1、Designation: D5323 92 (Reapproved 2018)D5323 19Standard Practice forDetermination of 2 % Secant Modulus for PolyethyleneGeomembranes1This standard is issued under the fixed designation D5323; the number immediately following the designation indicates the year oforiginal adoption or, in the case of r
2、evision, 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 practice presents a technique for calculating the 2 % secant modulus for polyethylene geomem
3、branes between 0.5 and5 mm (20 and 200 mil) using Test Method D638.1.2 This practice will facilitate modulus comparisons of similar materials by standardizing the method for deriving the pointson the stress-strain curve from which the calculations are performed.1.3 The values stated in SI units are
4、to be regarded as standard. The values given in parentheses are for information only.1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibilityof the user of this standard to establish appropriate safety, health, and environmen
5、tal practices and determine the applicability ofregulatory limitations prior to use.1.5 This international standard was developed in accordance with internationally recognized principles on standardizationestablished in the Decision on Principles for the Development of International Standards, Guide
6、s and Recommendations issuedby the World Trade Organization Technical Barriers to Trade (TBT) Committee.2. Referenced Documents2.1 ASTM Standards:2D638 Test Method for Tensile Properties of PlasticsD883 Terminology Relating to PlasticsD4439 Terminology for Geosynthetics3. Terminology3.1 DefinitionsS
7、ee Terminologies D883 and D4439 for general definitions.3.2 Definitions:Definitions of Terms Specific to This Standard:3.2.1 modulus of elasticity, MPa (FL2), nthe ratio of stress (nominal) to corresponding strain below the proportional limitof a material, expressed in force per unit area, such as m
8、egapascals (pounds-force per square inch).3.2.1.1 DiscussionThe stress-strain relations of many plastics do not conform to Hookes law throughout the elastic range, but rather deviatetherefrom even at strains well below the elastic limit. For such materials, the slope of the tangent to the stress-str
9、ain curve at a lowstrain is usually taken as the modulus of elasticity (or elastic modulus). Since the existence of a true proportional limit inpolyethylene is questionable, and with the impracticality of measuring it reliably, the use of secant modulus for comparativeevaluations is preferred.3.2.2
10、secant modulus, nthe ratio of stress (nominal) to corresponding strain at any specified point on the stress-strain curve.3.2.2.1 Discussion1 This practice is under the jurisdiction of ASTM Committee D35 on Geosynthetics and is the direct responsibility of Subcommittee D35.10 on Geomembranes.Current
11、edition approved July 1, 2018Jan. 15, 2019. Published July 2018February 2019. Originally approved in 1992. Last previous edition approved in 20112018 asD5323 92 (2011).(2018). DOI: 10.1520/D5323-92R18.10.1520/D5323-19.2 For referencedASTM standards, visit theASTM website, www.astm.org, or contactAST
12、M Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume information, refer 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
13、 to the previous version. Becauseit 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 versionof the standard as published by ASTM is to be considered the official document.Copyr
14、ight ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1The measurement units for secant modulus may change, depending on the standard used. For the purposes of this practice, themeasurement units shall be force per unit area (FL2), such as megapa
15、scals (pounds-force per square inch).4. Significance and Use4.1 Where to draw the tangent to determine the modulus of elasticity is often unclear when performing tensile tests withpolyethylene geomembranes. This problem results in a wide variation in test results and, therefore, makes this property
16、unreliablefor comparisons.4.2 A secant modulus based on 2 % strain can be useful when making comparisons between materials, in quality control, andin comparing the same sample after being subjected to a nonstandard environment.4.3 Secant modulus is an approximation of modulus of elasticity and gener
17、ally results in a lower value than that for the modulusof elasticity.4.4 Although the technique for measuring 2 % secant modulus is described here, other percent secant moduli can be measuredby this practice.5. Procedure5.1 Follow the test procedure described in Test Method D638.5.1.1 Acrosshead spe
18、ed of 50 mm/min (2 ipm)in./min) is recommended for determining secant modulus, regardless of the typeof geomembrane being evaluated. Faster crosshead speeds reduce resolution of the points on the curve.5.1.2 High resolution of load and crosshead movement is important for obtaining accurate and repro
19、ducible values. Wherepossible, use settings on the testing equipment that will magnify this region.5.2 Determine the load at 2 % strain.5.2.1 Industry standard practice uses Test Method D638 Type IV specimens and permits the test to be conducted without anextensometer. specimens. Hence, strain up to
20、 the yield point will be based on a gage length of 33 mm (1.3 in.). This representsthe reduced area of the specimen. A gage length of 33 mm (1.3 in.) requires a crosshead movement of 0.66 mm (0.026 in.) for2 % strain.5.2.2 Do not compare test results obtained with the use of extensometers to those o
21、btained without the use of extensometers.5.3 Calculate the 2 % secant modulus as follows:2%secant modulus5stressstrain (1)where:stress = force/area (at 2 % strain),area = initial cross section area, andstrain = 0.02 (for 2 % secant modulus).6. Calculations6.1 Normal Curve:6.1.1 Calculate the 2 % sec
22、ant modulus as follows and as shown in Annex A2:2%secant modulus5stressstrain (1)where:stress = force/area (at 2 % strain),area = initial cross section area, andstrain = 0.02 (for 2 % secant modulus).6.2 Toe Compensation Curve:6.2.1 Calculate the 2 % secant modulus for toe compensation as shown in A
23、nnex A2.6.3 Pre-Stress CurvesSee Annex A3.6.3.1 This test is invalid unless A3.2 is valid. Otherwise, do not use or perform any calculations.7. Report7.1 In addition to the reporting requirements given in Section 12 of Test Method D638, report the average 2 % secant modulusvalue and standard deviati
24、on based on the results from individual specimens tested from the sample.8. Keywords8.1 geomembranes; polyethylene; secant modulusD5323 192APPENDIXES(Nonmandatory Information)X1. NORMAL STRESS-STRAIN (FORCE-ELONGATION) CURVEX1.1 Fig. X1.1 represents the initial portion of the elastic region on what
25、would be considered the normal (true) stress-strain curvefor polyethylene. The 2 % secant modulus is the slope of the line AC. Point B represents 2 % strain and is equal to a distance thatis 0.02 times the original gage length.ANNEXES(Mandatory Information)A1. NORMAL STRESS-STRAIN (FORCE-ELONGATION)
26、 CURVEA1.1 Fig.A1.1 represents the initial portion of the elastic region on what would be considered the normal (true) stress-strain curvefor polyethylene. The 2 % secant modulus is the slope of the line AC. Point B represents 2 % strain and is equal to a distance thatis 0.02 times the original gage
27、 length.A2. TOE COMPENSATIONA2.1 In some stress-strain curves (Fig. A2.1), a toe region, AD, exists that does not represent a property of the material. It is anartifact caused by alignment, a take-up of slack, or seating of the specimen. In order to obtain the correct value of such a parameteras mod
28、ulus, this artifact must be compensated for to yield the corrected zero point on the strain axis.A2.2 To correct for this artifact so that the actual zero-strain point can be found, construct a tangent to the maximum slope at theinflection point (D). This is extended to intersect the strain axis at
29、Point A. Using Point A as zero strain, determine the new 2 %Strain Point B. Locate Point C on the curve that corresponds to B. Using these corrected points, calculate the 2 % secant modulusby obtaining the slope of Line AC.A3. PRE-STRESS CURVEA3.1 Opposite of toe compensation is the indication of a
30、load at 0 % strain (Fig. A3.1). This may be caused by the start of thechart not being synchronized precisely with the start of the crosshead, or by stressing the specimen when mounting it in the grips.If this problem exists, secant modulus cannot be calculated. To correct these problems, it is recom
31、mended that the chart be startedprior to starting the crosshead, or the specimen be remounted, as the case may be.FIG. X1.1A1.1 Normal CurveD5323 193A3.2 If the chart is started before the crosshead, 0 % strain is the point at which the load deviates distinctly from the base line.Note that the proce
32、dure for toe compensation may have to be used to determine 0 % strain if the chart looks similar to Fig. A2.1.X2. TOE COMPENSATIONX2.1 In some stress-strain curves (Fig. X2.1), a toe region, AD, exists that does not represent a property of the material. It is anartifact caused by alignment, a take-u
33、p of slack, or seating of the specimen. In order to obtain the correct value of such a parameteras modulus, this artifact must be compensated for to yield the corrected zero point on the strain axis.X2.2 To correct for this artifact so that the true zero-strain point can be found, construct a tangen
34、t to the maximum slope at theinflection point (D). This is extended to intersect the strain axis at Point A. Using Point A as zero strain, determine the new 2 %Strain Point B. Locate Point C on the curve that corresponds to B. Using these corrected points, calculate the 2 % secant modulusby obtainin
35、g the slope of Line AC.FIG. X2.1A2.1 Toe CompensationFIG. X3.1A3.1 Pre-Load Pre-Stress CurveD5323 194X3. PRE-STRESS CURVEX3.1 Opposite of toe compensation is the indication of a load at 0 % strain (Fig. X3.1). This may be caused by the start of thechart not being synchronized precisely with the star
36、t of the crosshead, or by stressing the specimen when mounting it in the grips.If this problem exists, secant modulus cannot be calculated. To correct these problems, it is recommended that the chart be startedprior to starting the crosshead, or the specimen be remounted, as the case may be.X3.2 If
37、the chart is started before the crosshead, 0 % strain is the point at which the load deviates distinctly from the base line.Note that the procedure for toe compensation may have to be used to determine 0 % strain if the chart looks similar to Fig. X2.1.ASTM International takes no position respecting
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