ASTM D2991-84

Recommended Practice for Testing Stress-Relaxation of Plastics (Withdrawn 1990)

General Information

• Status: Withdrawn
• Withdrawal Date: 25-Oct-1990
• ICS: 83.080.01 - Plastics in general
• Technical Committee: D20 - Plastics
• Drafting Committee: D20.10 - Mechanical Properties

Standards Content (Sample)

ASTM D2993 84 R 0759530 0028437 8 I
Designation: D 2991 - 84
4cni
, AXîERICAN SOCIETY FOR TESTING ANb.MATERIALS
1916 Rsce Ct., Philadelphia, Pa. 19103
Reprinted from the Annual Book of ASTM Standards, Copyright ASTM
If net listed in the current combined index, will appear in the next editio!.
Standard Practice for Testing
STRESS-RELAXATION OF PLASTICS’
This standard is issued under the fixed designation D 2991; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revkion. A number in parentheses indicates the year of last reapproval.
A superscript epsilon (e) indicates an editorial change since the lasf revision or reapproval.
1. Scope mental conditions and hence is useful in evalu-
ating the effect of such changes.
1, I This practice covers the determination of
the time-dependence of stress (stress relaxation)
5. Grips
of plastics resisting long-duration constant strains
5.1 The grips and gripping technique shall be
at conditions of constant temperature and rela-
designed to minimize eccentric loading of the
tive humidity and negligible vibration.
specimen. Swivel or universal joints shall be used
1.2 This standard may involve hazardoits ma-
beyond each end of the specimen. The grips shall
terials, operations, and equipment. This standard
be so designed that no slippage of the specimen
does not purport to address all of the safity prob-
occurs.
lems associated with its use. It is the responsibil-
NOTE I-It is recommended that grips permit the
ity of whoever uses this standard to consult and
final centering of the specimen prior to applying the
establish appropriate safety and health practices
strain or load. Grips that permit a displacement of the
and determine the applicability of regulatoiy limi-
specimen within the grips during load application are
tations prior io use.
not suitable.
2. Applicable Documents
6. Temperature Control and Measurement
2.1 ASTM Standards:
6.1 The temperature of the test space, espe-
D638 Test Method for Tensile Properties of
cially close to the gage length of the specimen,
Plastics’
shall be maintained within +_TC by a suitable
D695 Test Method for Compressive Proper-
automatic device and shall be stated in reporting
ties of Rigid Plastics’
the results.
NOTE 2-The thermal contraction and expansion
3. Defdtions
associated with small temperature changes during the
test may produce changes in the apparent relaxation
3.1 stress relaxation-the time-dependent de-
rate especially near transition temperatures. Small
crease in stress in a solid under given constraint
changes in temperature near transitions also produce
conditions.
significant changes in relaxation rate.
3.2 initial stress-the stress introduced into a
6.2 Care must be taken to ensure accurate
specimen by imposing the given constraint con-
temperature measurements over the gage length
ditions before stress relaxation takes place.
of the specimen throughout the test. The tem-
be checked reg-
4. Significance and Use perature-measuring devices shall
4.1 Data from stress-relaxation tests are useful
’ This practice is under the jurisdiction of ASTM Committee
. in predicting the reduction of stress in materials
D-20 on Plastics and is the direct responsibility ofSubcommittee
subjected to constant deformation for long times,
D20.10 on Mechanical Properiies.
such as the decrease in tightness of bolted or
Current edition approved Nov. 30, 1984. hbüshed January
1985.OriginallypubIishedasD2991- 71. Lastpreviousedition
riveted joints.
D 2991 - 71(1978). This practice and Methods D 2990 replace
4.2 This test is highly sensitive to small
Recommended Practices D 674, which have been discontinued.
‘Annual Book ofASTMStandards. Vol 08.01.
changes in material composition and environ-
-,

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ASTM D2991 84 m 0'759510 00284LB T m
D 2991
ularly against temperature standards and shall and strain within 1 % and the zero should not
drift with time.
indicate the temperature of the specimen gage
area. 9.2 In order to obtain sufficient sensitivity the
gage length of the specimen should be as long as
6.3 Temperature measurements shall be made
or continuously recorded is practical but consistent with other require-
at frequent intervals,
ments, such as uniformity of temperature distri-
to ensure an accurate determination of the aver-
age test temperature and compliance with 5.1. bution along the gage length. It is always desirable
and often necessary to use an averaging type
7. Environmental Control and Measurement extensometer or two extensometers acting on
opposite faces of the specimen. The extensome-
7.1 When the test environment is air, the rel-
ters and load cells should be built of materiais
ative humidity shall be controlled to within
that are dimensionally stable at the test temper-
f5 % during the test u
...