ISO/DTR 25777-1

ISO/TC 45/SC 2
ISO/CD TR 25777-1(en)
Secretariat:  JISC
Date: 2026-07-24
Rubber, vulcanized or thermoplastic — Resistance to ozone
cracking —
Part 1:
Test methods of ozone crack depth
Caoutchouc vulcanisé ou thermoplastique — Résistance au craquelage par l'ozone —
Partie 1: Méthodes d'évaluation de la profondeur des craquelures dues à l'ozone

ISO/CD TRDTR 25777-1:2026(en)
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
E-mail: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii
ISO/CD TRDTR 25777-1:2026(en)
Contents
Foreword . iv
Introduction . v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Test methods . 2
5 Principle . 2
6 Preparation of ozone crack test piece . 2
7 Method A . 3
8 Method B . 4
9 Method C . 8
Annex A (informative) Example of the test results of method A . 10
Annex B (informative) Example of the test results of method B . 14
Annex C (informative) Relationship between ozone crack length or width on surface and depth
by image analysis . 20
Bibliography . 27

iii
ISO/CD TRDTR 25777-1:2026(en)
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 document 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).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent rights
in respect thereof. As of the date of publication of this document, ISO [had/had not] received notice of (a)
patent(s) which may be required to implement this document. However, implementers are cautioned that this
may not represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
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 45, Rubber and rubber products, Subcommittee
SC 2, Testing and analysis.
A list of all parts in the ISO TR 25777 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/CD TRDTR 25777-1:2026(en)
Introduction
Diene rubbers have been widely used in many rubber products such as tires and anti-vibration rubber,
however, ozone cracking occurs due to the double bonds in the main molecular chain. These ozone cracks
grow over time, and there is a concern that they maycan cause damage to the rubber products. The damage
depends on the depth of the ozone cracks which practically determines the life of the rubber products.
ISO 1431-1ISO 1431-1 is the most widely accepted method for evaluating the ozone resistance of rubber,
however, the evaluation items by visual observation are only the number and length of cracks observed from
the surface of the test piece, and the depth is not evaluated. Deep ozone cracks cause stress concentration
when rubber deforms, and can become the starting point of destruction. For rubber products that require
mechanical strength, it is important to evaluate the depth of ozone cracks in addition to their number and
length.
This document describes methods for measuring and estimating the depth of ozone cracks.
v
ISO/CD TRDTR 25777-1:2026(en)
Rubber, vulcanized or thermoplastic — Resistance to ozone
cracking —
Part 1:
Test methods of ozone crack depth
1 Scope
This document provides test methods to measure ozone crack depth of vulcanized rubber or thermoplastic
after the exposure to ozone for specified periods.
WARNING — Persons using this document shouldmust be familiar with normal laboratory practice.
This document does not purport to address all of the safety problems, if any, associated with its use. It
is the responsibility of the user to establish appropriate safety and health practices and to determine
the applicability of any other restrictions.
WARNING — Certain procedures specified in this document can involve the use or generation of
substances, or the generation of waste, that couldcan constitute a local environmental hazard.
Reference shouldmust be made to appropriate documentation on safe handling and disposal after use.
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 37, Rubber, vulcanized or thermoplastic — Determination of tensile stress-strain properties
ISO 1431-1, Rubber, vulcanized or thermoplastic — Resistance to ozone cracking — Part 1: Static and dynamic
strain testing
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
ozone crack length
length of the crack perpendicular to the elongation direction on the surface of a test piece
3.2
ozone crack width
length of the crack parallel to the elongation direction on the surface of a test piece
ISO/CD TRDTR 25777-1:2026(en)
3.3
ozone crack depth from the surface of test piece
length of the perpendicular line from the surface of a test piece to the tip of the deepest part of the ozone crack
3.4
cylindrical dumbbell
dumbbell shaped test piece with cylindrical body
Note 1 to entry: An example is given in Annex B with its dimensions.
3.5
ozone crack depth by X-ray CT
length of cracks in the binarized image after the measurement by X-ray CTcomputed tomography (CT)
Note 1 to entry: CT is an abbreviation for computed tomography.
4 Test methods
There are three test methods as follows;:
a) Method A: Measurement of ozone crack depth by direct observation of a cut test piece.
b) Method B: Measurement of ozone crack depth using X-ray CT.
c) Method C: Estimation of ozone crack depth by image analysis.
5 Principle
A test piece is exposed to an atmosphere containing a fixed concentration of ozone in a chamber. The test piece
is removed from the chamber when the ozone cracks have reached the target level to be tested. The crack
depth of the test piece is measured using either method A or B, or both of them or estimated using method C.
6 Preparation of ozone crack test piece

6.1 Test piece
6.1.1 Wide strip test piece
This test piece consists of a strip of not less than 10 mm in width, of thickness (2,0 ± 0,5) mm and of length not
less than 40 mm between the grips before stretching. The test pieces are cut from a vulcanized sheet or from
rubber products. When the sheet is taken from a rubber product, buffing on the surfaces is not carried out.
6.1.2 Dumbbell test piece
Dumbbells with a wide centre section are used for observation of cracking. An example of a typical Dumbbell
test piece is given in Clause B.2B.2 of Annex BAnnex B,, however other dumbbells can be used such as type 1
or 1A in accordance with ISO 37ISO 37. The test pieces are cut from a vulcanized sheet or from rubber
products. When the sheet is taken from a rubber product, buffing on the surfaces is notcarried out.
ISO/CD TRDTR 25777-1:2026(en)
6.1.3 Cylindrical dumbbell
The shape of the cylindrical dumbbell is similar to dumbbell type 1A, but the narrow portion is cylindrical. It
is designed to obtain a uniform strain on the surface so that cracks grow evenly in the cylindrical body. The
test piece can be made by curing with the mould. The dimensions are given in Clause B.2B.2 of Annex BAnnex
B.
6.1.4 Sealing treatment of edges
Depending on the purpose of the test, the edges of the test piece can be sealed in accordance with ISO 1431-
1:2024ISO 1431-1 Annex D.
6.2 Apparatus
6.2.1 Test chamber for ozone exposure test and accessories, as specified in ISO 1431-1ISO 1431-1.
6.2.2 Clamps for test piece mounting, as specified in ISO 1431-1ISO 1431-1.
6.3 Exposure to ozone
A test piece is exposed, under static tensile strain, under continuous dynamic strain, or under alternate periods
of dynamic and static strain, in a closed chamber maintained at a specified temperature and, at high or
unspecified humidity, to an atmosphere containing a fixed concentration of ozone. The test piece is examined
periodically for cracking and is removed from the chamber when the cracks have reached a given degree of
deterioration.
7 Method A
7.1 General
The depth of ozone cracks is measured by the direct observation using a microscope on the cross section of
the test piece after cutting. This method does not require any special equipment and can easily measure the
depth of ozone cracks.
7.2 Apparatus
7.2.1 Razor knife, sharp enough to cut test pieces smoothly.
7.2.2 Microscope, with magnification at least x100 and capable of measuring the distance.
7.3 Procedure
7.3.1 Cut the centre part of the test piece in a direction parallel to the elongation with the knife (7.2.1(7.2.1)
() [see Figure 1Figure 1 a)).)].
7.3.2 Mount the cut test pieces in a clamp and extend it to 20% elongation ([see Figure 1Figure 1 b)).)]. A
smaller strain is to be used as long as it does not exceed the elongation level applied during ozone exposure.
ISO/CD TRDTR 25777-1:2026(en)
7.3.3 Take magnified photos of the section of the cut test piece through the microscope (7.2.2(7.2.2).).
Photograph both side of the centre of the cut section ([see Figure 1Figure 1 c)).)]. It is allowed to continue
without taking a picture if the microscope has the option to measure distances directly.
7.3.4 In measuring the depth of each ozone crack from the surface of the test piece, select the four deepest
cracks in the photo. Draw a line perpendicular to the surface from the tip of the crack to be measured, then
measure the length of the line between the tip and the point where the line intersects with the surface using
the measuring function of the microscope.

Key
1 cutting the test piece
2 mounting the test piece elongated
3 magnified photo of the cut cross section
4 cut
5 cut surface
Figure 1 — An example of the procedure to the magnified photo
7.4 Results
See Annex Aannex A.
8 Method B
8.1 General
The X-ray CT Scanning Systemscanning system makes it possible to obtain the internal structure of a sample
by utilizing the difference in the transmittance of X-rays when they pass through the target object. By
photographing the sample with X-rays from various directions and performing reconstruction processing, the
difference in density of the material can be shown by the shade of the image. This is possible not only for
composite materials composed of different materials, but also for the same substance, where the difference in
density generates a difference in the X-ray absorption coefficient. Similarly, it is possible to evaluate damages
and voids inside the sample without cutting it, and it is also possible to intermittently observe internal crack
growth in the same sample.
This document describes a measurement method for ozone crack depth by X-ray CT. The method uses a
microfocus X-ray CT device (X-ray Computed Tomography) to photograph test pieces after ozone exposure
ISO/CD TRDTR 25777-1:2026(en)
and simultaneously measure and quantify cracks on the surface and in the depth direction. This makes it
possible to observe the ozone deterioration morphology of rubber products, which was previously im
...