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

Status
Published
Publication Date
20-Dec-2021
Current Stage
5060 - Close of voting Proof returned by Secretariat
Start Date
27-Nov-2021
Completion Date
26-Nov-2021
Ref Project

RELATIONS

Buy Standard

Draft
ISO/FDIS 1352 - Metallic materials -- Torque-controlled fatigue testing
English language
26 pages
sale 15% off
Preview
sale 15% off
Preview

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
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 1352:2021(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 1352:2021(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
© ISO 2021 – All rights reserved
---------------------- Page: 2 ----------------------
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

iii
© ISO 2021 – All rights reserved
---------------------- Page: 3 ----------------------
ISO/FDIS 1352:2021(E)

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

© ISO 2021 – All rights reserved
---------------------- Page: 4 ----------------------
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

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.

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.
© ISO 2021 – All rights reserved
---------------------- Page: 5 ----------------------
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
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
min
lowest algebraic value of shear stress in the stress cycle
Note 1 to entry: See Figure 1.
3.3
mean stress
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:

© ISO 2021 – All rights reserved
---------------------- Page: 6 ----------------------
ISO/FDIS 1352:2021(E)
ττ+
maxmin
τ =
3.4
stress amplitude
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 =
3.5
number of cycles
number of cycles applied at any stage during the test
3.6
stress ratio

algebraic ratio of the minimum shear stress to the maximum shear stress in one cycle

Note 1 to entry: It is expressed as:
min
max
3.7
stress range
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
number of stress cycles to failure in a specified condition
3.9
fatigue strength at N cycles

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

twisting couple producing shear stress or twisting deformation about the axis of the specimen

© ISO 2021 – All rights reserved
---------------------- Page: 7 ----------------------
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
d inner diameter of test section of specimen of tubular cross-section
L axial separation of strain gauges
L parallel length

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
© ISO 2021 – All rights reserved
---------------------- Page: 8 ----------------------
ISO/FDIS 1352:2021(E)

T indicated temperature or measure temperature on the surface of the parallel length of the

specimen
° °
ε linear normal strain in the 0 directions of the 45 strain rosette
° °
ε linear normal strain in the 45 directions of the 45 strain rosette
° °
ε linear normal strain in the 90 directions of the 45 strain rosette
ε circumferential strain
ε longitudinal strain
γ shear strain
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.
© ISO 2021 – All rights reserved
---------------------- Page: 9 ----------------------
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:
— 10 cycles for structural steels, and
— 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.
© ISO 2021 – All rights reserved
---------------------- Page: 10 ----------------------
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

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
© ISO 2021 – All rights reserved
---------------------- Page: 11 ----------------------
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
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.
© ISO 2021 – All rights reserved
---------------------- Page: 12 ----------------------
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
Transition radius (from parallel section to grip
≥ 3d
end), r
Parallel length, L 1d to 3d
p o o
External diameter (grip end) D ≥ 1,5d
Concentricity between the outer diameter, d , and the inner diame-
ter, d , should be maintained within 0,01t.
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 .
© ISO 2021 – All rights reserved
---------------------- Page: 13 ----------------------
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

© ISO 2021 – All rights reserved
---------------------- Page: 14 ----------------------
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
...

Questions, Comments and Discussion

Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.