ASTM D6992-2016 red 6306 Standard Test Method for Accelerated Tensile Creep and Creep-Rupture of Geosynthetic Materials Based on Time-Temperature Superposition Using the Stepped Is.pdf

1、Designation: D6992 03 (Reapproved 2015)D6992 16Standard Test Method forAccelerated Tensile Creep and Creep-Rupture ofGeosynthetic Materials Based on Time-TemperatureSuperposition Using the Stepped Isothermal Method1This standard is issued under the fixed designation D6992; the number immediately fol

2、lowing the designation 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 metho

3、d covers accelerated testing for tensile creep, and tensile creep-rupture properties using the SteppedIsothermal Method (SIM).1.2 The test method is focused on geosynthetic reinforcement materials such as yarns, ribs of geogrids, or narrow geotextilespecimens.1.3 The SIM tests are laterally unconfin

4、ed 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 SIMtests defined in terms of the percentage of UltimateTensile Strength (TULT).Additionally, the tensile test can

5、be designed to provideestimates 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 additionalestimates of the initial elastic and initial rapid creep strain levels appr

6、opriate for the SIM results.1.6 This method can be used to establish the sustained load creep and creep-rupture characteristics of a geosynthetic. Resultsof this method are to be used to augment results of Test Method D5262 and may not be used as the sole basis for determinationof long term creep an

7、d 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 respons

8、ibilityof the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatorylimitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D2990 Test Methods for Tensile, Compressive, and Flexural Creep and Creep-Rupture of PlasticsD4439

9、 Terminology for GeosyntheticsD4595 Test Method for Tensile Properties of Geotextiles by the Wide-Width Strip MethodD5262 Test Method for Evaluating the Unconfined Tension Creep and Creep Rupture Behavior of Geosynthetics3. Terminology3.1 For definitions related to geosynthetics see Terminology D443

10、9.3.2 For definitions related to creep see Test Methods D2990 and D5262.3.3 Definitions of Terms Specific to This Standard:3.3.1 creep modulusin SIM analysis, the load divided by the percent strain at any given point in time.3.3.2 dwell timetime during which conditions (particular load) are held con

11、stant between temperature steps.1 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 May 1, 2015Feb. 15, 2016. Published June 2015February 2016. Originally approved

12、 in 2003. Last previous edition approved in 20092015 asD6992 03(2009).03(2015). DOI: 10.1520/D6992-03R15.10.1520/D6992-16.2 For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume information, refe

13、r to the standards Document Summary page on the ASTM website.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. Becauseit may not be technically possible to adequately depict all cha

14、nges accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current versionof the standard as published by ASTM is to be considered the official document.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. U

15、nited States13.3.3 mean test temperaturethe arithmetic average of all temperature readings of the atmosphere surrounding the testspecimen for a particular temperature step, starting at a time not later than established temperature ramp time, and finishing at atime just prior to the subsequent temper

16、ature reset.3.3.4 offset modulus method or pointingdata analysis method used to normalize any prestrain in the samples by shifting theorigin of a stress versus strain curve to an axis origin of coordinates; that is, to coordinates (0,0).3.3.5 ramp and hold (R+H) testa creep test of very short durati

17、on; for example, 100 to 1000 s.3.3.6 shift factorthe displacement along the log time axis by which a section of the creep or creep modulus curve is movedto create the master curve at the reference temperature. Shift factors are denoted by the symbol AT when the displacements aregenerally to shorter

18、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 creepresponse of a material being tested under load.3.3.8 tensile creeptime-dep

19、endent deformation that occurs when a specimen is subjected to a constant tensile load.3.3.9 tensile creep-rupturetime dependent rupture that terminates a creep test at high stress levels.3.3.10 time-temperature superpositionthe practice of shifting viscoelastic response curves obtained at different

20、 temperaturesalong a horizontal log time axis so as to achieve a master curve covering an extended range of time.3.3.11 ultimate tensile strength (TULT)short term strength value used to normalize creep rupture strengths.3.3.12 viscoelastic responserefers to polymeric creep, strain, stress relaxation

21、 or a combination thereof.4. Summary of Test Method4.1 SIMA procedure whereby specified temperature steps and dwell times are used to accelerate viscoelastic creepcharacteristics during which strain and load are monitored as a function of time.4.1.1 Tensile CreepConstant tensile load in conjunction

22、with specified temperature steps and dwell times are used toaccelerate creep strain response.4.1.2 Tensile Creep-RuptureA tensile creep test where high stress levels are used during testing to ensure rupture, whilespecified temperature steps and dwell times are used to accelerate creep strain respon

23、se characteristics. Strain is monitored as afunction of time.4.2 Tensile TestsTest specimens are rapidly loaded over a short period to achieve rupture. The selection of a suitable tensiletest is dependent upon the type of material tested (see Section 8). Tensile tests to support creep and creep-rupt

24、ure tests areperformed under the same control of loading or strain rate as used to load or strain the test specimens during creep or creep rupturetests.4.3 R+HTest specimens are ramp loaded at a predetermined loading rate to a predetermined load and held under constant load(short term creep test).5.

25、 Significance and Use5.1 Use of the Stepped Isothermal Method decreases the time required for creep to occur and the obtaining of the associateddata.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

26、 used to calculate the creep modulus of materials as a function of time. These data are then used to predictthe long-term creep deformation expected of geosynthetics used in reinforcement applications.NOTE 1Currently, SIM testing has focused mainly on woven and knitted geogrids and woven geotextiles

27、 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

28、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, strainand variations thereof for SIM tests.5.6 Ramp and Hold (R+H) testing is done to estab

29、lish the range of creep strains experienced in the brief period of very rapidresponse following the peak of the load ramp.6. Apparatus6.1 GripsGrips for SIM and R+H tests should be the same as the grips for ultimate strength tensile tests. Neither slippage norexcessive stress causing premature ruptu

30、re should be allowed to occur.6.2 Testing MachineA universal testing machine or a dead-weight loading system with the following capabilities andaccessories shall be used for testing.D6992 1626.2.1 Load measurement and control,6.2.2 Strain measurement and control,6.2.3 Time measurement,6.2.4 Environm

31、ental 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, and6.2.6 Computer data acquisition and control.7. Sampling7.1 The specimens used for tensile, R+H and SIM tests should all be t

32、aken from the same sample.7.2 Remove sufficient test specimens for tensile testing in accordance with the selected tensile testing procedure (see Section8).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 Sp

33、ecimens8.1 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 2Single ge

34、ogrid ribs and narrow strip specimens are preferred to determine the effect of applied load on the tensile creep properties of thematerial separate from the effect of sample width on the tensile properties of the material. However, correlation between narrow geotextile strips or singlegeogrid ribs t

35、o 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 Asingle specimen is usually sufficient to define a master creep or relaxation curve using

36、 the SIM. However, if only a singleSIM test is to be performed, the location of the onset of creep strain or modulus curve should be confirmed using at least two shortterm creep (R+H) tests.8.5.2 Generally 12 to 18 specimens are needed to define a stress-rupture curve representing multiple rupture t

37、imes. Fewerspecimens would be needed to define a specific region of the curve, for example the percent TULT at 1 106 h (= 110 year) rupturelife.9. Conditioning9.1 Tensile and SIM testing shall be conducted using 20 6 1C as the reference or temperature standard. If the laboratory isnot within this ra

38、nge, perform tensile tests in a suitable environmental chamber capable of controlled cooling and heating. Theenvironmental chamber should have a programmable or set-point controller so as to maintain temperature to 20 6 1C. Whenagreed to, a reference temperature other than 20C can be utilized. Also,

39、 when agreed to, the results of testing under this standardcan 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.

40、3 Record the relative humidity in the laboratory or environmental chamber for all tests.10. Selection of Test Conditions10.1 The standard environment for testing is dry, since the effect of elevated temperature is to reduce the humidity of ambientair without special controls.10.2 The standard refere

41、nce temperature is 20C unless otherwise agreed to. The individual reference temperature for each SIMtest is the average achieved temperature of the first isothermal dwell.10.3 Testing temperatures are to be within 62C of the target test temperatures. It is critically important that the test specimen

42、has equilibrated throughout its thickness so as to avoid nonisothermal conditions. Initial trials are necessary to establish thisminimum equilibrium time.NOTE 3Laboratory experience has suggested that the use of calibrated thermocouples located near, affixed to or embedded within the test specimenma

43、y facilitate a successful temperature compliance test for the specimen material. It is suggested that the laboratory perform the planned SIM temperaturesteps using an unloaded sacrificial test specimen and, with the use of these thermocouples, measure the temperature change of the specimen at its th

44、ickestor 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 upperlimit of the temperature ramp time is not known. Successful tests with some materials have been run with temperature ramp times of up to four m

45、inutes.10.4 Test temperatures are to be maintained within 61.0C of the mean achieved temperature.D6992 16310.4.1 Temperature steps and dwell times must be such that the steady state creep rate at the beginning of a new step is not sodifferent from that of the previous that it cannot be established w

46、ithin the identified ramp time.11. Procedures11.1 The same or similar load or strain control shall be applied to the tensile tests and the load ramp portion of R+H and SIM(creep and creep-rupture) tests. The load rate control (in units of kN per min) that is applied shall achieve a narrow range of s

47、trainrates expressed in percent per minute, as agreed upon. Generally 10 6 3 % per min (or 20 6 3 % per min for European practice)will be satisfactory.NOTE 4A linear ramp of load versus time will not generally result in a linear strain versus time relationship because stress versus strain curves are

48、not linear for most geosynthetic materials.11.2 Achieve the test loads for R+H and SIM tests within 62 % of the target loads, and maintain any achieved load within60.5 % of its values for the duration of the test. A brief overshoot of the target load that is within 62 % of the target load andlimited

49、 to a 1 to 2 s time duration is acceptable for load control systems.11.3 Replicate test loads for R+H and SIM tests should be within 60.5 % of the average of the achieved loads for a test set.11.4 Pretensioning up in accordance with the governing tensile test is acceptable. The method used to define zero strain is tobe identified and reported.11.5 The same or similar grips shall be used for tensile, R+H and SIM tests. Care should be taken to use grips that do not initiatefailure or incur slippage at stress levels which may produce specimen rupture