ISO 7905-1:2021

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

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ISO/FDIS 7905-1:2021(E)

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© ISO 2021
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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
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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.
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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
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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
el
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;
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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
0
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
,b
Rz are the height of the profile irregularities in ten points of the bearing and face respectively, which
,s
shall be determined in accordance with ISO 4287. Polishing during running-in allows the value of h to
0
be reduced but during fatigue testing it should not be less than the initial value of Rz . The running-
,s
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
...