ASTM E328-02(2008)
(Test Method)Standard Test Methods for Stress Relaxation Tests for Materials and Structures
Standard Test Methods for Stress Relaxation Tests for Materials and Structures
SIGNIFICANCE AND USE
Relaxation test data are necessary when designing most mechanically fastened joints to assure the permanent tightness of bolted or riveted assemblies, press or shrink-fit components, rolled-in tubes, etc. Other applications include predicting the decrease in the tightness of gaskets, in the hoop stress of solderless wrapped connections, in the constraining force of springs, and the stability of wire tendons in prestressed concrete.
The ability of a material to relax at high-stress concentrations such as are present at notches, inclusions, cracks, holes, fillets, etc., may be predicted from stress relaxation data. Such test data are also useful to judge the heat-treatment condition necessary for the thermal relief of residual internal stresses in forgings, castings, weldments, machined or cold-worked surfaces, etc. The tests outlined in these methods are limited to conditions of approximately constant constraint and environment.
The test results are highly sensitive to small changes in environmental conditions and thus require precise control of test conditions and methods.
The reproducibility of data will depend on the manner with which all test conditions are controlled. The effects of aging or residual stress may significantly affect results, as may variations in material composition.
SCOPE
Note 1—The method of testing for the stress relaxation of plastics has been withdrawn from this standard, and the responsibility has been transferred to Practice D 2991.
1.1 These test methods cover the determination of the time dependence of stress (stress relaxation) in materials and structures under conditions of approximately constant constraint, constant environment, and negligible vibration. In the procedures recommended, the material or structure is initially constrained by externally applied forces, and the change in the external force necessary to maintain this constraint is determined as a function of time.
1.2 Specific methods for conducting stress relaxation tests on materials subjected to tension, compression, bending and torsion stresses are described in Parts A, B, C, and D, respectively. These test methods also include recommendations for the necessary testing equipment and for the analysis of the test data.
1.3 It is recognized that the long time periods required for these types of tests are often unsuited for routine testing or for specification in the purchase of material. However, these tests are valuable tools in obtaining practical design information on the stress relaxation of materials subjected to the conditions enumerated, and in investigations of the fundamental behavior of materials.
1.4 Units—The values stated in inch-pound units are to be regarded as standard. The values given in parentheses are mathematical conversions to SI units that are provided for information only and are not considered standard.
1.5 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.
13.1 This test method covers the determination of the time-dependent decrease in stress in a specimen subjected to an uniaxial constant tension strain under conditions of uniform environment and negligible vibration. It also includes recommendations for the necessary testing equipment.
22.1 This test method covers the determination of the time-dependent decrease in stress in a specimen subjected to a long duration, uniaxial, constant compression strain in a uniform environment and negligible vibration. It also includes recommendations for the necessary testing equipment.
30.1 This test method covers the determination of the time-dependent decrease in stress in a specimen subject to long duration, constant bending strain, in a uniform environment, and negligible vibration...
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Designation: E328 − 02(Reapproved 2008)
Standard Test Methods for
1
Stress Relaxation for Materials and Structures
This standard is issued under the fixed designation E328; 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 (´) indicates an editorial change since the last revision or reapproval.
INTRODUCTION
These test methods cover a broad range of testing activities. To aid in locating the subject matter
pertinent to a particular test, the standard is divided into a general section, which applies to all stress
relaxationtestsformaterialsandstructures.Thisgeneralsectionisfollowedbyletter-designatedparts
that apply to tests for material characteristics when subjected to specific, simple stresses, such as
uniform tension, uniform compression, bending or torsion. To choose from among these types of
stress, the following factors should be considered:
(1) When the material data are to be applied to the design of a particular class of component, the
stress during the relaxation test should be similar to that imposed on the component. For example,
tension tests are suitable for bolting applications and bending tests for leaf springs.
(2) Tension and compression relaxation tests have the advantage that the stress can be reported
simply and unequivocally. During bending relaxation tests, the state of stress is complex, but can be
accurately determined when the initial strains are elastic. If plastic strains occur on application of
force, stresses can usually be determined within a bounded range only.Tension relaxation tests, when
compared to compression tests, have the advantage that it is unnecessary to guard against buckling.
Therefore,whenthetestmethodisnotrestrictedbythetypeofstressinthecomponent,tensiontesting
is recommended.
(3) Bending tests for relaxation, when compared to tension and compression tests, have the
advantage of using lighter and simpler apparatus for specimens of the same cross-sectional area.
Strains are usually calculated from deflection or curvature measurements. Since the specimens can
usually be designed so that these quantities are much greater than the axial deformation in a direct
stress test, strain is more easily measured and more readily used for machine control in the bending
tests.Duetothesmallforcesnormallyrequiredandthesimplicityoftheapparatuswhenstaticfixtures
are sufficient, many specimens can be placed in a single oven or furnace when tests are made at
elevated temperatures.
1. Scope the procedures recommended, the material or structure is
NOTE 1—The method of testing for the stress relaxation of plastics has
initially constrained by externally applied forces, and the
been withdrawn from this standard, and the responsibility has been
change in the external force necessary to maintain this con-
transferred to Practice D2991.
straint is determined as a function of time.
1.1 These test methods cover the determination of the time
1.2 Specific methods for conducting stress relaxation tests
dependence of stress (stress relaxation) in materials and
on materials subjected to tension, compression, bending and
structures under conditions of approximately constant
torsion stresses are described in Parts A, B, C, and D,
constraint, constant environment, and negligible vibration. In
respectively.Thesetestmethodsalsoincluderecommendations
for the necessary testing equipment and for the analysis of the
1
These test methods are under the jurisdiction of ASTM Committee E28 on
test data.
Mechanical Testing and is the direct responsibility of Subcommittee E28.04 on
Uniaxial Testing.
1.3 It is recognized that the long time periods required for
Current edition approved May 1, 2008. Published December 2008. Originally
these types of tests are often unsuited for routine testing or for
approved in 1967. Last previous approved in 2002 as E328–02. DOI: 10.1520/
E0328-02R08. specification in the purchase of material. However, these tests
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
1
---------------------- Page: 1 ----------------------
E328 − 02 (2008)
are valuable tools in obtaining practical design information on dure. However, the constraint is usually obtained initially by
the stress relaxation of materials subjected to the conditions the application of an external force at either a specific force
enumerated, and in investigations of the fundamental behavior application rate or a specific strain rate. The two methods will
of materials. produce the characteristic behavior shown in Fig. 1 when the
initial stress, σ , exceeds the proportional limit. Some testing
0
1.4 Units—The values stated in inch-po
...
This document is not anASTM standard and is intended only to provide the user of anASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
´1
Designation:E328–86 (Reapproved 1996) Designation:E328–02 (Reapproved 2008)
Standard Test Methods for
1
Stress Relaxation for Materials and Structures
This standard is issued under the fixed designation E328; 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 (´) indicates an editorial change since the last revision or reapproval.
1
´ NOTE—The title was changed editorially in January 1996.
INTRODUCTION
These test methods cover a broad range of testing activities. To aid in locating the subject matter
pertinent to a particular test, the standard is divided into a general section, which applies to all stress
relaxationtestsformaterialsandstructures.Thisgeneralsectionisfollowedbyletter-designatedparts
that apply to tests for material characteristics when subjected to specific, simple stresses, such as
uniform tension, uniform compression, bending or torsion. To choose from among these types of
loading,stress, the following factors should be considered:
(1) When the material data are to be applied to the design of a particular class of component, the
stress during the relaxation test should be similar to that imposed on the component. For example,
tension tests are suitable for bolting applications and bending tests for leaf springs.
(2) Tension and compression relaxation tests have the advantage that the stress can be reported
simply and unequivocally. During bending relaxation tests, the state of stress is complex, but can be
accuratelydeterminedwhentheinitialstrainsareelastic.Ifplasticstrainsoccuronloading,application
of force, stresses can usually be determined within a bounded range only. Tension relaxation tests,
when compared to compression tests, have the advantage that it is unnecessary to guard against
buckling. Therefore, when the test method is not restricted by the type of stress in the component,
tension testing is recommended.
(3) Bending tests for relaxation, when compared to tension and compression tests, have the
advantage of using lighter and simpler apparatus for specimens of the same cross-sectional area.
Strains are usually calculated from deflection or curvature measurements. Since the specimens can
usually be designed so that these quantities are much greater than the axial deformation in a direct
stress test, strain is more easily measured and more readily used for machine control in the bending
tests.Duetothesmallforcesnormallyrequiredandthesimplicityoftheapparatuswhenstaticfixtures
are sufficient, many specimens can be placed in a single oven or furnace when tests are made at
elevated temperatures.
1. Scope
NOTE 1—The method of testing for the stress relaxation of plastics has been withdrawn from this standard, and the responsibility has been transferred
to Practice D2991.
1.1 These test methods cover the determination of the time dependence of stress (stress relaxation) in materials and structures
under conditions of approximately constant constraint, constant environment, and negligible vibration. In the procedures
recommended, the material or structure is initially constrained by externally applied forces, and the change in the external force
necessary to maintain this constraint is determined as a function of time.
1.2 Specific methods for conducting stress relaxation tests on materials subjected to tension, compression, bending and torsion
loadsstresses are described in Parts A, B, C, and D, respectively. These test methods also include recommendations for the
necessary testing equipment and for the analysis of the test data.
1.3 It is recognized that the long time periods required for these types of tests are often unsuited for routine testing or for
1
These test methods are under the jurisdiction of ASTM Committee E28 on Mechanical Testing and is the direct responsibility of Subcommittee E28.10 on Effect of
Elevated Temperature on Properties.
Current edition approved Feb. 28, 1986. Published May 1986. Originally published as E328–67T. Last previous edition E328–78.
1
These test methods are under the jurisdiction of ASTM Committee E28 on Mechanical Testing and is the direct responsibility of Subcommittee E28.04 on Uniaxial
Testing.
Current edition approved May 1, 2008. Published December 2008. Originally approved in 1967. Last previous approved in 2002 as E328–02.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United State
...
This document is not anASTM standard and is intended only to provide the user of anASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation:E328–02 Designation:E328–02 (Reapproved 2008)
Standard Test Methods for
1
Stress Relaxation for Materials and Structures
This standard is issued under the fixed designation E328; 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 (´) indicates an editorial change since the last revision or reapproval.
INTRODUCTION
These test methods cover a broad range of testing activities. To aid in locating the subject matter
pertinent to a particular test, the standard is divided into a general section, which applies to all stress
relaxationtestsformaterialsandstructures.Thisgeneralsectionisfollowedbyletter-designatedparts
that apply to tests for material characteristics when subjected to specific, simple stresses, such as
uniform tension, uniform compression, bending or torsion. To choose from among these types of
stress, the following factors should be considered:
(1) When the material data are to be applied to the design of a particular class of component, the
stress during the relaxation test should be similar to that imposed on the component. For example,
tension tests are suitable for bolting applications and bending tests for leaf springs.
(2) Tension and compression relaxation tests have the advantage that the stress can be reported
simply and unequivocally. During bending relaxation tests, the state of stress is complex, but can be
accurately determined when the initial strains are elastic. If plastic strains occur on application of
force, stresses can usually be determined within a bounded range only.Tension relaxation tests, when
compared to compression tests, have the advantage that it is unnecessary to guard against buckling.
Therefore,whenthetestmethodisnotrestrictedbythetypeofstressinthecomponent,tensiontesting
is recommended.
(3) Bending tests for relaxation, when compared to tension and compression tests, have the
advantage of using lighter and simpler apparatus for specimens of the same cross-sectional area.
Strains are usually calculated from deflection or curvature measurements. Since the specimens can
usually be designed so that these quantities are much greater than the axial deformation in a direct
stress test, strain is more easily measured and more readily used for machine control in the bending
tests.Duetothesmallforcesnormallyrequiredandthesimplicityoftheapparatuswhenstaticfixtures
are sufficient, many specimens can be placed in a single oven or furnace when tests are made at
elevated temperatures.
1. Scope
NOTE 1—The method of testing for the stress relaxation of plastics has been withdrawn from this standard, and the responsibility has been transferred
to Practice D2991.
1.1 These test methods cover the determination of the time dependence of stress (stress relaxation) in materials and structures
under conditions of approximately constant constraint, constant environment, and negligible vibration. In the procedures
recommended, the material or structure is initially constrained by externally applied forces, and the change in the external force
necessary to maintain this constraint is determined as a function of time.
1.2 Specific methods for conducting stress relaxation tests on materials subjected to tension, compression, bending and torsion
stresses are described in Parts A, B, C, and D, respectively. These test methods also include recommendations for the necessary
testing equipment and for the analysis of the test data.
1.3 It is recognized that the long time periods required for these types of tests are often unsuited for routine testing or for
specification in the purchase of material. However, these tests are valuable tools in obtaining practical design information on the
stress relaxation of materials subjected to the conditions enumerated, and in investigations of the fundamental behavior of
materials.
1
These test methods are under the jurisdiction of ASTM Committee E28 on Mechanical Testing and is the direct responsibility of Subcommittee E28.04 on Uniaxial
Testing.
´1
Current edition approved Nov 10, 2002. Published April 2003. Originally approved in 1967. Last previous approved 1986 as E328–86(96) .
Current edition approved May 1, 2008. Published December 2008. Originally approved in 1967. Last previous approved in 2002 as E328–02.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
1
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