1、Designation: D7361 07 (Reapproved 2012)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 1C andmay not be used as the sole basis for determination of longterm compressive creep behavior of geosynthetic materia
6、l.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 a
7、ppro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D1621 Test Method for Compressive Properties of RigidCellular PlasticsD2990 Test Methods for Tensile, Compressive, and FlexuralCreep and Creep-Ru
8、pture 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 Definitions: For definitions related to geo
9、synthetics seeTerminology D4439.3.2 Definitions:For definitions related to creep see TestMethods D2990, D5262 and D4439.3.3 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 creepti
10、me-dependent 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 ex
11、tended range 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 (attenu
12、ation) or the 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
13、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 the jurisdiction o
14、f ASTM Committee D35 onGeosynthetics and is the direct responsibility of Subcommittee D35.02 on Endur-ance Properties.Current edition approved July 1, 2012. Published July 2012. DOI: 10.1520/D7361-07R12.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Ser
15、vice 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 Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States13.3.7 offset modulus method or pointingdata
16、analysismethod used to normalize any 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 w
17、hich conditions (particularload) are 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
18、 used to accelerate viscoelastic creepcharacteristics 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 sp
19、ecimens are ramp loaded at a predeter-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 Sectio
20、n 1.5 are very impor-tant in the context 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 drain
21、age applications.NOTE 1Currently, SIM 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
22、load ramp.6. Apparatus6.1 Loading PlatensLoading platens for SIM and R+Htests should conform to Test Method D6364, 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 followin
23、g capabilities andaccessories shall be used for testing:6.2.1 load measurement and control,6.2.2 strain measurement,6.2.3 time measurement,6.2.4 environmental temperature chamber to facilitate con-trol of test conditions,6.2.4.1 temperature measurement and control facilities,6.2.5 other environmenta
24、l 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 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 tes
25、t.8. Test Specimens8.1 Specimens should be at least 120 mm 120 mm (4.7 in. 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 stra
26、in or modulus curve should be confirmedusing at least two R+H tests.9. Conditioning9.1 Compression testing via Test Method D6364 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 environmen
27、tal chamber capable ofcontrolled 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 sta
28、ndard can be shifted fromone reference 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 e
29、nvi-ronmental chamber for all 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
30、 individual reference temperature 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 noniso
31、thermal conditions. Initial trials 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 thespe
32、cimen material. It is suggested that the laboratory perform the plannedSIM temperature steps using an unloaded sacrificial test specimen and,D7361 07 (2012)2with the use of these thermocouples, measure the temperature change ofthe specimen at its thickest or most mass-dense region. The time required
33、for the specimen to reach the target temperature is recorded and used asthe 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
34、 within61.0C of the mean achieved temperature.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 s
35、imilar 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 is applied shallachieve a narrow range of strain rates expressed in percent perminute, as agreed upon. Generally 10 % of the nominalthickness of the test s
36、pecimen per minute or 1.0 6 0.1 mm perminute (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 material
37、s.11.2 Achieve the test loads for R+H 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 acceptabl
38、efor load 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 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 c
39、ell used is calibrated properlysuch that 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 sh
40、all be collected at aminimum rate of two 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
41、 ramp is notnecessary.11.8 The environmental 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, th
42、e temperature stepsfor polyolefin geosynthetics 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, t
43、he total time for SIM tests notterminated 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 simulat
44、eunique environmental exposures.12. Calculation12.1 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 e
45、lastic 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 Results (See Appendix X1 for Examples):12.2.1 Compute and plot stress and secant (compressivecreep) modulus vs. strain for each specimen, us
46、ing the offsetmodulus method to point 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.
47、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 sub
48、tracting a time “t“ from each of the dwelltimes 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
49、thermal expansion.12.2.4 Report the compressive 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
