Metallic materials — Rotating bar bending fatigue testing

This document specifies the method for rotating bar bending fatigue testing of metallic materials. The tests are conducted at room temperature or elevated temperature in air, the specimen being rotated. Fatigue tests on notched specimens are not covered by this document, since the shape and size of notched specimens have not been standardized. However, fatigue test procedures described in this document can be applied to fatigue tests of notched specimens.

Matériaux métalliques — Essais de fatigue par flexion rotative de barreaux

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Status
Published
Publication Date
29-Jul-2021
Current Stage
6060 - International Standard published
Start Date
30-Jul-2021
Completion Date
30-Jul-2021
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INTERNATIONAL ISO
STANDARD 1143
Third edition
2021-07
Metallic materials — Rotating bar
bending fatigue testing
Matériaux métalliques — Essais de fatigue par flexion rotative de
barreaux
Reference number
ISO 1143:2021(E)
ISO 2021
---------------------- Page: 1 ----------------------
ISO 1143:2021(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2021

All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may

be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting

on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address

below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO 2021 – All rights reserved
---------------------- Page: 2 ----------------------
ISO 1143:2021(E)
Contents Page

Foreword ........................................................................................................................................................................................................................................iv

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative references ...................................................................................................................................................................................... 1

3 Terms and definitions ..................................................................................................................................................................................... 1

4 Symbols .......................................................................................................................................................................................................................... 2

5 Principle of test ...................................................................................................................................................................................................... 2

6 Shape and size of specimen ....................................................................................................................................................................... 3

6.1 Forms of the test section ................................................................................................................................................................ 3

6.2 Dimensions of specimens .............................................................................................................................................................. 8

7 Preparation of specimens ........................................................................................................................................................................... 8

7.1 General ........................................................................................................................................................................................................... 8

7.2 Selection of the specimen and marking ............................................................................................................................. 8

7.3 Machining procedure......................................................................................................................................................................... 9

7.3.1 Heat treatment of test material ........................................................................................................................... 9

7.3.2 Machining criteria ........................................................................................................................................................... 9

7.3.3 Surface condition of specimens .......................................................................................................................... 9

7.3.4 Dimensional checks ....................................................................................................................................................10

7.4 Storage and handling ......................................................................................................................................................................10

8 Accuracy of the testing apparatus ...................................................................................................................................................10

9 Heating device and temperature measurement ...............................................................................................................11

10 Test procedure .....................................................................................................................................................................................................11

10.1 Mounting the specimen ................................................................................................................................................................11

10.2 Application of force ..........................................................................................................................................................................12

10.3 Frequency selection .........................................................................................................................................................................12

10.4 End of test .................................................................................................................................................................................................13

10.5 Procedure for testing at elevated temperature ........................................................................................................13

11 Test report ................................................................................................................................................................................................................14

12 Presentation of fatigue test results ................................................................................................................................................15

12.1 Tabular presentation ......................................................................................................................................................................15

12.2 Graphical presentation ..................................................................................................................................................................15

13 Measurement uncertainty .......................................................................................................................................................................16

13.1 General ........................................................................................................................................................................................................16

13.2 Test conditions .....................................................................................................................................................................................16

13.3 Test results...............................................................................................................................................................................................16

Annex A (normative) Verification of the bending moment of rotating bar bending fatigue

machines ....................................................................................................................................................................................................................17

Annex B (informative) Example of a test report ....................................................................................................................................25

Bibliography .............................................................................................................................................................................................................................26

© ISO 2021 – All rights reserved iii
---------------------- Page: 3 ----------------------
ISO 1143:2021(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

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.

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).

Any trade name used in this document is information given for the convenience of users and does not

constitute an endorsement.

For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and

expressions related to conformity assessment, as well as information about ISO's adherence to the

World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see 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.

The third edition cancels and replaces the second edition (ISO 1143:2010), which has been technically

revised.
The main changes compared to the previous edition are as follows:
— A new Clause 13, Measurement uncertainty, has been added;
— a new Annex B, Example of a test report, has been added.

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.
iv © ISO 2021 – All rights reserved
---------------------- Page: 4 ----------------------
INTERNATIONAL STANDARD ISO 1143:2021(E)
Metallic materials — Rotating bar bending fatigue testing

WARNING — This document does not address safety or health concerns, should such issues

exist, that may be associated with its use or application. It is the responsibility of the user of this

document to establish any appropriate safety and health concerns, as well as to determine the

applicability of any national or local regulatory limitations regarding the use of this document.

1 Scope

This document specifies the method for rotating bar bending fatigue testing of metallic materials. The

tests are conducted at room temperature or elevated temperature in air, the specimen being rotated.

Fatigue tests on notched specimens are not covered by this document, since the shape and size of

notched specimens have not been standardized. However, fatigue test procedures described in this

document can be applied to fatigue tests of notched specimens.
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 376, Metallic materials — Calibration of force-proving instruments used for the verification of uniaxial

testing machines
ISO 1099, Metallic materials — Fatigue testing — Axial force-controlled method
ISO 12106, Metallic materials — Fatigue testing — Axial-strain-controlled method

ISO 12107, Metallic materials — Fatigue testing — Statistical planning and analysis of data

ISO 23718, Metallic materials — Mechanical testing — Vocabulary
3 Terms and definitions

For the purposes of this document, the terms and definitions given in ISO 1099, ISO 12106, ISO 12107,

ISO 23718 and the following apply.

ISO and IEC maintain terminology databases for use in standardization at the following addresses:

— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
fatigue

process of changes in properties which can occur in a metallic material due to the repeated application

of stresses or strains and that can lead to cracking or failure
3.2
fatigue life
number of applied cycles to achieve a defined failure criterion
© ISO 2021 – All rights reserved 1
---------------------- Page: 5 ----------------------
ISO 1143:2021(E)
3.3
S-N diagram
diagram that shows the relationship between stress and fatigue life (3.2)
3.4
bending moment
multiplication between force and length of lever arm at test temperature
3.5
section modulus

ratio of the moment of inertia of the cross-section of a beam undergoing flexure to the greatest distance

of an element of the beam from the neutral axis
3.6
machine lever ratio

ratio between the force applied to the weight hanger and the bending moment (3.4) applied to the

specimen
3.7
length of lever arm
distance between the supporting point and the loading point
Note 1 to entry: See Figures 1 to 7.
Note 2 to entry: Since these distances are length of level arm, L = L = L.
1 2
4 Symbols
Symbols and corresponding designations are given in Table 1
Table 1 — Symbols
Symbol Designation Unit
D Diameter of gripped or loaded end of specimen mm
d Diameter of specimen where stress is maximum mm
L Length of lever arm mm
M Bending moment N·mm
M Machine lever ratio /
N Fatigue life, cycles to failure cycle
r Radius at ends of test section that starts transition mm
from test diameter, d
W Section modulus mm
5 Principle of test

Nominally identical specimens are used, each being rotated and subjected to a constant bending

moment. The forces giving rise to the bending moment do not rotate. The specimen may be mounted

as a cantilever, with single-point or two-point loading, or as a beam, with four-point loading. The test

is continued until the specimen fails or until a pre-determined number of stress cycles have been

achieved, a stress cycle corresponds to a complete rotation of the specimen.
2 © ISO 2021 – All rights reserved
---------------------- Page: 6 ----------------------
ISO 1143:2021(E)
6 Shape and size of specimen
6.1 Forms of the test section
The test section may be

a) cylindrical, with tangentially blending fillets at one or both ends (see Figures 1, 4 and 5),

b) tapered (see Figure 2), or
c) hourglass-type (see Figures 3, 6 and 7).

NOTE A volume of material is tested in the gauge portion of a parallel specimen in two-point and four-point

loading conditions. This volume is equally under maximum stress. For all other loading conditions and for both

parallel and hourglass specimens, only a thin planar element of material is submitted to the maximum stress at

the minimum cross-section.
Key
D diameter of gripped or loaded end of specimen M bending moment
d diameter of specimen where stress is maximum r radius (see Table 1)
F applied force S stress
L length of lever arm x distance along specimen axis from fixed bearing face
to maximum stress plane
Figure 1 — Parallel specimen — Single-point loading
© ISO 2021 – All rights reserved 3
---------------------- Page: 7 ----------------------
ISO 1143:2021(E)
Key
D diameter of gripped or loaded end of specimen M bending moment
d diameter of specimen where stress is maximum S stress
F applied force x distance along specimen axis from fixed bearing face
to maximum stress plane
L length of lever arm
Figure 2 — Tapered specimen — Single-point loading
Key
D diameter of gripped or loaded end of specimen M bending moment
d diameter of specimen where stress is maximum S stress
F applied force x distance along specimen axis from fixed bearing face
L length of lever arm to maximum stress plane
r radius (see Table 1)
Figure 3 — Hourglass specimen — Single-point loading
4 © ISO 2021 – All rights reserved
---------------------- Page: 8 ----------------------
ISO 1143:2021(E)
Key
D diameter of gripped or loaded end of specimen M bending moment
d diameter of specimen where stress is maximum S stress
F applied force r radius (see Table 1)
L length of lever arm
Figure 4 — Parallel specimen — Two-point loading
Key
D diameter of gripped or loaded end of specimen M bending moment
d diameter of specimen where stress is maximum S stress
F applied force r radius (see Table 1)
L , L length of lever arm
1 2
NOTE L = L = L
1 2
Figure 5 — Parallel specimen — Four-point loading
© ISO 2021 – All rights reserved 5
---------------------- Page: 9 ----------------------
ISO 1143:2021(E)
Key
D diameter of gripped or loaded end of specimen L length of lever arm
d diameter of specimen where stress is maximum M bending moment
F applied force S stress
r radius (see Table 1)
Figure 6 — Hourglass specimen — Two-point loading
Key
D diameter of gripped or loaded end of specimen
d diameter of specimen where stress is maximum
F applied force
L , L length of lever arm
1 2
M bending moment
r radius (see Table 1)
S stress
NOTE L = L = L.
1 2
Figure 7 — Hourglass specimen — Four-point loading

In each case, the test section shall be of circular cross-section. Typical parallel and hourglass specimen

shapes and related dimensions are shown in Figures 8 and 9, respectively.
6 © ISO 2021 – All rights reserved
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ISO 1143:2021(E)
Key
n specimen code
a others
b two tops
Figure 8 — Cylindrical smooth specimen
Key
n specimen code
a others
b two tops
Figure 9 — Cylindrical hourglass specimen

The form of test section can be dependent on the type of loading to be employed. While cylindrical

or hourglass-type specimens may be loaded as beams, or as cantilevers with either single-point

or double-point loading, the tapered form of specimen is used only as a cantilever with single-point

loading. Figures 1 to 7 show, in schematic form, the bending moment and nominal stress diagrams for

the various practical cases.

The volumes of material subjected to greatest stresses are not the same for different forms of specimen,

and they may not necessarily give identical results. The test in which the largest volume of material is

highly stressed is recommended.

The use of single point loading machines should be done with great caution. One of the main drawbacks

is that the bending moment is not constant along the specimen. The section where the stress is maximum

© ISO 2021 – All rights reserved 7
---------------------- Page: 11 ----------------------
ISO 1143:2021(E)

and the corresponding stress depend not only on the specimen geometry but also on the length of level

arm. For this type of machines, cylindrical hour glass specimen geometry is recommended because the

higher stress is close to the one calculated for the minimum diameter section.

Experience has shown that a ratio of at least 2:1 between the cross-sectional areas of the gripping

regions and the test portion of the specimen is recommended. The grips which do not lead up to large

stress-concentration area are recommended.

In tests on certain materials, a combination of high stress and high speed may cause excessive hysteresis

heating of the specimen. This effect may be reduced by subjecting a smaller volume of the material or by

decreasing the test frequency (see 10.3). If the specimen is cooled, the test medium should be reported.

6.2 Dimensions of specimens

All the specimens employed in a test series for a fatigue-life determination shall have the same size,

shape and tolerance of diameter.

For the purpose of calculating the force to be applied to obtain the required stress, the actual minimum

diameter of each specimen shall be measured to an accuracy of 0,01 mm. Care shall be taken during the

measurement of the specimen prior to testing to ensure that the surface is not damaged.

On cylindrical specimens subject to constant bending moment (see Figures 4 and 5), the parallel test

section shall be parallel within 0,025 mm. For other forms of cylindrical specimen (see Figure 1),

the parallel test section shall be parallel within 0,05 mm. For material property determination, the

transition fillets at the ends of the test section should have a radius not less than 3d. For hourglass-type

specimens, the section formed by the continuous radius should have a radius not less than 5d.

Figure 8 shows the shape and dimensions of a typical cylindrical specimen. The recommended values of

d are 6 mm, 7,5 mm and 9,5 mm. The tolerance of diameter should be 0,005d. Figure 9 shows a typical

hourglass specimen suitable for fatigue testing at elevated temperature.
7 Preparation of specimens
7.1 General

In any rotating bar bending 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 possible reason for deviation from these recommendations is if the test program aims to determine

the influence of a specific factor (surface treatment, oxidation, etc.) that is incompatible with the

recommendations. In all cases, any deviation shall be noted in the test report.
7.2 Selection of the specimen 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 recorded and a

sampling drawing be prepared. This shall form part of the test report and shall indicate clearly

— the position of each of the specimens removed from the semi-finished product or component,

— the characteristic directions in which the semi-finished product has been worked (direction of

rolling, extrusion, etc., as appropriate), and
— the unique identification of each of the specimens.

The unique mark or identification of each specimen shall be maintained at each stage of its preparation.

This 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. Upon completion of the machining process, it is desirable

for both ends of each specimen to be uniquely marked so that, after failure of a specimen, each half can

still be identified.
8 © ISO 2021 – All rights reserved
---------------------- Page: 12 ----------------------
ISO 1143:2021(E)
7.3 Machining procedure
7.3.1 Heat treatment of test material

The heat treatment is generally performed on a rough machined specimen. Then final machining

followed by polishing should be performed on the specimen to remove any deformation of the specimen

due to the heat treatment process. If that is not possible, the heat treatment should be carried out in a

vacuum or in inert gas to prevent oxidation of the specimen. Subsequent stress relieving is recommended

in this case. The stress relieving treatment shall not alter the micro-structural characteristic of the

material under study. The specifics of the heat treatment and machining procedure shall be reported

with the test results.
7.3.2 Machining criteria

The machining procedure selected may produce residual stresses on the specimen surface likely to

affect the test results. These stresses may be induced by heat gradients at the machining stage or they

may be associated with deformation of the material or micro-structural alterations. Their influence

is less marked in tests at elevated temperatures because they are partially or totally relaxed once the

temperature is attained. However, they should be reduced by using an appropriate final machining

procedure, especially prior to a final polishing stage. For harder materials, grinding rather than turning

or milling may be preferred.

— Grinding: from 0,1 mm above the final diameter, at a rate of no more than 0,005 mm/pass.

— Polishing: remove the final 0,025 mm with abrasives of decreasing grit size. The final direction of

polishing shall be along the test specimen axis.

The phenomenon of alteration in the microstructure of the material 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 re-crystallization. The immediate effect of this is to make the test

specimen no longer representative of the initial material. Hence, every precaution should therefore be

taken to avoid this risk.

Contaminants can be introduced when the mechanical properties of certain materials deteriorate in

the presence of certain elements or compounds. An example of this is the effect of chlorine on steels and

titanium alloys. These elements should therefore be avoided in the products used (cutting fluids, etc.).

Rinsing and degreasing of specimens prior to storage is also recommended.
7.3.3 Surface condition of specimens

The surface condition of specimens influences the test results. This influence 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;
— the 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. 10 point

roughness or maximum height of irregularities). The importance of this variable on the results obtained

depends largely on the test conditions, and its influence is reduced by surface corrosion of the specimen

or plastic deformation.

It is preferable, whatever the test conditions, to specify a mean surface roughness, Ra, of less than

0,2 μm (or equivalent).
© ISO 2021 – All rights reserved 9
---------------------- Page: 13 ----------------------
ISO 1143:2021(E)

Another important parameter not covered by mean roughness is the presence of localized machining

scratches. A low-magnification check (at approximately × 20) shall not show any circumferential

scratches or abnormalities.

With specimens having tangentially blended fillets, often an undercut is observed at the transition from

the radius of the fillet to the cylindrical test section. This undercut may lead to a preferred failure of the

specimen in this area. The undercut can't easily be measured but can be found by visible inspection of

the reflections on the surface under a flat angle. No visible undercut shall be allowed.

If specimens are not manufactured according to the procedures defined in 7.3.2 or if there are doubts

about the correct machining, it is recommended to measure or evaluate:
— residual stress state, preferably a profile of residual stress over depth;
— surface roughness profile;
— surface hardness;

and state the values observed together with the test results in order to facilitate definite interpretation

of the test results.
7.3.4 Dimensional checks

The diameter shall be measured on each specimen. In the case of specimens with a parallel gauge

length, the diameter shall be measured at a minimum of three positions along the gauge length. The

measurement shall be performed using a method that does not damage the specimen.
7.4 Storage and handling

After preparation, the specimens shall be stored in such a way to prevent any risk of damage (scratching

by contact, oxidation, etc.). The use of individual boxes or tubes with end caps is recommended. In

certain cases, storage in a vacuum or in a desiccator containing silica gel may be necessary.

Handling shall be reduced to the minimum necessary. In all instances, the gauge length or test section

should not be touched. However, if this happens, cleaning the specimen with alcohol is allowed.

8 Accuracy of the testing apparatus

A number of different types of rotating bending fatigue machine are used. Figures 1 to 7 show the

principles of the main types of machine. Figure 10 shows the schematic of a kind of rotating bending

fatigue machine. Its operation shall satisfy the following requirement: the accuracy of the applied

bending moment shall be within 1 % (see Annex A).
10 © ISO 2021 – All rights reserved
---------------------- Page: 14 ----------------------
ISO 1143:2021(E)
Key
1 motor 10 specimen
2 triangle belt 11 right main axis box
3 weight 12 hanging hook
4 boom 13 pointer
5 button 14 balance weight
6 counting accelerator 15 counter
7 soft axis 16 lever
8 left main axis box 17 hand wheel
9 split collet
Figure 10 — Schematic of a rotating bend fatigue machine
9 Heating device and temperature measurement
9.1 The specimen is heated with a furnace or equivalent device.
9.2 The temperature of the specimen shall be kept uniform t
...

FINAL
INTERNATIONAL ISO/FDIS
DRAFT
STANDARD 1143
ISO/TC 164/SC 4
Metallic materials — Rotating bar
Secretariat: ANSI
bending fatigue testing
Voting begins on:
2021­05­03
Matériaux métalliques — Essais de fatigue par flexion rotative de
barreaux
Voting terminates on:
2021­06­28
RECIPIENTS OF THIS DRAFT ARE INVITED TO
SUBMIT, WITH THEIR COMMENTS, NOTIFICATION
OF ANY RELEVANT PATENT RIGHTS OF WHICH
THEY ARE AWARE AND TO PROVIDE SUPPOR TING
DOCUMENTATION.
IN ADDITION TO THEIR EVALUATION AS
Reference number
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO­
ISO/FDIS 1143:2021(E)
LOGICAL, COMMERCIAL AND USER PURPOSES,
DRAFT INTERNATIONAL STANDARDS MAY ON
OCCASION HAVE TO BE CONSIDERED IN THE
LIGHT OF THEIR POTENTIAL TO BECOME STAN­
DARDS TO WHICH REFERENCE MAY BE MADE IN
NATIONAL REGULATIONS. ISO 2021
---------------------- Page: 1 ----------------------
ISO/FDIS 1143:2021(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2021

All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may

be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting

on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address

below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH­1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO 2021 – All rights reserved
---------------------- Page: 2 ----------------------
ISO/FDIS 1143:2021(E)
Contents Page

Foreword ........................................................................................................................................................................................................................................iv

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative references ...................................................................................................................................................................................... 1

3 Terms and definitions ..................................................................................................................................................................................... 1

4 Symbols .......................................................................................................................................................................................................................... 2

5 Principle of test ...................................................................................................................................................................................................... 2

6 Shape and size of specimen ....................................................................................................................................................................... 3

6.1 Forms of the test section ................................................................................................................................................................ 3

6.2 Dimensions of specimens .............................................................................................................................................................. 8

7 Preparation of specimens ........................................................................................................................................................................... 8

7.1 General ........................................................................................................................................................................................................... 8

7.2 Selection of the specimen and marking ............................................................................................................................. 8

7.3 Machining procedure......................................................................................................................................................................... 9

7.3.1 Heat treatment of test material ........................................................................................................................... 9

7.3.2 Machining criteria ........................................................................................................................................................... 9

7.3.3 Surface condition of specimens .......................................................................................................................... 9

7.3.4 Dimensional checks ....................................................................................................................................................10

7.4 Storage and handling ......................................................................................................................................................................10

8 Accuracy of the testing apparatus ...................................................................................................................................................10

9 Heating device and temperature measurement ...............................................................................................................11

10 Test procedure .....................................................................................................................................................................................................11

10.1 Mounting the specimen ................................................................................................................................................................11

10.2 Application of force ..........................................................................................................................................................................12

10.3 Frequency selection .........................................................................................................................................................................12

10.4 End of test .................................................................................................................................................................................................13

10.5 Procedure for testing at elevated temperature ........................................................................................................13

11 Test report ................................................................................................................................................................................................................14

12 Presentation of fatigue test results ................................................................................................................................................15

12.1 Tabular presentation ......................................................................................................................................................................15

12.2 Graphical presentation ..................................................................................................................................................................15

13 Measurement uncertainty .......................................................................................................................................................................16

13.1 General ........................................................................................................................................................................................................16

13.2 Test conditions .....................................................................................................................................................................................16

13.3 Test results...............................................................................................................................................................................................16

Annex A (normative) Verification of the bending moment of rotating bar bending fatigue

machines ....................................................................................................................................................................................................................17

Annex B (informative) Example of a test report ....................................................................................................................................25

Bibliography .............................................................................................................................................................................................................................26

© ISO 2021 – All rights reserved iii
---------------------- Page: 3 ----------------------
ISO/FDIS 1143:2021(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

committee has been established has the right to be represented on that committee. International

organizations, governmental and non­governmental, 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.

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).

Any trade name used in this document is information given for the convenience of users and does not

constitute an endorsement.

For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and

expressions related to conformity assessment, as well as information about ISO's adherence to the

World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www .iso .org/

iso/ foreword .html.

This document was prepared by Technical Committee ISO/TC 164, Mechanical testing of metals,

Subcommittee SC 5, Fatigue, fracture and toughness testing.

The third edition cancels and replaces the second edition (ISO 1143:2010), which has been technically

revised.
The main changes compared to the previous edition are as follows:
— A new Clause 13, Measurement uncertainty, has been added;
— a new Annex B, Example of a test report, has been added.

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.
iv © ISO 2021 – All rights reserved
---------------------- Page: 4 ----------------------
FINAL DRAFT INTERNATIONAL STANDARD ISO/FDIS 1143:2021(E)
Metallic materials — Rotating bar bending fatigue testing

WARNING — This document does not address safety or health concerns, should such issues

exist, that may be associated with its use or application. It is the responsibility of the user of this

document to establish any appropriate safety and health concerns, as well as to determine the

applicability of any national or local regulatory limitations regarding the use of this document.

1 Scope

This document specifies the method for rotating bar bending fatigue testing of metallic materials. The

tests are conducted at room temperature or elevated temperature in air, the specimen being rotated.

Fatigue tests on notched specimens are not covered by this document, since the shape and size of

notched specimens have not been standardized. However, fatigue test procedures described in this

document can be applied to fatigue tests of notched specimens.
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 376, Metallic materials — Calibration of force-proving instruments used for the verification of uniaxial

testing machines
ISO 1099, Metallic materials — Fatigue testing — Axial force-controlled method
ISO 12106, Metallic materials — Fatigue testing — Axial-strain-controlled method

ISO 12107, Metallic materials — Fatigue testing — Statistical planning and analysis of data

ISO 23718, Metallic materials — Mechanical testing — Vocabulary
3 Terms and definitions

For the purposes of this document, the terms and definitions given in ISO 1099, ISO 12106, ISO 12107,

ISO 23718 and the following 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
fatigue

process of changes in properties which can occur in a metallic material due to the repeated application

of stresses or strains and that can lead to cracking or failure
3.2
fatigue life
number of applied cycles to achieve a defined failure criterion
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3.3
S-N diagram
diagram that shows the relationship between stress and fatigue life (3.2)
3.4
bending moment
multiplication between force and length of lever arm at test temperature
3.5
section modulus

ratio of the moment of inertia of the cross-section of a beam undergoing flexure to the greatest distance

of an element of the beam from the neutral axis
3.6
machine lever ratio

ratio between the force applied to the weight hanger and the bending moment (3.4) applied to the

specimen
3.7
length of lever arm
distance between the supporting point and the loading point
Note 1 to entry: See Figures 1 to 7.
Note 2 to entry: Since these distances are length of level arm, L = L = L.
1 2
4 Symbols
Symbols and corresponding designations are given in Table 1
Table 1 — Symbols
Symbol Designation Unit
D Diameter of gripped or loaded end of specimen mm
d Diameter of specimen where stress is maximum mm
L length of lever arm mm
M Bending moment N·mm
M machine lever ratio /
N Fatigue life, cycles to failure cycle
r Radius at ends of test section that starts transition mm
from test diameter, d
W Section modulus mm
5 Principle of test

Nominally identical specimens are used, each being rotated and subjected to a constant bending

moment. The forces giving rise to the bending moment do not rotate. The specimen may be mounted

as a cantilever, with single­point or two­point loading, or as a beam, with four­point loading. The test

is continued until the specimen fails or until a pre-determined number of stress cycles have been

achieved, a stress cycle corresponds to a complete rotation of the specimen.
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6 Shape and size of specimen
6.1 Forms of the test section
The test section may be

a) cylindrical, with tangentially blending fillets at one or both ends (see Figures 1, 4 and 5),

b) tapered (see Figure 2), or
c) hourglass-type (see Figures 3, 6 and 7).

NOTE A volume of material is tested in the gauge portion of a parallel specimen in two­point and four­point

loading conditions. This volume is equally under maximum stress. For all other loading conditions and for both

parallel and hourglass specimens, only a thin planar element of material is submitted to the maximum stress at

the minimum cross­section.
Key
D diameter of gripped or loaded end of specimen M bending moment
d diameter of specimen where stress is maximum r radius (see Table 1)
F applied force S stress
L length of lever arm x distance along specimen axis from fixed bearing face
tomaximum stress plane
Figure 1 — Parallel specimen — Single-point loading
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Key
D diameter of gripped or loaded end of specimen M bending moment
d diameter of specimen where stress is maximum S stress
F applied force x distance along specimen axis from fixed bearing face
to maximum stress plane
L length of lever arm
Figure 2 — Tapered specimen — Single-point loading
Key
D diameter of gripped or loaded end of specimen M bending moment
d diameter of specimen where stress is maximum S stress
F applied force x distance along specimen axis from fixed bearing face
L length of lever arm to maximum stress plane
r radius (see Table 1)
Figure 3 — Hourglass specimen — Single-point loading
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Key
D diameter of gripped or loaded end of specimen M bending moment
d diameter of specimen where stress is maximum S stress
F applied force r radius (see Table 1)
L length of lever arm
Figure 4 — Parallel specimen — Two-point loading
Key
D diameter of gripped or loaded end of specimen M bending moment
d diameter of specimen where stress is maximum S stress
F applied force r radius (see Table 1)
L , L length of lever arm
1 2
NOTE L = L = L
1 2
Figure 5 — Parallel specimen — Four-point loading
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Key
D diameter of gripped or loaded end of specimen L length of lever arm
d diameter of specimen where stress is maximum M bending moment
F applied force S stress
r radius (see Table 1)
Figure 6 — Hourglass specimen — Two-point loading
Key
D diameter of gripped or loaded end of specimen
d diameter of specimen where stress is maximum
F applied force
L , L length of lever arm
1 2
M bending moment
r radius (see Table 1)
S stress
NOTE L = L = L.
1 2
Figure 7 — Hourglass specimen — Four-point loading

In each case, the test section shall be of circular cross-section. Typical parallel and hourglass specimen

shapes and related dimensions are shown in Figure 8 and 9, respectively.
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Key
n specimen code
a others
b two tops
Figure 8 — Cylindrical smooth specimen
Key
n specimen code
a others
b two tops
Figure 9 — Cylindrical hourglass specimen

The form of test section can be dependent on the type of loading to be employed. While cylindrical

or hourglass-type specimens may be loaded as beams, or as cantilevers with either single-point

or double-point loading, the tapered form of specimen is used only as a cantilever with single-point

loading. Figures 1 to 7 show, in schematic form, the bending moment and nominal stress diagrams for

the various practical cases.

The volumes of material subjected to greatest stresses are not the same for different forms of specimen,

and they may not necessarily give identical results. The test in which the largest volume of material is

highly stressed is recommended.

The use of single point loading machines should be done with great caution. One of the main drawbacks

is that the bending moment is not constant along the specimen. The section where the stress is maximum

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and the corresponding stress depend not only on the specimen geometry but also on the length of level

arm. For this type of machines, cylindrical hour glass specimen geometry is recommended because the

higher stress is close to the one calculated for the minimum diameter section.

Experience has shown that a ratio of at least 2:1 between the cross-sectional areas of the gripping

regions and the test portion of the specimen is recommended. The grips which do not lead up to large

stress­concentration area are recommended.

In tests on certain materials, a combination of high stress and high speed may cause excessive hysteresis

heating of the specimen. This effect may be reduced by subjecting a smaller volume of the material or by

decreasing the test frequency (see 10.3). If the specimen is cooled, the test medium should be reported.

6.2 Dimensions of specimens

All the specimens employed in a test series for a fatigue-life determination shall have the same size,

shape and tolerance of diameter.

For the purpose of calculating the force to be applied to obtain the required stress, the actual minimum

diameter of each specimen shall be measured to an accuracy of 0,01 mm. Care shall be taken during the

measurement of the specimen prior to testing to ensure that the surface is not damaged.

On cylindrical specimens subject to constant bending moment (see Figures 4 and 5), the parallel test

section shall be parallel within 0,025 mm. For other forms of cylindrical specimen (see Figure 1),

the parallel test section shall be parallel within 0,05 mm. For material property determination, the

transition fillets at the ends of the test section should have a radius not less than 3d. For hourglass-type

specimens, the section formed by the continuous radius should have a radius not less than 5d.

Figure 8 shows the shape and dimensions of a typical cylindrical specimen. The recommended values of

d are 6 mm, 7,5 mm and 9,5 mm. The tolerance of diameter should be 0,005d. Figure 9 shows a typical

hourglass specimen suitable for fatigue testing at elevated temperature.
7 Preparation of specimens
7.1 General

In any rotating bar bending 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 possible reason for deviation from these recommendations is if the test program aims to determine

the influence of a specific factor (surface treatment, oxidation, etc.) that is incompatible with the

recommendations. In all cases, any deviation shall be noted in the test report.
7.2 Selection of the specimen 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 recorded and a

sampling drawing be prepared. This shall form part of the test report and shall indicate clearly

— the position of each of the specimens removed from the semi-finished product or component,

— the characteristic directions in which the semi-finished product has been worked (direction of

rolling, extrusion, etc., as appropriate), and
— the unique identification of each of the specimens.

The unique mark or identification of each specimen shall be maintained at each stage of its preparation.

This 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. Upon completion of the machining process, it is desirable

for both ends of each specimen to be uniquely marked so that, after failure of a specimen, each half can

still be identified.
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7.3 Machining procedure
7.3.1 Heat treatment of test material

The heat treatment is generally performed on a rough machined specimen. Then final machining

followed by polishing should be performed on the specimen to remove any deformation of the specimen

due to the heat treatment process. If that is not possible, the heat treatment should be carried out in a

vacuum or in inert gas to prevent oxidation of the specimen. Subsequent stress relieving is recommended

in this case. The stress relieving treatment shall not alter the micro­structural characteristic of the

material under study. The specifics of the heat treatment and machining procedure shall be reported

with the test results.
7.3.2 Machining criteria

The machining procedure selected may produce residual stresses on the specimen surface likely to

affect the test results. These stresses may be induced by heat gradients at the machining stage or they

may be associated with deformation of the material or micro-structural alterations. Their influence

is less marked in tests at elevated temperatures because they are partially or totally relaxed once the

temperature is attained. However, they should be reduced by using an appropriate final machining

procedure, especially prior to a final polishing stage. For harder materials, grinding rather than turning

or milling may be preferred.

— Grinding: from 0,1 mm above the final diameter, at a rate of no more than 0,005 mm/pass.

— Polishing: remove the final 0,025 mm with abrasives of decreasing grit size. The final direction of

polishing shall be along the test specimen axis.

The phenomenon of alteration in the microstructure of the material 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 re-crystallization. The immediate effect of this is to make the test

specimen no longer representative of the initial material. Hence, every precaution should therefore be

taken to avoid this risk.

Contaminants can be introduced when the mechanical properties of certain materials deteriorate in

the presence of certain elements or compounds. An example of this is the effect of chlorine on steels and

titanium alloys. These elements should therefore be avoided in the products used (cutting fluids, etc.).

Rinsing and degreasing of specimens prior to storage is also recommended.
7.3.3 Surface condition of specimens

The surface condition of specimens influences the test results. This influence 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;
— the 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. 10 point

roughness or maximum height of irregularities). The importance of this variable on the results obtained

depends largely on the test conditions, and its influence is reduced by surface corrosion of the specimen

or plastic deformation.

It is preferable, whatever the test conditions, to specify a mean surface roughness, Ra, of less than

0,2 μm (or equivalent).
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Another important parameter not covered by mean roughness is the presence of localized machining

scratches. A low-magnification check (at approximately × 20) shall not show any circumferential

scratches or abnormalities.

With specimens having tangentially blended fillets, often an undercut is observed at the transition from

the radius of the fillet to the cylindrical test section. This undercut may lead to a preferred failure of the

specimen in this area. The undercut can't easily be measured but can be found by visible inspection of

the reflections on the surface under a flat angle. No visible undercut shall be allowed.

If specimens are not manufactured according to the procedures defined in 7.3.2 or if there are doubts

about the correct machining, it is recommended to measure or evaluate:
— residual stress state, preferably a profile of residual stress over depth;
— surface roughness profile;
— surface hardness;

and state the values observed together with the test results in order to facilitate definite interpretation

of the test results.
7.3.4 Dimensional checks

The diameter shall be measured on each specimen. In the case of specimens with a parallel gauge

length, the diameter shall be measured at a minimum of three positions along the gauge length. The

measurement shall be performed using a method that does not damage the specimen.
7.4 Storage and handling

After preparation, the specimens shall be stored in such a way to prevent any risk of damage (scratching

by contact, oxidation, etc.). The use of individual boxes or tubes with end caps is recommended. In

certain cases, storage in a vacuum or in a desiccator containing silica gel may be necessary.

Handling shall be reduced to the minimum necessary. In all instances, the gauge length or test section

should not be touched. However, if this happens, cleaning the specimen with alcohol is allowed.

8 Accuracy of the testing apparatus

A number of different types of rotating bending fatigue machine are used. Figures 1 to 7 show the

principles of the main types of machine. Figure 10 shows the schematic of a kind of rotating bending

fatigue machine. Its operation shall satisfy the following requirement: th
...

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