FprEN ISO 18489
(Main)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)
- Abstract
This International Standard 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.
This International Standard 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.
- Status
- Not Published
- Publication Date
- 03-Mar-2027
- Technical Committee
- CEN/TC 155 - Plastics piping systems and ducting systems
- Current Stage
- 5020 - Submission to Vote - Formal Approval
- Start Date
- 08-Oct-2026
- Due Date
- 29-Jun-2027
- Completion Date
- 08-Oct-2026
FprEN ISO 18489 is a CEN draft for the Cracked Round Bar (CRB) test method. It specifies how to determine resistance to slow crack growth (SCG) under cyclic loading in thermoplastic materials for piping systems, with an accelerated fracture-mechanics test at 23 °C. The document is aimed at laboratories, pipe and fitting manufacturers, material suppliers, and specifiers who need a repeatable way to rank materials for long-term pipe applications.
What does FprEN ISO 18489 specify?
FprEN ISO 18489 specifies a cyclic tensile test on a notched cylindrical CRB specimen to measure slow crack growth resistance. It covers samples taken from compression moulded sheets, extruded rods, sheets or pipes, and injection moulded fittings of suitable thickness.
The document is organized into scope, normative references, terms and definitions, principle, apparatus, test specimen, test procedure, data treatment, and test report. It also includes four informative annexes.
| Annex | What it covers |
|---|---|
| Annex A | Recalculation between different specimen diameters and single-point interpolation |
| Annex B | Test parameters for PE |
| Annex C | Test parameters for PP |
| Annex D | Test parameters for PA-U (PA-U11, PA-U12) |
The scope also states that the method is suitable for accelerated fracture-mechanics characterization at ambient temperatures of 23 °C. It can be used for virgin and non-virgin thermoplastic materials, and the same approach can be adapted to other thermoplastics by developing suitable test parameters.
What are the key requirements of FprEN ISO 18489?
FprEN ISO 18489 is built around a controlled cyclic load, a defined CRB specimen geometry, and a post-test evaluation of the fracture surface. In practice, the result depends strongly on specimen preparation, notch quality, loading accuracy, and the way the fracture data are treated.
Test machine, notch and specimen geometry
Clause 5 requires a machine that can apply and record a sinusoidal cyclic load in load-control mode with constant maximum and minimum load, both to ±1 % accuracy. The load-cycle frequency also has to be controlled to ±1 %. That matters because small load errors change the number of cycles to failure.
Clause 5.2 and 5.3 require a microscope accurate to 0.03 mm and a razor-sharp notching system with a notch tip radius below 10 μm. In practice, the notch creates the crack starter, so a blunt or misaligned notch can change the failure mode.
Clause 6.1 defines the CRB specimen as a cylindrical bar with a length of 80 to 100 mm, a diameter of 14.0 ± 0.15 mm, and a target initial crack length of 1.40 mm. The notch must be at least 20 mm from the grips. If another diameter is used, Annex A requires comparison by stress intensity factor range rather than by stress range.
Specimen preparation and test conditions
Clauses 6.2 to 6.4 require machining in accordance with ISO 2818, conditioning at 23/50, Class 2 according to ISO 291 for at least 24 h after notching, and careful notching at (23 ± 2) °C. The document warns against frictional heating during notching and limits the use of one razor blade. That is important because worn blades and heating can damage the crack tip and distort the result.
Clause 7.3 sets the standard test atmosphere at 23/50, Class 2 unless a referring standard says otherwise. When another temperature is used, the specimen must be conditioned at that temperature for at least 2 h after mounting.
Loading, evaluation and validity
Clause 7.4 uses a load ratio R of 0.1 and selects target stress ranges so that the specimen fails by brittle slow crack growth rather than a predominantly ductile mode. At least four specimens are tested at different stress ranges. For PE, PP and PA-U, the annexes give typical ranges and frequencies to help select the test plan.
Clause 7.7 and Clause 8 define how the initial crack length is obtained after testing from the fracture surface, then used to correct the applied stress range. The failure cycle number Nf is plotted against stress range on a double-logarithmic diagram, and a linear regression is applied. If the coefficient of determination is below 98 %, one additional specimen is added to try to reach at least 95 %; below 95 %, the test is invalid. Only failures in the plane of the razor blade notch are valid.
Test report
Clause 9 requires the report to identify the material or product, specimen preparation and notching, specimen dimensions, test equipment, atmosphere, loading variables, the Δσ versus Nf diagram, and a photo of the fracture surfaces. If Annex A single-point evaluation is used, the report also includes the interpolated reference values.
What terms does FprEN ISO 18489 define?
- cycle - The repeated load-time or stress-time segment used as the basic unit of the test.
- failure cycle number - The total number of cycles from the start of the test until the specimen fails.
- frequency - The number of cycles per second, expressed in hertz (Hz).
- load ratio (R) - The ratio of minimum load to maximum load in one cycle.
- initial crack length - The crack depth at the start of the test, determined after testing from the fracture surface.
- initial ligament diameter - The remaining ligament diameter after notching at the start of the test, measured after testing.
- stress range - The difference between maximum and minimum stress at the start of the test.
- waveform - The shape of the load-time curve within one cycle.
Who uses FprEN ISO 18489?
FprEN ISO 18489 is used by testing laboratories, pipe and fitting manufacturers, polymer suppliers, recyclate processors, and quality or product approval teams. They use it to rank materials, compare grades, check the effect of virgin or non-virgin content, and generate data for product specifications and procurement decisions.
It is particularly relevant to thermoplastic piping systems, including PE, PP and PA-U materials, where long-term crack growth can control service life. It also supports work on material pre-selection and on setting material-specific test parameters in product standards.
What changed in FprEN ISO 18489 from the previous edition?
FprEN ISO 18489 cancels and replaces ISO 18489:2015, and the foreword states that it has been technically revised.
The stated changes are:
- Clause 7.7 was improved for calculating the initial crack length.
- Annex A was improved for recalculation between different specimen diameters, with added information for single-point evaluation.
- The test parameters were shifted into informative Annexes B, C and D.
- PP and PA-U were added as material-specific annexes.
- New photographs of PE fracture surfaces after testing were included.
Which standards are used with FprEN ISO 18489?
| Standard | What it contributes |
|---|---|
| ISO 291 | Standard atmospheres for conditioning and testing |
| ISO 2818 | Preparation of test specimens by machining |
| ISO 16396-1 | PA designation system and basis for specifications |
| ISO 16396-2 | Preparation of PA test specimens and determination of properties |
| ISO 16770 | PE conditioning and moulding conditions used in Annex B |
| CEN/TS 14541-2:2022 | Reference range for PP recyclates in Annex C |
| EN 14758-1:2023 | PP-MD pipe and fitting specification cited for PP recyclate guidance |
| ISO 16486-1 | PA-U pipe system designation cited in Annex D |
What does the FprEN ISO 18489 document contain?
FprEN ISO 18489 contains the full test method, from the principle of the CRB specimen to the final report content. It includes apparatus requirements, specimen geometry and preparation, loading calculation, cyclic testing steps, fracture-surface evaluation, and statistical treatment of the results.
The document also contains figures showing the CRB specimen, the loading setup, and the circle-construction method used to derive the initial ligament diameter after testing. Its tables and annexes provide specimen dimensions, material-specific test parameters, stress ranges, frequencies, and the recalculation method for different diameters.
For practical use, the annexes help laboratories choose a starting test plan and compare results across specimen sizes or material groups. The report clause then tells the user what to document so the test can be reviewed, compared, and repeated.
Relations
- Effective Date
- 28-Jan-2026
- Effective Date
- 28-Jan-2026
- Effective Date
- 28-Jan-2026
- Effective Date
- 28-Jan-2026
- Effective Date
- 28-Jan-2026
- Effective Date
- 28-Jan-2026
- Effective Date
- 12-Feb-2026
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Frequently Asked Questions
FprEN ISO 18489 is a draft published by the European Committee for Standardization (CEN). Its full title is "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)". This standard covers: This International Standard 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. This International Standard 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.
This International Standard 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. This International Standard 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.
FprEN ISO 18489 is classified under the following ICS (International Classification for Standards) categories: 23.040.45 - Plastics fittings. The ICS classification helps identify the subject area and facilitates finding related standards.
FprEN ISO 18489 has the following relationships with other standards: It is inter standard links to EN ISO 19403-2:2024, EN ISO 19403-3:2024, EN ISO 19403-5:2024, EN ISO 19403-6:2024, EN ISO 19403-4:2024, EN ISO 19403-7:2024, ISO/FDIS 18489. Understanding these relationships helps ensure you are using the most current and applicable version of the standard.
FprEN ISO 18489 is available in PDF format for immediate download after purchase. The document can be added to your cart and obtained through the secure checkout process. Digital delivery ensures instant access to the complete standard document.
Standards Content (Sample)
SLOVENSKI STANDARD
oSIST prEN ISO 18489:2025
01-december-2025
Plastomerni materiali za cevne sisteme - Ugotavljanje odpornosti proti počasnemu
razvoju razpok pod cikličnim obremenjevanjem - Preskusna metoda za lomljenje
okroglih palic (CRB) (ISO/DIS 18489:2025)
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)
Rohre aus Polyethylen - Bestimmung der Widerstandsfähigkeit gegen langsames
Risswachstum unter zyklischer Belastung - Prüfung an gekerbten Rundstäben (ISO/DIS
18489:2025)
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/DIS 18489:2025)
Ta slovenski standard je istoveten z: prEN ISO 18489
ICS:
23.040.45 Fitingi iz polimernih Plastics fittings
materialov
oSIST prEN ISO 18489:2025 en,fr,de
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
oSIST prEN ISO 18489:2025
oSIST prEN ISO 18489:2025
DRAFT
International
Standard
ISO/DIS 18489
ISO/TC 138/SC 5
Thermoplastic materials for
Secretariat: NEN
piping systems — Determination
Voting begins on:
of resistance to slow crack growth
2025-10-15
under cyclic loading — Cracked
Voting terminates on:
Round Bar (CRB) test method
2026-01-07
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)
ICS: 23.040.20; 23.040.45
THIS DOCUMENT IS A DRAFT CIRCULATED
FOR COMMENTS AND APPROVAL. IT
IS THEREFORE SUBJECT TO CHANGE
AND MAY NOT BE REFERRED TO AS AN
INTERNATIONAL STANDARD UNTIL
PUBLISHED AS SUCH.
This document has not been edited by the ISO Central Secretariat.
IN ADDITION TO THEIR EVALUATION AS
BEING ACCEPTABLE FOR INDUSTRIAL,
TECHNOLOGICAL, COMMERCIAL AND
USER PURPOSES, DRAFT INTERNATIONAL
STANDARDS MAY ON OCCASION HAVE TO
ISO/CEN PARALLEL PROCESSING
BE CONSIDERED IN THE LIGHT OF THEIR
POTENTIAL TO BECOME STANDARDS TO
WHICH REFERENCE MAY BE MADE IN
NATIONAL REGULATIONS.
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 SUPPORTING DOCUMENTATION.
Reference number
ISO/DIS 18489:2025(en)
oSIST prEN ISO 18489:2025
DRAFT
ISO/DIS 18489:2025(en)
International
Standard
ISO/DIS 18489
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)
ICS: 23.040.20; 23.040.45
THIS DOCUMENT IS A DRAFT CIRCULATED
FOR COMMENTS AND APPROVAL. IT
IS THEREFORE SUBJECT TO CHANGE
AND MAY NOT BE REFERRED TO AS AN
INTERNATIONAL STANDARD UNTIL
PUBLISHED AS SUCH.
This document has not been edited by the ISO Central Secretariat.
IN ADDITION TO THEIR EVALUATION AS
BEING ACCEPTABLE FOR INDUSTRIAL,
© ISO 2025
TECHNOLOGICAL, COMMERCIAL AND
USER PURPOSES, DRAFT INTERNATIONAL
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
STANDARDS MAY ON OCCASION HAVE TO
ISO/CEN PARALLEL PROCESSING
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
BE CONSIDERED IN THE LIGHT OF THEIR
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
POTENTIAL TO BECOME STANDARDS TO
WHICH REFERENCE MAY BE MADE IN
or ISO’s member body in the country of the requester.
NATIONAL REGULATIONS.
ISO copyright office
RECIPIENTS OF THIS DRAFT ARE INVITED
CP 401 • Ch. de Blandonnet 8
TO SUBMIT, WITH THEIR COMMENTS,
CH-1214 Vernier, Geneva
NOTIFICATION OF ANY RELEVANT PATENT
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RIGHTS OF WHICH THEY ARE AWARE AND TO
PROVIDE SUPPORTING DOCUMENTATION.
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland Reference number
ISO/DIS 18489:2025(en)
ii
oSIST prEN ISO 18489:2025
ISO/DIS 18489:2025(en)
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.4
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 between different test specimen diameters 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
oSIST prEN ISO 18489:2025
ISO/DIS 18489:2025(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 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 05, 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:
— Improved Clause 7.7 for initial crack length calculation
— Improved informative Annex A for recalculation between different specimen diameters 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
oSIST prEN ISO 18489:2025
ISO/DIS 18489:2025(en)
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
oSIST prEN ISO 18489:2025
oSIST prEN ISO 18489:2025
DRAFT International Standard ISO/DIS 18489:2025(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 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.
This document provides a method that is suitable for an accelerated fracture-mechanics 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
ISO 16396-1, Plastics — Polyamide (PA) moulding and extrusion materials — Part 1: Designation system and
basis for specifications
ISO 16396-2, Plastics — Polyamide (PA) moulding and extrusion materials — Part 2: Preparation of test
specimens and determination of properties
ISO 16770, Plastics — Determination of environmental stress cracking (ESC) of polyethylene — Full-notch creep
test (FNCT)
CEN/TS 14541-2:2022, Plastics pipes and fittings — Utilisation of thermoplastics recyclates — Part 2:
Recommendations for relevant characteristics
EN 14758-1:2023, Plastics piping systems for non-pressure underground drainage and sewerage — Polypropylene
with mineral modifiers (PP-MD) — Part 1: Specifications for pipes, fittings and the system
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
oSIST prEN ISO 18489:2025
ISO/DIS 18489:2025(en)
— 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 crack from the specimen surface through the crack 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)
oSIST prEN ISO 18489:2025
ISO/DIS 18489:2025(en)
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 crack from the specimen surface through the crack 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
reference specimen radius (D = 2r ), given in the product standard or requirement, used for recalculation
ref ref
after testing using Annex A
Note 1 to entry: It is expressed in millimetres (mm).
oSIST prEN ISO 18489:2025
ISO/DIS 18489:2025(en)
3.19
reference specimen diameter
D
ref
reference specimen diameter (D = 2r ), given in the product standard or requirement, used for
ref ref
recalculation after testing using Annex A
Note 1 to entry: It is expressed in millimetres (mm).
3.20
reference initial crack length
a
ini-ref
reference depth of the crack, given in the product standard or requirement, used for recalculation after
testing using Annex A
Note 1 to entry: It is expressed in millimetres (mm).
3.21
reference stress range
Δσ
0-ref
difference between the maximum and minimum stress calculated using equation 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 minimum and maximum stress intensity factor calculated using equation 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.
oSIST prEN ISO 18489:2025
ISO/DIS 18489:2025(en)
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 defined depth at the circumference of
the cylindrical specimen. The notch tip radius produced shall be less than 10 μm.
NOTE 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 th
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