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LJDC 669.14 : 620.178.3
IS0
IN TERN AT1 ON A L ORGAN I ZATl O N FOR STANDARD IZATl O N
IS0 RECOMMENDATION
R 1099
AXIAL LOAD FATIGUE TESTING
1st EDITION
July 1969
COPYRIGHT RESERVED
The copyright of IS3 Recommendations and IS0 Standards
belongs to IS0 Member Bodies. Reproduction of these
documents, in any country, may be authorized therefore only
by the national standards organization of that country, being
a member of ISO.
For each individual country the only valid standard is the national standard of that co&try.
Printed in Switzerland
Also issued in French and Russian. Copies to be obtained through the national standards organizations.
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BRIEF HISTORY
The IS0 Recommendation R 1099, Axial loud furigue resting, was drawn up by Technical Committee ISO/TC 17,
Sreel, the Secretariat of which is held by the British Standards Institution (BSI).
Work on this question led to the adoption of a Draft IS0 Recommendation.
In June 1968, this Draft IS0 Recommendation (No. 135 I) was circulated to all the IS0 Member Bodies for
,I
enquiry. It was approved, subject to a few modifications of an editorial nature, by the following Member Bodies :
L
Australia lndia Romania
Brazil Israel South Africa, Rep. of
Canada Italy
Spain
Colombia Japan Switzerland
Czechoslovakia Korea, Rep. of Thailand
Denmark Netherlands Turkey
Finland Norway United Kingdom
Germany Peru U.S.A.
Hungary Poland
U.S S.R.
Four Member Bodies opposed the approval of the Draft :
Belgium
France
New Zealand
Sweden
The Draft IS0 Recommendation was then submitted by correspondence to the IS0 Council, which decided,
in July 1969, to accept it as an IS0 RECOMMENDATION.
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ISO/R 1099-1969 (E)
IS0 Recommendation R 1099 July 1969
AXIAL LOAD FATIGUE TESTING
1. SCOPE
This IS0 Recommendation gives the conditions for carrying out axial load fatigue tests on test pieces
without deliberately introduced stress concentrations. The tests are carried out at room temperature, in
air, the loading applied to the test piece being along the longitudinal axis passing through the centroid
of each cross-section.
Whilst the form, preparation and testing of test pieces of circular and rectangular cross-section are described,
component testing and other specialised forms of test are not included in this IS0 Recommendation. Tests
on very thin test pieces of rectangular cross-section are not covered by this IS0 Recommendation.
Results of fatigue tests may be affected by atmospheric conditions, and where controlled conditions are
required, clause 2.1 of IS0 Recommendation R 554, Standard atmospheres for conditioning andlor testing
Standard reference atmosphere - Specifications, applies.
2. OBJECT OF TEST
Tests are made to determine fatigue properties such as the S/N curve described in IS0 Recommendation
R 373, General principles for fatigue testing of metals.
3. PRINCIPLE OF TEST
Nominally identical test pieces are mounted in an axial load type fatigue testing machine and subjected
to the required loading conditions, which introduce any one of the types of cyclic stress illustrated in
Figure 3 in IS0 Recommendation R 373. The test is continued until the test piece fails or until a pre-determi-
ned number of stress cycles has been exceeded. (See section 10.)
NOTE. - For definitions of failure see IS0 Recommendation R 373.
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ISO/R 1099-1969 (E)
4. SYMBOLS AND DEFINITIONS
In this IS0 Recommendation the following symbols (see Figures 1 and 2) are used :
Diameter of the gripped ends of the test piece if plain, or overall diameter of the threaded
D
ends
d Diameter of the test piece where the stress is a maximum
LC Parallel length
Y Radius* at the ends of the test section which starts the transition from the test diameter
d or test width b to the diameter D or width B of the gripped ends; or the continuous
radius between the gripped ends of the test piece
a Thickness of test section of test pieces of rectangular cross-section
b Width of test pieces of rectangular cross-section where the stress is a maximum
B Width of test pieces of rectangular cross-section at the gripped ends
Further symbols and defuiitions relating to fatigue testing are given in IS0 Recommendation R 373.
r >5d
I hl
FIG. lb
FIG. 1 - Test pieces of circular cross-section
FIG. 2a
FIG. 2b
FIG. 2 - Test pieces of rectangular crm9ection
This 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 test pieces of the types shown in Figures la and 2a.
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Im/R 1099-1969
5. SHAPE AND SIZE OF TEST PIECE
5.1 Form of test piece
The test piece may be of
circular cross-section, with tangentially blending fillets between the test section and the ends
(U)
(Fig. la), or with a continuous radius between the ends (Fig. lb);
rectangular cross-section of uniform thickness over the test section with tangentially blending
(b)
fdets* between the test section and the gripped ends (Fig. 2a), or with a continuous radius
between the ends (Fig. 2b).
The ends of the test piece should be of a form to suit the type of machine used and the material being
tested.
The gripped ends of the test piece should be symmetrical about the axis or axes of the reduced test
section. With certain types of axialload fatigue testing machines, it is important that the ends of the
test pieces should be machined truly square to the axis or axes of the test section.
For either form of test piece where the test section is formed by a continuous radius, this radius should
be not less than 5d or 5b.
The type of test piece employed will depend on the information required from the test and the form
in which the material is available. If basic fatigue properties of a material are to be determined, it is
preferable, where practicable, to use test pieces of circular cross-section. For materials in round bar
form, test pieces of circular cross-section are an obvious choice. Test pieces of rectangular cross-section
are always used for testing materials in the form of sheet or thin plate. For production material in large
sections, e.g. forgings, either form of test piece may be employed, but it should be noted that the form
of the cross-section of the test piece may affect the value of the results obtained from the test.
5.2 Dimensions of test pieces
Ali the test pieces employed for a fatigue determination should have the same nominal dimensions.
When fundamental characteristics of a metal from a fatigue point of view are required, the following
dimensions and tolerances apply :
(U) Circulm cross-section. The nominal value of the diameter d, where the stress is at a maximum,
should be between 6 mm (0.25 in) and 12.5 mm (0.5 in). Where possible, the tolerance on shape
of the cylindrical portion should be paraiiel within 0.02 mm (0.001 in).
In the case of test pieces taken from very short samples, a diameter of less than 6 mm may be
used to obtain a standard test piece.
For the purpose of calculating the load to be applied to obtain the required stress, the actual
minimum diameter of each test piece should be measured to an accuracy of 0.01 mm (0.0005 in).
Care should be taken during the measurement of the test piece prior to testing that the surface is
not damaged.
NOTE. - In tests where the stress cycle runs into compression the ratio LJd should not be greater than 4. It
may be necessary to reduce this ratio considerably, to avoid high stresses due to buckiing.
With te& pieces of rectangular croaa-aection, it may be required to reduce the test section in both width and thickness. If thh is
necessary, then blending fillets will be required in both the width and thickness directions.
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ISO/R 1099-1%9 (E)
Rectangular cross-section. Nominal values of the thickness, a, and the width, 6, should be such
(b)
that the area of the cross-section where the stress is at a maximum is between 32.2 mm2 (0.05 in2)
and 645 mm2 (1 .O in2). Where possible, the shape of the rectangular section should be parallel
within 0.02 mm (0.001 in).
For the purpose of calculating the load to be applied to obtain the required stress, the cross-sec-
tional area should be calculated from measurement of the appropriate dimensions with a tolerance
of not more than f 0.5 in each dimension. Care should be taken during the measurement of the
test piece prior to testing that the surface is not damaged.
NOTES
1. A larger range of cross-sectional area is permitted for test pieces of rectangular cross-section than for test
pieces of circular cross-section, as the rectangular form is frequently used for obtaining data on sheet and
plate of widely varying thicknesses.
2. The tolerance on the measurement permitted for test pieces of rectangular cross-section takes into account
the possibility that such test pieces may be tested with their surfaces in the “as received” condition.
3. In tests where the stress cycle runs into compression the ratio L,/b should not be greater than 4. it may be
necessary to reduce this ratio considerably to avoid high stresses due to buckling. it may be necessary. also,
to consider the ratio of the thickness to the width in relation to buckling stresses.
6. PREPARATION OF TEST PIECE
6.1 Method of machining
It is necessary to ensure that any cutting (e.g. contour profiling by flame cutting) or machining operation
required, either to rough the test piece out from the blank or to machine it to size, does not alter the
metallurgical structure or properties of the test piece. All cuts taken in machining should be such as to
minimize work-hardening of the surface of the test piece. Grinding may
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