ISO 23524:2022

INTERNATIONAL ISO
STANDARD 23524
First edition
2022-10
Plastics — Determination of fracture
toughness of films and thin sheets
— Essential work of fracture (EWF)
method
Plastiques — Détermination de la ténacité à la rupture des films et
feuilles minces — Méthode du travail essentiel de rupture (EWF)
Reference number
© ISO 2022
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ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms, definitions and symbols . 1
3.1 Terms and definitions . 1
3.2 Symbols . 3
4 Principle . 3
5 Apparatus . 4
6 Test specimens . 6
6.1 Specimen geometry . 6
6.2 Preparation of test specimens . 6
6.2.1 General . 6
6.2.2 Width and length . 7
6.2.3 Ligament length . 7
6.2.4 Number of specimens . 7
6.2.5 Specimen notching. 7
6.2.6 Conditioning . 8
7 Procedure for the determination of EWF . 8
7.1 Testing speed . 8
7.2 Force-displacement curves . 8
7.3 Calculation of the overall fracture energy W . 8
f
7.4 Stress criterion . 9
7.5 Linear regression . 9
7.6 Outlying data criterion . 10
7.7 Results table . 11
8 Precision .11
9 Test report .12
Annex A (informative) Example .13
Annex B (informative) Interlaboratory test results .18
Bibliography .21
iii
Foreword
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This document was prepared by Technical Committee ISO/TC 61, Plastics, Subcommittee SC 2,
Mechanical behavior.
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iv
Introduction
Fracture occurs under plane stress displaying gross ductility in many practical applications of
polymeric materials in which they are used as thin sheets or films (e.g. packaging and coatings). It is
inappropriate to adopt thicker test specimens, which are generally used in fracture tests, to measure
the fracture toughness in such cases. Thicker test specimens suppress crack tip ductility and bring
about a change in stress state which does not occur in practice. The essential work of fracture (EWF)
method, described in this document, provides toughness measurement under plane stress. The method
[1]
which is relatively simple is based on a suggestion by Broberg , further developed first by Cotterell,
[2],[3] [4]-[9]
Reddel and Mai for metals and then by a series of workers for ductile polymers. More recent
reviews on this method are given in References [10], [11], [12].
The method assumes that the overall energy associated with fracture can be partitioned into two
components: the essential work necessary to create new surfaces in the so-called fracture process
zone, and the non-essential work dissipated for the plastic deformation in the surrounding volume, the
process zone.
The essential work of fracture has been shown to be a material property, i.e. independent of the
[13],[14]
specimen geometry, for a given sheet thickness , when the condition of full yielding of the
specimen ligament before the onset of crack propagation is fulfilled. In this case, the essential work
of fracture is a parameter that gives an intrinsic material property dependent only on thickness and
therefore useful in product design. However, the condition of full yielding of the ligament is usually
difficult to verify without specific instrumentation, not commonly available in every laboratory.
Even if this condition is not fulfilled, the EWF test method can still be applied to determine the essential
work and non-essential work of the fracture energy, which are repeatable and reproducible parameters
useful in the development of new materials, in quality control and interlaboratory comparisons.
This document describes the EWF method independently of the verification of the full ligament yielding
condition.
v
INTERNATIONAL STANDARD ISO 23524:2022(E)
Plastics — Determination of fracture toughness of films
and thin sheets — Essential work of fracture (EWF)
method
1 Scope
1.1 This document specifies the principles and the method for determining the fracture toughness of
polymeric films and thin sheets in the crack opening mode (mode I) under plane stress conditions. The
essential work of fracture (EWF) method is based on the use of double edge notched tensile (DENT)
specimens.
1.2 The method is suitable for use with films or thin sheets, of thickness not greater than 1 mm,
made of ductile polymeric materials, in which fracture propagation is stable (crack growth is always
driven by the external applied force). If, at any time during the test, brittle fracture occurs, with fast
crack propagation driven by the elastic energy stored in the specimen, the sample is not suitable for the
application of the present test method.
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 dates 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 4593, Plastics — Film and sheeting — Determination of thickness by mechanical scanning
ISO 7500-1, Metallic materials — Calibration and verification of static uniaxial testing machines — Part 1:
Tension/compression testing machines — Calibration and verification of the force-measuring system
ISO 9513, Metallic materials — Calibration of extensometer systems used in uniaxial testing
ISO 16012, Plastics — Determination of linear dimensions of test specimens
3 Terms, definitions and symbols
3.1 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:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1.1
initial distance between the grips
L
g
distance between the grips before the beginning of the test
Note 1 to entry: It is expressed in millimetres (mm).
Note 2 to entry: See Figure 1.
3.1.2
gauge length
L
initial distance between the grips L (3.1.1) when the displacement is measured by the change in the
g
distance between the grips during the test
Note 1 to entry: It is expres
...