ISO 16770:2019

INTERNATIONAL ISO
STANDARD 16770
Second edition
2019-09
Plastics — Determination of
environmental stress cracking (ESC)
of polyethylene — Full-notch creep
test (FNCT)
Plastiques — Détermination de la fissuration sous contrainte dans un
environnement donné (ESC) du polyéthylène — Essai sur éprouvette
entièrement entaillée (FNCT)
Reference number
©
ISO 2019
© ISO 2019
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ii © ISO 2019 – 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
6 Test specimens. 6
6.1 General . 6
6.2 Test specimens geometry . 6
6.3 Test specimen preparation . 8
6.3.1 General. 8
6.3.2 Test specimens machined from compression moulded sheets . 8
6.3.3 Test specimens machined from injection-moulded type 1A multipurpose
test specimen . 8
6.3.4 Test specimens machined from finished products . 8
6.4 Test specimen notching . 8
6.5 Conditioning of the test specimens . 9
7 Test environment . 9
7.1 General . 9
7.2 Recommended test environment . 9
7.2.1 Test environment No. 1 . 9
7.2.2 Test environment No. 2 .10
7.3 Other test environments .11
8 Test procedure .11
8.1 Selection of detergent, reference tensile stress and test temperature .11
8.2 Number of test specimens to be tested .11
8.3 Calculation of the test load .13
8.4 Application of the load to the test specimen .13
8.5 Removing individual specimens from a chamber .13
8.6 Measurement of the ligament area after failure .13
9 Expression of results .14
9.1 Calculation of the actual tensile stress .14
9.2 Calculation of time to failure at the reference tensile stress .14
10 Precision .15
11 Test report .15
Annex A (informative) Precision statement .17
Annex B (informative) Example of a recommended test report for FNCT determination .20
Annex C (informative) Practical examples of fracture surfaces and corresponding definition
of failure mode.22
Bibliography .25
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
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electrotechnical standardization.
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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
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.org/iso/foreword .html.
This document was prepared by Technical Committee ISO/TC 61, Plastics, Subcommittee SC 9,
Thermoplastics.
This second edition cancels and replaces the first edition (ISO 16770:2004), which has been technically
revised.
The main changes compared to the previous edition are as follows:
— the test conditions for bimodal PE materials with substantially increased crack-resistance have
been extended on an alternative more aggressive detergent;
— the compression moulding conditions for 10 mm × 10 mm test specimen (Type A) have been
modified;
— the specimen types have been updated, with injection moulded test specimens being included;
— precision data (repeatability) from interlaboratory testing have been included for Type A test
specimen.
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 2019 – All rights reserved

Introduction
Since mid-2000, the full-notch creep test (FNCT) has been widely used as one of the tests characterizing
the environmental stress cracking (ESC) of polyethylene (PE) materials used in demanding applications.
Among current ESC tests, the FNCT is relatively simple, easy to perform and still a sensitive laboratory
scale test method to characterize ESC resistance of PE materials. The advantage of FNCT is that it
enables the evaluation of the whole PE product range by variation of test conditions (test specimen
geometry, temperature, medium and load conditions).
The FNCT method was standardized in 2004 as a PE material property, with partial precision statement
based on the repeatability for a 6 mm × 6 mm-cross-sectional test specimen (Type B). Since then, several
interlaboratory tests have been performed, resulting in a repeatability statement for 10 mm × 10 mm-
cross-sectional test specimen (Type A). Type A specimen is prepared by using modified compression
moulding conditions, which give more consistent test results compared to the original moulding
conditions.
In addition, due to recent development of new PE pipe materials, known as PE 100 RC, which exhibit
substantially improved crack resistance, it became necessary to define test conditions for these
materials. Testing of these materials using the conditions specified in the previous edition of this
document (i.e. ISO 16770:2004) resulted in failure times of one year or longer. As a consequence, this
document includes extended test conditions to cover PE materials with substantially increased crack
resistance. This accelerated test procedure using extended test conditions allows failure times to be
reduced substantially compared to conventional test conditions given in ISO 16770:2004. In addition, a
good correlation between accelerated and conventional test methods was derived; see References [4],
[7] and [9].
The FNCT is a material characterization and production monitoring test, which, by strictly maintaining
the test conditions defined, enables relevant and reliable comparison among similar PE materials or
group of PE materials.
INTERNATIONAL STANDARD ISO 16770:2019(E)
Plastics — Determination of environmental stress cracking
(ESC) of polyethylene — Full-notch creep test (FNCT)
1 Scope
This document specifies a method for determining the environmental stress cracking (ESC) resistance
of polyethylene (PE) materials in a defined test environment. The test is carried out on notched test
specimens machined from moulded sheets/specimens or from finished products. The test specimen is
subjected to a static tensile load when immersed into an environment such as a surfactant solution held
at a specified temperature. The time to failure is measured.
The method has been specifically developed for polyethylene materials but can be used to evaluate PE
products, such as pipes, fusion welds/fittings and blow-moulded PE containers to study the effect of
aggressive env
...