ASTM E466-21

Standard Practice for Conducting Force Controlled Constant Amplitude Axial Fatigue Tests of Metallic Materials

SIGNIFICANCE AND USE
4.1 The axial force fatigue test is used to determine the effect of variations in material, geometry, surface condition, stress, and so forth, on the fatigue resistance of metallic materials subjected to direct stress for relatively large numbers of cycles. The results may also be used as a guide for the selection of metallic materials for service under conditions of repeated direct stress.  
4.2 In order to verify that such basic fatigue data generated using this practice is comparable, reproducible, and correlated among laboratories, it may be advantageous to conduct a round-robin-type test program from a statistician's point of view. To do so would require the control or balance of what are often deemed nuisance variables; for example, hardness, cleanliness, grain size, composition, directionality, surface residual stress, surface finish, and so forth. Thus, when embarking on a program of this nature it is essential to define and maintain consistency a priori, as many variables as reasonably possible, with as much economy as prudent. All material variables, testing information, and procedures used should be reported so that correlation and reproducibility of results may be attempted in a fashion that is considered reasonably good current test practice.  
4.3 The results of the axial force fatigue test are suitable for application to design only when the specimen test conditions realistically simulate service conditions or some methodology of accounting for service conditions is available and clearly defined.
SCOPE
1.1 This practice covers the procedure for the performance of axial force controlled fatigue tests to obtain the fatigue strength of metallic materials in the fatigue regime where the strains are predominately elastic, both upon initial loading and throughout the test. This practice is limited to the fatigue testing of axial unnotched and notched specimens subjected to a constant amplitude, periodic forcing function in air at room temperature.  
1.2 The use of this test method is limited to specimens and does not cover testing of full-scale components, structures, or consumer products.  
1.3 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.  
1.4 The text of this standard references notes and footnotes that provide explanatory material. These notes and footnotes (excluding those in tables and figures) shall not be considered as requirements of the standard.
Note 1: The following documents, although not directly referenced in the text, are considered important enough to be listed in this practice:
E739 Practice for Statistical Analysis of Linear or Linearized Stress-Life (S-N) and Strain-Life (ε-N) Fatigue Data
STP 566 Handbook of Fatigue Testing2
STP 588 Manual on Statistical Planning and Analysis for Fatigue Experiments3
STP 731 Tables for Estimating Median Fatigue Limits4  
1.5 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

General Information

• Status: Published
• Publication Date: 31-May-2021
• ICS: 77.040.10 - Mechanical testing of metals
• Technical Committee: E08 - Fatigue and Fracture
• Drafting Committee: E08.05 - Cyclic Deformation and Fatigue Crack Formation

Relations

• Refers: ASTM E1823-24a - Standard Terminology Relating to Fatigue and Fracture Testing
• Effective Date: 15-Feb-2024
• Refers: ASTM E1823-24 - Standard Terminology Relating to Fatigue and Fracture Testing
• Effective Date: 01-Feb-2024
• Refers: ASTM E1823-20 - Standard Terminology Relating to Fatigue and Fracture Testing
• Effective Date: 01-Feb-2020
• Refers: ASTM E1823-12e - Standard Terminology Relating to Fatigue and Fracture Testing
• Effective Date: 15-Dec-2012
• Refers: ASTM E1823-12d - Standard Terminology Relating to Fatigue and Fracture Testing
• Effective Date: 15-Nov-2012
• Refers: ASTM E1823-12c - Standard Terminology Relating to Fatigue and Fracture Testing
• Effective Date: 01-Sep-2012
• Refers: ASTM E1823-12b - Standard Terminology Relating to Fatigue and Fracture Testing
• Effective Date: 01-Aug-2012
• Refers: ASTM E1012-12 - Standard Practice for Verification of Testing Frame and Specimen Alignment Under Tensile and Compressive Axial Force Application
• Effective Date: 01-Jun-2012
• Refers: ASTM E606/E606M-12 - Standard Test Method for Strain-Controlled Fatigue Testing
• Effective Date: 01-Jun-2012
• Refers: ASTM E1012-12e1 - Standard Practice for Verification of Testing Frame and Specimen Alignment Under Tensile and Compressive Axial Force Application
• Effective Date: 01-Jun-2012
• Refers: ASTM E1823-12a - Standard Terminology Relating to Fatigue and Fracture Testing
• Effective Date: 15-May-2012
• Refers: ASTM E1823-12 - Standard Terminology Relating to Fatigue and Fracture Testing
• Effective Date: 15-Mar-2012
• Refers: ASTM E467-08e1 - Standard Practice for Verification of Constant Amplitude Dynamic Forces in an Axial Fatigue Testing System
• Effective Date: 01-Nov-2011
• Refers: ASTM E468-11 - Standard Practice for Presentation of Constant Amplitude Fatigue Test Results for Metallic Materials
• Effective Date: 01-Oct-2011
• Refers: ASTM E1823-11 - Standard Terminology Relating to Fatigue and Fracture Testing
• Effective Date: 01-Jun-2011

Overview

ASTM E466-21 is the Standard Practice for Conducting Force Controlled Constant Amplitude Axial Fatigue Tests of Metallic Materials. Issued by ASTM International, this practice details procedures for evaluating the fatigue strength of metallic specimens subjected to direct, constant amplitude axial forces in situations where strains remain predominantly elastic. The standard is intended for use in laboratory settings, ensuring the reliability, repeatability, and comparability of fatigue resistance data among various materials, specimen designs, and laboratories.

This standard is widely recognized for its role in fatigue testing and the evaluation of metallic materials under cyclic loading, shaping decisions on material selection and design for components expected to endure repeated stress in service.

Key Topics

• Test Scope and Applicability

  • Applies to unnotched and notched metallic specimens tested in air at room temperature.
  • Limited to specimen testing; does not extend to full-scale structures, components, or consumer products.
  • Focuses on the fatigue regime with predominantly elastic strains throughout the loading cycle.

• Significance and Use

  • Determines the effect of material, geometry, surface conditions, and stress variations on fatigue resistance.
  • Supports material selection for applications requiring resistance to repeated direct stresses.
  • Stresses the need for consistency in test variables (such as hardness, grain size, orientation, surface residual stress) for reproducible results.

• Specimen and Test Design

  • Offers guidance for specimen shape and preparation, including preferred geometries to ensure failure occurs in the test section.
  • Highlights the importance of precise measurements, surface finishing, and control of variables like fillet radius to minimize stress concentrations.

• Test Execution and Data Reporting

  • Recommends continuous monitoring of force cycles and precise alignment to minimize bending stresses.
  • Defines standard reporting requirements for environmental conditions, loading function, test forces, failure criteria, and post-test analysis.
  • Emphasizes that design use of fatigue data is valid only if the test simulates actual service conditions or is properly accounted for.

Applications

• Material Evaluation and Selection

  • Used to qualify metallic materials for engineering components that must withstand repeated stress cycles, such as automotive, aerospace, and structural applications.
  • Guides the design and certification of parts where fatigue life is critical to safety and performance.

• Research and Development

  • Supports the comparison of fatigue resistance among materials, coatings, or surface treatments through controlled laboratory tests.
  • Facilitates round-robin testing and inter-laboratory comparisons to assess reproducibility of fatigue data.

• Quality Assurance and Standardization

  • Serves as a reference for validating manufacturing and processing practices, ensuring that material supplied meets fatigue life requirements.
  • Provides a framework for documenting and reporting fatigue test results to regulatory and certification bodies.

Related Standards

For comprehensive fatigue testing and data analysis, ASTM E466-21 is commonly used alongside the following standards:

• ASTM E3: Guide for Preparation of Metallographic Specimens
• ASTM E467: Practice for Verification of Constant Amplitude Dynamic Forces in an Axial Fatigue Testing System
• ASTM E468: Practice for Presentation of Constant Amplitude Fatigue Test Results for Metallic Materials
• ASTM E606/E606M: Test Method for Strain-Controlled Fatigue Testing
• ASTM E739: Practice for Statistical Analysis of Linear or Linearized Stress-Life (S-N) and Strain-Life (ε-N) Fatigue Data
• ASTM E1012: Practice for Verification of Testing Frame and Specimen Alignment Under Tensile and Compressive Axial Force Application
• ASTM E1823: Terminology Relating to Fatigue and Fracture Testing

These documents collectively provide detailed methodologies for specimen preparation, alignment, force verification, data presentation, and statistical analysis, enhancing the reliability of fatigue testing in line with ASTM E466-21.

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: E466 − 21
Standard Practice for
Conducting Force Controlled Constant Amplitude Axial
Fatigue Tests of Metallic Materials
This standard is issued under the fixed designation E466; 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. Scope Development of International Standards, Guides and Recom-
mendations issued by the World Trade Organization Technical
1.1 This practice covers the procedure for the performance
Barriers to Trade (TBT) Committee.
of axial force controlled fatigue tests to obtain the fatigue
strength of metallic materials in the fatigue regime where the
2. Referenced Documents
strains are predominately elastic, both upon initial loading and
2.1 ASTM Standards:
throughout the test. This practice is limited to the fatigue
E3Guide for Preparation of Metallographic Specimens
testing of axial unnotched and notched specimens subjected to
E467Practice for Verification of Constant Amplitude Dy-
a constant amplitude, periodic forcing function in air at room
namic Forces in an Axial Fatigue Testing System
temperature.
E468Practice for Presentation of Constant Amplitude Fa-
1.2 The use of this test method is limited to specimens and
tigue Test Results for Metallic Materials
does not cover testing of full-scale components, structures, or
E606/E606MTest Method for Strain-Controlled Fatigue
consumer products.
Testing
1.3 Thevaluesstatedininch-poundunitsaretoberegarded
E739PracticeforStatisticalAnalysisofLinearorLinearized
as standard. The values given in parentheses are mathematical
Stress-Life (S-N) and Strain-Life (ε-N) Fatigue Data
conversions to SI units that are provided for information only
E1012Practice for Verification of Testing Frame and Speci-
and are not considered standard.
men Alignment Under Tensile and Compressive Axial
Force Application
1.4 The text of this standard references notes and footnotes
E1823TerminologyRelatingtoFatigueandFractureTesting
that provide explanatory material. These notes and footnotes
(excluding those in tables and figures) shall not be considered
3. Terminology
as requirements of the standard.
3.1 Definitions:
NOTE 1—The following documents, although not directly referenced in
3.1.1 The terms used in this practice shall be as defined in
the text, are considered important enough to be listed in this practice:
Terminology E1823.
E739 Practice for Statistical Analysis of Linear or Linearized Stress-
Life (S-N) and Strain-Life (ε-N) Fatigue Data
STP 566 Handbook of Fatigue Testing
4. Significance and Use
STP 588 Manual on Statistical Planning and Analysis for Fatigue
3 4.1 The axial force fatigue test is used to determine the
Experiments
effect of variations in material, geometry, surface condition,
STP 731 Tables for Estimating Median Fatigue Limits
stress, and so forth, on the fatigue resistance of metallic
1.5 This international standard was developed in accor-
materials subjected to direct stress for relatively large numbers
dance with internationally recognized principles on standard-
of cycles. The results may also be used as a guide for the
ization established in the Decision on Principles for the
selection of metallic materials for service under conditions of
repeated direct stress.
4.2 In order to verify that such basic fatigue data generated
ThispracticeisunderthejurisdictionofASTMCommitteeE08onFatigueand
Fracture and is the direct responsibility of Subcommittee E08.05 on Cyclic using this practice is comparable, reproducible, and correlated
Deformation and Fatigue Crack Formation.
among laboratories, it may be advantageous to conduct a
CurrenteditionapprovedJune1,2021.PublishedJuly2021.Originallyapproved
round-robin-type test program from a statistician’s point of
in 1972. Last previous edition approved in 2015 as E466–15. DOI: 10.1520/
E0466-21.
Handbook of Fatigue Testing, ASTM STP 566, ASTM, 1974.
3 5
Little, R. E., Manual on Statistical Planning and Analysis, ASTM STP 588, For referenced ASTM standards, visit the ASTM website, www.astm.org, or
ASTM, 1975. contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
Little, R. E., Tables for Estimating Median Fatigue Limits, ASTM STP 731, Standards volume information, refer to the standard’s Document Summary page on
ASTM, 1981. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E466 − 21
view.Todosowouldrequirethecontrolorbalanceofwhatare dimensionslessthan0.200in.(5.08mm).Surfacesintendedto
often deemed nuisance variables; for example, hardness, be parallel and straight should be in a manner consistent with
cleanliness, grain size, composition, directionality, surface 8.2.
residual stress, surface finish, and so forth. Thus, when
NOTE 2—Measurements of dimensions presume smooth surface fin-
embarking on a program of this nature it is essential to define
ishes for the specimens. In the case of surfaces that are not smooth, due
and maintain consistency a priori, as many variables as
to the fact that some surface treatment or condition is being studied, the
reasonably possible, with as much economy as prudent. All dimensions should be measured as above and the average, maximum, and
minimum values reported.
material variables, testing information, and procedures used
should be reported so that correlation and reproducibility of
5.2 Specimen Dimensions:
results may be attempted in a fashion that is considered
5.2.1 Circular Cross Sections—Specimens with circular
reasonably good current test practice.
cross sections may be either of two types:
4.3 The results of the axial force fatigue test are suitable for 5.2.1.1 Specimens with tangentially blended fillets between
application to design only when the specimen test conditions the test section and the ends (Fig. 1)—The diameter of the test
realistically simulate service conditions or some methodology section should preferably be between 0.200 in. (5.08 mm) and
of accounting for service conditions is available and clearly 1.000 in. (25.4 mm). To ensure test section failure, the grip
defined.
cross-sectional area should be at least 1.5 times but, preferably
for most materials and specimens, at least four times the test
5. Specimen Design
section area. The blending fillet radius should be at least eight
times the test section diameter to minimize the theoretical
5.1 The type of specimen used will depend on the objective
stressconcentrationfactor, K ofthespecimen.Thetestsection
t
of the test program, the type of equipment, the equipment
length should be approximately two to three times the test
capacity, and the form in which the material is available.
sectiondiameter.Fortestsrunincompression,thelengthofthe
However, the design should meet certain general criteria
test section should be approximately two times the test section
outlined below:
diameter to minimize buckling.
5.1.1 Thedesignofthespecimenshouldbesuchthatfailure
5.2.1.2 Specimens with a continuous radius between ends
occurs in the test section (reduced area as shown in Fig. 1 and
(Fig. 3)—The radius of curvature should be no less than eight
Fig. 2). The acceptable ratio of the areas (test section to grip
timestheminimumdiameterofthetestsectiontominimize K.
section) to ensure a test section failure is dependent on the t
The reduced section length should be greater than three times
specimen gripping method. Threaded end specimens may
the minimum test section diameter. Otherwise, the same
prove difficult to align and failure often initiates at these stress
dimensional relationships should apply, as in the case of the
concentrationswhentestingintheliferegimeofinterestinthis
specimens described in 5.2.1.1.
practice. A caveat is given regarding the gage section with
5.2.2 Rectangular Cross Sections—Specimens with rectan-
sharp edges (that is, square or rectangular cross section) since
gular cross sections may be made from sheet or plate material
these are inherent weaknesses because the slip of the grains at
and may have a reduced test cross section along one
sharpedgesisnotconfinedbyneighboringgrainsontwosides.
dimension, generally the width, or they may be made from
Because of this, a circular cross section may be preferred if
material requiring dimensional reductions in both width and
material form lends itself to this configuration. The size of the
thickness. In view of this, no maximum ratio of area (grip to
gripped end relative to the gage section, and the blend radius
test section) should apply. The value of 1.5 given in 5.2.1.1
from gage section into the grip section, may cause premature
may be considered as a guideline. Otherwise, the sections may
failureparticularlyiffrettingoccursinthegripsectionorifthe
be either of two types:
radius is too small. Readers are referred to Ref (1) should this
occur. 5.2.2.1 Specimens with tangentially blended fillets between
5.1.2 For the purpose of calculating the force to be applied the uniform test section and the ends (Fig. 4)—The radius of
to obtain the required stress, the dimensions from which the the blending fillets should be at least eight times the specimen
area is calculated should be measured to the nearest 0.001 in. test section width to minimize K of the specimen.The ratio of
t
(0.03 mm) for dimensions equal to or greater than 0.200 in. specimentestsectionwidthtothicknessshouldbebetweentwo
(5.08 mm) and to the nearest 0.0005 in. (0.013 mm) for and six, and the reduced area should preferably be between
FIG. 1 Specimens with Tangentially Blending Fillets Between the Test Section and the Ends
E466 − 21
FIG. 2 Specimens with Continuous Radius Between Ends
FIG. 3 Specimens with a Continuous Radius Between Ends
FIG. 4 Specimens with Tangentially Blending Fillets Between the Uniform Test Section and the Ends
2 2 2 2
0.030 in. (19.4 mm ) and 1.000 in. (645 mm ), except in 6. Specimen Preparation
extreme cases where the necessity of sampling a product with
6.1 The condition of the test specimen and the method of
anunchangedsurfacemakestheaboverestrictionsimpractical.
specimen preparation are of the utmost importance. Improper
The test section length should be approximately two to three
methodsofpreparationcangreatlybiasthetestresults.Inview
times the test section width of the specimen. For specimens
of this fact, the method of preparation should be agreed upon
thatarelessthan0.100in.(2.54mm)thick,specialprecautions
priortothebeginningofthetestprogrambyboththeoriginator
are necessary particularly in reversed loading, such as R=−1.
andtheuserofthefatiguedatatobegenerated.Sincespecimen
For example, specimen alignment is of utmost importance and
preparation can strongly influence the resulting fatigue data,
the procedure outlined in Practice E606/E606M would be
the application or end use of that data, or both, should be
advantageous. Also, Refs (2-5), although they pertain to
considered when selecting the method of preparation. Appen-
strain-controlled testing, may prove of interest since they deal
with sheet specimens approximately 0.05 in. (1.25 mm) thick. dix X1 presents an example of a machining procedure that has
5.2.2.2 Specimens with continuous radius between ends been employed on some metals in an attempt to minimize the
(Fig. 2)—The same restrictions should apply in the case of this
variability of machining and heat treatment upon fatigue life.
type of specimen as for the specimen described in 5.2.1.2.The
6.2 Onceatechniquehasbeenestablishedandapprovedfor
area restrictions should be the same as for the specimen
a specific material and test specimen configuration, change
described in 5.2.2.1.
should not be made because of potential bias that may be
5.2.3 Notched Specimens—Inviewofthespecializednature
introduced by the changed technique. Regardless of the
of the test programs involving notched specimens, no restric-
machining, grinding, or polishing method used, the final metal
tions are placed on the design of the notched specimen, other
removal should be in a direction approximately parallel to the
than that it must be consistent with the objectives of the
long axis of the specimen. This entire procedure should be
program. Also, specific notched geometry, notch tip radius,
clearlyexplainedinthereportingsinceitisknowntoinfluence
information on the associated K for the notch, and the method
t
and source of its determination should be reported. fatigue behavior in the long-life regime.
E466 − 21
6.3 The effects to be most avoided are fillet undercutting 7.5 The action of the test machine should be analyzed to
and residual stresses introduced by specimen machining prac- ensure that the desired form and magnitude of loading is
tices. One exception may be where these parameters are under maintained for the duration of the test. Force deviations of the
study. Fillet undercutting can be readily determined by inspec- applied maximum and minimum force greater than2%ofthe
tion.Assurancethatsurfaceresidualstressesareminimizedcan desired force amplitude should be reported.
be achieved by careful control of the
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM 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: E466 − 15 E466 − 21
Standard Practice for
Conducting Force Controlled Constant Amplitude Axial
Fatigue Tests of Metallic Materials
This standard is issued under the fixed designation E466; 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 (´) indicates an editorial change since the last revision or reapproval.
1. Scope
1.1 This practice covers the procedure for the performance of axial force controlled fatigue tests to obtain the fatigue strength of
metallic materials in the fatigue regime where the strains are predominately elastic, both upon initial loading and throughout the
test. This practice is limited to the fatigue testing of axial unnotched and notched specimens subjected to a constant amplitude,
periodic forcing function in air at room temperature.
1.2 The use of this test method is limited to specimens and does not cover testing of full-scale components, structures, or consumer
products.
1.3 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.
1.4 This practice covers the procedure for the performance of axial force controlled fatigue tests to obtain the fatigue strength of
metallic materials in the fatigue regime where the strains are predominately elastic, both upon initial loading and throughout the
test. This practice is limited to the fatigue testing of axial unnotched and notched specimens subjected to a constant amplitude,
periodic forcing function in air at room temperature. This practice is not intended for application in axial fatigue tests of
components or parts. The text of this standard references notes and footnotes that provide explanatory material. These notes and
footnotes (excluding those in tables and figures) shall not be considered as requirements of the standard.
NOTE 1—The following documents, although not directly referenced in the text, are considered important enough to be listed in this practice:
E739 Practice for Statistical Analysis of Linear or Linearized Stress-Life (S-N) and Strain-Life (ε-N) Fatigue Data
STP 566 Handbook of Fatigue Testing
STP 588 Manual on Statistical Planning and Analysis for Fatigue Experiments
STP 731 Tables for Estimating Median Fatigue Limits
NOTE 1—The following documents, although not directly referenced in the text, are considered important enough to be listed in this practice:
E739 Practice for Statistical Analysis of Linear or Linearized Stress-Life (S-N) and Strain-Life (ε-N) Fatigue Data
STP 566 Handbook of Fatigue Testing
STP 588 Manual on Statistical Planning and Analysis for Fatigue Experiments
STP 731 Tables for Estimating Median Fatigue Limits
This practice is under the jurisdiction of ASTM Committee E08 on Fatigue and Fracture and is the direct responsibility of Subcommittee E08.05 on Cyclic Deformation
and Fatigue Crack Formation.
Current edition approved May 1, 2015June 1, 2021. Published June 2015July 2021. Originally approved in 1972. Last previous edition approved in 20072015 as
E466 – 07.E466 – 15. DOI: 10.1520/E0466-15.10.1520/E0466-21.
Handbook of Fatigue Testing,ASTM STP 566, ASTM, 1974.
Little, R. E., Manual on Statistical Planning and Analysis, ASTM STP 588, ASTM, 1975.
Little, R. E., Tables for Estimating Median Fatigue Limits,ASTM STP 731, ASTM, 1981.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E466 − 21
1.5 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
E3 Guide for Preparation of Metallographic Specimens
E467 Practice for Verification of Constant Amplitude Dynamic Forces in an Axial Fatigue Testing System
E468 Practice for Presentation of Constant Amplitude Fatigue Test Results for Metallic Materials
E606/E606M Test Method for Strain-Controlled Fatigue Testing
E739 Practice for Statistical Analysis of Linear or Linearized Stress-Life (S-N) and Strain-Life (ε-N) Fatigue Data
E1012 Practice for Verification of Testing Frame and Specimen Alignment Under Tensile and Compressive Axial Force
Application
E1823 Terminology Relating to Fatigue and Fracture Testing
3. Terminology
3.1 Definitions:
3.1.1 The terms used in this practice shall be as defined in Terminology E1823.
4. Significance and Use
4.1 The axial force fatigue test is used to determine the effect of variations in material, geometry, surface condition, stress, and
so forth, on the fatigue resistance of metallic materials subjected to direct stress for relatively large numbers of cycles. The results
may also be used as a guide for the selection of metallic materials for service under conditions of repeated direct stress.
4.2 In order to verify that such basic fatigue data generated using this practice is comparable, reproducible, and correlated among
laboratories, it may be advantageous to conduct a round-robin-type test program from a statistician’s point of view. To do so would
require the control or balance of what are often deemed nuisance variables; for example, hardness, cleanliness, grain size,
composition, directionality, surface residual stress, surface finish, and so forth. Thus, when embarking on a program of this nature
it is essential to define and maintain consistency a priori, as many variables as reasonably possible, with as much economy as
prudent. All material variables, testing information, and procedures used should be reported so that correlation and reproducibility
of results may be attempted in a fashion that is considered reasonably good current test practice.
4.3 The results of the axial force fatigue test are suitable for application to design only when the specimen test conditions
realistically simulate service conditions or some methodology of accounting for service conditions is available and clearly defined.
5. Specimen Design
5.1 The type of specimen used will depend on the objective of the test program, the type of equipment, the equipment capacity,
and the form in which the material is available. However, the design should meet certain general criteria outlined below:
5.1.1 The design of the specimen should be such that failure occurs in the test section (reduced area as shown in Fig. 1 and Fig.
FIG. 1 Specimens with Tangentially Blending Fillets Between the Test Section and the Ends
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
E466 − 21
2). The acceptable ratio of the areas (test section to grip section) to ensure a test section failure is dependent on the specimen
gripping method. Threaded end specimens may prove difficult to align and failure often initiates at these stress concentrations when
testing in the life regime of interest in this practice. A caveat is given regarding the gage section with sharp edges (that is, square
or rectangular cross section) since these are inherent weaknesses because the slip of the grains at sharp edges is not confined by
neighboring grains on two sides. Because of this, a circular cross section may be preferred if material form lends itself to this
configuration. The size of the gripped end relative to the gage section, and the blend radius from gage section into the grip section,
may cause premature failure particularly if fretting occurs in the grip section or if the radius is too small. Readers are referred to
Ref (1) should this occur.
5.1.2 For the purpose of calculating the force to be applied to obtain the required stress, the dimensions from which the area is
calculated should be measured to the nearest 0.001 in. (0.03 mm) for dimensions equal to or greater than 0.200 in. (5.08 mm) and
to the nearest 0.0005 in. (0.013 mm) for dimensions less than 0.200 in. (5.08 mm). Surfaces intended to be parallel and straight
should be in a manner consistent with 8.2.
NOTE 2—Measurements of dimensions presume smooth surface finishes for the specimens. In the case of surfaces that are not smooth, due to the fact
that some surface treatment or condition is being studied, the dimensions should be measured as above and the average, maximum, and minimum values
reported.
5.2 Specimen Dimensions:
5.2.1 Circular Cross Sections—Specimens with circular cross sections may be either of two types:
5.2.1.1 Specimens with tangentially blended fillets between the test section and the ends (Fig. 1)—The diameter of the test section
should preferably be between 0.200 in. (5.08 mm) and 1.000 in. (25.4 mm). To ensure test section failure, the grip cross-sectional
area should be at least 1.5 times but, preferably for most materials and specimens, at least four times the test section area. The
blending fillet radius should be at least eight times the test section diameter to minimize the theoretical stress concentration factor,
K of the specimen. The test section length should be approximately two to three times the test section diameter. For tests run in
t
compression, the length of the test section should be approximately two times the test section diameter to minimize buckling.
5.2.1.2 Specimens with a continuous radius between ends (Fig. 3)—The radius of curvature should be no less than eight times the
minimum diameter of the test section to minimize K . The reduced section length should be greater than three times the minimum
t
test section diameter. Otherwise, the same dimensional relationships should apply, as in the case of the specimens described in
5.2.1.1.
5.2.2 Rectangular Cross Sections—Specimens with rectangular cross sections may be made from sheet or plate material and may
have a reduced test cross section along one dimension, generally the width, or they may be made from material requiring
dimensional reductions in both width and thickness. In view of this, no maximum ratio of area (grip to test section) should apply.
The value of 1.5 given in 5.2.1.1 may be considered as a guideline. Otherwise, the sections may be either of two types:
5.2.2.1 Specimens with tangentially blended fillets between the uniform test section and the ends (Fig. 4)—The radius of the
blending fillets should be at least eight times the specimen test section width to minimize K of the specimen. The ratio of specimen
t
test section width to thickness should be between two and six, and the reduced area should preferably be between 0.030 in. (19.4
2 2 2
mm ) and 1.000 in. (645 mm ), except in extreme cases where the necessity of sampling a product with an unchanged surface
makes the above restrictions impractical. The test section length should be approximately two to three times the test section width
of the specimen. For specimens that are less than 0.100 in. (2.54 mm) thick, special precautions are necessary particularly in
reversed loading, such as R = −1. For example, specimen alignment is of utmost importance and the procedure outlined in Practice
FIG. 2 Specimens with Continuous Radius Between Ends
E466 − 21
FIG. 3 Specimens with a Continuous Radius Between Ends
FIG. 4 Specimens with Tangentially Blending Fillets Between the Uniform Test Section and the Ends
E606/E606M would be advantageous. Also, Refs (2-5), although they pertain to strain-controlled testing, may prove of interest
since they deal with sheet specimens approximately 0.05 in. (1.25 mm) thick.
5.2.2.2 Specimens with continuous radius between ends (Fig. 2)—The same restrictions should apply in the case of this type of
specimen as for the specimen described in 5.2.1.2. The area restrictions should be the same as for the specimen described in 5.2.2.1.
5.2.3 Notched Specimens—In view of the specialized nature of the test programs involving notched specimens, no restrictions are
placed on the design of the notched specimen, other than that it must be consistent with the objectives of the program. Also, specific
notched geometry, notch tip radius, information on the associated K for the notch, and the method and source of its determination
t
should be reported.
6. Specimen Preparation
6.1 The condition of the test specimen and the method of specimen preparation are of the utmost importance. Improper methods
of preparation can greatly bias the test results. In view of this fact, the method of preparation should be agreed upon prior to the
beginning of the test program by both the originator and the user of the fatigue data to be generated. Since specimen preparation
can strongly influence the resulting fatigue data, the application or end use of that data, or both, should be considered when
selecting the method of preparation. Appendix X1 presents an example of a machining procedure that has been employed on some
metals in an attempt to minimize the variability of machining and heat treatment upon fatigue life.
6.2 Once a technique has been established and approved for a specific material and test specimen configuration, change should
not be made because of potential bias that may be introduced by the changed technique. Regardless of the machining, grinding,
or polishing method used, the final metal removal should be in a direction approximately parallel to the long axis of the specimen.
This entire procedure should be clearly explained in the reporting since it is known to influence fatigue behavior in the long life
long-life regime.
6.3 The effects to be most avoided are fillet undercutting and residual stresses introduced by specimen machining practices. One
exception may be where these parameters are under study. Fillet undercutting can be readily determined by inspection. Assurance
that surface residual stresses are minimized can be achieved by careful control of the machining procedures. It is advisab
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