ASTM E466-96(2002)e1
(Practice)Standard Practice for Conducting Force Controlled Constant Amplitude Axial Fatigue Tests of Metallic Materials
Standard Practice for Conducting Force Controlled Constant Amplitude Axial Fatigue Tests of Metallic Materials
SIGNIFICANCE AND USE
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.
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’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.
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. This practice is not intended for application in axial fatigue tests of components or parts.
Note 1—The following documents, although not directly referenced in the text, are considered important enough to be listed in this practice:
E 739 Practice for Statistical Analysis of Linear or Linearized Stress-Life (S-N) and Strain-Life (-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
General Information
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Standards Content (Sample)
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e1
Designation:E466–96 (Reapproved 2002)
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 (e) indicates an editorial change since the last revision or reapproval.
e NOTE—Section 3.1.1 was editorially updated in June 2002.
1. Scope E606 Practice for Strain-Controlled Fatigue Testing
E739 Practice for Statistical Analysis of Linear or Linear-
1.1 This practice covers the procedure for the performance
ized Stress-Life (S-N) and Strain-Life (e-N) Fatigue Data
of axial force controlled fatigue tests to obtain the fatigue
E1012 Practice for Verification of Specimen Alignment
strength of metallic materials in the fatigue regime where the
Under Tensile Loading
strains are predominately elastic, both upon initial loading and
E1823 Terminology Relating to Fatigue and Fracture Test-
throughout the test. This practice is limited to the fatigue
ing
testing of axial unnotched and notched specimens subjected to
a constant amplitude, periodic forcing function in air at room
3. Terminology
temperature. This practice is not intended for application in
3.1 Definitions:
axial fatigue tests of components or parts.
3.1.1 The terms used in this practice shall be as defined in
NOTE 1—Thefollowingdocuments,althoughnotdirectlyreferencedin
Terminology E1823.
the text, are considered important enough to be listed in this practice:
E739 Practice for Statistical Analysis of Linear or Linearized Stress-
4. Significance and Use
Life (S-N) and Strain-Life (e-N) Fatigue Data
2 4.1 The axial force fatigue test is used to determine the
STP 566 Handbook of Fatigue Testing
effect of variations in material, geometry, surface condition,
STP 588 Manual on Statistical Planning and Analysis for Fatigue
Experiments stress, and so forth, on the fatigue resistance of metallic
STP 731 Tables for Estimating Median Fatigue Limits
materials subjected to direct stress for relatively large numbers
of cycles. The results may also be used as a guide for the
2. Referenced Documents
selection of metallic materials for service under conditions of
2.1 ASTM Standards:
repeated direct stress.
E3 Practice for Preparation of Metallographic Specimens
4.2 In order to verify that such basic fatigue data generated
E467 Practice for Verification of Constant Amplitude Dy-
using this practice is comparable, reproducible, and correlated
namic Forces in an Axial Fatigue Testing System
among laboratories, it may be advantageous to conduct a
E468 Practice for Presentation of Constant Amplitude Fa-
round-robin-type test program from a statistician’s point of
tigue Test Results for Metallic Materials
view.Todosowouldrequirethecontrolorbalanceofwhatare
oftendeemednuisancevariables;forexample,hardness,clean-
liness, grain size, composition, directionality, surface residual
ThispracticeisunderthejurisdictionofASTMCommitteeE08onFatigueand
stress, surface finish, and so forth.Thus, when embarking on a
Fracture and is the direct responsibility of Subcommittee E08.05 on Cyclic
Deformation and Fatigue Crack Formation. program of this nature it is essential to define and maintain
Current edition approved May 10, 2002. Published June 2002. Originally
consistency a priori, as many variables as reasonably possible,
published as E466–72 T. Last previous edition E466–95.
with as much economy as prudent. All material variables,
Handbook of Fatigue Testing, ASTM STP 566, ASTM, 1974.
testinginformation,andproceduresusedshouldbereportedso
Little, R. E., Manual on Statistical Planning and Analysis, ASTM STP 588,
ASTM, 1975.
thatcorrelationandreproducibilityofresultsmaybeattempted
Little, R. E., Tables for Estimating Median Fatigue Limits, ASTM STP 731,
in a fashion that is considered reasonably good current test
ASTM, 1981.
5 practice.
Annual Book of ASTM Standards, Vol 03.01.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
E466
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
5.1 The type of specimen used will depend on the objective times the test section diameter to minimize the theoretical
of the test program, the type of equipment, the equipment
stressconcentrationfactor, K ofthespecimen.Thetestsection
t
capacity, and the form in which the material is available.
length should be approximately two to three times the test
However, the design should meet certain general criteria
sectiondiameter.Fortestsrunincompression,thelengthofthe
outlined below:
test section should be approximately two times the test section
5.1.1 Thedesignofthespecimenshouldbesuchthatfailure
diameter to minimize buckling.
occurs in the test section (reduced area as shown in Fig. 1 and
5.2.1.2 Specimens with a continuous radius between ends
Fig. 2). The acceptable ratio of the areas (test section to grip
(Fig. 3). The radius of curvature should be no less than eight
section) to ensure a test section failure is dependent on the
times the minimum diameter of the test section to minimize K
t
specimen gripping method. Threaded end specimens may
.The reduced section length should be greater than three times
prove difficult to align and failure often initiates at these stress
the minimum test section diameter. Otherwise, the same
concentrationswhentestingintheliferegimeofinterestinthis
dimensional relationships should apply, as in the case of the
practice. A caveat is given regarding the gage section with
specimens described in 5.2.1.1.
sharp edges (that is, square or rectangular cross section) since
5.2.2 Rectangular Cross Sections—Specimens with rectan-
these are inherent weaknesses because the slip of the grains at
gular cross sections may be made from sheet or plate material
sharpedgesisnotconfinedbyneighboringgrainsontwosides.
and may have a reduced test cross section along one dimen-
Because of this, a circular cross section may be preferred if
sion, generally the width, or they may be made from material
material form lends itself to this configuration. The size of the
requiring dimensional reductions in both width and thickness.
gripped end relative to the gage section, and the blend radius
In view of this, no maximum ratio of area (grip to test section)
from gage section into the grip section, may cause premature
should apply. The value of 1.5 given in 5.2.1.1 may be
failureparticularlyiffrettingoccursinthegripsectionorifthe
considered as a guideline. Otherwise, the sections may be
radius is too small. Readers are referred to Ref (1) should this
either of two types:
occur.
5.2.2.1 Specimens with tangentially blended fillets between
5.1.2 For the purpose of calculating the force to be applied
to obtain the required stress, the dimensions from which the theuniformtestsectionandtheends(Fig.4).Theradiusofthe
area is calculated should be measured to the nearest 0.001 in. blending fillets should be at least eight times the specimen test
(0.03 mm) for dimensions equal to or greater than 0.200 in. section width to minimize K of the specimen. The ratio of
t
(5.08 mm) and to the nearest 0.0005 in. (0.013 mm) for specimentestsectionwidthtothicknessshouldbebetweentwo
dimensionslessthan0.200in.(5.08mm).Surfacesintendedto
and six, and the reduced area should preferably be between
2 2 2 2
be parallel and straight should be in a manner consistent with 0.030 in. (19.4 mm ) and 1.000 in. (645 mm ), except in
8.2.
extreme cases where the necessity of sampling a product with
anunchangedsurfacemakestheaboverestrictionsimpractical.
NOTE 2—Measurements of dimensions presume smooth surface fin-
The test section length should be approximately two to three
ishes 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 times the test section width of the specimen. For specimens
dimensions should be measured as above and the average, maximum, and
thatarelessthan0.100in.(2.54mm)thick,specialprecautions
minimum values reported.
are necessary particularly in reversed loading, R =−1. For
5.2 Specimen Dimensions: example, specimen alignment is of utmost importance and the
5.2.1 Circular Cross Sections—Specimens with circular procedure outlined in Practice E606 would be advantageous.
cross sections may be either of two types: Also, Refs (2-5), although they pertain to strain-controlled
FIG. 1 Specimens with Tangentially Blending Fillets Between the Test Section and the Ends
E466
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
testing, may prove of interest since they deal with sheet considered when selecting the method of preparation. Appen-
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 ma-
of the test programs involving notched specimens, no restric- chining, 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 fatigue behavior in the long life regime.
t
and source of its determination should be reported. 6.3 The effects to be most avoided are fillet undercutting
and residual stresses introduced by specimen machining prac-
6. Specimen Preparation
tices. One exception may be where these parameters are under
6.1 The condition of the test specimen and the method of study. Fillet undercutting can be readily determined by inspec-
specimen preparation are of the utmost importance. Improper tion.Assurancethatsurfaceresidualstressesareminimizedcan
methodsofpreparationcangreatlybiasthetestresults.Inview be achieved by careful control of the machining procedures. It
of this fact, the method of preparation should be agreed upon is advisable to determine these surface residual stresses with
priortothebeginningofthetestprogrambyboththeoriginator X-raydiffractionpeakshiftorsimilartechniquesandthevalue
andtheuserofthefatiguedatatobegenerated.Sincespecimen of the surface residual stress reported along with the direction
preparation can strongly influence the resulting fatigue data, ofdetermination(thatis,longitudinal,transverse,radial,andso
the application or end use of that data, or both, should be forth).
E466
6.4 Storage—Specimens that are subject to corrosion in 8.2 Alignment Verification—To minimize bending stresses
room temperature air should be accordingly protected, prefer- (strains), specimen fixtures should be aligned such that the
ablyinaninertmedium.Thestoragemediumshouldgenerally majoraxisofthespecimencloselycoincideswiththeloadaxis
be removed before testing using appropriate solvents, if nec- throughout each cycle. It is important that the accuracy of
essary, without adverse effects upon the life of the specimens. alignment be kept consistent from specimen to specimen.
6.5 Inspection—Visual inspections with unaided eyes or Alignmentshouldbecheckedbymeansofatrialtestspecimen
with low power magnification up to 203 should be conducted with longitudinal strain gages placed at four equidistant loca-
on all specimens. Obvious abnormalities, such as cracks, tions around the minimum diameter. The trial test specimen
machining marks, gouges, undercuts, and so forth, are not should be turned about its axis, installed, and checked for each
acceptable. Specimens should be cleaned prior to testing with of four orientations within the fixtures. The bending stresses
solvent(s) noninjurous and nondetremental to the mechanical (strains)sodeterminedshouldbelimitedtolessthan5%ofthe
properties of the material in order to remove any surface oil greater of the range, maximum or minimum stresses (strains),
films, fingerprints, and so forth. Dimensional analysis and imposed during any test program. For specimens having a
inspection should be conducted in a manner that will not uniform gage length, it is advisable to place a similar set of
visibly mark, scratch, gouge, score, or alter the surface of the gages at two or three axial positions within the gage section.
One set of strain gages should be placed at the center of the
specimen.
gagelengthtodetectmisalignmentthatcausesrelativerotation
ofthespecimenendsaboutaxesperpendiculartothespecimen
7. Equipment Characteristics
axis. The lower the bending stresses (strains), the more
7.1 Generally, the tests will be performed on one of the
repeatable the test results will be from specimen to specimen.
following types of fatigue testing machines:
This is especially important for materials with low ductility
7.1.1 Mechanical (eccentric crank, power screws, rotating
(thatis,bendingstresses(strains)shouldnotexceed5%ofthe
masses),
minimum stress (strain) amplitude).
7.1.2 Electromecha
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