ISO 20064:2019

Metallic materials — Steel — Method of test for the determination of brittle crack arrest toughness, Kca

This document specifies a test method for the determination of brittle crack arrest toughness. It is applicable to ferritic steel base metals exhibiting ductile to brittle transition behaviour. Applicable materials are rolled steel plates. It is intended for materials with a tensile strength of 950 MPa or less and a test piece thickness of 200 mm or less. The range of arrest temperatures is between −196 °C and +100 °C. This document can be applied to flat rolled steel plates but not to flattened steel pipes because the flattening can cause changes in arrest toughness.

Matériaux métalliques — Acier — Méthode d'essai pour déterminer la ténacité à la rupture fragile, Kca

General Information

• Status: Published
• Publication Date: 21-Jul-2019
• ICS: 77.040.10 - Mechanical testing of metals
• Technical Committee: ISO/TC 164/SC 4 - Fatigue, fracture and toughness testing
• Drafting Committee: ISO/TC 164/SC 4/WG 3 - Fracture toughness
• Current Stage: 9060 - Close of review
• Completion Date: 04-Mar-2030

Standards Content (Sample)

INTERNATIONAL ISO
STANDARD 20064
First edition
2019-07
Metallic materials — Steel — Method
of test for the determination of
brittle crack arrest toughness, K
ca
Matériaux métalliques — Acier — Méthode d'essai pour déterminer
la ténacité à la rupture fragile, K
ca
Reference number
©
ISO 2019
© ISO 2019
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
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Published in Switzerland
ii © ISO 2019 – All rights reserved

Contents Page
Foreword .v
Introduction .vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols . 2
5 Test equipment. 3
5.1 General . 3
5.2 Testing machine . 3
5.2.1 Force implementation . 3
5.2.2 Calibration of the load cell . 3
5.2.3 Force measurement . 4
5.2.4 Method for force transfer to integrated test piece . 4
5.2.5 Loading direction . 4
5.2.6 Distance between the loading pins . 4
5.3 Impact equipment . 4
5.3.1 Impact methods . 4
5.3.2 Impact energy calculation. 6
5.3.3 Reaction force receivers . 6
6 Test pieces . 7
6.1 Test piece configurations . 7
6.2 Configurations of extension plates and tab plates . 9
6.2.1 General. 9
6.2.2 Extension plates .11
6.2.3 Tab plates .11
6.3 Welding of test piece and extension plates .11
7 Test methods .12
7.1 Temperature control method .12
7.1.1 Determination of temperature gradient .12
7.1.2 Method of temperature control and monitoring .13
7.2 Crack initiation methods .14
8 Test procedures .15
8.1 Pretest procedures .15
8.2 Impacting procedures .16
8.3 Post-test operations . .16
8.4 Observation of fracture surfaces .17
9 Determination of arrest toughness .22
9.1 Validation of arrested crack .22
9.2 Assessment of impact energy .23
9.3 Calculation of arrest toughness .24
10 Reporting .24
Annex A (informative) Devices and method for controlling and monitoring the temperature
of test pieces .28
Annex B (normative) Method for obtaining K at a specific temperature .31
ca
Annex C (normative) Calculation of stress intensity factors for a curved crack .33
Annex D (informative) Double tension type arrest test .34
Annex E (informative) Duplex type arrest test .37
Annex F (informative) Dynamic measurement methods .40
Bibliography .44
iv © ISO 2019 – All rights reserved

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
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
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ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
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
editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www .iso .org/patents).
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constitute an endorsement.
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expressions related to conformity assessment, as well as information about ISO's adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see www .iso
.org/iso/foreword .html.
This document was prepared by Technical Committee ISO/TC 164, Mechanical testing of metals,
Subcommittee SC 4, Fatigue, fracture and toughness testing.
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.
Introduction
This document provides a test method for determining the crack arrest toughness of steels. Experimental
[2]
methods of crack propagation and arrest are documented in Reference [1] Among these, ASTM E1221
is a test method to evaluate lower bound crack arrest toughness, K , under plane strain conditions. On
Ia
[3]
the other hand, crack arrest testing methods using wide plates were developed in the 1950s and have
[3] [4][5][6]
been used for assessing the crack arrest capabilities of cryogenic tanks and pressure vessels .
In recent years, these methods have been extensively used for evaluating the crack arrest toughness of
[7]
ship steels .
The wide plate crack arrest test is intended to evaluate the arrest toughness, K , of steel plate at
ca
its thickness of actual use and not the lower bound arrest toughness, K . However, the relationship
Ia
[4][6]
between the two arrest toughness values has been investigated . It was shown that K and
Ia
K values agreed at lower bound of K . Moreover, the wide plate crack arrest tests were shown to
ca ca
evaluate the arrest toughness at a higher temperature range at which K evaluation is impossible. The
Ia
theoretical background of crack arrest toughness testing with a temperature gradient is described in
References [8] and [9].
This document provides a test method for the determination of brittle crack arrest toughness of steel
by using wide plates with a temperature gradient.
The test method can be summarized as follows: after setting a temperature gradient across the width
of a test piece and applying uniform stress to the test piece, the test piece is struck to initiate a brittle
crack from a mechanical notch in either edge of the test piece and cause crack arrest after propagating
in the width direction (temperature gradient type arrest testing). Annex A describes typical devices
and a method of setting the temperature gradient on the piece. Using the stress intensity factor, the
arrest toughness, K , is calculated from the applied stress and the arrest crack length. This value is
ca
the arrest toughness at the temperature at the point of crack arrest (arrest temperature). To determine
K at a specific temperature, such as the design temperature of a structure, the method specified in
ca
Annex B is applicable.
The method described in Annex C can be used to determine the stress intensity factor for a curved
crack, in order to check the validity of a crack propagation path.
As a method for initiating a brittle crack, a secondary loading mechanism can be used (see Annex D).
The arrest characteristics of the test piece can also be evaluated by welding a crack starter plate to the
test plate in the width direction to enable a brittle crack initiated from the mechanical notch at the edge
of the test piece to propagate in the crack running plate and observing the propagation behaviour of the
crack immediately after entering the test plate (see Annex E).
The method explained in Annex F can be used to determine the dynamic behaviour of crack propagation
and measure the dynamic strain of a test piece.
vi © ISO 2019 – All rights reserved

INTERNATIONAL STANDARD ISO 20064:2019(E)
Metallic materials — Steel — Method of test for the
determination of brittle crack arrest toughness, K
ca
1 Scope
This document specifies a test method for the determination of brittle crack arrest toughness.
It is applicable to ferritic steel base metals exhibiting ductile to brittle transition behaviour. Applicable
materials are rolled steel plates. It is intended for materials with a tensile strength of 950 MPa or less
and a test piece thickness of 200 mm or less. The range of arrest temperatures is between −196 °C and
+100 °C. This document can be applied to flat rolled steel plates but not to flattened steel pipes because
the flattening can cause changes in arrest toughness.
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 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
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
brittle fracture
fracture with predominantly cleavage
3.2
arrest
sudden halt of a propagating brittle crack (3.4)
3.3
arrest toughness
materials resistance against brittle crack (3.4) propagation expressed in terms of stress intensity factor
3.4
brittle crack
crack propagating at approximately 300 m/s or more due to a brittle fracture (3.1)
3.5
arrest temperature
temperature at the point where a brittle crack (3.4) is arrested in the temperature gradient type arrest
toughness (3.3) test
3.6
test piece
flat steel plate in which arrest toughness (3.3) is to be evaluated
3.7
tab plate
thick end inserted for transferring force from a testing machine
3.8
extension plate
flat plate welded between the test piece (3.6) and tab plates (3.7)
3.9
integrated test piece
weld assembly of test piece (3.6), extension plates (3.8) and tab plates (3.7)
3.10
loading pin
pin used for the transfer of the force from the testing machine into the integrated test piece (3.9)
3.11
distance between loading pins
distance between the centres of the loading pins (3.10) inserted into the holes of the tab plates (3.7)
3.12
impact energy
energy applied to a wedge placed on a notch formed at the edge of a test piece (3.6) to initiate a brittle
crack (3.4)
3.13
crack branching
case when two or more cracks form during initiation or propagation of a brittle crack (3.4)
Note 1 to entry: Secondary cracks that are not a main crack are called branch cracks.
3.14
main crack
crack with the longest propagation length when crack branching (3.13) occurs
3.15
shear lip
fracture surface generated by ductile fracture adjacent to the front and back surfaces of a steel plate
3.16
stretch zone
plastic deformation at tip of the arrested crack front
4 Symbols
For the purposes of this document, the symbols given in Table 1 apply.
Table 1 — Symbols used in this document
Symbol Unit Designation
a mm Arrest crack length
ca
B mm Test piece thickness
B mm Extension plate thickness
ex
a 1/2 = -3/2 -3/2
0,031 6 MPa m 1 N mm =0,031 6 MN m .
2 © ISO 2019 – All rights reserved

Table 1 (continued)
Symbol Unit Designation
B mm Tab plate thickness
tb
E MPa Modulus of elasticity
E J Impact energy
i
E J Strain energy stored in a test piece
s
E J Total strain energy stored in extension plates and tab plates
t
F MN Applied force
1/2
MPa m
K Stress intensity factor
3/2 a
(N/mm )
1/2
MPa m
K Arrest toughness
ca
3/2 a
(N/mm )
L mm Test piece length
L mm Distance between loading pins
p
L mm Extension plate length
ex
L mm Tab plate length
tb
R MPa Yield stress at room temperature
p
T °C
ca
Arrest temperature
T K
caK
W mm Test piece width
W mm Extension plate width
ex
W mm Tab plate width
tb
x mm Coordinate of the main crack tip in the width direction
a
x mm Coordinate of the longest branch crack tip in the width direction
br
y mm Coordinate of the main crack tip in the loading direction
a
y mm Coordinate of the longest branch crack tip in the loading direction
br
σ MPa Applied stress in unnotched cross section
a 1/2 = -3/2 -3/2
0,031 6 MPa m 1 N mm =0,031 6 MN m .
5 Test equipment
5.1 General
The following provides specifications for the testing machine needed for conducting the test. The
testing machine is used to apply tensile force to an integrated test piece, and the impact equipment is
used to initiate a brittle crack on the test piece.
5.2 Testing machine
5.2.1 Force implementation
Tensile force to an integrated test piece can be either hydraulically or mechanically applied using either
force or displacement control.
5.2.2 Calibration of the load cell
Load cells shall be calibrated to check the accuracy of force measurement. The force-measuring system
of the testing machine shall be calibrated in accordance with ISO 7500-1, class 1, or better.
The accuracy of the load cells shall be 1 % of the full scale or less.
5.2.3 Force measurement
Force is measured using a calibrated load cell attached to the testing machine.
5.2.4 Method for force transfer to integrated test piece
The force applied to an integrated test piece by the test machine shall be via a clevis pin type loading
method as shown in Figure 1. Centres of the loading pins at both ends shall align with the neutral axis
of the integrated test piece.
Key
1 integrated test piece
2 load clevis
3 pin
a
Force.
Figure 1 — Method for loading an integrated test piece through loading pins
5.2.5 Loading direction
The test machine may be either horizontal or vertical. In the case of the horizontal direction, the test
piece surfaces shall be placed either perpendicular or parallel to the ground. However, when using the
parallel position, care should be taken to ensure that the temperature difference between the top and
bottom surfaces of the test piece is within the values specified in 7.1.1.2.
5.2.6 Distance between the loading pins
The distance between the loading pins, L , as defined in Figure 8, shall be 3,4W or more for preventing
p
force drop by a reflection of stress wave at the loading pins. Since the distance between the loading
pins potentially has an effect on the force drop associated with crack propagation, especially for a long
[11]
arrested crack, the validity of the test results shall be verified using the method described in 9.1 .
5.3 Impact equipment
5.3.1 Impact methods
Recommended methods for applying an impact force to a wedge mounted on the notch of an integrated
test piece include the drop-weight type and the air gun type, as shown in Figure 2 a) and Figure 2 b),
respectively. The drop weight type method applies an impact force to the wedge by freely dropping a
weight from a predetermined height. The air gun type method applies an impact force to the wedge by
4 © ISO 2019 – All rights reserved

introducing a predetermined gas pressure into a piston-sealed cylinder, and then releasing the lock of
the piston.
The wedge shall be of sufficient hardness not to plastically deform during impact. The wedge thickness
shall be equal to or greater than that of the test piece, and the wedge angle shall be greater than that
of the notch formed in the test piece and shall have a shape capable of opening up the notch of the test
piece. The recommended shape of the wedge is shown in Figure 3.
a) Drop weight type b) Air gun type
Key
1 drop weight (before impact)
2 drop weight (after impact)
3 wedge
4 cylinder
5 piston (before impact)
6 piston (after impact)
a
Free fall of drop weight.
Figure 2 — Impact apparatus
Dimensions in millimetres
Key
1 wedge
2 test piece
Figure 3 — Recommended wedge shape
5.3.2 Impact energy calculation
Formula (1) shall be used to calculate the impact energy for the drop weight type method.
Em= gh (1)
i
where
m is the mass of the drop weight (kg);
g is the acceleration of gravity (9,81 m/s );
h is the height from the wedge to the drop weight (m).
For the air gun type method, an energy conversion table specific to the impact apparatus used for
testing shall be used to calculate the impact energy. Impact energy shall be controlled by changing the
cylinder pressure.
NOTE The energy conversion table is generally provided by the manufacturer of the air gun type impact
apparatus.
Setting of the impact energy value before the test and its validity check after the test are described in
7.2 and 9.2, respectively.
5.3.3 Reaction force receivers
To suppress the bending moment caused by impact, a reaction force receiver shall be applied opposite
the impact edge of the integrated test piece. Two types of recommended reaction force receivers are
shown in Figure 4. The floor type, shown in Figure 4 a), is fixed on the ground. The hold type, shown
[12][13][14]
in Figure 4 b), connects to the frame of the impact apparatus . Other methods which are
equivalent to the methods shown in Figure 4 a) and Figure 4 b) may be applied.
6 © ISO 2019 – All rights reserved

a) Floor type b) Hold type
Key
1 impact apparatus
2 wedge
3 test piece
4 reaction force receiver
5 ground
6 frame
Figure 4 — Fixing methods of reaction force receivers
6 Test pieces
6.1 Test piece configurations
The standard test piece configuration is shown in Figure 5. Table 2 shows the ranges of test piece
[11][12][15]
thicknesses, widths and width-to-thickness ratios .
The test piece length shall be equal to or greater than 500 mm or W, whichever is greater.
A crack starter notch shall be introduced at a test piece edge. The notch may be a mechanical or pressed
notch. The pressed notch can be formed by placing a jig having a sharp edge on the bottom of the
mechanical notch and applying hydraulic pressure to the jig. The length of the notch shall be 29 mm.
No other requirements are specified for the notch shape, but the notch edge shape shall be designed so
that a brittle crack is initiated by impact within the impact energy value specified in 9.2 but does not
initiate during force increase before attaining a specified force value. Figure 6 shows the recommended
notch configurations. Side-grooves at the notch-root may be machined on both faces of the test piece to
minimize crack deviation and branching. However, the side-groove depth shall be equal to or less than
0,1B and the side-groove length measured from the notch-root shall be equal to or less than B or 0,1W,
whichever is smaller. A notch of the same length shall be introduced at the opposite edge to avoid bending
moment by matching the net-section centre with the loading axis. In case the side-grooves are applied,
however, the notch length at the opposite edge shall be determined so that there is no bending moment.
Table 2 — Dimensions of test pieces
Thickness Width Width to thickness ratio
350 mm ≤ W ≤ 1 000 mm
6 mm ≤ B ≤ 200 mm W/B ≥ 5
(standard width: W = 500 mm)
Dimensions in millimetres
Key
W 500
L 500
Figure 5 — Standard test piece configuration
Dimensions in millimetres
a) Mechanical notch b) Pressed notch
Key
1 pressed notch
Figure 6 — Recommended notch configurations of test pieces
8 © ISO 2019 – All rights reserved

6.2 Configurations of extension plates and tab plates
6.2.1 General
The definitions of the dimensions of the extension plates and tab plates are shown in Figure 7. Typical
examples are shown in Figure 8.
As for loading pins, either the single-pin type or the double-pin type shall be used.
a) Single-pin type
b) Double-pin type
Key
1 tab plate (thickness: B )
tb
2 extension plate (thickness: B )
ex
3 test piece (thickness: B)
Figure 7 — Definitions of dimensions of extension plates and tab plates
a) Example 1
b) Example 2
c) Example 3
10 © ISO 2019 – All rights reserved

d) Example 4
Figure 8 — Examples of configurations of extension plates and tab plates
6.2.2 Extension plates
[10][11][15]
The tolerances of extension plate dimensions are shown in Table 3 . When the lengths of the
extension plates attached to the two ends of a test piece are different, the shorter length shall be used
as the extension length, L .
ex
Table 3 — Tolerances of extension plate dimensions
Thickness 0,8t ≤ B ≤ 1,5t
ex
Width W ≤ W ≤ 2,0W
ex
Total length of a test piece and extension plates L + 2L ≥ 3,0W
ex
(Total length of a test piece and a single extension plate L + L ) (L + L ≥ 2,0W)
ex ex
Length to width ratio L /W ≥ 1,0
ex
6.2.3 Tab plates
The tab plate width, W , shall be equal to or greater than the extension plate width, W . The tab plates
tb ex
shall be designed to have sufficient strength to transfer the full magnitude of the applied force to the
extension plate and test piece. When the tab plates attached to the two ends of an integrated test piece
are asymmetric, the length of the shorter one shall be used as the tab plate length, L .
tb
The distance between the pins, L , is calculated by using Formula (2):
p
LL=+22LL+ (2)
pextb
6.3 Welding of test piece and extension plates
The test piece, extension plates and tab plates shall be connected by welding. The welds shall have
sufficient strength to carry the full magnitude of the applied force.
As shown in Figure 9 a), the flatness (angular distortion, linear misalignment) of the weld between a
test piece and an extension plate shall be 4 mm or less per 1 m. However, when preloading is applied,
welding residual stress and distortion can be reduced. In this case, flatness may be measured after the
preloading. The force of the preloading shall be equal to or less than 95 % the applied force specified
in 8.1. As shown in Figure 9 b), the accuracy of the in-plane loading axis shall be 0,5 % of the distance
between the pins or less, and the accuracy of the out-of-plane loading axis shall be 0,4 % of the distance
between the pins or less.
a) Flatness of weld between test piece and extension plate
b) Accuracy of in-plane and out-of-plane loading axes
Figure 9 — Dimensional accuracy of weld between test piece and extension plate
7 Test methods
7.1 Temperature control method
7.1.1 Determination of temperature gradient
7.1.1.1 Temperature measurement shall be performed by attaching thermocouples to the test piece. The
temperature shall be measured either at the surfaces or at the test piece thickness centre. In the former
case, measurements shall be performed on both the front and back faces of the test piece. In the latter
case, the temperature measurement shall be performed by attaching thermocouples into holes drilled to
the thickness centre of the test piece. The diameter of the holes is recommended as 2,5 mm or less.
A predetermined temperature gradient shall be established across the test piece width by attaching
at least nine thermocouples across the front and at least nine across the back face of the test piece for
temperature measurement and control. In addition, thermocouples shall be attached at ±100 mm in the
test piece length direction at width central position for temperature measurement to either the front
or the back face. Examples of temperature measurement positions are shown in Figure 10. Calibration
of temperature measurement by the thermocouples shall be performed by an appropriate method.
Accuracy of the temperature measurement shall be 0,2 °C or less.
The temperature gradient shall be established in accordance with the conditions described in 7.1.1.2 to
7.1.1.4.
7.1.1.2 A temperature gradient of 0,25 °C/mm to 0,35 °C/mm shall be established in a test piece
width range between 0,3W and 0,7W. When measuring the temperature at the central position of the
test piece thickness, it shall be kept within ±2 °C for 10 minutes or more, whereas when measuring
12 © ISO 2019 – All rights reserved

the temperatures on the front and back face positions of the test piece, it shall be kept within ±2 °C for
[10 + 0,1B (mm)] minutes or more, considering the time needed for temperature homogenization.
The temperature measurement before 150 mm and after 350 mm is not mandatory; however, in order
to keep stable linearity of temperature gradient between 0,3W and 0,7W, it is recommended to monitor
the temperature before 150 mm and 350 mm as shown in Figure 10.
NOTE 1 The value of temperature gradient can be evaluated from a temperature distribution curve, as shown
in Figure 16.
NOTE 2 This document is intended to obtain arrest toughness comparable to that obtained by a test without
temperature gradient, e.g. Annex E. If the gradient between 0,3W and 0,7W is larger than 0,35 °C/mm, the obtained
[10][15]
arrest toughness will be lower than that by a test without temperature gradient . Thus, temperature
gradient is controlled to be as small as possible within the testable range. In the specified temperature gradient
range, the influence of the temperature gradient on K can be ignored. If the temperature gradient between
ca
0,3W and 0,7W is less than 0,25 °C/mm, crack arrest will be unlikely.
7.1.1.3 At the test piece width central position (i.e. 0,5W), and in the range of ±100 mm in the test piece
length direction, the deviation from the temperature at the central position in the length direction shall
be controlled to within ±5 °C. However, as shown in Figure 10 b), when the temperature is not measured
at the central position in the length direction, the average temperature at the closest position [±30 mm in
the case of Figure 10 b)] shall be used as the temperature at the central position in the length direction.
7.1.1.4 At the same position in the width direction, the deviation of the temperature on the front and
back surfaces shall be controlled within ±5 °C.
7.1.2 Method of temperature control and monitoring
To establish the temperature gradients described in 7.1.1, a cooling device and a heating device may be
used to control the temperatures. Recommended cooling and heating devices are shown in Annex A.
Methods other than those may be used provided that the above conditions are met.
a) Measurement on both front and back b) Measurement at thickness centre surfaces
Key
Measuring point
top surface
bottom surface
top side (hole)
bottom side (hole)
Figure 10 — Examples of temperature measurement positions
7.2 Crack initiation methods
The test piece shall be impacted to initiate a crack so that the crack propagation and arrest event are
accomplished under a desired applied stress but not during force increase, unlike quasi-static fracture
toughness testing. However, if the impact energy is excessive, it can enhance crack propagation,
leading to over-conservative evaluation of arrest toughness because impact energy is not considered
[12][13][14]
in evaluating arrest toughness; see Formulae (13), (14) and (15) . In that case, the results
shall be treated as invalid in accordance with the criteria specified in 9.2 and Formula (10). However,
this formula shall be evaluated after the test. Formula (3) and Figure 11 can be used to determine the
impact energy before conducting the test:
E
i
≤−min[(1,2σ 40),200] (3)
B
where min is the minimum of the two values.
No specific minimum impact energy value is specified because the impacting is intended only to initiate
the brittle crack, so if very low impact energy is successful in crack initiation, the test is considered valid.
The following methods may be used in case the first impact is unsuccessful.
a) If no crack initiation has occurred after the impact, the test may be conducted again by applying
another impact. The temperature gradient is often distorted by impact and, in that case, the
temperature gradient shall be corrected prior to further impact.
b) If no crack initiation has occurred after the impact, a brittle bead may be placed on the notch tip,
in which case the integrated test piece shall be unloaded and warmed to room temperature before
the brittle bead is applied. In this case, preloading may be applied at room temperature to prevent
autonomous crack initiation before attaining the predetermined applied force. The preloading
force shall be 95 % of the predetermined applied force or less. The brittle bead weld metal shall be
selected so that it assists brittle fracture initiation from the notch tip.
14 © ISO 2019 – All rights reserved

Key
a
Recommended region of impact energy.
Figure 11 — Recommended range of impact energy
8 Test procedures
8.1 Pretest procedures
8.1.1 Install an integrated test piece, a temperature control device and an impact apparatus as per a)
to c). The order of a) to c) may be arbitrary.
a) Install an integrated test piece in the testing machine.
b) Mount a temperature control device on the test piece, as specified in 7.1 and recommended in
Annex A.
c) Install an impact apparatus, as specified in 5.2, on the testing machine. Place an appropriate
reaction force receiver as necessary.
8.1.2 After checking that all thermocouples indicate room temperature, start cooling the test piece.
The temperature distribution and the holding time shall be in accordance with 7.1.
8.1.3 Set an impact apparatus, as specified in 5.2.
8.1.4 Apply force, F, to the test piece until the predetermined value is obtained. In case the force is
applied by a displacement control device, the force shall be controlled by monitoring a load cell output.
This force is applied after the predetermined temperature distribution has been set to the test piece.
Otherwise, brittle fracture can be initiated during the cooling process due to thermal stress near the
notch-tip. Alternatively, temperature control may be implemented after loading. In this case, cooling shall
be slow enough to prevent brittle fracture initiation during cooling due to thermal stress. In the case
of temperature control after loading, the cooling rate is recommended as 2 °C/min or less. The applied
stress shall satisfy the condition given by Formula (4).
σ ≤ R (4)
p
NOTE 1 In this document, measurement outcome is independent of loading rate.
NOTE 2 Correlation of K values and temperature shows consistent Arrhenius regression if applied stresses
ca
are according to Formula (4). In contrast, if the applied stress is larger than that specified by Formula (4), the
test gives a higher arrest toughness value than that tested in accordance with Formula (4) (see Figure 18). This
[8][9]
feature was proven by a numerical analysis . This upper bound applied stress/yield stress ratio value was
determined from a series of tests using steel plates having R from 321 MPa to 416 MPa and plate thickness from
p
[10]
16 mm to 80 mm .
8.1.5 The notch may be cooled further immediately before impact on the condition that the cooling
does not disturb the temperature in the range 0,3W to 0,7W. Continuous temperature monitoring is
necessary to ensure that there is no disturbance of the temperature distribution. The test temperature in
this case shall be the measured temperature obtained from the temperature record immediately before
the additional notch cooling.
8.1.6 Record the force value measured by the load cell immediately before the impact.
8.2 Impacting procedures
8.2.1 After holding the predetermined applied force, as determined in 8.1.6, for 30 s or more, apply an
impact to the wedge using the impact apparatus. In case the force is applied by a displacement control
device, the force shall be continuously monitored and controlled by a load cell output. If a crack initiates
autonomously and the force value at the time of crack initiation is recorded, the test is valid; use the force
value at the time of crack initiation as applied force, F.
8.2.2 Record the force value after the impact.
8.2.3 When the force after the impact is smaller than the applied force by 10 % or more, crack initiation
is considered to have occurred and another impact shall not be applied. If there is no indication of crack
initiation, another impact may be applied.
8.2.4 An increase in the number of impacts can cause a change in the shape of the notch of the test
piece. Since the number of impacts has no effect on the value of arrest toughness, no limit is specified for
the number of impacts. However, because the temperature gradient can be disturbed by impact, the test
should be conducted again, beginning from temperature control, when applying repeated impact.
8.2.5 If the test piece is still intact, remove the force.
8.3 Post-test operations
8.3.1 Remove the impact apparatus.
8.3.2 Remove the temperature controlling device and any lead wires attached to the test piece. Spray
fracture surfaces with rust inhibitor (light oil) if no heat tinting is planned.
8.3.3 Allow the temperature of the test piece to gradually return to room temperature. If a rapid return
to room temperature is desired, the test piece may be heated using a heat gun or gas torch or the like. If it
is necessary to prevent heat tinting of the fracture surface, this method shall be avoided.
8.3.4 If the test piece is still intact, the fracture surfaces can be separated using one of the following
methods.
a) Most of the remaining ligament can be cut by mechanical means and the resulting ligament pulled
apart by the testing machine.
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b) Most of the remaining ligament can be cut using a gas torch, provided that heat tinting of the
fracture surfaces is not an issue. This is followed by the resulting ligament being pulled apart by
the testing machine.
c) If the remaining ligament cross-sectional area is small enough, it can be pulled apart by the testing
machine without cutting the remaining ligament.
8.4 Observation of fracture surfaces
8.4.1 Photograph the fracture surfaces and crack propagation path. Figure 12 shows examples of
photographs.
If the drilled hole for attaching thermocouples appears at the crack arrest position on the fracture
surface, the test is invalid.
8.4.2 Measure an arrested crack length at the longest position on the fracture surface and record
the result as the arrest crack length, a . The arrest crack length shall include the notch length. In cases
ca
where a crack deviates from the direction transverse to the loading direction, the length projected along
the plane transverse to the loading line, i.e. x in Figure 15, is defined as the arrest crack length. In the
a
following cases, however, assess the results according to the methods described for each case.
a) Re-initiation of a crack
In the case where a brittle crack has re-initiated from an arrested crack, ignore the re-initiated
crack. Here re-initiation is defined as the case where an arrested crack and re-initiated crack are
completely separated by a stretch zone and brittle crack re-initiation from the stretch zone can
clearly be observed. Figure 13 shows an example of a re-initiated crack.
In the case where a crack continuously propagates partially in the thickness direction, the position
of the longest brittle crack is define
...