1、Designation: D 5323 92 (Reapproved 2006)Standard Practice forDetermination of 2 % Secant Modulus for PolyethyleneGeomembranes1This standard is issued under the fixed designation D 5323; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revisio
2、n, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) 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
3、 between0.5 and 5 mm (20 and 200 mil) using Test Method D 638.1.2 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 r
4、egarded as thestandard. 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 consult andestablish appropriate safety and health practic
5、es and deter-mine the applicability of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D 638 Test Method for Tensile Properties of Plastics3. Terminology3.1 Definitions:3.1.1 modulus of elasticity, MPa (FL2), nthe ratio ofstress (nominal) to corresponding strain below
6、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 strains well belowthe
7、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 measuring it reliabl
8、y, 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 standard used. For
9、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 withpolyethylene geomembr
10、anes. 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 quality con-trol, and in comparing the same sample after being subjected toa n
11、onstandard 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 bemeasured by this pract
12、ice.5. Procedure5.1 Follow the test procedure described in Test MethodD 638.5.1.1 A cross-head speed of 50 mm/min (2 ipm) is recom-mended for determining secant modulus, regardless of the typeof geomembrane being evaluated. Faster cross-head speedsreduce resolution of the points on the curve.5.1.2 H
13、igh resolution of load and cross-head 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 % strain.1This practice is under the jurisdiction of ASTM Committee D35 on Geosyn-t
14、hetics and is the direct responsibility of Subcommittee D35.10 on Geomembranes.Current edition approved Jan. 1, 2006. Published February 2006. Originallyapproved in 1992. Last previous edition approved in 1999 as D 532392(1999).2For referenced ASTM standards, visit the ASTM website, www.astm.org, or
15、contact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.5.2.1 Industry sta
16、ndard practice uses Test Method D 638Type 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 specimen. A gage length of33 mm (1.3 in.) requires a cross-
17、head 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 5stressstrain(1)where:stress = force/area (at 2 % strain),
18、area = initial cross-section area, andstrain = 0.02 (for 2 % secant modulus).6. Report6.1 In addition to the reporting requirements given insection 12 ofTest Method D 638, report the average 2 % secantmodulus value and standard deviation based on the results fromindividual specimens tested from the
19、sample.7. Keywords7.1 geomembranes; secant modulus; polyethyleneAPPENDIXES(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 the normal (true) stress-strain curve for polyethylene.
20、The 2 % secant modulus is theslope of the lineAC. Point B represents 2 % strain and is equalto a distance that is 0.02 times the original gage length.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. Itis an
21、 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 zero point on the strain axis.FIG. X1.1 Normal CurveFIG. X2.1 Toe CompensationD 5323 92 (2006)
22、2X2.2 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 PointA8. Using PointA8 as zero strain, determinethe new 2 % Strain Point B8. Locate Point C8 on the
23、curve thatcorresponds to B8. Using these corrected points, calculate the2 % secant modulus by obtaining the slope of Line A8C8.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 chart not being synchronize
24、d precisely with the start ofthe cross-head, 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 cross-head, or thespecimen be remounted, as
25、the case may be.X3.2 If the chart is started before the cross-head, 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.ASTM International takes
26、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 patent rights, and the riskof infringement of such rights, are entirely their own respo
27、nsibility.This standard is subject to revision at any time by the responsible technical committee and must be reviewed every five years andif not revised, either reapproved or withdrawn. Your comments are invited either for revision of this standard or for additional standardsand should be addressed
28、 to ASTM International Headquarters. Your comments will receive careful consideration at a meeting of theresponsible technical committee, which you may attend. 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 a
29、ddress 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 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).FIG. X3.1 Pre-Load CurveD 5323 92 (2006)3
