ASTM D5323-92(1999)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
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Designation:D5323–92 (Reapproved 1999)
Standard Practice for
Determination of 2% Secant Modulus for Polyethylene
Geomembranes
This standard is issued under the fixed designation D5323; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope 3.1.2 secant modulus, n—the ratio of stress (nominal) to
corresponding strain at any specified point on the stress-strain
1.1 This practice presents a technique for calculating the
curve.
2% secant modulus for polyethylene geomembranes between
3.1.2.1 Discussion—The measurement units for secant
0.5 and 5 mm (20 and 200 mil) using Test Method D638.
modulus may change, depending on the standard used. For the
1.2 This practice will facilitate modulus comparisons of
purposes of this practice, the measurement units shall be force
similar materials by standardizing the method for deriving the
−2
per unit area (FL ), such as megapascals (pounds-force per
points on the stress-strain curve from which the calculations
square inch).
are performed.
1.3 The values stated in SI units are to be regarded as the
4. Significance and Use
standard. The values given in parentheses are for information
4.1 Where to draw the tangent to determine the modulus of
only.
elasticity is often unclear when performing tensile tests with
1.4 This standard does not purport to address all of the
polyethylene geomembranes. This problem results in a wide
safety concerns, if any, associated with its use. It is the
variation in test results and therefore makes this property
responsibility of the user of this standard to consult and
unreliable for comparisons.
establish appropriate safety and health practices and deter-
4.2 A secant modulus based on 2% strain can be useful
mine the applicability of regulatory limitations prior to use.
when making comparisons between materials, in quality con-
2. Referenced Documents trol,andincomparingthesamesampleafterbeingsubjectedto
a nonstandard environment.
2.1 ASTM Standards:
4.3 Secant modulus is an approximation of modulus of
D638 Test Method for Tensile Properties of Plastics
elasticityandgenerallyresultsinalowervaluethanthatforthe
3. Terminology modulus of elasticity.
4.4 Althoughthetechniqueformeasuring2%secantmodu-
3.1 Definitions:
−2
lus is described here, other percent secant moduli can be
3.1.1 modulus of elasticity, MPa (FL ), n—the ratio of
measured by this practice.
stress(nominal)tocorrespondingstrainbelowtheproportional
limit of a material, expressed in force per unit area, such as
5. Procedure
megapascals (pounds-force per square inch).
5.1 Follow the test procedure described in Test Method
3.1.1.1 Discussion—The stress-strain relations of many
D638.
plastics do not conform to Hooke’s law throughout the elastic
5.1.1 A cross-head speed of 50 mm/min (2 ipm) is recom-
range, but rather deviate therefrom even at strains well below
mendedfordeterminingsecantmodulus,regardlessofthetype
the elastic limit. For such materials, the slope of the tangent to
of geomembrane being evaluated. Faster cross-head speeds
the stress-strain curve at a low strain is usually taken as the
reduce resolution of the points on the curve.
modulus of elasticity (or elastic modulus). Since the existence
5.1.2 High resolution of load and cross-head movement is
ofatrueproportionallimitinpolyethyleneisquestionable,and
important for obtaining accurate and reproducible values.
with the impracticality of measuring it reliably, the use of
Where possible, use settings on the testing equipment that will
secant modulus for comparative evaluations is preferred.
magnify this region.
5.2 Determine the load at 2% strain.
5.2.1 Industry standard practice uses Test Method D638
This practice is under the jurisdiction of ASTM Committee D-35 on Geosyn-
Type IV specimens and permits the test to be conducted
thetics and is the direct responsibility of Subcommittee D35.10 on Geomembranes.
without an extensometer. Hence, strain up to the yield point
Current edition approved Oct. 15, 1992. Published December 1992.
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