ISO 13586:2018

INTERNATIONAL ISO
STANDARD 13586
Second edition
2018-08
Plastics — Determination of fracture
toughness (G and K ) — Linear
IC IC
elastic fracture mechanics (LEFM)
approach
Plastiques — Détermination de la ténacité à la rupture (G et K ) —
IC IC
Application de la mécanique linéaire élastique de la rupture (LEFM)
Reference number
©
ISO 2018
© ISO 2018
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ii © ISO 2018 – All rights reserved

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Test specimens. 4
4.1 Shape and size . 4
4.2 Preparation . 4
4.3 Notching . 5
4.4 Conditioning . 6
5 Testing . 6
5.1 Testing machine . 6
5.2 Load indicator . 6
5.3 Displacement transducer . 6
5.4 Loading rigs . 6
5.5 Displacement correction . 7
5.6 Test atmosphere .10
5.7 Thickness, width and crack length of test specimens .10
5.8 Test conditions .10
6 Expression of results .10
6.1 Determination of F .10
Q
6.2 Provisional result G .11
Q
6.3 Provisional result K .11
Q
6.4 Size criteria and validation of results .11
6.5 Cross-check of results .12
7 Precision .13
8 Test report .13
Annex A (normative) Calibration factors .15
Annex B (informative) Testing of plastics containing short fibres .17
Bibliography .22
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
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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 2,
Mechanical behaviour.
This second edition cancels and replaces the first edition (ISO 13586:2000), which has been technically
revised. It also incorporates the Amendment ISO 13586:2000/Amd.1:2003, with the introduction of a
new Annex B.
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 2018 – All rights reserved

Introduction
This document is based on a testing protocol developed by the European Structural Integrity Society
(ESIS), Technical Committee 4, Polymers, Polymer Composites and Adhesives, who carried out the
preliminary enabling research through a series of round-robin exercises which covered a range of
material samples, specimen geometries, test instruments and operational conditions. This activity
involved nearly 10 laboratories from different countries. See References [1] and [3].
INTERNATIONAL STANDARD ISO 13586:2018(E)
Plastics — Determination of fracture toughness (G and
IC
K ) — Linear elastic fracture mechanics (LEFM) approach
IC
1 Scope
This document specifies the principles for determining the fracture toughness of plastics in the crack-
opening mode (mode I) under defined conditions. Two test methods with cracked specimens are
defined, namely three-point-bending tests and compact-specimen tensile tests in order to suit different
types of equipment available or different types of material.
The methods are suitable for use with the following range of materials, including their compounds
containing short fibres of the length ≤ 7,5 mm:
— rigid and semi-rigid thermoplastic moulding, extrusion and casting materials;
— rigid and semi-rigid thermosetting moulding and casting materials.
In general, short fibre lengths of 0,1 mm to 7,5 mm are known to cause heterogeneity and anisotropy
in the crack tip fracture process zone. Therefore, where relevant, Annex B offers some guidelines to
extend the application of the same testing procedure, with some reservations, to rigid and semi-rigid
thermoplastic or thermosetting plastics containing such short fibres.
Certain restrictions on the linearity of the load-displacement diagram, on the specimen width and on
the thickness are imposed to ensure validity (see 6.4) since the scheme used assumes linear elastic
behaviour of the cracked material and a state of plane strain at the crack tip. Finally, the crack needs
to be sharp enough so that an even sharper crack does not result in significantly lower values of the
measured properties.
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 527-1, Plastics — Determination of tensile properties — Part 1: General principles
ISO 604, Plastics — Determination of compressive properties
ISO 2818, Plastics — Preparation of test specimens by machining
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
3 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 http:/ /www.e lectropedia. org/
3.1
energy release rate
G
change in the external work δU and strain energy δU of a deformed body due to enlargement of the
ext s
cracked area δA
δU δU
exts
G=−
δA δA
Note 1 to entry: It is expressed in joules per square metre, J/m .
3.2
critical energy release rate
G
IC
value of the energy release rate (3.1) in a precracked specimen under plane-strain loading conditions,
when the crack starts to grow
Note 1 to entry: It is expressed in joules per square metre, J/m .
3.3
stress intensity factor
K
limiting value of the product of the stress σ(r) perpendicular to the crack area at a distance r from the
crack tip and of the square root of 2πr, for small values of r
Kr=limσ × 2πr
()
r→0
Note 1 to entry: It is expressed in Pa × √m.
Note 2 to entry: The term factor is used here because it is common usage, even though the value has dimensions.
3.4
critical stress intensity factor
K
IC
value of the stress intensity factor (3.3) when the crack under load actually starts to enlarge under a
plane-strain loading condition around the crack tip
Note 1 to entry: It is expressed in Pa × √m.
Note 2 to entry: The critical stress intensity factor K of a material is related to its critical energy release rate G
IC IC
by the formula:
GK= E
IC IC
where E is the modulus of elasticity, determined under similar conditions of loading time (up to crack initiation)
and temperature.
In the case of plane-strain conditions:
E
t
E =
1−μ
where
E is the tensile modulus (see ISO 527-1);
t
μ is Poisson’s ratio (see ISO 527-1).
2 © ISO 2018 – All rights reserved

3.5
displacement
displacement of the loading device
Note 1 to entry: It is expressed in metres, m.
Note 2 to entry: In the fracture test, the displacement of the loading device is designated as s . The displacement
a
of the loading device corrected as specified in 5.4, is designated as s.
Note 3 to entry: In the indentation test, the displacement of the loading device is designated as s .
ai
3.6
stiffness
S
initial slope of the force-displacement diagram
dF 
S =
 
ds
 
s→0
Note 1 to entry: It is expressed in newtons per metre, N/m.
3.7
force
F
Q
applied load at the initiation of crack growth
Note 1 to entry: It is expressed in newtons, N.
Note 2 to entry: See also 6.1.
3.8
energy
W
B
input energy when crack growth initiates
Note 1 to entry: It is expressed in joules, J.
Note 2 to entry: W is based upon the corrected load-displacement curve.
B
3.9
crack length
a
crack length up to the tip of the initial crack
Note 1 to entry: It is expressed in metres, m.
Note 2 to entry: The initial crack is prepared as specified in 4.3.
Note 3 to entry: For three-point-bending test specimens, the crack length is measured from the notched face. For
compact tensile-test specimens, the crack length is measured from the load line, i.e. from the line through the
centres of the holes for the loading pins (see Figures 1 and 2).
Note 4 to entry: The crack length a is normalized by the width w of the test specimen (α = a/w).
3.10
energy calibration factor
ϕ
factor to account for the crack length dependent stiffness of the test specimen, given by the formula:
−1
dS
 
φ aw =−S
()
 
dα
 
where
S is the stiffness of the specimen;
α (= a/w) is the normalized crack length (see 3.9).
Note 1 to entry: Values of ϕ (a/w) are given in Annex A for both types of specimen.
3.11
geometry calibration factor
f
factor to account for the configuration and the dimensions of the test specimen
Note 1 to entry: Values of f (a/w) are given in Annex A for both types of specimen.
3.12
characteristic length
r
size of the plastic deformation zone around the crack tip
Note 1 to entry: It is required for checking fulfilment of the size criteria (see 6.4).
4 Test specimens
4.1 Shape and size
Test specimens for three-point-bending tests [also called single-edge-notch bending (SENB)] and for
compact tensile (CT) tests shall be prepared in accordance with Figure 1 and Figure 2, respectively.
It is usually convenient to make the thickness h of the test specimens equal to the thickness of a sheet
sample and to make the test specimen width w equal to 2h. The crack length a should preferably be in
the range given by 0,45 ≤ a/w ≤ 0,55.
4.2 Preparation
Test specimens shall be prepared in accordance with the relevant material International Standard for
the material under test and in accordance with ISO 2818. In the case of anisotropic specimens, take
care to indicate the reference direction on each test specimen.
4 © ISO 2018 – All rights reserved

Key
w width
l overall length l > 4,2w
h thickness w/4 < h < w/2
a crack length 0,45w ≤ a ≤ 0,55w
Figure 1 — Three-point-bending (SENB) test specimen
Key
w width
W overall width W = 1,25w ± 0,01w
l length l = 1,2w ± 0,01w
1 1
l distance between centres of two holes located l = 0,55w ± 0,005w
2 2
symmetrically to the crack plane
R radius R = 0,125w ± 0,005w
h thickness 0,4w < h < 0,6w
a crack length 0,45w ≤ a ≤ 0,55w
(The loading pins and holes shall be smooth and a loose fit to minimize friction.)
Figure 2 — Compact tensile (CT) test specimen
4.3 Notching
Method a), b) or c) can be used for notching.
a) Machine a sharp notch into the test specimen and then generate a natural crack by tapping on a
new razor blade placed in the notch (it is essential to practice this since, in brittle test specimens,
a natural crack can be generated by this process, but some skill is required in avoiding too long
a crack or local damage). The length of the crack thus created shall be more than four times the
original notch tip radius.
b) If a natural crack cannot be generated, as in tough test specimens, then sharpen the notch by sliding
a razor blade across the notch. Use a new razor blade for each test specimen. The length of the crack
thus created shall be more than four times the original notch tip radius.
c) Cooling tough test specimens and then performing razor tapping is sometimes successful.
Pressing the blade into the notch is not recommended because of induced residual stresses.
4.4 Conditioning
Condition test specimens as specified in the International Standard for the material under test, unless
otherwise agreed upon by the interested parties. In the absence of this information, the preferred
atmosphere is (23 ± 2) °C and (50 ± 10) % relative humidity, except when the properties of the material
are known to be insensitive to moisture, in which case humidity control is unnecessary.
5 Testing
5.1 Testing machine
The machine shall comply with ISO 7500-1 and ISO 9513, and meet the specifications given in 5.2 to 5.4.
5.2 Load indicator
The load measurement system shall comply with class 1 as defined in ISO 7500-1. The load indicator
shall show the total load carried by the test specimen. This device shall be essentially free from inertia
lag at the test speeds used. It shall indicate the load with an accuracy of at least 1 % of the actual value.
5.3 Displacement transducer
The displacement is recorded during the test. The continuously measuring displacement transducer
shall be essentially free from inertia lag at the test speeds used. It shall be able to measure the relevant
displacement within class 1 of ISO 9513 or better. The effects of the displacement transducer on the
load measurement shall be < 1 % of the load reading or they shall be corrected.
5.4 Loading rigs
A rig with moving rollers is used for three-point-bending (SENB) tests, as shown in Figure 3. Indentation
into the test specimen is minimized by the use of rollers with a large diameter (>w/2). The measurement
of the displacement shall be taken at the centre of the span L (see Figure 3).
For the compact tensile test, the test specimen is loaded by means of two pins in holes in the specimen.
The displacement of the load points during the test is measured, for example by a clip gauge near the
pins (see 5.3).
6 © ISO 2018 – All rights reserved

Key
L span between rollers L = 4w ± 0,1w 1 distance monitored by displacement transducer
R radius w/8 < R < w/2 2 bosses for rubber bands
h thickness
Figure 3 — Rig with two rollers and displacement transducer for three-point-bending
(SENB) tests
5.5 Displacement correction
The measured displacement s shall be corrected for the indentation of the loading pins, compression
a
of the test specimen and the machine compliance in order to determine properly the stiffness S of
the specimen and the work W at crack growth initiation. The calibration of the test system shall be
B
performed as follows.
The load-displacement correction curve (see Figure 4) is generated by analogy with the fracture test
but by using unnotched test specimens, as indicated in Figure 5 and Figure 6. The rollers of the three-
point-bending rig are moved together to reduce even further the small flexing of the unnotched test
specimen under load. The displacement correction shall be performed for each material and at each
different temperature and test speed since polymers are generally sensitive to temperature and test
speed. The degree of loading-pin penetration and specimen compression can vary with changes in
these variables. The indentation tests shall be performed such that the loading times are the same as
in the fracture tests. This will involve lower test speeds to reach the same load in the same time, for
example about half the speed.
In practice, a linear correction curve is usually obtained up to loads even exceeding the fracture load
of cracked test specimens (see Figure 4). Any initial nonl
...