ISO/FDIS 18489

• Abstract:

  ISO 18489:2015 specifies a method to determine the resistance to slow crack growth (SCG) of polyethylene materials, pipes, and fittings. The test is applicable to samples taken from compression moulded sheet or extruded pipes and injection moulded fittings of suitable thickness. ISO 18489:2015 provides a method that is suitable for an accelerated fracture-mechanics characterization at ambient temperatures of 23 °C of different polyethylene grades, especially for PE 80 and PE 100 types for pipe applications. NOTE This test method could be adapted for other thermoplastics materials by developing the procedure using different test parameters.

• Status: Not Published
• ICS: 23.040.20 - Plastics pipes
• ICS: 23.040.45 - Plastics fittings
• Technical Committee: ISO/TC 138/SC 5 - General properties of pipes, fittings and valves of plastic materials and their accessories -- Test methods and basic specifications
• Drafting Committee: ISO/TC 138/SC 5/WG 20 - Slow crack growth (SCG)
• Current Stage: 5000 - FDIS registered for formal approval
• Start Date: 22-Jul-2026
• Completion Date: 29-Apr-2026

• Consolidates: prEN ISO 18489 - Thermoplastic materials for piping systems - Determination of resistance to slow crack growth under cyclic loading - Cracked Round Bar (CRB) test method (ISO/DIS 18489:2025)
• Effective Date: 12-Feb-2026
• Consolidates: ISO 19403-1:2022 - Paints and varnishes — Wettability — Part 1: Vocabulary and general principles
• Effective Date: 12-Apr-2025
• Revises: ISO 18489:2015 - Polyethylene (PE) materials for piping systems — Determination of resistance to slow crack growth under cyclic loading — Cracked Round Bar test method
• Effective Date: 24-Feb-2024

Overview

ISO/FDIS 18489 addresses the cracked round bar (CRB) test method for evaluating the resistance to slow crack growth (SCG) in thermoplastic materials used for piping systems. The standard is designed for polyethylene (PE) and also provides test parameters for polypropylene (PP) and unplasticized polyamide (PA-U).

This method is especially useful for pipe, fitting, and material qualification where long-term crack resistance is critical. It supports accelerated fracture-mechanics characterization at 23 °C, helping laboratories assess material performance in a practical timeframe without relying on elevated temperatures or time-reducing liquids.

The scope includes test specimens prepared from:

• Compression moulded sheets
• Extruded rods or pipes
• Injection moulded fittings of suitable thickness

ISO 18489 is widely relevant for evaluating both virgin and non-virgin thermoplastic materials, including reused and recycled materials.

Key Topics

The standard focuses on a controlled cyclic tensile test using a cylindrical specimen with a circumferential razor-sharp notch. The notch promotes crack initiation and allows measurement of the specimen’s resistance to slow crack growth under repeated loading.

Key elements include:

• Cyclic loading under load control
• Sinusoidal waveform with constant maximum and minimum load values
• Load ratio, R, and load-cycle frequency
• Initial crack length determined after testing
• Data treatment using stress range and failure cycle number
• Log-log evaluation of stress range versus failure cycles

The document also defines:

• Test specimen geometry and dimensions
• Notching requirements
• Conditioning and test atmosphere
• Reporting requirements
• Optional recalculation and single-point interpolation for reference geometries

For PE, the informative annexes provide practical guidance on specimen preparation and typical test parameter ranges, supporting consistent laboratory test methods and more reliable comparison of results.

Applications

ISO 18489 is valuable in the plastics piping industry where slow crack growth resistance affects service life and product reliability. Typical applications include:

• Material ranking and pre-selection
• Pipe and fitting qualification
• Quality control for thermoplastic pipe materials
• Comparative testing of PE grades, especially PE 80 and PE 100
• Assessment of recycled or reused thermoplastics
• Research and development of new piping compounds

Because the method is designed for accelerated testing at ambient temperature, it is well suited to performance screening in product development and compliance workflows.

Related Standards

ISO 18489 references and aligns with several important standards used in plastics testing:

• ISO 291 - Plastics - Standard atmospheres for conditioning and testing
• ISO 2818 - Plastics - Preparation of test specimens by machining
• ISO 16770 - Relevant for PE specimen moulding conditions mentioned in the annexes

Together, these standards support a consistent framework for thermoplastic materials testing, slow crack growth evaluation, and piping system performance assessment.

FINAL DRAFT
International
Standard
ISO/TC 138/SC 5
Thermoplastic materials for
Secretariat: NEN
piping systems — Determination
Voting begins on:
of resistance to slow crack growth
2026-10-06
under cyclic loading — Cracked
Voting terminates on:
round bar (CRB) test method
2026-12-01
Matériaux thermoplastiques pour systèmes de canalisations —
Détermination de la résistance à la propagation lente de fissures
sous un chargement cyclique — Méthode d'essai de la barre
ronde fissurée (CRB)
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
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO­
ISO/CEN PARALLEL PROCESSING 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.
Reference number
FINAL DRAFT
International
Standard
ISO/TC 138/SC 5
Thermoplastic materials for
Secretariat: NEN
piping systems — Determination
Voting begins on:
of resistance to slow crack growth
under cyclic loading — Cracked
Voting terminates on:
round bar (CRB) test method
Matériaux thermoplastiques pour systèmes de canalisations —
Détermination de la résistance à la propagation lente de fissures
sous un chargement cyclique — Méthode d'essai de la barre
ronde fissurée (CRB)
© ISO 2026
All rights reserved.
RECIPIENTS OF THIS DRAFT ARE INVITED TO SUBMIT,
WITH THEIR COMMENTS, NOTIFICATION OF ANY
This ISO publication is protected by copyright and is owned by ISO and/or its licensors.
RELEVANT PATENT RIGHTS OF WHICH THEY ARE AWARE
The content of this ISO publication is provided under licence, not sold. Use is subject to the applicable licence terms issued by ISO,
AND TO PROVIDE SUPPOR TING DOCUMENTATION.
an ISO member body, or an authorized third-party distributor.
IN ADDITION TO THEIR EVALUATION AS
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO­
Except as required for implementation or expressly permitted by a separate licence, no part of this ISO publication may be
ISO/CEN PARALLEL PROCESSING
LOGICAL, COMMERCIAL AND USER PURPOSES, DRAFT
reproduced, distributed, modified, used, or made available in any form or by any means – electronic or mechanical, including
INTERNATIONAL STANDARDS MAY ON OCCASION HAVE
photocopying, scanning, recording, or posting on internal or external digital platforms. TO BE CONSIDERED IN THE LIGHT OF THEIR POTENTIAL
TO BECOME STAN DARDS TO WHICH REFERENCE MAY BE
Any use beyond the scope of the granted rights is prohibited and may result in legal action.
MADE IN NATIONAL REGULATIONS.
ISO copyright office
CP 401 • CH-1214 Vernier, Geneva
Phone: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
Reference number
ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 4
5 Apparatus . 4
5.1 Test machine .4
5.1.1 Loading system .4
5.1.2 Grips.5
5.1.3 Temperature chamber .5
5.2 Microscope .5
5.3 Notching apparatus .5
6 Test specimen . 5
6.1 Specimen geometry and dimensions .5
6.2 Test specimen preparation .6
6.3 Specimen notching .6
6.4 Specimen conditioning .6
7 Test procedure . 7
7.1 Measurement of specimen dimensions .7
7.2 Specimen mounting . .7
7.3 Test atmosphere .7
7.4 Calculation of test load .7
7.5 Load-cycle frequency .8
7.6 Load application .8
7.7 Initial crack length calculation .8
8 Data treatment . 9
9 Test report .10
Annex A (informative) Recalculation and single point interpolation .12
Annex B (informative) Test parameters for PE . 14
Annex C (informative) Test parameters for PP .16
Annex D (informative) Test parameters for PA-U (PA-U11, PA-U12) . 17
Bibliography . 19

iii
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).
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 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 138, Plastics pipes, fittings and valves for the
transport of fluids, Subcommittee SC 5, General properties of pipes, fittings and valves of plastic materials and
their accessories — Test methods and basic specifications.
This second edition cancels and replaces the first edition (ISO 18489:2015), which has been technically
revised.
The main changes are as follows:
— 7.7 was improved for initial crack length calculation;
— Annex A was improved for recalculation and single point interpolation and added information in A.2 and
A.3 for the single point evaluation;
— all test parameters for different materials are shifted in the informative Annexes B, C and D and materials
PP and PA-U added. New photographs of fracture surfaces after testing for PE included.
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
Introduction
Knowledge about the resistance to long-term failure mechanisms as a result of crack initiation and slow
crack growth (SCG) is important for the ranking and pre-selection of thermoplastic materials, especially
for long-term applications such as pipes and fittings made of thermoplastic pipe materials. Several tests to
determine the relevant failure mechanisms are available today where elevated temperatures and also the
combination with stress cracking liquids are used to decrease the time frame for testing.
Developments in modern polyethylene materials have led to a significant increase of resistance to crack
initiation and slow crack growth so that testing with available methods exceeds practical time frames.
Therefore, new accelerated methods, preferably at application relevant temperatures and without additional
time reducing liquids, are required.
This test method achieves a significant decrease of testing time even at ambient temperatures of 23 °C. This
is more relevant to the temperature range of many applications, and testing at this temperature does not
change the structural status of the polymer. Acceleration of material testing is achieved by the specimen
[2][3][4]
geometry and the cyclic loading regime to result in completion of testing in a relatively short time .

v
FINAL DRAFT International Standard ISO/FDIS 18489:2026(en)
Thermoplastic materials for piping systems — Determination
of resistance to slow crack growth under cyclic loading —
Cracked round bar (CRB) test method
1 Scope
This document specifies a method used to determine the resistance to slow crack growth (SCG) of
thermoplastic materials, pipes and fittings. The test is applicable to samples taken from compression
moulded sheets, extruded rods, sheets or pipes and injection moulded fittings of suitable thickness.
The method is suitable for an accelerated slow crack growth characterization at ambient temperatures of
23 °C.
This document specifies test parameters for polyethylene (PE), polypropylene (PP) and unplasticized
polyamide (PA-U).
Furthermore, this test can be applied to characterise the slow crack growth resistance of virgin, as well as
[5]
non-virgin (reused, recycled) thermoplastic materials .
This test method can be adapted for other thermoplastics materials by developing the procedure using
different test parameters.
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 291, Plastics — Standard atmospheres for conditioning and testing
ISO 2818, Plastics — Preparation of test specimens by machining
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
cycle
N
smallest segment of a load-time or stress-time function which is repeated periodically
3.2
failure cycle number
N
f
total number of cycles (3.1) from the beginning until failure of the test specimen

3.3
frequency
f
number of cycles (3.1) within one second
Note 1 to entry: It is expressed in Hertz (Hz).
3.4
initial crack length
a
ini
depth of the razor-sharp notch from the specimen surface up to the notch tip at the beginning of the test,
calculated after testing
Note 1 to entry: It is expressed in millimetres (mm).
3.5
initial ligament diameter
D
ini
ligament diameter of the cylindrical specimen after notching at the beginning of the test, measured after
testing
Note 1 to entry: It is expressed in millimetres (mm).
3.6
load ratio
R
ratio of the minimum load, F (3.19) to the maximum load, F (3.8) in one cycle (3.1)
min max
Note 1 to entry: It is calculated by:
F
min
R=
F
max
3.7
load range
ΔF
difference between the maximum load, F (3.8) and minimum load, F (3.9) in one cycle (3.1)
max min
Note 1 to entry: It is expressed in Newtons (N).
3.8
maximum load
F
max
highest value of the applied load, in Newtons (N), in one cycle (3.1)
3.9
minimum load
F
min
lowest value of the applied load, in Newtons (N), in one cycle (3.1)
3.10
notch distance
L
min
minimum distance from notch to clamping system
Note 1 to entry: It is expressed in millimetres (mm).

3.11
target initial crack length
a *
ini
target depth of the razor-sharp notch from the specimen surface up to the notch tip after notching, prior to
testing
Note 1 to entry: It is expressed in millimetres (mm).
3.12
target initial ligament diameter
D *
ini
target ligament diameter of the cylindrical specimen after notching, prior to testing
Note 1 to entry: It is expressed in millimetres (mm).
Note 2 to entry: It is calculated by D * = D – 2 a *
ini ini
3.13
target stress range
Δσ *
target difference between the maximum and minimum stress at the beginning of the test
Note 1 to entry: It is expressed in megapascals (MPa).
3.14
specimen diameter
D
diameter of the cylindrical specimen measured prior to testing, measured after notching at the vicinity of
notch location
Note 1 to entry: It is expressed in millimetres (mm).
3.15
specimen length
L
total length of the test specimen
Note 1 to entry: It is expressed in millimetres (mm).
3.16
stress range
Δσ
applied difference between the maximum and minimum stress at the beginning of the test
Note 1 to entry: It is expressed in megapascals (MPa).
3.17
waveform
shape of the load-time curve within a single cycle (3.1)
3.18
reference specimen radius
r
ref
specimen radius (r = D /2), given in the product standard or requirement
ref ref
Note 1 to entry: It is used for recalculation after testing using Annex A.
Note 2 to entry: It is expressed in millimetres (mm).

3.19
reference specimen diameter
D
ref
specimen diameter (D = 2r ), given in the product standard or requirement
ref ref
Note 1 to entry: It is used for recalculation after testing using Annex A.
Note 2 to entry: It is expressed in millimetres (mm).
3.20
reference initial crack length
a
ini,ref
depth of the razor-sharp notch, given in the product standard or requirement
Note 1 to entry: It is used for recalculation after testing using Annex A.
Note 2 to entry: It is expressed in millimetres (mm).
3.21
reference stress range
Δσ
0,ref
difference between the maximum and the minimum stress calculated using Formula (A.3) based on a
reference specimen diameter and reference initial crack length
Note 1 to entry: It is expressed in megapascals (MPa).
3.22
reference stress intensity factor
ΔK
I,ref
difference between the minimum and the maximum stress intensity factor calculated using Formula (A.1)
based on a reference specimen diameter and reference initial crack length
0,5
Note 1 to entry: It is expressed in megapascals per square root metre (MPa m ).
4 Principle
A cyclic tensile test with constant load range is imposed on a cylindrical specimen under suitable test
conditions within the stress range where SCG is achieved. A circumferential notch is machined in the centre
of the test specimen to enable crack initiation and SCG to final failure of the specimen. The number of cycles
until final failure, N , is recorded as a function of the stress range, Δσ , at the initial crack length, a . The
f 0 ini
specimen geometry ensures quick crack initiation and short testing times due to the high constraint and low
plastics deformations along the crack tip.
5 Apparatus
5.1 Test machine
5.1.1 Loading system
The loading system shall be capable of imposing and recording a cyclic load.
The cyclic load shall follow a sinusoidal waveform which is characterized by the maximum load, F , and
max
the load ratio, R. The maximum and minimum loading values shall be constant (load control mode) during
the entire test with an accuracy of ±1 %.
The load-cycle frequency shall have an accuracy of ±1 %.

5.1.2 Grips
The grips shall be suitable to clamp cylindrical specimens. It shall ensure that the load distribution is in
alignment with the specimen axis.
5.1.3 Temperature chamber
For testing at low or high temperatures, the test machine shall be equipped with a suitable chamber that
contains the environment and ensures complete exposure of the specimen. The chamber shall be constructed
of materials which do not affect the environment, and which are not affected by it. The temperature of
the environment shall be controlled in order to maintain the test specimens within ±2 °C of the specified
temperature.
5.2 Microscope
A microscope with an accuracy of 0,03 mm or an equivalent device shall be used to determine the initial
crack length after the finished cyclic tests.
5.3 Notching apparatus
The device used shall be capable of producing a razor-sharp notch of specified depth at the circumference of
the cylindrical specimen. The notch tip radius produced shall be less than 10 μm.
NOTE 1 Usually, razor blades meet this requirement.
A conventional lathe in combination with a razor blade tool may be suitable for this purpose. Bending of
the razor blade shall be avoided and notching perpendicular to the specimen axis shall be ensured. It is
recommended to use a razor blade support where the free length of the razor blade for notching is limited to
approximately 2 mm for notch depths of 1,4 mm.
6 Test specimen
6.1 Specimen geometry and dimensions
The specimen configuration of the cracked round bar (CRB) specimen is shown in Figure 1. A cylindrical
bar of length, L, and diameter, D, is prepared with a circumferential razor-sharp notch with a depth of a *
ini
(target initial crack length) in the middle of the specimen resulting in a target initial ligament diameter, D *.
ini
Specimen dimensions shall be as specified in Table 1. The initial crack shall be perpendicular to the specimen
axis.
To avoid clamping effects at the crack tip, the notch distance, L , shall be at least 20 mm from the grips.
min
Table 1 — Specimen dimensions
Dimension
Parameter
mm
L specimen length 80 to 120
D specimen diameter 14,0 ± 0,15
a * target initial crack length 1,40
ini
minimum distance between
L ≥20
min
notch and clamping system
Clamping part of the specimen may be threaded, for example, M 14 × 1,0 metric fine thread, in which case
matching grips shall be used.
NOTE 1 Residual stresses can cause bending of the test specimen which can influence the test results. Bending can
be minimized by taking the specimen from the location where the residual stress is minimum e.g. from the centre of
the pipe wall.
Key
L specimen length
L minimum distance between notch and clamping system
min
a * target initial crack length
ini
D * target initial ligament diameter
ini
D specimen diameter
1 razor-sharp notch
Figure 1 — Principal configuration of CRB test specimen with optional metric fine thread
6.2 Test specimen preparation
The test specimens shall be machined from compression moulded sheets, extruded rods or directly from
pipe or fittings. The use of diffe
...

ISO/TC 138/SC 5
Secretariat: NEN
Date: 2026-07-27xx
Thermoplastic materials for piping systems — Determination of
resistance to slow crack growth under cyclic loading —
crackedCracked round bar (CRB) test method
This draft is submitted to a parallel vote in ISO, CEN.

© Matériaux thermoplastiques pour systèmes de canalisations — Détermination de la résistance à la
propagation lente de fissures sous un chargement cyclique — Méthode d'essai de la barre ronde fissurée (CRB)
FDIS stage
This draft is submitted to a parallel vote in ISO, CEN.
2 © ISO #### – All rights reserved

© ISO 2026
All rights reserved. Unless otherwise specified,
This ISO publication is protected by copyright and is owned by ISO and/or its licensors.
The content of this ISO publication is provided under licence, not sold. Use is subject to the applicable licence terms issued
by ISO, an ISO member body, or an authorized third-party distributor.
Except as required in the context of its for implementation or expressly permitted by a separate licence, no part of this
ISO publication may be reproduced or utilized otherwise, distributed, modified, used, or made available in any form or
by any means, – electronic or mechanical, including photocopying, scanning, recording, or posting on internal or external
digital platforms.
Any use beyond 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 countryscope of the requestergranted rights is prohibited and may
result in legal action.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: + 41 22 749 01 11
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
iii
Contents
Foreword . Error! Bookmark not defined.
Introduction . Error! Bookmark not defined.
1 Scope . Error! Bookmark not defined.
2 Normative references . Error! Bookmark not defined.
3 Terms and definitions . Error! Bookmark not defined.
4 Principle. Error! Bookmark not defined.
5 Apparatus . Error! Bookmark not defined.
5.1 Test machine . Error! Bookmark not defined.
5.2 Microscope . Error! Bookmark not defined.
5.3 Notching apparatus. Error! Bookmark not defined.
6 Test specimen . Error! Bookmark not defined.
6.1 Specimen geometry and dimensions. Error! Bookmark not defined.
6.2 Test specimen preparation . Error! Bookmark not defined.
6.3 Specimen notching . Error! Bookmark not defined.
6.4 Specimen conditioning . Error! Bookmark not defined.
7 Test procedure . Error! Bookmark not defined.
7.1 Measurement of specimen dimensions . Error! Bookmark not defined.
7.2 Specimen mounting . Error! Bookmark not defined.
7.3 Test atmosphere . Error! Bookmark not defined.
7.4 Calculation of test load . Error! Bookmark not defined.
7.5 Load-cycle frequency . Error! Bookmark not defined.
7.6 Load application . Error! Bookmark not defined.
7.7 Initial crack length calculation . Error! Bookmark not defined.
8 Data treatment . Error! Bookmark not defined.
9 Test report . Error! Bookmark not defined.
(informative) Recalculation and single point interpolation . Error! Bookmark not defined.
(informative) Test parameters for PE . Error! Bookmark not defined.
(informative) Test parameters for PP . Error! Bookmark not defined.
(informative) Test parameters for PA-U (PA-U11, PA-U12) . Error! Bookmark not defined.
Bibliography . Error! Bookmark not defined.

iv
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).
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 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 138, Plastics pipes, fittings and valves for the
transport of fluids, Subcommittee SC 5, General properties of pipes, fittings and valves of plastic materials and
their accessories — Test methods and basic specifications.
This second edition cancels and replaces the first edition (ISO 18489:2015), which has been technically
revised.
The main changes are as follows:
— 7.7— was improved subclause 7.7 for initial crack length calculation;
— Annex A— was improved Annex A for recalculation and single point interpolation and added information
in A.2A.2 and A.3A.3 for the single point evaluation;
— — Allall test parameters for different materials are shifted in the informative Annexes BAnnexes B, C, C
and DD and materials PP and PA-U added. New photographs of fracture surfaces after testing for PE
included.
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.
v
Introduction
Knowledge about the resistance to long-term failure mechanisms as a result of crack initiation and slow crack
growth (SCG) is important for the ranking and pre-selection of thermoplastic materials, especially for long-
term applications such as pipes and fittings made of thermoplastic pipe materials. Several tests to determine
the relevant failure mechanisms are available today where elevated temperatures and also the combination
with stress cracking liquids are used to decrease the time frame for testing.
Developments in modern polyethylene materials have led to a significant increase of resistance to crack
initiation and slow crack growth so that testing with available methods exceeds practical time frames.
Therefore, new accelerated methods, preferably at application relevant temperatures and without additional
time reducing liquids, are required.
This test method achieves a significant decrease of testing time even at ambient temperatures of 23 °C. This is
more relevant to the temperature range of many applications, and testing at this temperature does not change
the structural status of the polymer. Acceleration of material testing is achieved by the specimen geometry
[2] [3] [4][2] [3] [4]
and the cyclic loading regime to result in completion of testing in a relatively short time , , .
vi
Thermoplastic materials for piping systems — Determination of
resistance to slow crack growth under cyclic loading — Cracked Round
Barround bar (CRB) test method
1 Scope
This document specifies a method used to determine the resistance to slow crack growth (SCG) of
thermoplastic materials, pipes and fittings. The test is applicable to samples taken from compression moulded
sheets, extruded rods, sheets or pipes and injection moulded fittings of suitable thickness.
The method is suitable for an accelerated slow crack growth characterization at ambient temperatures of
23 °C.
This document specifies test parameters for polyethylene (PE), polypropylene (PP) and unplasticized
polyamide (PA-U).
Furthermore, this test can be applied to characterise the slow crack growth resistance of virgin, as well as non-
[5][5]
virgin (reused, recycled) thermoplastic materials .
This test method can be adapted for other thermoplastics materials by developing the procedure using
different test parameters.
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 291, Plastics — Standard atmospheres for conditioning and testing
ISO 2818, Plastics — Preparation of test specimens by machining
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— — ISO Online browsing platform: available at https://www.iso.org/obp
— — IEC Electropedia: available at https://www.electropedia.org/
3.1 3.1
cycle
N
smallest segment of a load-time or stress-time function which is repeated periodically
3.2 3.2
failure cycle number
N
f
total number of cycles (3.1(3.1)) from the beginning until failure of the test specimen
3.3 3.3
frequency
f
number of cycles (3.1(3.1)) within one second
Note 1 to entry: It is expressed in Hertz (Hz).
3.4 3.4
initial crack length
a
ini
depth of the razor-sharp notch from the specimen surface up to the notch tip at the beginning of the test,
calculated after testing
Note 1 to entry: It is expressed in millimetres (mm).
3.5 3.5
initial ligament diameter
D
ini
ligament diameter of the cylindrical specimen after notching at the beginning of the test, measured after
testing
Note 1 to entry: It is expressed in millimetres (mm).
3.6 3.6
load ratio
R
ratio of the minimum load, F (3.19(3.19)) to the maximum load, F (3.8(3.8)) in one cycle (3.1(3.1))
min max
Note 1 to entry: It is calculated by:

3.7
𝐹𝐹
min
𝑅𝑅 =
𝐹𝐹
max
3.7
load range
ΔF
difference between the maximum load, F (3.8(3.8)) and minimum load, F (3.9(3.9)) in one cycle (3.1(3.1))
max min
Note 1 to entry: It is expressed in Newtons (N).
3.73.8 3.8
maximum load
F
max
highest value of the applied load, in Newtons (N), in one cycle (3.1(3.1))
3.83.9 3.9
minimum load
F
min
lowest value of the applied load, in Newtons (N), in one cycle (3.1(3.1))
3.93.10 3.10
notch distance
L
min
minimum distance from notch to clamping system
Note 1 to entry: It is expressed in millimetres (mm).
3.103.11 3.11
target initial crack length
a *
ini
target depth of the razor-sharp notch from the specimen surface up to the notch tip after notching, prior to
testing
Note 1 to entry: It is expressed in millimetres (mm).
3.113.12 3.12
target initial ligament diameter
D *
ini
target ligament diameter of the cylindrical specimen after notching, prior to testing
Note 1 to entry: It is expressed in millimetres (mm).
Note 2 to entry: It is calculated by Dini* = D – 2 aini*
3.123.13 3.13
target stress range
Δσ *
target difference between the maximum and minimum stress at the beginning of the test
Note 1 to entry: It is expressed in megapascals (MPa).
3.133.14 3.14
specimen diameter
D
diameter of the cylindrical specimen measured prior to testing, measured after notching at the vicinity of
notch location
Note 1 to entry: It is expressed in millimetres (mm).
3.143.15 3.15
specimen length
L
total length of the test specimen
Note 1 to entry: It is expressed in millimetres (mm).
3.153.16 3.16
stress range
Δσ
applied difference between the maximum and minimum stress at the beginning of the test
Note 1 to entry: It is expressed in megapascals (MPa).
3.163.17 3.17
waveform
shape of the load-time curve within a single cycle (3.1(3.1))
3.173.18 3.18
reference specimen radius
r
ref
specimen radius (r = D /2), given in the product standard or requirement
ref ref
Note 1 to entry: It is used for recalculation after testing using Annex AAnnex A.
Note 2 to entry: It is expressed in millimetres (mm).
3.183.19 3.19
reference specimen diameter
D
ref
specimen diameter (D = 2r ), given in the product standard or requirement
ref ref
Note 1 to entry: It is used for recalculation after testing using Annex AAnnex A.
Note 2 to entry: It is expressed in millimetres (mm).
3.193.20 3.20
reference initial crack length
a
ini - ,ref
depth of the razor-sharp notch, given in the product standard or requirement
Note 1 to entry: It is used for recalculation after testing using Annex AAnnex A.
Note 2 to entry: It is expressed in millimetres (mm).
3.203.21 3.21
reference stress range
Δσ
0 -, ref
difference between the maximum and the minimum stress calculated using equation A.3Formula (A.3) based
on a reference specimen diameter and reference initial crack length
Note 1 to entry: It is expressed in megapascals (MPa).
3.213.22 3.22
reference stress intensity factor
ΔK
I - ,ref
difference between the minimum and the maximum stress intensity factor calculated using
equation A.1Formula (A.1) based on a reference specimen diameter and reference initial crack length
0,5
Note 1 to entry: It is expressed in megapascals per square root metre (MPa m ).
4 Principle
A cyclic tensile test with constant load range is imposed on a cylindrical specimen under suitable test
conditions within the stress range where SCG is achieved. A circumferential notch is machined in the centre
of the test specimen to enable crack initiation and SCG to final failure of the specimen. The number of cycles
until final failure, N , is recorded as a function of the stress range, Δσ , at the initial crack length, a . The
f 0 ini
specimen geometry ensures quick crack initiation and short testing times due to the high constraint and low
plastics deformations along the crack tip.
5 Apparatus
5.1 Test machine
5.1.1 Loading system
The loading system shall be capable of imposing and recording a cyclic load.
The cyclic load shall follow a sinusoidal waveform which is characterized by the maximum load, F , and the
max
load ratio, R. The maximum and minimum loading values shall be constant (load control mode) during the
entire test with an accuracy of ±1 %.
The load-cycle frequency shall have an accuracy of ±1 %.
5.1.2 Grips
The grips shall be suitable to clamp cylindrical specimens. It shall ensure that the load distribution is in
alignment with the specimen axis.
5.1.3 Temperature chamber
For testing at low or high temperatures, the test machine shall be equipped with a suitable chamber that
contains the environment and ensures complete exposure of the specimen. The chamber shall be constructed
of materials which do not affect the environment, and which are not affected by it. The temperature of the
environment shall be controlled in order to maintain the test specimens within ±2 °C of the specified
temperature.
5.2 Microscope
A microscope with an accuracy of 0,03 mm or an equivalent device shall be used to determine the initial crack
length after the finished cyclic tests.
5.3 Notching apparatus
The device used shall be capable of producing a razor-sharp notch of specified depth at the circumference of
the cylindrical specimen. The notch tip radius produced shall be less than 10 μm.
NOTE 1 Usually, razor blades meet this requirement.
A conventional lathe in combination with a razor blade tool may be suitable for this purpose. Bending of the
razor blade shall be avoided and notching perpendicular to the specimen axis shall be ensured. It is
recommended to use a razor blade support where the free length of the razor blade for notching is limited to
approximately 2 mm for notch depths of 1,4 mm.
6 Test specimen
6.1 Specimen geometry and dimensions
The specimen configuration of the cracked round bar (CRB) specimen is shown in Figure 1Figure 1. A
cylindrical bar of length, L, and diameter, D, is prepared with a circumferential razor-sharp notch with a depth
of a * (target initial crack length) in the middle of the specimen resulting in a target initial ligament diameter,
ini
D *.
ini
Specimen dimensions shall be as specified in Table 1Table 1. The initial crack shall be perpendicular to the
specimen axis.
To avoid clamping effects at the crack tip, the notch distance, L , shall be at least 20 mm from the grips.
min
Table 1 — Specimen dimensions
Dimension
Parameter
mm
L specimen length 80 to 120
D specimen diameter 14,0 ± 0,15
a * target initial crack length 1,40
ini
minimum distance between
Lmin ≥20
notch and clamping system
Clamping part of the specimen may be threaded, for example, M 14 × 1,0 metric fine thread, in which case
matching grips shall be used.
NOTE 1 Residual stresses can cause bending of the test specimen which can influence the test results. Bending can be
minimized by taking the specimen from the location where the residual stress is minimum e.g. from the centre of the pipe
wall.
18489_ed2fig1.EPS
Key
L specimen length
Lmin minimum distance between notch and clamping system
aini* target initial crack length
Dini* target initial ligament diameter
D specimen diameter
1 razor-sharp notch
Figure 1 — Principal configuration of CRB test specimen with optional metric fine thread
6.2 Test specimen preparation
The test specimens shall be machined from compression moulded sheets, extruded rods or directly from pipe
or fittings. The use of different processing conditions can affect the results. Recommended conditions for
compression moulding of test specimens are given in Annex BAnnex B for PE, Annex CAnnex C for PP and
Annex DAnnex D for PA-U.
The specimens shall be machined in accordance with ISO 2818.
6.3 Specimen notching
Specimens shall be notched at ambient temperature of (23 ± 2) °C with a notching apparatus according to
5.35.3. To avoid frictional heating which may lead to notch tip damage such as blunting and introduction of
residual stresses, select a sufficiently low driving speed and feed. Favourable values for the specimen notching
are a driving speed of maximum 100 rpmr/min and a razor blade feed of maximum 0,03 mm/rotation.
Special attention shall be paid to notching perpendicular to the specimen axis.
A razor blade shall be used for no more than 10 notches for virgin PE materials. For other materials, filled
materials and recyclates not more than 5 notches shall be done per razor blade.
NOTE 1 Both non-perpendicular notching and the use of damaged razor blades have a significant influence on the
failure cycle number, N .
f
6.4 Specimen conditioning
Unless otherwise specified, specimens shall be conditioned at 23/50, Class 2 according toin accordance with
ISO 291 for a minimum of 24 h after notching and prior to testing.
7 Test procedure
7.1 Measurement of specimen dimensions
Before testing, the diameter, D, shall be recorded on both sides of the notch at a distance of 1 mm to 2 mm
from the notch with an accuracy of at least 0,1 mm. An average of the two measurements shall be taken.
Measuring the diameter directly at the notch shall be avoided.
7.2 Specimen mounting
Depending on the clamping system, the specimen shall be mounted into the test machine without inducing
additional forces. Bending or twisting of the specimen shall be avoided. The distance from the grips to the
notch shall be of a sufficient length, L , (see Figure 1Figure 1)) to avoid any clamping effects at the crack tip.
min
7.3 Test atmosphere
The test shall be carried out at condition 23/50, Class 2 according toin accordance with ISO 291, unless
specified otherwise in a referring standard. In case of testing at other temperatures, the unloaded specimen
shall be conditioned at the test temperature for at least 2 h after mounting in the test apparatus.
7.4 Calculation of test load
The calculation of the maximum load, F , and the minimum load, F , shall be carried out in accordance with
max min
Figure 2 and Formulae (1) to (3)according to Figure 2 and Formulae (1) to (3).
...