ISO 1099:2006
(Main)Metallic materials — Fatigue testing — Axial force-controlled method
Metallic materials — Fatigue testing — Axial force-controlled method
ISO 1099:2006 specifies the conditions for carrying out axial, constant-amplitude, force-controlled fatigue tests at ambient temperature on metallic specimens, without deliberately introduced stress concentrations. The object of testing is to provide fatigue information, such as the relation between applied stress and number of cycles to failure for given materials at various stress ratios. While the form, preparation and testing of specimens of circular and rectangular cross-section are described, component testing and other specialized forms of testing are not included in ISO 1099:2006.
Matériaux métalliques — Essais de fatigue — Méthode par force axiale contrôlée
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Standards Content (Sample)
INTERNATIONAL ISO
STANDARD 1099
Second edition
2006-04-15
Metallic materials — Fatigue testing —
Axial force-controlled method
Matériaux métalliques — Essais de fatigue — Méthode par force axiale
contrôlée
Reference number
ISO 1099:2006(E)
©
ISO 2006
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ISO 1099:2006(E)
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ISO 1099:2006(E)
Contents Page
Foreword. iv
Introduction . v
1 Scope. 1
2 Normative references. 1
3 Terms and definitions. 1
4 Test plan. 3
4.1 General outline. 3
4.2 Presentation of fatigue results. 4
4.2.1 Wöhler or S-N curve . 4
4.2.2 Mean stress diagrams . 4
4.2.3 Alignment. 4
5 Shape and size of specimen. 5
5.1 Form of specimens. 5
5.2 Specimen temperature measurement. 5
6 Specimens. 6
6.1 Geometry. 6
6.1.1 Products (bars, flat sheets over 5 mm thick). 6
6.1.2 Flat products with thickness of 5 mm or less. 6
6.2 Preparation of specimens. 7
6.2.1 Machining procedure. 7
6.2.2 Sampling and marking . 7
6.2.3 Surface condition of the specimen . 8
6.2.4 Dimensional checks. 8
6.2.5 Storage and handling . 8
7 Apparatus. 8
7.1 Testing machine. 8
7.1.1 Force transducer. 9
7.1.2 Gripping of specimen. 9
7.1.3 Alignment check . 9
7.2 Instrumentation for test monitoring. 9
7.2.1 Recording systems. 9
7.2.2 Cycle counter. 9
7.3 Checking and verification. 10
8 Testing machine. 10
9 Mounting of specimen. 10
10 Speed of testing. 10
11 Application of force . 11
12 Recording of temperature and humidity . 11
13 Criterion of failure and test termination . 11
13.1 Criterion of failure. 11
13.2 Test termination. 11
14 Test report. 12
Bibliography . 21
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ISO 1099:2006(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies
(ISO member bodies). The work of preparing International Standards is normally carried out through ISO
technical committees. Each member body interested in a subject for which a technical committee has been
established has the right to be represented on that committee. International organizations, governmental and
non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the
International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights.
ISO 1099 was prepared by Technical Committee ISO/TC 164, Mechanical testing of metals, Subcommittee
SC 5, Fatigue testing.
This second edition cancels and replaces the first edition (ISO 1099:1975), which has been technically revised.
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ISO 1099:2006(E)
Introduction
This International Standard is intended to provide guidance for conducting axial, constant-amplitude, force-
controlled cyclic fatigue tests on specimens of a metal for the sake of generating fatigue-life data (i.e. stress vs.
cycles to failure).
Nominally identical specimens are mounted on an axial force-type fatigue testing machine and subjected to
the required loading conditions that introduce any one of the types of cyclic stress illustrated in Figure 1. The
test waveform shall be of constant amplitude, and sinusoidal unless otherwise specified.
The force being applied to the specimen is along the longitudinal axis passing through the centroid of each
cross-section.
The test is continued until the specimen fails or until a predetermined number of stress cycles has been
exceeded. (See Clauses 4 and 13.)
The test is typically conducted at ambient temperature (ideally between 10 °C and 35 °C).
NOTE The results of a fatigue test may be affected by atmospheric conditions, and where controlled conditions are
required, subclause 2.1 of ISO 554:1976 applies.
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INTERNATIONAL STANDARD ISO 1099:2006(E)
Metallic materials — Fatigue testing — Axial force-controlled
method
1 Scope
This International Standard specifies the conditions for carrying out axial, constant-amplitude, force-controlled
fatigue tests at ambient temperature on metallic specimens, without deliberately introduced stress
concentrations. The object of testing is to provide fatigue information, such as the relation between applied
stress and number of cycles to failure for given materials at various stress ratios.
While the form, preparation and testing of specimens of circular and rectangular cross-section are described,
component testing and other specialized forms of testing are not included in this International Standard.
NOTE Fatigue tests on notched specimens are not covered by this International Standard since the shape and size
of notched test pieces have not been standardized. However, fatigue-test procedures described in this standard may be
applied to fatigue tests on notched specimens.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated
references, only the edition cited applies. For undated references, the latest edition of the referenced
document (including any amendments) applies.
ISO 554:1976, Standard atmospheres for conditioning and/or testing — Specifications
ISO 4287:1997, Geometrical Product Specifications (GPS) — Surface texture: Profile method — Terms,
definitions and surface texture parameters
ISO 4288:1996, Geometrical Product Specifications (GPS) — Surface texture: Profile method — Rules and
procedures for the assessment of surface texture
ISO 4965:1979, Axial load fatigue testing machines — Dynamic force calibration – Strain gauge technique
ISO 7500-1:2004, Metallic materials — Verification of static uniaxial testing machines — Part 1:
Tension/compression testing machines – Verification and calibration of the force-measuring system
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
test diameter
d
diametral distance or width of the specimen or test piece where the stress is a maximum
See Figures 3 and 4
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ISO 1099:2006(E)
3.2
thickness of test section
a
thickness of a rectangular cross-section specimen or test piece
3.3
width of test section
b
width of a rectangular cross-section specimen or test piece
3.4
parallel length
L
c
length in the gauge test section of a specimen or test piece that has equal test diameter or test width
and is parallel
See Figures 3 and 4.
3.5
radius
r
curvature at the ends of the test section that starts the transition from the test diameter, d, or test width, b, to
the diameter or width of the gripped ends; or the continuous radius between the gripped ends of the specimen
or test piece
NOTE The curve need not be a true arc of a circle over the whole of the distance between the end of the test section
and the start of the enlarged end for the types shown in Figures 3a) and 4a).
3.6
maximum stress
σ , S
max max
highest algebraic value of stress in a stress cycle
See Figure 2.
3.7
mean stress
σ , S
m m
one-half the algebraic sum of the maximum stress and the minimum stress in a stress cycle
See Figure 2.
3.8
minimum stress
σ , S
min min
lowest algebraic value of stress in a stress cycle
See Figure 2.
3.9
stress amplitude
σ , S
a a
one-half the algebraic difference between the maximum stress and the minimum stress in a stress cycle
See Figure 2.
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ISO 1099:2006(E)
3.10
stress range
∆σ, ∆S
arithmetic difference between the maximum and minimum stress
∆σ = σ – σ or ∆S = S – S
max min max min
See Figure 2.
3.11
stress ratio
R
s
ratio of minimum to maximum stress during any single cycle of fatigue operation
R = σ /σ
s min max
See Figure 2.
3.12
stress cycle
variation of stress with time, repeated periodically and identically
See Figure 2.
3.13
number of cycles
N
number of smallest segments of the force-time, stress-time, strain-time, etc., function that is repeated
periodically
3.14
fatigue life
endurance
N
f
number of applied cycles to achieve a defined failure criterion
3.15
fatigue strength at N cycles
σ
N
value of the stress amplitude at a stated stress ratio under which the specimen would have a life of N cycles
4 Test plan
4.1 General outline
Before commencing testing, the following shall be agreed by the parties concerned, unless specified
otherwise in the relevant product standard:
a) The form of specimen to be used (see 5.1).
b) The stress ratio(s) to be used.
c) The objective of the tests, i.e., which of the following is to be determined:
⎯ the fatigue life at a specified stress amplitude;
⎯ the fatigue strength at a specified “endurance”;
⎯ a full Wöhler or S-N curve.
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ISO 1099:2006(E)
d) The number of specimens to be tested and the testing sequence.
e) The number of cycles at which a test on an unfailed specimen shall be terminated.
f) The testing temperature if different from the requirements given in 5.2.
7 8
Commonly employed “endurances” are, for example, 10 cycles for structural steels and 10 cycles for other
steels and non-ferrous alloys. In the light of recent research, however, it is of importance to note that metals
generally do not exhibit an “endurance limit” or “fatigue limit” per se, that is, a stress below which the metal will
endure an “infinite number of cycles”. Typically, the “plateau(s)” in stress-life are referred to as the
conventional “fatigue limit(s)” or “endurance limit(s)”, but failures below these levels have been reported and
do occur. See, for example, References [1] to [3] in the Bibliography.
4.2 Presentation of fatigue results
The design of the investigation, and the use to be made of the results, govern the choice of the most suitable
method of presenting the results from the many available, graphically and otherwise. The results of fatigue
tests are usually presented graphically. In reporting fatigue data, the test conditions should be clearly defined.
In addition to graphical presentations, tabulated numerical data are desirable where the presentation format
permits.
4.2.1 Wöhler or S-N curve
The most general method of presenting the results graphically is to plot the number of cycles to failure, N, as
abscissa and the values of stress amplitude or, depending on the type of stress cycle, those of any other
stress, as ordinate. The curve drawn smoothly as an approximate middle line through the experimental points
is called a Wöhler or S-N curve. A logarithmic scale is used for the number of cycles and the choice of whether
a linear or logarithmic scale is used for the stress axis lies with the experimenter. Individual curves are plotted
for each set of tests for each R-ratio. Experimental results are usually plotted on the same figure. An example
of these graphical representations is shown in Figure 5, where a linear stress scale is used.
4.2.2 Mean stress diagrams
The fatigue strengths derived from the Wöhler or S-N curve are plotted in fatigue strength diagrams. The
results can be represented by a graph giving directly, for particular “endurances”, the stress amplitude against
the mean stress, as shown in Figure 6 (Haigh diagram); or by plotting the maximum and minimum stresses
against the mean stress, as shown in Figure 7 (Smith diagram); or by plotting the maximum stress against the
minimum stress, as shown in Figure 8 (Ros diagram). Experimental results may be plotted on the same figure.
4.2.3 Alignment
The alignment check shall be carried out using a standard calibration specimen. The alignment specimen
illustrated in Figure 9 should be of a geometry similar to the specimens being tested. It is suggested that the
alignment specimen be made from a hardened heat-treated steel or similar material capable of totally elastic
strains up to at least 0,4 % or the force corresponding to the maximum strain imposed on the specimen used
in the test series.
In order to check the misalignment due to angular offset, lateral offset and/or load-train offset, the alignment
specimen should have resistance strain gauges secured at the locations A, B and C illustrated in Figure 9.
With the top or bottom (not both) of the strain-gauged specimen secured in the gripping arrangement, the
temperature should be allowed to equilibrate and the zero reference adjustments to the bridge amplifiers
accomplished. At this time, the alignment specimen should then be gripped in both the upper and lower grip.
The gauged specimen should then be loaded in tension to a maximum strain of 0,4 % or the force
corresponding to the maximum strain to be imposed on the specimens in the test series, if this value does not
exceed 0,4 % strain on the gauge specimen. The force shall be applied to the gauged specimen four (4) times,
corresponding to the specimen positions of 0, 90, 180, 270 degrees. The percent bending is calculated for
each of the four specimen positions according to the scheme in Figure 9. If the percent bending exceeds 5 %
on one or more of the three instrumented planes for any of the four specimen positions, adjustments should
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ISO 1099:2006(E)
be made in the test frame actuator or fixtures and/or force transducer, followed by repeating the procedure
until the less than 5 % limit on percent bending is achieved.
The procedure should be repeated in compression to ascertain that the alignment is within that specified
(i.e. u 5 %).
If the check is not satisfactory:
⎯ The reproducibility of the measurements shall be verified by carrying out the process several times.
⎯ It shall be established that the results are attributable to the test assembly and not to the specimen.
⎯ The elements making up the gripping train (instruments, cell, machine) shall be checked for their
geometric accuracy.
5 Shape and size of specimen
5.1 Form of specimens
Generally, a specimen having a fully machined test section of one of the types shown in Figures 3 and 4 shall
be used.
The specimens may be of the following:
⎯ circular cross-section, with tangentially blending fillets between the test section and the ends [Figure 3 a)],
or with a continuous radius between the ends [Figure 3 b)];
⎯ rectangular cross-section of uniform thickness over the test section with tangentially blending fillets
between the test section and the gripped ends [Figure 4 a)], or with a continuous radius between the ends
[Figure 4 b)].
It is important to mention that, for specimens of rectangular cross-section, it may be necessary to reduce the
test section in both width and thickness. If this is necessary, then blending fillets will be required in both the
width and thickness directions. Also, for a rectangular-section specimen, where it is desired to take account of
the surface condition in which the metal will be used in actual application, then at least one surface of the test
section of the test piece should remain unmachined. It is often the case, for fatigue tests conducted using a
rectangular-section piece, that the results are not always comparable to those determined on cylindrical
specimens, because of the difficulty in obtaining an adequate surface finish or because fatigue cracks initiate
preferentially at the corner(s) of the rectangular test piece.
For either form of specimen where the test section is formed by a continuous radius, this radius shall be at
least 3d (or 3b) and the elastic stress concentration factor shall be included in the test report.
5.2 Specimen temperature measurement
The test is typically conducted at ambient temperature (ideally between 10 °C and 35 C). In a high or low
temperature test, the specimen temperature may be measured using thermocouples in contact with the
specimen surface, or other appropriate devices accurate to within ± 2 °C. The specimen temperature, T, must
be documented if it is considered “high” (H), that is, greater than or equal to 0,3 × homologous temperature of
the metal [i.e. W 0,3T = T (K) / T (K)].
H test melt
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ISO 1099:2006(E)
6 Specimens
6.1 Geometry
6.1.1 Products (bars, flat sheets over 5 mm thick)
The gauge portion of the specimen represents a volume element of the material under study, which implies
that the geometry of the specimen shall not affect the use of the results.
The geometric dimensions in Table 1 (see Figure 3) are recommended.
Table 1
Parameter Dimension
Diameter of cylindrical gauge length d W 3 mm
Transition radius (from parallel section to grip end) r W 2d
External diameter (grip end) D W 2d
Length of reduced section L u 8d
C
Other geometric cross-sections and gauge lengths may be used. It is important that general tolerances of the
specimens respect the three following properties:
⎯ Parallelism // u 0,005d
⎯ Concentricity ο u 0,005d
⎯ Perpendicularity ⊥ u 0,005d
(These values are expressed in relation to the axis or reference plane.)
6.1.2 Flat products with thickness of 5 mm or less
In general, the considerations discussed in the 6.1.1 also apply to tests on the above products.
Because low loads are generally applied, more sensitive force transducers than usual may be required.
In general, the width of the specimen is reduced in the gauge length to avoid failures in the grips. In some
applications, it might be necessary to add end-tabs to increase the grip and thickness, as well as to avoid
failure in the grips (Figure 10).
The correct alignment of the specimen shall be carefully checked with a trial specimen for
⎯ parallelism and alignment of grips, and
⎯ alignment of the specimen with the loading axis.
This verification shall be carried out using a specimen with geometry as similar as possible to that of the test
specimen, instrumented with strain gauges on the two faces. In some instances, the use of anti-buckling
restraints may be required on the faces of the specimen. An example of an anti-buckling restraint is shown in
Figure 11. However, the use of anti-buckling restraints is generally discouraged.
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ISO 1099:2006(E)
6.2 Preparation of specimens
In any fatigue-test program designed to characterize the intrinsic properties of a material, it is important to
observe the following recommendations in the preparation of specimens. A deviation from these
recommendations is possible if the test program aims to determine the influence of a specific factor (surface
treatment, oxidation, etc.) that is incompatible with these recommendations. In all cases, these deviations
shall be noted in the test report.
6.2.1 Machining procedure
6.2.1.1 General
The machining procedure selected may produce residual stresses on the specimen surface that are likely to
affect the test results. These stresses may be induced by heat gradients at the machining stage, stresses
associated with deformation of the material or microstructural alterations. Their influence is less when tested
at elevated temperatures because they are partially or totally relaxed at high temperatures. However, they are
to be reduced by using an appropriate final machining procedure, especially prior to a final polishing stage.
For harder materials, grinding rather than tool operation (turning or milling) may be preferred. This is followed
by polishing.
⎯ Grinding: from 0,1 mm of the final diameter at a rate of no more than 0,005 mm/pass.
⎯ Polishing: remove the final 0,025 mm with papers of decreasing grit size. It is recommended that the final
direction of the polishing be along the specimen axis.
6.2.1.2 Alteration in the microstructure of the material
This phenomenon may be caused by the increase in temperature and by the strain-hardening induced by
machining. It may be a matter of a change in phase or, more frequently, of surface recrystallization. The
immediate effect of this is to make the test invalid, as the material tested is no longer the initial material. Every
precaution should therefore be taken to avoid this risk.
6.2.1.3 Introduction of contaminants
The mechanical properties of certain materials deteriorate when in the presence of certain elements or
compounds. An example of this is the effect of chlorine on steels and titanium alloys. These elements shall
therefore be avoided in the products used (cutting fluids, etc.). Rinsing and degreasing of specimens prior to
storage is also recommended.
6.2.2 Sampling and marking
The sampling of test materials from a semi-finished product or a component may have a major influence on
the results obtained during the test. It is therefore necessary for this sampling to be carried out with full
knowledge of the situation. A sampling drawing, attached to the test report, should indicate clearly:
⎯ the position of each of the specimens,
⎯ the characteristic directions in which the semi-finished product has been worked (direction of rolling,
extrusion, etc., as appropriate), and
⎯ the marking/identifying of each of the specimens.
The specimens shall carry a mark/identification during each different stage of their preparation. Such a
mark/identification may be applied using any reliable method in an area not likely to disappear during
machining or likely to adversely affect the quality of the test.
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6.2.3 Surface condition of the specimen
The surface conditions of the specimens have an effect on the test results. This effect is generally associated
with one or more of the following factors:
⎯ the specimen surface roughness;
⎯ the presence of residual stresses;
⎯ alteration in the microstructure of the material;
⎯ introduction of contaminants.
The recommendations below allow the influence of these factors to be reduced to a minimum.
The surface condition is commonly quantified by the mean roughness or equivalent (e.g. ten-point roughness
or maximum height of irregularities). The influence o
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