IEC 61747-40-1:2019

Liquid crystal display devices - Part 40-1: Mechanical testing of display cover glass for mobile devices - Guidelines

IEC 61747-40-1:2019 provides mechanical performance testing guidelines for cover glass used in electronic flat panel displays in mobile devices. This document focuses on key mechanical testing performance parameters and covers mainly strength and damage resistance attributes. The test methods focus on the cover glass level testing only. This edition includes the following significant technical changes with respect to the previous edition:
- withdrawal of test methods unsuitable for mobile display cover,
- revision of test methods based on newly developed market relevance,
- addition of test method for abraded strength,
- addition of explanations about the relevance between the test methods and the fracture mode, and
- revision of terms and definitions.

General Information

• Status: Published
• Publication Date: 16-Apr-2019
• ICS: 31.120 - Electronic display devices
• Technical Committee: TC 110 - Electronic displays
• Drafting Committee: MT 61747 - TC 110/MT 61747
• Current Stage: PPUB - Publication issued
• Start Date: 17-Apr-2019
• Completion Date: 13-May-2019

Relations

• Revises: IEC 61747-40-1:2013 - Liquid crystal display devices - Part 40-1: Mechanical testing of display cover glass for mobile devices - Guidelines
• Effective Date: 05-Sep-2023

Standards Content (Sample)

IEC 61747-40-1 ®
Edition 2.0 2019-04
INTERNATIONAL
STANDARD
Liquid crystal display devices –
Part 40-1: Mechanical testing of display cover glass for mobile devices –
Guidelines
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 IEC or IEC's member National Committee in the country of the requester. If you have any questions about IEC
copyright or have an enquiry about obtaining additional rights to this publication, please contact the address below or
your local IEC member National Committee for further information.

IEC Central Office Tel.: [phone]
3, rue de Varembé [e-mail]
CH-1211 Geneva 20 www.iec.ch
Switzerland
About the IEC
The International Electrotechnical Commission (IEC) is the leading global organization that prepares and publishes
International Standards for all electrical, electronic and related technologies.

About IEC publications
The technical content of IEC publications is kept under constant review by the IEC. Please make sure that you have the
latest edition, a corrigendum or an amendment might have been published.

IEC publications search - webstore.iec.ch/advsearchform Electropedia - www.electropedia.org
The advanced search enables to find IEC publications by a The world's leading online dictionary on electrotechnology,
variety of criteria (reference number, text, technical containing more than 22 000 terminological entries in English
committee,…). It also gives information on projects, replaced and French, with equivalent terms in 16 additional languages.
and withdrawn publications. Also known as the International Electrotechnical Vocabulary

(IEV) online.
IEC Just Published - webstore.iec.ch/justpublished
Stay up to date on all new IEC publications. Just Published IEC Glossary - std.iec.ch/glossary
details all new publications released. Available online and 67 000 electrotechnical terminology entries in English and
once a month by email. French extracted from the Terms and Definitions clause of
IEC publications issued since 2002. Some entries have been
IEC Customer Service Centre - webstore.iec.ch/csc collected from earlier publications of IEC TC 37, 77, 86 and
If you wish to give us your feedback on this publication or CISPR.

need further assistance, please contact the Customer Service

Centre: [e-mail].
IEC 61747-40-1 ®
Edition 2.0 2019-04
INTERNATIONAL
STANDARD
Liquid crystal display devices –

Part 40-1: Mechanical testing of display cover glass for mobile devices –

Guidelines
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 31.120 ISBN 978-2-8322-6800-1

– 2 – IEC 61747-40-1:2019  IEC 2019
CONTENTS
FOREWORD . 3
INTRODUCTION . 5
1 Scope . 6
2 Normative references . 6
3 Terms and definitions . 6
4 Mechanical performance testing guidelines . 7
4.1 General . 7
4.2 Mechanical testing guidelines for display cover glass for mobile devices . 8
5 Brief overview of mechanical test methods . 9
5.1 Edge strength . 9
5.2 Surface impact resistance (energy-to-failure) . 9
5.3 Surface strength . 9
5.4 Resistance against sharp contact surface damage and propagation under
rigid support (energy-to-failure) . 9
5.5 Retained surface strength . 10
Bibliography . 11

Table 1 – Comprehensive list of cover glass testing methods . 8
Table 2 – Matrix of cover glass test methods and glass condition . 9

INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
LIQUID CRYSTAL DISPLAY DEVICES –

Part 40-1: Mechanical testing of display cover glass
for mobile devices – Guidelines

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
international co-operation on all questions concerning standardization in the electrical and electronic fields. To
this end and in addition to other activities, IEC publishes International Standards, Technical Specifications,
Technical Reports, Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC
Publication(s)”). Their preparation is entrusted to technical committees; any IEC National Committee interested
in the subject dealt with may participate in this preparatory work. International, governmental and non-
governmental organizations liaising with the IEC also participate in this preparation. IEC collaborates closely
with the International Organization for Standardization (ISO) in accordance with conditions determined by
agreement between the two organizations.
2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
consensus of opinion on the relevant subjects since each technical committee has representation from all
interested IEC National Committees.
3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC
Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any
misinterpretation by any end user.
4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
transparently to the maximum extent possible in their national and regional publications. Any divergence
between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in
the latter.
5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity
assessment services and, in some areas, access to IEC marks of conformity. IEC is not responsible for any
services carried out by independent certification bodies.
6) All users should ensure that they have the latest edition of this publication.
7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and
members of its technical committees and IEC National Committees for any personal injury, property damage or
other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and
expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC
Publications.
8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 61747-40-1 has been prepared by IEC technical committee 110:
Electronic displays.
This second edition cancels and replaces the first edition published in 2013. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) withdrawal of test methods unsuitable for mobile display cover,
b) revision of test methods based on newly developed market relevance,
c) addition of test method for abraded strength,
d) addition of explanations about the relevance between the test methods and the fracture
mode, and
– 4 – IEC 61747-40-1:2019  IEC 2019
e) revision of terms and definitions.
The text of this International Standard is based on the following documents:
CDV Report on voting
110/1040/CDV 110/1093/RVC
Full information on the voting for the approval of this International Standard can be found in
the report on voting indicated in the above table.
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.
This document has been drafted in accordance with the ISO/IEC Directives, Part 2.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under "http://webstore.iec.ch" in the data related to
the specific document. At this date, the document 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 incorporate
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 document is to provide mechanical testing guidelines for cover glasses
used in such applications. Such glasses can be strengthened or not, for example via an ion-
exchange process, which acts to increase mechanical strength through the introduction of a
surface compressive layer.
It is assumed that all measurements – described in detail in individual test method standards
– are performed by personnel skilled in the general art of mechanical property measurements.
Furthermore, it is recommended that all equipment is suitably calibrated as is known to skilled
personnel and that records of the calibration data and traceability are kept.

– 6 – IEC 61747-40-1:2019  IEC 2019
LIQUID CRYSTAL DISPLAY DEVICES –
...

IEC 61747-40-1 ®
Edition 2.0 2019-04
REDLINE VERSION
INTERNATIONAL
STANDARD
colour
inside
Liquid crystal display devices –
Part 40-1: Mechanical testing of display cover glass for mobile devices –
Guidelines
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 IEC or IEC's member National Committee in the country of the requester. If you have any questions about IEC
copyright or have an enquiry about obtaining additional rights to this publication, please contact the address below or
your local IEC member National Committee for further information.

IEC Central Office Tel.: [phone]
3, rue de Varembé [e-mail]
CH-1211 Geneva 20 www.iec.ch
Switzerland
About the IEC
The International Electrotechnical Commission (IEC) is the leading global organization that prepares and publishes
International Standards for all electrical, electronic and related technologies.

About IEC publications
The technical content of IEC publications is kept under constant review by the IEC. Please make sure that you have the
latest edition, a corrigendum or an amendment might have been published.

IEC publications search - webstore.iec.ch/advsearchform Electropedia - www.electropedia.org
The advanced search enables to find IEC publications by a The world's leading online dictionary on electrotechnology,
variety of criteria (reference number, text, technical containing more than 22 000 terminological entries in English
committee,…). It also gives information on projects, replaced and French, with equivalent terms in 16 additional languages.
and withdrawn publications. Also known as the International Electrotechnical Vocabulary

(IEV) online.
IEC Just Published - webstore.iec.ch/justpublished
Stay up to date on all new IEC publications. Just Published IEC Glossary - std.iec.ch/glossary
details all new publications released. Available online and 67 000 electrotechnical terminology entries in English and
once a month by email. French extracted from the Terms and Definitions clause of
IEC publications issued since 2002. Some entries have been
IEC Customer Service Centre - webstore.iec.ch/csc collected from earlier publications of IEC TC 37, 77, 86 and
If you wish to give us your feedback on this publication or CISPR.

need further assistance, please contact the Customer Service

Centre: [e-mail].
IEC 61747-40-1 ®
Edition 2.0 2019-04
REDLINE VERSION
INTERNATIONAL
STANDARD
colour
inside
Liquid crystal display devices –

Part 40-1: Mechanical testing of display cover glass for mobile devices –

Guidelines
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 31.120 ISBN 978-2-8322-6854-4

– 2 – IEC 61747-40-1:2019 RLV  IEC 2019
CONTENTS
FOREWORD . 3
INTRODUCTION . 5
1 Scope . 6
2 Normative references . 6
3 Terms and definitions . 6
4 Mechanical performance testing guidelines . 8
4.1 General . 8
4.2 Mechanical testing guidelines for display cover glass for mobile devices . 8
5 Brief overview of mechanical test methods . 10
5.1 Edge strength . 10
5.2 Surface impact resistance (energy-to-failure) . 10
5.3 Surface strength . 10
5.4 Resistance against sharp contact surface damage and propagation under
rigid support (energy-to-failure) . 11
5.5 Retained surface strength . 11
Bibliography . 12

Table 1 – Mechanical attributes and measurement methods .
Table 1 – Comprehensive list of cover glass testing methods . 9
Table 2 – Matrix of cover glass test methods and glass condition . 10

INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
LIQUID CRYSTAL DISPLAY DEVICES –

Part 40-1: Mechanical testing of display cover glass
for mobile devices – Guidelines

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
international co-operation on all questions concerning standardization in the electrical and electronic fields. To
this end and in addition to other activities, IEC publishes International Standards, Technical Specifications,
Technical Reports, Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC
Publication(s)”). Their preparation is entrusted to technical committees; any IEC National Committee interested
in the subject dealt with may participate in this preparatory work. International, governmental and non-
governmental organizations liaising with the IEC also participate in this preparation. IEC collaborates closely
with the International Organization for Standardization (ISO) in accordance with conditions determined by
agreement between the two organizations.
2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
consensus of opinion on the relevant subjects since each technical committee has representation from all
interested IEC National Committees.
3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC
Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any
misinterpretation by any end user.
4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
transparently to the maximum extent possible in their national and regional publications. Any divergence
between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in
the latter.
5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity
assessment services and, in some areas, access to IEC marks of conformity. IEC is not responsible for any
services carried out by independent certification bodies.
6) All users should ensure that they have the latest edition of this publication.
7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and
members of its technical committees and IEC National Committees for any personal injury, property damage or
other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and
expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC
Publications.
8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
This redline version of the official IEC Standard allows the user to identify the changes
made to the previous edition. A vertical bar appears in the margin wherever a change
has been made. Additions are in green text, deletions are in strikethrough red text.

– 4 – IEC 61747-40-1:2019 RLV  IEC 2019
International Standard IEC 61747-40-1 has been prepared by IEC technical committee 110:
Electronic displays.
This second edition cancels and replaces the first edition published in 2013. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) withdrawal of test methods unsuitable for mobile display cover,
b) revision of test methods based on newly developed market relevance,
c) addition of test method for abraded strength,
d) addition of explanations about the relevance between the test methods and the fracture
mode, and
e) revision of terms and definitions.
The text of this International Standard is based on the following documents:
CDV Report on voting
110/1040/CDV 110/1093/RVC
Full information on the voting for the approval of this International Standard can be found in
the report on voting indicated in the above table.
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.
This document has been drafted in accordance with the ISO/IEC Directives, Part 2.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under "http://webstore.iec.ch" in the data related to
the specific document. At this date, the document will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
IMPORTANT – The “colour inside” logo on the cover page of this publication indicates
that it contains colours which are considered to be useful for the correct understanding
of its contents. Users should therefore print this publication using a colour printer.

INTRODUCTION
Mobile electronic devices have become increasingly sophisticated and often incorporate
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 document is to provide mechanical testing guidelines for cover glasses
utilized used in such applications. Such glasses may or may not can be strengthened or not,
for example via an ion-exchange process, which acts to increase mechanical strength through
the introduction of a surface compressive layer.
It is assumed that all measurements – described in detail in individual test method standards
– are performed by personnel skilled in the general art of mechanical property measurements.
Furthermore, it should be assured is recommended that all equipment is suitably calibrated as
is known to skilled personnel and that records of the calibration data and traceability are kept.

– 6 – IEC 61747-40-1:2019 RLV  IEC 2019
LIQUID CRYSTAL DISPLAY DEVICES –

Part 40-1: Mechanical testing of display cover glass
for mobile devices – Guidelines

1 Scope
This part of IEC 61747 is a provides mechanical performance testing guidelines for cover
glass used in electronic flat panel displays in mobile devices. This document focuses on key
mechanical testing performance parameters and covers mainly strength and damage
resistance attributes. The test methods will focus on the cover glass level testing only.
NOTE The glass used for cover glasses for electronic mobile devices can be chemically strengthened by an ion-
exchange process. This ion exchange process increases the mechanical strength of the glass.
2 Normative references
There are no normative references in this document.
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:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp
3.1
abraded
subjected to a defined process which introduces mechanical abrasive damage to a portion of
the specimen to be placed under tension during subsequent flexural strength testing
EXAMPLE Biaxial flexure via ring-on-ring.
3.2
as-received
representative of standard sample preparation and handling practices, and therefore free of
intentional mechanical damage such as abrasion, scratching, or indentation
Note 1 to entry: The strength of glass is not an intrinsic material property, and like other brittle elastic materials,
is highly dependent upon the surface flaw population. The term “as-received” is meant to represent the surface
condition upon specimen receipt and should be is distinguished from a condition where damage has been
intentionally introduced prior to testing.
3.3
central tension
CT
tensile stress generated within the interior of a glass article which serves to counteract (i.e.,
force balance) compressive stress acting at or near the article surface
Note 1 to entry: This note applies to the French language only.

3.4
chemically strengthened
subjected to a molten salt bath containing alkali ions typically larger than those residing in the
glass, resulting in the generation of residual compressive stress (3.5) and central tension (3.3)
3.5
compressive stress
CS
maximum residual stress in compression measured near the glass surface
Note 1 to entry: This note applies to the French language only.
3.6
cover glass
cover lens
glass that typically protects an optical component such as a display from damage
3.7
damage resistance
ability to resist certain potential damage-inducing events such as abrasion, indentation or
scratching
2.8
depth of layer
DOL
distance from the surface of a strengthened glass to the depth of zero stress or the depth of
transition from compressive to tensile stress
Note 1 to entry: The ability to approximate this depth is dependent upon the measurement methodology chosen.
Note 2 to entry: This note applies to the French language only.
3.8
edge strength
measured stress at failure in the case where failure is known to have originated from a
specimen edge
3.9
mobile device
electronic device that includes a battery and is designed to be carried about by consumers
3.10
retained surface strength
abraded surface strength
measured stress (or measured load or impact energy when stress cannot be measured) at
failure in the case where failure is known to have originated from a specimen surface which
has experienced a prescribed specified abrasion or mechanical damage event
3.11
strength
stress, load, or impact energy at which a specimen fails for a given loading condition
3.12
thermally strengthened
subjected to fast cooling of the glass exterior relative to the glass interior, resulting in the
generation of residual compressive stress (3.5) and central tension (3.3)

– 8 – IEC 61747-40-1:2019 RLV  IEC 2019
4 Mechanical performance testing guidelines
4.1 General
The appropriate attribute(s) and test method(s) shall be selected based on the detail
specification or depending on the purpose of the evaluation.
The standard environment for testing shall be as follows:
– temperature: 23 °C ± 3 °C
– relative humidity: 50 % ± 5 %
unless otherwise specified in the detail specification. These standard requirements are
established to control fatigue effects when performing mechanical testing on glass. If
environmental conditions differ from the standard environment, the conditions shall be
reported with the test data.
4.2 Mechanical testing guidelines for display cover glass for mobile devices
The mechanical attributes and measurement methods are given in Table 1.
Table 1 – Mechanical attributes and measurement methods
Category Attributes Unit Test method
Strength (as-received) Edge strength MPa Uniaxial flexural strength (4-point bend)
Strength (as-received) Surface strength N Biaxial flexural strength (ring-on-ring)
Impact resistance Surface energy-to-failure Joules Biaxial flexural energy-to-failure (ball drop)
Surface damage Scratch performance gF Scratch lateral crack visibility/retained
resistance N strength
Surface damage Retained surface strength N Abraded biaxial flexural strength (ring-on-
resistance ring)
Surface damage Resistance to indentation gF Visual median radial crack
resistance cracking N resistance/retained strength

A comprehensive list of all cover glass test methods and failure mechanisms is given
in Table 1.
Table 1 – Comprehensive list of cover glass testing methods
Failure Failure Subject (typical) Attribute Test methods Units Corresponding
location mechanism document
Edge Overstress of As-received glass Edge strength Uniaxial MPa IEC 61747-40-2
edge flaws flexure
strength (four-
point bend)
Surface Overstress from As-received glass Surface Biaxial flexure J IEC 61747-40-3
blunt impact impact energy-to-
resistance failure (ball
drop)
Surface Overstress of As-received glass Surface Biaxial flexure N IEC 61747-40-4
surface flaws strength stress (ring-
on-ring)
Surface Sharp contact As-received glass Resistance Sharp contact J IEC 61747-40-5
damage against impact under
introduction surface sharp rigid support
propagated by contact condition (ball
central tension damage and drop on coated
under rigid propagation abrasives)
support condition under rigid
support
condition
Surface Sharp contact Abraded glass Retained Abraded N IEC 61747-40-6
damage in strength biaxial flexural
combination with strength
or followed (abraded ring-
immediately by on-ring)
flexural stress
In case the samples to be tested are that of strengthened glass – for example, via chemical or
thermal means – the results of mechanical testing will depend on the degree of strengthening.
This degree of strengthening may be characterized by attributes such as compressive stress,
depth of layer, or other attributes. While these are to be stated with any in the test reports, the
measurement methods for these parameters are outside the scope of this guideline document.
Strengthened glasses may result in non-linearities (such as in load to stress conversion) due
to high deformations and the formation of membrane stresses, which shall be taken into
consideration during data analysis and reporting.
Table 2 summarizes the comprehensive list of test methods for cover glasses described in
Table 1. Test methods described in IEC 61747-40 (all parts) can be classified according to the
types of external load applied and pre-conditioning. In Table 2, “n/a” means that a test method
does not exist for the condition because the failure mechanism is not well understood, the
failure mechanism is not common, the failure mechanism has not been observed for cover
glasses, or the pre-condition is not relevant to the failure mechanism being tested.

– 10 – IEC 61747-40-1:2019 RLV  IEC 2019
Table 2 – Matrix of cover glass test methods and glass condition
Strength evaluation
(Quasi) Static Dynamic
Concentrated
Uniaxial bend Biaxial bend Biaxial bend

load
Contact with
Four-point
Ring-on-ring Ball drop coated
Pre-conditioning bend
abrasives
None
IEC 61747-40-2 IEC 61747-40-4 IEC 61747-40-3 IEC 61747-40-5
(pristine or as-received)
Grit particle abrasion n/a IEC 61747-40-6 n/a n/a

5 Brief overview of mechanical test methods
5.1 Edge strength
Uniaxial flexural strength (four-point bend):
A uniaxial flexural test via a four-point bend methodology has been selected as the best
representative test for edge strength. This is related to the observations of failures occurring
from edge flaws rather than surface flaws in the specimen.
The test method can be used to evaluate cover glass edge failures caused by uniaxial stress
to edge flaws, for example.
5.2 Surface impact resistance (energy-to-failure)
Biaxial flexural energy-to-failure (ball drop):
A biaxial flexural test via a ball drop provides an indirect measurement of surface strength by
applying a biaxial stress to the glass surface upon ball impact. Measurement of the impact
energy is used to approximate equivalent performances for different ball sizes, weights and
drop heights.
The test method can be used to assess cover glass surface failures caused by biaxial stress
to pre-existing surface damage (e.g. damage caused to the surface during the fabrication
process), for example.
5.3 Surface strength
Biaxial flexural strength (ring-on-ring):
A biaxial flexural test via a ring-on-ring methodology is designed to test surface strength. A
note of caution: It is important to be aware that when the specimen deflects more than 1/2 of
its thickness, the load-to-stress relationship is no longer linear, and non-linear effects shall be
taken into account to properly convert load to stress.
The test method can be used to assess cover glass surface failures caused by biaxial stress
to pre-existing surface damage, for example.
Scratch performance
Scratch lateral crack visibility/retained strength
Lateral cracks are cracks originating from the sub-surface of the glass (not from the surface)
which initially extend nearly parallel to the surface. These cracks may ultimately propagate to
intersect the surface of the glass resulting in visible chipping. The test is performed in a step-

load manner utilizing sliding indentation with, for example, a Knoop or Vickers diamond tip.
Retained strength after sliding indentation may be measured via biaxial flexure (ring-on-ring)
with the indentation site oriented in tension.
5.4 Resistance against sharp contact surface damage and propagation under rigid
support (energy-to-failure)
Sharp contact impact resistance under rigid support condition (ball crop on coated abrasives):
Ball drop methodology with rigid support is employed to indirectly measure surface strength
during sharp particle impact. This is achieved by dropping a ball onto a glass specimen with a
sheet of coated abrasives placed on top of the glass. The test is focused on glass surface
flaw generation and propagation by central tension when the glass is rigidly supported.
The te
...