ASTM D2990-95
(Test Method)Standard Test Methods for Tensile, Compressive, and Flexural Creep and Creep-Rupture of Plastics
Standard Test Methods for Tensile, Compressive, and Flexural Creep and Creep-Rupture of Plastics
SCOPE
1.1 These test methods cover the determination of tensile and compressive creep and creep-rupture of plastics under specified environmental conditions (see 3.1.3).
1.2 While these test methods outline the use of three-point loading for measurement of creep in flexure, four-point loading (which is used less frequently) can also be used with the equipment and principles as outlined in Test Methods D790.
1.3 For measurements of creep-rupture, tension is the preferred stress mode because for some ductile plastics rupture does not occur in flexure or compression.
1.4 Test data obtained by these test methods are relevant and appropriate for use in engineering design.
1.5 The values stated in SI units are to be regarded as the standard. The values in parentheses are for information only.
1.6 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. A specific warning statement is given in 6.8.2.
Note 1—This standard and ISO 899 are similar in content, but are not equivalent.
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Designation: D 2990 – 95 An American National Standard
Standard Test Methods for
Tensile, Compressive, and Flexural Creep and
Creep-Rupture of Plastics
This standard is issued under the fixed designation D 2990; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the Department of Defense.
1. Scope D 1822 Test Method for Tensile-Impact Energy to Break
Plastics and Electrical Insulating Materials
1.1 These test methods cover the determination of tensile
D 2236 Test Method for Dynamic Mechanical Properties of
and compressive creep and creep-rupture of plastics under
Plastics by Means of a Torsional Pendulum
specified environmental conditions (see 3.1.3).
D 4000 Classification System for Specifying Plastic Mate-
1.2 While these test methods outline the use of three-point
rials
loading for measurement of creep in flexure, four-point loading
(which is used less frequently) can also be used with the
3. Terminology
equipment and principles as outlined in Test Methods D 790.
3.1 Definitions of Terms Specific to This Standard:
1.3 For measurements of creep-rupture, tension is the pre-
3.1.1 creep modulus—the ratio of initial applied stress to
ferred stress mode because for some ductile plastics rupture
creep strain.
does not occur in flexure or compression.
3.1.2 creep strain—the total strain, at any given time,
1.4 Test data obtained by these test methods are relevant and
produced by the applied stress during a creep test.
appropriate for use in engineering design.
3.1.2.1 Discussion—The term creep, as used in this test
1.5 The values stated in SI units are to be regarded as the
method, reflects current plastics engineering usage. In scientific
standard. The values in parentheses are for information only.
practice, creep is often defined to be the nonelastic portion of
1.6 This standard does not purport to address all of the
strain. However, this definition is not applicable to existing
safety concerns, if any, associated with its use. It is the
engineering formulas. Plastics have a wide spectrum of retar-
responsibility of the user of this standard to establish appro-
dation times, and elastic portions of strain cannot be separated
priate safety and health practices and determine the applica-
in practice from nonelastic. Therefore, wherever “strain” is
bility of regulatory limitations prior to use. A specific warning
mentioned in these test methods, it refers to the sum of elastic
statement is given in 6.8.2.
strain plus the additional strain with time.
2. Referenced Documents 3.1.3 deformation—a change in shape, size or position of a
test specimen as a result of compression, deflection, or exten-
2.1 ASTM Standards:
sion:
D 543 Test Method for Resistance of Plastics to Chemical
3.1.4 compression—in a compressive creep test, the de-
Reagents
crease in length produced in the gage length of a test specimen.
D 618 Practice for Conditioning Plastics and Electrical
2 3.1.5 deflection—in a flexural creep test, the change in
Insulating Materials for Testing
mid-span position of a test specimen.
D 621 Test Methods for Deformation of Plastics Under
2 3.1.6 extension—in a tensile creep test, the increase in
Load
length produced in the gage length of a test specimen.
D 638 Test Method for Tensile Properties of Plastics
3.1.7 slenderness ratio—the ratio of the length of a column
D 695 Test Method for Compressive Properties of Rigid
of uniform cross section to its least radius of gyration. For
Plastics
specimens of uniform rectangular cross section, the radius of
D 790 Test Methods for Flexural Properties of Unreinforced
gyration is 0.289 times the smaller cross-sectional dimension.
and Reinforced Plastics and Electrical Insulating Materi-
2 For specimens of uniform circular cross section, the radius of
als
gyration is 0.250 times the diameter.
3.1.8 stress—for tensile or compressive creep, the ratio of
These test methods are under the jurisdiction of ASTM Committee D-20 on
the applied load to the initial cross-sectional area. For flexural
Plastics and are the direct responsibility of Subcommittee D20.10 on Mechanical
Properties.
Current edition approved Oct. 10, 1995. Published December 1995. Originally
published as D 2990 – 71. Last previous edition D 2990 – 93a. These test methods
and Practice D 2991 replace Practices D 674, which has been discontinued. Discontinued, see 1984 Annual Book of ASTM Standards, Vol 08.02.
2 4
Annual Book of ASTM Standards, Vol 08.01. Annual Book of ASTM Standards, Vol 08.02.
Copyright © ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.
D 2990
creep, maximum fiber stress is as calculated according to Test 6.1.2 It is recommended that grips permit the final centering
Methods D 790. of the specimen prior to applying the load. Grips that permit a
displacement of the specimen within the grips during load
4. Summary of Test Methods
application are not suitable.
4.1 These test methods consist of measuring the extension
6.2 Compressive Creep:
or compression as a function of time and time-to-rupture, or
6.2.1 Anvils—Parallel anvils shall be used to apply the load
failure of a specimen subject to constant tensile or compressive
to the unconfined-type specimen (see 8.2). One of the anvils of
load under specified environmental conditions.
the machine shall preferably be self-aligning and shall, in order
that the load may be applied evenly over the face of the
5. Significance and Use
specimen, be arranged so that the specimen is accurately
5.1 Data from creep and creep-rupture tests are necessary to
centered and the resultant of the load is through its center.
predict the creep modulus and strength of materials under
Suitable arrangements are shown in Fig. 1 and Fig. 2 of Test
long-term loads and to predict dimensional changes that may
Methods D 621.
occur as a result of such loads.
6.2.2 Guide Tube—A guide tube and fixtures shall be used
5.2 Data from these test methods can be used: (1)to
when testing slender specimens (see 8.3) to prevent buckling.
compare materials, (2) in the design of fabricated parts, (3)to
A suitable arrangement is shown in Fig. 1. The guide tube is a
characterize plastics for long-term performance under constant
3.2-mm (0.125-in.) Schedule 40 stainless steel pipe nipple
load, and ( 4) under certain conditions, for specification
approximately 150 mm (6 in.) long reamed to 6.860 6
purposes.
0.025-mm (0.270 6 0.001-in.) inside diameter.
5.3 For many materials, there may be a specification that
6.3 Flexural Creep:
requires the use of this test method, but with some procedural
6.3.1 Test Rack—A rigid test rack shall be used to provide
modifications that take precedence when adhering to the
support of the specimen at both ends with a span equal to 16
specification. Therefore, it is advisable to refer to that material
( + 4, − 2) times the thickness of the specimen. In order to
specification before using this test method. Table 1 of Classi-
avoid excessive indentation of the specimen, the radius of the
fication D 4000 lists the ASTM materials standards that cur-
support shall be 3.2 mm (0.125 in). Sufficient space must be
rently exist.
allowed below the specimen for dead-weight loading at mid-
6. Apparatus
span.
6.1 Tensile Creep: 6.3.2 Stirrup—A stirrup shall be used which fits over the
6.1.1 Grips—The grips and gripping technique shall be test specimen from which the desired load may be suspended
designed to minimize eccentric loading of the specimen. to provide flexural loading at mid-span. In order to prevent
Swivel or universal joints shall be used beyond each end of the excessive indentation or failure due to stress concentration
specimen. under the stirrup, the radius of the stirrup shall be 3.2 mm
FIG. 1 A Compressive Creep Apparatus Including Details When Used in an Environmental Chamber
D 2990
(0.125 in.). Connection between stirrup and weight shall be strain within the gage length may be calculated. These correc-
made in a manner to avoid nonuniform loading caused by tion factors are dependent on the geometry of the specimen and
misalignment or rack not being level. its drawing behavior, and they must be measured with respect
6.3.3 A suitable arrangement is shown in Fig. 2. to these variables.
6.4 Loading System—The loading system must be so de- 6.5.2 The deflection of the specimen at mid-span shall be
signed that the load applied and maintained on the specimen is measured using a dial gage (with loading springs removed,
within 6 1 % of the desired load. The loading mechanism must with its measuring foot resting on stirrup) or a cathetometer.
allow reproductively rapid and smooth loading as specified in 6.5.3 The accuracy of the deformation measuring device
11.3. In creep-rupture tests, provision must be made to ensure shall be within 6 1 % of the deformation to be measured.
that shock loading, caused by a specimen failure, is not 6.5.4 Deformation measuring devices shall be calibrated
transferred to other specimens undergoing testing. against a precision micrometer screw or other suitable standard
6.4.1 Loading systems that provide a mechanical advantage under conditions as nearly identical as possible with those
require careful design to maintain constant load throughout the encountered in the test. Caution is necessary when using
test. For example, lever systems must be designed so that the deformation measuring devices whose calibration is subject to
load does not change as the lever arm moves during the test. drifting with time and is dependent on temperature and
6.5 Extension, Compression, and Deflection Measurement: humidity.
6.5.1 The extension or compression of specimen gage 6.5.5 Deformation measuring devices shall be firmly at-
length under load shall be measured by means of any device tached to or seated on the specimen so that no slippage occurs.
that will not influence the specimen behavior by mechanical Electrical resistance gages are suitable only if the material
(undesirable deformation, notches, etc.), physical (heating of tested will permit perfect adhesion to the specimen and if they
specimen, etc.), or chemical effects. Preferably the extension are consistent with 6.5.1.
shall be measured directly on the specimen, rather than by grip 6.6 Time Measurement—The accuracy of the time measur-
separation. Anvil displacement may be used to measure com- ing device shall be 6 1 % of the time-to-rupture or failure or
pression. If extension measurements are made by grip separa- the elapsed time of each creep measurement, or both.
tion, suitable correction factors must be determined, so that 6.7 Temperature Control and Measurement:
FIG. 2 Flexural Creep Test Apparatus
D 2990
6.7.1 The temperature of the test space, especially close to 7.2 Purity of Water—Unless otherwise indicated, references
the gage length of the specimen, shall be maintained within 6 to water shall be understood to mean distilled water or water of
2°C by a suitable automatic device and shall be stated in equal purity.
reporting the results. 7.3 Specified Reagents—Should this test method be refer-
enced in a material specification, the specific reagent to be used
NOTE 1—The thermal contraction and expansion associated with small
shall be as stipulated in the specification.
temperature changes during the test may produce changes in the apparent
7.4 Standard Reagents—A list of standard reagents is also
creep rate, especially near transition temperatures.
available in Test Method D 543.
6.7.2 Care must be taken to ensure accurate temperature
measurements over the gage length of the specimen throughout
8. Test Specimens
the test. The temperature measuring devices shall be checked
8.1 Test specimens for tensile creep measurements shall be
regularly against temperature standards and shall indicate the
either Type I or Type II as specified in Test Method D 638. In
temperature of the specimen gage area.
addition to these, specimens specified in Test Method D 1822
6.7.3 Temperature measurements shall be made at frequent
may be used for creep-rupture testing. Tabs may be trimmed to
intervals, or continuously recorded to ensure an accurate
fit grips, as long as the gripping requirements in 6.1.1 are met.
determination of the average test temperature and compliance
8.2 Specimens for unconfined compressive creep tests may
with 6.7.1.
be suitably prepared in the manner described in Test Method
6.8 Environmental Control and Measurement:
D 695, except that the length should be increased so that the
6.8.1 When the test environment is air, the relative humidity
slenderness ratio lies between 11 and 15. The standard test
shall be controlled to within 6 5 % during the test unless
specimen shall be in the form of a right cylinder or prism.
otherwise specified, or unless the creep behavior of the
Preferred specimen cross sections are 12.7 by 12.7 mm (0.50
material under testing has been shown to be unaffected by
by 0.50 in.) or 12.7 mm (0.50 in.) in diameter. Surfaces of the
humidity. The controlling and measuring instruments shall be
test specimens shall be plane and parallel.
stable for long time intervals and accurate to within 6 1%.
8.3 Test specimens for the compressive creep measure-
(The control of relative humidity is known to be difficult at
ments, using the guide tube specified in 6.2.2, shall be slender
temperatures much outside the range of 10 to 40°C (50 to
bars of square cross section with sides measuring 4.850 6
100°F).)
0.025 mm (0.1916 0.001 in.) and the diagonals 6.860 6 0.025
6.8.2 The composition of the test environment shall be
mm (0.270 6 0.001 in.). The specimen shall be 51 mm (2.0 in.)
maintained constant throughout the test. Warning: Safety
long with the ends machined perpendicular to the sides.
precautions should be taken to avoid personal contact, to
8.4 Test specimens for flexural creep measurements shall be
eliminate toxic vapors, and to guard against explosion hazards
rectangular bars conforming to the requirements of Section 5 of
in accordance with any possible hazardous nature of the
Test Methods D 790. Preferred specimen sizes are 63.5 by 12.7
particular environment being used.
by 3.18 mm (2.5 by 0.5 by 0.125 in.) or 127 by 12.7 by 6.4 mm
6.9 Vibration Control—Creep tests are quite sensitive to
(5.0 by 0.5 by 0.25 in.). Close tolerances of specimen and span
shock and vibration. The location of the apparatus, the test
dimensions are not critical as long as
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