IEC 61747-40-2:2015

IEC 61747-40-2 ®
Edition 1.0 2015-01
INTERNATIONAL
STANDARD
Liquid crystal display devices –
Part 40-2: Mechanical testing of display cover glass for mobile devices – Uni-
axial flexural strength (4-point bend)
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IEC 61747-40-2 ®
Edition 1.0 2015-01
INTERNATIONAL
STANDARD
Liquid crystal display devices –

Part 40-2: Mechanical testing of display cover glass for mobile devices – Uni-

axial flexural strength (4-point bend)

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 31.120 ISBN 978-2-8322-2210-2

– 2 – IEC 61747-40-2:2015 © IEC 2015
CONTENTS
FOREWORD . 3
INTRODUCTION . 5
1 Scope . 6
2 Normative references . 6
3 Terms, definitions and abbreviations . 6
3.1 Terms and definitions . 6
3.2 Abbreviations . 7
4 General . 7
5 Apparatus . 7
5.1 Testing environment and pre-conditioning . 7
5.2 Testing frame . 7
5.3 Test fixture and setup . 9
5.4 Test fixture dimensions . 12
5.5 Loading rate . 13
6 Procedure . 13
6.1 Safety . 13
6.1.1 Hazard – Broken glass. 13
6.1.2 Crush hazard – Only one person may operate the testing frame . 13
6.1.3 Crush hazard – Take care when installing or removing a specimen . 13
6.1.4 Hazard – Press the emergency stop button when an unsafe condition is
observed . 14
6.1.5 Flying debris hazard – Ensure that specimens are installed correctly . 14
6.1.6 Hazard – Protect control cables from damage or disconnection . 14
6.2 Sample . 14
6.3 Individual specimen . 14
6.4 Complete the report . 16
7 Calculations . 17
7.1 Strength calculations . 17
7.2 Statistical calculations . 17
8 Reporting. 18
8.1 Information to be reported for each test . 18
8.2 Information to be made available upon request . 19
9 Specifications . 19

Figure 1 – Testing frame . 9
Figure 2 – Support assembly (side view) . 10
Figure 3 – Support assembly (top view) . 10
Figure 4 – Load assembly (side view) . 11
Figure 5 – Load assembly (bottom view) . 11
Figure 6 – Example load traces for appropriate and inappropriate span settings . 13
Figure 7 – Edge fracture originating from between the load bars . 15
Figure 8 – Edge fracture originating from underneath the load bar . 16
Figure 9 – Surface fracture originating from between the load bars . 16
Figure 10 – Example Weibull plot . 18

INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
LIQUID CRYSTAL DISPLAY DEVICES –

Part 40-2: Mechanical testing of display cover glass for mobile devices –
Uni-axial flexural strength (4-point bend)

FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote
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International Standard IEC 61747-40-2 has been prepared by technical committee 110:
Electronic display devices.
The text of this standard is based on the following documents:
CDV Report on voting
110/568/CDV 110/608A/RVC
Full information on the voting for the approval of this standard can be found in the report on
voting indicated in the above table.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.

– 4 – IEC 61747-40-2:2015 © IEC 2015
A list of all parts in the IEC 61747 series, published under the general title Liquid crystal
display devices, can be found on the IEC website.
The committee has decided that the contents of this publication will remain unchanged until
the stability date indicated on the IEC web site under "http://webstore.iec.ch" in the data
related to the specific publication. At this date, the publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
A bilingual version of this publication may be issued at a later date.

INTRODUCTION
Mobile electronic devices have become increasingly sophisticated and often include displays
for the purposes of user interface and viewing. Such displays commonly incorporate a
transparent cover glass which aids in protecting the display against the introduction of
damage through routine device transport and use, as well as occasional or accidental misuse.
The purpose of this standard is to provide mechanical testing procedures for cover glasses
utilized in such applications. Such glasses can be strengthened, for example via an ion-
exchange process, which acts to increase mechanical strength through the introduction of a
surface compressive layer.
– 6 – IEC 61747-40-2:2015 © IEC 2015
LIQUID CRYSTAL DISPLAY DEVICES –

Part 40-2: Mechanical testing of display cover glass for mobile devices –
Uni-axial flexural strength (4-point bend)

1 Scope
This part of IEC 61747-40 is a mechanical performance testing procedure for cover glass
used in electronic flat panel displays in mobile devices. This standard is focused on the
measurement of as-received edge strength via uni-axial flexure generated by a four-point
bend.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and
are indispensable for its application. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any
amendments) applies.
IEC 61747-40-1, Liquid crystal display devices – Part 40-1: Mechanical testing of display
cover glass for mobile devices – Guidelines
IEC 61649:2008, Weibull analysis
3 Terms, definitions and abbreviations
3.1 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1.1
specimen
individual piece of glass to be tested to failure
3.1.2
sample
group of specimens sharing a common pedigree (such as manufacturing process and period
of production), for which failure statistics can be generated and reported
3.1.3
sample size
number of specimens in a sample
3.1.4
nominal value
value about which a tolerance range is specified
3.1.5
strength
normalized load at which fracture occurs

Note 1 to entry: For glasses without a compressive surface layer, strength can be equated to the fracture stress.
In cases where non-linearities prevent a suitable conversion from load to strength (or stress), load at fracture
should instead be reported.
3.2 Abbreviations
PTFE polytetrafluoroethylene
4 General
This test measures edge strength by forcing a pair of parallel load bars (anvils) through a
specimen that is supported by a pair of parallel support bars. The two pairs of bars shall be
parallel and the applied force shall be perpendicular to the surface formed by the support bar
pair. The loads at fracture are measured and converted to strength. Strength calculations are
found in Clause 7.
The test is applied to a sample of several specimens. The sample statistics of the strength
values are defined in Clause 7. The statistical values to be reported or specified are given in
Clauses 8 and 9.
The specimens to be tested are typically 44 mm to 60 mm in width and 60 mm to 110 mm in
length, with thickness ranging from 0,55 mm to 2,0 mm. When the specimen is placed on the
support bars, a pair of opposite edges shall be aligned to be parallel with the support bars.
Before the specimen is placed on the support bars, the surface that will contact the load bars
is covered with a layer of polymeric adhesive tape to preserve the fracture surface, reduce the
scattering of glass fragments upon fracture, and minimize contact damage. The support rods
are also covered with PTFE tape and may be rollers, also to minimize contact damage and
friction.
The general requirements of the apparatus are given in Clause 5. Apparatus dimensions can
be affected by specimen dimensions. These relationships are outlined in 5.4. It should be
noted that direct comparisons cannot be made between specimens tested under different
apparatus/fixture dimensions or at different cross head traverse rates.
Testing procedures are given in Clause 6.
It is assumed that all measurements are performed by personnel skilled in the general art of
mechanical property measurements. Furthermore, it should be assured that all equipment is
suitably calibrated as is known to skilled personnel and that records of the calibration data
and traceability are kept.
5 Apparatus
5.1 Testing environment and pre-conditioning
The standard testing environment is specified in IEC 61747-40-1. Specimens shall be stored
in such an environment for at least four hours before testing.
5.2 Testing frame
The testing frame provi
...