughout its thickness so as toavoid nonisothermal conditions. Initial tr
31、ials are necessary toestablish this minimum equilibrium time.NOTE 2Laboratory experience has suggested 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 suggeste
32、d that the laboratory perform the plannedSIM temperature steps using an unloaded sacrificial 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 temperatu
33、re is recorded and used asD7361072the minimum dwell time. The upper limit of the temperature ramp time isnot known. Successful tests with some materials have been run withtemperature ramp times of up to four minutes.10.4 Testing temperatures are to be maintained within61.0C of the mean achieved temp
34、erature.10.4.1 Temperature steps and dwell times must be such thatthe steady state creep rate at the beginning 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 be
35、applied to the load ramp portion of R+H and SIM tests. Theload rate control (in units of kN per min.) that is 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 per
36、minute (0.04 6 0.004 inches per minute), whichever is greaterwill be satisfactory.NOTE 3A linear ramp of load vs. time will not generally result in alinear strain vs. time relationship because stress vs. strain curves are notlinear for most geosynthetic materials.11.2 Achieve the test loads for R+H
37、and SIM tests within 62 % of the target loads, and maintain any achieved load within6 0.5 % of its values for the duration of the test. A briefovershoot of the target load that is within 6 2% of the targetload and limited toa1to2second time duration is acceptablefor load control systems.11.3 Replica
38、te test loads for R+H and SIM tests should bewithin 60.5 % of the average of the achieved loads for a testset.11.4 Inspect 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 th
39、at it will accurately measure the range of compressiveloads anticipated.11.6 Ensure that the extensometer used (if any) is calibratedproperly such that it will accurately measure the range ofcompressive strains anticipated.11.7 Time, load and deformation data shall be collected at aminimum rate of t
40、wo readings per second during the initialloading ramp portions of tests and a minimum rate of tworeadings per minute during 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 environ
41、mental chamber and temperature coolershall be capable of maintaining the specimen temperaturewithin 61C in range of 0 to 100C, and of changing thespecimen temperature by up to 15C, within the identifiedramp time (see Note 2).11.9 Unless otherwise agreed upon, the temperature stepsfor polyolefin geos
42、ynthetics shall not exceed 7C.NOTE 4Examples that have been successful are a 7C step with a 10000 second dwell time for HDPE.11.10 Unless otherwise agreed upon, the dwell time for allSIM tests shall not be less than 10 000 seconds. Unlessotherwise agreed upon, the total time for SIM tests nottermina
43、ted in rupture shall not be less than 60 000 sec.11.11 The temperature data acquisition rate during SIMshall be a minimum of once per minute.11.12 If desired, accelerated compressive property tests canbe conducted in liquid, vapor, or gaseous mixtures to simulateunique environmental exposures.12. Ca
44、lculation12.1 Ramp and Hold (R+H) Results:12.1.1 Plot stress and secant (creep) modulus vs. strain, andstrain and secant (creep) modulus vs. linear and log time. Usethe offset modulus method to point the curves as described inSection 12.1.2.12.1.2 Identify the elastic strains at the ramp peaks and t
45、heinitial rapid creep strain levels for comparison to the ramp andinitial creep portions of the SIM results.12.2 SIM Test Results (See Appendix X1 for Examples):12.2.1 Compute and plot stress and secant (compressivecreep) modulus vs. strain for each specimen, using the offsetmodulus method to point
46、the curve. Then plot compressivecreep strain, compressive creep modulus, stress and tempera-ture as a function of linear time. Inspect these plots to identifythat the test objectives were achieved.12.2.2 Plot compressive creep modulus (or compressivestrain) vs. log time after rescaling the elevated
47、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 9t9 from each of the d
48、welltimes of higher temperature steps.12.2.3 Re-plot the compressive creep modulus (or strain) vs.log time after rescaling as above and after employing verticalshifts of the modulus (or compressive strain) data for eachelevated temperature to account for system thermal expansion.12.2.4 Report the co
49、mpressive creep modulus and compres-sive strain vs. log time curves as rescaled and vertically shiftedabove and after employing horizontal shifts of the elevatedtemperature segments to the right of the initial referencetemperature dwell segment. The result of this final manipula-tion should be a smooth master curve for each specimensubjected to SIM.12.2.5 The rescaling, vertical shifting and horizontal shift-ing steps generally require some iteration to achieve smoothmaster curves.12.2.6 Prepare a plot of the logarithm of the cumulative shiftfactor vs.
