ISO 1352:2021
(Main)Metallic materials — Torque-controlled fatigue testing
Metallic materials — Torque-controlled fatigue testing
This document specifies the conditions for performing torsional, constant-amplitude, nominally elastic stress fatigue tests on metallic specimens without deliberately introducing stress concentrations. The tests are typically carried out at ambient temperature or an elevated temperature in air by applying a pure couple to the specimen about its longitudinal axis. While the form, preparation and testing of specimens of circular cross-section and tubular cross-section are described in this document, component and other specialized types of testing are not included. Similarly, low-cycle torsional fatigue tests carried out under constant-amplitude angular displacement control, which lead to failure in a few thousand cycles, are also excluded.
Matériaux métalliques — Essais de fatigue par couple de torsion commandé
General Information
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Standards Content (Sample)
FINAL
INTERNATIONAL ISO/FDIS
DRAFT
STANDARD 1352
ISO/TC 164/SC 4
Metallic materials — Torque-
Secretariat: ANSI
controlled fatigue testing
Voting begins on:
2021-10-01
Matériaux métalliques — Essais de fatigue par couple de torsion
commandé
Voting terminates on:
2021-11-26
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BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO-
ISO/FDIS 1352:2021(E)
LOGICAL, COMMERCIAL AND USER PURPOSES,
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NATIONAL REGULATIONS. © ISO 2021
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ISO/FDIS 1352:2021(E)
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ISO/FDIS 1352:2021(E)
Contents Page
Foreword .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols and abbreviated terms.3
5 Principle of test . 4
6 Test plan . 5
7 Shape and size of specimen . 5
7.1 Form . 5
7.2 Dimensions . 7
7.2.1 Specimens of circular cross-section . 7
7.2.2 Specimens with tubular cross-section . 8
8 Preparation of specimens .8
8.1 General . 8
8.2 Machining procedure . 8
8.3 Sampling and marking . . 9
8.4 Surface conditions of specimen . 9
8.5 Dimensional checks . 10
8.6 Storage and handling . 10
9 Apparatus .10
9.1 Testing machine . . 10
9.1.1 General . 10
9.1.2 Torque cell . 10
9.1.3 Gripping of specimen . 11
9.1.4 Alignment check . 11
9.1.5 Axial force. 11
9.2 Heating system .12
9.3 Instrumentation for test monitoring .12
9.3.1 Recording system .12
9.3.2 Cycle counter . .12
9.3.3 Checking and verification .12
10 Test procedure .13
10.1 Mounting of specimen . 13
10.2 Frequency of testing .13
10.3 Heating for the isothermal elevated temperature test . 13
10.4 Application of torque . 13
10.5 Calculation of nominal torsional (shear) stress . 13
10.6 Recording of temperature and humidity . 14
10.7 Failure and termination criteria . 14
10.7.1 Failure . 14
10.7.2 Termination . 14
11 Measurement uncertainty .14
12 Test report .14
Annex A (informative) Presentation of results .16
Annex B (informative) Verification of alignment of torsional fatigue testing machines .19
Annex C (informative) Measuring uniformity of torsional strain (stress) state .21
Annex D (informative) Estimation of measurement uncertainty .24
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ISO/FDIS 1352:2021(E)
Bibliography .26
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ISO/FDIS 1352:2021(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
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ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
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. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www.iso.org/patents).
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expressions related to conformity assessment, as well as information about ISO's adherence to
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www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 164, Mechanical testing of metals,
Subcommittee SC 4, Fatigue, fracture and toughness testing.
This third edition cancels and replaces the second edition (ISO 1352:2011), which has been technically
revised.
The main changes compared to the previous edition are as follows:
— addition of the test apparatus and procedure for the elevated temperature testing;
— addition of measurement uncertainty estimation.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
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FINAL DRAFT INTERNATIONAL STANDARD ISO/FDIS 1352:2021(E)
Metallic materials — Torque-controlled fatigue testing
1 Scope
This document specifies the conditions for performing torsional, constant-amplitude, nominally elastic
stress fatigue tests on metallic specimens without deliberately introducing stress concentrations. The
tests are typically carried out at ambient temperature or an elevated temperature in air by applying a
pure couple to the specimen about its longitudinal axis.
While the form, preparation and testing of specimens of circular cross-section and tubular cross-section
are described in this document, component and other specialized types of testing are not included.
Similarly, low-cycle torsional fatigue tests carried out under constant-amplitude angular displacement
control, which lead to failure in a few thousand cycles, are also excluded.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements 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 23788, Metallic materials — Verification of the alignment of fatigue testing machines
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
3.1
maximum stress
τ
max
highest algebraic value of shear stress at the outer diameter in the stress cycle
Note 1 to entry: See Figure 1.
3.2
minimum stress
τ
min
lowest algebraic value of shear stress in the stress cycle
Note 1 to entry: See Figure 1.
3.3
mean stress
τ
m
static component of the shear stress
Note 1 to entry: It is one half of the algebraic sum of the maximum shear stress and the minimum shear stress:
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ISO/FDIS 1352:2021(E)
ττ+
maxmin
τ =
m
2
3.4
stress amplitude
τ
a
variable component of shear stress
Note 1 to entry: It is one half of the algebraic difference between the maximum shear stress and the minimum
shear stress:
ττ−
maxmin
τ =
a
2
3.5
number of cycles
N
number of cycles applied at any stage during the test
3.6
stress ratio
R
algebraic ratio of the minimum shear stress to the maximum shear stress in one cycle
Note 1 to entry: It is expressed as:
τ
min
R=
τ
max
3.7
stress range
Δτ
range between the maximum and minimum shear stresses
Note 1 to entry: It is expressed as:
Δτ =−ττ
maxmin
3.8
fatigue life at failure
N
f
number of stress cycles to failure in a specified condition
3.9
fatigue strength at N cycles
τ
N
value of the shear stress amplitude (3.4) at a stated stress ratio (3.6) under which the specimen would
have a life of N cycles
3.10
torque
M
twisting couple producing shear stress or twisting deformation about the axis of the specimen
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ISO/FDIS 1352:2021(E)
Key
X time
Y stress
1 one stress cycle
Figure 1 — Fatigue stress cycle
4 Symbols and abbreviated terms
D diameter or width across flats of the gripped ends of the specimen
NOTE 1 The value of D may be different for each end of the specimen.
d diameter of specimen of circular cross-section
d outer diameter of test section of specimen of tubular cross-section
o
d inner diameter of test section of specimen of tubular cross-section
i
L axial separation of strain gauges
g
L parallel length
p
r transition blending radius at ends of test section which starts the transition from d to D
(see Figures 3 and 4)
NOTE 2 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 specimens of the types shown in
Figure 3.
t wall thickness in the test section of the thin-walled tube specimen
T specified temperature at which the test should be performed
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ISO/FDIS 1352:2021(E)
T indicated temperature or measure temperature on the surface of the parallel length of the
i
specimen
° °
ε linear normal strain in the 0 directions of the 45 strain rosette
a
° °
ε linear normal strain in the 45 directions of the 45 strain rosette
b
° °
ε linear normal strain in the 90 directions of the 45 strain rosette
c
ε circumferential strain
θθ
ε longitudinal strain
zz
γ shear strain
θz
5 Principle of test
Nominally identical specimens are mounted on a torsional fatigue testing machine and subjected to the
loading condition required to introduce cycles of torsional stress. Any one of the types of cyclic stress
illustrated in Figure 2 may be used. The test waveform shall be constant-amplitude sinusoidal, unless
otherwise specified.
In an axially symmetrical specimen, change of mean torque does not introduce a different type of stress
system and mean stress in torsion may always be regarded as positive in sign.
The torque is applied to the specimen about the longitudinal axis passing through the centroid of the
cross-section.
The test is continued until the specimen fails or until a predetermined number of stress cycles has been
exceeded.
NOTE Typically, cracks produced by torsional fatigue testing are parallel or orthogonal to the longitudinal
axis (shear stress driven) or helical at approximately +/-45° to the longitudinal axis (principal stress driven).
Tests conducted at ambient temperature shall be performed between 10 °C and 35 °C unless otherwise
agreed with the customer.
The results of fatigue testing can be affected by atmospheric conditions, and where controlled
conditions are required, ISO 554:1976, 2.1, applies.
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ISO/FDIS 1352:2021(E)
Key
X time
Y stress
1 reversed
2 fluctuating
Figure 2 — Types of cyclic stress
6 Test plan
Before commencing testing, the following shall be agreed by the parties concerned and any
modifications shall be mutually agreed upon:
a) the form of specimen to be used (see Clause 7);
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 number of cycles;
— a full Wöhler or S–N curve;
d) the number of specimens to be tested and the test sequence;
e) the number of cycles a specimen is subjected to before the test is terminated.
[3]
NOTE 1 Some methods of data presentation are given in Annex A. See ISO 12107 for details, including data
analysis procedure and statistical presentation.
NOTE 2 Commonly employed numbers of cycles for test termination are:
7
— 10 cycles for structural steels, and
8
— 10 cycles for other steels and non-ferrous alloys.
7 Shape and size of specimen
7.1 Form
Generally, a specimen having a fully machined test section of one of the types shown in Figures 3 and 4
should be used.
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ISO/FDIS 1352:2021(E)
The specimen may be of:
— solid circular cross-section, with tangentially blending fillets between the test section and the ends
(see Figure 3); or
— tubular cross-section, with tangentially blending fillets between the test section and the ends in the
outer surface (see Figure 4).
The hourglass specimen is not recommended because the crack under torsional loads may propagate at
o
45 to the loading axis.
For tubular specimens, the diameter of the inner surface at the ends may be greater than or equal to
that at the test section. For a specimen having an inner diameter at the ends greater than that at the test
section, crack initiation or failure outside the test section invalidates the test, which should be counted
as a discontinued (stopped) test at the number of cycles completed.
Fatigue test results determined using the specimen of tubular cross-section are not always comparable
to those obtained from the specimen of solid circular cross-section (due to absence or existence of
elastic constraint). Therefore, caution should be exercised when comparing fatigue lives obtained on
the same material from specimens having different cross-sections.
Typical specimen ends are shown in Figure 5. It is recommended that ends suitable for meeting the
alignment criterion be chosen.
Figure 3 — Specimens with circular cross-section
Figure 4 — Specimen with tubular cross-section
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ISO/FDIS 1352:2021(E)
Figure 5 — Typical specimen ends
7.2 Dimensions
7.2.1 Specimens of circular cross-section
It is recommended that the geometric dimensions given in Table 1 be used (see also Figure 3).
Table 1 — Dimensions for specimens of circular cross-section
Diameter of cylindrical parallel length, in millime-
5 ≤ d ≤ 12
tres
Parallel length L ≤ 5d
p
Transition radius (from parallel section to grip
r ≥ 3d
end)
External diameter (grip end) D ≥ 2d
The tolerance on d shall be ±0,05 mm.
To calculate the applied torque loading, the actual diameter of each specimen shall be measured to an
accuracy of 0,01 mm. Care should be taken not to damage the surface when measuring the specimen
prior to testing.
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ISO/FDIS 1352:2021(E)
It is important that general tolerances of the specimen respect the two following properties:
— parallelism: 0,005d or better;
— concentricity: 0,005d or better.
These values are expressed in relation to the axis or reference plane.
7.2.2 Specimens with tubular cross-section
In general, the considerations applicable to specimens of circular cross-section also apply to tests on
tubular specimens.
The specimen wall thickness shall be large enough to avoid instabilities during cyclic loading without
violating the thin-walled tube criterion, i.e. a mean diameter-to-wall thickness ratio of 10:1 or greater
is required.
It is recommended that the geometric dimensions given in Table 2 be used (see also Figure 4).
Table 2 — Dimensions for specimens of tubular cross-section
Wall thickness in test section, t 0,05d to 0,1d
o o
Outer diameter of test section d
o
Transition radius (from parallel section to grip
≥ 3d
o
end), r
Parallel length, L 1d to 3d
p o o
External diameter (grip end) D ≥ 1,5d
o
Concentricity between the outer diameter, d , and the inner diame-
o
ter, d , should be maintained within 0,01t.
i
8 Preparation of specimens
8.1 General
In any fatigue test programme designed to characterize the intrinsic properties of a material, it is
important to observe the following recommendations in the preparation of specimens. Deviation from
these recommendations is permitted if the test program aims to determine the influence of a specific
factor (surface treatment, oxidation, etc.). In all cases, any deviations shall be noted in the test report.
Specimens should be machined from normally stress-free material unless otherwise agreed with the
customer.
8.2 Machining procedure
Machining the specimens can induce residual stress on the specimen surface that could affect the test
results. These stresses can be induced by heat gradients at the machining stage — stresses associated
with deformation of the material or microstructural alterations. However, they can 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 preferable.
— Grinding: from 0,1 mm of the final dimension 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 polishing be along the specimen axial direction.
— For tubular specimens the bore should be fine-honed, so that surface finish on the internal surface
of the bore is either equal to or better than the surface finish on the external cylindrical surface in
[4]
the parallel section .
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ISO/FDIS 1352:2021(E)
Failure to observe the above can result in alteration in the microstructure of the material. This
phenomenon can be caused by an increase in temperature and by the strain-hardening induced by
machining; it can be a matter of a change in phase or, more frequently, of surface recrystallization. This
invalidates the test as the material mechanical properties are changed.
Introduction of contaminants: the mechanical properties of some materials deteriorate when in the
presence of certain elements or compounds. An example is the effect of chlorine on steels and titanium
alloys. These elements should therefore be avoided in the products used during specimen preparation
(cutting fluids, etc.). Rinsing and degreasing of specimens prior to storage is also recommended.
8.3 Sampling and marking
The sampling of test materials from a semi-finished product or component can have a major influence
on the results obtained during the test. It is therefore necessary to clearly identify the location and
orientation of each specimen.
A sampling drawing, attached to the test report, shall 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);
— the marking of each of the specimens.
Specimens shall carry a unique identifying mark throughout their preparation. This may be applied
using any reliable method in an area not likely to disappear during machining or to adversely affect the
quality of the test.
Identification shall be applied to each end of the specimen before testing.
8.4 Surface conditions of specimen
The surface conditions of the specimens can affect the test results. This is generally associated with
one or more of the following factors:
— specimen surface roughness;
— presence of residual stresses;
— alteration in the microstructure of the material;
— introduction of contaminants.
To minimize the impact of these factors, the following is recommended.
The impact of surface roughness on the results obtained depends largely on the test conditions and its
effect is reduced by surface corrosion of the specimen or inelastic deformation.
It is preferable, whatever the test conditions, to achieve a mean surface roughness of less than 0,2 µm
Ra (or equivalent) within the parallel section. This includes both internal and external surfaces for a
tubular specimen.
Another important parameter not covered by mean roughness is the presence of localized machining
scratches. Finishing operations should eliminate all circumferential scratches produced during turning.
Final grinding followed by mechanical polishing is highly recommended. A visual inspection at low
magnification (approximately ×20) should only show polishing marks appropriate to the grade of the
final polishing medium.
It is preferable to carry out a final polishing operation after heat treatment. If this is not possible, the
heat treatment should be carried out in a vacuum or in inert gas to prevent oxidation of the specimen
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ISO/FDIS 1352:2021(E)
surface. This treatment should not alter the microstructural characteristics of the material under study.
The details of the heat treatment and machining procedure shall be reported with the test results.
8.5 Dimensional checks
The dimensions should be measured on completion of the final machining stage using a method of
metrology which does not alter the surface condition.
8.6 Storage and handling
After preparation, the specimens should be stored so as to prevent any risk of
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