ISO 14628:2012

Fine ceramics (advanced ceramics, advanced technical ceramics) - Test method for rolling contact fatigue of silicon nitride ceramics at room temperature by balls-on-flat method

ISO 14628:2012 specifies a test method for rolling contact fatigue of silicon nitride ceramics under stepwise loading that is carried out at room temperature. This test may be used as follows: relative comparison of the rolling contact fatigue performance, a pass/fail test for material qualification of rolling elements or choosing an appropriate load level for RCF testing under constant load.

Céramiques techniques — Méthode d'essai de fatigue de contact de roulement des céramiques au nitrure de silicium à température ambiante par la méthode des billes sur surface plane

General Information

• Status: Published
• Publication Date: 05-Jul-2012
• ICS: 81.060.30 - Advanced ceramics
• Technical Committee: ISO/TC 206 - Fine ceramics
• Drafting Committee: ISO/TC 206/WG 12 - Engineering applications
• Current Stage: 9093 - International Standard confirmed
• Start Date: 29-Sep-2023
• Completion Date: 13-Dec-2025

Overview

ISO 14628:2012 defines a standardized balls-on-flat test method for assessing rolling contact fatigue (RCF) of silicon nitride ceramics at room temperature. The method uses balls rolling unidirectionally on a flat ceramic plate under stepwise loading to determine the number of cycles to surface failure. It is intended for relative comparison of RCF performance, pass/fail material qualification of rolling elements, and for choosing an appropriate load level for constant-load RCF testing.

Key Topics and Requirements

• Test principle: Measure cycles to surface failure of a flat plate under cyclic rolling contact produced by balls-on-flat configuration.
• Testing machine: Balls held in a retainer roll in a circle on a rotating shaft washer; load is typically applied by dead weights on a lever. Machine must stop automatically on detected failure and prevent unwanted restart.
• Loading precision: Load fluctuation shall be within ±1%.
• Stepwise loading: Load is increased in agreed regular intervals until final failure; starting load and step size are specified by agreement.
• Test specimens: Flat plates with parallelism tolerance of 0.015 mm, adequate thickness to prevent flexural oscillation, and enough margin outside the contact track.
• Surface finish: Ground and polished with surface roughness ≤ 0.1 µm Ra; subsurface damage must be removed. Measure skewness (Rsk) to assess surface integrity.
• Balls: Use bearing-grade silicon nitride balls (grade G5 or G3 per ISO 3290-2) for bearing-material tests; steel balls (ISO 3290-1) may be used in some qualification tests. Common configurations use three or six balls.
• Lubrication: Specimen and balls immersed in oil to maintain partial or full elastohydrodynamic lubrication; higher-viscosity paraffinic oil (e.g., ~68 mm²/s) is recommended to achieve EHL.
• Failure detection: Vibrational acceleration monitoring (accelerometer) on a mechanically amplified point; automatic shutoff threshold typically 2–3× the initial vibration level.
• Results: Compute mean effective load using a Lundberg–Palmgren-based equation (p commonly taken as 3 for practical comparisons) and calculate maximum Hertzian stress for mechanical input assessment.

Applications and Users

• Bearing manufacturers and designers selecting or qualifying bearing-grade silicon nitride for rolling elements.
• Materials suppliers seeking comparative RCF performance data to improve formulations and processes.
• R&D and testing laboratories performing comparative tests, pass/fail qualification, or determining load levels for constant-load RCF tests.
• Quality and reliability engineers concerned with component life under rolling contact.

Related Standards

• ISO 3290-1 / ISO 3290-2 (balls: steel and ceramic)
• ISO 3611 (micrometer measurement)
• ISO 4287 (surface texture parameters)
• ISO/IEC 17025 (laboratory competence)

Keywords: ISO 14628:2012, rolling contact fatigue, silicon nitride, balls-on-flat method, fine ceramics, RCF testing, Hertzian stress, elastohydrodynamic lubrication, bearing-grade silicon nitride.

Standards Content (Sample)

INTERNATIONAL ISO
STANDARD 14628
First edition
2012-07-15
Fine ceramics (advanced ceramics,
advanced technical ceramics) — Test
method for rolling contact fatigue
of silicon nitride ceramics at room
temperature by balls-on-flat method
Céramiques techniques — Méthode d’essai de fatigue de contact
de roulement des céramiques au nitrure de silicium à température
ambiante par la méthode des billes sur surface plane
Reference number
©
ISO 2012
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means,
electronic or mechanical, including photocopying and microfilm, without permission in writing from either ISO at the address below or ISO’s
member body in the country of the requester.
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Published in Switzerland
ii © ISO 2012 – All rights reserved

Contents Page
Foreword .iv
Introduction . v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 2
5 Testing machine . 2
5.1 Structure of testing machine . 2
5.2 Loading precision . 4
6 Test specimens . 4
6.1 Test specimen geometry . 4
6.2 Fixation of test specimen . 5
6.3 Specimen thickness . 5
6.4 Surface finish . 5
6.5 Number of test specimens . 5
7 Test method . 5
7.1 Balls . 5
7.2 Loading method . 5
7.3 Lubrication . 6
7.4 Detection of surface failure . 6
8 Treatment of test result . 7
8.1 Mean effective load . 7
8.2 Mean effective mechanical input . 7
8.3 Flaking of ball surface . 8
9 Test report . 8
Annex A (informative) General information .10
Bibliography .12
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.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
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.
ISO 14628 was prepared by Technical Committee ISO/TC 206, Fine ceramics.
iv © ISO 2012 – All rights reserved

Introduction
Rolling contact fatigue (RCF) performance is essential for predicting the life of a rolling element. In general,
RCF performance is evaluated from the life at a specific failure probability obtained by the Weibull analysis of
test data under constant loading conditions. This International Standard specifies a fast and reliable method to
compare RCF performance under stepwise loading as an alternative to accurate quantification by RCF tests
under constant load. Ranking candidate materials, in other words comparison of performance among them,
would be of value for choosing materials of required performance for bearings. In addition, material suppliers
would receive feedback from the test results, allowing them to achieve a higher level of RCF performance.
INTERNATIONAL STANDARD ISO 14628:2012(E)
Fine ceramics (advanced ceramics, advanced technical
ceramics) — Test method for rolling contact fatigue of silicon
nitride ceramics at room temperature by balls-on-flat method
1 Scope
This International Standard specifies a test method for rolling contact fatigue of silicon nitride ceramics under
stepwise loading that is carried out at room temperature. This test may be used as follows: relative comparison
of the rolling contact fatigue performance, a pass/fail test for material qualification of rolling elements or
choosing an appropriate load level for RCF testing under constant load.
2 Normative references
The following referenced documents are indispensable for the application 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 3290-1:2008, Rolling bearings — Balls — Part 1: Steel balls
ISO 3290-2:2008, Rolling bearings — Balls — Part 2: Ceramic balls
ISO 3611:2010, Geometrical product specifications (GPS) — Dimensional measuring equipment: Micrometers
for external measurements — Design and metrological characteristics
ISO 4287:1997, Geometrical Product Specification (GPS) ―Surface texture: Profile method―Terms, definitions
and surface texture parameters
ISO/IEC 17025:2005, General requirements for the competence of testing and calibration laboratories.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
rolling contact
contact between rolling elements
NOTE Under pure rolling contact conditions, the relative velocity at the point of contact is zero. The relative velocity
between real rolling elements is not, however, zero in most cases.
3.2
surface failure
flaking of test specimen surface
3.3
rolling contact fatigue
formation of surface failure due to cyclic rolling contact stress well below the stress when surface failure occurs
under monotonic loading
3.4
rolling contact fatigue test
test where repeated rolling contact stress is applied to a test specimen, and the number of cycles to surface
failure is measured
3.5
stepwise loading
loading method in which load is increased stepwise at regular intervals until the final failure of the test specimen
3.6
contact track
circular trail formed on a test specimen by repeated rolling contact of balls
3.7
mean effective load
constant load equivalent to stepwise loading
3.8
maximum Hertzian stress
maximum contact stress between two bodies using the elastic stress analyzing theory by Hertz
3.9
bearing-grade silicon nitride
silicon nitride ceramics specially designed for rolling elements
4 Principle
The life of flat plate under cyclic rolling contact stress, which is applied by balls rotating unidirectionally thereon,
is determined by measuring the number of stress cycles to the final surface failure of the plate.
5 Testing machine
5.1 Structure of testing machine
A testing machine shall be so constructed that rolling contact stress can be applied to the surface of a flat plate
test specimen by balls thereon equally spaced with a retainer (see Figure 1). The balls shall be rolling in a circle
with the rotation of the shaft washer of a 90° contact angle thrust ball bearing of a specified bore diameter. The
shaft washer shall be rotated unidirectionally.
The testing machine is shown schematically in Figure 2. Load is applied by dead weights at the end of loading arm.
The testing machine shall be equipped with an automatic shutoff with a device detecting the surface failure,
an apparatus capable of obtaining the number of rotations until the stop of testing, and a mechanism where its
automatic reactivation is prevented when the testing machine is stopped for reasons of power failure or others.
NOTE 1 The shaft washer should be chosen on the basis of diameters of the ball and main shaft of the testing machine.
NOTE 2 The dimensions of the retainer depend on those of the shaft washer, ball diameter and number of balls.
2 © ISO 2012 – All rights reserved

D
A
A
O
Section A-O-A
Key
1 ball of diameter D
2 test specimen
3 main shaft of a testing machine
4 shaft washer of a 90° contact angle thrust bearing
5 retainer
Figure 1 —Balls-on-flat configurations
©
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