ISO 18489:2015

INTERNATIONAL ISO
STANDARD 18489
First edition
2015-09-01
Polyethylene (PE) materials for
piping systems — Determination
of resistance to slow crack growth
under cyclic loading — Cracked
Round Bar test method
Matériaux polyéthylène (PE) pour systèmes de tuyauterie —
Détermination de la résistance à la propagation lente de fissures sous
un chargement cyclique — Méthode d’essai de la barre ronde fissurée
Reference number
©
ISO 2015
© ISO 2015, Published in Switzerland
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ii © ISO 2015 – All rights reserved

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 3
5 Apparatus . 3
5.1 Test machine . 3
5.1.1 Loading system. 3
5.1.2 Load-cycle frequency . 4
5.1.3 Grips . . . 4
5.1.4 Temperature chamber . 4
5.2 Microscope . 4
5.3 Notching apparatus . 4
6 Test specimen . 4
6.1 Specimen geometry and dimensions . 4
6.2 Test specimen preparation . 5
6.3 Specimen notching . 5
6.4 Specimen conditioning . . 6
7 Test procedure . 6
7.1 Measurement of specimen dimensions . 6
7.2 Specimen mounting . 6
7.3 Test atmosphere . 6
7.4 Calculation of test load . 6
7.5 Load application . 7
7.6 Notch depth measurement . 7
8 Data treatment . 7
9 Test report . 9
Annex A (informative) Comparison of different test specimen diameters .10
Bibliography .11
Foreword
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The committee responsible for this document is 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.
iv © ISO 2015 – All rights reserved

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 polyethylene. 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.
However, developments in modern raw materials have led to a significant increase of resistance of
polyethylene to crack initiation and SCG so that testing with available methods exceeds practical time
frames. Therefore, new acceleration 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 and the cyclic loading regime to result in completion of testing in a relatively short
[2] [3] [4]
time. , ,
INTERNATIONAL STANDARD ISO 18489:2015(E)
Polyethylene (PE) materials for piping systems —
Determination of resistance to slow crack growth under
cyclic loading — Cracked Round Bar test method
1 Scope
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.
NOTE This test method could be adapted for other thermoplastics materials by developing the procedure
using different test parameters.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are
indispensable for its application. For dated references, only the edition cited applies. For undated
references, the latest edition of the referenced document (including any amendments) applies.
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.
3.1
crack length
a
depth of the crack at any time during a test measured from the specimen surface to the crack tip
Note 1 to entry: It is expressed in millimetres (mm).
3.2
cycle
N
smallest segment of a load-time or stress-time function which is repeated periodically
3.3
failure cycle number
N
f
total number of cycles (3.2) from the beginning until failure of the test specimen
3.4
frequency
f
number of cycles (3.2) within one second
Note 1 to entry: It is expressed in hertz (Hz).
3.5
initial crack length
a
ini
measured depth of the crack from the specimen surface through the crack tip at the beginning of the test
Note 1 to entry: It is expressed in millimetres (mm).
3.6
initial ligament diameter
D
ini
inner diameter of the cylindrical specimen after notching
Note 1 to entry: It is expressed in millimetres (mm).
Note 2 to entry: It is calculated by
DD=−2⋅a
iniini
3.7
load ratio
R
ratio of the minimum to the maximum load (3.9) in one cycle (3.2)
Note 1 to entry: It is calculated by
F
min
R=
F
max
3.8
load range
ΔF
difference between the maximum and minimum load (3.10), in Newtons (N), in one cycle (3.2)
3.9
maximum load
F
max
highest value of the applied load, in Newtons (N), in one cycle (3.2)
3.10
minimum load
F
min
lowest value of the applied load, in Newtons (N), in one cycle (3.2)
3.11
notch distance
L
min
minimum distance from notch to clamping system
Note 1 to entry: It is expressed in millimetres (mm).
3.12
target initial crack length
a *
ini
target depth of the crack from the specimen surface through the crack tip after notching
Note 1 to entry: It is expressed in millimetres (mm).
2 © ISO 2015 – All rights reserved

3.13
target initial ligament diameter
D *
ini
target inner diameter of the cylindrical specimen after notching
Note 1 to entry: It is expressed in millimetres (mm).
3.14
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).
3.15
specimen diameter
D
diameter of the cylindrical specimen
Note 1 to entry: It is expressed in millimetres (mm).
3.16
specimen length
L
total length of the test specimen
Note 1 to entry: It is expressed in millimetres (mm).
3.17
...