ASTM E606-92(1998)
(Practice)Standard Practice for Strain-Controlled Fatigue Testing
Standard Practice for Strain-Controlled Fatigue Testing
SCOPE
1.1 This practice covers the determination of fatigue properties of nominally homogeneous materials by the use of uniaxially loaded test specimens. It is intended as a guide for fatigue testing performed in support of such activities as materials research and development, mechanical design, process and quality control, product performance, and failure analysis. While this practice is intended primarily for strain-controlled fatigue testing, some sections may provide useful information for load-controlled or stress-controlled testing.
1.2 The use of this practice is limited to specimens and does not cover testing of full-scale components, structures, or consumer products.
1.3 This practice is applicable to temperatures and strain rates for which the magnitudes of time-dependent inelastic strains are on the same order or less than the magnitudes of time-independent inelastic strains. No restrictions are placed on environmental factors such as temperature, pressure, humidity, medium, and others, provided they are controlled throughout the test, do not cause loss of or change in dimension with time, and are detailed in the data report. Note 1-The term inelastic is used herein to refer to all nonelastic strains. The term plastic is used herein to refer only to the time-independent (that is, noncreep) component of inelastic strain. To truly determine a time-independent strain the load would have to be applied instantaneously, which is not possible. A useful engineering estimate of time-independent strain can be obtained when the strain rate exceeds some value. For example, a strain rate of 1 X 10 -3 sec -1 is often used for this purpose. This value should increase with increasing test temperature.
1.4 This practice is restricted to the testing of axially loaded uniform gage section test specimens as shown in Fig. 1(a). Testing is limited to strain-controlled cycling. The practice may be applied to hourglass specimens, see Fig. 1(b), but the user is cautioned about uncertainties in data analysis and interpretation. Testing is done primarily under constant amplitude cycling and may contain interspersed hold times at repeated intervals. The practice may be adapted to guide testing for more general cases where strain or temperature may vary according to application specific histories. Data analysis may not follow this practice in such cases.
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Designation: E 606 – 92 (Reapproved 1998)
Standard Practice for
Strain-Controlled Fatigue Testing
This standard is issued under the fixed designation E606; 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 (ε) indicates an editorial change since the last revision or reapproval.
1. Scope according to application specific histories. Data analysis may
not follow this practice in such cases.
1.1 This practice covers the determination of fatigue prop-
erties of nominally homogeneous materials by the use of
2. Referenced Documents
uniaxially loaded test specimens. It is intended as a guide for
2.1 ASTM Standards:
fatigue testing performed in support of such activities as
A370 TestMethodsandDefinitionsforMechanicalTesting
materials research and development, mechanical design, pro-
of Steel Products
cess and quality control, product performance, and failure
E3 Methods of Preparation of Metallographic Specimens
analysis. While this practice is intended primarily for strain-
E4 Practices for Force Verification of Testing Machines
controlled fatigue testing, some sections may provide useful
E8 TestMethodsforTensionTestingofMetallicMaterials
information for load-controlled or stress-controlled testing.
E9 Test Methods of Compression Testing of Metallic Ma-
1.2 Theuseofthispracticeislimitedtospecimensanddoes
terials at Room Temperature
not cover testing of full-scale components, structures, or
E83 Practice for Verification and Classification of Exten-
consumer products.
someters
1.3 This practice is applicable to temperatures and strain
E111 TestMethodforYoung’sModulus,TangentModulus,
rates for which the magnitudes of time-dependent inelastic
and Chord Modulus
strains are on the same order or less than the magnitudes of
E112 Test Methods for Determining Average Grain Size
time-independent inelastic strains. No restrictions are placed
E132 Test Method for Poisson’s Ratio at Room Tempera-
on environmental factors such as temperature, pressure, hu-
ture
midity, medium, and others, provided they are controlled
E157 PracticeforAssigningCrystallographicPhaseDesig-
throughoutthetest,donotcauselossoforchangeindimension
nations in Metallic Systems
with time, and are detailed in the data report.
E209 Practice for Compression Tests of Metallic Materials
NOTE 1—The term inelastic is used herein to refer to all nonelastic
at Elevated Temperatures with Conventional or Rapid
strains. The term plastic is used herein to refer only to the time-
Heating Rates and Strain Rates
independent (that is, noncreep) component of inelastic strain. To truly
E337 Test Method for Measuring Humidity with a Psy-
determine a time-independent strain the load would have to be applied
chrometer (the Measurement of Wet- and Dry-Bulb Tem-
instantaneously, which is not possible. A useful engineering estimate of
peratures)
time-independentstraincanbeobtainedwhenthestrainrateexceedssome
−3 −1
E384 Test Method for Microhardness of Materials
value. For example, a strain rate of 1 310 sec is often used for this
purpose. This value should increase with increasing test temperature. E399 Test Method for Plane-Strain Fracture Toughness of
Metallic Materials
1.4 Thispracticeisrestrictedtothetestingofaxiallyloaded
E466 Practice for Conducting Force Controlled Constant
uniform gage section test specimens as shown in Fig. 1(a).
Amplitude Axial Fatigue Tests of Metallic Materials
Testingislimitedtostrain-controlledcycling.Thepracticemay
E467 Practice for Verification of Constant Amplitude Dy-
beappliedtohourglassspecimens,seeFig.1(b),buttheuseris
namic Loads on Displacements in an Axial Load Fatigue
cautioned about uncertainties in data analysis and interpreta-
Testing System
tion. Testing is done primarily under constant amplitude
E468 Practice for Presentation of Constant Amplitude Fa-
cycling and may contain interspersed hold times at repeated
tigue Test Results for Metallic Materials
intervals. The practice may be adapted to guide testing for
E739 Practice for Statistical Analysis of Linear or Linear-
more general cases where strain or temperature may vary
ized Stress-Life (S-N) and Strain-Life (ε-N) Fatigue Data
E1012 Practice for Verification of Specimen Alignment
This practice is under the jurisdiction ofASTM Committee E-8 on Fatigue and
Fracture and is the direct responsibility of Subcommittee E08.05 on Cyclic
Deformation and Fatigue Crack Formation. Annual Book of ASTM Standards, Vol 01.03.
Current edition approved Oct. 15, 1992. Published March 1993. Originally Annual Book of ASTM Standards, Vol 03.01.
published as E606–77T. Last previous edition E606–80. Annual Book of ASTM Standards, Vol 11.03.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
E 606 – 92 (1998)
NOTE 1—*Dimension d is recommended to be 6.35 mm (0.25 in.). See 7.1. Centers permissible. **This diameter may be made greater or less than
2d depending on material hardness. In typically ductile materials diameters less than 2d are often employed and in typically brittle materials diameters
greater than 2d may be found desirable.
FIG. 1 Recommended Low-Cycle Fatigue Specimens
Under Tensile Loading
(τ = sum of all the hold portions of the cycle and
h
E1049 Practices for Cycle Counting in Fatigue Analysis
(τ = sum of all the nonhold portions of the cycle.
nh
E1150 Definitions of Terms Relating to Fatigue
τ also is equal to the reciprocal of the overall frequency when
t
the frequency is held constant.
3. Terminology
3.2.4 The following equations are often used to define the
3.1 The definitions in this practice are in accordance with
instantaneous stress and strain relationships for many metals
Definitions E1150.
and alloys:
3.2 Additional definitions associated with time-dependent
e5e 1e (2)
in e
deformationbehaviorobservedintestsatelevatedhomologous
s
temperatures are as follows:
e 5 ~seeNote2!
e
E*
3.2.1 hold period, τ —the time interval within a cycle
h
during which the stress or strain is held constant.
andthechangeinstrainfromanypoint(1)toanyotherpoint
3.2.2 inelastic strain, ε —the strain that is not elastic. For
in
(3), as illustrated in Fig. 2, can be calculated as follows:
isothermal conditions, ε is calculated by subtracting the
in
s s
3 1
elastic strain from the total strain.
e 2e 5 e 1 2 e 1 (3)
S D S D
3 1 3in 1in
E* E*
3.2.3 total cycle period, τ—the time for the completion of
t
one cycle. The parameter τ can be separated into hold and Allstrainpointstotherightofandallstresspointsabovethe
t
nonhold components:
origin are positive. The equation would then show an increase
in inelastic strain from 1 to 3 or:
t 5 (t 1 (t (1)
t h nh
s s
1 3
where:
e 2e 5e 2e 1 2 (4)
3in 1in 3 1
E* E*
E 606 – 92 (1998)
situations in which components or portions of components
undergo either mechanically or thermally induced cyclic plas-
tic strains that cause failure within relatively few (that is,
approximately <10 ) cycles. Information obtained from strain-
controlled fatigue testing may be an important element in the
establishment of design criteria to protect against component
failure by fatigue.
4.3 Strain-controlled fatigue test results are useful in the
areas of mechanical design as well as materials research and
development, process and quality control, product perfor-
mance, and failure analysis. Results of a strain-controlled
fatigue test program may be used in the formulation of
empirical relationships between the cyclic variables of stress,
total strain, plastic strain, and fatigue life. They are commonly
usedindatacorrelationssuchascurvesofcyclicstressorstrain
versuslifeandcyclicstressversuscyclicplasticstrainobtained
from hysteresis loops at some fraction (often half) of material
life. Examination of the cyclic stress–strain curve and its
comparison with monotonic stress–strain curves gives useful
information regarding the cyclic stability of a material, for
example, whether the values of hardness, yield strength,
FIG. 2 Analyses of a Total Strain versus Stress Hystersis Loop
ultimate strength, strain-hardening exponent, and strength
Containing a Hold Period
coefficient will increase, decrease, or remain unchanged (that
is,whetheramaterialwillharden,soften,orbestable)because
ofcyclicplasticstraining (1). Thepresenceoftime-dependent
Similarly, during the strain hold period, the change in the
inelastic strains during elevated temperature testing provides
inelastic strain will be equal to the change in the stress divided
the opportunity to study the effects of these strains on fatigue
by E*, or:
life and on the cyclic stress-strain response of the material.
s 2s
2 3
e 2e 5 (5)
Information about strain rate effects, relaxation behavior, and
3in 2in
E*
creep also may be available from these tests. Results of the
NOTE 2—E* represents a material parameter that may be a function of
uniaxial tests on specimens of simple geometry can be applied
environment and test conditions. It also may vary during a test as a result
to the design of components with notches or other complex
of metallurgical or physical changes in the specimen. In many instances,
shapes, provided that the strains can be determined and
however, E* is practically a constant quantity and is used rather exten-
multiaxial states of stress or strain and their gradients are
sively in isothermal, constant-rate testing, in the analysis of hysteresis
correctly correlated with the uniaxial strain data.
loops. In such cases, a value for E* can best be determined by cycling the
specimen prior to the test at stress or strain levels below the elastic limit.
5. Functional Relationships
E* is NOT the monotonic Young’s modulus.
5.1 Empirical relationships that have been commonly used
4. Significance and Use
for description of strain-controlled fatigue data are given in
4.1 Strain-controlled fatigue is a phenomenon that is influ-
AppendixX1.Theserelationshipsmaynotbevalidwhenlarge
enced by the same variables that influence load-controlled
time-dependent inelastic strains occur. For this reason original
fatigue.Thenatureofstrain-controlledfatigueimposesdistinc-
data should be reported to the greatest extent possible. Data
tive requirements on fatigue testing methods. In particular,
reduction methods should be detailed along with assumptions.
cyclic total strain should be measured and cyclic plastic strain
Sufficient information should be developed and reported to
should be determined. Furthermore, either of these strains
permit analysis, interpretation, and comparison with results for
typicallyisusedtoestablishcycliclimits;totalstrainusuallyis
other materials analyzed using currently popular methods.
controlled throughout the cycle. The uniqueness of this prac-
5.2 If use is made of hourglass geometries, original data
tice and the results it yields are the determination of cyclic
should be reported along with results analyzed using the
stresses and strains at any time during the tests. Differences in
relationships in Appendix X2.
strain histories other than constant-amplitude alter fatigue life
as compared with the constant amplitude results (for example, 6. Methodology
periodic overstrains and block or spectrum histories). Like-
6.1 Testing Machine—Testing should be conducted with a
wise, the presence of nonzero mean strains and varying
tension-compression fatigue testing machine that has been
environmental conditions may alter fatigue life as compared
verified in accordance with Practices E4 and E467, unless
with the constant-amplitude, fully reversed fatigue tests. Care
more stringent requirements are called for in this specification.
must be exercised in analyzing and interpreting data for such
cases.
4.2 Strain-controlled fatigue can be an important consider-
Theboldfacenumbersinparenthesesrefertothelistofreferencesattheendof
ation in the design of industrial products. It is important for this standard.
E 606 – 92 (1998)
of strain gaging specimens.
The testing machine, together with any fixtures used in the test
program, must meet the bending strain criteria in 6.3.1. The
6.3.2 Several commonly used fixturing techniques are
machine should be one in which specific measures have been
shown schematically in Fig. 3. The selection of any one
taken to minimize backlash in the loading train.
fixturing technique depends primarily upon the user’s speci-
NOTE 3—Load measuring capability of 45 kN (approximately 10 kips) men design. Fixtures should be constructed of hardened steel
orgreaterwouldbesufficientfortherecommendedspecimens(Section7)
for high strength and abrasion resistance. The collet type grip
and most test materials. The machine load capacity used for these
shown, or other fixturing techniques that provide high preci-
specimens would not be required to exceed 110 kN (approximately 25
sion lateral stiffness to hold precise alignment are acceptable.
kips);however,large-capacityfatiguemachinesmaybebeneficialbecause
Fixtures not capable of high alignment may be coupled with
of increased axial stiffness and decreased lateral deflection of these
the Woods metal pot (2, 3) of Fig. 4 or a similar device. Such
systems.Achievingachangeinaxialconcentricityoflessthanorequalto
a device may help to compensate for misalignment in the load
0.05 mm (0.002 in.) TIR (total indicator reading), as measured between
the top and bottom specimen fixture under cyclic load, is a measure of train that would induce bending strains in the specimen during
success with respect to minimizing lateral deflection of the load train.
fixturing. Placement of the fixtures within die-set or flex bars
reduces relative lateral motion of specimen ends and increases
6.2 Strain Control—Testingmachinecontrolsshouldpermit
lateral stiffness that is important in machines that do not
cycling between constant strain limits. If material behavior
provide adequate safeguards against compressive buckling of
permits (for example, aging effects do not hinder), control
the test specimen.
stabilityshouldbesuchthatthestrainmaximumandminimum
6.3.3 For elevated-temperature testing it is usually neces-
limits are repeatable over the test duration to within 1% of the
sary to provide some means for cooling the fixtures to prevent
range between maximum and minimum control limits.
damage to other load-train components such as load cells. One
NOTE 4—See 6.4.1 and 6.5 on use of load and strain transducers in
method commonly used employs water-cooling coils attached
relation to repeatability requirements.
tothefixturesortootherapp
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