ISO 29221:2014

INTERNATIONAL ISO
STANDARD 29221
First edition
2014-01-15
Plastics — Determination of mode I
plane-strain crack-arrest toughness
Plastiques — Détermination de la ténacité d’arrêt de fissure en
déformation plane
Reference number
©
ISO 2014
© ISO 2014
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ii © ISO 2014 – All rights reserved

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 2
5 Apparatus . 2
5.1 General . 2
5.2 Loading arrangement . 2
5.3 Displacement gauge . 4
6 Test specimen . 5
6.1 General . 5
6.2 Dimensions . 5
6.3 Starter notch . 6
7 Procedure. 7
7.1 Measurements of specimen dimensions. 7
7.2 Conditioning . 7
7.3 Loading . 7
7.4 Displacement measurement. 8
7.5 Arrested crack length (a ) measurement . 8
a
7.6 Number of tests . 9
8 Calculation and validation of results .10
8.1 Calculation of K and K .
ο Qa 10
8.2 Validity requirement .10
9 Precision .11
10 Test report .11
10.1 Test details .11
10.2 Calculations .12
10.3 Validity requirements (see Table 1) .12
10.4 Photographic record of fracture surface and descriptive comments (optional) .12
Annex A (informative) Determination of the initial crack length, a , when using the
o
chevron notch .13
Annex B (informative) Procedure for measuring the arrested crack length (a ) .15
o
Annex C (informative) Fracture surface acceptability.16
Annex D (informative) Comment on precision statement .17
Bibliography .18
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
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different types of ISO documents should be noted. This document was drafted in accordance with the
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The committee responsible for this document is ISO/TC 61, Plastics, Subcommittee SC 2, Mechanical
properties.
iv © ISO 2014 – All rights reserved

Introduction
There has been much interest in a better understanding of the fracture behaviour of polymeric materials
and, as a consequence, several International Standard methods for evaluating the fracture properties
have been developed. In the light of the fact that these standard methods provide critical information
on fracture prevention of structures and products made from polymeric materials, as well as give
directions for the research and development of materials, any additional test methods of importance
to fracture need to be added to the list. In line with such importance, in particular, a test method for
evaluating the resistance to rapid crack propagation in terms of a material’s ability to arrest the fast-
[1]-[4][10]-[12][14]
running crack would be of interest for polymers.
The value of the stress intensity factor, K, during the short time interval in which a fast-running crack
arrests is a measure of the ability of materials to arrest such a crack. The values of the stress intensity
factor of this kind, which are determined using the dynamic methods of analysis, provide a value for the
crack-arrest fracture toughness, K . To ease complexity arising from the dynamic effects, static methods
A
of analysis, which are much less complex, can often be used to determine the stress intensity factor at a
short time (1 ms to 2 ms) after crack arrest. The estimate of the crack-arrest fracture toughness obtained
in this fashion is termed K and the difference between K and K can be made small by minimizing the
a A a
[5]-[8]
macroscopic dynamic effects during the test. For cracks propagating under the conditions of crack-
front plane-strain, in situations where the dynamic effects are also known to be small, K determinations
la
using laboratory-sized specimens have been used successfully to estimate whether, and at what point, a
[9]-[11]
crack arrests in a structure. Depending upon the component design, the loading compliance, and
the crack-jump length, a dynamic analysis of a fast-running crack propagation event can be necessary
in order to predict whether crack arrest will occur and the arrest position. In such cases, values of K
la,
determined by this International Standard can be used to identify those values of K below which the
crack speed is zero. More details on the use of dynamic analyses can be found in Reference [8].
This International Standard describes a method for mode I plane-strain crack-arrest toughness
measurement for polymers.
INTERNATIONAL STANDARD ISO 29221:2014(E)
Plastics — Determination of mode I plane-strain crack-
arrest toughness
1 Scope
This International Standard specifies a method for the determination of the plane-strain crack-arrest
fracture toughness, K , of polymeric materials by using a side-grooved, crack-line-wedge-loaded
la
compact tension specimen to obtain a rapid crack run-arrest segment of flat-tensile separation with a
satisfactory crack front. This International Standard employs a static fracture analysis determination
of the stress intensity factor at a short time after crack arrest. The estimate is denoted as K and when
a
certain size requirements are met, the test result provides an estimate, termed as K , of the plane-strain
la
crack-arrest toughness of the polymer. The specimen size requirements provide for in-plane dimensions
large enough to allow the specimen to be modelled by linear elastic analysis. If the specimen does not
exhibit rapid crack propagation and arrest, K cannot be determined.
a
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 527-1, Plastics — Determination of tensile properties — Part 1: General principles
ISO 16012, Plastics — Determination of linear dimensions of test specimens
ISO 18872, Plastics — Determination of tensile properties at high strain rates
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
conditional value of the plane-strain crack-arrest fracture toughness
K
Qa
conditional value of K , calculated from the test result and subject to the validity criteria specified for
la
the side-grooved, crack-line-wedge-loaded specimen used
Note 1 to entry: The calculation of K is
...