ASTM D5323-2019a Standard Practice for Determination of 2&x2009 % Secant Modulus for Polyethylene Geomembranes.pdf

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1、Designation: D5323 19aStandard 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 revision, the year of last

2、 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 the2 % secant modulus for polyethylene geomembranes between0.5 and 5 mm

3、 (20 and 200 mil) using Test Method D6693/D6693M.1.2 This practice will facilitate modulus comparisons ofsimilar materials by standardizing the method for deriving thepoints on the stress-strain curve from which the calculationsare performed.1.3 The values stated in SI units are to be regarded assta

4、ndard. The values given in parentheses are for informationonly.1.4 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 safety, health, and environmental practices and dete

5、r-mine the applicability of regulatory limitations prior to use.1.5 This international standard was developed in accor-dance with internationally recognized principles on standard-ization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recom-mendat

6、ions issued by the World Trade Organization TechnicalBarriers to Trade (TBT) Committee.2. Referenced Documents2.1 ASTM Standards:2D883 Terminology Relating to PlasticsD4439 Terminology for GeosyntheticsD6693/D6693M Test Method for Determining Tensile Prop-erties of Nonreinforced Polyethylene and Non

7、reinforcedFlexible Polypropylene Geomembranes3. Terminology3.1 DefinitionsSee Terminologies D883 and D4439 forgeneral definitions.3.2 Definitions of Terms Specific to This Standard:3.2.1 modulus of elasticity, MPa (FL2), nthe ratio ofstress (nominal) to corresponding strain below the proportionallim

8、it of a material, expressed in force per unit area, such asmegapascals (pounds-force per square inch).3.2.1.1 DiscussionThe stress-strain relations of manyplastics do not conform to Hookes law throughout the elasticrange, but rather deviate therefrom even at strains well belowthe elastic limit. For

9、such materials, the slope of the tangent tothe stress-strain curve at a low strain is usually taken as themodulus of elasticity (or elastic modulus). Since the existenceof a true proportional limit in polyethylene is questionable, andwith the impracticality of measuring it reliably, the use ofsecant

10、 modulus for comparative evaluations is preferred.3.2.2 secant modulus, nthe ratio of stress (nominal) tocorresponding strain at any specified point on the stress-straincurve.3.2.2.1 DiscussionThe measurement units for secantmodulus may change, depending on the standard used. For thepurposes of this

11、 practice, the measurement units shall be forceper unit area (FL2), such as megapascals (pounds-force persquare inch).4. Significance and Use4.1 Where to draw the tangent to determine the modulus ofelasticity is often unclear when performing tensile tests withpolyethylene geomembranes. This problem

12、results in a widevariation in test results and, therefore, makes this propertyunreliable for comparisons.4.2 A secant modulus based on 2 % strain can be usefulwhen making comparisons between materials, in qualitycontrol, and in comparing the same sample after being sub-jected to a nonstandard enviro

13、nment.4.3 Secant modulus is an approximation of modulus ofelasticity and generally results in a lower value than that for themodulus of elasticity.1This practice is under the jurisdiction of ASTM Committee D35 on Geosyn-thetics and is the direct responsibility of Subcommittee D35.10 on Geomembranes.

14、Current edition approved Feb. 1, 2019. Published February 2019. Originallyapproved in 1992. Last previous edition approved in 2019 as D5323 19. DOI:10.1520/D5323-19A.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual B

15、ook 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 StatesThis international standard was developed in accordance with internationally recog

16、nized principles on standardization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.14.4 Although the technique for measuring 2 % secant modu-lus is

17、described here, other percent secant moduli can bemeasured by this practice.5. Procedure5.1 Follow the test procedure described in Test MethodD6693/D6693M.5.1.1 A crosshead speed of 50 mm/min (2 in./min) isrecommended for determining secant modulus, regardless ofthe type of geomembrane being evaluat

18、ed. Faster crossheadspeeds reduce resolution of the points on the curve.5.1.2 High resolution of load and crosshead movement isimportant for obtaining accurate and reproducible values.Where possible, use settings on the testing equipment that willmagnify this region.5.2 Determine the load at 2 % str

19、ain.5.2.1 Industry standard practice uses Test Method D6693/D6693M Type IV specimens. Hence, strain up to the yieldpoint will be based on a gage length of 33 mm (1.3 in.). Thisrepresents the reduced area of the specimen. A gage length of33 mm (1.3 in.) requires a crosshead movement of 0.66 mm(0.026

20、in.) for 2 % strain.6. Calculations6.1 Normal Curve:6.1.1 Calculate the 2 % secant modulus as follows and asshown in Annex A2:2 % secant modulus 5stressstrain(1)where:stress = force/area (at 2 % strain),area = initial cross section area, andstrain = 0.02 (for 2 % secant modulus).6.2 Toe Compensation

21、 Curve:6.2.1 Calculate the 2 % secant modulus for toe compensa-tion as shown in Annex A2.6.3 Pre-Stress CurvesSee Annex A3.6.3.1 This test is invalid unless A3.2 is valid. Otherwise, donot use or perform any calculations.7. Report7.1 In addition to the reporting requirements given inSection 12 of Te

22、st Method D6693/D6693M, report the average2 % secant modulus value and standard deviation based on theresults from individual specimens tested from the sample.8. Keywords8.1 geomembranes; polyethylene; secant modulusANNEXES(Mandatory Information)A1. NORMAL STRESS-STRAIN (FORCE-ELONGATION) CURVEA1.1

23、Fig. A1.1 represents the initial portion of the elasticregion on what would be considered the normal (true) stress-strain curve for polyethylene. The 2 % secant modulus is theslope of the line AC. Point B represents 2 % strain and is equalto a distance that is 0.02 times the original gage length.D53

24、23 19a2A2. 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. Itis an artifact caused by alignment, a take-up of slack, or seatingof the specimen. In order to obtain the correct value of such aparameter as modulu

25、s, this artifact must be compensated for toyield the corrected zero point on the strain axis.A2.2 To correct for this artifact so that the actual zero-strainpoint can be found, construct a tangent to the maximum slopeat the inflection point (D). This is extended to intersect thestrain axis at Point

26、A. Using Point A as zero strain, determinethe new 2 % Strain Point B. Locate Point C on the curve thatcorresponds to B. Using these corrected points, calculate the2 % secant modulus by obtaining the slope of Line AC.A3. PRE-STRESS CURVEA3.1 Opposite of toe compensation is the indication of aload at

27、0 % strain (Fig. A3.1). This may be caused by the startof the chart not being synchronized precisely with the start ofthe crosshead, or by stressing the specimen when mounting itin the grips. If this problem exists, secant modulus cannot becalculated. To correct these problems, it is recommended tha

28、tthe chart be started prior to starting the crosshead, or thespecimen be remounted, as the case may be.A3.2 If the chart is started before the crosshead, 0 % strainis the point at which the load deviates distinctly from the baseline. Note that the procedure for toe compensation may have tobe used to

29、 determine 0 % strain if the chart looks similar to Fig.A2.1.FIG. A1.1 Normal CurveFIG. A2.1 Toe CompensationD5323 19a3ASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentioned inthis standard. Users of this standard are expressl

30、y advised that determination of the validity of any such patent rights, and the riskof infringement of such rights, are entirely their own responsibility.This standard is subject to revision at any time by the responsible technical committee and must be reviewed every five years andif not revised, e

31、ither reapproved or withdrawn. Your comments are invited either for revision of this standard or for additional standardsand should be addressed to ASTM International Headquarters. Your comments will receive careful consideration at a meeting of theresponsible technical committee, which you may atte

32、nd. If you feel that your comments have not received a fair hearing you shouldmake your views known to the ASTM Committee on Standards, at the address shown below.This standard is copyrighted by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959,United States. I

33、ndividual reprints (single or multiple copies) of this standard may be obtained by contacting ASTM at the aboveaddress or at 610-832-9585 (phone), 610-832-9555 (fax), or serviceastm.org (e-mail); or through the ASTM website(www.astm.org). Permission rights to photocopy the standard may also be secured from the Copyright Clearance Center, 222Rosewood Drive, Danvers, MA 01923, Tel: (978) 646-2600; http:/ A3.1 Pre-Stress CurveD5323 19a4