1、Designation: D5323 92 (Reapproved 2018)Standard 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,
2、 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 the2 % secant modulus for polyethylene geomembranes be
3、tween0.5 and 5 mm (20 and 200 mil) using Test Method D638.1.2 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 regar
4、ded asstandard. 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
5、 and deter-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 Rec
6、om-mendations issued by the World Trade Organization TechnicalBarriers to Trade (TBT) Committee.2. Referenced Documents2.1 ASTM Standards:2D638 Test Method for Tensile Properties of Plastics3. Terminology3.1 Definitions:3.1.1 modulus of elasticity, MPa (FL2), nthe ratio ofstress (nominal) to corresp
7、onding strain below the proportionallimit of a material, expressed in force per unit area, such asmegapascals (pounds-force per square inch).3.1.1.1 DiscussionThe stress-strain relations of manyplastics do not conform to Hookes law throughout the elasticrange, but rather deviate therefrom even at st
8、rains well belowthe elastic limit. For 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
9、measuring it reliably, the use ofsecant modulus for comparative evaluations is preferred.3.1.2 secant modulus, nthe ratio of stress (nominal) tocorresponding strain at any specified point on the stress-straincurve.3.1.2.1 DiscussionThe measurement units for secantmodulus may change, depending on the
10、 standard used. For thepurposes of this 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 withp
11、olyethylene geomembranes. This problem 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 b
12、eing sub-jected to a nonstandard environment.4.3 Secant modulus is an approximation of modulus ofelasticity and generally results in a lower value than that for themodulus of elasticity.4.4 Although the technique for measuring 2 % secant modu-lus is described here, other percent secant moduli can be
13、measured by this practice.5. Procedure5.1 Follow the test procedure described in Test MethodD638.5.1.1 A crosshead speed of 50 mm/min (2 ipm) is recom-mended for determining secant modulus, regardless of the type1This practice is under the jurisdiction of ASTM Committee D35 on Geosyn-thetics and is
14、the direct responsibility of Subcommittee D35.10 on Geomembranes.Current edition approved July 1, 2018. Published July 2018. Originally approvedin 1992. Last previous edition approved in 2011 as D5323 92 (2011). DOI:10.1520/D5323-92R18.2For referenced ASTM standards, visit the ASTM website, www.astm
15、.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.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United StatesThis interna
16、tional standard was developed in accordance with internationally recognized 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) Commi
17、ttee.1of geomembrane being evaluated. Faster crosshead speedsreduce 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
18、.5.2 Determine the load at 2 % strain.5.2.1 Industry standard practice uses Test Method D638Type IV specimens and permits the test to be conductedwithout an extensometer. Hence, strain up to the yield pointwill be based on a gage length of 33 mm (1.3 in.). Thisrepresents the reduced area of the spec
19、imen. A gage length of33 mm (1.3 in.) requires a crosshead movement of 0.66 mm(0.026 in.) for 2 % strain.5.2.2 Do not compare test results obtained with the use ofextensometers to those obtained without the use of extensom-eters.5.3 Calculate the 2 % secant modulus as follows:2 % secant modulus 5str
20、essstrain(1)where:stress = force/area (at 2 % strain),area = initial cross section area, andstrain = 0.02 (for 2 % secant modulus).6. Report6.1 In addition to the reporting requirements given inSection 12 of Test Method D638, report the average 2 % secantmodulus value and standard deviation based on
21、 the results fromindividual specimens tested from the sample.7. Keywords7.1 geomembranes; polyethylene; secant modulusAPPENDIXES(Nonmandatory Information)X1. NORMAL STRESS-STRAIN (FORCE-ELONGATION) CURVEX1.1 Fig. X1.1 represents the initial portion of the elasticregion on what would be considered th
22、e 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.FIG. X1.1 Normal CurveD5323 92 (2018)2X2. TOE COMPENSATIONX2.1 In some stress-strain curves (Fi
23、g. X2.1), 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 modulus, this artifact must be compensated for toyield the corrected z
24、ero point on the strain axis.X2.2 To correct for this artifact so that the true 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 A. Using Point A as zero strain, determinethe new 2 % Strain Point
25、 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.X3. PRE-STRESS CURVEX3.1 Opposite of toe compensation is the indication of aload at 0 % strain (Fig. X3.1). This may be caused by the startof the char
26、t 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 thatthe chart be started prior to starting the crosshead, or thespeci
27、men be remounted, as the case may be.X3.2 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 determine 0 % strain if the chart looks similar to Fig.X2.1.FIG.
28、X2.1 Toe CompensationFIG. X3.1 Pre-Load CurveD5323 92 (2018)3ASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this standard. Users of this standard are expressly advised that determination of the validity of any such p
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31、r 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. Individual reprints (single or multiple copies) of this sta
32、ndard 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:/ 92 (2018)4
