Plain bearings — Bearing fatigue — Part 1: Plain bearings in test rigs and in applications under conditions of hydrodynamic lubrication

This document specifies a method of improving test result comparability by evaluating the stresses in the bearing layers leading to fatigue (see Annex A). A similar evaluation is required in practical applications. Because the stresses are the result of pressure build-up in the hydrodynamic film, it is essential to fully state the conditions of operation and lubrication. In addition to dynamic loading, dimensional and running characteristics, the inclusion of the following adequately defines the fatigue system: a) under conditions of dynamic loading the minimum bearing oil film thickness as a function of time and location to ensure no excessive local overheating or shearing as a result of mixed lubrication when running in; b) the distribution of pressure circumferentially and axially with time under dynamic loading; c) from this the resulting stresses in the bearing layers as a function of time and location, especially the maximum alternating stress. Furthermore, bearing fatigue can be affected by mixed lubrication, wear, dirt, tribochemical reactions and other effects encountered in use thus complicating the fatigue problem. This document is therefore restricted to fatigue under full hydrodynamic separation of the bearing surfaces by a lubricant film. This document applies to oil-lubricated plain cylindrical bearings, in test rigs and application running in conditions of full hydrodynamic lubrication. It comprises dynamic loading in bi-metal and multilayer bearings. NOTE The number of practical applications with different requirements has led to the development of many bearing test rigs. If the conditions of lubrication employed on these test rigs are not defined in detail, test results from different rigs are generally neither comparable nor applicable in practice. Different test rigs can yield inconsistent ranking among equal materials.

Paliers lisses — Fatigue des paliers — Partie 1: Paliers dans les machines d'essai et dans les applications en lubrification hydrodynamique

General Information

Status
Published
Publication Date
28-Apr-2021
Current Stage
6060 - International Standard published
Start Date
29-Apr-2021
Completion Date
29-Apr-2021
Ref Project

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INTERNATIONAL ISO
STANDARD 7905-1
Second edition
2021-04
Plain bearings — Bearing fatigue —
Part 1:
Plain bearings in test rigs and in
applications under conditions of
hydrodynamic lubrication
Paliers lisses — Fatigue des paliers —
Partie 1: Paliers dans les machines d'essai et dans les applications en
lubrification hydrodynamique
Reference number
ISO 7905-1:2021(E)
ISO 2021
---------------------- Page: 1 ----------------------
ISO 7905-1:2021(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 7905-1:2021(E)
Contents Page

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

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

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

3 Terms and definitions ..................................................................................................................................................................................... 2

4 Objective of testing ............................................................................................................................................................................................. 2

5 Requirements .......................................................................................................................................................................................................... 2

5.1 Test rigs ......................................................................................................................................................................................................... 2

5.2 Test methods ............................................................................................................................................................................................. 2

6 Test procedures ..................................................................................................................................................................................................... 3

6.1 General ........................................................................................................................................................................................................... 3

6.2 Characteristic conditions ............................................................................................................................................................... 3

6.2.1 Effective running-in procedure ........................................................................................................................... 3

6.2.2 Avoidance of deviation in the geometry of the structural elements of the

plain bearing assembly ........................................................................................................................................... .... 3

6.2.3 Effective temperature of the bearing and hydrodynamic film ................................................. 4

6.2.4 Dynamic load amplitude and direction as a function of time ................................................... 4

6.2.5 Number of load cycles required to effect the first fatigue damage ....................................... 4

6.3 Characteristic information ............................................................................................................................................................ 4

6.3.1 General...................................................................................................................................................................................... 4

6.3.2 Test rig description ........................................................................................................................................................ 4

6.3.3 Test bearing description .................. ......................................................................................................................... . 4

6.3.4 Test journal description ............................................................................................................................................. 4

6.3.5 Specific details of test load ...................................................................................................................................... 5

6.3.6 Designation of lubricant and supply ............................................................................................................... 5

6.3.7 Test temperatures description .................. ........................................................................................................... 5

6.3.8 Test film thickness description ............................................................................................................................ 5

6.3.9 Test film pressure description ............................................................................................................................. 5

6.3.10 Description of the dynamic stresses of the test .................................................................................... 5

6.3.11 Other test results ............................................................................................................................................................. 5

7 Evaluation of stress in bearing materials ................................................................................................................................... 5

Annex A (informative) Evaluation of stress ................................................................................................................................................... 7

Bibliography .............................................................................................................................................................................................................................15

© ISO 2021 – All rights reserved iii
---------------------- Page: 3 ----------------------
ISO 7905-1:2021(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 123, Plain bearing, Subcommittee SC 2,

Material and lubricants, their properties, characteristics, test methods and testing conditions.

This second edition cancels and replaces the first edition (ISO 7905-1:1995), which has been editorially

revised.
The main changes compared to the previous edition are as follows:
— normative references have been updated;
— additional explanation for the test methods have been added.
A list of all parts in the ISO 7905 series can be found on the ISO website.

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 7905-1:2021(E)
Plain bearings — Bearing fatigue —
Part 1:
Plain bearings in test rigs and in applications under
conditions of hydrodynamic lubrication
1 Scope

This document specifies a method of improving test result comparability by evaluating the stresses in the

bearing layers leading to fatigue (see Annex A). A similar evaluation is required in practical applications.

Because the stresses are the result of pressure build-up in the hydrodynamic film, it is essential to

fully state the conditions of operation and lubrication. In addition to dynamic loading, dimensional and

running characteristics, the inclusion of the following adequately defines the fatigue system:

a) under conditions of dynamic loading the minimum bearing oil film thickness as a function of time

and location to ensure no excessive local overheating or shearing as a result of mixed lubrication

when running in;

b) the distribution of pressure circumferentially and axially with time under dynamic loading;

c) from this the resulting stresses in the bearing layers as a function of time and location, especially

the maximum alternating stress.

Furthermore, bearing fatigue can be affected by mixed lubrication, wear, dirt, tribochemical reactions

and other effects encountered in use thus complicating the fatigue problem. This document is therefore

restricted to fatigue under full hydrodynamic separation of the bearing surfaces by a lubricant film.

This document applies to oil-lubricated plain cylindrical bearings, in test rigs and application running

in conditions of full hydrodynamic lubrication. It comprises dynamic loading in bi-metal and multilayer

bearings.

NOTE The number of practical applications with different requirements has led to the development of many

bearing test rigs. If the conditions of lubrication employed on these test rigs are not defined in detail, test results

from different rigs are generally neither comparable nor applicable in practice. Different test rigs can yield

inconsistent ranking among equal materials.
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 4287, Geometrical Product Specifications (GPS) — Surface texture: Profile method — Terms, definitions

and surface texture parameters

ISO 7902-1, Hydrodynamic plain journal bearings under steady-state conditions — Circular cylindrical

bearings — Part 1: Calculation procedure

ISO 7902-2, Hydrodynamic plain journal bearings under steady-state conditions — Circular cylindrical

bearings — Part 2: Functions used in the calculation procedure

ISO 7902-3, Hydrodynamic plain journal bearings under steady-state conditions — Circular cylindrical

bearings — Part 3: Permissible operational parameters
© ISO 2021 – All rights reserved 1
---------------------- Page: 5 ----------------------
ISO 7905-1:2021(E)
3 Terms and definitions
No terms and definitions are listed in this document.

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/
4 Objective of testing

In this document the objective of testing with plain bearing test rigs, operating in conditions of full

hydrodynamic lubrication, is to measure the dynamic load-carrying capacity e.g. the fatigue endurance

limit of the bearing layer material in terms of amplitude of stress and number of cycles. This may be

presented as a σ -N curve (endurance limit stress plotted against number of cycles), or as the endurance

limit stress for a specified number of cycles. Endurance limit is reached when cracks (greater than

5 mm in length) appear in the bearing surface.

In terms of current understanding, the restriction to full hydrodynamic lubrication is a necessary

simplification of the fatigue problem. This implies that the essential running-in of the bearing under test

shall be carefully controlled to avoid significant predamage from excessive temperature and frictional

shear stress which may cause surface microcracks.

It should be noted that fatigue testing of bearing materials may be conducted also by utilizing the more

classic methods of testing. See ISO 7905-2 to ISO 7905-4.
5 Requirements
5.1 Test rigs

In order to define the operating and lubricating conditions, the test rig shall have the following

characteristics:
a) simple and clear mechanical construction;
b) easy dismantling, preferably with an in situ bearing inspection capability;

c) bearing dimensional stability under test together with resistance to deformation of housing and

shaft deflection;
d) adequate lubricant supply without impairing oil film pressure development;

e) be capable of exceeding the entire range of load/stress and temperature encountered in practice.

5.2 Test methods
The test methods shall have the following characteristics:

a) the ability to apply specialized measuring techniques for oil film thickness, lubricant temperature,

pressure distribution and crack disintegration debris; such techniques for the latter aspect include

continuous radio nuclide measurement of wear or X-ray fluorescent analysis of intermittently

drained lubricant samples;

b) well-defined, experimentally verified hydrodynamic conditions (e.g the verification of viscosity

and operating conditions indicative of hydrodynamic behaviour);

c) clear distinction between mixed lubrication during running-in and full hydrodynamic lubrication

during fatigue testing;
2 © ISO 2021 – All rights reserved
---------------------- Page: 6 ----------------------
ISO 7905-1:2021(E)

d) the stress can traverse the bearing as uniformly as possible (rotating load) in order to detect

irregularities in the bearing material;

e) simple, theoretically and experimentally reproducible hydrodynamic conditions (i.e. a rotating

load produces a hydrodynamic film and pressure distribution equal to a static load);

f) repeatable and reliable assembly of components.
6 Test procedures
6.1 General

In order to assure the compatibility of test results from different test rigs and their putting into practice,

all parameters controlling the hydrodynamic oil film shall be detailed, starting with test conditions,

bearing dimensions, lubricant and other factors influencing hydrodynamic oil film. The following

constitute the essential characteristic conditions and parameters for fatigue testing.

6.2 Characteristic conditions
6.2.1 Effective running-in procedure

This is designed in order to avoid excessive temperature and frictional shear stress due to heavy

asperity contact. The progress of running-in may be monitored by measurements of temperature,

electrical resistance, impedance or continuous radio nuclide measurement. For guidance h should

initially be greater than (Rz + Rz ), where h equals the minimum oil film thickness and shall be

b s 0

determined by measurement or calculation in accordance with ISO 7902-1 to ISO 7902-3, and Rz and

Rz are the height of the profile irregularities in ten points of the bearing and the shaft face respectively,

which shall be determined in accordance with ISO 4287. Polishing during running-in allows the value of

h to be reduced but during fatigue testing it should not be less than the initial value of Rz . The running-

0 s

in procedure progressively reduces the minimum oil film thickness by a combination of reduced oil

viscosity through increases in temperature, and by stepwise increases of load. The magnitude of load

steps should be controlled by minimizing temperature spikes, excessive radio nuclide wear indication,

or excessive duration of zero electrical contact resistance.

For electrical contact resistance control, the bearing is electrically isolated from the test rig. The

electrical scheme should provide for monitoring a 10 mV difference of potential between the shaft

and bearing at a supply point with 100 Ω. internal resistance, which drops to 0,01 mV during asperity

contact. Load increments should be adjusted so as to minimize the duration of asperity contact.

WARNING — Radionuclides that find their way into the environment may cause harmful effects

as radioactive contamination. They can also cause damage if they are excessively used during

treatment or in other ways exposed to living beings, by radiation poisoning. Potential health

damage from exposure to radionuclides depends on a number of factors and can damage the

functions of healthy tissue/organs. Radiation exposure can produce effects ranging from skin

redness and hair loss, to radiation burns and acute radiation syndrome. Prolonged exposure

can lead to cells being damaged and in turn lead to cancer. Signs of cancerous cells might not

[16]
show up until years, or even decades, after exposure .

6.2.2 Avoidance of deviation in the geometry of the structural elements of the plain bearing

assembly

This is to avoid results being affected and their transferability reduced. Such geometrical discrepancies

may include housing distortion, shaft deflection or misalignment and uneven hard rub marks in the

plain bearing surface.
© ISO 2021 – All rights reserved 3
---------------------- Page: 7 --------------
...

FINAL
INTERNATIONAL ISO/FDIS
DRAFT
STANDARD 7905-1
ISO/TC 123/SC 2
Plain bearings — Bearing fatigue —
Secretariat: DIN
Voting begins on:
Part 1:
2021-01-29
Plain bearings in test rigs and in
Voting terminates on:
applications under conditions of
2021-03-26
hydrodynamic lubrication
Paliers lisses — Fatigue des paliers —
Partie 1: Paliers dans les machines d'essai et dans les applications en
lubrification hydrodynamique
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 7905-1:2021(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 7905-1:2021(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/FDIS 7905-1:2021(E)
Contents Page

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

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

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

3 Terms and definitions ..................................................................................................................................................................................... 2

4 Objective of testing ............................................................................................................................................................................................. 2

5 Requirements .......................................................................................................................................................................................................... 2

5.1 Test rigs ......................................................................................................................................................................................................... 2

5.2 Test methods ............................................................................................................................................................................................. 2

6 Test procedures ..................................................................................................................................................................................................... 3

6.1 General ........................................................................................................................................................................................................... 3

6.2 Characteristic conditions ............................................................................................................................................................... 3

6.2.1 Effective running-in procedure ........................................................................................................................... 3

6.2.2 Avoidance of deviation in the geometry of the structural elements of the

plain bearing assembly ........................................................................................................................................... .... 3

6.2.3 Effective temperature of the bearing and hydrodynamic film ................................................. 4

6.2.4 Dynamic load amplitude and direction as a function of time ................................................... 4

6.2.5 Number of load cycles required to effect the first fatigue damage ....................................... 4

6.3 Characteristic information ............................................................................................................................................................ 4

6.3.1 General...................................................................................................................................................................................... 4

6.3.2 Test rig description ........................................................................................................................................................ 4

6.3.3 Test bearing description .................. ......................................................................................................................... . 4

6.3.4 Test journal description ............................................................................................................................................. 4

6.3.5 Specific details of test load ...................................................................................................................................... 5

6.3.6 Designation of lubricant and supply ............................................................................................................... 5

6.3.7 Test temperatures description .................. ........................................................................................................... 5

6.3.8 Test film thickness description ............................................................................................................................ 5

6.3.9 Test film pressure description ............................................................................................................................. 5

6.3.10 Description of the dynamic stresses of the test .................................................................................... 5

6.3.11 Other test results ............................................................................................................................................................. 5

7 Evaluation of stress in bearing materials ................................................................................................................................... 5

Annex A (informative) Evaluation of stress ................................................................................................................................................... 7

Bibliography .............................................................................................................................................................................................................................15

© ISO 2021 – All rights reserved iii
---------------------- Page: 3 ----------------------
ISO/FDIS 7905-1:2021(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 123, Plain bearing, Subcommittee SC 2,

Material and lubricants, their properties, characteristics, test methods and testing conditions.

This second edition cancels and replaces the first edition (ISO 7905-1:1996), which has been editorially

revised.
The main changes compared to the previous edition are as follows:
— normative references have been updated;
— additional explanation for the test methods have been added.
A list of all parts in the ISO 7905 series can be found on the ISO website.

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 7905-1:2021(E)
Plain bearings — Bearing fatigue —
Part 1:
Plain bearings in test rigs and in applications under
conditions of hydrodynamic lubrication
1 Scope

This document specifies a method of improving test result comparability by evaluating the stresses in the

bearing layers leading to fatigue (see Annex A). A similar evaluation is required in practical applications.

Because the stresses are the result of pressure build-up in the hydrodynamic film, it is essential to

fully state the conditions of operation and lubrication. In addition to dynamic loading, dimensional and

running characteristics, the inclusion of the following adequately defines the fatigue system:

a) under conditions of dynamic loading the minimum bearing oil film thickness as a function of time

and location to ensure no excessive local overheating or shearing as a result of mixed lubrication

when running in;

b) the distribution of pressure circumferentially and axially with time under dynamic loading;

c) from this the resulting stresses in the bearing layers as a function of time and location, especially

the maximum alternating stress.

Furthermore, bearing fatigue can be affected by mixed lubrication, wear, dirt, tribochemical reactions

and other effects encountered in use thus complicating the fatigue problem. This document is therefore

restricted to fatigue under full hydrodynamic separation of the bearing surfaces by a lubricant film.

This document applies to oil-lubricated plain cylindrical bearings, in test rigs and application running

in conditions of full hydrodynamic lubrication. It comprises dynamic loading in bi-metal and multilayer

bearings.

NOTE The number of practical applications with different requirements has led to the development of many

bearing test rigs. If the conditions of lubrication employed on these test rigs are not defined in detail, test results

from different rigs are generally neither comparable nor applicable in practice. Different test rigs can yield

inconsistent ranking between equal materials.
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 4287, Geometrical Product Specifications (GPS) — Surface texture: Profile method — Terms, definitions

and surface texture parameters

ISO 7902-1, Hydrodynamic plain journal bearings under steady-state conditions — Circular cylindrical

bearings — Part 1: Calculation procedure

ISO 7902-2, Hydrodynamic plain journal bearings under steady-state conditions — Circular cylindrical

bearings — Part 2: Functions used in the calculation procedure

ISO 7902-3, Hydrodynamic plain journal bearings under steady-state conditions — Circular cylindrical

bearings — Part 3: Permissible operational parameters
© ISO 2021 – All rights reserved 1
---------------------- Page: 5 ----------------------
ISO/FDIS 7905-1:2021(E)
3 Terms and definitions
No terms and definitions are listed in this document.

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/
4 Objective of testing

In this document the objective of testing with plain bearing test rigs, operating in conditions of full

hydrodynamic lubrication, is to measure the dynamic load-carrying capacity e.g. the fatigue endurance

limit of the bearing layer material in terms of amplitude of stress and number of cycles. This may be

presented as a σ -N curve (endurance limit stress plotted against number of cycles), or as the endurance

limit stress for a specified number of cycles. Endurance limit is reached when cracks (greater than

5 mm in length) appear in the bearing surface.

In terms of current understanding, the restriction to full hydrodynamic lubrication is a necessary

simplification of the fatigue problem. This implies that the essential running-in of the bearing under test

shall be carefully controlled to avoid significant predamage from excessive temperature and frictional

shear stress which may cause surface microcracks.

It should be noted that fatigue testing of bearing materials may be conducted also by utilizing the more

classic methods of testing. See ISO 7905-2 to ISO 7905-4.
5 Requirements
5.1 Test rigs

In order to define the operating and lubricating conditions, the test rig shall have the following

characteristics:
a) simple and clear mechanical construction;
b) easy dismantling, preferably with an in situ bearing inspection capability;

c) bearing dimensional stability under test together with resistance to deformation of housing and

shaft deflection;
d) adequate lubricant supply without impairing oil film pressure development;

e) be capable of exceeding the entire range of load/stress and temperature encountered in practice.

5.2 Test methods
The test methods shall have the following characteristics:

a) the ability to apply specialized measuring techniques for oil film thickness, lubricant temperature,

pressure distribution and crack disintegration debris; such techniques for the latter aspect include

continuous radio nuclide measurement of wear or X-ray fluorescent analysis of intermittently

withdrawn lubricant samples;

b) well-defined, experimentally verified hydrodynamic conditions (e.g the verification of viscosity

and operating conditions indicative of hydrodynamic behaviour);

c) clear distinction between mixed lubrication during running-in and full hydrodynamic lubrication

during fatigue testing;
2 © ISO 2021 – All rights reserved
---------------------- Page: 6 ----------------------
ISO/FDIS 7905-1:2021(E)

d) the stress can traverse the bearing as uniformly as possible (rotating load) in order to detect

irregularities in the bearing material;

e) simple, theoretically and experimentally reproducible hydrodynamic conditions (i.e. a rotating

load produces a hydrodynamic film and pressure distribution equal to a static load);

f) repeatable and reliable assembly of components.
6 Test procedures
6.1 General

In order to assure the compatibility of test results from different test rigs and their putting into practice,

all parameters controlling the hydrodynamic oil film shall be detailed, starting with test conditions,

bearing dimensions, lubricant and other factors influencing hydrodynamic oil film. The following

constitute the essential characteristic conditions and parameters for fatigue testing.

6.2 Characteristic conditions
6.2.1 Effective running-in procedure

This is designed in order to avoid excessive temperature and frictional shear stress due to heavy

asperity contact. The progress of running-in may be monitored by measurements of temperature,

electrical resistance, impedance or continuous radio nuclide measurement. For guidance h should

initially be greater than (Rz + Rz ), where h equals the minimum oil film thickness and shall be

b s 0

determined by measurement or calculation in accordance with ISO 7902-1 to ISO 7902-3, and Rz and

Rz are the height of the profile irregularities in ten points of the bearing and face respectively, which

shall be determined in accordance with ISO 4287. Polishing during running-in allows the value of h to

be reduced but during fatigue testing it should not be less than the initial value of Rz . The running-

in procedure progressively reduces the minimum oil film thickness by a combination of reduced oil

viscosity through increases in temperature, and by stepwise in-creases of load. The magnitude of load

steps should be controlled by minimizing temperature spikes, excessive radio nuclide wear indication,

or excessive duration of zero electrical contact resistance.

For electrical contact resistance control, the bearing is electrically isolated from the test rig. The

electrical scheme should provide for monitoring a 10 mV difference of potential between the shaft

and bearing at a supply point with 100 Ω. internal resistance, which drops to 0,01 mV during asperity

contact. Load increments should be adjusted so as to minimize the duration of asperity contact.

WARNING — Radionuclides that find their way into the environment may cause harmful effects

as radioactive contamination. They can also cause damage if they are excessively used during

treatment or in other ways exposed to living beings, by radiation poisoning. Potential health

damage from exposure to radionuclides depends on a number of factors and can damage the

functions of healthy tissue/organs. Radiation exposure can produce effects ranging from skin

redness and hair loss, to radiation burns and acute radiation syndrome. Prolonged exposure

can lead to cells being damaged and in turn lead to cancer. Signs of cancerous cells might not

[16]
show up until years, or even decades, after exposure .

6.2.2 Avoidance of deviation in the geometry of the structural elements of the plain bearing

assembly
This is to avoid results being affected a
...

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